Abstract CT023: Prostate cancer in situ autovaccination with the intratumoral viral mimic poly-ICLC: Making a cold tumor hot

Abstract PURPOSE To test the safety of sequential intratumoral plus systemic intramuscular injection of poly-ICLC, and its efficacy in priming antitumor immune responses in patients with prostate cancer (PCa). EXPERIMENTAL PROCEDURES This is an open-label dose-escalating phase 1 neoadjuvant clinical trial of poly-ICLC (NCT03262103) in 12 patients diagnosed with clinically localized PCa with plans to undergo radical prostatectomy (RP). Poly-ICLC was administered intratumorally (Artemis MRI-TRUS-guided) and intramuscularly (e.g., deltoid muscle). Comprehensive transcriptional profiling of tissues, phenotypic and transcriptional analysis of longitudinally collected peripheral blood, and analysis of the prostate tumor microenvironment (TME) were performed before and after poly-ICLC treatment in order to identify innate and adaptive antitumor immune responses within the tumor and in peripheral blood. This trial is the first to use human intratumoral immunotherapy instead of systemic immunomodulation for high-risk PCa patients. RESULTS Poly-ICLC was well tolerated (safe) in all 12 patients. There were no dose-limiting toxicities or TEAE (treatment-emergent adverse events) withdrawals during treatment. Eight of 10 evaluable patients (80%) had undetectable PSA (<0.1 ng/ml) at 1 year of follow-up post-RP. Eight of 12 evaluable patients (66.7%) and 7 of 10 patients (70%) with biopsy Gleason 8-10 had a lower Gleason score in the post-treatment RP specimen. Transcriptome profiling of paired biopsy and RP specimens showed significant upregulation of gene signatures associated with immune cell infiltration and TP53-associated metabolic genes, but downregulation of gene signatures associated with metastasis and DNA replication. Genes upregulated by poly-ICLC were associated with a good prognosis. Treatment with poly-ICLC increased systemic immune responses, as demonstrated by an increase in cytolytic signatures, T- and NK-cell signatures, and NK-cell subsets in the blood. Multiplex immunohistochemistry analysis revealed a significant increase in the densities of CD4- and CD8-T cells and B cells, as well as evidence of tertiary lymphoid structures (TLS) within the TME of post-treatment RP specimens compared to baseline. CONCLUSIONS Poly-ICLC treatment can reliably transform the cold TME of PCa into a hot, immune-enhanced ecosystem. The identified baseline and response biomarkers, tertiary lymphoid structures, potential clinical benefit, and immunologic correlates require validation in larger studies. Citation Format: Sujit S. Nair, Dimple Chakravarty, Sreekumar Balan, Alexander Hakansson, Manuel Duval, Elai Davicioni, Yang Liu, Swati Bhardwaj, Tin Htwe Thin, Monica Garcia-barros, Kenneth Haines, Majd Al Shaarani, Rachel Weil, Marcia Meseck, Parita Ratnani, Monali Fatterpekar, Ivan Jambor, Elena Gonzalez-Gugel, Adam Farkas, Vinayak Wagaskar, Kacie Schlussel, Cristina Pasat-karasik, Kamala Bhatt, Zachary Dovey, Adriana Pedraza, Akriti Gupta, Dara Lundon, Ante Peros, Sneha Parekh, Lily Davenport, Xiangfu Zhang, Raghav Gupta, Macy Robison, Cynthia Knauer, Ethan Ellis, Dmitry Rykunov, Boris Reva, Babu Padanilam, Matthew D. Galsky, Rachel Brody, Mani Menon, Andres Salazar, Nina Bhardwaj, Ashutosh K. Tewari. Prostate cancer in situ autovaccination with the intratumoral viral mimic poly-ICLC: Making a cold tumor hot [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT023.