IL-15-secreting CAR natural killer cells directed toward the pan-cancer target CD70 eliminate both cancer cells and cancer-associated fibroblasts

BACKGROUND

It remains challenging to obtain positive outcomes with chimeric antigen receptor (CAR)-engineered cell therapies in solid malignancies, like colorectal cancer (CRC) and pancreatic ductal adenocarcinoma (PDAC). A major obstacle is the lack of targetable surface antigens that are not shared by healthy tissues. CD70 emerges as interesting target, due to its stringent expression pattern in healthy tissue and its apparent role in tumor progression in a considerable amount of malignancies. Moreover, CD70 is also expressed on cancer-associated fibroblasts (CAFs), another roadblock for treatment efficacy in CRC and PDAC. We explored the therapeutic potential of CD70 as target for CAR natural killer (NK) cell therapy in CRC, PDAC, focusing on tumor cells and CAFs, and lymphoma.

METHODS

RNA-seq data and immunohistochemical analysis of patient samples were used to explore CD70 expression in CRC and PDAC patients. In addition, CD70-targeting CAR NK cells were developed to assess cytotoxic activity against CD70+ tumor cells and CAFs, and the effect of cytokine stimulation on their efficacy was evaluated. The in vitro functionality of CD70-CAR NK cells was investigated against a panel of tumor and CAF cell lines with varying CD70 expression. Lymphoma-bearing mice were used to validate in vivo potency of CD70-CAR NK cells. Lastly, to consider patient variability, CD70-CAR NK cells were tested on patient-derived organoids containing CAFs.

RESULTS

In this study, we identified CD70 as a target for tumor cells and CAFs in CRC and PDAC patients. Functional evaluation of CD70-directed CAR NK cells indicated that IL-15 stimulation is essential to obtain effective elimination of CD70+ tumor cells and CAFs, and to improve tumor burden and survival of mice bearing CD70+ tumors. Mechanistically, IL-15 stimulation resulted in improved potency of CD70-CAR NK cells by upregulating CAR expression and increasing secretion of pro-inflammatory cytokines, in a mainly autocrine or intracellular manner.

CONCLUSIONS

We disclose CD70 as an attractive target both in hematological and solid tumors. IL-15 armored CAR NK cells act as potent effectors to eliminate these CD70+ cells. They can target both tumor cells and CAFs in patients with CRC and PDAC, and potentially other desmoplastic solid tumors.

Establishment of head and neck squamous cell carcinoma mouse models for cetuximab resistance and sensitivity

Aim: Acquired resistance to the targeted agent cetuximab poses a significant challenge in finding effective anti-cancer treatments for head and neck squamous cell carcinoma (HNSCC). To accurately study novel combination treatments, suitable preclinical mouse models for cetuximab resistance are key yet currently limited. This study aimed to optimize an acquired cetuximab-resistant mouse model, with preservation of the innate immunity, ensuring intact antibody-dependent cellular cytotoxicity (ADCC) functionality. Methods: Cetuximab-sensitive and acquired-resistant HNSCC cell lines, generated in vitro, were subcutaneously engrafted in Rag2 knock-out (KO), BALB/c Nude and CB17 Scid mice with/without Matrigel or Geltrex. Once tumor growth was established, mice were intraperitoneally injected twice a week with cetuximab for a maximum of 3 weeks. In addition, immunohistochemistry was used to evaluate the tumor and its microenvironment. Results: Despite several adjustments in cell number, cell lines and the addition of Matrigel, Rag2 KO and BALB/C Nude mice proved to be unsuitable for xenografting our HNSCC cell lines. Durable tumor growth of resistant SC263-R cells could be induced in CB17 Scid mice. However, these cells had lost their resistance phenotype in vivo. Immunohistochemistry revealed a high infiltration of macrophages in cetuximab-treated SC263-R tumors. FaDu-S and FaDu-R cells successfully engrafted into CB17 Scid mice and maintained their sensitivity/resistance to cetuximab. Conclusion: We have established in vivo HNSCC mouse models with intact ADCC functionality for cetuximab resistance and sensitivity using the FaDu-R and FaDu-S cell lines, respectively. These models serve as valuable tools for investigating cetuximab resistance mechanisms and exploring novel drug combination strategies.

