A Neoadjuvant Study of Androgen Ablation Combined With Cyclophosphamide and GVAX Vaccine for Localized Prostate Cancer

Cancer immunotherapy refers broadly to approaches which attempt to treat cancer by activating immune responses directed against malignant tissue. Prostate GVAX is an allogeneic cell-based prostate cancer vaccine composed of two irradiated cell lines (PC3 and LNCaP) that have been genetically modified to secrete granulocyte-macrophage colony-stimulating factor (granulocytemacrophage-colony stimulating factor). The release of granulocytemacrophage-colony stimulating factor by these modified tumor cells serves to recruit dendritic cells which then present tumor antigens to T-cells, thus initiating antitumor immune responses. However, abundant preclinical data show that, when used alone, cell-based immunotherapy is unable to break specific T-cell tolerance in tumor-bearing hosts. Studies in an autochthonous prostate cancer mouse model have shown that giving low-dose cyclophosphamide prior to a cell-based granulocytemacrophage-colony stimulating factor-secreting vaccine abrogates immune tolerance through augmentation of CD8+ T cell infiltration in the prostate, transient depletion of regulatory T cells (Tregs), and increased expression of dendritic cell maturation markers. Enhancement of antitumor immunity has also been observed in other preclinical models where cyclophosphamide was given in sequence with granulocytemacrophage-colony stimulating factor-secreting immunotherapy for the treatment of breast and pancreatic cancers. These preclinical data are supported by early-phase clinical trials combining GVAX with low-dose cyclophosphamide in pancreatic and breast cancers. Furthermore, emerging evidence suggests that androgen deprivation therapy (ADT) itself has profound effects on the host immune system, resulting in thymic regeneration and enhancement of antitumor immunity. In addition, preclinical and clinical studies demonstrate that ADT augments prostate cancer-specific immune responses induced by immunotherapy, suggesting that ADT may act synergistically with immunotherapy. Based on data from mouse models as well as human clinical trials, it has been suggested that prostate cancer immunotherapy may be most effective when administered in the setting of an androgen-suppressed environment. Building on these findings, investigators have designed a study to assess the use of ADT given alone or administered following immunization with low-dose cyclophosphamide and prostate GVAX, in patients undergoing radical prostatectomy. Investigators aim (1) to determine whether ADT is immunogenic in men with localized prostate cancer by evaluating T-cell infiltration in harvested prostate glands; (2) to determine whether administering ADT after low-dose cyclophosphamide and prostate GVAX augments immune infiltration into the prostate gland; and (3) to investigate whether this combinatorial immuno-hormonal approach is safe and feasible. Investigators hypothesize that the combination of ADT and cyclophosphamide/GVAX will produce significantly greater antitumor immune responses than would ADT used alone.