Clonotypic T-cell responses in metastatic castration-resistant prostate cancer (mCRPC) patients (pts) treated with standard sipuleucel-T (sip-T) compared with patients receiving a booster treatment.

107Background: Sip-T is an FDA-approved autologous cellular immunotherapy for asymptomatic or minimally symptomatic mCRPC. Neoadjuvant sip-T induced activated T-cell infiltration to the prostate tissue (Fong 2014) and broadened the T cell receptor (TCR) repertoire vs control (Sheikh 2016). To test if sip-T induces memory T-cell responses, we compared treatment-induced changes in TCR repertoire of treatment-naive pts (STRIDE) with those retreated with sip-T (P10-1). Methods: In STRIDE (N=52), pts received sip-T with concurrent or sequential enzalutamide (Petrylak 2015). In P10-1 (N=8), pts previously treated with sip-T in an androgen-dependent setting were retreated with a booster course after a median of 8.6 years (Beer 2013). PBMCs were collected at baseline and during/post–sip-T. Deep sequencing was performed using the ImmunoSEQ assay (Adaptive Biotechnologies). TCR diversity was assessed by Shannon diversity index and clonality. TCR dynamics was evaluated by Morisita’s distance (Zhang 2017). Results: B...