One-step CRISPR-Cas9-mediated knockout of native TCRαβ genes in human T cells using RNA electroporation

To avoid mispairing between native and introduced T cell receptors (TCRs) and to prevent graft-versus-host disease in allogeneic T cell therapies, TCRα and TCRβ chains of native TCRs are knocked out via CRISPR-Cas9. We demonstrate the isolation and activation of CD8+ T cells followed by electroporation of T cells with in vitro transcribed eSpCas9(1.1)-P2A-EGFP mRNA and single-guide RNAs targeting the TCRα and TCRβ constant regions. We then describe a flow cytometric analysis to determine TCR knockout efficiency.

Acquired non-thermal plasma resistance mediates a shift towards aerobic glycolysis and ferroptotic cell death in melanoma

AIMS

To gain insights into the underlying mechanisms of NTP therapy sensitivity and resistance, using the first-ever NTP-resistant cell line derived from sensitive melanoma cells (A375).

METHODS

Melanoma cells were exposed to NTP and re-cultured for 12 consecutive weeks before evaluation against the parental control cells. Whole transcriptome sequencing analysis was performed to identify differentially expressed genes and enriched molecular pathways. Glucose uptake, extracellular lactate, media acidification, and mitochondrial respiration was analyzed to determine metabolic changes. Cell death inhibitors were used to assess the NTP-induced cell death mechanisms, and apoptosis and ferroptosis was further validated via Annexin V, Caspase 3/7, and lipid peroxidation analysis.

RESULTS

Cells continuously exposed to NTP became 10 times more resistant to NTP compared to the parental cell line of the same passage, based on their half-maximal inhibitory concentration (IC50). Sequencing and metabolic analysis indicated that NTP-resistant cells had a preference towards aerobic glycolysis, while cell death analysis revealed that NTP-resistant cells exhibited less apoptosis but were more vulnerable to lipid peroxidation and ferroptosis.

CONCLUSIONS

A preference towards aerobic glycolysis and ferroptotic cell death are key physiological changes in NTP-resistance cells, which opens new avenues for further, in-depth research into other cancer types.

The prognostic impact of the immune signature in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a heterogeneous group of tumors that retain their poor prognosis despite recent advances in their standard of care. As the involvement of the immune system against HNSCC development is well-recognized, characterization of the immune signature and the complex interplay between HNSCC and the immune system could lead to the identification of novel therapeutic targets that are required now more than ever. In this study, we investigated RNA sequencing data of 530 HNSCC patients from The Cancer Genome Atlas (TCGA) for which the immune composition (CIBERSORT) was defined by the relative fractions of 10 immune-cell types and expression data of 45 immune checkpoint ligands were quantified. This initial investigation was followed by immunohistochemical (IHC) staining for a curated selection of immune cell types and checkpoint ligands markers in tissue samples of 50 advanced stage HNSCC patients. The outcome of both analyses was correlated with clinicopathological parameters and patient overall survival. Our results indicated that HNSCC tumors are in close contact with both cytotoxic and immunosuppressive immune cells. TCGA data showed prognostic relevance of dendritic cells, M2 macrophages and neutrophils, while IHC analysis associated T cells and natural killer cells with better/worse prognostic outcome. HNSCC tumors in our TCGA cohort showed differential RNA over- and underexpression of 28 immune inhibitory and activating checkpoint ligands compared to healthy tissue. Of these, CD73, CD276 and CD155 gene expression were negative prognostic factors, while CD40L, CEACAM1 and Gal-9 expression were associated with significantly better outcomes. Our IHC analyses confirmed the relevance of CD155 and CD276 protein expression, and in addition PD-L1 expression, as independent negative prognostic factors, while HLA-E overexpression was associated with better outcomes. Lastly, the co-presence of both (i) CD155 positive cells with intratumoral NK cells; and (ii) PD-L1 expression with regulatory T cell infiltration may hold prognostic value for these cohorts. Based on our data, we propose that CD155 and CD276 are promising novel targets for HNSCC, possibly in combination with the current standard of care or novel immunotherapies to come.

