Transcriptomic analysis-guided assessment of precision-cut tumor slices (PCTS) as an ex-vivo tool in cancer research

With cancer immunotherapy and precision medicine dynamically evolving, there is greater need for pre-clinical models that can better replicate the intact tumor and its complex tumor microenvironment (TME). Precision-cut tumor slices (PCTS) have recently emerged as an ex vivo human tumor model, offering the opportunity to study individual patient responses to targeted therapies, including immunotherapies. However, little is known about the physiologic status of PCTS and how culture conditions alter gene expression. In this study, we generated PCTS from head and neck cancers (HNC) and mesothelioma tumors (Meso) and undertook transcriptomic analyses to understand the changes that occur in the timeframe between PCTS generation and up to 72 h (hrs) in culture. Our findings showed major changes occurring during the first 24 h culture period of PCTS, involving genes related to wound healing, extracellular matrix, hypoxia, and IFNγ-dependent pathways in both tumor types, as well as tumor-specific changes. Collectively, our data provides an insight into PCTS physiology, which should be taken into consideration when designing PCTS studies, especially in the context of immunology and immunotherapy.

Red blood cells function as reservoirs of tumor DNA

Novel screening techniques for early detection of lung cancer are urgently needed. Profiling circulating tumor cell-free DNA (ctDNA) has emerged as a promising tool for biopsy-free tumor genotyping. However, both the scarcity and short half-life of ctDNA substantially limit the sensitivity and clinical utility of ctDNA detection methodologies. Our discovery that red blood cells (RBCs) sequester mitochondrial DNA opens a new avenue for detecting circulating nucleic acids, as RBCs represent an unrecognized reservoir of circulating nucleic acid. Here, we show that RBCs acquire tumor DNA following coculture with lung cancer cell lines harboring Kirsten rat sarcoma viral oncogene homolog (KRAS) and epidermal growth factor receptor (EGFR) mutations. RBC-bound tumor DNA is detectable in patients with early-stage non-small cell lung cancer (NSCLC) but not in healthy controls by qPCR. Our results collectively uncover a previously unrecognized yet easily accessible reservoir of tumor DNA, offering a promising foundation for future RBC-based tumor diagnostics.NEW & NOTEWORTHY We present a novel method for lung cancer detection by revealing RBCs as a reservoir for tumor DNA, overcoming the limitations of current circulating tumor ctDNA methodologies. By demonstrating that RBCs can capture tumor DNA, including critical mutations found in lung cancer, we provide a promising, biopsy-free avenue for early cancer diagnostics. This discovery opens up exciting possibilities for developing RBC-based diagnostic tools, significantly enhancing the sensitivity and clinical utility of noninvasive cancer detection.

Human Tumor-Associated Macrophages and Neutrophils Regulate Antitumor Antibody Efficacy through Lethal and Sublethal Trogocytosis

The clinical benefits of tumor-targeting antibodies (tAb) are modest in solid human tumors. The efficacy of many tAbs is dependent on Fc receptor (FcR)-expressing leukocytes that bind Fc fragments of tAb. Tumor-associated macrophages (TAM) and neutrophils (TAN) represent the majority of FcR+ effectors in solid tumors. A better understanding of the mechanisms by which TAMs and TANs regulate tAb response could help improve the efficacy of cancer treatments. Here, we found that myeloid effectors interacting with tAb-opsonized lung cancer cells used antibody-dependent trogocytosis (ADT) but not antibody-dependent phagocytosis. During this process, myeloid cells "nibbled off" tumor cell fragments containing tAb/targeted antigen (tAg) complexes. ADT was only tumoricidal when the tumor cells expressed high levels of tAg and the effectors were present at high effector-to-tumor ratios. If either of these conditions were not met, which is typical for solid tumors, ADT was sublethal. Sublethal ADT, mainly mediated by CD32hiCD64hi TAM, led to two outcomes: (i) removal of surface tAg/tAb complexes from the tumor that facilitated tumor cell escape from the tumoricidal effects of tAb; and (ii) acquisition of bystander tAgs by TAM with subsequent cross-presentation and stimulation of tumor-specific T-cell responses. CD89hiCD32loCD64lo peripheral blood neutrophils (PBN) and TAN stimulated tumor cell growth in the presence of the IgG1 anti-EGFR Ab cetuximab; however, IgA anti-EGFR Abs triggered the tumoricidal activity of PBN and negated the stimulatory effect of TAN. Overall, this study provides insights into the mechanisms by which myeloid effectors mediate tumor cell killing or resistance during tAb therapy.

SIGNIFICANCE

The elucidation of the conditions and mechanisms by which human FcR+ myeloid effectors mediate cancer cell resistance and killing during antibody treatment could help develop improved strategies for treating solid tumors.

IL7 increases targeted lipid nanoparticle-mediated mRNA expression in T cells in vitro and in vivo by enhancing T cell protein translation

The use of lipid nanoparticles (LNP) to encapsulate and deliver mRNA has become an important therapeutic advance. In addition to vaccines, LNP-mRNA can be used in many other applications. For example, targeting the LNP with anti-CD5 antibodies (CD5/tLNP) can allow for efficient delivery of mRNA payloads to T cells to express protein. As the percentage of protein expressing T cells induced by an intravenous injection of CD5/tLNP is relatively low (4-20%), our goal was to find ways to increase mRNA-induced translation efficiency. We showed that T cell activation using an anti-CD3 antibody improved protein expression after CD5/tLNP transfection in vitro but not in vivo. T cell health and activation can be increased with cytokines, therefore, using mCherry mRNA as a reporter, we found that culturing either mouse or human T cells with the cytokine IL7 significantly improved protein expression of delivered mRNA in both CD4+ and CD8+ T cells in vitro. By pre-treating mice with systemic IL7 followed by tLNP administration, we observed significantly increased mCherry protein expression by T cells in vivo. Transcriptomic analysis of mouse T cells treated with IL7 in vitro revealed enhanced genomic pathways associated with protein translation. Improved translational ability was demonstrated by showing increased levels of protein expression after electroporation with mCherry mRNA in T cells cultured in the presence of IL7, but not with IL2 or IL15. These data show that IL7 selectively increases protein translation in T cells, and this property can be used to improve expression of tLNP-delivered mRNA in vivo.

CAR T cell therapy for patients with solid tumours: key lessons to learn and unlearn

Chimeric antigen receptor (CAR) T cells have been approved for use in patients with B cell malignancies or relapsed and/or refractory multiple myeloma, yet efficacy against most solid tumours remains elusive. The limited imaging and biopsy data from clinical trials in this setting continues to hinder understanding, necessitating a reliance on imperfect preclinical models. In this Perspective, I re-evaluate current data and suggest potential pathways towards greater success, drawing lessons from the few successful trials testing CAR T cells in patients with solid tumours and the clinical experience with tumour-infiltrating lymphocytes. The most promising approaches include the use of pluripotent stem cells, co-targeting multiple mechanisms of immune evasion, employing multiple co-stimulatory domains, and CAR ligand-targeting vaccines. An alternative strategy focused on administering multiple doses of short-lived CAR T cells in an attempt to pre-empt exhaustion and maintain a functional effector pool should also be considered.

A genetically encoded protein tag for control and quantitative imaging of CAR T cell therapy

Chimeric antigen receptor (CAR) T cell therapy has been successful for hematological malignancies. Still, a lack of efficacy and potential toxicities have slowed its application for other indications. Furthermore, CAR T cells undergo dynamic expansion and contraction in vivo that cannot be easily predicted or controlled. Therefore, the safety and utility of such therapies could be enhanced by engineered mechanisms that engender reversible control and quantitative monitoring. Here, we use a genetic tag based on the enzyme Escherichia coli dihydrofolate reductase (eDHFR), and derivatives of trimethoprim (TMP) to modulate and monitor CAR expression and T cell activity. We fused eDHFR to the CAR C terminus, allowing regulation with TMP-based proteolysis-targeting chimeric small molecules (PROTACs). Fusion of eDHFR to the CAR does not interfere with cell signaling or its cytotoxic function, and the addition of TMP-based PROTACs results in a reversible and dose-dependent inhibition of CAR activity via the proteosome. We show the regulation of CAR expression in vivo and demonstrate imaging of the cells with TMP radiotracers. In vitro immunogenicity assays using primary human immune cells and overlapping peptide fragments of eDHFR showed no memory immune repertoire for eDHFR. Overall, this translationally-orientied approach allows for temporal monitoring and image-guided control of cell-based therapies.

Surgical Inflammation Alters Immune Response to Intraoperative Photodynamic Therapy

Surgical cytoreduction for patients with malignant pleural mesothelioma (MPM) is used for selected patients as a part of multi-modality management strategy. Our group has previously described the clinical use of photodynamic therapy (PDT), a form of non-ionizing radiation, as an intraoperative therapy option for MPM. Although necessary for the removal of bulk disease, the effects of surgery on residual MPM burden are not understood. In this bedside-to-bench study, Photofrin-based PDT introduced the possibility of achieving a long-term response in murine models of MPM tumors that were surgically debulked by 60% to 90%. Thus, the addition of PDT provided curative potential after an incomplete resection. Despite this success, we postulated that surgical induction of inflammation may mitigate the comprehensive response of residual disease to further therapy. Utilizing a previously validated tumor incision (TI) model, we demonstrated that the introduction of surgical incisions had no effect on acute cytotoxicity by PDT. However, we found that surgically induced inflammation limited the generation of antitumor immunity by PDT. Compared with PDT alone, when TI preceded PDT of mouse tumors, splenocytes and/or CD8+ T cells from the treated mice transferred less antitumor immunity to recipient animals. These results demonstrate that addition of PDT to surgical cytoreduction significantly improves long-term response compared with cytoreduction alone, but at the same time, the inflammation induced by surgery may limit the antitumor immunity generated by PDT. These data inform future potential approaches aimed at blocking surgically induced immunosuppression that might improve the outcomes of intraoperative combined modality treatment.

