Human Cytotoxic T Lymphocytes

A limiting‐dilution system was established to measure the frequency of alloreactive cytotoxic T‐lymphocyte precursors (CTL‐p) in human peripheral blood T cells. Culture medium supple mented with recombinant interleukin‐2 enabled clonal expansion of all CTL‐p stimulated by allogeneic peripheral blood or spleen cells. The range of CTL‐p frequencies in fully HLA‐mismatched responder‐stimulator combinations was 1:240 to 1:1230. Split‐well analysis of individual microwells showed that the cytotoxic T‐cell clones generated under limiting‐dilution conditions showed exquisite specificity for the stimulating alloantigens. Alloreactive CTL‐p were enriched in the OKT4 T‐cell subset. This limiting‐dilution system was highly reproduci ble and can thus be applied to investigate human cytotoxic T‐eell precursor frequencies in various clinically relevant situations.