Enhancing efficacy of recombinant anticancer vaccines with prime/boost regimens that use two different vectors

Abstract

Background: The identification of tumor-associated antigens and the cloning of DNA sequences encoding them have enabled the development of anticancer vaccines. Such vaccines target tumors by stimulating an immune response against the antigens. One method of vaccination involves the delivery of antigen-encoding DNA sequences, and a number of recombinant vectors have been used for this purpose. To optimize the efficacy of recombinant vaccines, we compared primary and booster treatment regimens that used a single vector (i.e., homologous boosting) with regimens that used two different vectors (i.e., heterologous boosting). Methods: Pulmonary tumors (experimental metastases) were induced in BALB/c mice inoculated with CT26.CL25 murine colon carcinoma cells, which express recombinant bacterial β-galactosidase (the model antigen). Protocols for subsequent vaccination used three vectors that encoded β-galactosidase-vaccinia (cowpox) virus, fowlpox virus, naked bacterial plasmid DNA. Mouse survival was evaluated in conjunction with antibody and cytotoxic T-lymphocyte responses to β- galactosidase. Results: Heterologous boosting resulted in significantly longer mouse survival than homologous boosting (all P