Preoperative immune checkpoint inhibition and cryoablation in early-stage breast cancer

Local cryoablation can engender systemic immune activation/anticancer responses in tumors otherwise resistant to immune checkpoint blockade (ICB). We evaluated the safety/tolerability of preoperative cryoablation plus ipilimumab and nivolumab in 5 early-stage/resectable breast cancers. The primary endpoint was met when all 5 patients underwent standard-of-care primary breast surgery undelayedly. Three patients developed transient hyperthyroidism; one developed grade 4 liver toxicity (resolved with supportive management). We compared this strategy with cryoablation and/or ipilimumab. Dual ICB plus cryoablation induced higher expression of T cell activation markers and serum Th1 cytokines and reduced immunosuppressive serum CD4+PD-1hi T cells, improving effector-to-suppressor T cell ratio. After dual ICB and before cryoablation, T cell receptor sequencing of 4 patients showed increased T cell clonality. In this small subset of patients, we provide preliminary evidence that preoperative cryoablation plus ipilimumab and nivolumab is feasible, inducing systemic adaptive immune activation potentially more robust than cryoablation with/without ipilimumab.

APR-246 increases tumor antigenicity independent of p53

We previously reported that activation of p53 by APR-246 reprograms tumor-associated macrophages to overcome immune checkpoint blockade resistance. Here, we demonstrate that APR-246 and its active moiety, methylene quinuclidinone (MQ) can enhance the immunogenicity of tumor cells directly. MQ treatment of murine B16F10 melanoma cells promoted activation of melanoma-specific CD8+ T cells and increased the efficacy of a tumor cell vaccine using MQ-treated cells even when the B16F10 cells lacked p53. We then designed a novel combination of APR-246 with the TLR-4 agonist, monophosphoryl lipid A, and a CD40 agonist to further enhance these immunogenic effects and demonstrated a significant antitumor response. We propose that the immunogenic effect of MQ can be linked to its thiol-reactive alkylating ability as we observed similar immunogenic effects with the broad-spectrum cysteine-reactive compound, iodoacetamide. Our results thus indicate that combination of APR-246 with immunomodulatory agents may elicit effective antitumor immune response irrespective of the tumor's p53 mutation status.

Phase Ib Trial of Phenformin in Patients with V600-mutated Melanoma Receiving Dabrafenib and Trametinib

PURPOSE

Preclinical studies show that activation of AMP kinase by phenformin can augment the cytotoxic effect and RAF inhibitors in BRAF V600-mutated melanoma. We conducted a phase Ib dose-escalation trial of phenformin with standard dose dabrafenib/trametinib in patients with metastatic BRAF V600-mutated melanoma.

EXPERIMENTAL DESIGN

We used a 3+3 dose-escalation design which explored phenformin doses between 50 and 200 mg twice daily. Patients also received standard dose dabrafenib/trametinib. We measured phenformin pharmacokinetics and assessed the effect of treatment on circulating myeloid-derived suppressor cells (MDSC).

RESULTS

A total of 18 patients were treated at dose levels ranging from 50 to 200 mg twice daily. The planned dose-escalation phase had to be cancelled because of the COVID 19 pandemic. The most common toxicities were nausea/vomiting; there were two cases of reversible lactic acidosis. Responses were seen in 10 of 18 patients overall (56%) and in 2 of 8 patients who had received prior therapy with RAF inhibitor. Pharmacokinetic data confirmed drug bioavailability. MDSCs were measured in 7 patients treated at the highest dose levels and showed MDSC levels declined on study drug in 6 of 7 patients.

CONCLUSIONS

We identified the recommended phase II dose of phenformin as 50 mg twice daily when administered with dabrafenib/trametinib, although some patients will require short drug holidays. We observed a decrease in MDSCs, as predicted by preclinical studies, and may enhance immune recognition of melanoma cells.

SIGNIFICANCE

This is the first trial using phenformin in combination with RAF/MEK inhibition in patients with BRAF V600-mutated melanoma. This is a novel strategy, based on preclinical data, to increase pAMPK while blocking the MAPK pathway in melanoma. Our data provide justification and a recommended dose for a phase II trial.

Activation of STING in Response to Partial-Tumor Radiation Exposure

PURPOSE

To determine the mechanisms involved in partial volume radiation therapy (RT)-induced tumor response.

METHODS AND MATERIALS

We investigated 67NR murine orthotopic breast tumors in Balb/c mice and Lewis lung carcinoma (LLC cells; WT, Crispr/Cas9 Sting KO, and Atm KO) injected in the flank of C57Bl/6, cGAS, or STING KO mice. RT was delivered to 50% or 100% of the tumor volume using a 2 × 2 cm collimator on a microirradiator allowing precise irradiation. Tumors and blood were collected at 6, 24, and 48 hours post-RT and assessed for cytokine measurements.

RESULTS

There is a significant activation of the cGAS/STING pathway in the hemi-irradiated tumors compared with control and to 100% exposed 67NR tumors. In the LLC model, we determined that an ATM-mediated noncanonical activation of STING is involved. We demonstrated that the partial exposure RT-mediated immune response is dependent on ATM activation in the tumor cells and on the STING activation in the host, and cGAS is dispensable. Our results also indicate that partial volume RT stimulates a proinflammatory cytokine response compared with the anti-inflammatory profile induced by 100% tumor volume exposure.

CONCLUSIONS

Partial volume RT induces an antitumor response by activating STING, which stimulates a specific cytokine signature as part of the immune response. However, the mechanism of this STING activation, via the canonical cGAS/STING pathway or a noncanonical ATM-driven pathway, depends on the tumor type. Identifying the upstream pathways responsible for STING activation in the partial RT-mediated immune response in different tumor types would improve this therapy and its potential combination with immune checkpoint blockade and other antitumor therapies.

Apoptotic contraction drives target cell release by cytotoxic T cells

Cytotoxic T lymphocytes (CTLs) fight intracellular pathogens and cancer by identifying and destroying infected or transformed target cells1. To kill, CTLs form a specialized cytotoxic immune synapse (IS) with a target of interest and then release toxic perforin and granzymes into the interface to elicit programmed cell death2-5. The IS then dissolves, enabling CTLs to search for additional prey and professional phagocytes to clear the corpse6. While the mechanisms governing IS assembly have been studied extensively, far less is known about target cell release. Here, we applied time-lapse imaging to explore the basis for IS dissolution and found that it occurred concomitantly with the cytoskeletal contraction of apoptotic targets. Genetic and pharmacological perturbation of this contraction response indicated that it was both necessary and sufficient for CTL dissociation. We also found that mechanical amplification of apoptotic contractility promoted faster CTL detachment and serial killing. Collectively, these results establish a biophysical basis for IS dissolution and highlight the importance of mechanosensory feedback in the regulation of cell-cell interactions.

Cytotoxic T Lymphocytes Control Growth of B16 Tumor Cells in Collagen-Fibrin Gels by Cytolytic and Non-Lytic Mechanisms

Cytotoxic T lymphocytes (CTLs) are important in controlling some viral infections, and therapies involving the transfer of large numbers of cancer-specific CTLs have been successfully used to treat several types of cancers in humans. While the molecular mechanisms of how CTLs kill their targets are relatively well understood, we still lack a solid quantitative understanding of the kinetics and efficiency by which CTLs kill their targets in vivo. Collagen-fibrin-gel-based assays provide a tissue-like environment for the migration of CTLs, making them an attractive system to study T cell cytotoxicity in in vivo-like conditions. Budhu.et al. systematically varied the number of peptide (SIINFEKL)-pulsed B16 melanoma cells and SIINFEKL-specific CTLs (OT-1) and measured the remaining targets at different times after target and CTL co-inoculation into collagen-fibrin gels. The authors proposed that their data were consistent with a simple model in which tumors grow exponentially and are killed by CTLs at a per capita rate proportional to the CTL density in the gel. By fitting several alternative mathematical models to these data, we found that this simple "exponential-growth-mass-action-killing" model did not precisely describe the data. However, determining the best-fit model proved difficult because the best-performing model was dependent on the specific dataset chosen for the analysis. When considering all data that include biologically realistic CTL concentrations (E≤107cell/mL), the model in which tumors grow exponentially and CTLs suppress tumor's growth non-lytically and kill tumors according to the mass-action law (SiGMA model) fit the data with the best quality. A novel power analysis suggested that longer experiments (∼3-4 days) with four measurements of B16 tumor cell concentrations for a range of CTL concentrations would best allow discriminating between alternative models. Taken together, our results suggested that the interactions between tumors and CTLs in collagen-fibrin gels are more complex than a simple exponential-growth-mass-action killing model and provide support for the hypothesis that CTLs' impact on tumors may go beyond direct cytotoxicity.

Abstract 2517: Optimizing breast cancer therapy by inhibiting the adenosine receptor and oxygen consumption

Immune checkpoint blockade has shown remarkable promise in melanoma and other tumor types. However, a large proportion of patients do not respond or develop acquired resistance. Tumors can activate multiple checkpoints and immunosuppressive pathways to evade immune surveillance, which are likely a cause of treatment failure. Therefore, inhibition of multiple checkpoints may be necessary for maximal efficacy of immunotherapies. The adenosine A2 receptor (A2aR), was shown to function as an immune checkpoint. Its blockade inhibited tumor growth and metastases and synergized with other checkpoint inhibitors. We propose that using AZD4635, a potent and selective A2aR antagonist, will enhance the therapeutic efficacy of anti-PD-1/PD-L1. In addition, we propose that blocking tumor oxygen consumption using deferiprone (DFP), phenformin (Phen) and metformin (Met) will further enhance A2aR and PD-1/PD-L1 blockade efficacy. We evaluated the effects of MET, Phen, DFP, and AZD4635 on tumor cells, T cell, and macrophage proliferation and effector function in vitro. IC50 measurements showed that T cells are the most sensitive to inhibition by these drugs, while 4T1 tumor cells appear to be the least sensitive. Naïve mouse T cells were activated with anti-CD3 and anti-CD28 coated dynabeads in the presence of titrating doses of all four drugs for 72 hours then analyzed by flow cytometry for proliferation and activation status. AZD4635 and DFP increased the expression of the activation marker CD25 (IL2Ra) on CD8 T cells. In addition, AZD4635 also increased expression of Granzyme B on both CD4 and CD8 T cells. Met appears to have little to no effect on T cell proliferation activation. We utilized the Seahorse XF Mito Stress Test assay to measure the mitochondrial respiratory activity of T cells in the presence these drugs. T cells were activated with dynabeads for 72 hours and then incubated with titrating doses of the drugs overnight before running on the Seahorse assay. DFP and Phen had the strongest effect on Maximal Respiration and Spare Respiratory Capacity at dilutions of 1uM followed by 16uM. A similar, albeit less profound effect was observed in groups treated with Met and AZD4635. Lastly, we obtained and generated two mouse breast cancer cell lines (4T1 and E0771) bearing HIF-1 reporter systems. We treated 4T1-HRE and E0771 cells with increasing doses of cobalt chloride (CoCl2) to chemically mimic hypoxia by inducing HIF1a expression. Both 4T1-HRE and E0771-HRE demonstrated increased luciferase activity that correlated with increasing doses of CoCl2 in vitro. Future experiments will focus on characterizing the adenosine pathway in vivo in 4T1-HRE and E0771-HRE tumors and examine how drugs that target the adenosine A2AaR receptor (AZD4635), and oxygen consumption (DFP, Phen and Met) influence tumor oxygen consumption in vivo as well as the activation states of immune cells in the tumor microenvironment.

Citation Format: Sadna Budhu, Mayuresh Mane, Mamadou A. Bah, Juan Zurita, Inna Serganova, Soe Min, Anais Assouvie, Jedd D. Wolchok, Jason Koutcher, Vladimir Ponomarev, Taha Merghoub. Optimizing breast cancer therapy by inhibiting the adenosine receptor and oxygen consumption [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2517.