The CD70-CD27 axis in oncology: the new kids on the block

The immune checkpoint molecule CD70 and its receptor CD27 are aberrantly expressed in many hematological and solid malignancies. Dysregulation of the CD70-CD27 axis within the tumor and its microenvironment is associated with tumor progression and immunosuppression. This is in contrast to physiological conditions, where tightly controlled expression of CD70 and CD27 plays a role in co-stimulation in immune responses. In hematological malignancies, cancer cells co-express CD70 and CD27 promoting stemness, proliferation and survival of malignancy. In solid tumors, only expression of CD70 is present on the tumor cells which can facilitate immune evasion through CD27 expression in the tumor microenvironment. The discovery of these tumor promoting and immunosuppressive effects of the CD70-CD27 axis has unfolded a novel target in the field of oncology, CD70.

In this review, we thoroughly discuss current insights into expression patterns and the role of the CD70-CD27 axis in hematological and solid malignancies, its effect on the tumor microenvironment and (pre)clinical therapeutic strategies.

Auranofin and Cold Atmospheric Plasma Synergize to Trigger Distinct Cell Death Mechanisms and Immunogenic Responses in Glioblastoma

Targeting the redox balance of malignant cells via the delivery of high oxidative stress unlocks a potential therapeutic strategy against glioblastoma (GBM). We investigated a novel reactive oxygen species (ROS)-inducing combination treatment strategy, by increasing exogenous ROS via cold atmospheric plasma and inhibiting the endogenous protective antioxidant system via auranofin (AF), a thioredoxin reductase 1 (TrxR) inhibitor. The sequential combination treatment of AF and cold atmospheric plasma-treated PBS (pPBS), or AF and direct plasma application, resulted in a synergistic response in 2D and 3D GBM cell cultures, respectively. Differences in the baseline protein levels related to the antioxidant systems explained the cell-line-dependent sensitivity towards the combination treatment. The highest decrease of TrxR activity and GSH levels was observed after combination treatment of AF and pPBS when compared to AF and pPBS monotherapies. This combination also led to the highest accumulation of intracellular ROS. We confirmed a ROS-mediated response to the combination of AF and pPBS, which was able to induce distinct cell death mechanisms. On the one hand, an increase in caspase-3/7 activity, with an increase in the proportion of annexin V positive cells, indicates the induction of apoptosis in the GBM cells. On the other hand, lipid peroxidation and inhibition of cell death through an iron chelator suggest the involvement of ferroptosis in the GBM cell lines. Both cell death mechanisms induced by the combination of AF and pPBS resulted in a significant increase in danger signals (ecto-calreticulin, ATP and HMGB1) and dendritic cell maturation, indicating a potential increase in immunogenicity, although the phagocytotic capacity of dendritic cells was inhibited by AF. In vivo, sequential combination treatment of AF and cold atmospheric plasma both reduced tumor growth kinetics and prolonged survival in GBM-bearing mice. Thus, our study provides a novel therapeutic strategy for GBM to enhance the efficacy of oxidative stress-inducing therapy through a combination of AF and cold atmospheric plasma.

The Right Partner in Crime: Unlocking the Potential of the Anti-EGFR Antibody Cetuximab via Combination With Natural Killer Cell Chartering Immunotherapeutic Strategies

Cetuximab has an established role in the treatment of patients with recurrent/metastatic colorectal cancer and head and neck squamous cell cancer (HNSCC). However, the long-term effectiveness of cetuximab has been limited by the development of acquired resistance, leading to tumor relapse. By contrast, immunotherapies can elicit long-term tumor regression, but the overall response rates are much more limited. In addition to epidermal growth factor (EGFR) inhibition, cetuximab can activate natural killer (NK) cells to induce antibody-dependent cellular cytotoxicity (ADCC). In view of the above, there is an unmet need for the majority of patients that are treated with both monotherapy cetuximab and immunotherapy. Accumulated evidence from (pre-)clinical studies suggests that targeted therapies can have synergistic antitumor effects through combination with immunotherapy. However, further optimizations, aimed towards illuminating the multifaceted interplay, are required to avoid toxicity and to achieve better therapeutic effectiveness. The current review summarizes existing (pre-)clinical evidence to provide a rationale supporting the use of combined cetuximab and immunotherapy approaches in patients with different types of cancer.

