Defect of NK activity in children with untreated acute lymphocytic leukemia (ALL). I. Dependence on the blast count and phenotype, and response to exogenous and endogenous alpha-interferon.

Endogenous NK-activity (eNK) against K-562 cells was determined in peripheral blood of 68 children with acute lymphocytic leukemia (ALL) before treatment. In 53% of them it was depressed, and in 47% it was within the range of control children (27) and adults (104). There was a significant negative correlation between blast contamination of peripheral blood and the level of eNK-activity. In spite of this general trend, 8 patients with high blast count have had normal eNK-activity, and 10 patients with relatively low blast count (below 50%) have had depressed eNK-activity. Examples of T ALL showed significantly lower eNK-activity than CALLA ALL. The ability of exogenous alpha-interferon (IFN) to stimulate eNK-activity was impaired in 18 of 40 examples of ALL and preserved in 22. The IFN-induced NK-response was also negatively correlated to the blast burden, but again with exceptions: Six nonresponders in spite of low blast count, and six responders in spite of high blast count in peripheral blood. IFN-inducer, poly-IC, stimulated eNK-activity only in 6 of 26 ALL samples. Surprisingly, positive correlation was found between poly-IC-induced NK-stimulation and blast count in peripheral blood. Poly-IC induced significant IFN production only in one of six cultures of ALL. Impaired eNK-activity has been attributed, in part, to "dilution" of NK cells by the blasts. Defects in production of IFN, and in response to it, may be additional reasons for depressed NK-activity in about 50% of children with untreated ALL.