IMMUNOSUPPRESSIVE ACTIVITY OF CLONED NATURAL-KILLER (NK1.1(-CELLS ESTABLISHED FROM MURINE TUMOR-INFILTRATING LYMPHOCYTES()) T)

To elucidate the role of NK1.1(+) T cells in the antitumor immune resp onse, we established cloned NK1.1(+) T cell lines from tumor-infiltrat ing lymphocytes (TIL) of B16 melanoma, and examined their mode of acti on in generating antitumor effector T cells both in vitro and in vivo. An NK1.1(+) T cell clone (TM4.2) was phenotypically CD3(+)TCR-alpha b eta(+)CD4(-)CD8(-)NK1.1(+), and CD28(+). The TM4.2 cells suppressed th e in vitro generation of anti-B16 melanoma CTLs, but not the effector function of CTLs. The results using a transwell membrane suggested tha t their suppressive activity was mediated by both soluble factors and a direct cell to cell interaction. As for the soluble factors, the sup pressive activity of the culture supernatant of TM4.2 cells was neutra lized by anti-TGF-beta mAb, and the TM4.2 cells actually produced a co nsiderable amount of TGF-beta. On the other hand, the TM4.2 cells show ed a high level of cytolytic activity against B cell blasts and CD80-t ransfected P815, and such cytolytic activity was reduced by the additi on of anti-CD80 mAb. In addition, NK1.1(+) T cells in the freshly isol ated TIL were revealed to express CD28. Furthermore, the TM4.2 cells s uppressed the in vitro generation of anti-allo CTLs irrespective of th e MHC haplotype. Finally, the TM4.2 cells suppressed the in vivo antit umor immune response. Collectively, these findings demonstrate that NK 1.1(+) T cells in TIL show immunosuppressive activity in the antitumor immune response through the production of TGF-beta and the preferenti al cytolysis of B7-expressing cells.