Single-Cell RNAseq Analysis Reveals Robust, Anti-PD-1-Mediated Increase of Immune Infiltrate in Metastatic Castration-Sensitive Prostate Cancer

Compared to other malignancies, the tumor microenvironment (TME) of primary and castration-resistant prostate cancer (CRPC) is relatively devoid of immune infiltrates. While androgen deprivation therapy (ADT) induces a complex immune infiltrate in localized prostate cancer, both in animal models and humans, the TME composition of metastatic, castration-sensitive prostate cancer (mCSPC) is relatively unknown and the effects of ADT and other treatments are poorly characterized in this context. To address this challenge, we analyzed metastatic sites from patients enrolled on a phase 2 clinical trial ([NCT03951831][1]), in which men were treated with standard-of-care chemo-hormonal therapy with anti-PD-1 immunotherapy, at the single cell level. Longitudinal protein activity-based analysis of TME subpopulations identified immune subpopulations conserved across multiple metastatic sites, their dynamic, treatment-mediated evolution, and associated clinical response features. Our study revealed a therapy-resistant, transcriptionally distinct tumor subpopulation, which comprises an increasing number of cells in treatment-refractory patients, and identified several druggable targets in both tumor and immune cells as candidates to advance treatment and improve outcomes for patients with mCSPC. ### Competing Interest Statement Dr. Hawley has served as a paid consultant to Seagen and has received sponsored research funding to her institution from Regeneron and Dendreon. Dr. Drake is a co-inventor on patents licensed from JHU to BMS and Janssen and is currently an employee of Janssen Research. Dr. Califano is founder, equity holder, and consultant of DarwinHealth Inc., a company that has licensed some of the algorithms used in this manuscript from Columbia University. Columbia University is also an equity holder in DarwinHealth Inc. Dr. Lowy is an employee and stockholder of Regeneron Pharmaceuticals. [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT03951831&atom=%2Fbiorxiv%2Fearly%2F2022%2F05%2F09%2F2022.05.06.490968.atom