Intratumoral T-cell Infiltration Research Articles

IMMU-14. TRANS-SPECIES ANALYSIS OF REPLICATION-REPAIR DEFICIENT (RRD) MEDULLOBLASTOMA AND RESPONSE TO IMMUNE CHECKPOINT INHIBITION: AN IRRDC REPORT

Abstract BACKGROUND Replication-repair deficiency (RRD) stemming from mismatch repair and polymerase proofreading gene defects (MMRD/PPD) lead to hypermutant childhood cancers, most frequently brain tumors. While medulloblastoma is reported, the clinical, genomic and immune landscape remains unknown. METHODS We analysed the genome, methylome, transcriptome (bulk, single-nuclei) and immune-microenvironment of the largest cohort of RRD-medulloblastoma patients enrolled by the International RRD Consortium and correlated these to clinical outcomes. RRD mice-models were used to preclinically assess response to immunotherapy. Results: RESULTS RRD-medulloblastoma (n=43) were enriched for anaplasia (61%) and localised disease (77%). Methylation/nano-string-based subgrouping failed to classify 40%, while the remaining clustered with the SHH-subgroup. Copy-number changes were notably infrequent (<20%). All tumors harboured hypermutation and microsatellite instability in contrast to non-RRD controls (p<0.0001). Pathogenic variants were frequent in POLE/POLD1 (80%), TP53 (48%) and SHH-pathway genes (PTCH1, SUFU, SMO: 56%). Interestingly, some tumors additionally had glioma-driver alterations (ATRX, NF1: ~50%), similar to RRD cerebellar glioblastoma, but distinct from both non-RRD medulloblastoma (n=791) and hemispheric glioblastoma (n=733) controls. Moreover, although bulk-transcriptome matched non-RRD SHH medulloblastoma, single-nuclei analyses suggested an earlier cell-of-origin potentially explaining the heterogenous phenotypes resulting from the driver mutations. Uniquely, immune analyses (gene expression and immunohistochemistry) demonstrated high intra-tumoral CD8 T-cell infiltration. Three-year progression-free survival was 60%. Outcome was worse for RRD-medulloblastoma harbouring TP53-mutation (p=0.04) and failing subgroup-classification (p=0.004). Nestin/Cre MSH2-/- POLE;p.S459F mice developing medulloblastoma recapitulated human disease and demonstrated response to anti-PD1 monotherapy. Recurrent/progressive human tumors including those harbouring TP53-mutations exhibited radiological responses to anti-PD1 monotherapy, which was associated with prolonged ongoing survival in comparison to those not treated with checkpoint-inhibitors (p=0.02). CONCLUSIONS Hypermutant RRD-medulloblastoma reveal heterogenous phenotypes due to unique spectrum of driver mutations and an early cell of origin. Their immune-hot microenvironment allows successful salvage treatment with checkpoint-inhibitors for those failing chemo-radiation, including the high-risk SHH/TP53-mutant and unclassified subgroups.

IMMU-44. EXTRINSIC ELECTRICAL MODULATION OF THE GLIOBLASTOMA TUMOR MICROENVIRONMENT

Abstract BACKGROUND Approximately 30 to 50% of patients with glioblastoma (GBM) present with glioma-related epilepsy (GRE). Despite morbidity associated with seizures, GRE constitutes an independent positive predictive predictor for survival in GBM. Our prior results showed that repeated seizure induction through extrinsic electrical modulation (EEM, a technique in which an electrical stimulus sufficient to produce a therapeutic seizure is applied) slows intracranial tumor growth and prolongs overall survival in immunocompetent CT-2A glioma-bearing mice. However, the overall survival advantage following EEM treatment was diminished in immunocompromised mice bearing human patient derived xenografts. We hypothesized that EEM induces immune-related tumor microenvironment (TME) changes that prolong survival in mice. METHODS C57BL/6J mice were orthotopically implanted with CT-2A xenografts and subjected to EEM of 2.0 millicoulombs or sham treatment. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) was performed at 3 and 24 hours to determine mRNA level of inflammatory cytokines. Immunohistochemistry (IHC) and bulk RNA sequencing analysis were utilized to assess CD3+ T-cell infiltration and identify immune-related secreted genes, respectively. Flow cytometry at 3 and 96 hours was utilized to characterize tumor-infiltrating immune cell populations. Samples were subjected to Percoll gradient enrichment of immune cell populations and stained for extracellular (CD45, CD4, CD8, CD11b, F4/80, CD80, Ly6G, Ly6C, and CX3CR1) and intracellular (TNF-a, Il-1b, CCL2, and Arg1) antigens. RESULTS RT-qPCR showed an increase in pro-inflammatory cytokines TNF-α (P = 0.0087) and IL-1β (P = 0.000349). IHC analysis demonstrated an increase in intratumoral CD3+ T-cells in EEM-treated samples (P = 0.0171). From 1855 upregulated genes, 3 immune-related secreted genes (C1QTNF4, FAM19A4, and GREM2) were identified. Flow cytometric analysis showed a significant increase in CD11b+, CX3RC1+ microglia (P = 0.0306) and CD45+, CD11b+ tumor-associated myeloid cells (TAMCs) (P = 0.0192) at 3 hours post-EEM. CONCLUSIONS EEM treatment promotes an inflammatory TME with increased intratumoral microglia, TAMCs and T-cell infiltration. These inflammatory changes may prolong survival of CT-2A glioma-bearing mice.