Abstract 5873: LDH inhibition boosts effector T cells while destabilizing regulatory T cells and improves responses to CTLA-4 blockade

Tumor reliance on glycolysis is a hallmark of cancer and a mechanism of resistance to immunotherapy. This resistance is due to lactate-mediated immune suppression and competition for glucose between T cells and tumor cells within the tumor microenvironment. We have shown that CTLA-4 blockade is more effective in glycolysis-low tumors, or tumors lacking functional lactate dehydrogenase A (LDH-A), primarily due to functional destabilization of regulatory T cell suppression. LDH inhibitors (LDHi) have been reported to inhibit tumor glucose uptake and slow tumor cell proliferation in pre-clinical models of cancer. However, their effect on immune cells has not been explored in depth. In addition, the optimal conditions for pharmacological inhibition of LDH in combination with immunotherapy to maximize anti-tumor immune and therapeutic responses require further investigation. At baseline, tumor cells express higher levels of ldha and consume more glucose than tumor-infiltrating T cells, creating a therapeutic window for tumor-specific targeting of the glycolysis pathway. In vivo, LDHi relies on the adaptive immune system and the overexpression of tumor LDH to delay B16F10 murine melanoma progression. We found that treatment with LDHi has two effects: 1) reduction of tumor cell glucose uptake and 2) increase in glucose uptake by tumor-infiltrating T cells. Thus, LDH inhibition is an effective, tumor-specific strategy to reduce tumor cell glucose uptake and increase glucose availability within the tumor microenvironment, consequently boosting tumor-infiltrating T cell glucose uptake. In vitro, increased glucose levels improve effector T cell killing of tumor cells while reducing regulatory T cell suppressive ability. Accordingly, inhibiting LDH in combination with CTLA-4 blockade is more effective in controlling tumor progression compared to CTLA-4 blockade alone, and that this combination promotes effector T cell infiltration and activation, while destabilizing regulatory T cell function. Additionally, we observe serum LDH and lactate levels correlate with primary tumor burden as well as tumor LDH levels. Therefore, serum LDH may serve as a biomarker for tumor burden and tumor LDH, as well as clinical response to LDHi. This study provides a comprehensive rationale for combining immune checkpoint blockade with inhibitors of glycolysis for patients with highly glycolytic cancers.

Citation Format: Svena Verma, Inna Serganova, Lauren Dong, Sadna Budhu, Levi Mangarin, Roberta Zappasodi, Taha Merghoub, Jedd D. Wolchok. LDH inhibition boosts effector T cells while destabilizing regulatory T cells and improves responses to CTLA-4 blockade. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5873.

Abstract 2421: WST-11 vascular-targeted photodynamic therapy induced immune modulation in upper tract urothelial cancer

Introduction: Vascular-targeted photodynamic therapy (VTP) with the photosensitizing agent padeliporfin (WST-11/TOOKAD Soluble; STEBA Biotech) has been approved for treating men with low-risk prostate cancer. A phase 1 trial of VTP evaluating treatment of upper tract urothelial carcinoma (UTUC) showed an acceptable safety profile with strong potential as an effective, kidney-sparing endoscopic management option. These results support a recently initiated multi-center Phase 3 trial (ENLIGHTED). Here we conducted a correlative study to assess immune modulatory activities of VTP and its potential association with treatment response.

Methods: 19 patients with UTUC received up to two endoscopic VTP treatments in a phase I trial evaluating the safety of VTP. Treatment was applied by endoscopic illumination for 10 minutes at the involved site in the upper tract with three light fluence doses at 100 mW/cm, 150 mW/cm, or 200 mW/cm after intravenous injection of 4 mg/kg WST-11. Complete response was defined by absence of visible tumor and negative urine cytology at 30 days post treatment. To investigate the impact of VTP on the immune system, patient blood samples were collected and banked at 6 time points (base line, 4-6 hrs, 1 day, 1 week, 2 weeks, and 4 weeks post-treatment). Peripheral blood mononuclear cells (PBMCs) were subjected to flow cytometry analyses for T cell activation status and the abundance of myeloid derived suppressive cell (MDSC). Patient analyses were further stratified by complete responders (CR) and partial responders (PR). Mice bearing a murine bladder cell line MB49 or MB49 expressing ovalbumin (MB49-ova) was utilized for the assessment of efficacy and immune modulation by VTP.

Results and Conclusions: An increase of the MDSC population in PBMC was observed immediately after VTP treatment (up to 24 hrs) in both CR and PR. However, the MDSC level returned close to pretreatment level in the majority of cases. The frequency of CD8 T cells among the total (CD3 positive) T cells in PBMC was increased immediately after VTP in both CR and PR. However, this increase was more prominent and durable among CR than PR, suggesting an association of treatment response with CD8 T cell driven immune modulation. Analysis of VTP induced antigen-specific immune responses using ovalbumin (ova) tetramers on MB49-ova model showed an increase in ova specific CD8 T cells in the blood and tumor samples at day 7 post VTP, indicating that VTP might induce tumor antigen specific adaptive response. Future analysis will be focused on the analysis of T cell receptor repertoire and immune correlation with clinical benefit. In summary, our pre-clinical and clinical data suggests that VTP induces antigen-specific CD8 T cell responses that may be durable.

Citation Format: Kwanghee Kim, Sadna Budhu, Wesley Yip, Andrew Tracey, Andreas Aulitzky, Jasmine Thomas, Karan Nagar, Laura Alvim, Rebecca Dubrovsky, Caoimhe Ryan, Natalia Kudinova, Phillip Wong, Taha Merghoub, Avigdor Scherz, Jonathan Coleman. WST-11 vascular-targeted photodynamic therapy induced immune modulation in upper tract urothelial cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2421.

T cell immunotherapies engage neutrophils to eliminate tumor antigen escape variants

Cancer immunotherapies, including adoptive T cell transfer, can be ineffective because tumors evolve to display antigen-loss-variant clones. Therapies that activate multiple branches of the immune system may eliminate escape variants. Here, we show that melanoma-specific CD4+ T cell therapy in combination with OX40 co-stimulation or CTLA-4 blockade can eradicate melanomas containing antigen escape variants. As expected, early on-target recognition of melanoma antigens by tumor-specific CD4+ T cells was required. Surprisingly, complete tumor eradication was dependent on neutrophils and partly dependent on inducible nitric oxide synthase. In support of these findings, extensive neutrophil activation was observed in mouse tumors and in biopsies of melanoma patients treated with immune checkpoint blockade. Transcriptomic and flow cytometry analyses revealed a distinct anti-tumorigenic neutrophil subset present in treated mice. Our findings uncover an interplay between T cells mediating the initial anti-tumor immune response and neutrophils mediating the destruction of tumor antigen loss variants.

Mathematical modeling suggests cytotoxic T lymphocytes control growth of B16 tumor cells in collagin-fibrin gels by cytolytic and non-lytic mechanisms

Cytotoxic T lymphocytes (CTLs) are important in controlling some viral infections, and therapies involving transfer of large numbers of cancer-specific CTLs have been successfully used to treat several types of cancers in humans. While molecular mechanisms of how CTLs kill their targets are relatively well understood we still lack solid quantitative understanding of the kinetics and efficiency at which CTLs kill their targets in different conditions. Collagen-fibrin gel-based assays provide a tissue-like environment for the migration of CTLs, making them an attractive system to study the cytotoxicity in vitro. Budhu et al. [1] systematically varied the number of peptide (SIINFEKL)- pulsed B16 melanoma cells and SIINFEKL-specific CTLs (OT-1) and measured remaining targets at different times after target and CTL co-inoculation into collagen-fibrin gels. The authors proposed that their data were consistent with a simple model in which tumors grow exponentially and are killed by CTLs at a per capita rate proportional to the CTL density in the gel. By fitting several alternative mathematical models to these data we found that this simple "exponential-growth-mass-action-killing" model does not precisely fit the data. However, determining the best fit model proved difficult because the best performing model was dependent on the specific dataset chosen for the analysis. When considering all data that include biologically realistic CTL concentrations ( E ≤ 10 ⁷ cell/ml) the model in which tumors grow exponentially and CTLs suppress tumor's growth non-lytically and kill tumors according to the mass-action law (SiGMA model) fitted the data with best quality. Results of power analysis suggested that longer experiments (∼ 3 - 4 days) with 4 measurements of B16 tumor cell concentrations for a range of CTL concentrations would best allow to discriminate between alternative models. Taken together, our results suggest that interactions between tumors and CTLs in collagen-fibrin gels are more complex than a simple exponential-growth- mass-action killing model and provide support for the hypothesis that CTLs impact on tumors may go beyond direct cytotoxicity.

Increased p53 expression induced by APR-246 reprograms tumor-associated macrophages to augment immune checkpoint blockade

In addition to playing a major role in tumor cell biology, p53 generates a microenvironment that promotes antitumor immune surveillance via tumor-associated macrophages. We examined whether increasing p53 signaling in the tumor microenvironment influences antitumor T cell immunity. Our findings indicate that increased p53 signaling induced either pharmacologically with APR-246 (eprenetapopt) or in p53-overexpressing transgenic mice can disinhibit antitumor T cell immunity and augment the efficacy of immune checkpoint blockade. We demonstrated that increased p53 expression in tumor-associated macrophages induces canonical p53-associated functions such as senescence and activation of a p53-dependent senescence-associated secretory phenotype. This was linked with decreased expression of proteins associated with M2 polarization by tumor-associated macrophages. Our preclinical data led to the development of a clinical trial in patients with solid tumors combining APR-246 with pembrolizumab. Biospecimens from select patients participating in this ongoing trial showed that there was a suppression of M2-polarized myeloid cells and increase in T cell proliferation with therapy in those who responded to the therapy. Our findings, based on both genetic and a small molecule–based pharmacological approach, suggest that increasing p53 expression in tumor-associated macrophages reprograms the tumor microenvironment to augment the response to immune checkpoint blockade.

Abstract 4175: Combining a novel MEK inhibitor with immunomodulation to promote an anti-tumor response

To enhance the therapeutic scope of MEK inhibitors (MEKis), we aim to develop new strategies to extend their usage to MEKi resistant RAS mutant cancers, which represent an unmet clinical need. CH5126766 (CKI27) binds the allosteric site of MEK to inhibit its kinase activity but is novel due to its interaction with MEK S218 and 228, which blocks their phosphorylation by RAF. CKI27 bound MEK binds to RAF and cannot be released by phosphorylation, thus becoming a dominant negative inhibitor of RAF activation. This prevents the induction of MEK phosphorylation observed with other MEKis. Although this results in more potent tumor control, CKI27 is also capable of inhibiting T cell function because the MAPK/ERK pathway is activated downstream of T cell receptor signaling. We aim to balance the positive and negative immunomodulatory effects of MEKis for optimal combination with immunotherapy. We observed that CKI27 increased MHC expression on tumor cells and improved T cell mediated killing. Yet, CKI27 also decreased T cell proliferation, activation, and cytolytic activity. Intermittent administration of CKI27 allowed T cells to recover and partially relieved these inhibitory effects. Further combination with agonist antibodies anti-OX40 and GITR completely alleviated T cell inhibition and increased combination efficacy with immune checkpoint blockade antibody anti-CTLA-4. We also observed an increase in proliferation and T cell activation markers in LLC tumor bearing mice treated with the combination of CKI27, anti-GITR, and anti-CTLA-4. Understanding the immunomodulatory effects of combining CKI27 with immunotherapy will elucidate the mechanism behind this increased efficacy. This will allow us to make more informed decisions in dosing regimens, overcoming resistance, and generating long-term immune responses in future clinical trials treating patients with RAS mutant cancers.

Citation Format: Lauren Dong, Hyejin Choi, Sadna Budhu, Isabell Schulze, Svena Verma, Nezar Mehanna, Neal Rosen, Taha Merghoub, Jedd Wolchok. Combining a novel MEK inhibitor with immunomodulation to promote an anti-tumor response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4175.

Abstract 6056: Activation of Sting in response to partial-tumor radiation exposure

Purpose: It has been shown that ionizing radiation can mediate antitumor immunity via the activation of the cytosolic DNA sensor cGAS/STING pathway. Therefore, the purpose of this study was to determine whether STING activation is involved in partial volume radiation therapy (RT).

Materials/Methods: We investigated 67NR murine orthotopic breast tumors in Balb/c mice and LLC cells injected in the flank of C57Bl/6, cGAS, or STING KO mice. RT was delivered to 50% or 100% of the tumor volume using a 2X2 cm collimator on a microirradiator allowing precise irradiation. Tumors were collected at different time points post-RT and assessed for different measurements.

Results: We previously showed that a single dose of radiation delivered to half of the tumor (50% RT) activated an anti-tumor immune response comparable to the response in a fully-irradiated tumor in the immunogenic 67NR murine breast carcinoma tumor model and in the less immunogenic and more radioresistant Lewis lung carcinoma (LLC) tumor model. We have also demonstrated that this immune response was due to the infiltration of CD8+ T cells along with an increased expression of ICAM adhesion molecules. Treatment with either anti-CD8 or anti-ICAM antibodies abrogated the hemi-RT response. Furthermore, a significant abscopal effect was observed after partial irradiation with a single dose of 10Gy in a bilateral 67NR tumors model. In this study, we tested whether the hemi-irradiation-mediated immune response involves the cGAS/STING canonical pathway, or a non-canonical activation of STING, in the 67NR or LLC tumor models. It has been reported that STING can be activated, independently of cGAS, via non-canonical activation of STING, involving ATM and TRAF6, among other factors. We found significant activation of the cGAS/STING pathway in the hemi-irradiated tumors as compared to control and to 100% exposed 67NR tumors. Interestingly, the increased expression of the cGAS/STING pathway was found in the hemi-irradiated tumor but, also in the non-irradiated part of this hemi-irradiated tumor. In the LLC model, a non-canonical activation of STING was involved. Using both cGAS and STING KO mice, we demonstrated that the partial exposure RT-mediated immune response is dependent on STING activation in the host while cGAS is dispensable.

