Abstract 4158: High dimensional analysis of sipuleucel T from metastatic castration resistant prostate cancer patients using mass cytometry
Authors: Saeed Muhammad , Kim Kevin , Borkowski Ariel , Pachynski Russell Kent 
Published: June 2022

Abstract
Background: Prostate cancer is the most commonly diagnosed non-skin cancer in men, and metastatic castration-resistant prostate cancer (mCRPC) represents the most lethal form of the disease. Sipuleucel T (sip T) is an autologous active cellular immunotherapy approved by FDA for patients with mCRPC and has been shown effective in improving overall survival (OS) among individuals with mCRPC. To date, detailed analysis of the sip T product has not been studied using an advanced mass cytometry approach. Here, we present high dimensional data describing the specific leukocyte subsets and phenotype of sip-T in detail.
Methods: We performed a comprehensive assessment of sip T (n=14 samples, collected under an IRB approved protocol) from 11 different patients with mCRPC, using high-throughput mass cytometry (CyTOF) comprised of 37 different antibodies/markers. Sip T samples were then analyzed for various leukocyte subsets, as well as markers of activation and exhaustion. Furthermore, clinical correlations were drawn between immune cell subsets/markers and patient clinical data such, as prostate specific antigen (PSA) levels.
Results: CyTOF analysis revealed that CD3+ T cells (including CD4+ and CD8+) constituted the highest proportion (median, range: 63%, 9-89%) of sip T, followed by CD19+ B cells (4%, 1-82%), CD3-CD14-CD56+ natural killer (NK) cells (4%, 1-18%), and CD3-CD19-CD56-HLA-DR+CD11c+CD14+ monocytes (1%, 1-37%) besides a small proportion (&lt;1%) of conventional dendritic cells (cDC), innate lymphoid cells (ILC), plasmacytoid DC (pDC), myeloid-derived suppressor cells (MDSC) and NK T-cells (NKT). The majority of CD8+ T cells were either CD45RA+CCR7-effector (Teff: 43%, 9-70%), CD45RA-CCR7- effector memory (Tem: 23%, 11-59%) and CD45RA+CCR7+ naive (Tn: 22%, 4-50%). Contrarily, most CD4+ T cells belonged to CD45RA-CCR7+ central memory (Tcm: 45%, 24-78%), effector memory (Tem: 27%, 6-61%) and naive (Tn: 22%, 1-50%) subtypes. Interestingly, the majority of monocytes (86%, 78-97%) were CD86+ suggesting a role in inducing lymphocyte activation. Of activation/exhaustion markers, the highest proportion of PDL1+, PD1+, IFNg+ and ICOS+ cells were observed in monocytes, cDC, NK and CD4+ T cells respectively. Likewise, CTLA4+, VISTA+ and TIGIT+ cells were most commonly found among CD8+ T cells, suggesting a potential regulatory effect on sip T CD8+ T cell proliferation and effector function.
Conclusion: This is the first comprehensive study to evaluate the composition of sip T from mCRPC patients using high dimensional CyTOF analysis. Given the increasing use of CyTOF in translational research, this data set serves as an important reference source, which could be used in future studies to help guide therapeutic modulation of activation/exhaustion markers to improve sip T efficacy and enhance beneficial immune responses.
Citation Format: Muhammad Saeed, Kevin Kim, Ariel Borkowski, Russell Kent Pachynski. High dimensional analysis of sipuleucel T from metastatic castration resistant prostate cancer patients using mass cytometry [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 4158.