A systematic review on poly(I:C) and poly-ICLC in glioblastoma: adjuvants coordinating the unlocking of immunotherapy

Immunotherapy is currently under intensive investigation as a potential breakthrough treatment option for glioblastoma. Given the anatomical and immunological complexities surrounding glioblastoma, lymphocytes that infiltrate the brain to develop durable immunity with memory will be key. Polyinosinic:polycytidylic acid, or poly(I:C), and its derivative poly-ICLC could serve as a priming or boosting therapy to unleash lymphocytes and other factors in the (immuno)therapeutic armory against glioblastoma. Here, we present a systematic review on the effects and efficacy of poly(I:C)/poly-ICLC for glioblastoma treatment, ranging from preclinical work on cellular and murine glioblastoma models to reported and ongoing clinical studies. MEDLINE was searched until 15 May 2021 to identify preclinical (glioblastoma cells, murine models) and clinical studies that investigated poly(I:C) or poly-ICLC in glioblastoma. A systematic review approach was conducted according to PRISMA guidelines. ClinicalTrials.gov was queried for ongoing clinical studies. Direct pro-tumorigenic effects of poly(I:C) on glioblastoma cells have not been described. On the contrary, poly(I:C) changes the immunological profile of glioblastoma cells and can also kill them directly. In murine glioblastoma models, poly(I:C) has shown therapeutic relevance as an adjuvant therapy to several treatment modalities, including vaccination and immune checkpoint blockade. Clinically, mostly as an adjuvant to dendritic cell or peptide vaccines, poly-ICLC has been demonstrated to be safe and capable of eliciting immunological activity to boost therapeutic responses. Poly-ICLC could be a valuable tool to enhance immunotherapeutic approaches for glioblastoma. We conclude by proposing several promising combination strategies that might advance glioblastoma immunotherapy and discuss key pre-clinical aspects to improve clinical translation.

Immuno-PET Molecular Imaging of RANKL in Cancer

PURPOSE

The involvement of RANK/RANKL signaling in the tumor microenvironment (TME) in driving response or resistance to immunotherapy has only very recently been recognized. Current quantification methods of RANKL expression suffer from issues such as sensitivity, variability, and uncertainty on the spatial heterogeneity within the TME, resulting in conflicting reports on its reliability and limited use in clinical practice. Non-invasive molecular imaging using immuno-PET is a promising approach combining superior targeting specificity of monoclonal antibodies (mAb) and spatial, temporal and functional information of PET. Here, we evaluated radiolabeled anti-RANKL mAbs as a non-invasive biomarker of RANKL expression in the TME.

EXPERIMENTAL DESIGN

Anti-human RANKL mAbs (AMG161 and AMG162) were radiolabeled with ⁸⁹Zr using the bifunctional chelator DFO in high yield, purity and with intact binding affinity. After assessing the biodistribution in healthy CD-1 nude mice, [⁸⁹Zr]Zr-DFO-AMG162 was selected for further evaluation in ME-180 (RANKL-transduced), UM-SCC-22B (RANKL-positive) and HCT-116 (RANKL-negative) human cancer xenografts to assess the feasibility of in vivo immuno-PET imaging of RANKL.

RESULTS

[⁸⁹Zr]Zr-DFO-AMG162 was selected as the most promising tracer for further validation based on biodistribution experiments. We demonstrated specific accumulation of [⁸⁹Zr]Zr-DFO-AMG162 in RANKL transduced ME-180 xenografts. In UM-SCC-22B xenograft models expressing physiological RANKL levels, [⁸⁹Zr]Zr-DFO-AMG162 imaging detected significantly higher signal compared to control [⁸⁹Zr]Zr-DFO-IgG2 and to RANKL negative HCT-116 xenografts. There was good visual agreement with tumor autoradiography and immunohistochemistry on adjacent slides, confirming these findings.

CONCLUSIONS

[⁸⁹Zr]Zr-DFO-AMG162 can detect heterogeneous RANKL expression in the TME of human cancer xenografts, supporting further translation of RANKL immuno-PET to evaluate tumor RANKL distribution in patients.

Auranofin reveals therapeutic anticancer potential by triggering distinct molecular cell death mechanisms and innate immunity in mutant p53 non-small cell lung cancer

Auranofin (AF) is an FDA-approved antirheumatic drug with anticancer properties that acts as a thioredoxin reductase 1 (TrxR) inhibitor. The exact mechanisms through which AF targets cancer cells remain elusive. To shed light on the mode of action, this study provides an in-depth analysis on the molecular mechanisms and immunogenicity of AF-mediated cytotoxicity in the non-small cell lung cancer (NSCLC) cell line NCI–H1299 (p53 Null) and its two isogenic derivates with mutant p53 R175H or R273H accumulation.

