Uzendu, Chisom

Abstract Description Combination of radiotherapy (RT) and immunotherapy has gained popularity to turn up the heat on cold tumors. However, intrinsic resistance is prevalent, hence better therapeutic strategies are needed to improve the outcome of patients. We recently demonstrated in metastatic prostate cancer that circulating levels of tumor-derived extracellular vesicles (tdEVs) increased shortly after RT and was associated with poor survival. TdEVs are mediators of antitumor immunity but their role in response to RT remains unknown. Our study elucidates the impact of RT on immunomodulatory roles of tdEVs. Mouse tumors models expressing a bioluminescent EV reporter were treated with clinically used doses of RT. TdEV organotropism was measured by ex-vivo imaging at different timepoints. TdEVs were detected in blood, spleen, lymph nodes and immune cells. OT-1 transgenic mice and in vitro co-culture assays showed a reduction in CD8 T-cell cytotoxic activity in presence of tdEVs from irradiated cells. To identify key players of tdEV-mediated immunosuppression in response to RT, proteomic analysis revealed the immune checkpoint molecule B7-H3 was overexpressed in tdEVs after irradiation. Genetic deletion of B7-H3 inhibited the suppressive activity of tdEVs from irradiated cells resulting in enhanced T-cell cytotoxicity. This study describes tdEVs as a mediator of systemic immunosuppression in response to radiotherapy and B7-H3 as a potential therapeutic target to boost antitumor immunity. Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)

Abstract Description Background Castration-resistant prostate cancers (CRPC) do not respond to immunotherapy.1,2 Prostate cancer-derived immune factors (IF) like sPD-L1 drive immunosuppression and resistance.3 Circulating tumor-reactive T cells (TTR; CD8+CD11ahigh) and other immune subsets predict progression-free survival in oligometastatic CRPC after radiotherapy.4 A better understanding of the levels and changes in IF in CRPC—a tumor immune “circulome”—may lead to better immunotherapeutic approaches. Methods 79 men with oligometastatic castration-resistant prostate cancer were treated with radiation and blood was collected before and after treatment (NCT02816983). Peripheral blood mononuclear cells (PBMC) were subjected to immunophenotyping, and plasma was subjected to the Olink Explore panel assay measuring levels of 5,416 IFs using a proximity extension assay technology. Results High baseline soluble levels of PD-L1, PD-L2, TIM-3, and other selected immunotherapy-related IFs predicted inferior outcomes, including overall survival. Conversely, high soluble CTLA-4 levels strongly predicted superior outcomes (p < 0.0001). These results additionally correlated with changes in circulating tumor-reactive (TTR) T cells in these patients. Discussion IF influence systemic immunity in CRPC. These results suggest a multifactorial mechanism by which prostate cancers drive systemic immunosuppression and resistance to immunotherapy. Ongoing efforts to address IFs may help overcome CRPC immunotherapy resistance.5 Funding Sources Department of Defense HT9425-24-1-0622, An Atlas of the Tumor Immune Circulome (PI: Orme) Prostate Cancer Foundation Young Investigator Award (PI: Orme) National Cancer Institute K12 CA90628-23 (PI: Orme) Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)

Abstract Metastasis-ablative radiotherapy is a new therapeutic approach that prolongs survival in patients with advanced cancers. Tumour irradiation can elicit an immunogenic cell death resulting in the expansion of tumour-reactive T cells and eradication of both irradiated and distant non-irradiated metastases, referred to as the “abscopal effect”. This abscopal response, nevertheless, is observed in a minority of patients suggesting uncharacterized mechanisms that prevent robust systemic anti-tumor immune response. Tumour-derived extracellular vesicles (TdEVs) have recently emerged as mediators of antitumor immunity but their immunomodulatory role in response to radiotherapy remains largely unknown. Recent clinical studies by our lab have demonstrated that circulating levels of tumour-derived extracellular vesicles (tdEVs) are elevated in response to radiotherapy and high tdEV concentrations are associated with reduced levels of peripheral cytotoxic CD8+ T cells and higher risk of disease recurrence in advanced prostate cancer. Based on our findings, we hypothesize that radiotherapy induces the release of tumor-derived EVs that suppress anti-tumor immunity. Prostate cancer cells (PC3 and DU145) were irradiated with clinically used doses of ionizing radiation (20Gy x 1 or 10Gy x 3 fractions) and tdEVs were co-cultured with human CD8+ T cells to measure their proliferation and cytotoxic activity. Increased levels of tdEVs were released by tumour cells treated with radiotherapy. A higher frequency of impaired T cell cytotoxic activity and a reduction in CD8 T cell proliferation was found in the 10Gy x 3 radiation regimen. Proteomic analysis and western blot showed an increased expression of the immune checkpoint molecule B7-H3 on the tumour cell surface and tdEVs in response to radiotherapy. While coculture of CD8 T cells with B7-H3 depleted tdEVs led to recovery of T-cell cytotoxic ability, overexpression of the B7-H3 in tdEVs inhibited cytotoxic activity. This study provides a rationale for future studies in which we will test the immune-mediated effects of radiotherapy-induced tdEVs in immunocompetent mouse models and investigate B7-H3 blockade as a therapeutic approach to boost abscopal response in the treatment of advanced prostate cancer. Citation Format: Chisom J. Uzendu, Yohan Kim, Roxane R. Lavoie, Haidong Dong, Sean Park, Fabrice Lucien-Matteoni. Impact of radiotherapy on extracellular vesicle mediated anti-tumor immunity in oligometastatic prostate cancer [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 4995.

Most gene-based severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines are nonreplicating vectors. They deliver the gene or messenger RNA to the cell to express the spike protein but do not replicate to amplify antigen production. This study tested the utility of replication in a vaccine by comparing replication-defective adenovirus (RD-Ad) and replicating single-cycle adenovirus (SC-Ad) vaccines that express the SARS-CoV-2 spike protein. SC-Ad produced 100 times more spike protein than RD-Ad and generated significantly higher antibodies against the spike protein than RD-Ad after single immunization of Ad-permissive hamsters. SC-Ad–generated antibodies climbed over 14 weeks after single immunization and persisted for more than 10 months. When the hamsters were challenged 10.5 months after single immunization, a single intranasal or intramuscular immunization with SC-Ad-Spike reduced SARS-CoV-2 viral loads and damage in the lungs and preserved body weight better than vaccination with RD-Ad-Spike. This demonstrates the utility of harnessing replication in vaccines to amplify protection against infectious diseases.