Recent accomplishments of our immunotherapy clinical trials include the following: PROSTVAC VACCINE: --- We recently reported the clinical results of a Phase I trial combining ipilimumab with a vaccine containing transgenes for prostate-specific antigen (PSA) and for a triad of costimulatory molecules (PROSTVAC) in patients with metastatic castration-resistant prostate cancer. Thirty patients were treated with escalating ipilimumab and a fixed dose of vaccine. Of 24 chemotherapy-naive patients, 58% had a PSA decline. Combination therapy did not exacerbate the immune-related adverse events associated with ipilimumab. We have now updated survival data and an evaluation of 36 immune cell subsets pre- and post-therapy. There were clear trends toward associations for longer OS and several immune cell subsets before immunotherapy. These results should be considered as hypothesis generating and should be further evaluated in larger immunotherapy trials. --- PROSTVAC is a novel vector-based vaccine designed to generate a robust immune response against PSA-expressing tumor cells. The purpose of this study was to present an overview evaluation of immune responses to the PSA-TRICOM vaccine platform, currently in phase III testing. Of 104 patients tested for T-cell responses, 57% (59/104) demonstrated a greater than or equal to 2-fold increase in PSA-specific T cells after vaccine (median 5-fold increase) compared with pre-vaccine, and 68% (19/28) of patients tested mounted post-vaccine immune responses to tumor-associated antigens not present in the vaccine (antigen spreading). --- Samarium-153-ethylene diamine tetramethylene phosphonate (Sm-153-EDTMP; Quadramet), a radiopharmaceutical, binds osteoblastic bone lesions and emits beta particles causing local tumor cell destruction. Preclinically, Sm-153-EDTMP alters tumor cell phenotype facilitating immune-mediated killing. This phase 2 multi-center trial randomized patients to Sm-153-EDTMP alone or with PSA-TRICOM vaccine. Eligibility required mCRPC, bone metastases, prior docetaxel and no visceral disease. No patient in the Sm-153-EDTMP alone arm achieved prostate-specific antigen (PSA) decline 30% compared with four patients (of 21) in the combination arm, including three with PSA decline 50%. Toxicities were similar between arms and related to number of Sm-153-EDTMP doses administered. These results provide the rationale for clinical evaluation of new radiopharmaceuticals, such as Ra-223, in combination with PSA-TRICOM. PANVAC VACCINE: --- The goal of this study was to determine if the combination of docetaxel and PANVAC vaccine could provide evidence of improved clinical outcomes in patients with metastatic breast cancer vs. docetaxel alone. This open-label randomized Phase II, dual-center trial was designed to enroll 48 patients with metastatic breast cancer to receive docetaxel with PANVAC (arm A) or 38 docetaxel alone (arm B). This pilot study was powered to detect a trend of approximately this magnitude toward improvement in PFS. The results suggest the combination of PANVAC with docetaxel in metastatic breast cancer may provide a clinical benefit. This study was hypothesis generating and provides both rationale and statistical assumptions for a larger definitive randomized study. PERIPHERAL IMMUNOSCORE: --- Tumor immunoscore analyses, especially for primary colorectal cancer and melanoma lesions, have provided valuable prognostic information. Metastatic lesions of many carcinoma types, however, are often not easily accessible. We hypothesized that immune cells in peripheral blood may differ among individual patients with metastatic disease, which, in turn, may influence their response to immunotherapy. We thus analyzed immune cell subsets within peripheral blood mononuclear cells to determine if a peripheral immunoscore would have any prognostic significance for patients prior to receiving immunotherapy. Patients with metastatic breast cancer were randomized to receive docetaxel +/- PANVAC vaccine. In another trial, prostate cancer patients with metastatic bone lesions were randomized to receive a bone-seeking radionuclide +/- PROSTVAC vaccine. Predefined analyses of classic immune cell types (CD4, CD8, NK, Tregs, MDSCs, and ratios) revealed no differences in progression-free survival (PFS) for either arm in both trials. Predefined analyses of refined immune cell subsets for which a biologic function had been previously reported also revealed no significant prognostic value in PFS in patients receiving either docetaxel or radionuclide alone; however, in patients receiving these agents in combination with vaccine, the peripheral immunoscore of refined subsets revealed statistically significant differences in PFS (P 0.001) for breast cancer patients receiving docetaxel plus vaccine, and in prostate cancer patients receiving radionuclide plus vaccine (P = 0.004). Larger randomized studies will be required to validate these findings. These studies, however, provide the rationale for the evaluation of refined immune cell subsets to help determine which patients may benefit most from immunotherapy. BRACHYURY: --- The nuclear transcription factor brachyury has previously been shown to be a strong mediator of the epithelial-to-mesenchymal transition (EMT) in human carcinoma cells and a strong negative prognostic factor in several tumor types. Brachyury is overexpressed in a range of human carcinoma as well as in chordoma, a rare tumor for which there is no standard systemic therapy. Preclinical studies have shown a recombinant Saccharomyces cerevisiae (yeast) vaccine encoding brachyury (GI-6301) can activate human T cells in vitro. A Phase I dose escalation trial enrolled 34 patients at 4 dose levels. Expansion cohorts were enrolled for analysis of immune response and clinical activity. We observed brachyury-specific T-cell immune responses in the majority of evaluable patients despite most having been heavily pretreated. No evidence of autoimmunity or other serious adverse events were observed. Two chordoma patients showed evidence of disease control (one mixed response and one partial response). A patient with colorectal carcinoma, who enrolled on study with a large progressing pelvic mass and rising carcinoembryonic antigen (CEA), remains on study for greater than 1 year with stable disease, evidence of decreased tumor density and decreased serum CEA. This study is the first-in-human to demonstrate the safety and immunogenicity of this therapeutic cancer vaccine and provides rationale for exploration in Phase II studies. A randomized Phase II chordoma study is enrolling.
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