Conclusions: Upstream pathways responsible for STING activation are tumor type-specific. Identifying the upstream pathways responsible for STING activation in the partial RT-mediated immune response in different tumor types would improve this therapy and its potential combination with immune checkpoint blockade.

Citation Format: Mickael Mathieu, Prerna R. Nepali, Sadna Budhu, Simon N. Powell, John Humm, Joseph Deasy, Adriana Haimovitz-Friedman. Activation of Sting in response to partial-tumor radiation exposure [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6056.

Abstract 250: Activating canonical p53 functions in tumor-associated macrophages improves immune checkpoint blockade efficacy

Canonical p53-activated pathways can influence a microenvironment that promotes antitumor immune surveillance via tumor-associated macrophages (TAMs). We examined whether p53 activity in the tumor microenvironment (TME) influences antitumor immunity and show that p53 signaling induced pharmacologically with APR-246 (eprenetapopt) can augment the efficacy of immune checkpoint blockade (ICB) in preclinical models, a strategy that is also being tested in patients (NCT04383938). We first investigated the effects of combining APR-246 with ICB in wildtype C57BL6 (B6) mice bearing syngeneic p53 wildtype MC38 colon cancer and B16 melanoma tumors. The combination of an anti-PD-1 antibody (RMP1-14) with APR-246 in mice significantly delayed tumor growth (p < 0.001) and improved survival of tumor-bearing mice, compared to monotherapies (p < 0.01). To further dissect the effects of APR-246 on myeloid and T cells in the TME, we used a conditional knockout of p53 in CSF1R+myeloid cells (CSF1Rcre/p53fl mice), or T cells (CD8cre/p53fl mice). CSF1Rcre/p53fl had loss of tumor control and worse survival with APR-246+anti-PD-1. CD8cre/p53fl had intact tumor control. To study enhanced p53 activity in the TME, we performed flow cytometry, cytokine multiplex and global transcriptional profiling by RNA seq. We found enhanced p53-activity led to increased infiltration of T cells, increased MHC-II expression in TAMs and downregulation of M2-associated cytokines. This was associated with cellular senescence in TAMs and induction of canonical p53-induced senescence-associated secretory phenotype (SASP). Our preclinical findings informed the development of a phase I/II clinical trial using APR-246 with pembrolizumab for patients with advanced solid tumors (NCT04383938). We studied peripheral blood samples from two of the patients with tumor regression and two patients in whom tumors progressed on therapy. We analyzed peripheral blood mononuclear cells (PBMCs) and serum prior to therapy, and at the beginning of cycle 2 and 5 for the patients with tumor control, and at the end of therapy for patients who had progression. Single cell RNA-seq of PBMCs demonstrated a signature consistent with T cell activation and proliferation, and SASP-associated changes in the myeloid compartment as seen in mice. T cell profiling of PBMCs by flow cytometry demonstrated strong proliferation of T cells in patients with tumor control. Serum cytokine analysis demonstrated robust in IL-12, IFN-gamma and Eotaxin-1 in the two responders, which was not seen in the patients whose tumors progressed. Our study illustrates p53-induced SASP in TAMs as a mechanism to reprogram the TME and augment responses to ICB. Ongoing studies will help determine biomarkers that are predictive of response to APR-246+ICB therapy.

Citation Format: Arnab Ghosh, Judith Michel, Divya Venkatesh, Riccardo Mezzadra, Lauren Dong, Fadi Samaan, Ricardo Gomez, Nathan Suek, Aliya Holland, Yu-Jui Ho, Mohsen Abu-Akeel, Luis Felipe Campesato, Levi Mark Bala Mangarin, Cailian Liu, Hong Zhong, Sadna Budhu, Andrew Chow, Roberta Zappasodi, Marcus Ruscetti, Scott W. Lowe, Taha Merghoub, Jedd D. Wolchok. Activating canonical p53 functions in tumor-associated macrophages improves immune checkpoint blockade efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 250.

Abstract LB135: Deferiprone alters macrophage function and metabolism

We studied the effects of the intracellular, clinically approved, iron chelator deferiprone (DFP) on macrophage characteristics, function, and metabolism. This research expands on our previous studies investigating the ability of DFP to alter metabolism of breast and prostate cancer tumors and enhance treatment response. We used the murine macrophage cell line RAW 264.7, unpolarized (M0) & polarized (to M1 by LPS, to M2 by IL-4), in vitro to evaluate the effects of DFP on macrophage (i) doubling times (cell count assay), (ii) polarization (flow cytometry), (iii) functional response by measuring cytokine (IL-12, IL-10, TNFα), secretion (Luminex multiplex cytokine detection system, Millipore), phagocytosis (IgG-coated latex beads), and reactive oxygen species production (fluorometric detection), (iv) glycolytic and oxidative metabolism (Agilent xFe96 analyzer), and (v) glycolytic metabolism (measuring incorporation of 1-13C-glucose by 1H & 13C magnetic resonance spectroscopy (MRS) of cell extracts and supernatants). The EC50s of 48 h DFP exposure are 79±5 µM, 93±3 µM, and 114±5 µM for M0, M1, and M2-polarized RAW 264.7 cells, respectively. The effect of DFP is cytostatic and increases cell doubling times. Exposure to 100 µM DFP for 48 h increases the number of M1-polarized cells in M0 and M1 cultures, but not in M2-polarized cells. While M2-polarized cells secreted more anti-inflammatory IL-10 and less pro-inflammatory TNFα than M0 cells, their cytokine secretion was unaffected by DFP. M1-polarized cells stimulated the secretion of TNFα and IL-10. The IL-10 secretion may be a feedback mechanism to curtail the pro-inflammatory effects of LPS. DFP decreased IL-10 secretion by ~33% in M1-polarized cells, enhancing their M1 activation state. IL-12 secretion was minimal and inconsistent. The ~21% phagocytosis in M0 cells remained unchanged by M2 polarization and increased to ~37% in M1-polarized cells. DFP exposure increased phagocytosis efficiency in M0, M1, and M2-polarized cells but highest in M1 cells. While no detectable H2O2 was produced, RAW 264.7 cells make detectable nitric oxide (NO), with M1-polarized cells yielding the most NO. NO yield was unchanged by DFP. Like the results above, we found the greatest effect of DFP to be on mitochondrial metabolism in M1 macrophages, specifically, significant reductions of maximal, basal, and ATP-linked respiration. The increased suppression of oxidative metabolism in M1-polarized macrophages by DFP conforms with the observed reduction of anti-inflammatory cytokines. The DFP increased phagocytosis, specifically dominant in M1 macrophages, suggests an increased reliance on glycolysis. To support the above observations, we currently study the incorporation of 1-13C-Glucose into cellular metabolites of M0, M1, and M2-polarized cells without & with DFP. Our data support a pro-inflammatory effect of DFP on macrophages, which may enhance their anti-tumor effect in vivo through altering tumor and macrophage metabolism.

Citation Format: Ellen Ackerstaff, Sadna Budhu, Dov P. Winkleman, Soe S. Min, Jenny N. Ijoma, Inna S. Serganova, Ronald G. Blasberg, Taha Merghoub, Jason A. Koutcher. Deferiprone alters macrophage function and metabolism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB135.

Abstract 6150: Potential role of CD47 in T cell exhaustion program

Multiple suppressive mechanisms within the tumor microenvironment (TME) are capable of blunting anti-tumor T cell responses. These include engagement of inhibitory receptors expressed in tumor-associated, exhausted CD8 T cells, such as programmed cell death protein 1 (PD-1), T-cell immunoglobulin and mucin-domain containing-3 (TIM-3), lymphocyte-activation gene 3 (LAG-3), 2B4 (also known as CD244), and T cell immunoreceptor with Ig and ITIM domains (TIGIT). While immune checkpoint blockade therapies aimed at reversing the dysfunctional state of tumor-associated T cells have demonstrated clinical effectiveness, not all cancer patients achieve long-term disease control. This is due, at least in part, to the refractory nature of what are categorized as terminally exhausted CD8 T cells to be reinvigorated by, for example, PD-1/PD-L1 blockade. As CD8 T cell exhaustion (or dysfunction) is a major therapeutic challenge, gaps in our understanding of cellular and molecular mechanisms underlying the T cell exhaustion (or dysfunction) program in cancer warrant further study of pathways that program T cells toward exhaustion (or dysfunction). Through comprehensive immune profiling of tumor-infiltrating T lymphocytes (TILs), we found that CD47 expression in CD8 TILs isolated from melanoma patients significantly correlates with expression of several checkpoint inhibitory molecules (e.g., TIM-3, PD-1 and LAG-3). Additionally, our re-analysis of single cell data from melanoma patients revealed that terminally exhausted T cells (Tex) and TCF7hi Tex precursor cells exhibit high levels of CD47 transcripts, suggesting phenotypic association of CD47 with T cell exhaustion. We confirmed our observations in murine B16-F10 melanoma where CD47 expression is significantly upregulated in exhausted CD8 TILs. We also show that CD47 functions as a negative regulator for T cell proliferation and function during T cell priming. To address the role of CD47 during the development of CD8 T cell exhaustion/dysfunction in cancer, we performed adoptive T cell transfer of the naïve-sorted Cd47+/+ (WT) and Cd47+/- (Het) antigen specific Pmel-1 CD8 T cells (but not Cd47-deficient Pmel-1 CD8 T cells as they would be subject to innate immune clearance) into B16 tumor-bearing mice and found that Cd47-Het Pmel-1 CD8 TILs, as compared to the Cd47-WT Pmel-1 CD8 TILs, exhibit less expression of exhaustion-related genes (e.g. Pdcd1, Lag3 and Tox), and increased expression of genes associated with T cell activation and proliferation (e.g. Mki67, Lck, Cd69, Gzma, Gzmk). We further confirmed that thrombospondin-1 (TSP-1), as an extracellular matrix protein and a ligand of CD47, contributes to driving the differentiation of CD8 T cells toward exhaustion. Our data highlight for the first time the potential of extracellular matrix protein TSP-1 in programming CD8 T cell exhaustion in cancer through its interaction with CD47 expressed on CD8 T cells.

Citation Format: Chien-Huan Weng, Fadi Samaan, Sadna Budhu, Levi Mangarin, Sébastien Monette, Cailian Liu, Stephane Pourpe, Linda Hamadene, Hong Zhong, Xia Yang, David Schroder, Roberta Zappasodi, Pamela Holland, Jedd D. Wolchok, Taha Merghoub. Potential role of CD47 in T cell exhaustion program [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6150.

Abstract 1291: APR-246 enhances tumor immunogenicity even in the absence of p53

Despite the significant success of immunotherapy, more than 40% of cancer patients remain unresponsive or exhibit an insufficient response. Well-designed combinations of targeted therapy and immunotherapy have the potential to increase effectiveness of cancer treatment and overcome the absence of response to either therapy alone. Since targeted therapies that enhance tumor antigenicity can enhance the effectiveness of immune based therapies, we have built a compendium of in vitro and in vivo assays to evaluate the effect of multiple immunogenic drugs. In these assays, we use the preclinical melanoma cell line B16-F10 model as it is highly metastatic and responds poorly to immunotherapy alone. The tumor suppressor p53 is a key target both in terms of targeted therapy owing to its role in halting tumor progression as well as in combination with immunotherapy, since p53 has varied roles in immune modulation. APR-246 can activate p53 and elicit some p53-independent effects in various tumor models predominantly through the induction of endoplasmic reticulum stress and oxidative stress. Since these cellular stressors (including p53) have been shown to be capable of rendering tumor cells immunogenic, we hypothesized that APR-246 may also increase the antigenicity of tumor cells. Indeed, we observed that treatment of B16 cells with APR-246 increases their MHC expression. Additionally, in our in vitro co-culture assays, cells treated with APR-246 were able to activate antigen-specific cytotoxic T cells either directly or via CD11c+ cells. We also observed that mice immunized with APR-246-treated B16 cells and then implanted with healthy untreated melanoma cells, were able to confer prolonged tumor free survival. Taken together, we believe that APR-246 has the potential to make for a strong combination with immunomodulatory therapies owing to its immunogenic potential. Based on these observations, we rationally designed a combination treatment regimen that would further enhance the immunogenic effects elicited by APR-246 on tumor cells. The triple combination of APR-246 with the TLR4 agonist, Monophosphoryl lipid A (MPL) and the anti-CD40 antibody significantly reduced the growth of B16 tumor in C57BL/6J mice. Strikingly, using CRISPR generated B16 p53 KO cells, we have discovered that these effects of APR-246 exist even in the absence of p53, albeit slightly reduced. Therefore, our results indicate that combination of APR-246 with immunomodulatory agents may be effective in treating cancers irrespective of their genetic status of p53. Our finding suggests that drugs with immunogenic potential, in addition to their original therapeutic indication, such as APR-246 are good candidates for the improvement of various clinically relevant immune modulatory therapies. Note: D.V. and J.M. contributed equally to this work.

