One recurrent finding in recent large controlled immunotherapies studies for cancer has been improved overall survival (OS) without an improvement in median progression free survival (PFS). This provides a hurdle for timely completion of proof-of-concept efficacy studies. This lack of improvement in PFS with eventual demonstration of improved OS may be due to the time-lag between administering the immunotherapy and a clinically significant immune-mediated slowing of the growth-rate of the tumor. Approval of the first therapeutic cancer vaccine has conferred higher priority on the effort to augment the immunologic impact of novel experimental therapeutic vaccines with other therapies. Careful preclinical studies have highlighted the ability of standard therapies to a) kill cells in an immunologically relevant manner and b) change the phenotype of surviving cells to make them more susceptible to immune mediated recognition and killing. This has led to rationally designed studies combining therapeutic cancer vaccines with standard therapies. These recent preclinical and clinical studies have demonstrated the ability to mount immune responses to vaccine despite standard therapies (e.g., chemotherapy). These combination studies provide a platform for testing the ability of combination strategies to impact more traditional phase 2 endpoints such as PFS. If the above hypothesis on growth rate is correct, it suggests that if one could rationally combine therapeutic vaccines (associated with delayed effects) with standard therapies (associated with early but transient decrease in tumor volume) in a manner that doesnt decrease the immune responses, then one might be able to use events such as PFS to discriminate between standard of care and combination regimens. Vaccine plus standard of care therapies Preliminary data from 2 ongoing prostate cancer trials and a breast cancer study support this hypothesis. The prostate cancer trials suggesting an improvement in time to progression (TTP) for the combination are Quadramet +/- PROSTVAC vaccine (2.1 vs 3.9 months, n=32) and flutamide +/- PROSTVAC vaccine (84 vs 161 days, n=26);and the breast cancer trial compares docetaxel +/- PANVAC vaccine with preliminary data favoring the combination (2.9 vs 8.0 months, n=21). Thus rationally designed combination studies have the potential to significantly speed up efficacy analysis in proof-of-concept efficacy studies (phase 2). This approach may be especially useful in tumors with an increasing number of therapies available that impact OS, and earlier in the disease course when follow-up for survival is more remote. Final analysis of ongoing studies may ultimately help determine the utility of this approach. Vaccine plus experimental therapies Monoclonal antibodies have been combined with vaccines for the treatment of various tumor types. In prostate cancer, a human cytotoxic T-lymphocyte antigen-4 (CTLA-4) mono-clonal antibody has been tested in combination with vaccines. CTLA-4 is a T-cell surface glycoprotein that is upregulated following T-cell activation to inhibit the immune response. Its main function is to prevent autoimmunity by regulating the bodys immune activity. T cells express two counteracting receptors on their cell surface CD28 and CTLA-4. Both bind to the same ligands or costimulatory molecules on the surface of APCs (B7.1 and B7.2, also known as CD80 and CD86). Binding of these costimulatory molecules to CD28 activates T cells, while interacting with CTLA-4 inhibits T-cell stimulation. Blocking CTLA-4 with a neutralizing antibody has been shown to sustain and potentiate immune responses. A Phase I study of ipilimumab, an anti-CTLA-4 monoclonal antibody, and GVAX in 16 patients with metastatic prostate cancer suggested a correlation between immune-related adverse events and immune response . Another Phase I trial, with results soon to be published, combined ipilimumab and PSA-TRICOM vaccine in metastatic prostate cancer patients. An interim analysis demonstrated a significant increase in PSA doubling time (from 2.6 months pre-study to 11.4 months post-study;p = 0.01) in 11 patients at a dose of 10 mg/kg. Dr. Gulley and his colleagues in the Laboratory of Tumor Immunology and Biology (LTIB) and the Medical Oncology Branch (MOB), Center for Cancer Research (CCR), NCI, have ongoing or recently completed in FY10-11 the following combination vaccine clinical trials at the NCI Clinical Center. A randomized Phase II trial combining vaccine therapy with PROSTVAC/TRICOM and Flutamide, vs. Flutamide alone in men with androgen insensitive non metastatic (D0.5) prostate cancer, MOB, CCR, NCI. This was the first randomized trial to combine a vaccine with this second-line hormone therapy in D0.5 prostate cancer patients. A phase I Trial of a PSA based vaccine and an anti-CTLA-4 antibody in patients with Metastatic Androgen Independent Prostate Cancer. This trial is the first clinical trial to combine an anti-CTLA-4 antibody and a vector-based vaccine in prostate cancer. A manuscript on this study has been submitted for publication. A randomized phase 2.5 study of 153Sm-EDTMP (Quadramet) with or without a PSA/TRICOM vaccine in men with androgen-insensitive metastatic prostate cancer, MOB, CCR, NCI. This trial is the first clinical trial to combine vaccine with a bone seeking radionuclide for use in patients with androgen independent prostate cancer. A randomized Pilot Phase II study of Docetaxel alone or in combination with PANVAC-V (vaccinia) and PANVAC-F (fowlpox) in adults with metastatic breast cancer. MOB, CCR, NCI. This is the first randomized trial to combine vaccine with Docetaxel in this breast cancer patient population. Collaborative Trials with Extramural Cancer Centers A Phase I study of sequential vaccinations with fowlpox-CEA(6D)-TRICOM and vaccinia-CEA(6D)-TRICOM, in combination with GM-CSF and Interferon-Alfa-2B in patients with CEA expressing carcinomas. (Ohio State Comprehensive Cancer Center) A phase II study of vaccine followed by standard chemotherapy vs. standard chemotherapy in patients with metastatic castration-resistant prostate cancer. (Eastern Cooperative Oncology Group). We are currently in discussions with the RTOG on a multi-center cooperative group study of Alpharadin and PSA-TRICOM for patients with bone metastasis based on the preliminary results of the Quadramet with or without vaccine study.
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