Abstract 3979: Immune correlates of pathologic response in bladder cancer patients undergoing neoadjuvant chemotherapy

Abstract

Abstract Introduction and Objective: The immune system is increasingly recognized as both a key player in cancer control and as druggable target. We hypothesized that the immune system impacts pathologic response in patients undergoing cisplatin-based neoadjuvant chemotherapy (NAC) for muscle-invasive bladder cancer though the immune system. Methods: Whole exome sequencing (WES) was performed on tumor DNA from patients in two independent cohorts who underwent cisplatin-based NAC. The Memorial Sloan Kettering/Dana Farber Cancer Institute (n=50; 25 responders) and Philadelphia cohorts (n=48; 20 responders) were treated with gemcitabine / cisplatin or methotrexate / vinblastine / doxorubicin / cisplatin. Mutation analysis was performed using standard analytical pipelines. Macrohistocompatibility complex (MHC)-restricted neoantigens were identified with netMHCpan and PolySolver. High affinity neoantigens were defined to have ≤500 nM binding affinity (Kd). Pathologic response was defined as ≤ypTis cystectomy specimen. CIBERSORT was used to infer immune cell infiltrate based on DASL Illumina microarray expression profiles (n=41; 17 responders). Results: Chemoresponders had >twice as many putative neoantigens as nonresponders (471 vs 207 neoantigens respectively; p=1x10-6, Wilcoxon). This relationship maintained significance when neoantigens were limited to Kd≤100 nM or ≤50 nM, and when chemoresponse was defined as ypT0-only, or ≤ypT1. ERCC2 loss-of-function mutations were 36% sensitive in identifying chemoresponders but 96% specific. Above-median neoantigen burden was 81% sensitive in identifying chemoresponders and 78% specific. CD8+ cells were enriched in responders (13.5% vs 8.4% of infiltrate; p<0.008, t-test) as were activated NK cells (15.5% vs 12.7%; p=0.05). In 28 samples where WES and CIBERSORT data was available, the neoantigen burden was correlated to the CD8+ infiltrate value (R2=0.33, Pearson). Conclusions: Neoantigen burden and CD8+ infiltrate correlate strongly with chemoresponse. Neoantigen burden and CD8+ infiltrate are directly proportional. NAC may therefore exert known tumor cell autonomous effects and an extrinsic effect involving the immune system via neoantigens. Anti-neoantigen responses have been shown to impact immune checkpoint responses and a similar mechanism may mediate cytotoxic chemoresponse. Experiments are underway to directly and functionally characterize the effect of the immune system in chemoresponse. Citation Format: Philip H. Abbosh, David Liu, Woonyoung Choi, Wafik S. El-Deiry, Jonathan E. Rosenberg, David McConkey, Elizabeth R. Plimack, Eliezer M. Van Allen. Immune correlates of pathologic response in bladder cancer patients undergoing neoadjuvant chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3979. doi:10.1158/1538-7445.AM2017-3979