The effects of intercellular adhesion molecule-1 (ICAM-1) expression on-tumor rejection and induction of antitumor immunity in a murine melanoma system was studied. K1735 melanoma cells genetically engineered to express the murine ICAM-1 gene were rejected in immunocompetent hosts, and that this rejection was mediated by CD4(+) as well as by CD8(+) T lymphocytes. We also found that ICAM-1 transfected tumor cells provided costimulatory signals to both CD4(+) and CD8(+) T cells in vitro. In addition, immunization of mice with K1735-ICAM-1 transfectants induced protective immunity against the parental ICAM-1-negative tumor. Our findings suggest that ICAM-1 expression on nonimmunogenic tumor cells causes tumor rejection and augments tumor-specific immunity.

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