Sipuleucel-T is an autologous cellular immunotherapy, administered up to 3 infusions, for metastatic castrationresistant prostate cancer (mCRPC). Sipuleucel-T induces T-and B-cell responses to prostatic acid phosphatase (PAP), correlating to improved survival. The long-term impact of sipuleucel-T on tumor antigenspecific immunologic memory remains unknown. In particular, B cell responses, as measured by antigenspecific antibody responses and B cell receptor (BCR) sequences, remain unknown. To evaluate whether sipuleucel-T could induce long-term immunologic memory, we examined circulating B cell responses before and after sipuleucel-T treatment in two groups of mCRPC patients: those who had previously received sipuleucel-T (treated; median, 8.9 years since the previous treatment) versus those who had not (naïve). Before re-treatment, previously treated patients exhibited persistent antibody responses as well as more focused and convergent BCR repertoires with distinct V(D)J gene usage compared with naïve patients. After retreatment, previously treated patients maintained high frequency clones and developed more convergent BCRs at earlier time points unlike naive patients. With the first sipuleucel-T infusion specifically, previouslytreated patients had less shuffling within the 100-most abundant baseline clones. In contrast, naïve patients exhibited great BCR turnover with a continued influx of new B cell clones. Social network analysis showed that previously treated patients had more highly organized B cell repertoires, consistent with greater clonal maturation. Higher treatment-induced BCR clonality correlated with longer survival for naïve patients. These results demonstrated the capacity of sipuleucel-T to induce long-term immune memory and lasting changes to the B cell repertoire.