TrxR is highly expressed in a panel of 72 NSCLC patients, making it a valid druggable target in NSCLC for AF. The presence of mutant p53 overexpression was identified as an important sensitizer for AF in (isogenic) NSCLC cells as it was correlated with reduced thioredoxin (Trx) levels in vitro. Transcriptome analysis revealed dysregulation of genes involved in oxidative stress response, DNA damage, granzyme A (GZMA) signaling and ferroptosis. Although functionally AF appeared a potent inhibitor of GPX4 in all NCI–H1299 cell lines, the induction of lipid peroxidation and consequently ferroptosis was limited to the p53 R273H expressing cells. In the p53 R175H cells, AF mainly induced large-scale DNA damage and replication stress, leading to the induction of apoptotic cell death rather than ferroptosis. Importantly, all cell death types were immunogenic since the release of danger signals (ecto-calreticulin, ATP and HMGB1) and dendritic cell maturation occurred irrespective of (mutant) p53 expression. Finally, we show that AF sensitized cancer cells to caspase-independent natural killer cell-mediated killing by downregulation of several key targets of GZMA.

Our data provides novel insights on AF as a potent, clinically available, off-patent cancer drug by targeting mutant p53 cancer cells through distinct cell death mechanisms (apoptosis and ferroptosis). In addition, AF improves the innate immune response at both cytostatic (natural killer cell-mediated killing) and cytotoxic concentrations (dendritic cell maturation).

Novel combination immunotherapy for pancreatic cancer: potent anti-tumor effects with CD40 agonist and interleukin-15 treatment

Objectives

With the poorest 5‐year survival of all cancers, improving treatment for pancreatic cancer is one of the biggest challenges in cancer research. We sought to explore the potential of combining both priming and activation of the immune system. To achieve this, we combined a CD40 agonist with interleukin‐15 and tested its potential in pancreatic cancer.

Methods

Response to this combination regimen was assessed in pancreatic ductal adenocarcinoma mouse models, and a thorough analysis of the tumor microenvironment was performed.

Results

We demonstrated profound reduction in tumor growth and increased survival of mice with the majority of mice being cured when both agents were combined, including an unprecedented 8‐fold dose reduction of CD40 agonist without losing any efficacy. RNAseq analysis showed involvement of natural killer (NK) cell‐ and T‐cell‐mediated anti‐tumor responses and the importance of antigen‐presenting cell pathways. This combination resulted in enhanced infiltration of tumors by both T cells and NK cells, as well as a striking increase in the ratio of CD8⁺ T cells over Tregs. We also observed a significant increase in numbers of dendritic cells (DCs) in tumor‐draining lymph nodes, particularly CD103⁺ DCs with cross‐presentation potential. A critical role for CD8⁺ T cells and involvement of NK cells in the anti‐tumor effect was highlighted. Importantly, strong immune memory was established, with an increase in memory CD8⁺ T cells only when both interleukin‐15 and the CD40 agonist were combined.

Conclusion

These novel preclinical data support initiation of a first‐in‐human clinical trial with this combination immunotherapy strategy in pancreatic cancer.

Abstract 2414: Immunogenic properties of chemotherapeutic agents in the treatment of non-small cell lung cancer

Introduction. Accumulating evidence suggests that the clinical success of chemotherapy is not only attributed to direct tumor cell toxicity, but also relies on its anti-tumor effects by immunomodulation. In this regard, the concept of immunogenic cell death (ICD) has emerged as a cornerstone of therapy-induced anti-tumor immunity. To this end, we assessed different chemotherapeutic agents on their ability to induce ICD in vitro and in vivo in non-small cell lung cancer (NSCLC).

Material and methods. NSCLC cell lines (NCI-H1975, A549, NCI-H1650 and LLC) were treated with the IC50 of different chemotherapeutic agents: docetaxel (DOC), carboplatin (CARBO), cisplatin (CDDP), oxaliplatin (OXA) and mafosfamide (MF). In addition, combinations of DOC (IC50) with CARBO (IC40) or CDDP (IC40) were included. Release of important damage-associated molecular patterns (DAMPs) was evaluated: ATP (bioluminescence), ecto-CRT (flow cytometry) and HMGB1 (ELISA) after 24h, 48h and 72h of treatment, respectively. In addition, phagocytosis and maturation status of dendritic cells (DCs) were assessed. Finally, a vaccination assay was performed to validate in vitro findings using 6-week old female C57BL/6J mice (5 mice/condition). Mice were vaccinated twice (1 × 106 treated cells/mouse) before receiving the challenge (5 × 104 live cells/mouse).

