P10-1 open-label, multicenter study of sipuleucel-T in metastatic castrate-resistant prostate cancer (mCRPC) patients (pts) previously treated with sipuleucel-T: Evaluation of antigen-presenting cell (APC) activation.

Abstract

147 Background: Sipuleucel-T is an autologous cellular immunotherapy that has demonstrated an improvement in survival among men with asymptomatic or minimally symptomatic mCRPC. P10-1 (NCT01338012) is an open-label, multicenter study of sipuleucel-T in men with mCRPC previously treated with sipuleucel-T in the androgen-dependent setting on the PROTECT trial (a prospective, randomized, controlled Phase III study of sipuleucel-T in men with prostate-specific antigen recurrence following radical prostatectomy; NCT00779402). This preliminary analysis of P10-1 evaluates the pattern of APC activation in pts re-treated with sipuleucel-T after progression to mCRPC. Methods: Eligible pts include those previously treated with at least one infusion of sipuleucel-T on PROTECT and who progressed to the mCRPC state. Pts receive up to three additional infusions of sipuleucel-T. APC activation is assessed by CD54 upregulation expressed as the ratio of the average number of CD54 molecules on post-culture vs. pre-culture cells. Results: As of September 14, 2012, 7 pts have been enrolled and have received an infusion of sipuleucel-T. The median interval between the last infusion in PROTECT and the first infusion in P10-1 was 8.6 years. The Table shows a higher fold change in CD54 expression in the first P10-1 treatment compared with the initial infusion in PROTECT. Conclusions: This is the first report of pts re-treated with sipuleucel-T after prior treatment in an earlier disease setting. These preliminary data are consistent with the presence of an immunological memory response to the immunizing antigen several years following initial treatment. Clinical trial information: NCT01338012. [Table: see text]