Lymphokine-activated killer activity induced by in vivo interleukin 2 therapy: predominant role for lymphocytes with increased expression of CD2 and Leu19 antigens but negative expression of CD16 antigens

The phenotype and function of lymphocytes from cancer patients treated with repetitive weekly cycles of continuous i.v. infusions of recombinant interleukin 2 (IL-2) were examined. Peripheral blood lymphocytes (PBL) obtained after IL-2 therapy showed an increased percentage of cells bearing the CD16 and leu19 markers which are associated with natural killer cells. These PBL mediated significantly increased levels of IL-2-dependent lymphokine-activated killer (LAK) activity against the Daudi cell line. Depletion of CD16+ cells from PBL obtained after in vivo IL-2 caused only slight inhibition of their LAK activity or their proliferative response to IL-2 in vitro. This indicates that CD16+ cells are involved but play only a minor role in these responses. In contrast, depletion of leu19+ cells, from PBL activated in vivo with IL-2, virtually abrogated their LAK activity and their proliferative response to IL-2. Two-color flow cytometry studies showed that a leu19+/CD16- population was expanded by in vivo IL-2 therapy and was responsible for the majority of LAK activity by in vivo-activated PBL. Moreover, this CD16- population showed an increased density of leu19 and CD2 (E rosette receptor) antigens when compared to the resting PBL obtained prior to IL-2 treatment. These data show that the predominant population mediating in vitro LAK activity, induced by in vivo IL-2 therapy, consists of activated natural killer cells with a high density of leu19 and CD2 antigens but negative for the CD16 antigen.