Allogeneic Melanoma Vaccine Expressing αGal Epitopes Induces Antitumor Immunity to Autologous Antigens in Mice Without Signs of Toxicity

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Abstract

Owing to the absence of αGal epitopes in human cells and constant stimulation of the immune system by the symbiotic bacterial flora, humans develop high titers of natural antibodies against these epitopes. It has been demonstrated that syngeneic whole cell vaccines modified to express αGal epitopes could be used to generate a potent anticancer vaccine. In this study, we tested whether allogeneic whole cell cancer vaccines modified to express αGal epitopes would be effective for the treatment of murine melanoma. The α(1,3)galactosyltransferase (αGT) knockout mice (H-2b/b) with preexisting subcutaneous and pulmonary tumors [αGal(−) B16, H-2b/b] received therapeutic vaccinations with S91M3αGal(+) (H-2d/d) whole cell allogeneic vaccines. These mice had better survival and reduced pulmonary metastasis burden compared with control mice treated with S91M3 vaccine cells. Vaccination with S91M3αGal-induced cytotoxic CD8+ T cells recognizing the syngeneic αGal(−) B16 tumors measured by adoptive transfer to recipients bearing pulmonary metastases. The presence of allo-antigens did not dominate the induction of immunity to “cryptic” tumor antigens and had helped in the generation of a more efficient vaccine to treat preexisting tumors when compared with classic autologous vaccines. Vaccination with allogeneic αGal(+) vaccines did not induce signs of toxicity including changes in weight, hematology, chemistry, and histopathology of major perfused organs or autoimmunity in long-term murine models for breast, lung, and melanoma. This study established the safety and efficacy data of allogeneic αGal(+) whole cell vaccines and constituted the basis for the initiation of human clinical trials to treat human malignancies.

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