Background: Sip-T is an autologous cellular immunotherapy targeting prostatic acid phosphatase (PAP) that is approved by the FDA and EMA for the treatment of certain patients with asymptomatic/minimally symptomatic metastatic castration-resistant prostate cancer. The STAND trial (NCT01431391) evaluated optimal sequencing of sip-T and ADT in men with BRPC at high risk of developing metastases (PSA-DT ≤12 mos). Methods: Men (N=68) were randomized (1:1) to Arm 1: sip-T followed by ADT (2 wks after infusion 3) or Arm 2: ADT (3 mo lead-in) followed by sip-T. Men received 3 doses of sip-T and 12 mos of ADT (leuprolide). The primary endpoint was cellular immune response to target antigen (ELISPOT to PA2024). Secondary endpoints included humoral and cytokine responses, product parameters, clinical efficacy, and safety. Here we report preliminary clinical data and longer-term immune responses. Results: 65 men have been followed for ≥9 mos from last ADT injection: 10/32 (31.3%) in Arm 1 and 14/33 (42.4%) in Arm 2 achieved undetectable PSA (<0.02 ng/mL) and testosterone (T; <0.35 ng/mL) at 9 mos from last ADT injection; 4/65 men (6.2%) developed PSA progression (2 consecutive PSA measurements, 4 wks apart, ≥50% above nadir, >5ng/mL). In both arms, sip-T induced robust and prolonged immune responses to PA2024 and PAP (measured by T cell memory and ELISA antibody responses), although no significant differences have yet emerged between arms. There appear to be higher levels of serum cytokines in Arm 2 vs Arm 1, with a pattern suggesting a mixed T_H1/T_H2 cellular immune response; significant increases were seen in T_H1 (IFNg, IL-12), T_H2 (IL-4, IL-10, IL-13), and T_H17 (IL-17) subsets (P<0.05). Conclusions: These data suggest that tumor-specific T cell responses and broad-based immune responses are augmented in both arms, and cytokine responses may be superior when sipuleucel-T is given after (rather than before) ADT initiation. In addition, augmented PA2024- and PAP-specific humoral responses have persisted for at least 12 mos, and are equally robust in both groups. Longer-term T cell responses and cytokine responses will be presented. Clinical trial information: (NCT01431391).