Citation Format: Divya Venkatesh, Judith Michels, Cailian Liu, Sadna Budhu, Mariam M. George, Lars Abrahmsen, Roberta Zappasodi, Jedd D. Wolchok, Taha Merghoub. APR-246 enhances tumor immunogenicity even in the absence of p53 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1291.

Abstract 3537: Pharmacologic inhibition of the glycolytic pathway improves response to immune checkpoint blockade

Preferential engagement in glycolysis is a hallmark of cancer cells and contributes to the progression and metastasis of many tumor types, including melanoma and triple-negative breast cancer (TNBC). Tumor reliance on glycolysis is emerging as a mechanism of resistance to immunotherapy, due in part to lactate-mediated immunosuppression and competition for glucose between effector T cells and tumor cells within the tumor microenvironment. Elevated serum lactate dehydrogenase (LDH) levels are associated with poor outcomes in cancer patients, and we observed that serum lactate and LDH levels correlate with primary tumor burden in mice. We recently demonstrated that genetic dampening of LDH subunit A in 4T1 TNBC results in improved and long-lasting anti-tumor responses to CTLA-4 blockade in mice. Therefore, we hypothesize that combining LDH inhibitors (LDHi) with CTLA-4 blockade will be an effective strategy to combat resistance to anti-CTLA-4 therapy. Since activated T cells rely on glycolysis, we first determined that glycolytic cancers overexpress LDH (compared with immune cells) by analyzing single-cell transcripts from patient melanoma biopsies. LDHA gene expression is significantly higher in malignant cells than infiltrating CD8+ T cells, and we replicated these findings at the protein level in whole cell lysate from B16-F10 melanoma and 4T1 TNBC tumor cells and tumor-antigen specific T cells in vitro. We show that LDHi reduces tumor lactate production and glucose consumption without inhibiting anti-tumor T-cell killing in vitro. The anti-tumor effect of LDH inhibition requires adaptive immunity, as daily treatment with LDHi results in reduced tumor burden in immunocompetent but not immune-deficient mice. Finally, we show that targeting LDH in combination with CTLA-4 blockade is more effective in slowing B16-F10 growth compared with CTLA-4 blockade alone, and that this combination promotes effector T cell activation while destabilizing regulatory T cell function.

Citation Format: Svena Verma, Inna Serganova, Sadna Budhu, Lauren Dong, Myat Ko, Levi Mangarin, Taha Merghoub, Jedd Wolchok, Roberta Zappasodi. Pharmacologic inhibition of the glycolytic pathway improves response to immune checkpoint blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3537.

Abstract 5217: Defining the balance of anti-viral and anti-tumor T cell responses to oncolytic virus therapy using single cell approaches

Preclinical and clinical studies have shown that intratumoral oncolytic viruses (OVs) can potentiate host anti-tumor immunity and overcome resistance to immune checkpoint blockade, although clinical responses to OVs have been modest to date. While T cell infiltration of tumors is frequently cited as a measure of OV immunogenicity, this measure is non-specific as OVs elicit a strong virus-directed T cell response, and it remains unknown what proportion of T cells expanded by OV therapy are virus-specific vs. tumor-specific or how these T cells distribute across virus-treated and distant tumors. We employed oncolytic Newcastle disease virus (NDV) in a bilateral flank melanoma mouse model to identify and phenotypically characterize anti-viral and anti-tumor T cells using single cell (sc) RNA and T cell receptor (TCR) sequencing. Intratumoral NDV therapy to a single flank tumor resulted in increased infiltration of CD4+ and CD8+ T cells in the injected (enestic) and distant (non-enestic) tumors and increased the breadth of the TCR repertoire at both sites with preferential expansion of several dominant clonotypes. There was substantial expansion of the proportion of T cell clonotypes shared between enestic and nonenestic tumors as well as the spleen, indicative of inter-tumor TCR repertoire normalization. In both treated and distant tumors, we observed a significant increase in the frequency of convergent TCR clonotypes, i.e. TCRs encoded by different nucleotide sequences that converge on the same amino acid sequence, implying that the presence of these TCRs in tumors is non-random. Using scRNA and paired TCR sequencing, we demonstrate that NDV therapy leads to expansion of unique clusters of terminally differentiated and activated CD4+ and CD8+ T cells associated with distinct TCR-based clonotypes. Notably, the predominant phenotypic clusters were distinct between the enestic and non-enestic tumors. Enestic tumors were dominated by CD8+ T cells exhibiting a signature associated with terminal dysfunction (PDCD1, LAG3, TOX), while the predominant expanded CD8+ T cells in non-enestic tumors exhibited an activation signature associated with high expression of cytolytic markers. While phenotypic states were conserved for the dominant TCR clones shared across the enestic and non-enestic tumors, TCRs unique to the non-enestic tumor were predominantly associated with an activated T cell state. Taken together, these studies highlight that T cells expanded by OV therapy exhibit unique functional states and TCRs in treated and distant tumors and imply that virus- and tumor-specific T cells may be identified by distinct TCR repertoires and phenotypes. Understanding the balance between virus- and tumor-directed T cells elicited by OV therapy will be key to engineering OVs and designing combination strategies that drive stronger tumor-directed T cell response.

Citation Format: Bharat Burman, Nicholas Ceglia, Daniel Hirschhorn, Sadna Budhu, Levi Mangarin, Anton Oseledchyk, Yonina Bykov, Andrew McPherson, Sohrab Shah, Jedd Wolchok, Taha Merghoub, Dmitriy Zamarin. Defining the balance of anti-viral and anti-tumor T cell responses to oncolytic virus therapy using single cell approaches [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5217.

Tumor-induced double positive T cells display distinct lineage commitment mechanisms and functions

Transcription factors ThPOK and Runx3 regulate the differentiation of "helper" CD4+ and "cytotoxic" CD8+ T cell lineages respectively, inducing single positive (SP) T cells that enter the periphery with the expression of either the CD4 or CD8 co-receptor. Despite the expectation that these cell fates are mutually exclusive and that mature CD4+CD8+ double positive (DP) T cells are present in healthy individuals and augmented in the context of disease, yet their molecular features and pathophysiologic role are disputed. Here, we show DP T cells in murine and human tumors as a heterogenous population originating from SP T cells which re-express the opposite co-receptor and acquire features of the opposite cell type's phenotype and function following TCR stimulation. We identified distinct clonally expanded DP T cells in human melanoma and lung cancer by scRNA sequencing and demonstrated their tumor reactivity in cytotoxicity assays. Our findings indicate that antigen stimulation induces SP T cells to differentiate into DP T cell subsets gaining in polyfunctional characteristics.

Isoform specific anti-TGFβ therapy enhances antitumor efficacy in mouse models of cancer

TGFβ is a potential target in cancer treatment due to its dual role in tumorigenesis and homeostasis. However, the expression of TGFβ and its inhibition within the tumor microenvironment has mainly been investigated in stroma-heavy tumors. Using B16 mouse melanoma and CT26 colon carcinoma as models of stroma-poor tumors, we demonstrate that myeloid/dendritic cells are the main sources of TGFβ1 and TGFβ3. Depending on local expression of TGFβ isoforms, isoform specific inhibition of either TGFβ1 or TGFβ3 may be effective. The TGFβ signature of CT26 colon carcinoma is defined by TGFβ1 and TGFβ1 inhibition results in tumor delay; B16 melanoma has equal expression of both isoforms and inhibition of either TGFβ1 or TGFβ3 controls tumor growth. Using T cell functional assays, we show that the mechanism of tumor delay is through and dependent on enhanced CD8+ T cell function. To overcome the local immunosuppressive environment, we found that combining TGFβ inhibition with immune checkpoint blockade results in improved tumor control. Our data suggest that TGFβ inhibition in stroma poor tumors shifts the local immune environment to favor tumor suppression.

99 T cell immunotherapies trigger neutrophil activation to eliminate tumor antigen escape variants

Background

Targeted immune-based therapies such as adoptive T cell transfer (ACT) are often ineffective because tumors evolve over time and under selective pressure display antigen loss variant clones. A classic example in melanoma is de-differentiation and loss of expression of antigenic proteins. Therapies that activate multiple branches of the immune system may eliminate such escape variants

Methods

Here we show that melanoma-specific CD4+ ACT therapy in combination with OX40 co-stimulation or CTLA-4 blockade can eradicate large melanoma tumors with clonal escape variants.

Results

Early on-target recognition of melanoma antigens by adoptively transferred tumor-specific CD4+ T cells was required. Surprisingly, however, complete tumor eradication was partially dependent on neutrophils. Supporting these findings, extensive neutrophil activation and neutrophil extracellular traps were found in mouse tumors and in biopsies of melanoma patients treated with immune checkpoint blockade.

Conclusions

Our findings uncover a novel interplay between T cells mediating the initial tumor- and tissue-specific immune response, and neutrophils mediating tumor destruction of antigen loss variants.

Ethics Approval

All tissues were collected at MSKCC following study protocol approval by the MSKCC Institutional Review Board. All mouse procedures were performed in accordance with institutional protocol guidelines at Memorial Sloan-Kettering Cancer Center (MSKCC) under an approved protocol.

604 Combining a novel dual RAF/MEK inhibitor with immunomodulation to promote an anti-tumor response

Background

The therapeutic scope of MEK inhibitors (MEKis) is currently limited to use in BRAF mutant melanoma. Therefore, we aim to develop new strategies to extend their usage to MEKi resistant RAS mutant cancers, which represent an unmet clinical need. In Ras mutant murine lung cancers, CH5126766 (CKI27) is novel due to its ability to inhibit both RAF and MEK, preventing the rebound of p-ERK that normally results from the relief of negative feedback in the MAPK/ERK pathway. However, CKI27 is also capable of inhibiting T cell functions because the MAPK/ERK pathway is activated downstream of T cell receptor signaling. We aim to balance the positive and negative immunomodulatory effects of MEKis for optimal combination with immunotherapy.

Methods

To evaluate the effects of CKI27 on tumor cells and T cells in vitro, we performed flow cytometry, cytokine analysis, and functional co-culture assays. Lewis lung carcinoma (LLC) tumor bearing mice were treated either with CKI27 combined with co-stimulatory agonist antibody targeting GITR and checkpoint blockade antibody targeting CTLA-4 or the appropriate controls to determine efficacy and changes in the tumor microenvironment.

Results

We observed that CKI27 increased MHC expression on tumor cells and T cell mediated killing. Yet, CKI27 also decreased T cell proliferation, activation, and cytolytic activity. Implementing a break for T cells to recover with intermittent dosing of CKI27 partially relieved these inhibitory effects. Further combination with agonist antibodies anti-OX40 and GITR completely alleviated these T cell toxicities and increased combination efficacy with checkpoint blockade antibody anti-CTLA-4.

Conclusions

Understanding the immunomodulatory effects of combining CKI27 with immunotherapy will elucidate the mechanism behind their increased efficacy. This will allow us to make more informed decisions in dosing regimens, overcoming resistance, and generating long-term immune responses in current and future clinical trials treating patients with RAS mutant cancers.

567 Isoform specific anti-TGFβ therapy enhances antitumor efficacy in mouse models of stroma poor cancers

Background

TGFβ is a potential target in cancer treatment due to its dual role in tumorigenesis and homeostasis. There are three isoforms of TGFβ (TGFβ1, TGFβ2 and TGFβ3), which are secreted by immune and non-immune cells as an inactive latent complex. Depending on the local context and players, TGFβ can adopt opposing roles in carcinogenesis and in modulating the immune system. However, the expression of TGFβ and its inhibition within the tumor microenvironment has mainly been investigated in stroma-rich tumors.