Results. Three out of four NSCLC cell lines (NCI-H1975, A549 and LLC) showed significant higher levels of ATP, ecto-CRT and HMGB1 after treatment with DOC, DOC+CARBO and DOC+CDDP compared to vehicle. In addition, phagocytosis of treated tumor cells and maturation (CD86) of DCs were significantly increased in all three human NSCLC cell lines after treatment with the above-mentioned chemotherapeutic regimens. Furthermore, murine LLC cells treated with DOC, MF, DOC+CARBO and DOC+CDDP resulted in a significant release of all three DAMPs in vitro, as opposed to treatment with OXA. Along similar lines, 0%, (DOC+CDDP), 20% (MF and DOC+CARBO) and 80% (OXA) of the mice developed a tumor at the challenge site in vivo. This was not the case for treatment with DOC, which resulted in tumor growth at the challenge site in 60% of the mice.

Conclusion. Overall, these findings demonstrate the immunostimulatory effects of clinically relevant chemotherapeutic regimens, especially DOC+CARBO and DOC+CDDP, making it worthwhile to investigate these agents in combination strategies with immunotherapy in NSCLC.

Citation Format: Tal Flieswasser, Jinthe Van Loenhout, Laurie Freire Boullosa, Astrid Van den Eynde, Jorrit De Waele, Jonas Van Audenaerde, Filip Lardon, Evelien Smits, Patrick Pauwels, Jacobs Julie. Immunogenic properties of chemotherapeutic agents in the treatment of non-small cell lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2414.

Uncovering the immune-modulating role of anti-RANKL therapy for cervical cancer: Preliminary results

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Background: Conventional treatments for cervical cancer (CC) have reached a plateau and only limited progress for targeted therapy has been made over the last decades, resulting in a meager five-year survival rate of only 17% for the advanced stages. To improve long-term benefits for the patient, a promising hot field of research in oncology that opens new perspectives is immunotherapy. Even though CC has shown to be immunogenic, only a minority of patients respond to this type of treatment. In recent years, the RANKL/RANK signaling pathway has been implicated as a key immune modulating factor in the tumor microenvironment, allowing the cancer cells to evade the immune response by disrupting the immune-intrinsic crosstalk. Both RANKL and RANK are highly co-expressed in CC, which correlates with inferior clinicopathological parameters and an increased risk of death. Targeting this pathway may therefore be of great value in the treatment of CC and the quest to release the brakes on the immune system, thereby reinvigorating the tumors’ susceptibility to immunotherapy. Hence, we aim to elucidate the effects of anti-RANKL therapy on the tumor-immune microenvironment in CC. Methods: Two cervical biopsies were taken before and after anti-RANKL therapy in CC patients. One fresh biopsy was immediately processed to a single cell suspension for flow cytometry (FCM) using enzymatic digestion, while the other was formalin-fixed and paraffin-embedded for immunohistochemistry (IHC) and RNA sequencing. For FCM and IHC, the samples were stained with different markers for RANK/L signaling, the immune infiltrate and immune checkpoints. FCM was performed on a BD FACSAria IIä cytometer and analyzed with FlowJo. IHC staining was performed on a Ventana Benchmark Ultra and Ventana Discovery Ultra and scored by a pathologist or by HistoScientist using Visiopharm, while RNA sequencing was performed with the Truseq RNA exome panel on the NextSeq 500 system. Results: Our preliminary results show a relative increase of the CD8+ population, while a trend is observed in increased lymphocyte activation after anti-RANKL therapy. Updated results will be presented in more detail at the conference, including RNA sequencing data. Conclusions: Preliminary findings indicate that anti-RANKL therapy modifies the tumor-immune microenvironment in CC. Higher patient accrual will allow to dissect targets for combination therapy with anti-RANKL to further optimize this treatment strategy.