Significance

Although mesothelioma is difficult to treat, we have shown that combining surgery with a form of radiation, photodynamic therapy, may help people with mesothelioma live longer. In this study, we demonstrate in mice that this regimen could be further improved by addressing the inflammation induced as a by-product of surgery.

Desmoplastic stroma restricts T cell extravasation and mediates immune exclusion and immunosuppression in solid tumors

The desmoplastic stroma in solid tumors presents a formidable challenge to immunotherapies that rely on endogenous or adoptively transferred T cells, however, the mechanisms are poorly understood. To define mechanisms involved, here we treat established desmoplastic pancreatic tumors with CAR T cells directed to fibroblast activation protein (FAP), an enzyme highly overexpressed on a subset of cancer-associated fibroblasts (CAFs). Depletion of FAP+ CAFs results in loss of the structural integrity of desmoplastic matrix. This renders these highly treatment-resistant cancers susceptible to subsequent treatment with a tumor antigen (mesothelin)-targeted CAR T cells and to anti-PD-1 antibody therapy. Mechanisms include overcoming stroma-dependent restriction of T cell extravasation and/or perivascular invasion, reversing immune exclusion, relieving T cell suppression, and altering the immune landscape by reducing myeloid cell accumulation and increasing endogenous CD8+ T cell and NK cell infiltration. These data provide strong rationale for combining tumor stroma- and malignant cell-targeted therapies to be tested in clinical trials.

Desmoplastic stroma restricts T cell extravasation and mediates immune exclusion and immunosuppression in solid tumors

The desmoplastic stroma in solid tumors presents a formidable challenge to immunotherapies that rely on endogenous or adoptively transferred T cells, however, the mechanisms are poorly understood. To define mechanisms involved, we treat established desmoplastic pancreatic tumors with CAR T cells directed to fibroblast activation protein (FAP), an enzyme highly overexpressed on a subset of cancer-associated fibroblasts (CAFs). Depletion of FAP+CAFs results in loss of the structural integrity of desmoplastic matrix. This renders these highly treatment-resistant cancers susceptible to subsequent treatment with a tumor antigen (mesothelin)-targeted CAR and to anti-PD1 antibody therapy. Mechanisms include overcoming stroma-dependent restriction of T cell extravasation and/or perivascular invasion, reversing immune exclusion, relieving T cell suppression, and altering the immune landscape by reducing myeloid cell accumulation and increasing endogenous CD8+ T cell and NK cell infiltration. These data provide strong rationale for combining tumor stroma- and malignant cell-targeted therapies to be tested in clinical trials.

Two cases of severe pulmonary toxicity from highly active mesothelin-directed CAR T cells

Multiple clinical studies have treated mesothelin (MSLN)-positive solid tumors by administering MSLN-directed chimeric antigen receptor (CAR) T cells. Although these products are generally safe, efficacy is limited. Therefore, we generated and characterized a potent, fully human anti-MSLN CAR. In a phase 1 dose-escalation study of patients with solid tumors, we observed two cases of severe pulmonary toxicity following intravenous infusion of this product in the high-dose cohort (1-3 × 108 T cells per m2). Both patients demonstrated progressive hypoxemia within 48 h of infusion with clinical and laboratory findings consistent with cytokine release syndrome. One patient ultimately progressed to grade 5 respiratory failure. An autopsy revealed acute lung injury, extensive T cell infiltration, and accumulation of CAR T cells in the lungs. RNA and protein detection techniques confirmed low levels of MSLN expression by benign pulmonary epithelial cells in affected lung and lung samples obtained from other inflammatory or fibrotic conditions, indicating that pulmonary pneumocyte and not pleural expression of mesothelin may lead to dose-limiting toxicity. We suggest patient enrollment criteria and dosing regimens of MSLN-directed therapies consider the possibility of dynamic expression of mesothelin in benign lung with a special concern for patients with underlying inflammatory or fibrotic conditions.

Tissue-resident memory CAR T cells with stem-like characteristics display enhanced efficacy against solid and liquid tumors

Chimeric antigen receptor (CAR) T cells demonstrate remarkable success in treating hematological malignancies, but their effectiveness in non-hematopoietic cancers remains limited. This study proposes enhancing CAR T cell function and localization in solid tumors by modifying the epigenome governing tissue-residency adaptation and early memory differentiation. We identify that a key factor in human tissue-resident memory CAR T cell (CAR-T_RM) formation is activation in the presence of the pleotropic cytokine, transforming growth factor β (TGF-β), which enforces a core program of both "stemness" and sustained tissue residency by mediating chromatin remodeling and concurrent transcriptional changes. This approach leads to a practical and clinically actionable in vitro production method for engineering peripheral blood T cells into a large number of "stem-like" CAR-T_RM cells resistant to tumor-associated dysfunction, possessing an enhanced ability to accumulate in situ and rapidly eliminate cancer cells for more effective immunotherapy.

Monitoring Therapeutic Response to Anti-FAP CAR T Cells Using [18F]AlF-FAPI-74

PURPOSE

Despite the success of chimeric antigen receptor (CAR) T-cell therapy against hematologic malignancies, successful targeting of solid tumors with CAR T cells has been limited by a lack of durable responses and reports of toxicities. Our understanding of the limited therapeutic efficacy in solid tumors could be improved with quantitative tools that allow characterization of CAR T-targeted antigens in tumors and accurate monitoring of response.

EXPERIMENTAL DESIGN

We used a radiolabeled FAP inhibitor (FAPI) [18F]AlF-FAPI-74 probe to complement ongoing efforts to develop and optimize FAP CAR T cells. The selectivity of the radiotracer for FAP was characterized in vitro, and its ability to monitor changes in FAP expression was evaluated using rodent models of lung cancer.

RESULTS

[18F]AlF-FAPI-74 showed selective retention in FAP+ cells in vitro, with effective blocking of the uptake in presence of unlabeled FAPI. In vivo, [18F]AlF-FAPI-74 was able to detect FAP expression on tumor cells as well as FAP+ stromal cells in the tumor microenvironment with a high target-to-background ratio. We further demonstrated the utility of the tracer to monitor changes in FAP expression following FAP CAR T-cell therapy, and the PET imaging findings showed a robust correlation with ex vivo analyses.

CONCLUSIONS

This noninvasive imaging approach to interrogate the tumor microenvironment represents an innovative pairing of a diagnostic PET probe with solid tumor CAR T-cell therapy and has the potential to serve as a predictive and pharmacodynamic response biomarker for FAP as well as other stroma-targeted therapies. A PET imaging approach targeting FAP expressed on activated fibroblasts of the tumor stroma has the potential to predict and monitor therapeutic response to FAP-targeted CAR T-cell therapy. See related commentary by Weber et al., p. 5241.

Abstract B19: FAP CAR T cell therapy for solid tumors with PET imaging

Two of the major obstacles that adoptive cell transfer immunotherapy needs to overcome to be successful in solid tumors are 1) the immunosuppressive tumor microenvironment (TME) and 2) the lack of robust biomarkers that allow for the identification of patients that would benefit from the therapy and for monitoring of the treatment response. Here we paired a CAR T cell therapy with a companion Positron Emission Tomography (PET) imaging approach that allows for serial, non-invasive, whole-body visualization of a biological target of interest -in this specific case, Fibroblast Activating Protein (FAP). FAP is a cell surface serine protease that is highly expressed by cancer associated fibroblasts in the TME that participate in the generation of the immunosuppressive stromagenic response in solid tumors. We designed a novel FAP CAR construct based on the scFv of the 4G5 antibody developed, in house, against canine FAP that cross-reacts against mouse and human FAP. In this study, we utilized the 18F-radiolabeled FAP inhibitor (FAPI), [18F]AlF-FAPI-74, to image FAP in two different mouse tumor models. First, the probe specificity was evaluated in the I45 human mesothelioma tumor model (a line which does not induce FAP+ fibroblasts). I45 WT and I45 cells transduced with human FAP were injected s.c. into the opposite flanks of a mouse and imaged following 2 weeks of tumor growth. We observed a 7.5-fold higher uptake of [18F]AlF-FAPI-74 in the I45 huFAP tumor compared to the WT, demonstrating the high specificity of the probe for FAP. Next, we used a more clinically-relevant A549 model where the tumor cells do not express FAP but induce a stromagenic response and drive the recruitment of FAP+ stromal cells in the TME. [18F]AlF-FAPI-74 PET/CT following 3 weeks of tumor growth showed a 6.5-fold increased radiotracer uptake in the tumor relative to the muscle at the baseline scan. Using this model, we evaluated the potential of our new CAR T cells to reduce tumor burden, as well as evaluating the potential of the [18F]AlF-FAPI-74 tracer as a tool to monitor the clearance of FAP-expressing cells in response to FAP CAR T cell therapy. Immediately after the baseline scan, we injected 5x106 FAP CAR T cells iv. At day 14 post-T cell injection, mice treated with FAP CAR T cells had significantly smaller tumors relative to the control group, which were treated with T cells that do not express the CAR, highlighting the therapeutic efficacy of the FAP CAR T cell therapy. Moreover, [18F]AlF-FAPI-74 PET/CT imaging showed no detectable tracer uptake in the tumors treated with FAP targeted CAR T. These findings were confirmed by immunofluorescence, indicating successful clearance of the FAP+ stroma by the injected FAP CAR T cells. In conclusion, the new 4G5 FAP CAR shows specific targeting toward mouse stroma infiltrating lung adenocarcinoma xenografts. PET imaging of FAP could be a highly useful approach to stratify patients prior to FAP CAR T therapy, as well as to monitor the pharmacodynamic response for FAP-targeted therapies.

