What’s next in prostate cancer immunotherapy?

Prostate stem cell antigen (PSCA) is a cell surface antigen found in normal human prostate tissue and over-expressed in men who have prostate cancer. Elevated levels of PSCA protein in men with prostate cancer are know to correlate with higher tumor stage and grade, and with androgen independence. Higher levels of expression of PSCA are also observed in men who have bone metastases.

Ahmad et al. isolated the PSCA gene from a special transgenic adenocarcinoma mouse prostate cell line (TRAMPC1), and used the gene to develop a prostate cancer vaccine — strictly speaking a “vaccine plasmid construct” — referred to as pmPSCA. pmPSCA was used to treat subcutaneous TRAMPC1 tumors in mice, and induced effective antitumor immune responses. The pmPSCA vaccine:

  • Inhibited tumor growth, resulting in cure or prolongation in survival
  • Inhibited metastases in certain types of PSCA-expressing tumors
  • Activated Th-1 type tumor-specific immunity against PSCA, indicating the breaking of tolerance to a self-antigen

The authors conclude that treatment with the pmPSCA vaccine evoked strong specific responses and could, in neoadjuvant or adjuvant settings, provide a safe and effective means to induce immune control of prostate cancer.

Although there is a long way to go in developing an actual immunotherapeutic agent or agents based on this type of science, it is now increasingly clear that immunobiology holds the potential to significantly modify the course of disease in men with prostate cancer.

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