Beta 2M-/- knockout mice contain low levels of CD8+ cytotoxic T lymphocyte that mediate specific tumor rejection.

C57BL/6 mice with a disrupted beta 2M gene (beta 2M-/- mice) express very low levels of MHC class I molecules and are deficient for CD8+ T lymphocytes. Because CD8+ T cells are thought to be a principle effector cell in tumor rejection, we have assessed the ability of beta 2M-/- mice to respond to tumors. beta 2M-/- knockout mice were challenged with seven independent MHC allogeneic and syngeneic tumors. The beta 2M-/- mice responded very similarly to their CD8+ beta 2M+/- littermates in that they rejected high dose challenges of 4/5 allogeneic tumors and were susceptible to 3/3 syngeneic tumors. In vivo depletion of CD4+ or CD8+ cells from the beta 2M-/- mice resulted in susceptibility to allogeneic tumor. The apparent requirement for CD8+ cells for tumor immunity was corroborated by in vitro assays in which depletion of CD8+ but not CD4+ T cells eliminated tumor-specific CTL activity. mAb blocking studies in which target tumor cells were incubated with MHC class I-specific mAb demonstrated that the tumor-specific CD8+ activity was MHC class I restricted. beta 2M-/- mice therefore contain very small quantities of potent, CD8+ T cells that are capable of rejecting large challenges of allogeneic tumor cells.