The Induction of Enhanced Antitumor Effect against a Nonimmunogenic Tumor by Highly Immunogenic Variants Obtained by Mutagen Treatment

Nonimmunogenic 1767‐3 fibrosarcoma was treated with the mutagen N‐methyl‐N′‐nitro‐N‐nitrosoguanidine, and stable variant cell clones (M‐clones) were obtained that were able to elicit an immunological rejection response in syngenic C3H mice. Mice immunized with some M‐clones were protected against a challenge from the original nonimmunogenic fibrosarcoma. Furthermore, when spleen cells of immunized syngenic mice were restimulated in vitro with M‐clones, cytotoxic T lymphocytes (CTL) were obtained that were able to lyse not only M‐clones but also the original nonimmunogenic tumor. These in vivo and in vitro results demonstrate the immunogenicity of M‐clones and the existence of a singular antigenic specificity between the original nonimmunogenic tumor and M‐clones. For the purpose of application of this mutagen treatment to cancer therapy, we combined it with lymphokine‐activated killer (LAK) adoptive immunotherapy (AIT). With interleukin 2 and in vitro stimulation with highly immunogenic variant clones, we tried to induce transfer cells that had not only nonspecific LAK cells but also CTL with specific immunity against the original nonimmunogenic tumor. Successful results were obtained in the LAK AIT models. These findings indicate that an immunotherapy of human cancers that are thought to be weakly or nonimmunogenic may be possible by the application of this approach to LAK AIT.