Methods

We examined expression of TGFβ1 and TGFβ3 isoforms on immune cells in two stroma-poor mouse tumor models (B16 melanoma and CT26 colon carcinoma) and investigated the anti-tumor efficacy of antibodies that block TGFβ1 and TGFβ3 in these two models.

Results

Depending on local expression of TGFβ isoforms, specific inhibition of either TGFβ1 or TGFβ3 may be effective. The ”TGFβ signature” of CT26 colon carcinoma is defined by TGFβ1 expression on immune cells and TGFβ1 inhibition results in tumor delay; B16 melanoma has equal expression of both TGFβ1 or TGFβ3 isoforms and inhibition of either TGFβ1 or TGFβ3 controls tumor growth. We show that the mechanism of tumor growth delay is enhanced CD8+ T cell activation and effector function. In addition, we found that combining TGFβ inhibition with immune checkpoint blockade results in improved tumor control and survival.

Conclusions

Our findings suggests that expression of TGFβ isoforms in the TME is variable in different tumor types and their expression may be used to predict anti-tumor responses to TGFβ inhibition. Isoform specific TGFβ inhibition in stroma poor tumors shifts the local immune environment to favor tumor regression alone or in combination with immune checkpoint blockade.

Cyclophosphamide enhances the antitumor potency of GITR engagement by increasing oligoclonal cytotoxic T cell fitness

Only a subset of cancer patients responds to checkpoint blockade inhibition in the clinic. Strategies to overcome resistance are promising areas of investigation. Targeting glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) has shown efficacy in preclinical models, but GITR engagement is ineffective in controlling advanced, poorly immunogenic tumors, such as B16 melanoma, and has not yielded benefit in clinical trials. The alkylating agent cyclophosphamide (CTX) depletes regulatory T cells (Tregs), expands tumor-specific effector T cells (Teffs) via homeostatic proliferation, and induces immunogenic cell death. GITR agonism has an inhibitory effect on Tregs and activates Teffs. We therefore hypothesized that CTX and GITR agonism would promote effective antitumor immunity. Here we show that the combination of CTX and GITR agonism controlled tumor growth in clinically relevant mouse models. Mechanistically, we show that the combination therapy caused tumor cell death, clonal expansion of highly active CD8+ T cells, and depletion of Tregs by activation-induced cell death. Control of tumor growth was associated with the presence of an expanded population of highly activated, tumor-infiltrating, oligoclonal CD8+ T cells that led to a diminished TCR repertoire. Our studies show that the combination of CTX and GITR agonism is a rational chemoimmunotherapeutic approach that warrants further clinical investigation.

Tim-4+ cavity-resident macrophages impair anti-tumor CD8+ T cell immunity

Immune checkpoint blockade (ICB) has been a remarkable clinical advance for cancer; however, the majority of patients do not respond to ICB therapy. We show that metastatic disease in the pleural and peritoneal cavities is associated with poor clinical outcomes after ICB therapy. Cavity-resident macrophages express high levels of Tim-4, a receptor for phosphatidylserine (PS), and this is associated with reduced numbers of CD8+ T cells with tumor-reactive features in pleural effusions and peritoneal ascites from patients with cancer. We mechanistically demonstrate that viable and cytotoxic anti-tumor CD8+ T cells upregulate PS and this renders them susceptible to sequestration away from tumor targets and proliferation suppression by Tim-4+ macrophages. Tim-4 blockade abrogates this sequestration and proliferation suppression and enhances anti-tumor efficacy in models of anti-PD-1 therapy and adoptive T cell therapy in mice. Thus, Tim-4+ cavity-resident macrophages limit the efficacy of immunotherapies in these microenvironments.

Abstract 1663: Activation of STING in response to partial-tumor radiation exposure

Purpose: To determine whether STING activation is involved in partial volume radiation therapy.

Background: The potential of radiotherapy (RT) to induce immune recognition of cancer cells is a growing topic of research. It has been suggested that partial volume irradiation used in GRID therapy/Lattice RT, a type of RT in which radiation does not cover the entire tumor intentionally but rather is spatially fractionated, sometimes induces an immune response. We previously showed that a single dose of radiation delivered to half of the tumor (50% RT) activated an anti-tumor immune response comparable to the response in a fully-irradiated tumor in the immunogenic 67NR murine tumor model (breast carcinoma) and in the less immunogenic and more radioresistant Lewis lung carcinoma (LLC) tumor model. We have also demonstrated that this immune response was due to the infiltration of CD8+ T cells along with an increased expression of ICAM adhesion molecules. Treatment with either anti-CD8 or anti-ICAM antibodies abrogated the hemi-RT response. Furthermore, a significant abscopal effect was observed after partial irradiation with a single dose of 10Gy in a bilateral 67NR tumors model. It has been shown that ionizing radiation can mediate antitumor immunity via the activation of the cytosolic DNA sensor cGAS/STING pathway. Therefore, in this study, we tested whether the hemi-irradiation-mediated immune response involves the cGAS/STING canonical pathway, or a non-canonical activation of STING, in the 67NR or LLC tumor models. It has been reported that STING can be activated, independently of cGAS, via non-canonical activation of STING, involving ATM and TRAF6, among other factors.

Brief methods: We investigated 67NR murine orthotopic breast tumors in Balb/c mice and LLC cells injected in the flank of C57Bl/6, cGAS or STING KO mice. RT was delivered to 50% or 100% of the tumor volume using a 2X2 cm collimator on a microirradiator allowing precise irradiation. Tumors were collected at different time points post-RT and assessed for different measurements.

Results: There is significant activation of the cGAS/STING pathway in the hemi-irradiated tumors as compared to control and to 100% exposed 67NR tumors. Interestingly, the increased expression of the cGAS/STING pathway was found in the hemi-irradiated tumor but, also in the non-irradiated part of the tumor. In the LLC model, a non-canonical activation of STING is involved. Using both cGAS and STING KO mice, we demonstrated that the partial exposure RT-mediated immune response is dependent on STING activation in the host while cGAS is dispensable.

Conclusions: Identifying the upstream pathways responsible for STING activation in the partial RT-mediated immune response in different tumor types would improve this therapy and its potential combination with immune checkpoint blockade.

Citation Format: Mickael Mathieu, Prerna R. Nepali, Sadna Budhu, Simon N. Powell, John L. Humm, Joseph O. Deasy, Adriana Haimovitz-Friedman. Activation of STING in response to partial-tumor radiation exposure [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1663.

Neoadjuvant vascular-targeted photodynamic therapy improves survival and reduces recurrence and progression in a mouse model of urothelial cancer

Locally advanced urothelial cancer has high recurrence and progression rates following surgical treatment. This highlights the need to develop neoadjuvant strategies that are both effective and well-tolerated. We hypothesized that neoadjuvant sub-ablative vascular-targeted photodynamic therapy (sbVTP), through its immunotherapeutic mechanism, would improve survival and reduce recurrence and progression in a murine model of urothelial cancer. After urothelial tumor implantation and 17 days before surgical resection, mice received neoadjuvant sbVTP (WST11; Tookad Soluble, Steba Biotech, France). Local and systemic response and survival served as measures of therapeutic efficacy, while immunohistochemistry and flow cytometry elucidated the immunotherapeutic mechanism. Data analysis included two-sided Kaplan-Meier, Mann-Whitney, and Fischer exact tests. Tumor volume was significantly smaller in sbVTP-treated animals than in controls (135 mm3 vs. 1222 mm3, P < 0.0001) on the day of surgery. Systemic progression was significantly lower in sbVTP-treated animals (l7% vs. 30%, P < 0.01). Both median progression-free survival and overall survival were significantly greater among animals that received sbVTP and surgery than among animals that received surgery alone (P < 0.05). Neoadjuvant-treated animals also demonstrated significantly lower local recurrence. Neoadjuvant sbVTP was associated with increased early antigen-presenting cells, and subsequent improvements in long-term memory and increases in effector and active T-cells in the spleen, lungs, and blood. In summary, neoadjuvant sbVTP delayed local and systemic progression, prolonged progression-free and overall survival, and reduced local recurrence, thereby demonstrating therapeutic efficacy through an immune-mediated response. These findings strongly support its evaluation in clinical trials.

Abstract IA04: Overcoming immune resistance with rationally designed combination immunotherapy

Over the past decade, blockade of the immune checkpoints CTLA-4, PD-1, and PD-L1 has been demonstrated to significantly extend survival of cancer patients across multiple tumor types, including metastatic melanoma, formally proving that immunotherapy is a viable option for the treatment of cancer. These successes have paved the way for the development of additional immune-modulatory antibodies, blocking alternative inhibitory receptors, or engaging costimulatory receptors such as the TNF receptor family member GITR. However, the clinical experience accumulated thus far with checkpoint blockade has clearly shown that only a limited fraction of patients achieve durable clinical benefit with these treatments. This highlights the need to deepen our understanding of the molecular mechanisms underlying response and resistance to immunotherapy and design more personalized and rational combinations based on these therapies. Immune-regulatory mechanisms are one of the major barriers limiting efficacy of immunotherapy. CTLA-4 blockade and GITR costimulation are two immunotherapeutic strategies known to interfere with conventional immunosuppressive regulatory T cells (Tregs). We thus investigated the effects of CTLA-4 blockade and GITR costimulation on suppressive T cells in in vivo mouse melanoma models resistant to these therapies with the aim to clarify the molecular mechanisms underlying refractoriness and provide the rationale to develop more effective therapeutic combinations. To understand the clinical relevance of these findings, we explored the same effects in cancer patients treated with CTLA-4 blockade or GITR costimulation. We found that CTLA-4 blockade, while counteracting conventional Tregs, promotes the expansion of a subset of CD4+Foxp3-T cells expressing high levels of PD-1 (4PD1hi), which constitute a new immunosuppressive T-cell population with T-follicular-helper-like features. Importantly, we observed that anti-CTLA-4 increases the frequency of circulating 4PD1hi in a dose-dependent manner. In contrast, PD-1 blockade decreases 4PD1hi in function of its clinical activity, underscoring the relevance of this cell subset as a pharmacodynamic and prognostic biomarker of checkpoint blockade. These findings indicate that optimizing checkpoint blockade doses and combination regimens so as to keep 4PD1hi in the right balance may favor a positive outcome. In mouse melanoma models of response (early tumors) and refractoriness (advanced tumors) to GITR agonism, we found that anti-GITR efficiently reduces Tregs and increases effector:Treg ratios in both curative and refractory treatment conditions. However, T-cell activation and cytotoxic functions are favored selectively in the presence of low tumor burden. Counteracting exhaustion with PD-1 blockade in combination with GITR agonism restored responsiveness of advanced tumors and CD8+ T-cell functionality. Aligned with the effects of anti-GITR in mice, we found that the agonist anti-human GITR antibody TRX518 decreases Tregs in peripheral blood and tumor to similar extents in patients treated in the first-in-human single-dose monotherapy trial (NCT01239134). However, coincident downregulation of Tregs in the peripheral blood and at the tumor site upon TRX518 was not sufficient to achieve substantial clinical responses in this population of advanced solid cancer patients. This suggests that Treg elimination from advanced tumors may not be sufficient to activate cytotoxic T-cell responses unless the T-cell exhaustion process is concurrently blocked. Based on these preclinical and clinical observations, we have started to explore anti-GITR in combination with PD-1 pathway blockade in patients with advanced solid tumors (NCT02628574). Taken as a whole, these findings illustrate the value of conventional and nonconventional immune-suppressive T cells as biomarkers of biologic and therapeutic activity of immunotherapy in melanoma and other tumor types. In addition, these results indicate that inhibition of immune-regulatory mechanisms, such as immunosuppressive T cells, may need to be associated with strategies able to positively activate T-cell responses to achieve significant clinical benefit.

Citation Format: Roberta Zappasodi, Sadna Budhu, Cynthia Sirard, Jingjing Qi, Cailian Liu, Yanyun Li, Yasin Senbabaoglu, Sasikanth Manne, Billel Gasmi, Hong Zhong, Xia Yang, Moshen Abu-Akeel, David Schaer, Alexander Huang, Walter Newman, Philip Wong, Katherine S. Panageas, Michael A. Postow, Henry Koon, Vamsidhar Velcheti, Margaret K. Callahan, Matthew D. Hellmann, E. John Wherry, Taha Merghoub, Jedd D. Wolchok. Overcoming immune resistance with rationally designed combination immunotherapy [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr IA04.