Citation Format: Estela Noguera-Ortega, Iris K Lee, Zebin Xiao, Leslie Todd, John Scholler, Decheng Song, Maria Liousia, Katheryn Lohith, Kexiang Xu, Kimberly J Eduards, Michael D Farwell, Carl H June, Steven M Albelda, Ellen Puré, Mark A Sellmyer. FAP CAR T cell therapy for solid tumors with PET imaging [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy; 2022 Oct 21-24; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(12 Suppl):Abstract nr B19.

Na+/H+-exchanger 1 enhances antitumor activity of engineered NK-92 natural killer cells

Adoptive cell transfer (ACT) immunotherapy has remarkable efficacy against some hematological malignancies. However, its efficacy in solid tumors is limited by the adverse tumor microenvironment (TME) conditions, most notably that acidity inhibits T and natural killer (NK) cell mTOR complex 1 (mTORC1) activity and impairs cytotoxicity. In several reported studies, systemic buffering of tumor acidity enhanced the efficacy of immune checkpoint inhibitors. Paradoxically, we found in a c-Myc-driven hepatocellular carcinoma model that systemic buffering increased tumor mTORC1 activity, negating inhibition of tumor growth by anti-PD1 treatment. Therefore, in this proof-of-concept study, we tested the metabolic engineering of immune effector cells to mitigate the inhibitory effect of tumor acidity while avoiding side effects associated with systemic buffering. We first overexpressed an activated RHEB in the human NK cell line NK-92, thereby rescuing acid-blunted mTORC1 activity and enhancing cytolytic activity. Then, to directly mitigate the effect of acidity, we ectopically expressed acid extruder proteins. Whereas ectopic expression of carbonic anhydrase IX (CA9) moderately increased mTORC1 activity, it did not enhance effector function. In contrast, overexpressing a constitutively active Na⁺/H⁺-exchanger 1 (NHE1; SLC9A1) in NK-92 did not elevate mTORC1 but enhanced degranulation, target engagement, in vitro cytotoxicity, and in vivo antitumor activity. Our findings suggest the feasibility of overcoming the inhibitory effect of the TME by metabolically engineering immune effector cells, which can enhance ACT for better efficacy against solid tumors.

Abstract 3602: Mechanisms of CAR T cell dysfunction and identification of transcription factors that drive the exhaustion phenotype

Chimeric antigen receptor (CAR) T cell immunotherapy is FDA approved for the treatment of a subset of B cell malignancies but has shown limited clinical success in solid tumor therapy. T cell exhaustion is an important factor involved in treatment failure, and can, in part, result from continuous stimulation of the CAR by tumor cells expressing the cognate antigen. To gain deeper understanding of CAR T cell exhaustion induced by chronic antigen exposure (CAE), we developed and validated a robust in vitro model, in which mesothelin-redirected CAR T cells (M5CAR) were continuously stimulated with mesothelin-expressing AsPC-1 pancreatic tumor cells such that tumor cells were never cleared, and we characterized these CAE CAR T cells by gene expression at population and single-cell levels, and by epigenetic analyses.

CAE M5CAR T cells recapitulate the hallmarks of T cell exhaustion, including reduced proliferation, down-modulation of surface CAR, decreased cytokine production, and reduced cytotoxicity. In addition, CAR T cells undergoing CAE have a transcriptional signature and an epigenetic landscape consistent with exhaustion. Further, transcriptomic analysis revealed that CAE M5CAR T cells undergo a transition from T cells to a post-thymic NK-like T cell phenotype. This plasticity was confirmed by TCR lineage tracing and was also detected in CD19 CAR T cells analyzed from post-infusion blood from DLBCL patients and in M5CAR T cells infiltrating relapsed tumors derived from a xenograft NSG/AsPC-1 mouse model. The dysfunctional signature and the NK phenotype were further detected in vivo by transcriptomic analysis in Ly95 TCR-specific TILs infiltrating NY-ESO-1 tumors. Among the genes included in the dysfunctional signature, the transcription factors SOX4 and ID3 were identified as potential regulators of dysfunction by differential gene expression and pathway analyses. To determine their role in the establishment of a dysfunctional phenotype, we generated ID3KO.M5 and SOX4KO.M5 CAR T cells using CRISPR technology in primary human lymphocytes. The cytotoxic potential of the M5 CAR T cell product generated was not modified by the genetic disruption of the transcription factors. However, when CAR T cells were challenged with chronic antigen stimulation, KO CAR T cells showed a significant reduction of the dysfunctional signature and the NK-like T cell gene expression. Importantly, CAE KO CAR T cells exhibit improved cytotoxicity as compared to Mock.M5CAR T cells.

In summary, we have developed a robust in vitro model that recapitulates the hallmarks of T cell exhaustion and that facilitated the identification of a gene signature defining CAR dysregulation, a T-to-NK-like-T cell transition as a novel feature of CAR T cell dysfunction and the transcription factors SOX4 and ID3 as key regulators of CAR T cell exhaustion.

Citation Format: M. Angela Aznar, Charly R. Good, Shunichiro Kuramitsu, Parisa Samareh, Sangya Agarwal, Greg Donahue, Kenichi Ishiyama, Nils Wellhausen, Austin K. Rennels, Yujie Ma, Lifeng Tian, Sonia Guedan, Katherine A. Alexander, Zhen Zhang, Philipp C. Rommel, Nathan Singh, Karl M. Glastad, Max W. Richardson, Keisuke Watanabe, Janos L. Tanyi, Mark H. O’Hara, Marco Ruella, Simon F. Lacey, Edmund K. Moon, Stephen J. Schuster, Steven M. Albelda, Lewis L. Lanier, Regina M. Young, Shelley L. Berger, Carl H. June. Mechanisms of CAR T cell dysfunction and identification of transcription factors that drive the exhaustion phenotype [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 3602.

CAR T cells produced in vivo to treat cardiac injury

Fibrosis affects millions of people with cardiac disease. We developed a therapeutic approach to generate transient antifibrotic chimeric antigen receptor (CAR) T cells in vivo by delivering modified messenger RNA (mRNA) in T cell–targeted lipid nanoparticles (LNPs). The efficacy of these in vivo–reprogrammed CAR T cells was evaluated by injecting CD5-targeted LNPs into a mouse model of heart failure. Efficient delivery of modified mRNA encoding the CAR to T lymphocytes was observed, which produced transient, effective CAR T cells in vivo. Antifibrotic CAR T cells exhibited trogocytosis and retained the target antigen as they accumulated in the spleen. Treatment with modified mRNA-targeted LNPs reduced fibrosis and restored cardiac function after injury. In vivo generation of CAR T cells may hold promise as a therapeutic platform to treat various diseases.

CAR T cells produced in vivo to treat cardiac injury

Cardiac fibrosis is the stiffening and scarring of heart tissue and can be fatal. Rurik et al . designed an immunotherapy strategy to generate transient chimeric antigen receptor (CAR) T cells that can recognize the fibrotic cells in the heart (see the Perspective by Gao and Chen). By injecting CD5-targeted lipid nanoparticles containing the messenger RNA (mRNA) instructions needed to reprogram T lymphocytes, the researchers were able to generate therapeutic CAR T cells entirely inside the body. Analysis of a mouse model of heart disease revealed that the approach was successful in reducing fibrosis and restoring cardiac function. The ability to produce CAR T cells in vivo using modified mRNA may have a number of therapeutic applications. —PNK

An NK-like CAR T cell transition in CAR T cell dysfunction

Chimeric antigen receptor (CAR) T cell therapy has achieved remarkable success in hematological malignancies but remains ineffective in solid tumors, due in part to CAR T cell exhaustion in the solid tumor microenvironment. To study dysfunction of mesothelin-redirected CAR T cells in pancreatic cancer, we establish a robust model of continuous antigen exposure that recapitulates hallmark features of T cell exhaustion and discover, both in vitro and in CAR T cell patients, that CAR dysregulation is associated with a CD8+ T-to-NK-like T cell transition. Furthermore, we identify a gene signature defining CAR and TCR dysregulation and transcription factors, including SOX4 and ID3 as key regulators of CAR T cell exhaustion. Our findings shed light on the plasticity of human CAR T cells and demonstrate that genetic downmodulation of ID3 and SOX4 expression can improve the efficacy of CAR T cell therapy in solid tumors by preventing or delaying CAR T cell dysfunction.

Abstract 60: Induction of T cell dysfunction and NK-like T cell differentiation in vitro and in patients after CAR T cell treatment

Chimeric antigen receptor (CAR) T cell therapy has achieved remarkable success in hematological malignancies but remains largely ineffective in solid tumors. A major factor leading to the reduced efficacy of CAR T cell therapy is T cell dysfunction, and the mechanisms mediating this dysfunction are under investigation. Here we establish a robust model to study dysfunction of mesothelin-redirected CAR T cells in pancreatic cancer. Continuous antigen exposure results in hallmark features of exhaustion including reduced proliferation capacity and cytotoxicity, and severe defects in cytokine production. Here we identified a transcriptional signature at both population and single-cell levels in CAR T cells after continuous antigen exposure. In addition, TCR lineage tracing revealed a CD8+ T-to-NK-like T cell plasticity that results in reduced tumor cell killing. The transcription factors SOX4 and ID3 are specifically expressed in the dysfunctional CAR NK-like T cells and are predicted to be master regulators of the dysfunction gene expression signature and the post-thymic acquisition of an NK-like T cell fate. Finally, we identified the emergence of NK-like CAR T cells in a subset of patients after infusion of CAR T cells. The findings gleaned from this study shed light on the plasticity of human CAR T cells and suggest new approaches to improve the efficacy of CAR T cell therapy in solid tumors by preventing or revitalizing CAR T cell dysfunction.

