Circulating lymphokine-activated killer (LAK) cell activity in cancer patients receiving recombinant interleukin 2 (rIL-2) therapy is confined to cells expressing the CD56 surface marker. However, CD56- cells from these patients but not normal individuals have been reported to exhibit LAK cytotoxicity only following in vitro activation with rIL-2. Studies were performed to document the existence of CD56- LAK precursor cells and to phenotypically characterize this population in patients receiving rIL-2 therapy using fluorescence-activated cell sorter-purified CD56- cell subsets. Initial studies confirmed that CD56- cells exhibit NK activity [20 ± 7 (SE) LU/106 cells] but not LAK activity (0 ± 0 LU/106 cells) when evaluated directly from peripheral blood of patients receiving rIL-2. CD56- cells from patients but not normal individuals developed significant LAK cytolytic activity against NK-resistant COLO 205 targets (16 ± 3 LU/106 cells) when cultured for 3 days with 1500 units/ml rIL-2. The CD56-∼ LAK precursor activity was confined to cells expressing a CD56-CD16+ phenotype and a large granular lymphocyte morphology; little or no NK or LAK precursor activity was detectable in CD56-CD5+ T-cells from patients. Phenotypic characterization of CD16+CD56- cells revealed that this population is uniformly CD11a+, CD18+, and CD38+ and is heterogeneous in its expression of CD11b, CD11c, and CD16/Leu 11c. These results indicate that rIL-2 administration induces enhanced LAK precursor activity in a novel population of CD5-CD16+CD56- cells.
Supported by Grant CA48069 from the National Cancer Institute.