Building a Bridge between Chemotherapy and Immunotherapy in Malignant Pleural Mesothelioma: Investigating the Effect of Chemotherapy on Immune Checkpoint Expression

In light of the promising results of immune checkpoint blockade (ICPB) in malignant pleural mesothelioma (MPM), we investigated the effect of different chemotherapeutic agents on the expression of immune checkpoints (ICPs) in order to rationally design a good treatment schedule for their combination with ICP blocking antibodies. Cisplatin, oxaliplatin and pemetrexed are interesting chemotherapeutic agents to combine with immunotherapy given their immunomodulatory capacities. We looked into cisplatin and pemetrexed because their combination is used as first-line treatment of MPM. Additionally, the effect of the immunogenic chemotherapeutic agent, oxaliplatin, was also studied. Three different MPM cell lines were used for representation of both epithelioid and sarcomatoid subtypes. The desired inhibitory concentrations of the chemotherapeutic agents were determined with the SRB-assay. Allogeneic co-cultures of MPM cells with healthy donor peripheral blood mononuclear cells (PBMC) were set up to assess the effect of these chemotherapeutic agents on the expression of ICPs (PD-1, LAG-3, TIM-3) and their ligands (PD-L1, PD-L2, galectin-9). Cisplatin might be a promising treatment to combine with ICP blocking antibodies since our MPM cell lines were most susceptible to this stand-alone treatment. We found that the expression of ICPs and their ligands on both MPM cells and PBMC was mostly downregulated or unaltered when treated with chemotherapeutic agents, though no clear trend could be determined.

Poly(I:C) primes primary human glioblastoma cells for an immune response invigorated by PD-L1 blockade

Prognosis of glioblastoma remains dismal, underscoring the need for novel therapies. Immunotherapy is generating promising results, but requires combination strategies to unlock its full potential. We investigated the immunomodulatory capacities of poly(I:C) on primary human glioblastoma cells and its combinatorial potential with programmed death ligand (PD-L) blockade. In our experiments, poly(I:C) stimulated expression of both PD-L1 and PD-L2 on glioblastoma cells, and a pro-inflammatory secretome, including type I interferons (IFN) and chemokines CXCL9, CXCL10, CCL4 and CCL5. IFN-β was partially responsible for the elevated PD-1 ligand expression on these cells. Moreover, real-time PCR and chloroquine-mediated blocking experiments indicated that poly(I:C) triggered Toll-like receptor 3 to elicit its effect. Cocultures of poly(I:C)-treated glioblastoma cells with peripheral blood mononuclear cells enhanced lymphocytic activation (CD69, IFN-γ) and cytotoxic capacity (CD107a, granzyme B). Additional PD-L1 blockade further propagated immune activation. Besides activating immunity, poly(I:C)-treated glioblastoma cells also doubled the attraction of CD8⁺ T cells, and to a lesser extent CD4⁺ T cells, via a mechanism which included CXCR3 and CCR5 ligands. Our results indicate that by triggering glioblastoma cells, poly(I:C) primes the tumor microenvironment for an immune response. Secreted cytokines allow for immune activation while chemokines attract CD8⁺ T cells to the front, which are postulated as a prerequisite for effective PD-1/PD-L1 blockade. Accordingly, additional blockade of the concurrently elevated tumoral PD-L1 further reinforces the immune activation. In conclusion, our data proposes poly(I:C) treatment combined with PD-L1 blockade to invigorate the immune checkpoint inhibition response in glioblastoma.

Abundant expression of TIM-3, LAG-3, PD-1 and PD-L1 as immunotherapy checkpoint targets in effusions of mesothelioma patients

Malignant pleural mesothelioma (MPM) is an aggressive cancer with an increasing incidence, poor prognosis and limited effective treatment options. Hence, new treatment strategies are warranted which include immune checkpoint blockade approaches with encouraging preliminary data. Research on the immunological aspects of the easily accessible mesothelioma microenvironment could identify prognostic and/or predictive biomarkers and provide useful insights for developing effective immunotherapy. In this context, we investigated the immune cell composition of effusions (pleural and ascites fluids) from 11 different chemotherapy-treated MPM patients. We used multicolor flow cytometry to describe different subsets of immune cells and their expression of immune checkpoint molecules TIM-3, LAG-3, PD-1 and PD-L1. We demonstrate a patient-dependent inter- and intraspecific variation comparing pleural and ascites fluids in immune cell composition and immune checkpoint expression. We found CD4⁺ and CD8⁺ T cells, B cells, macrophages, natural killer cells, dendritic cells and tumor cells in the fluids. To the best of our knowledge, we are the first to report TIM-3 and LAG-3 expression and we confirm PD-1 and PD-L1 expression on different MPM effusion-resident immune cells. Moreover, we identified two MPM effusion-related factors with clinical value: CD4+ T cells were significantly correlated with better response to chemotherapy, while the percentage of PD-L1⁺ podoplanin (PDPN)⁺ tumor cells is a significant prognostic factor for worse outcome. Our data provide a basis for more elaborate research on MPM effusion material in the context of treatment follow-up and prognostic biomarkers and the development of immune checkpoint-targeted immunotherapy.

