A critical role for natural killer T cells in immunosurveillance of methylcholanthrene-induced sarcomas.

Natural killer (NK) T cells initiate potent antitumor responses when stimulated by exogenous factors such as interleukin (IL)-12 or alpha-galactosylceramide (alpha-GalCer), however, it is not clear whether this reflects a physiological role for these cells in tumor immunity. Through adoptive transfer of NK T cells from wild-type to NK T cell-deficient (T cell receptor [TCR] Jalpha281-/-) mice, we demonstrate a critical role for NK T cells in immunosurveillance of methylcholanthrene (MCA)-induced fibrosarcomas, in the absence of exogenous stimulatory factors. Using the same approach with gene-targeted and/or antibody-depleted donor or recipient mice, we have shown that this effect depends on CD1d recognition and requires the additional involvement of both NK and CD8+ T cells. Interferon-gamma production by both NK T cells and downstream, non-NK T cells, is essential for protection, and perforin production by effector cells, but not NK T cells, is also critical. The protective mechanisms in this more physiologically relevant system are distinct from those associated with alpha-GalCer-induced, NK T cell-mediated, tumor rejection. This study demonstrates that, in addition to their importance in tumor immunotherapy induced by IL-12 or alpha-GalCer, NK T cells can play a critical role in tumor immunosurveillance, at least against MCA-induced sarcomas, in the absence of exogenous stimulation.