T lymphocyte recruitment to melanoma brain tumors depends on distinct venous vessels

To improve immunotherapy for brain tumors, it is important to determine the principal intracranial site of Tcell recruitment from the bloodstream and their intracranial route to brain tumors. Using intravital microscopy in mouse models of intracranial melanoma, we discovered that circulating Tcells preferably adhered and extravasated at a distinct type of venous blood vessel in the tumor vicinity, peritumoral venous vessels (PVVs). Other vascular structures were excluded as alternative Tcell routes to intracranial melanomas. Anti-PD-1/CTLA-4 immune checkpoint inhibitors increased intracranial Tcell motility, facilitating migration from PVVs to the tumor and subsequently inhibiting intracranial tumor growth. The endothelial adhesion molecule ICAM-1 was particularly expressed on PVVs, and, in samples of human brain metastases, ICAM-1 positivity of PVV-like vessels correlated with intratumoral Tcell infiltration. These findings uncover a distinct mechanism by which the immune system can access and control brain tumors and potentially influence other brain pathologies.

SOX12 Facilitates Hepatocellular Carcinoma Progression and Metastasis through Promoting Regulatory T-Cells Infiltration and Immunosuppression.

Despite the success of immunotherapy in treating hepatocellular carcinoma (HCC), HCC remains a severe threat to health. Here, a crucial transcription factor, SOX12, is revealed that induces the immunosuppression of liver tumor microenvironment. Overexpressing SOX12 in HCC syngeneic models increases intratumoral regulatory T-cell (Treg) infiltration, decreases CD8+T-cell infiltration, and hastens HCC metastasis. Hepatocyte-specific SOX12 knockout attenuates DEN/CCl4-induced HCC progression and metastasis, whereas hepatocyte-specific SOX12 knock-in accelerates these effects. Mechanistically, SOX12 transcriptionally activates C-C motif chemokine ligand 22 (CCL22) expression to promote the recruitment and suppressive activity of Tregs. Moreover, SOX12 transcriptionally upregulates CD274 expression to suppress CD8+T-cell infiltration. Either knockdown of CCL22 or PD-L1 dampens SOX12-mediated HCC metastasis. Blocking of CC chemokine receptor 4 (CCR4), a receptor for CCL22, by inhibitor C-021 or Treg-specific knockout of CCR4 inhibits SOX12-mediated HCC metastasis. Transforming growth factor-β1 (TGF-β1)/TGFβR1-Smad2/3/4 is identified as a key upstream signaling for SOX12 overexpression in HCC cells. Combining C-021 or TGFβR1 inhibitor galunisertib with anti-PD-L1 exhibits an enhanced antitumor effect in two HCC models. Collectively, the findings demonstrate that SOX12 contributes to HCC immunosuppression through the CCL22/CCR4-Treg and PD-L1-CD8+T axes. Blocking of CCR4 or TGFβR1 improves the efficacy of anti-PD-L1 in SOX12-mediated HCC.

Intratumoral T-cell infiltration and response to nivolumab plus ipilimumab in patients with metastatic clear cell renal cell carcinoma from the CheckMate-214 trial.