Phosphatidylserine targeting antibody enhances anti-tumor activity of adoptive cell therapies in a mouse melanoma model

Adoptive cell therapy has emerged as a viable strategy to treat cancer. T cells that recognize tumor antigens can be reinvigorated ex-vivo or autologous T cells can be genetically modified to express anti-tumor T cell receptors (TCRs) or chimeric antigen receptors (CARs). However, once re-infused into patients, these tumor specific T cells are subjected to immunosuppressive signals within the tumor. A critical immune checkpoint within tumors is phosphatidylserine (PS), a phospholipid that is exposed on apoptotic cells and tumor cells. Innate cells exposed to PS secrete suppressive cytokines that can significantly impair the function of tumor specific T cells. Antibodies that target PS can reactivate anti-tumor immunity by reducing the number of MDSCs in tumors and promoting the maturation of functional APCs. Our lab has shown that the mouse chimeric version of PS Targeting monoclonal antibody Bavituximab (1N11), in combination with transgenic CD4+ T cells that recognize melanoma antigen Trp1, can regress advanced melanoma tumors in mice. Here, we demonstrate a 2nd generation CAR T cell, that binds Trp1 on the surface of B16 melanoma, in combination with 1N11 can improve anti-tumor activity and survival in B16 tumor bearing mice. Flow cytometry analysis of immune responses in the tumor of mice treated with tumor specific T cells and 1N11 shows a decrease in M2 macrophages and FoxP3+ regulatory T cells. These findings highlight that diminishing suppressive mechanisms locally with PS targeting can enhance the efficacy of transgenic TCR and CAR T cells to improve the outcome in patients with advanced-stage melanoma. Our studies may inform the design of clinical trials combining PS Targeting antibodies with CAR T cell therapy in solid tumors.

Combining a novel dual RAF/MEK inhibitor with immunomodulation to promote an anti-tumor response

The therapeutic scope of MEK inhibitors (MEKis) is currently limited to use in BRAF mutant melanoma. Therefore, we aim to develop new strategies to extend their usage to MEKi resistant RAS mutant cancers, which represent an unmet clinical need. A strategy we investigated is to balance the positive and negative immunomodulatory effects of MEKis for optimal combination with immunotherapy. In Ras mutant murine lung cancers, CH5126766 (CKI27) is novel due to its ability to inhibit both RAF and MEK, preventing the rebound of ERK that normally results from the relief of negative feedback in the MAPK pathway. We observed that CKI27 increased MHC expression on tumor cells and T cell mediated killing. Yet, CKI27 also decreased T cell proliferation, activation, and cytolytic activity. Implementing a break for T cells to recover with intermittent dosing of CKI27 partially relieved these inhibitory effects. Further combination with co-stimulatory agonist antibodies targeting OX40 and GITR completely alleviated these T cell toxicities and increased combination efficacy with checkpoint blockade antibody anti-CTLA-4. Understanding the immunomodulatory effects of combining CKI27 with immunotherapy will elucidate the mechanism behind their increased efficacy. This will allow us to make more informed decisions in dosing regimens, overcoming resistance, and generating long-term immune responses in current and future clinical trials treating patients with RAS mutant cancers.

Abstract PR05: Blockade of AHR activation by IDO/TDO-derived kynurenine restricts cancer immune suppression

Immune checkpoint blockade (ICB) has been shown to convey significant clinical activity across a spectrum of malignancies, yet there is now recognition that multiple mechanisms of resistance can impair response. The catabolism of tryptophan into metabolites known as kynurenines (Kyn) by enzymes such as indoleamine 2,3-dioxygenase (IDO) or tryptophan 2,3-dioxygenase (TDO) plays a major suppressive role. Recently it was shown that Kyn acts as an endogenous agonist of the Aryl hydrocarbon receptor (AhR). In order to gain a better understanding of this pathway, we sought to characterize the mechanisms of immunosuppression associated with AhR and evaluate its potential as therapeutic target. Gene-expression analysis of IDO-overexpressing melanomas (B16-IDO vs. B16-WT) demonstrated reduced expression levels of Type 1 inflammatory genes, including IFNy, TNF, GzmB, and CD40. In addition, B16-IDO presents higher infiltration of tumor-associated macrophages TAMs, which upregulate the AHR as well as classic AhR-regulated genes (Cyp1a1 and Cyp1b1) and are differentially skewed towards an immunosuppressive M2 phenotype. Tumor-antigen specific CD8+T cells show reduced expression of activation markers (GzmB and CD44) and proliferation rate when primed by Kyn-treated antigen-presenting cells. In addition, TAMs from B16-IDO tumors suppressed activation of CD8+T cells in vitro and their depletion delayed tumor growth. When B16-IDO cells are implanted in mice depleted of Foxp3 expressing cells, TAMs do not accumulate. Treatment of B16-IDO tumors with an AhR-specific antagonist (CH-223191) upregulates MHC II in APCs, activation markers in CD8s, and reduced frequency of T-regs in B16-IDO tumors. AhR inhibition slows tumor growth and prolongs survival of tumors with active IDO/TDO/Kyn pathway (B16-IDO and B16-TDO), and this is enhanced when PD-1 blockade is used in combination. In summary, our findings demonstrate that targeting the Kyn pathway through AhR inhibition could overcome key suppressive mechanisms and sensitize tumors to ICB.

This abstract is also being presented as Poster A57.

Citation Format: Luis F. Campesato, Sadna Budhu, Mathieu Gigoux, Jeremy Tchaicha, Stephane Pourpe, Cailian Liu, Dmitriy Zamarin, Mark G. Manfredi, Karen McGovern, Jedd D. Wolchok, Taha Merghoub. Blockade of AHR activation by IDO/TDO-derived kynurenine restricts cancer immune suppression [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr PR05.

In situ vaccination with defined factors overcomes T cell exhaustion in distant tumors

Irreversible T cell exhaustion limits the efficacy of programmed cell death 1 (PD-1) blockade. We observed that dual CD40-TLR4 stimulation within a single tumor restored PD-1 sensitivity and that this regimen triggered a systemic tumor-specific CD8+ T cell response. This approach effectively treated established tumors in diverse syngeneic cancer models, and the systemic effect was dependent on the injected tumor, indicating that treated tumors were converted into necessary components of this therapy. Strikingly, this approach was associated with the absence of exhausted PD-1hi T cells in treated and distant tumors, while sparing the intervening draining lymph node and spleen. Furthermore, patients with transcription changes like those induced by this therapy experienced improved progression-free survival with anti-PD-1 treatment. Dual CD40-TLR4 activation within a single tumor is thus an approach for overcoming resistance to PD-1 blockade that is unique in its ability to cause the loss of exhausted T cells within tumors while sparing nonmalignant tissues.

Abstract 2711: Rational combination of GITR agonism with PD-1 blockade

The clinical successes of checkpoint blockade have demonstrated that proper modulation of T cell co-inhibitory/co-stimulatory pathways can achieve substantial anti-tumor activity. However, many patients are or become refractory to checkpoint blockade. Additional forms of immunotherapy targeting alternative immune pathways are thus needed. Antibodies (Abs) engaging the TNF receptor GITR can enhance T cell functions and counteract regulatory T cell (Treg) suppression and have shown potent anti-tumor activity in animal models. Based on this evidence, we initiated the first in-human phase-I trial with the humanized aglycosylated anti-GITR Ab TRX518 (NCT01239134). Here, we report the immune effects of a single ascending dose of TRX518 monotherapy in 37 advanced cancer patients in this phase-I trial and provide mechanistic preclinical evidence to rationally combine GITR agonism with checkpoint blockade. We found that TRX518 frequently reduces circulating Tregs. In 8 patients for whom pre- and post-treatment tumor biopsies were available, reductions in intra-tumor and circulating Tregs after TRX518 were positively correlated. Yet, these patients did not experience substantial clinical responses. To explain this outcome, we modeled sensitivity and refractoriness to anti-GITR by treating B16F10-melanoma-bearing mice with the Ab DTA-1 on day 4 (curative regimen) or day 7 (refractory regimen) after tumor implantation respectively. We found that Tregs were significantly reduced and CD8+:Treg and Teff:Treg ratios increased in both responding and refractory tumors. Interestingly, CD8+ T cells from refractory tumors overexpressed T cell exhaustion markers and did not up-regulate memory and functional markers. We thus tested whether counteracting exhaustion could overcome resistance of advanced tumors to anti-GITR. PD-1 blockade in combination with anti-GITR starting on day 7 after tumor implantation controlled tumor growth similar to the curative anti-GITR monotherapy regimen (day 4 treatment) and achieved 50% complete response rate associated with long-lasting anti-tumor immunological memory. This was associated with more activated and less exhausted profiles of intra-tumor CD8+ T cells, which displayed enhanced tumor-lytic capacity compared to CD8+ T cells from non-responding tumors treated with each agent alone. These results indicate that Treg reduction can serve as a pharmacodynamic biomarker of anti-GITR in patients. However, Treg elimination from advanced tumors may not be sufficient to activate cytotoxic CD8+ T cell responses unless the T cell exhaustion process is concurrently blocked. This provides the rationale to combine immunotherapies targeting Tregs with strategies able to counteract exhaustion, such as anti-PD-1, to regress advanced tumors. Based on these observations, we have started to investigate TRX518 in combination with PD-1 pathway blockade in patients with advanced solid tumors (NCT02628574).

Citation Format: Roberta Zappasodi, Cynthia Sirard, Yanyun Li, Sadna Budhu, Moshen Abu-Akeel, Cailian Liu, Xia Yang, Hong Zhong, Walter Newman, Jingjing Qi, Philip Wong, David Schaer, Henry Koon, Vamsidhar Velcheti, Margaret K. Callahan, Jedd Wolchok, Taha Merghoub. Rational combination of GITR agonism with PD-1 blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2711.

Abstract 3735: An anti-tumor immune response is evoked by partial-volume single dose radiation

Purpose: To study tumor growth delay resulting from partial irradiation in preclinical mouse models.

Methods and Materials: We investigated 67NR murine orthotopic breast tumors in both immunocompetent and nude mice. Treatment was delivered to 50% or 100% of the tumor using a 2x2 cm collimator on a micro-irradiator. Radiation response was modulated by treating with anti-CD8 and anti-ICAM antibodies. Similar experiments were performed using the less immunogenic Lewis Lung Carcinoma (LLC) mouse model. Tumor growth delay and γH2AX phosphorylation were measured and immune response was assessed by immunofluorescence and flow cytometry at 1 and 7 days post-radiotherapy (RT). Tumor expression of cellular adhesion molecules was also measured at different times post-RT.

Results: Partial irradiation led to tumor responses similar to fully exposed tumors in immunocompetent mice, but not in nude mice. After a single dose of 10Gy, infiltration of CD8+ T cells was observed, along with increased expression of ICAM. The response to 10Gy in hemi-irradiated tumors was abrogated by treatment with either anti-CD8 or anti-ICAM antibodies. Similar responses were obtained in the less immunogenic LLC mouse model delivering 15Gy to half the tumor volume. Treatment with FTY720, a compound that inhibits T cell egress from lymph nodes, did not affect tumor response at the time of CD8+ T cells infiltration in the non-irradiated area of the tumor, indicating that the most likely source of these cells is the irradiated portion of the hemi-irradiated tumors. In addition, a significant abscopal effect was observed after partial irradiation with a single dose of 10Gy in the 67NR model.

Conclusions: In these models, radiation controls tumor growth both directly through cell killing and indirectly through immune activation. This raises the possibility that this effect could be induced in the clinic.

Citation Format: Adriana Haimovitz-Friedman, Johnn Humm, Joseph O. Deasy, Jedd Wolchok, Taha Merghoub, James Russell, Hongyan Li, Robert Samstein, Sadna Budhu, Simon Powell, Chloe Bodden, Ela Markovsky, Qing Chen. An anti-tumor immune response is evoked by partial-volume single dose radiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3735.