Citation Format: Charly R. Good, Shunichiro Kuramitsu, Parisa Samareh, Greg Donahue, Kenichi Ishiyama, Yujie Ma, Nils Wellhausen, Lifeng Tian, Sangya Agarwal, Sonia Guedan, M. Angela Aznar, Katherine A. Alexander, Zhen Zhang, Nathan Singh, Max W. Richardson, Keisuke Watanabe, Janos L. Tanyi, Mark H. O'Hara, Marco Ruella, Simon F. Lacey, Edmund K. Moon, Stephen J. Schuster, Steven M. Albelda, Lewis L. Lanier, Regina M. Young, Shelley L. Berger, Carl H. June. Induction of T cell dysfunction and NK-like T cell differentiation in vitro and in patients after CAR T cell treatment [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 60.

Abstract 1585: T-regulatory cells impair CAR T cell-mediated antitumor activity in a murine solid tumor model

Introduction: Chimeric antigen receptor (CAR) T cell immunotherapy has had only modest success in solid malignancies due in part to tumor antigen heterogeneity and the immunosuppressive tumor microenvironment. We have previously demonstrated that administration of cyclophosphamide (CTX) prior to CAR T infusion promoted the eradication of solid tumors that lacked homogenous expression of the CAR target antigen. Although CTX has multiple effects, we hypothesized that one potential mechanism was depletion of T-regulatory cells (Treg). To test this, we used a genetic model of Treg depletion involving mice with FOXP3-driven diphtheria toxin receptor expression (FOXP3-DTR) and an orally administered chemokine receptor 4 (CCR4) antagonist called CCR4-351. Treg express CCR4 and migrate toward CCL17 and CCL22 which are frequently upregulated by tumors. We have previously shown that the tool compound CCR4-351 decreases Treg accumulation in tumors.

Methods: Transgenic FOXP3-DTR C57BL/6 mice were injected s.c. in the flank with a syngeneic murine mesothelioma cell line expressing human mesothelin. When tumors reached ~85 mm3, diphtheria toxin was given i.p. and 24 hours later, 2 doses of 107 transduced human anti-mesothelin CAR T cells (M11) were injected i.v. 2 days apart. In our pharmacologic study, wild type, tumor-bearing C57BL/6 mice were given CCR4-351 daily at 50 mg/kg by oral gavage. Mice were treated with M11 CAR T cells as above, starting one day after CCR4-351 therapy. Tumor growth and mouse survival were determined.

Results: Genetic depletion of Treg alone did not significantly slow tumor growth compared to untreated control. However, the combination of M11 CAR T cells plus genetic depletion of Treg significantly slowed tumor growth compared to vehicle control (p<0.05, one-way ANOVA). Compared to untreated controls, treatment with CCR4-351 (p<0.04, log rank) or M11 CAR T cells (p<0.001, log rank) alone significantly improved survival, however there was no significant difference in survival between CAR and CCR4-351 only treated mice. In contrast, the combination of M11 CAR T cells with CCR4-351 resulted in enhanced antitumor activity with 4/9 mice cured and significantly increased survival compared to CAR (p<0.01, log rank) and CCR4-351 (p<0.006, log rank) monotherapies.

Conclusions: Treg depletion via systemic ablation or inhibition of trafficking, resulted in augmentation of the antitumor effects of CAR T cells in our pre-clinical immunocompetent solid tumor model. If generalizable, these data support further investigation as to whether the orally bioavailable CCR4 antagonist currently in clinical development, FLX475, may be used to augment human CAR T cell therapy for solid tumors.

Citation Format: Michael S. Leibowitz, Nicholas S. Olimpo, Liqing Wang, Aparna Jorapur, Deepa Pookot, Maria Liousia, Evguenia Arguiri, Jing Sun, Astero Klampatsa, Dirk G. Brockstedt, Wayne W. Hancock, Steven M. Albelda. T-regulatory cells impair CAR T cell-mediated antitumor activity in a murine solid tumor model [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 1585.

Neoadjuvant Gene-Mediated Cytotoxic Immunotherapy for Non-Small-Cell Lung Cancer: Safety and Immunologic Activity

Gene-mediated cytotoxic immunotherapy (GMCI) is an immuno-oncology approach involving local delivery of a replication-deficient adenovirus expressing herpes simplex thymidine kinase (AdV-tk) followed by anti-herpetic prodrug activation that promotes immunogenic tumor cell death, antigen-presenting cell activation, and T cell stimulation. This phase I dose-escalation pilot trial assessed bronchoscopic delivery of AdV-tk in patients with suspected lung cancer who were candidates for surgery. A single intra-tumoral AdV-tk injection in three dose cohorts (maximum 1012 viral particles) was performed during diagnostic staging, followed by a 14-day course of the prodrug valacyclovir, and subsequent surgery 1 week later. Twelve patients participated after appropriate informed consent. Vector-related adverse events were minimal. Immune biomarkers were evaluated in tumor and blood before and after GMCI. Significantly increased infiltration of CD8+ T cells was found in resected tumors. Expression of activation, inhibitory, and proliferation markers, such as human leukocyte antigen (HLA)-DR, CD38, Ki67, PD-1, CD39, and CTLA-4, were significantly increased in both the tumor and peripheral CD8+ T cells. Thus, intratumoral AdV-tk injection into non-small-cell lung cancer (NSCLC) proved safe and feasible, and it effectively induced CD8+ T cell activation. These data provide a foundation for additional clinical trials of GMCI for lung cancer patients with potential benefit if combined with other immune therapies.

Serum soluble mesothelin-related protein (SMRP) and fibulin-3 levels correlate with baseline malignant pleural mesothelioma (MPM) tumor volumes but are not useful as biomarkers of response in an immunotherapy trial

OBJECTIVES

Soluble mesothelin-related protein (SMRP) and fibulin-3 serum levels may serve as diagnostic and prognostic biomarkers of malignant pleural mesothelioma (MPM). Here, we evaluate these markers for correlation to tumor volume, prognosis and response assessment in a clinical trial of immunogene therapy in combination with chemotherapy.

MATERIALS AND METHODS

Serial serum levels of SMRP and fibulin-3 were measured in adult patients with biopsy-proven MPM enrolled in two prospective clinical trials. Pre-therapy computed tomography (CT) measurements of tumor burden were calculated and correlated with pre-therapy serum SMRP and fibulin-3 levels in these two trials. Serological data were also correlated with radiological assessment of response using Modified RECIST criteria over the first 6 months of intrapleural delivery of adenovirus-IFN alpha (Ad.IFN-α) combined with chemotherapy.

RESULTS

A cohort of 58 patients who enrolled in either a photodynamic therapy trial or immunotherapy clinical trial had available imaging and SMRP serological data for analysis of whom 45 patients had serological fibulin-3 data. The cohort mean total tumor volume was 387 cm³ (STD 561 cm³). Serum SMRP was detectable in 57 of 58 patients (mean 3.8 nM, STD 6.0). Serum fibulin-3 was detected in 44 of 45 patients (mean 23 ng/mL, STD 14). At pre-therapy baseline in these two trials, there was a strong correlation between tumor volume and serum SMRP levels (r = 0.61, p < 0.001), and a moderate correlation between tumor volume and serum fibulin-3 levels (r = 0.36, p = 0.014). Twenty-eight patients in the immunotherapy trial had longitudinal serologic and radiographic data. Fold-changes in SMRP and fibulin-3 did not show significant correlations with modified RECIST measurements.

CONCLUSIONS

Although our data show correlations of SMRP and fibulin-3 with initial tumor volumes as measured by CT scanning, the use of SMRP and fibulin-3 as serological biomarkers in the immunotherapy trial were not useful in following tumor response longitudinally.

Mesothelin-targeted CAR-T cell therapy for solid tumors

Introduction: Mesothelin (MSLN) is a tumor differentiation antigen normally restricted to the body's mesothelial surfaces, but significantly overexpressed in a broad range of solid tumors. For this reason, MSLN has emerged as an important target for the development of novel immunotherapies. This review focuses on anti-MSLN chimeric antigen receptor (CAR) T cell immunotherapy approaches.Areas covered: A brief overview of MSLN as a therapeutic target and existing anti-MSLN antibody-based drugs and vaccines is provided. A detailed account of anti-MSLN CAR-T cell approaches utilized in preclinical models is presented. Finally, a comprehensive summary of currently ongoing and completed anti-MSLN CAR-T cell clinical trials is discussed.Expert opinion: Initial trials using anti-MSLN CAR-T cells have been safe, but efficacy has been limited. Employing regional routes of delivery, introducing novel modifications leading to enhanced tumor infiltration and persistence, and improved safety profiles and combining anti-MSLN CAR-T cells with standard therapies, could render them more efficacious in the treatment of solid malignancies.

Gene signature of antigen processing and presentation machinery predicts response to checkpoint blockade in non-small cell lung cancer (NSCLC) and melanoma

Background

Limited data exist on the role of alterations in HLA Class I antigen processing and presentation machinery in mediating response to immune checkpoint blockade (ICB).