4536 Background: We have previously shown that levels of antigen-experienced but not terminally exhausted CD8+ TILs (i.e. CD8+PD1+TIM3-LAG3- TILs) are associated with improved clinical outcomes in patients (pts) with metastatic clear cell RCC (mccRCC) treated with nivolumab monotherapy within three independent clinical trials (CheckMate-010, CheckMate-025, HCRN GU16-260). Here, we aimed to evaluate the performance of this biomarker in patients with mccRCC treated with nivolumab plus ipilimumab (Nivo+Ipi) versus sunitinib (Sun) as part of the CheckMate-214 (CM-214) clinical trial. Methods: Pre-treatment, formalin fixed paraffin embedded (FFPE) tumor samples from the CM-214 clinical trial were stained with a multiplex immunofluorescence (mIF) assay and the density of CD8+PD1+TIM3-LAG3- TILs (mIF biomarker) was quantified using Halo image analysis software. The correlation between the mIF biomarker and clinical outcomes, including progression-free survival (PFS), and objective response rate (ORR), was evaluated using Cox proportional hazards and logistic regression models. The significance level was set at 5% (2-sided). Results: Following quality control, mIF data were obtained for 255 intermediate-and poor-risk patients (Nivo+Ipi= 136, Sun= 119). A comparison between patients with mIF biomarker data available and those without, showed no imbalance with regards to ORR and PFS in the Nivo+Ipi group. However, in the Sun group, pts with mIF biomarker data showed a higher ORR compared to pts without available data (33% vs 24%). In Nivo+Ipi-treated pts, the mIF biomarker measured as continuous variable showed a trend for a positive association with ORR (OR = 1.23, p = 0.1162) but no association with PFS (HR 0.97, p = 0.688). In Sun-treated pts, the mIF biomarker measured as continuous variable showed a trend for a positive association with ORR (OR = 1.32, p = 0.0726) and a significant positive association with PFS (HR= 0.78, p = 0.004. However, given that Sun-treated pts with available mIF data were enriched for responders, results obtained in the Sun group should be interpreted with caution. Conclusions: In contrast to Nivo monotherapy, pre-treatment levels of CD8+ PD1+ TIM-3-LAG-3- TILs were not associated with improved clinical outcomes to Nivo+Ipi. These results suggest that the baseline levels of intratumoral T-cell inflammation do not represent a strong determinant of response to anti-CTLA4-based therapy in mccRCC, which is consistent with the knowledge that anti-CTLA4 therapy (Ipi) can recruit new T cells into the tumor. The association between CD8+ PD1+ TIM-3-LAG-3- TILs and outcomes on sunitinib needs further investigation.

Abstract 3718: Deciphering the role of TREM2+ tumor-associated macrophages as mediators of immunoresistance in micro-satellite stable colorectal metastases

Abstract Introduction: Most Colorectal Cancer (CRC)-related deaths are caused by metastatic disease, and more than 95% of CRC metastases (mCRC) are microsatellite stable (MSS) which respond poorly to Immune checkpoint inhibitors (ICI). Tumor-associated macrophages (TAMs) have been recognized as major drivers of immunoresistance in primary CRC; however, their role in mCRC remains poorly understood. We analyzed primary CRC and major metastatic sites (Liver, Peritoneum, Lungs) using single-cell RNA-sequencing (scRNAseq) to elucidate the TAM driven mechanisms of immunoresistance in the mCRC tumor microenvironment (TME) and used a novel TAM directed targeting strategy to improve responses to ICI in a preclinical orthotopic model of MSS-mCRC. Methods: Using scRNA-seq, we analyzed 22 samples from 14 patients with mCRC. Target antigens identified were validated using flow cytometry and immunofluorescence (IF). The antitumor activity of anti-TREM2 and anti-PD1 mABs was evaluated in-vivo using CT26 CRC cell line in BALB-C mice, assessing tumor immune response via flow cytometry. Results: We characterized the TME in MSS-mCRC and identified 17 clusters of malignant epithelial, immune, and stromal cells. Our sub-clustering analysis revealed 6 unique sub-populations of TAMs which were differentially distributed across liver, lung, and peritoneal metastases (PM).Two subsets of TAMs, 5 and 6, were enriched in PM and malignant ascites. TAMs 5/6 expressed canonical lipid-associated genes; TREM2, APOE, and PLTP. TREM2+ TAMs were also enriched in immunosuppressive and pro-angiogenic pathways, and expressed genes known to drive EMT and ECM remodeling in the TME. Thus, TREM2 was identified as a potential therapeutic target. We validated our transcriptomic findings using flow cytometry and IF analysis of MSS-mCRC showing an abundance of TREM2+ TAMs in PM. TREM2+ TAMs co-expressed CD163, known marker for M2-TAMs and stained positive for BODIPY. In an aggressive PM mouse model, treatment with anti-PD1, anti-TREM2, or combination anti-PD1/anti-TREM2 was insufficient to reduce tumor burden. However, a trend towards a reduction in total intratumoral F4/80+CD11b+ TAMs was observed in the combination treatment compared to other groups. All three treatments trended towards increased CD8+ intratumoral T-cell infiltration compared to control mice. Conclusion: Our study provides new insights into the TME of MSS-CRC metastases at a single-cell level. Our findings indicate that TREM2+ TAMs contribute to the immunosuppressive milieu of MSS-CRC metastases. Targeting TREM2 in combination with anti-PD1 resulted in a modulation of TME via reduction of TAMs paralleled by an increased infiltration of CD8+ T cells. This reprogramming of TME suggests that inhibiting TREM2 might augment response to ICI in MSS-CRC metastases, traditionally resistant to ICI. Citation Format: Muhammad Bilal Mirza, Matthew Alexander Cottam, Mustafa Raoof, Kamran Idrees. Deciphering the role of TREM2+ tumor-associated macrophages as mediators of immunoresistance in micro-satellite stable colorectal metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3718.

