Vaccination of Colorectal Cancer Patients with Modified Vaccinia Ankara Encoding the Tumor Antigen 5T4 (TroVax) Given Alongside Chemotherapy Induces Potent Immune Responses

Purpose: The attenuated strain of vaccinia virus, modified vaccinia Ankara (MVA) encoding the tumor antigen 5T4 (TroVax), has been evaluated in an open-label phase II study in metastatic colorectal cancer patients. The primary objective was to assess the safety and immunogenicity of TroVax injected before, during, and after treatment with cycles of 5-fluorouracil, folinic acid, and oxaliplatin. Experimental Design: TroVax was administered to 17 patients with metastatic colorectal cancer. In total, 11 patients were considered to be evaluable for assessment of immunologic responses having received a total of six injections of TroVax, administered before, during, and following completion of chemotherapy. Antibody and cellular responses specific for 5T4 and MVA were monitored throughout the study. Results: Administration of TroVax alongside 5-fluorouracil, folinic acid, and oxaliplatin was safe and well tolerated with no serious adverse events attributed to TroVax. Ten of the 11 evaluable patients mounted 5T4-specific antibody responses with titers ranging from 10 to >1,000. IFNγ enzyme-linked immunospot responses specific for 5T4 were detected in 10 patients with precursor frequencies exceeding 1 in 1,000 peripheral blood mononuclear cells in 4 patients. Of the 11 evaluable patients, 6 had complete or partial responses. 5T4-specific immune responses, but not MVA-specific immune responses, correlated with clinical benefit. Conclusions: Potent 5T4-specific cellular and/or antibody responses were induced in all evaluable patients and were still detectable during the period in which chemotherapy was administered. These results suggest that TroVax can be added to chemotherapy regimens without any evidence of enhanced toxicity or reduced immunologic efficacy and may provide additional clinical benefit.