942P - Antigen Presenting Cell (APC) Activation in Sipuleucel-T: Is Activation Increased in Earlier Prostate Cancer Disease States?

Abstract

ABSTRACT Background Sipuleucel-T is an autologous cellular immunotherapy approved by the US FDA for the treatment of asymptomatic or minimally symptomatic metastatic castrate resistant prostate cancer (mCRPC). In the Phase 3 mCRPC trials, APC activation in the sipuleucel-T product correlated with overall survival. In this analysis, sipuleucel-T product characteristics were compared across a range of disease states. Methods Sipuleucel-T product parameters were assessed in 4 trials of the following treatment settings: neoadjuvant, n = 42; serologic progression following local therapy, n = 12; asymptomatic or minimally symptomatic mCRPC, n = 341; and mCRPC (asymptomatic and symptomatic), n = 104. Cellular composition and APC activation (CD54 upregulation) were evaluated for all 3 sipuleucel-T doses; cumulative CD54 upregulation was calculated for each patient. In some studies, cytokines and T cell and B cell activation markers were assessed during sipuleucel-T manufacture. Results Baseline demographics were generally representative of each disease state: patients in the neoadjuvant setting were younger with lower disease burden; those with mCRPC had the highest disease burden and more patients had received prior chemotherapy. APC activation patterns were similar among trials, with increased CD54 upregulation at the second and third treatment. The median cumulative fold increase in CD54 upregulation in patients with earlier disease (neoadjuvant: 35.5, serological progression: 43.5) was significantly greater than in patients with asymptomatic or minimally symptomatic mCRPC (28.7) and mCRPC (21.8) (p Conclusion The process of manufacturing sipuleucel-T activates APCs in both early and late disease states, and generates similar T and B cell activation and cytokine profiles consistent with immunological prime-boost. However, APC activation was more robust in earlier disease states, raising the possibility that patients with less advanced disease may derive greater benefit. Disclosure E.J. Small: Honoraria from Dendreon. J.D. Wesley: Employee and Stockholder of Dendreon. D.I. Quinn: Consultant/Advisor to Dendreon, Pfizer, Bayer, Novartis, Genentech, C. Higano: Consultant/advisory role, honoraria, and research funding from Dendreon, D. Lin: Honoraria from Dendreon. H. Haynes: Employee and Stockholder of Dendreon. F. Stewart: Employee and Stockholder of Dendreon. J.B. Trager: Employee and Stockholder of Dendreon. N. Sheikh: Employee and Stockholder of Dendreon.