Intratumoral T-cell receptor repertoire composition predicts overall survival in patients with pancreatic ductal adenocarcinoma

ABSTRACT Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy that is refractory to immune checkpoint inhibitor therapy. However, intratumoral T-cell infiltration correlates with improved overall survival (OS). Herein, we characterized the diversity and antigen specificity of the PDAC T-cell receptor (TCR) repertoire to identify novel immune-relevant biomarkers. Demographic, clinical, and TCR-beta sequencing data were collated from 353 patients across three cohorts that underwent surgical resection for PDAC. TCR diversity was calculated using Shannon Wiener index, Inverse Simpson index, and “True entropy.” Patients were clustered by shared repertoire specificity. TCRs predictive of OS were identified and their associated transcriptional states were characterized by single-cell RNAseq. In multivariate Cox regression models controlling for relevant covariates, high intratumoral TCR diversity predicted OS across multiple cohorts. Conversely, in peripheral blood, high abundance of T-cells, but not high diversity, predicted OS. Clustering patients based on TCR specificity revealed a subset of TCRs that predicts OS. Interestingly, these TCR sequences were more likely to encode CD8+ effector memory and CD4+ T-regulatory (Tregs) T-cells, all with the capacity to recognize beta islet-derived autoantigens. As opposed to T-cell abundance, intratumoral TCR diversity was predictive of OS in multiple PDAC cohorts, and a subset of TCRs enriched in high-diversity patients independently correlated with OS. These findings emphasize the importance of evaluating peripheral and intratumoral TCR repertoires as distinct and relevant biomarkers in PDAC.

Oncolytic viruses improve cancer immunotherapy by reprogramming solid tumor microenvironment.

Immunotherapies using immune checkpoint inhibitors (ICIs) and chimeric antigen receptor (CAR) T-cell therapy have achieved successful results against several types of human tumors, particularly hematological malignancies. However, their clinical results for the treatment of solid tumors remain poor and unsatisfactory. The immunosuppressive tumor microenvironment (TME) plays an important role by interfering with intratumoral T-cell infiltration, promoting effector T-cell exhaustion, upregulating inhibitory molecules, inducing hypoxia, and so on. Oncolytic viruses are an encouraging biocarrier that could be used in both natural and genetically engineered platforms to induce oncolysis in a targeted manner. Oncolytic virotherapy (OV) contributes to the reprogramming of the TME, thus synergizing the functional effects of current ICIs and CAR T-cell therapy to overcome resistant barriers in solid tumors. Here, we summarize the TME-related inhibitory factors affecting the therapeutic outcomes of ICIs and CAR T cells and discuss the potential of OV-based approaches to alleviate these barriers and improve future therapies for advanced solid tumors.

Novel combinatorial therapy of oncolytic adenovirus AdV5/3-D24-ICOSL-CD40L with anti PD-1 exhibits enhanced anti-cancer efficacy through promotion of intratumoral T-cell infiltration and modulation of tumour microenvironment in mesothelioma mouse model.

Malignant mesothelioma is a rare and aggressive form of cancer. Despite improvements in cancer treatment, there are still no curative treatment modalities for advanced stage of the malignancy. The aim of this study was to evaluate the anti-tumor efficacy of a novel combinatorial therapy combining AdV5/3-D24-ICOSL-CD40L, an oncolytic vector, with an anti-PD-1 monoclonal antibody. The efficacy of the vector was confirmed in vitro in three mesothelioma cell lines - H226, Mero-82, and MSTO-211H, and subsequently the antineoplastic properties in combination with anti-PD-1 was evaluated in xenograft H226 mesothelioma BALB/c and humanized NSG mouse models. Anticancer efficacy was attributed to reduced tumour volume and increased infiltration of tumour infiltrating lymphocytes, including activated cytotoxic T-cells (GrB+CD8+). Additionally, a correlation between tumour volume and activated CD8+ tumour infiltrating lymphocytes was observed. These findings were confirmed by transcriptomic analysis carried out on resected human tumour tissue, which also revealed upregulation of CD83 and CRTAM, as well as several chemokines (CXCL3, CXCL9, CXCL11) in the tumour microenvironment. Furthermore, according to observations, the combinatorial therapy had the strongest effect on reducing mesothelin and MUC16 levels. Gene set enrichment analysis suggested that the combinatorial therapy induced changes to the expression of genes belonging to the "adaptive immune response" gene ontology category. Combinatorial therapy with oncolytic adenovirus with checkpoint inhibitors may improve anticancer efficacy and survival by targeted cancer cell destruction and triggering of immunogenic cell death. Obtained results support further assessment of the AdV5/3-D24-ICOSL-CD40L in combination with checkpoint inhibitors as a novel therapeutic perspective for mesothelioma treatment.

