Requirement for Valpha14 NKT cells in IL-12-mediated rejection of tumors.

A lymphocyte subpopulation, the Valpha14 natural killer T (NKT) cells, expresses both NK1.1 and a single invariant T cell receptor encoded by the Valpha14 and Jalpha281 gene segments. Mice with a deletion of the Jalpha281 gene segment were found to exclusively lack this subpopulation. The Valpha14 NKT cell-deficient mice could no longer mediate the interleukin-12 (IL-12)-induced rejection of tumors. Although the antitumor effect of IL-12 was thought to be mediated through natural killer cells and T cells, Valpha14 NKT cells were found to be an essential target of IL-12, and they mediated their cytotoxicity by an NK-like effector mechanism after activation with IL-12.