Background: ADT is a standard treatment for men with BRPC after failure of local therapy, and has immunomodulatory effects. Sipuleucel-T is an autologous cellular immunotherapy approved for asymptomatic/minimally symptomatic metastatic castrate resistant prostate cancer. The STAND trial (NCT01431391) aimed to evaluate optimal sequencing of sipuleucel-T and ADT in men with BRPC at high risk for metastases (ie PSA doubling time ≤12 mo). Methods: Men were randomized (1:1) to Arm 1: sipuleucel-T followed by ADT (2 wks after 3rd infusion); or Arm 2: ADT (3 mo lead in) followed by sipuleucel-T. All men had 3 doses of sipuleucel-T and 12 mo of ADT (45 mg leuprolide SQ at 6 mo intervals). The primary endpoint is cellular immune response (ELISPOT to PA2024 [PAP-GMCSF]). Secondary endpoints are humoral and cytokine responses, product parameters and safety. Results: 68 men were randomized. Preliminary data show higher levels of serum cytokines in Arm 2 vs Arm 1, with a pattern suggesting a mixed T_H1/T_H2 cellular immune response; elevations were seen in T_H1 (IFNγ, IL 12), T_H2 (IL 4, 5, 10, 13) and T_H17 (IL 17) subsets (all P<.05). The increase in T_H1 cytokines was consistent with a trend toward higher PA2024-specific ELISPOT responses 2 wk after the 3rd sipuleucel-T infusion in Arm 2 vs Arm 1 (40.5 vs 12.8 spots; P=.086), suggesting increased T cell activation in Arm 2. Antigen-specific humoral responses were induced in both arms with no differences yet observed between arms. Sipuleucel-T product parameters were roughly equivalent in both arms with APC activation data indicating a robust prime-boost effect. Conclusions: While confirmation is required, these preliminary data suggest that tumor-specific T cell responses and broad based immune responses are augmented when sipuleucel-T is given after rather than before ADT initiation. These data are consistent with preclinical studies showing that ADT enhances T cell activity, and provide preliminary evidence that combining ADT with sipuleucel-T may augment adaptive immunity. Further follow up will determine whether augmented immune responses correlate with clinical parameters (eg PSA recurrence). Clinical trial information: NCT01431391.