Tumor-infiltrating CD3- NK cells are more effective than CD3+ T cells in killing autologous melanoma cells.

We have studied the phenotype and functional activity of tumor-infiltrating lymphocytes (TIL) derived from eight human melanomas cultured for up to 60 d in the presence of recombinant IL-2. In the early period of the cultures, TIL were predominantly T cells of CD8+ phenotype and contained 10-30% of CD3- cells. Four of the five early TIL cultures tested in a cytotoxicity assay displayed a degree of MHC-unrestricted lysis on a series of autologous and allogenic melanoma cell lines as well as the K562 natural killer-sensitive target. With longer periods of time in culture, all TIL lines showed a decrease in lytic activity that was associated with the loss of CD3- cells. Thus, most of the killing of short-term TIL cultures appeared to be mediated by CD3- natural killer cells, whereas CD3+ T cells were found to be weak anti-tumor effectors. Even though the CD3+ T cells were not cytotoxic on K562 targets, their lytic activity (even weak) against melanoma cells appeared to be non-MHC restricted, and was blocked by anti-CD3 antibodies. In addition, cytotoxicity of the CD3+ TIL cultures was compared to that of a CD3-/NKH1+ cell line purified from peripheral blood. It was found that natural killer cells were much more potent than CD3+ TIL on the melanoma cell lines tested.