Methods

This retrospective cohort study analyzed transcriptional profiles from pre-treatment tumor samples of 51 chemotherapy-refractory advanced non-small cell lung cancer (NSCLC) patients and two independent melanoma cohorts treated with ICB. An antigen processing machinery (APM) score was generated utilizing eight genes associated with APM (B2M, CALR, NLRC5, PSMB9, PSME1, PSME3, RFX5, and HSP90AB1). Associations were made for therapeutic response, progression-free survival (PFS) and overall survival (OS).

Results

In NSCLC, the APM score was significantly higher in responders compared with non-responders (p=0.0001). An APM score above the median value for the cohort was associated with improved PFS (HR 0.34 (0.18 to 0.64), p=0.001) and OS (HR 0.44 (0.23 to 0.83), p=0.006). The APM score was correlated with an inflammation score based on the established T-cell-inflamed resistance gene expression profile (Pearson’s r=0.58, p<0.0001). However, the APM score better predicted response to ICB relative to the inflammation score with area under a receiving operating characteristics curve of 0.84 and 0.70 for PFS and OS, respectively. In a cohort of 14 high-risk resectable stage III/IV melanoma patients treated with neoadjuvant anti-PD1 ICB, a higher APM score was associated with improved disease-free survival (HR: 0.08 (0.01 to 0.50), p=0.0065). In an additional independent melanoma cohort of 27 metastatic patients treated with ICB, a higher APM score was associated with improved OS (HR 0.29 (0.09 to 0.89), p=0.044).

Conclusion

Our data demonstrate that defects in antigen presentation may be an important feature in predicting outcomes to ICB in both lung cancer and melanoma.

Tumor Antigen Heterogeneity: The "Elephant in the Room" of Adoptive T-cell Therapy for Solid Tumors

A major hurdle to the efficacy of adoptive cell therapy and chimeric antigen receptors T-cell therapy is the choice of antigen(s) to target. An article in this issue addresses this by capitalizing on the synergistic effect of pathogen-based immunotherapy and adoptive cell therapy that results in epitope/antigen spreading and enhancement of the endogenous T-cell response against antigens not originally targeted.See article by Xin et al., p. 7.

Current Advances in CAR T Cell Therapy for Malignant Mesothelioma

Malignant mesothelioma is a relatively rare malignancy arising in the body's serosal surfaces, with malignant pleural mesothelioma (MPM) being the most common type. It is characterized by local spread within the thorax, poor prognosis and resistance to treatment. The development of various immunotherapeutic options has provided a new way- and hope- in treating cancer patients. Chimeric antigen receptor (CAR) T cell therapy has been proven very successful in treating hematological cancers, like leukemias and lymphomas, and its use is now being tested in solid tumors. CARs that recognize and bind to a specific tumor-associated antigen on the tumor's cell surface, are engineered and transduced into T cells. Interaction of the CAR T cell with the tumor then results in T cell activation and subsequent tumor cell lysis. In this review, we provide a current update on our previous comprehensive study summarizing the CAR T cell preclinical studies and clinical trials in MM, and discuss the future perspectives of CAR T cell therapy in this disease.

Analysis and Augmentation of the Immunologic Bystander Effects of CAR T Cell Therapy in a Syngeneic Mouse Cancer Model

The therapeutic efficacy of adoptive transfer of T cells transduced with chimeric antigen receptors (CARs) has been limited in the treatment of solid cancers, partly due to tumor antigen heterogeneity. Overcoming lack of universal tumor antigen expression would be achieved if CAR T cells could induce bystander effects. To study this process, we developed a system where CAR T cells targeting mesothelin could cure tumors containing 100% antigen-positive cells in immunocompetent mice. Using this model, we found that the CAR T cells were unable to cure tumors, even when only 10% of the tumor cells were mesothelin negative. A bystander effect was not induced by co-administration of anti-PD-1, anti-CTLA-4, or anti-TGF-β (transforming growth factor β) antibodies; agonistic CD40 antibodies; or an IDO (indoleamine 2,3-dioxygenase) inhibitor. However, pretreatment with a non-lymphodepleting dose of cyclophosphamide (CTX) prior to CAR T cells resulted in cures of tumors with up to 25% mesothelin-negative cells. The mechanism was dependent on endogenous CD8 T cells but not on basic leucine zipper transcription factor ATF-like 3 (BATF3)-dependent dendritic cells. These data suggest that CAR T cell therapy of solid tumors, in which the targeted antigen is not expressed by the vast majority of tumor cells, will not likely be successful unless combination strategies to enhance bystander effects are used.

Ligand-Induced Degradation of a CAR Permits Reversible Remote Control of CAR T Cell Activity In Vitro and In Vivo

Chimeric antigen receptor (CAR)-modified T cells are endowed with novel antigen specificity and are most often administered to patients without an engineered mechanism to control the CAR T cells once infused. "Suicide switches" such as the small molecule-controlled, inducible caspase-9 (iCas9) system afford the ability to selectively eliminate engineered T cells; however, these approaches are designed for all-or-none, irreversible termination of an ongoing immune response. In order to permit reversible and adjustable modulation, we have created a CAR that is capable of on-demand downregulation by fusing the CAR to a previously developed ligand-induced degradation (LID) domain. Addition of a small molecule ligand triggers exposure of a cryptic degron within the LID domain, resulting in proteasomal degradation of the CAR-LID fusion protein and loss of CAR on the surface of T cells. This fusion construct allowed for reversible and "tunable" inhibition of CAR T cell activity in vitro. Delivery of the triggering molecule in CAR-LID-treated tumor-bearing mice temporarily reduced CAR activity through modulation of CAR surface expression. The ability to more flexibly modulate CAR T cell expression through a small molecule provides a platform for controlling possible adverse side effects, as well as preclinical investigations of CAR T cell biology.

Gene signature of antigen processing and presentation machinery (APM) as highly predictive of response to checkpoint blockade in lung cancer and melanoma

3121

Background: Treatment of non-small cell lung cancer (NSCLC) with immune checkpoint blockade (ICB) has resulted in striking clinical responses, but only in a subset of patients (pts), underscoring the need to identify genomic and molecular determinants of immune evasion. Limited data exist on the potential role of alterations in HLA Class I antigen processing and presentation machinery (APM) in mediating response to ICB. Methods: We conducted a retrospective cohort study analyzing transcriptional profiles from pre-treatment tumor samples of chemotherapy-refractory advanced NSCLC pts treated with ICB. RNA was analyzed using the AmpliSeq transcriptomic platform. An APM signature was generated utilizing 8 genes associated with antigen processing ( B2M, CALR, NLRC5, PSMB9, PSME1, PSME3, RFX5, HSP90AB1) and was examined for its association with response to therapy and progression-free and overall survival (PFS, OS). The APM signature was then evaluated in two independent melanoma cohorts treated with ICB. Results: We analyzed pre-treatment tumor samples from 51 advanced NSCLC pts treated with ICB, median age 64 (range 31-92), smokers (n = 43), adenocarcinoma (n = 31). There were 23 responders and 28 non-responders. The APM signature was significantly higher in responders compared to non-responders (average z-score 2.69 vs. -2.49, p = 0.0001). An APM score above the median value for the entire cohort was significantly associated with improved PFS (HR 0.24, 95% CI, 0.12-0.47, log-rank = 0.001) and OS (HR 0.34, 95% CI, 0.18-0.67, log-rank = 0.005). The APM score was significantly correlated with the well-validated T-cell-inflamed resistance gene expression profile (GEP) score (R2 = 0.32, p < 0.0001). However, the APM score demonstrated improved ability to predict response to ICB relative to the GEP score with AUCs of 0.83 and 0.69, respectively. In an independent cohort of 14 high-risk resectable stage III/IV melanoma pts treated with neoadjuvant anti-PD1 therapy, upregulation of genes involved in antigen processing was associated with improved disease free survival (HR: 0.08, 95% CI, 0.01-0.50, p = 0.0065). In an additional independent melanoma cohort of 28 metastatic pts treated with ICB, a higher APM score was associated with improved overall survival (HR 0.31, 95% CI, 0.09-0.89, log-rank = 0.044). Conclusions: Our data demonstrate that defects in antigen presentation may be an important feature in predicting outcomes to ICB in both lung cancer and melanoma.

