Human lymphokine-activated killer (LAK) cells: identification of two types of effector cells

We analyzed the antigenic phenotype of lymphokine-activated killer (LAK) effector cells. Human blood lymphocytes were cultured for 3 days with 100 U/ml recombinant interleukin 2 (rIL 2), subpopulations isolated with monoclonal antibodies and a fluorescence-activated cell sorter (FACS) and assayed for cytotoxic activity against 51chromium labeled noncultured melanoma tumor cells. Initial experiments compared the LAK effector function of CD5+ T lymphocytes vs CD5- cells (predominantly CD16+ NK cells). The mean percent specific release at a 10:1 effector:target (E:T) ratio was 25% +/- 16 for CD5- cells, 10% +/- 6 for CD5+ cells, and 22% +/- 9 for unsorted cells. In contrast, when lymphocyte subpopulations were isolated before rIL 2 culture (LAK precursors), CD5- cells but not CD5+ cells developed LAK activity (28% +/- 12 vs 1% +/- 1, mean percent specific release, 10:1 E:T ratio), confirming our previous results showing that only CD16+ cells were LAK precursors. The discrepancy between LAK effector and precursor phenotypes suggested that LAK precursors acquired CD5 determinants during rIL 2 culture; however, double label immunofluorescence of rIL 2 cultured CD16+ cells showed that this was not the case. The data suggested that in the presence of other cell types, some T lymphocytes may develop LAK activity, but purified blood T lymphocytes do not develop LAK function when cultured with rIL 2 alone. We also analyzed LAK effector function in lymphocyte subpopulations defined by CD4 and CD8 antigens. The data showed that lymphocytes with a low density expression of CD8 and no expression of CD4 were enriched for LAK effector cells, whereas CD4+ and CD8- had less activity than unsorted cells. Lymphocytes with a high density expression of CD8 had activity similar to unsorted cells. We also assessed the contribution of Leu-7 (HNK-1) granular lymphocytes to LAK effector function. After culture with IL 2, lymphocytes were depleted of Leu-7+ cells by antibody and complement treatment and then were sorted into CD5+ and CD5- fractions. The cytotoxic activity of Leu-7-CD5+ cells was a mean 5% +/- 5 vs a mean 14% +/- 8 for the total CD5+ population (20:1 E:T ratio). The activity of Leu-7- CD5- was slightly less than the total CD5- fraction (21% +/- 9 vs 28% +/- 14, 10:1 E:T ratio). In conclusion, LAK effector function was highest in non-T cell (CD5- CD16+) populations and some activity was also present in T cell populations (CD5+ and predominantly Leu-7+).