Abstract PR08: Personalized therapeutic mRNA nano-vaccines are effective across multiple preclinical and translational models of head and neck cancer

Abstract Objectives: The translational pipeline for novel immunotherapeutics is often stymied due to the lack of relevant immune-competent pre-clinical animal models which can facilitate the path to human clinical trials. The objective of this study is to demonstrate anti-tumor activity and feasibility of our novel formulation of patented therapeutic personalized mRNA lipid nanoparticle vaccines in head and neck pre-clinical models including murine models of oral cancer (metastatic and primary), metastatic thyroid cancer, and a client-owned felines with spontaneously occurring oral squamous cell carcinoma. Methods: (1) C57B/6 mice were implanted with syngeneic murine cells lines to generate; oral tongue cancer models (MOC1/MOC2 cells), flank models of oral cancer (MOC1 cells), oral cancer lung metastasis models (MOC1 cells), and thyroid cancer lung metastasis models (hRAS cells). Mice were treated with tumor derived mRNA nano-vaccines weekly, x5 weeks. Tumor volumes and survival curves were recorded. MOC1 tumors and blood were analyzed for immune cell infiltration using flow cytometry. (2) Client-owned felines (N=5) with spontaneously occurring oral squamous cell carcinoma, were enrolled into our clinical trial (conducted at the University Veterinary School) after owner consent was obtained. Tumor biopsy was used to make tumor-specific mRNA-nano-vaccines from the surgical specimen. Feline patients were administered weekly vaccines intravenously x3 and monitored for adverse events. Results: 1) Mice treated with tumor-derived mRNA nano-vaccines demonstrated significantly decreased tumor volumes and increased overall survival when compared with untreated controls in both MOC1 and the more aggressive MOC2 cell lines (p<0.001). Vaccine treated mice also had significantly decreased metastatic MOC1 and hRAS tumor burden in the lungs. Orthotopic models for MOC1 tumors were more responsive to mRNA nano-vaccine therapy than subcutaneous (flank) models (p<0.05). Immune responses were characterized by significantly increased intratumoral and systemic CD4 and CD8 T-cell infiltration and decreased tumor myeloid derived suppressor cells (MDSCs). 2) Feline patients tolerated initial dosing of mRNA nano-vaccine administration with no significant toxicities or adverse events (stable vital signs and CBC). Overall survival of feline patients was significantly improved when compared to untreated patients (mean of 690 days vs 100 days respectively, p<0.03). Conclusion: Personalized mRNA nano-vaccines are effective and safe in preclinical murine head and neck and feline patient models. Our vaccine formulation has FDA IND (Investigation New Drug) approval for human use in solid tumors. Utilizing murine models in addition to large animals of head and neck cancer has facilitated the translational research pipeline in development of novel immunotherapeutics and will guide us in designing our first-in-human clinical trial for head and neck cancer patients which will open in 2023. Citation Format: Natalie L. Silver, Johnathan Chardon-Robles, Jin Dai, Rekha Garg, John Ligon, Carlos Souza, Paul Castillo, Rowan Milner, Bikash Sahay, Timothy Chan, Duane Mitchell, Elias Sayour. Personalized therapeutic mRNA nano-vaccines are effective across multiple preclinical and translational models of head and neck cancer [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Innovating through Basic, Clinical, and Translational Research; 2023 Jul 7-8; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2023;29(18_Suppl):Abstract nr PR08.

Pattern recognition receptor agonists in pathogen vaccines mediate antitumor T-cell cross-priming

BackgroundCancer immunotherapies are generally effective in patients whose tumors contain a priori primed T-cells reactive to tumor antigens (TA). One approach to prime TA-reactive T-cells is to administer immunostimulatory molecules,...

The CD58-CD2 axis is co-regulated with PD-L1 via CMTM6 and shapes anti-tumor immunity.

The cell-autonomous balance of immune-inhibitory and -stimulatory signals is a critical process in cancer immune evasion. Using patient-derived co-cultures, humanized mouse models, and single-cell RNA-sequencing of patient melanomas biopsied before and on immune checkpoint blockade, we find that intact cancer cell-intrinsic expression of CD58 and ligation to CD2 is required for anti-tumor immunity and is predictive of treatment response. Defects in this axis promote immune evasion through diminished Tcell activation, impaired intratumoral Tcell infiltration and proliferation, and concurrently increased PD-L1 protein stabilization. Through CRISPR-Cas9 and proteomics screens, we identify and validate CMTM6 as critical for CD58 stability and upregulation of PD-L1 upon CD58 loss. Competition between CD58 and PD-L1 for CMTM6 binding determines their rate of endosomal recycling over lysosomal degradation. Overall, we describe an underappreciated yet critical axis of cancer immunity and provide a molecular basis for how cancer cells balance immune inhibitory and stimulatory cues.