Neoadjuvant endobronchial delivery of gene mediated cytotoxic immunotherapy (GMCI) for non-small cell lung cancer (NSCLC): Safety and immunologic activity

9050

Background: GMCI is a tumor-specific immuno-oncology approach implemented through local delivery of aglatimagene besadenovec(AdV-tk) followed by anti-herpetic prodrug. This leads to immunogenic tumor cell death, antigen presenting cell activation, and T cell stimulation resulting in CD8+ T cell dependent protection, as demonstrated in preclinical models and clinical trials in other tumor types. This is the first study to assess endobronchial delivery of AdV-tk for NSCLC. Methods: This Phase I dose escalation trial enrolled patients with suspected NSCLC who were candidates for surgery. A single AdV-tk injection was performed by endobronchial ultrasound (n = 11) or mediastinoscopy (n = 1) during the diagnostic staging procedure 3 weeks prior to surgery. Three dose levels were evaluated: 2.5x 1011, 5x1011, and 1x1012 vector particles (vp) in a 3+3 design. Valacyclovir was administered for 14 days, starting the day after AdV-tk injection. To assess the local and systemic effects of GMCI, immune biomarkers were evaluated in blood and tumor samples before and after GMCI. Results: From 2017-2019, 12 patients (9 men, 3 women, median age 65 [range 55-80]) received GMCI followed by surgery. Average tumor size was 5.1 cm (largest diameter) and final pathologic stage was I (n = 4), II (n = 3), and III (n = 5). Treatment-related adverse events were CTC grade 1 fever (n = 1), flu-like symptoms (n = 1) and nausea/vomiting/diarrhea (n = 1). The only > grade 2 lab abnormality was transient grade 3 lymphopenia (n = 2). A measurable reduction in tumor size was observed in one patient. The average amount of tumor necrosis was 29.4%. Significant infiltration of CD8+T cells (5.2-fold compared to baseline, p = 0.001) was found in tumor 19-22 days after AdV-tk injection. Within the CD8+tumor infiltrating lymphocytes, there was increased expression of CD38 (2.5-fold, p = 0.002), Ki67 (4.8-fold, p = 0.02), PD1 (1.9-fold, p = 0.002), CD39 (2.9-fold, p = 0.04) and CTLA-4 (4.8-fold, p < 0.001), without significant detected differences in Tim3 or TIGIT. Simultaneously, peripheral blood CD8+ cells displayed significant increases in CD38 (3.4-fold, p = 0.006), HLA-DR (4.2-fold, p = 0.002), and Ki67 (5.8-fold, p = 0.017). Conclusions: Intratumoral injection of AdV-tk into lung tumors was safe and feasible. Further, AdV-tk effectively induced peripheral blood and intra-tumoral CD8 T cell activation. Consequent upregulation of inhibitory receptors suggests a potential benefit for combination therapies. Clinical trial information: NCT03131037.

4-1BB costimulation promotes CAR T cell survival through noncanonical NF-κB signaling

Clinical response to chimeric antigen receptor (CAR) T cell therapy is correlated with CAR T cell persistence, especially for CAR T cells that target CD19⁺ hematologic malignancies. 4-1BB-costimulated CAR (BBζ) T cells exhibit longer persistence after adoptive transfer than do CD28-costimulated CAR (28ζ) T cells. 4-1BB signaling improves T cell persistence even in the context of 28ζ CAR activation, which indicates distinct prosurvival signals mediated by the 4-1BB cytoplasmic domain. To specifically study signal transduction by CARs, we developed a cell-free, ligand-based activation and ex vivo culture system for CD19-specific CAR T cells. We observed greater ex vivo survival and subsequent expansion of BBζ CAR T cells when compared to 28ζ CAR T cells. We showed that only BBζ CARs activated noncanonical nuclear factor κB (ncNF-κB) signaling in T cells basally and that the anti-CD19 BBζ CAR further enhanced ncNF-κB signaling after ligand engagement. Reducing ncNF-κB signaling reduced the expansion and survival of anti-CD19 BBζ T cells and was associated with a substantial increase in the abundance of the most pro-apoptotic isoforms of Bim. Although our findings do not exclude the importance of other signaling differences between BBζ and 28ζ CARs, they demonstrate the necessary and nonredundant role of ncNF-κB signaling in promoting the survival of BBζ CAR T cells, which likely underlies the engraftment persistence observed with this CAR design.

Abstract A62: Inhibition of tumor growth by novel CART redirected against cells expressing high levels of fibroblast activation protein

Cancer-associated fibroblasts (CAFs) support tumor growth and metastasis of virtually all solid tumors, making them a potential “universal therapeutic target.” However, there are challenges to designing CAF targeted therapies. First, CAFs are heterogeneous, consisting of tumor-promoting and tumor-restraining populations. Second, molecular targets expressed strictly by tumor-promoting CAFs have yet to be defined. Nonetheless, Fibroblast Activation Protein (FAP) is selectively overexpressed on tumor-promoting CAFs. Moreover, deleting FAP+ cells inhibits tumor growth in preclinical models due to reductions in stroma-dependent signals that support tumor cell survival, growth, and progression and in stroma-derived immunosuppressive factors and can enhance efficacy of other therapies when given in combination. Prior studies in preclinical models suggest, however, that selective elimination of FAPhigh cells while sparing normal FAP+ cells that typically express lower levels of FAP may be necessary to avoid toxicity due to on-target, off-tumor effects. Thus, the aim of this study was to generate a FAP-chimeric antigen receptor (CAR) that selectively targets FAPhigh cells but that exhibits minimal activity against FAPlow cells for use in future clinical trials. We generated a FAP-CAR containing a scFv based on a monoclonal antibody (mAb) we generated that reacts with human and mouse FAP, the CD8 transmembrane region, and the CD3z and 41BB cytoplasmic domains. We show that primary human T cells transduced with this novel FAP-CAR exhibit strong reactivity against cells expressing high levels of human or mouse FAP but not FAPlow or FAP-negative cells. Moreover, these FAP-CART cells inhibited the growth of human FAP-negative A549 tumor xenografts infiltrated by FAP+ murine CAFs in NSG mice. Based on these characteristics, this novel FAP-CAR will be developed for use in clinical trials for human cancer patients.

Citation Format: Estela Noguera-Ortega, Leslie Todd, James Monslow, Jing Sun, Steven M. Albelda, Ellen Pure. Inhibition of tumor growth by novel CART redirected against cells expressing high levels of fibroblast activation protein [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A62.

Human tumor-associated monocytes/macrophages and their regulation of T cell responses in early-stage lung cancer

Data from mouse tumor models suggest that tumor-associated monocyte/macrophage lineage cells (MMLCs) dampen antitumor immune responses. However, given the fundamental differences between mice and humans in tumor evolution, genetic heterogeneity, and immunity, the function of MMLCs might be different in human tumors, especially during early stages of disease. Here, we studied MMLCs in early-stage human lung tumors and found that they consist of a mixture of classical tissue monocytes and tumor-associated macrophages (TAMs). The TAMs coexpressed M1/M2 markers, as well as T cell coinhibitory and costimulatory receptors. Functionally, TAMs did not primarily suppress tumor-specific effector T cell responses, whereas tumor monocytes tended to be more T cell inhibitory. TAMs expressing relevant MHC class I/tumor peptide complexes were able to activate cognate effector T cells. Mechanistically, programmed death-ligand 1 (PD-L1) expressed on bystander TAMs, as opposed to PD-L1 expressed on tumor cells, did not inhibit interactions between tumor-specific T cells and tumor targets. TAM-derived PD-L1 exerted a regulatory role only during the interaction of TAMs presenting relevant peptides with cognate effector T cells and thus may limit excessive activation of T cells and protect TAMs from killing by these T cells. These results suggest that the function of TAMs as primarily immunosuppressive cells might not fully apply to early-stage human lung cancer and might explain why some patients with strong PD-L1 positivity fail to respond to PD-L1 therapy.

Neutrophil content predicts lymphocyte depletion and anti-PD1 treatment failure in NSCLC

Immune checkpoint inhibitor (ICI) treatment has recently become a first-line therapy for many non-small cell lung cancer (NSCLC) patients. Unfortunately, most NSCLC patients are refractory to ICI monotherapy, and initial attempts to address this issue with secondary therapeutics have proven unsuccessful. To identify entities precluding CD8+ T cell accumulation in this process, we performed unbiased analyses on flow cytometry, gene expression, and multiplexed immunohistochemical data from a NSCLC patient cohort. The results revealed the presence of a myeloid-rich subgroup, which was devoid of CD4+ and CD8+ T cells. Of all myeloid cell types assessed, neutrophils were the most highly associated with the myeloid phenotype. Additionally, the ratio of CD8+ T cells to neutrophils (CD8/PMN) within the tumor mass optimally distinguished between active and myeloid cases. This ratio was also capable of showing the separation of patients responsive to ICI therapy from those with stable or progressive disease in 2 independent cohorts. Tumor-bearing mice treated with a combination of anti-PD1 and SX-682 (CXCR1/2 inhibitor) displayed relocation of lymphocytes from the tumor periphery into a malignant tumor, which was associated with induction of IFN-γ-responsive genes. These results suggest that neutrophil antagonism may represent a viable secondary therapeutic strategy to enhance ICI treatment outcomes.

Author Correction: Targeting cardiac fibrosis with engineered T cells

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

Gene signatures of tumor inflammation and epithelial-to-mesenchymal transition (EMT) predict responses to immune checkpoint blockade in lung cancer with high accuracy

OBJECTIVES

Treatment of non-small cell lung cancer (NSCLC) with immune checkpoint blockade (ICB) has resulted in striking clinical responses, but only in a subset of patients. The goal of this study was to evaluate transcriptional signatures previously reported in the literature in an independent cohort of NSCLC patients receiving ICB.

MATERIALS AND METHODS

This retrospective study analyzed transcriptional profiles from pre-treatment tumor samples of 52 chemotherapy-refractory advanced NSCLC patients treated with anti-PD1/PD-L1 therapy. Gene signatures based on published reports were created and examined for their association with response to therapy and progression-free and overall survival (PFS, OS).

RESULTS

Two signatures predicting response and outcomes were identified. One reflected the degree of immune infiltration and upregulation of interferon-gamma-induced genes. A second reflected the EMT status. Compared to those not responding to therapy, patients whose tumors responded to ICB had higher scores in an inflammatory gene signature (6.0 ± 2.9 vs -5.5 ± 3.4, p = 0.014) or a more epithelial phenotype (-1.7 ± 1.0 vs 2.1 ± 1.2, p = 0.016). Both signatures demonstrated a satisfactory predictive accuracy for response: AUC of 0.69 (95% CI: 0.54, 0.84) for the inflammatory and 0.70 (95% CI: 0.55, 0.85) for EMT signatures, respectively. A weighted score combining EMT and inflammatory signatures showed increased predictive value with AUC of 0.92 (95% CI: 0.85, 0.99). Kaplan-Meier curves for patients above and below the median combined score showed a significant separation for PFS and OS (all p < 0.01, log rank test).

