We previously reported that personalized
peptide vaccine (PPV)
therapy in combination with leutenizing
hormone-releasing
hormone (
LH-RH) analog and
estramustine phosphate in certain cases is safe and capable of inducing both immune responses and clinical responses for metastatic
castration-resistant
prostate cancer (CRPC) patients. In the present study, PPV monotherapy was given to CRPC patients. Twenty-three patients with metastatic CRPC were treated with PPV without any additional treatment modalities, including
LH-RH analogs. Samples were analyzed for
peptide-specific cytotoxic T-lymphocyte (CTL) precursor analysis and
peptide-reactive
IgG. Toxicity and immunological and clinical responses were assessed on a three-monthly basis. Seventeen patients were available for immunological and clinical evaluation. The
vaccines were well tolerated, with grade 3
erythema at injection sites in only one patient. Augmentation of CTL or
IgG responses to at least one of the
peptides was observed in six of 17 (35%) and 15 of 17 (88%) patients tested, respectively. Among 57
peptides used, 9 and 36
peptides induced CTL and
IgG responses, respectively. Delayed-type
hypersensitivity reaction was observed in eight of 17 patients. More than 30%
prostate-specific antigen (PSA) decline was observed in four of 17 patients. Of these, one patient achieved a complete PSA response and another patient showed a partial PSA response with profound shrinking of
lymph node metastases and prostate. The overall median survival time was 24 months (range, 5-37 months). These results suggest that PPV monotherapy appears to be safe and capable of inducing
peptide-specific immune responses and clinical responses in CRPC patients. This trial was registered with University Hospital Medical Information Network (UMIN) number R000003339.