High frequency of precursors of anomalous killer cells in human peripheral blood: evidence for T-cell regulation.

The frequency of precursors (P) of the anomalous killer (AK) cells able to kill a melanoma target cell line without prior sensitization was determined by limiting dilution analysis. The frequencies obtained from the peripheral blood mononuclear cells of six healthy individuals ranged from 1/250 to 1/750, which was considerably higher than those of alloreactive cytolytic T-lymphocyte (CTL) precursors induced in the same cultures (range 1/900 to 1/7500). The presence of phytohemagglutinin (PHA) inhibited the appearance of both CTL and AK in bulk cocultures, and in limiting dilution analysis the presence of the lectin resulted in multiphasic cell dose-response curves rather than linear single hit responses for both types of precursor cells. The results suggest that AK-P are under the same type of regulation as are CTL-P.