MDB-12. TRANS-SPECIES ANALYSIS OF REPLICATION-REPAIR DEFICIENT (RRD) MEDULLOBLASTOMA AND RESPONSE TO IMMUNE-CHECKPOINT INHIBITION: AN IRRDC REPORT

Abstract BACKGROUND Replication-repair deficiency (RRD) stemming from mismatch repair and polymerase-proofreading gene defects (MMRD/PPD) lead to hypermutant childhood cancers, most frequently brain tumors. While medulloblastoma is reported, the clinical, genomic and immune landscape remains unknown. METHODS We analysed the genome, methylome, transcriptome (bulk, single-nuclei) and immune-microenvironment of the largest cohort of RRD-medulloblastoma patients enrolled by the International RRD Consortium, and correlated these to clinical outcomes. RRD mice-models were used to preclinically assess response to immunotherapy. RESULTS RRD-medulloblastoma (n=40) were enriched for anaplasia (55%) and localised disease (85%). Methylation/nano-string-based subgrouping failed to classify 40%, while the remaining clustered with the SHH-subgroup. Copy-number changes were notably infrequent (<20%). All tumors harboured hypermutation and microsatellite instability in contrast to non-RRD controls (p<0.0001). Pathogenic variants were frequent in POLE/POLD1 (80%), TP53 (48%) and SHH-pathway genes (PTCH1, SUFU, SMO: 56%). Interestingly, some tumors additionally had glioma-driver alterations (ATRX, NF1: ~50%), similar to RRD cerebellar glioblastoma, but distinct from both non-RRD medulloblastoma (n=791) and hemispheric glioblastoma (n=733) controls. Moreover, although bulk-transcriptome matched non-RRD SHH-medulloblastoma, single-nuclei analyses suggested an earlier cell-of-origin potentially explaining the heterogenous phenotypes resulting from the driver mutations. Uniquely, immune analyses (gene expression and immunohistochemistry) demonstrated high intra-tumoral CD8 T-cell infiltration. Three-year progression-free survival was 60%. Outcome was worse for RRD-medulloblastoma harbouring TP53-mutation (p=0.04) and failing subgroup-classification (p=0.004). Nestin/Cre MSH2-/- POLE;p.S459F mice developing medulloblastoma recapitulated human disease and demonstrated response to anti-PD1 monotherapy. Recurrent/progressive human tumors including those harbouring TP53-mutations exhibited radiological responses to anti-PD1 monotherapy, which was associated with prolonged ongoing survival in comparison to those not treated with checkpoint-inhibitors (p=0.02). CONCLUSIONS Hypermutant RRD-medulloblastoma reveal heterogenous phenotypes due to unique spectrum of driver mutations and an early cell of origin. Their immune-hot microenvironment allows successful salvage treatment with checkpoint-inhibitors for those failing chemo-radiation, including the high-risk SHH/TP53-mutant and unclassified subgroups.

Silencing of tumoral carbohydrate sulfotransferase 15 reactivates lymph node pancreatic cancer T cells in mice.

Limited intratumoral T-cell infiltration in pancreatic ductal adenocarcinoma (PDAC) is an obstacle to immunotherapy, yet the efficient approach to enhance tumor-infiltrating T cells is not fully established. Here, we show that tumor-specific knockdown of carbohydrate sulfotransferase 15 (CHST15), a tumor stromal proteoglycan-synthetic enzyme, suppresses tumor growth in a T-cell-dependent manner in a murine model of PDAC. Silencing of tumoral CHST15 unexpectedly expanded CD4+ and CD8+ T cells in tumor draining LN (TDLN), leading to accelerated accumulation of EdU+ proliferating CD4+ and CD8+ T cells and granzyme B+ CD8+ T cells in the tumor. RNA expression analysis indicated that tumoral CHST15 knockdown (KD) downregulated matrix remodeling-related genes, while upregulated anti-tumor T-cell activity-related genes in both tumor and TDLN. CHST15 KD significantly diminished intratumoral and TDLN Ly6C/G+ myeloid-derived suppressor cells prior to TDLN T-cell expansion, suggesting that tumoral CHST15 remotely regulated myeloid-derived suppressor cell mediated T-cell suppression in the TDLN. Our findings illustrate a novel immunotherapeutic potential of tumoral CHST15 blockage by reactivating T cells in immune suppressive TDLN of PDAC.

