IL-2-dependent HTLV-I-infected T cells escape from non-specific, MHC-unrestricted cellular cytotoxicity.

The susceptibility of NK cell-mediated cytolysis was compared between 5 human HTLV-I-transformed T cell lines and 10 newly established IL-2-dependent HTLV-I-infected lines. None of the cell lines were killed after 4 hr incubation with normal PBMC. However, after 20 hr, 3 HTLV-I-transformed lines were significantly lysed. All the HTLV-I-infected lines, except 2, weakly inhibited the NK cell-mediated lysis of K562 targets. They showed a reduced ability to bind normal PBMC as compared with control NK-sensitive T cell lines. The IL-2-dependent lines remained unaffected by PBMC from HTLV-I-infected individuals, including the autologous donors. In contrast to the HTLV-I-transformed lines, they were weakly lysed or not lysed at all by LAK cells and only 5 were killed by ADCC with HTLV-I+ sera and normal PBMC. Taken together, the results show that IL-2-dependent HTLV-I-infected T cells strongly resist NK cell-mediated cytolysis at a post-binding level and suggest that such cells may escape in vivo from non-specific, MHC-unrestricted cellular cytotoxicity.