A clonal analysis of human peripheral blood lymphocytes displaying natural killer-like activity

Abstract

Human Fcγ receptor‐bearing lymphocytes and T cells, prepared by sorting peripheral blood lymphocytes using the B73.1 monoclonal antibody, have been cloned by limiting dilution. Although quiescent lymphocytes of either cell type were unresponsive to interleukin 2 (IL2), following induction with phytohemagglutinin and/or the BSM B lymphoblastoid cell line they could be expanded in IL2 utilizing a mixed irradiated feeder system. Clones originating from B73.1⁺ lymphocytes displayed a characteristic large granular lymphocyte (LGL) morphology but were otherwise functionally and phenotypically heterogeneous. Of 36 clones analyzed 19 displayed significant natural killer (NK)‐like activity, each clone having a target cell repertoire identical to uncloned NK effectors. Furthermore, only a minority of clones (i.e. 5) displayed significant antibody‐dependent cellular cytotoxicity, while levels of lectin‐induced cellular cytotoxicity were normally commensurate with a clones level of NK‐like activity. No correlation was evident between the phenotype of a clone and its cytotoxic activity since of 12 cytotoxic clones phenotyped, 8 expressed the OKT3 antigen but lacked the B73.1 antigen; 2 lacked the OKT3 antigen but expressed the B73.1 antigen and one lacked both OKT3 and B73.1 antigens. In addition the expression of OKT8 and OKT4 antigens was not in any way predictive of the cytotoxic capacity of a given clone. Several clones expressing T cell associated antigens bore a phenotype that distinguished them from T cell clones insofar as T cell subset antigens were expressed in the absence of the OKT3 antigen and vice versa. Although prior to culture NK activity was restricted to B73.1⁺ lymphocytes, B73.1⁻ lymphocytes propagated in IL2 acquired an NK‐like cytotoxic capacity. Cloned effectors of B73.1⁻ provenance with NK‐like activity had a target cell repertoire indistinguishable from uncloned effectors. All T cell clones appeared agranular and were phenotypically much less diverse than their LGL counterparts, being OKT3⁺ and either OKT8⁺ or OKT4⁺. These data suggest that cells with NK‐like activity are broadly reactive with a number of NK‐susceptible targets, possibly recognizing a common determinant. However, cloned LGL display phenotypic heterogeneity with preferential expression of early hematopoietic and/or T cell antigens. Consequently, the antigen profile of many clones was uncharacteristic of resting LGL. Such observations support the contention that LGL attributed with NK‐like activity are heterogeneous with a majority acquiring T cell‐like characteristics after appropriate induction.