Utilizing chemotherapy-induced tumor RNA nanoparticles to improve cancer chemoimmunotherapy.

Chemotherapy has become a popular combination strategy to improve the response rate of immunotherapy since certain chemotherapeutic drugs kill tumor cells by an immunogenic cell death (ICD) pathway, which activates antitumor immune responses. Unfortunately, the synergistic effect of chemoimmunotherapy can be impaired due to the toxicities of chemotherapeutic agent-induced lymphatic depletion and immunosuppression. In this study, we present an approach to improve immunotherapy by using tumor RNA nanoparticles (RNA-NPs) where RNA is directly extracted from chemotherapy-treated cancer cells and then condensed by protamine via electrostatic interactions to form complexes. Such RNA-NPs can be effectively taken up by dendritic cells (DCs) in the draining lymph nodes after subcutaneous injection. Compared with noninduced tumor RNA nanoparticles (N-RNA-NPs), chemotherapy-induced tumor RNA nanoparticles (C-RNA-NPs) can significantly promote DC maturation and stimulate a stronger immune response against established CT-26 colon carcinoma. Besides, C-RNA-NPs can improve the efficacy of immune checkpoint blockade (ICB) therapy by facilitating the infiltration of intratumoral T cells and increasing the ratio of CD8+ T cells to regulatory T cells (Tregs). More importantly, the synergistic effect of chemoimmunotherapy is also enhanced by treatment with C-RNA-NPs. STATEMENT OF SIGNIFICANCE: Although immune checkpoint blockade therapy has been demonstrated to be effective in some advanced cancers, the low response rate has significantly limited its clinical application. To address this issue, a new strategy for improving cancer immunotherapy using chemotherapy-induced tumor RNA nanoparticles (C-RNA-NPs) is developed in this work. The proposed C-RNA-NPs could be captured by dendritic cells, which were then stimulated to the maturation status to initiate an anticancer immune response. Furthermore, the response rate to immunotherapy was significantly increased by promoting intratumoral T-cell infiltration and elevating the intratumoral ratio of CD8+ T cells to regulatory T cells after treatment with C-RNA-NPs. Therefore, C-RNA-NPs have the potential to improve cancer immunotherapy.

EGFR-phosphorylated GDH1 harmonizes with RSK2 to drive CREB activation and tumor metastasis in EGFR-activated lung cancer

The cancer metastasis process involves dysregulated oncogenic kinase signaling, but how this orchestrates metabolic networks and signal cascades to promote metastasis is largely unclear. Here we report that inhibition of glutamate dehydrogenase 1 (GDH1) and ribosomal S6 kinase 2 (RSK2) synergistically attenuates cell invasion, anoikis resistance, and immune escape in lung cancer and more evidently in tumors harboring epidermal growth factor receptor (EGFR)-activating or EGFR inhibitor-resistant mutations. Mechanistically, GDH1 is activated by EGFR through phosphorylation at tyrosine 135 and, together with RSK2, enhances the cAMP response element-binding protein (CREB) activity via CaMKIV signaling, thereby promoting metastasis. Co-targeting RSK2 and GDH1 leads to enhanced intratumoral CD8 Tcell infiltration. Moreover, GDH1, RSK2, and CREB phosphorylation positively correlate with EGFR mutation and activation in lung cancer patient tumors. Our findings reveal a crosstalk between kinase, metabolic, and transcription machinery in metastasis and offer an alternative combinatorial therapeutic strategy to target metastatic cancers with activated EGFRs that are often EGFR therapy resistant.

Oncolytic vaccinia virus expressing a bispecific T-cell engager enhances immune responses in EpCAM positive solid tumors.

Insufficient intratumoral T-cell infiltration and lack of tumor-specific immune surveillance in tumor microenvironment (TME) hinder the progression of cancer immunotherapy. In this study, we explored a recombinant vaccinia virus encoding an EpCAM BiTE (VV-EpCAM BiTE) to modulate the immune suppressive microenvironment to enhance antitumor immunity in several solid tumors. VV-EpCAM BiTE effectively infected, replicated and lysed malignant cells. The EpCAM BiTE secreted from infected malignants effectively mediated the binding of EpCAM-positive tumor cells and CD3ϵ on T cells, which led to activation of naive T-cell and the release of cytokines, such as IFN-γ and IL-2. Intratumoral administration of VV-EpCAM BiTE significantly enhanced antitumor activity in malignancies with high other than with low EpCAM expression level. In addition, immune cell infiltration was significantly increased in TME upon VV-EpCAM BiTE treatment, CD8+ T cell exhaustion was reduced and T-cell-mediated immune activation was markedly enhanced. Taken together, VV-EpCAM BiTE sophistically combines the antitumor advantages of bispecific antibodies and oncolytic viruses, which provides preclinical evidence for the therapeutic potential of VV-EpCAM BiTE.