Abstract 4843: TP53-stabilization with APR-246 enhances antitumor effects of immune checkpoint blockade in preclinical models

An emerging body of literature suggests a role of TP53 pathway in antitumor immunity including antigen presentation and T cell proliferation. Stabilization of TP53 could therefore alter the immune tumor microenvironment, enabling the immune system to target tumor cells more effectively. APR-246 covalently modifies the core domain of cellular TP53 through the alkylation of thiol groups, leading to reactivation of endogenous TP53 activity. To further study the effect of APR-246 on antitumor immunity we used a B16 pre-clinical melanoma mouse model. In vitro treatment of B16 cells with APR-246 caused intracellular accumulation of TP53, leading to increased apoptosis. However, treatment of B16-melanoma bearing mice with APR-246 monotherapy did not result in a statistically significant change in tumor growth or survival. Analyses of the tumor immune microenvironment showed increased immune potentiating M1 polarized tumor-associated macrophages, and Granzyme B activity in CD8+ T cells, suggesting enhanced anti-tumor immunity. Concomitantly, there was increased PD-L1 expression in the macrophages, PD-1 expression on CD8+ T cells, and Foxp3+ Tregs in tumors from APR-246 treated animals. Therefore, we decided to combine anti-PD-1 antibody (RMP-1) to APR-246 treatment in tumor-bearing mice. The combination led to a significant delay in tumor growth (P &lt; 0.001) and improved survival of B16-bearing mice compared to anti-PD1 or APR-246 monotherapies (P &lt; 0.01). Improved responses were also seen in MC38 colorectal cancer-bearing mice (P &lt; 0.01). The anti-tumor effects of APR-246 and anti-PD1 were T cell dependent and abrogated in hosts lacking T cells. Analyses of the tumor immune microenvironment showed that the combination decreases proliferation but increases cytolytic activity of CD8+ T cells compared to anti-PD1 alone. We next studied the effect of combining APR-246 with anti-PD1+ anti-CTLA-4 (9B9). Combination of APR-246 with dual immune checkpoint blockade using anti-PD1 and anti-CTLA-4 showed further tumor growth inhibition in B16-melanoma compared to monotherapies (P &lt; 0.001). Our studies support a role for restoring TP53 in the tumor microenvironment and provide evidence that reactivation of TP53 by APR-246 can enhance anti-tumor immune responses and inhibit tumor growth in preclinical models.

Citation Format: Arnab Ghosh, Judith Michel, Lauren Dong, Nathan Suek, Hong Zhong, Sadna Budhu, Olivier de Henau, Jedd Wolchok, Taha Merghoub. TP53-stabilization with APR-246 enhances antitumor effects of immune checkpoint blockade in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4843.

Preoperative checkpoint inhibition (CPI) and cryoablation (Cryo) in women with early-stage breast cancer (ESBC)

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Background: Checkpoint inhibition (CPI) combined with local strategies that cause local tumor destruction, such as cryo may augment tumor specific immunity and improve survival. We previously demonstrated in 18 ESBC patients (pts) that pre-operative (pre-op) cryo with ipilimumab (ipi) is not only safe but also generates robust local and systemic immune responses (NCT01502592). Given the added activity of dual CPI in other tumors, we undertook a second pilot study of pre-op ipi/nivolumab (nivo)/cryo to confirm the safety of this combination and the impact on immune biomarkers. Methods: In both pilot studies, eligible pts had operable ≥1.5cm invasive HER2 negative ESBC. CPI was administered 8-15d prior to, and cryo was performed 7-10d prior to, standard-of-care (SOC) surgery. Toxicity evaluation continued for 12wks after drug administration. Blood for immune correlates was obtained at baseline, cryo, surgery and 2-4 weeks thereafter. Tumor samples were obtained at cryo and surgery. Flow-cytometry of peripheral lymphocytes was compared to previously reported ipi/cryo responses. Results: After a median follow-up of 66 months all 18 ESBC ipi/cryo pts, including 3 TNBC pts, are recurrence free. In the ipi/nivo/cryo study, the safety primary endpoint was met when 5 pts underwent SOC surgery without delay. Ipi/nivo/cryo was well tolerated overall. One pt on an aromatase inhibitor had grade 4 liver toxicity 8 weeks after surgery. One pt, 3 weeks after her SOC surgery, developed grade 1 hyperthyroidism, preventing a secondary axillary dissection from proceeding as scheduled. Robust activation of peripheral CD4+ and CD8+ T cells peaked at week 2 post ipi/nivo with the majority of activated CD8+ T cells expressing PD1. Comparing the correlatives of the ipi/nivo/cryo study with the prior ipi/cryo study, we observed higher expression of activation markers (Ki-67, ICOS, CTLA-4, LAG-3) on peripheral T cells and downregulation of suppressor cells. Conclusions: Ipi/cryo-treated pts, including 3 TNBC pts, remain recurrence free after > 5y. Combining cryo with ipi/nivo preop is feasible, safe, and associated with greater T cell activation than ipi/cryo alone. These results informed an ongoing randomized phase 2 study of pre-op ipi/nivo/cryo versus SOC in women with residual TNBC after neoadjuvant chemotherapy (NCT03546686). Clinical trial information: NCT02833233.

Isoform specific anti-TGFβ therapy enhances antitumor efficacy in mouse models of cancer

TGFβ is a pleotropic cytokine, which has emerged as a potential target in cancer treatment due to its dual role in tumorigenesis and homeostasis. There are three isoforms of TGFβ (TGFβ1, TGFβ2 and TGFβ3), which are secreted by immune and nonimmune cells as an inactive latent complex. Depending on the local context and players, TGFβ can adopt opposing roles in carcinogensis and in modulating the immune system. However, the expression of TGFβ isoforms within the tumor microenvironment and isoform specific inhibition remains to be investigated. The main source of TGFβ isoforms in the tumor microenvironment of B16 melanoma are infiltrating immune cells, with TGFβ1 and TGFβ3 being highly expressed on myeloid and dendritic cells. The CD45− population from B16 tumors demonstrated a lower expression of both TGFβ isoforms. Compared to untreated control animals, anti-TGFβ3 therapy resulted in the greatest delay in B16 tumor growth, followed by anti-TGFβ1 therapy and pan-TGFβ blockade. However, none of the therapies resulted in improved overall survival. Similar results were achieved in a 4T1 breast model. T cell functional assays demonstrated that anti-TGFβ3 resulted in CD8+ T cells with greater cytolytic ability as they showed higher granzyme B expression and killing against B16 cells when plated ex-vivo. Anti-TGFβ1 treatment resulted in greater interferon-γ production by CD8+ T cells, suggesting an increase in antigen-specificity. Isoform specific TGFβ inhibition in combination with immune checkpoint blockade demonstrated improved tumor control and survival. This provides rationale for the use of anti-TGFβ therapy in stroma poor tumors, such as melanoma, and for its potential to enhance the effectiveness of existing therapies.

Blockade of IDO/TDO downstream effectors restricts cancer immune suppression

Immune checkpoint blockade (ICB) results in clinical benefit for a subset of cancer patients, yet multiple mechanisms of resistance can impair optimal response. The catabolism of tryptophan into metabolites known as kynurenines (Kyn) by the expression of enzymes such as IDO or TDO is a frequent phenomenon that plays a suppressive role in tumor immunity. Recently it was shown that Kyn acts as agonist of the aryl hydrocarbon receptor (AHR). Here we sought to characterize the mechanisms of immune suppression associated with the AHR pathway and to evaluate its potential as therapeutic target. RNAseq analysis of human cancers revealed a correlation between the expressions of AHR-related genes with markers associated with immunotherapy resistance (PD-1, FOXP3, CD206). By using IDO or TDO-overexpressing variants of a melanoma cell model (B16-F10), we found that myeloid cells, such as tumor-associated macrophages (TAMs) and dendritic cells (DCs), present up-regulation of the AHR. IDO-expressing tumors (B16-IDO) show higher myeloid cell infiltration, which present a tolerogenic phenotype. Tumor-antigen specific CD8T cells present reduced expression of activation markers and proliferation rate when primed by Kyn-treated BMDCs. Treatment of B16-IDO-bearing mice with an AHR-specific antagonist (CH-223191) leads to an increase of MHC II in TAMs, of activation markers in CD8 T cells and reduced frequency of T-regs. AHR inhibition delays progression of tumors with an active IDO/TDO/Kyn pathway (B16-IDO and B16-TDO), and efficacy is further improved when ICB is used in combination. In summary, our findings demonstrate that targeting the Kyn pathway through AHR inhibition could overcome key suppressive mechanisms and sensitize tumors to ICB.

Rational design of anti-GITR-based combination immunotherapy

Modulating T cell homeostatic mechanisms with checkpoint blockade can efficiently promote endogenous anti-tumor T cell responses1-11. However, many patients still do not benefit from checkpoint blockade12, highlighting the need for targeting of alternative immune pathways13. Glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) is an attractive target for immunotherapy, owing to its capacity to promote effector T cell (Teff) functions14,15 and hamper regulatory T cell (Treg) suppression16-20. On the basis of the potent preclinical anti-tumor activity of agonist anti-GITR antibodies, reported by us and others16,21,22, we initiated the first in-human phase 1 trial of GITR agonism with the anti-GITR antibody TRX518 ( NCT01239134 ). Here, we report the safety profile and immune effects of TRX518 monotherapy in patients with advanced cancer and provide mechanistic preclinical evidence to rationally combine GITR agonism with checkpoint blockade in future clinical trials. We demonstrate that TRX518 reduces circulating and intratumoral Treg cells to similar extents, providing an easily assessable biomarker of anti-GITR activity. Despite Treg reductions and increased Teff:Treg ratios, substantial clinical responses were not seen. Similarly, in mice with advanced tumors, GITR agonism was not sufficient to activate cytolytic T cells due to persistent exhaustion. We demonstrate that T cell reinvigoration with PD-1 blockade can overcome resistance of advanced tumors to anti-GITR monotherapy. These findings led us to start investigating TRX518 with PD-1 pathway blockade in patients with advanced refractory tumors ( NCT02628574 ).

Abstract PR01: Mechanistic rationale to combine GITR agonism with PD-1 blockade in cancer patients

Immune checkpoint blockade has evidenced the therapeutic activity of modulating T-cell co-inhibition/co-stimulation processes. However, many patients are refractory to these therapies, highlighting the need for developing additional forms of immunotherapy targeting alternative immune pathways. In this regard, the T-cell co-stimulatory receptor glucocorticoid-induced TNFR-related protein (GITR, TNFRSF18) is an attractive target for agonist antibodies (Abs). By promoting effector T-cell (Teff) function and hampering regulatory T-cell (Treg) suppression, GITR engagement may exert a dual positive effect on anti-tumor immune responses. We and others have reported potent antitumor effects of anti-GITR Abs in preclinical mouse models. Based on this rationale, we initiated the first-in-human phase-I trial of GITR stimulation with the GITR agonist monoclonal Ab (mAb) TRX518 (NCT01239134). TRX518 is a humanized aglycosylated IgG1κ mAb that binds and stimulates human GITR without engaging Fc effector functions. Here, we report the immune effects of a single ascending dose of TRX518 monotherapy in advanced cancer patients and provide mechanistic preclinical evidence to rationally combine GITR agonism with checkpoint blockade in future clinical trials. Analysis of peripheral blood mononuclear cells (PBMCs) from 37 advanced refractory solid cancer patients treated with &gt;/= 0.005 mg/kg TRX518 (cohorts 3-9) revealed frequent reductions in circulating Tregs after treatment, with GITR+ Tregs and activated CD45RA-Foxp3hi effector Tregs (eTregs) being preferentially affected. In 8 patients for whom pre- and post-treatment PBMC samples and tumor biopsies were available, reductions in intratumor and circulating Tregs after TRX518 were positively correlated. However, coincident down-regulation of circulating and intratumor Tregs upon TRX518 was not sufficient to achieve a clinical benefit. To clarify the mechanisms underlying this outcome, we modeled tumor sensitivity and refractoriness to anti-GITR therapy by treating B16F10-melanoma-bearing mice with the mAb DTA-1 on day 4 (curative regimen, early tumors) or day 7 (refractory regimen, advanced/established tumors) after tumor implantation respectively. Time course analysis of T-cell infiltrates revealed that intratumor Tregs were significantly reduced and Teff:Treg ratios increased in both responding and refractory tumors. However, in responding tumors, Tregs completely failed to accumulate, suggesting that the presence of Tregs during tumor formation and progression could affect T-cell functionality. Gene expression analysis of intratumor CD8+ T-cells showed up-regulation of activation/memory T-cell markers and down-regulation of exhaustion markers in responding but not in refractory tumors. To overcome resistance to anti-GITR, we thus combined the anti-GITR refractory regimen (day 7 treatment) with PD-1 blockade starting on day 7 after tumor implantation. This combination controlled tumor growth similar to the curative anti-GITR monotherapy (day 4 treatment) and achieved 50% long-lasting complete response. This was associated with more activated and less exhausted profiles of intratumor CD8+ T-cells, which showed enhanced anti-tumor cytotoxicity compared to CD8+ T-cells from nonresponding tumors treated with each agent alone. These results indicate for the first time that Treg reduction may be a pharmacodynamic biomarker of anti-GITR therapy in patients. However, Treg elimination from advanced tumors is not sufficient to activate cytotoxic CD8+ T-cell responses unless the T-cell exhaustion process is concurrently blocked. This underscores the need to combine Treg-inhibiting/depleting immunotherapies with strategies able to counteract exhaustion, such as PD-1 blockade, to regress advanced tumors. Based on these observations, we have initiated a clinical trial exploring TRX518 in combination with PD-1 pathway blockade in patients with advanced solid tumor malignancies (NCT02628574).

