Coexpression of H-2D^d and B7-1 on a B16 melanoma variant B78H1 promotes expansion and effector function of NK cells. (A) Profile of H-2D^d (open histograms) and B7-1 (shaded histograms) on 4 transfectants of MJ, the TAP-2-transfected B78H1 cells. (B) Proliferation of NK cells in RAG-1(-/-) C57BL/6j mice at 2 days after challenge with PBS or 4 transfectants depicted in (A). Data shown were representative dot plots of gated NK1.1⁺ cells from an experiment involving 2-3 mice per group. Numbers in the panels show the percent of cells in each quadrant. The enhanced proliferation of NK cells induced by MJ/B7/D^d tumor cells has been reproduced with 2 independent clones. (C) Coexpression of B7-1 and H-2D^d enhanced cytolysis of IL-15-activated NK cells. Note that a significant difference was observed between the lysis of M/J/D^d/B7 target and the next most susceptible target (M/J/B7). The results have been repeated 3 times. Data are means ± SEM. ^*P < 0.05. ^**P < 0.01.