ATM Regulates Differentiation of Myofibroblastic Cancer-Associated Fibroblasts and Can Be Targeted to Overcome Immunotherapy Resistance.

ATM signaling supports the differentiation of myoCAFs to suppress T-cell infiltration and antitumor immunity, supporting the potential clinical use of ATM inhibitors in combination with checkpoint inhibition in myoCAF-rich, immune-cold tumors.

Abstract 3572: Oncolytic virotherapy with the HSV-1 (VC2) vaccine strain induces anti-tumor T-cell responses in the murine 4T1 breast cancer model

Abstract The tumor microenvironment (TME) plays important roles in suppression of anti-tumor immune responses. Immune suppression is achieved by multiple mechanisms including interfering with antigen presentation and inhibition of effector T-cell tissue infiltration. Altering specific TME properties can reduce immune-suppression and improve anti-tumor immunity with abscopal effects. Oncolytic Virotherapy (OV) is a promising approach for cancer treatment. We evaluated the efficacy of the HSV-1 (VC2) vaccine strain for the treatment of breast cancer using the murine stage-4 (4T1) syngeneic and immunocompetent breast cancer mouse model. Following Intratumoral (IT) injection of VC2 in mice bearing implanted 4T1 tumors, treatment efficacy was evaluated by monitoring tumor weight, immune infiltration, and metastasis in the lung. Animals treated with VC2 via the IT route exhibited significantly reduced metastasis and improved intra-tumoral T-cell infiltration. Improved T-cell infiltration was not due to viral replication since improved parameters were observed during late times post VC2 treatment when no viral replication was detectable. The total area of metastasis in the lung was significantly reduced compared to control groups. VC2 treated animals via the IT route had significantly higher cytotoxic splenocytes, evident by the in-vitro killing of 4T1 cells, compared to the control group. This improved cytotoxic activity, intratumoral T-cell infiltration, and reduced metastasis in the lung suggest that IT administration of VC2 altered TME in a way that induced better antigen recognition, processing, and presentation resulting in improved anti-tumor immune responses with an abscopal effect in the lung. Further understanding of the mechanisms involved in the observed improved anti-tumor immune responses will help improve treatment efficacy and provide new approaches for the treatment of solid tumors. Citation Format: Rafiq Nabi, Farhana Musarrat, Vladimir Chouljenko, Konstantin Kousoulas. Oncolytic virotherapy with the HSV-1 (VC2) vaccine strain induces anti-tumor T-cell responses in the murine 4T1 breast cancer model [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 3572.

Impact of Chemoembolic Regimen on Immune Cell Recruitment and Immune Checkpoint Marker Expression following Transcatheter Arterial Chemoembolization in a VX2 Rabbit Liver Tumor Model

PurposeTo characterize the effects of commonly used transcatheter arterial chemoembolization (TACE) regimens on the immune response and immune checkpoint marker expression using a VX2 rabbit liver tumor model. Materials and MethodsTwenty-four VX2 liver tumor-bearing New Zealand white rabbits were assigned to 7 groups (n = 3 per group) undergoing locoregional therapy as follows: (a) bicarbonate infusion without embolization, (b) conventional TACE (cTACE) using a water-in-oil emulsion containing doxorubicin mixed 1:2 with Lipiodol, drug-eluting embolic-TACE with either (c) idarubicin-eluting Oncozene microspheres (40 μm) or (d) doxorubicin-eluting Lumi beads (40–90 μm). For each therapy arm (b–d), a tandem set of 3 animals with additional bicarbonate infusion before TACE was added, to evaluate the effect of pH modification on the immune response. Three untreated rabbits served as controls. Tissue was harvested 24 hours after treatment, followed by digital immunohistochemistry quantification (counts/μm2 ± SEM) of tumor-infiltrating cluster of differentiation 3+ T-lymphocytes, human leukocyte antigen DR type antigen-presenting cells (APCs), cytotoxic T-lymphocyte–associated protein-4 (CTLA-4), and programmed cell death protein-1 (PD-1)/PD-1 ligand (PD-L1) pathway axis expression. ResultsLumi-bead TACE induced significantly more intratumoral T-cell and APC infiltration than cTACE and Oncozene-microsphere TACE. Additionally, tumors treated with Lumi-bead TACE expressed significantly higher intratumoral immune checkpoint markers compared with cTACE and Oncozene-microsphere TACE. Neoadjuvant bicarbonate demonstrated the most pronounced effect on cTACE and resulted in a significant increase in intratumoral cluster of differentiation 3+ T-cell infiltration compared with cTACE alone. ConclusionsThis preclinical study revealed significant differences in evoked tumor immunogenicity depending on the choice of chemoembolic regimen for TACE.