Depletion of natural killer cells in mice by monoclonal antibody to NK-1.1. Reduction in host defense against malignancy without loss of cellular or humoral immunity.

Weekly injections of a monoclonal antibody (MAb) to the antigen NK-1.1 were used to sustain depletion of NK cells from the spleens of adult C57BL/6 mice for up to 8 wk. Mice depleted of NK cells in this manner had no lasting alteration in the distribution of other lymphocyte subsets in the spleen and did not demonstrate reduced cellular or humoral immunity. Depletion of NK cells, however, markedly increased the localization and growth of B16 melanoma cells or CT 38 colon carcinoma cells in the lung after i.v. administration of tumor cells. Moreover, mice given B16 tumors and treated with anti-NK-1.1 had reduced survival. NK cells were important in host resistance to sublines of B16 that had been passaged either in vivo or in vitro, which express, respectively, high and low levels of class I major histocompatibility antigens. These findings support a role for NK cells in host defense against malignancy. The ability to selectively remove NK cells in vivo by MAb will permit a better understanding of their physiologic role.