CONCLUSIONS

The EMT/Inflammation signature score may be useful in directing checkpoint inhibitor therapy in lung cancer and suggests that reversal of EMT might augment efficacy of ICB.

Molecular Characterization of Malignant Mesothelioma: Time for New Targets?

Malignant pleural mesothelioma (MPM) is an aggressive lethal malignancy for which very few therapeutic options exist. In this issue of Cancer Discovery, Hmeljak and colleagues report on a comprehensive integrative analysis of histology-independent genomic characteristics of MPM. They confirm previous observations that inactivation of tumor suppressor genes is the predominant oncogenic mechanism. This study provides a scientific rationale for potentially novel therapeutic options, including immune-checkpoint targeting VISTA and small-molecule inhibitors targeting the epigenome, DNA-repair pathways, and aurora kinase.See related article by Hmeljak et al., p. 1548.

Phase I Study of Lentiviral-Transduced Chimeric Antigen Receptor-Modified T Cells Recognizing Mesothelin in Advanced Solid Cancers

This phase I study investigated the safety and activity of lentiviral-transduced chimeric antigen receptor (CAR)-modified autologous T cells redirected against mesothelin (CART-meso) in patients with malignant pleural mesothelioma, ovarian carcinoma, and pancreatic ductal adenocarcinoma. Fifteen patients with chemotherapy-refractory cancer (n = 5 per indication) were treated with a single CART-meso cell infusion. CART-meso cells were engineered by lentiviral transduction with a construct composed of the anti-mesothelin single-chain variable fragment derived from the mouse monoclonal antibody SS1 fused to intracellular signaling domains of 4-1BB and CD3zeta. Patients received 1-3 × 10⁷ or 1-3 × 10⁸ CART-meso cells/m² with or without 1.5 g/m² cyclophosphamide. Lentiviral-transduced CART-meso cells were well tolerated; one dose-limiting toxicity (grade 4, sepsis) occurred at 1-3 × 10⁷/m² CART-meso without cyclophosphamide. The best overall response was stable disease (11/15 patients). CART-meso cells expanded in the blood and reached peak levels by days 6-14 but persisted transiently. Cyclophosphamide pre-treatment enhanced CART-meso expansion but did not improve persistence beyond 28 days. CART-meso DNA was detected in 7/10 tumor biopsies. Human anti-chimeric antibodies (HACA) were detected in the blood of 8/14 patients. CART-meso cells were well tolerated and expanded in the blood of all patients but showed limited clinical activity. Studies evaluating a fully human anti-mesothelin CAR are ongoing.

Phenotypic and functional analysis of malignant mesothelioma tumor-infiltrating lymphocytes

Given the growing interest and promising preliminary results of immunotherapy in malignant pleural mesothelioma (MPM), it has become important to more fully understand the immune landscape in this tumor. This may be especially relevant in deciding who might benefit most from checkpoint blockade or agonist antibody therapy. Since the phenotype of tumor infiltrating lymphocytes (TILs) in MPM has not been fully described and their function has not been carefully assessed, we collected fresh tumor and blood from 22 patients undergoing surgical resection and analysed single cell suspensions by flow cytometry. The functionality of TILs was assessed by measurement of cytokine expression (IFN-γ) following overnight stimulation ex vivo. Results showed low numbers of CD8+ TILs whose function was either moderately or severely suppressed. The degree of TIL hypofunction did not correlate with the presence of co-existing macrophages or neutrophils, nor with expression of the inhibitory receptors PD-1, CD39 and CTLA-4. Hypofunction was associated with higher numbers of CD4 regulatory T cells (Tregs) and with expression of the inhibitory receptor TIGIT. On the other hand, presence of tissue-resident memory (Trm) cells and expression of TIM-3 on CD8+ cells were positively associated with cytokine production. However, Trm function was partially suppressed when the transcription factor Eomesodermin (Eomes) was co-expressed. Understanding the function of TILs in malignant mesothelioma may have clinical implications for immunotherapy, especially in choosing the best immunotherapy targets. Our data suggests that Treg cell blocking agents or TIGIT inhibitor antibodies might be especially valuable in these patients.

Loss of cells expressing fibroblast activation protein has variable effects in models of TGF-β and chronic bleomycin-induced fibrosis

Fibroblast activation protein (FAP), a cell surface serine protease, is upregulated on a subset of activated fibroblasts (often distinct from α-smooth muscle actin-expressing myofibroblasts) associated with matrix remodeling, including fibroblasts in idiopathic pulmonary fibrosis (Acharya PS, Zukas A, Chandan V, Katzenstein AL, Puré E. Hum Pathol 37: 352-360, 2006.). As FAP⁺ fibroblasts could be pivotal in either breakdown and/or production of collagen and other matrix components, the goal of this study was to define the role of FAP⁺ cells in pulmonary fibrosis in two established, but different, mouse models of chronic lung fibrosis: repetitive doses of intratracheal bleomycin and a single dose of an adenoviral vector encoding constitutively active TGF-β1 (Ad-TGFβ). To determine their role in fibrotic remodeling, FAP-expressing cells were depleted by injection of T cells expressing a chimeric antigen receptor specific for murine FAP in mice with established fibrosis. The contribution of FAP to the function of FAP-expressing cells was assessed in FAP knockout mice. Using histological analyses, quantification of soluble collagen content, and flow cytometry, we found that loss of FAP⁺ cells exacerbated fibrosis in the bleomycin model, a phenotype largely recapitulated by the genetic deletion of FAP, indicating that FAP plays a role in this model. In contrast, depletion of FAP⁺ cells or genetic deletion of FAP had little effect in the Ad-TGFβ model highlighting the potential for distinct mechanisms driving fibrosis depending on the initiating insult. The role of FAP in human lung fibrosis will need to be well understood to guide the use of FAP-targeted therapeutics that are being developed.

Function of Human Tumor-Infiltrating Lymphocytes in Early-Stage Non-Small Cell Lung Cancer

Cancer progression is marked by dysfunctional tumor-infiltrating lymphocytes (TIL) with high inhibitory receptor (IR) expression. Because IR blockade has led to clinical responses in some patients with non-small cell lung cancer (NSCLC), we investigated how IRs influenced CD8⁺ TIL function from freshly digested early-stage NSCLC tissues using a killing assay and intracellular cytokine staining after in vitro T-cell restimulation. Early-stage lung cancer TIL function was heterogeneous with only about one third of patients showing decrements in cytokine production and lytic function. TIL hypofunction did not correlate with clinical factors, coexisting immune cells (macrophages, neutrophils, or CD4⁺ T regulatory cells), nor with PD-1, TIGIT, TIM-3, CD39, or CTLA-4 expression. Instead, we found that the presence of the integrin α_eβ₇ (CD103), characteristic of tissue-resident memory cells (T_RM), was positively associated with cytokine production, whereas expression of the transcription factor Eomesodermin (Eomes) was negatively associated with TIL function. These data suggest that the functionality of CD8⁺ TILs from early-stage NSCLCs may be influenced by competition between an antitumor CD103⁺ T_RM program and an exhaustion program marked by Eomes expression. Understanding the mechanisms of T-cell function in the progression of lung cancer may have clinical implications for immunotherapy.

Synthetic secoisolariciresinol diglucoside (LGM2605) inhibits Libby amphibole fiber-induced acute inflammation in mice

BACKGROUND

Exposure to the Libby amphibole (LA) asbestos-like fibers found in Libby, Montana, is associated with inflammatory responses in mice and humans, and an increased risk of developing mesothelioma, asbestosis, pleural disease, and systemic autoimmune disease. Flaxseed-derived secoisolariciresinol diglucoside (SDG) has anti-inflammatory, anti-fibrotic, and antioxidant properties. We have previously identified potent protective properties of SDG against crocidolite asbestos exposure modeled in mice. The current studies aimed to extend those findings by evaluating the immunomodulatory effects of synthetic SDG (LGM2605) on LA-exposed mice.

METHODS

Male and female C57BL/6 mice were given LGM2605 via gavage initiated 3 days prior to and continued for 3 days after a single intraperitoneal dose of LA fibers (200 μg) and evaluated on day 3 for inflammatory cell influx in the peritoneal cavity using flow cytometry.

RESULTS

LA exposure induced a significant increase (p < 0.0001) in spleen weight and peritoneal influx of white blood cells, all of which were reduced with LGM2605 with similar trends among males and females. Levels of peritoneal PMN cells were significantly (p < 0.0001) elevated post LA exposure, and were significantly (p < 0.0001) blunted by LGM2605. Importantly, LGM2605 significantly ameliorated the LA-induced mobilization of peritoneal B1a B cells.

CONCLUSIONS

LGM2605 reduced LA-induced acute inflammation and WBC trafficking supporting its possible use in mitigating downstream LA fiber-associated diseases.

SUMMARY

Following acute exposure to Libby amphibole (LA) asbestos-like fibers, synthetic SDG (LGM2605), a small synthetic molecule, significantly reduced the LA-induced increase in spleen weight and peritoneal inflammation in C57BL/6 male and female mice. Our findings highlight that LGM2605 has immunomodulatory properties and may, thus, likely be a chemopreventive agent for LA-induced diseases.

