Induction of tumor NK-cell immunity by anti-CD69 antibody therapy

The leukocyte activation marker CD69 is a novel regulator of the immune response, modulating the production of cytokines including transforming growth factor-beta (TGF-beta). We have generated an antimurine CD69 monoclonal antibody (mAb), CD69.2.2, which down-regulates CD69 expression in vivo but does not deplete CD69-expressing cells. Therapeutic administration of CD69.2.2 to wild-type mice induces significant natural killer (NK) cell-dependent antitumor responses to major histocompatibility complex (MHC) class I low RMA-S lymphomas and to RM-1 prostatic carcinoma lung metastases. These in vivo antitumor responses are comparable to those seen in CD69(-/-) mice. Enhanced host NK cytotoxic activity correlates with a reduction in NK-cell TGF-beta production and is independent of tumor priming. In vitro studies demonstrate the novel ability of anti-CD69 mAbs to activate resting NK cells in an Fc receptor-independent manner, resulting in a substantial increase in both NK-cell cytolytic activity and interferon gamma (IFNgamma) production. Modulation of the innate immune system with monoclonal antibodies to host CD69 thus provides a novel means to antagonize tumor growth and metastasis.