Citation Format: Roberta Zappasodi, Cynthia Sirard, Yanyun Li, Sadna Budhu, Moshen Abu-Akeel, Cailian Liu, Xia Yang, Hong Zhong, Walter Newman, Jinjin Qi, Phillip Wong, David Schaer, Henry Koon, Vamsidhar Velcheti, Michael Postow, Margaret K Callahan, Jedd D. Wolchok, Taha D. Merghoub. Mechanistic rationale to combine GITR agonism with PD-1 blockade in cancer patients [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr PR01.

An Antitumor Immune Response Is Evoked by Partial-Volume Single-Dose Radiation in 2 Murine Models

PURPOSE

This study examined tumor growth delay resulting from partial irradiation in preclinical mouse models.

METHODS AND MATERIALS

We investigated 67NR murine orthotopic breast tumors in both immunocompetent and nude mice. Treatment was delivered to 50% or 100% of the tumor using a 2 × 2 cm collimator on a microirradiator. Radiation response was modulated by treatment with anti-CD8 and anti-intercellular adhesion molecule (anti-ICAM) antibodies. Similar experiments were performed using the less immunogenic Lewis lung carcinoma mouse model. Tumor growth delay and γ-H2AX phosphorylation were measured, and immune response was assessed by immunofluorescence and flow cytometry at 1 and 7 days after radiation therapy. Tumor expression of cellular adhesion molecules was also measured at different times after radiation therapy.

RESULTS

Partial irradiation led to tumor responses similar to those of fully exposed tumors in immunocompetent mice, but not in nude mice. After a single dose of 10 Gy, infiltration of CD8⁺ T cells was observed along with increased expression of ICAM. The response to 10 Gy in hemi-irradiated tumors was abrogated by treatment with either anti-CD8 or anti-ICAM antibodies. Similar responses were obtained in the less immunogenic Lewis lung carcinoma mouse model delivering 15 Gy to half the tumor volume. Treatment with FTY720, a compound that inhibits T-cell egress from lymph nodes, did not affect tumor response at the time of CD8⁺ T cells infiltration in the nonirradiated area of the tumor. This result indicated that the most likely source of these cells is the irradiated portion of the hemi-irradiated tumors. In addition, a significant abscopal effect was observed after partial irradiation with a single dose of 10 Gy in the 67NR model.

CONCLUSIONS

In these models, radiation controls tumor growth both directly through cell killing and indirectly through immune activation. This outcome raises the possibility that this effect could be induced in the clinic.

Abstract 4716: Targeting specific TGF-β isoforms in combination with radiation therapy leads to differential antitumor effects in mouse models of cancer

Background: TGF-β is a pleotropic cytokine, which has emerged as a potential target in cancer treatment due to its dual role in tumorigenesis and homeostasis. There are three isoforms of TGF-β (TGF-β1, TGF-β2 and TGF-β3), which are secreted by immune and nonimmune cells as a latent complex. Depending on the local context, TGF-β adopts opposing roles in carcinogensis and in modulating the immune system. These dueling roles of TGF-β are dependent on its secretion and activation. Local radiation therapy (RT) can activate TGF-β via reactive oxygen species. Such TGF-β expression is linked to radioresistance and dose-limiting toxicities, reducing the effectiveness of RT. In these studies, we aim to characterize the effect of RT on the temporal and cell-specific expression patterns of TGF-β isoforms in mouse tumor models. This will inform treatment regimens combining isoform specific anti-TGF-β therapy with RT.

Methods: Fluorescence-activated cell sorting (FACS): C57BL/6 mice were implanted on the hind limb with B16-F10 melanoma cells. On day 10, tumors were irradiated locally with 15 Gy. Expression of TGF-β isoforms was measured at 1, 3 and 5 days post-RT by FACS. In vivo: C57BL/6 mice were implanted with tumors and irradiated as described. Mice were treated (10/group) with anti-TGF-β1, anti-TGF-β3 or a pan-TGF-β antibody beginning 1 day after RT given intraperitoneally (200 ug/mouse) every other day for 8 doses. Tumor growth and overall survival were monitored. A similar experiment was conducted in the 4T1 breast cancer model, in which mice were treated 1 day prior to radiation.

Results: FACS data indicated that TGF-β1 and TGF-β3 expression increases on most immune cells in the tumor 1 day after RT, decreases 3 days after RT and reaches a peak 5 days after RT. Preliminary in vivo studies demonstrate that both αTGF-β1 and αTGF-β3 as monotherapies have activity against B16 melanoma. In combination with RT, αTGF-β3 shows greater antitumor activity compared to αTGF-β1 in melanoma. Similar observations were obtained in a 4T1 breast model; however, αTGF-β3 alone and in combination with RT as well as αTGF-β1 + RT showed a significant delay against tumor growth. No significant differences in survival were seen in either tumor model.

Conclusions: TGF-β1 and TGF-β3 are expressed on numerous lymphoid and myeloid cells in B16 tumors and spleens. TGF-β isoform expression peaks 5 days post-RT. Anti-TGF-β therapy is effective in delaying tumor growth and may synergize with RT in certain cancers. This demonstrates rationale for the use of anti-TGF-β therapy to enhance the effectiveness of RT in cancer.

Citation Format: Aditi Gupta, Sadna Budhu, Rachel Giese, Jacques van Snick, Catherine Uyttenhove, Gerd Ritter, Jedd Wolchok, Taha Merghoub. Targeting specific TGF-β isoforms in combination with radiation therapy leads to differential antitumor effects in mouse models of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4716.

Abstract 5009: Defined factors overcome T-cell exhaustion via abscopal effect

Irreversible exhaustion of tumor-associated T cells is an important factor limiting the efficacy of PD-1 blockade in a number of cancers. Recent data suggest that PD-1 blockade functions largely by augmenting T cell costimulation. Given that activated APCs provide necessary T-cell costimulation, we hypothesized that enforced activation of intratumoral APCs would prime tumor-specific T cells and synergize with PD-1 blockade to overcome T-cell exhaustion. After screening various agents in syngeneic murine models, we found that dual CD40/TLR4 activation within a single tumor triggers a systemic tumor-specific CD8 T-cell response that is dependent on BATF3+ dendritic cells. Remarkably, this approach abolishes exhausted PD-1+ intratumoral T cells in treated as well as distant tumors while sparing more proximal T cells outside the tumors. In addition to treating large established tumors, this approach also confers persistent immunity allowing animals to reject reimplanted tumors 90 days after treatment. Dual CD40/TLR4 activation within a single tumor is thus a promising method for overcoming tumor-associated T-cell exhaustion in a manner that may provide durable systemic control of metastatic human cancers while sparing healthy tissues.

Citation Format: Danny Khalil, Luis Felipe Campesato, Sadna Budhu, Yanyun Li, Caitlin Jones, Nathan Suek, Cailian Liu, Billel Gasmi, Rachel Giese, Stephane Pourpe, Taha Merghoub, Jedd D. Wolchok. Defined factors overcome T-cell exhaustion via abscopal effect [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5009.

Abstract 3568: Phosphatidylserine targeting antibody enhances antitumor activity of CAR T cells in mouse melanoma

A viable strategy to treat advanced cancers includes transferring of tumor-specific T cells. T cells that recognize tumor antigens can be expanded and reinvigorated ex-vivo. Furthermore, autologous T cells can be genetically modified to express antitumor T cell receptors or chimeric antigen receptors (CARs). Although the potency and specificity of tumor-specific T cells can be manipulated ex vivo, once reinfused into patients, the T cells are subjected to immunosuppressive mechanisms established by the tumor. An important immune checkpoint regulator within tumors is phosphatidylserine (PS), a phospholipid that is exposed on apoptotic cells, tumor cells and tumor endothelium. Innate immune cells exposed to PS secrete suppressive cytokines and chemokines that can significantly impair the function and activation of antitumor T cells. Antibodies that target PS have been shown to reactivate antitumor immunity by polarizing tumor-associated macrophages into a proinflammatory M1 phenotype, reducing the number of MDSCs in tumors and promoting the maturation of dendritic cells into functional APCs. Our lab has previously shown that a PS targeting monoclonal antibody (mch1N11), in combination with transgenic CD4+ T cells that recognize the melanoma antigen Trp1, can regress very advanced melanomas in all treated mice. Here, we further those studies with data showing that a 2nd-generation CAR T cell that binds Trp1 on the surface of B16 melanoma, in combination with mch1N11 can improve antitumor activity and overall survival in B16 tumor-bearing mice. Additionally, in vitro killing assays with antigen-specific T cells sorted from the tumor reveal that mch1N11 enhances the cytolytic function of these T cells against B16 melanoma. Flow cytometry analysis of local immune responses in the tumors of animals treated with tumor-specific T cells and mch1N11 showed a decrease in anti-inflammatory (M2) macrophages and FoxP3+ regulatory T cells. These findings highlight that diminishing suppressive mechanisms locally with mch1N11 can enhance the efficacy of transgenic TCR and CAR T cells to improve the outcome in patients with advanced-stage melanoma. Our studies may inform the design of clinical trials combining PS targeting antibodies with CAR T cell therapy in solid tumors.

Citation Format: Sara Schad, Daniel Hirschhorn-Cymerman, Sadna Budhu, Hong Zhong, Xia Yang, Joseph Shan, Steven King, Taha Merghoub, Jedd Wolchok. Phosphatidylserine targeting antibody enhances antitumor activity of CAR T cells in mouse melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3568.

Abstract 2767: Phosphatidylserine targeting and radiation improves survival in a mouse tumor model resistant to checkpoint blockade

Background: Despite the excitement surrounding checkpoint blockade, many tumors remain resistant thus there is a need to sensitize tumors to immunotherapy and augment tumor rejection. Phosphatidylserine (PS) is a phospholipid expressed on the outer surface of apoptotic cells and a variety of immune cell types. PS signaling polarizes macrophages to the M2 phenotype, inhibits TLR signaling and is upregulated on the surface of tumor cells by radiotherapy (RT). RT also promotes infiltration of CD8 T-cells to the tumor microenvironment. Accordingly, RT may improve CD8 T-cell mediated tumor rejection in the context of checkpoint blockade and sensitize tumors to PS antagonism. We hypothesize PS-targeting antibody, mch1n11, in combination with local RT, may be an effective adjuvant or alternative treatment in patients with tumors resistant to checkpoint blockade such as anti-PD-1 (aPD-1). Furthermore, we hypothesize the combination of aPD-1 with mch1n11 and RT will synergize to improve the effector function of CD8 T-cells and enhance tumor elimination.

Methods: B16-F10 murine melanoma was injected into the hind limb of C57BL/6 mice. One cohort received triple combination therapy comprised of aPD-1, mch1n11, and RT given simultaneously at an early time point. Another cohort that showed continued tumor growth after therapy with aPD-1 was used to model checkpoint blockade resistance. These mice received delayed treatment with intra-peritoneal mch1n11 in combination with a one-time 15 Gy RT dose targeted to the tumor-bearing hind limb. The aPD-1 resistant cohort was subdivided into two groups: in one cohort aPD-1 was administered prior to and continued with mch1n11+RT therapy. In the other cohort, aPD-1 was discontinued prior to mch1n11+RT administration. Untreated mice, mice treated with aPD-1 alone, mice treated with isotype antibodies, and mice treated without initial aPD-1 therapy that received delayed mch1n11+RT therapy served as controls.

Results: Early triple combination therapy results in almost complete tumor elimination and leads to statistically significant prolonged survival. In the aPD-1 resistant cohort, both prior and continuous aPD-1 treatment with mch1n11+RT improved survival compared to all four controls. There was no significant difference in tumor size or survival between the adjuvant and alternative experimental groups. Experiments are ongoing to characterize immune infiltrates of tumors and the individual effects of aPD-1, RT and mch1n11.

Conclusion: This preclinical model suggests a phosphatidylserine targeting antibody combined with single dose RT presents an alternative or adjuvant therapy for tumors resistant to checkpoint blockade. The data from this preclinical model will be used to develop a clinical trial for patients with tumors resistant to checkpoint blockade.

Citation Format: Rachel Giese, Sadna Budhu, Christopher Barker, Aditi Gupta, Steve King, Joseph Shan, Jedd Wolchok, Taha Merghoub. Phosphatidylserine targeting and radiation improves survival in a mouse tumor model resistant to checkpoint blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2767.