Interleukin-15 stimulates natural killer cell-mediated killing of both human pancreatic cancer and stellate cells

Pancreatic ductal adenocarcinoma (PDAC) is the 4^th leading cause of cancer-related death in Western countries with a 5-year survival rate below 5%. One of the hallmarks of this cancer is the strong desmoplastic reaction within the tumor microenvironment (TME), orchestrated by activated pancreatic stellate cells (PSC). This results in a functional and mechanical shield which causes resistance to conventional therapies. Aiming to overcome this resistance by tackling the stromal shield, we assessed for the first time the capacity of IL-15 stimulated natural killer (NK) cells to kill PSC and pancreatic cancer cells (PCC). The potency of IL-15 to promote NK cell-mediated killing was evaluated phenotypically and functionally. In addition, NK cell and immune checkpoint ligands on PSC were charted. We demonstrate that IL-15 activated NK cells kill both PCC and PSC lines (range 9-35% and 20-50%, respectively) in a contact-dependent manner and significantly higher as compared to resting NK cells. Improved killing of these pancreatic cell lines is, at least partly, dependent on IL-15 induced upregulation of TIM-3 and NKG2D. Furthermore, we confirm significant killing of primary PSC by IL-15 activated NK cells in an ex vivo autologous system. Screening for potential targets for immunotherapeutic strategies, we demonstrate surface expression of both inhibitory (PD-L1, PD-L2) and activating (MICA/B, ULBPs and Galectin-9) ligands on primary PSC. These data underscore the therapeutic potential of IL-15 to promote NK cell-mediated cytotoxicity as a treatment of pancreatic cancer and provide promising future targets to tackle remaining PSC.

Prognostic and predictive aspects of the tumor immune microenvironment and immune checkpoints in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive cancer with a poor prognosis and an increasing incidence, for which novel therapeutic strategies are urgently required. Since the immune system has been described to play a presumed role in the protection against MPM, characterization of its tumor immune microenvironment (TME) and immune checkpoints can identify new immunotherapeutic targets and their predictive and/or prognostic value. To characterize the TME and the immune checkpoint expression profile, we performed immunohistochemistry (IHC) on formalin-fixed paraffin embedded (FFPE) tissue sections from 54 MPM patients (40 at time of diagnosis; 14 treated with chemotherapy). We stained for PD-1, PD-L1, TIM-3, LAG-3, CD4, CD8, CD45RO, granzyme B, FoxP3 and CD68. Furthermore, we analyzed the relationship between the immunological parameters and survival, as well as response to chemotherapy. We found that TIM-3, PD-1 and PD-L1 were expressed on both immune and tumor cells. Strikingly, PD-1 and PD-L1 expression on tumor cells was only seen in unpretreated samples. No LAG-3 expression was observed. CD45RO expression in the stroma was an independent negative predictive factor for response on chemotherapy, while CD4 and TIM-3 expression in lymphoid aggregates were independent prognostic factors for better outcome. Our data propose TIM-3 as a promising new target in mesothelioma. Chemotherapy influences the expression of immune checkpoints and therefore further research on the best combination treatment schedule is required.

Poly(I:C) as cancer vaccine adjuvant: knocking on the door of medical breakthroughs

Although cancer vaccination has yielded promising results in patients, the objective response rates are low. The right choice of adjuvant might improve the efficacy. Here, we review the biological rationale, as well as the preclinical and clinical results of polyinosinic:polycytidylic acid and its derivative poly-ICLC as cancer vaccine adjuvants. These synthetic immunological danger signals enhanced vaccine-induced anti-tumor immune responses and contributed to tumor elimination in animal tumor models and patients. Supported by these results, poly-ICLC-containing cancer vaccines are currently extensively studied in the ongoing trials, making it highly plausible that poly-ICLC will be part of the future approved cancer immunotherapies.