Novel therapies for malignant pleural mesothelioma

Malignant pleural mesothelioma is a rare cancer that is typically associated with exposure to asbestos. Patients with malignant pleural mesothelioma have poor outcomes with suboptimal therapeutic options and currently no treatment is curative. The standard frontline treatment, cisplatin plus pemetrexed chemotherapy, has only short and insufficient efficacy, and no validated treatment beyond first-line therapy is available. New therapeutic strategies are therefore needed. The addition of bevacizumab (an anti-VEGF antibody) combined with cisplatin plus pemetrexed has shown some promise. However, immunotherapy, especially immune checkpoint inhibitors, has generated a lot of excitement because of data suggesting the potential value of immune checkpoint inhibitors for patients who have failed chemotherapy. In this Review, we describe immune checkpoint inhibitors, other immunotherapies, targeted therapies, or combinations of novel drugs being investigated in malignant pleural mesothelioma, as well as the issues surrounding the selection of the best candidates for these treatments.

Epigenomic-Guided Mass Cytometry Profiling Reveals Disease-Specific Features of Exhausted CD8 T Cells

Exhausted CD8 T (Tex) cells are immunotherapy targets in chronic infection and cancer, but a comprehensive assessment of Tex cell diversity in human disease is lacking. Here, we developed a transcriptomic- and epigenetic-guided mass cytometry approach to define core exhaustion-specific genes and disease-induced changes in Tex cells in HIV and human cancer. Single-cell proteomic profiling identified 9 distinct Tex cell clusters using phenotypic, functional, transcription factor, and inhibitory receptor co-expression patterns. An exhaustion severity metric was developed and integrated with high-dimensional phenotypes to define Tex cell clusters that were present in healthy subjects, common across chronic infection and cancer or enriched in either disease, linked to disease severity, and changed with HIV therapy. Combinatorial patterns of immunotherapy targets on different Tex cell clusters were also defined. This approach and associated datasets present a resource for investigating human Tex cell biology, with implications for immune monitoring and immunomodulation in chronic infections, autoimmunity, and cancer.

Luminol Chemiluminescence Reports Photodynamic Therapy-Generated Neutrophil Activity In Vivo and Serves as a Biomarker of Therapeutic Efficacy

Inflammatory cells, most especially neutrophils, can be a necessary component of the antitumor activity occurring after administration of photodynamic therapy. Generation of neutrophil responses has been suggested to be particularly important in instances when the delivered photodynamic therapy (PDT) dose is insufficient. In these cases, the release of neutrophil granules and engagement of antitumor immunity may play an important role in eliminating residual disease. Herein, we utilize in vivo imaging of luminol chemiluminescence to noninvasively monitor neutrophil activation after PDT administration. Studies were performed in the AB12 murine model of mesothelioma, treated with Photofrin-PDT. Luminol-generated chemiluminescence increased transiently 1 h after PDT, followed by a subsequent decrease at 4 h after PDT. The production of luminol signal was not associated with the influx of Ly6G⁺ cells, but was related to oxidative burst, as an indicator of neutrophil function. Most importantly, greater levels of luminol chemiluminescence 1 h after PDT were prognostic of a complete response at 90 days after PDT. Taken together, this research supports an important role for early activity by Ly6G⁺ cells in the generation of long-term PDT responses in mesothelioma, and it points to luminol chemiluminescence as a potentially useful approach for preclinical monitoring of neutrophil activation by PDT.

Abstract 3790: Human tumor-infiltrating monocytes/macrophages do not predominantly inhibit tumor-specific effector T cell responses in early-stage lung cancer: The role of macrophage versus tumor PD-L1

Our current understanding of tumor-associated monocyte/macrophage lineage cells (MMLC) as being immunosuppressive is based largely on murine tumor models that generated a widespread interest in targeting these cells therapeutically. Unfortunately, this approach has not yet been successful in many clinical trials. One potential explanation is that there are fundamental differences between mice and humans in tumor evolution and immunity that might impact the function of human MMLC, limiting the success of myeloid cell-related therapies. Moreover, despite recent successes with checkpoint blockade therapy, the contribution of PD-L1 expressed on MMLC to T cell suppression in humans remains unclear. Thus, the overall purpose of this study was to determine the phenotypic composition of monocyte-macrophage cell lineage in a large cohort of early stage (resected) human lung tumors and delineate how different cell populations of this lineage regulate the effector phase of tumor-specific T cell responses. In addition we also explored the role of MMLC-expressed PD-L1 by interrogating the tripartite functional interactions between tumor-specific effector T cells, PD-L1+ or PD-L1- tumor cells, and TAM that possess a varied surface PD-L1 expression. Phenotypically, we find that (i) MMLC are not the predominate cell population of infiltrating leukocytes within the early-stage lung tumors, (ii) tumor MMLC consist primarily of tumor-associated macrophages (TAM), (iii) the TAM phenotype is complex and does not fit the conventional M1 and M2 phenotype denominations, (iv) TAM are able to co-express T cell co-inhibitory and co-stimulatory receptors. Functionally, MMLC are not primarily suppressive, but have diverse effects, including stimulation of the effector phase of tumor-specific T cell responses. Mechanistically, TAM-expressed PD-L1 (in contrast to tumor-expressed PD-L1), does not inhibit the interaction between tumor-specific effector T cells and tumor cells, but does protect TAMs expressing a tumor antigenic peptide/MHC class I complex from being killed by effector T cells recognizing the cognate peptide on the tumor. These data provide new insights into the phenotype of tumor MMLC and functional cross-talk between TAM, tumor-specific T cells, and tumor cells. Our results show that the prevailing premise that TAMs are predominantly immunosuppressive does not apply to early-stage human lung cancer and thus the current MMLC-targeted approaches would not be helpful in majority of early-stage lung cancer patients.

Citation Format: Jason Stadanlick, Abhishek Rao, Sunil Singhal, Michael Annunziata, Pratick Bhojnagarwala, Shaun Obrien, Edmund Moon, Edward Cantu, Gwenn Danet-Desnoyers, Hyun-Jeong Ra, Leslie Litzky, Wayne W. Hancock, Steven M. Albelda, Evgeniy Eruslanov. Human tumor-infiltrating monocytes/macrophages do not predominantly inhibit tumor-specific effector T cell responses in early-stage lung cancer: The role of macrophage versus tumor PD-L1 [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 3790.

A preclinical model to investigate the role of surgically-induced inflammation in tumor responses to intraoperative photodynamic therapy

OBJECTIVE

Inflammation is a well-known consequence of surgery. Although surgical debulking of tumor is beneficial to patients, the onset of inflammation in injured tissue may impede the success of adjuvant therapies. One marker for postoperative inflammation is IL-6, which is released as a consequence of surgical injuries. IL-6 is predictive of response to many cancer therapies, and it is linked to various molecular and cellular resistance mechanisms. The purpose of this study was to establish a murine model by which therapeutic responses to photodynamic therapy (PDT) can be studied in the context of surgical inflammation.

MATERIALS AND METHODS

Murine models with AB12 mesothelioma tumors were treated with either surgical resection or sham surgery with tumor incision but no resection. The timing and extent of IL-6 release in the tumor and/or serum was measured using enzyme-linked immunosorbent assay (ELISA) and compared to that measured in the serum of 27 consecutive, prospectively enrolled patients with malignant pleural mesothelioma (MPM) who underwent macroscopic complete resection (MCR).

RESULTS

MPM patients showed a significant increase in IL-6 at the time MCR was completed. Similarly, IL-6 increased in the tumor and serum of mice treated with surgical resections. However, investigations that combine resection with another therapy make it necessary to grow tumors for resection to a larger volume than those that receive secondary therapy alone. As the larger size may alter tumor biology independent of the effects of surgical injury, we assessed the tumor incision model. In this model, tumor levels of IL-6 significantly increased after tumor incision.

CONCLUSION

The tumor incision model induces IL-6 release as is seen in the surgical setting, yet it avoids the limitations of surgical resection models. Potential mechanisms by which surgical induction of inflammation and IL-6 could alter the nature and efficacy of tumor response to PDT are reviewed. These include a wide spectrum of molecular and cellular mechanisms through which surgically-induced IL-6 could change the effectiveness of therapies that are combined with surgery. The tumor incision model can be employed for novel investigations of the effects of surgically-induced, acute inflammation on therapeutic response to PDT (or potentially other therapies). Lasers Surg. Med. 50:440-450, 2018. © 2018 Wiley Periodicals, Inc.

Early detection of pemetrexed-induced inhibition of thymidylate synthase in non-small cell lung cancer with FLT-PET imaging

Inhibition of thymidylate synthase (TS) results in a transient flare in DNA thymidine salvage pathway activity measurable with FLT ([¹⁸F]thymidine)-positron emission tomography (PET). Here we characterize this imaging strategy for potential clinical translation in non-small cell lung cancer (NSCLC). Since pemetrexed acts by inhibiting TS, we defined the kinetics of increases in thymidine salvage pathway mediated by TS inhibition following treatment with pemetrexed in vitro. Next, using a mouse model of NSCLC, we validated the kinetics of the pemetrexed-mediated flare in thymidine salvage pathway activity in vivo using FLT-PET imaging. Finally, we translated our findings into a proof-of-principle clinical trial of FLT-PET in a human NSCLC patient. In NSCLC cells in vitro, we identified a burst in pemetrexed-mediated thymidine salvage pathway activity, assessed by ³H-thymidine assays, thymidine kinase 1 (TK1) expression, and equilibrative nucleoside transporter 1 (ENT1) mobilization to the cell membrane, that peaked at 2hrs. This 2hr time-point was also optimal for FLT-PET imaging of pemetrexed-mediated TS inhibition in murine xenograft tumors and was demonstrated to be feasible in a NSCLC patient. FLT-PET imaging of pemetrexed-induced TS inhibition is optimal at 2hrs from therapy start; this timing is feasible in human clinical trials.