Effect of pharmacological purging on natural killer cell number and activity in human bone marrow

We assayed natural killer (NK) cell activity and phenotype from human bone marrow (BM) following "purge" with 4-hydroperoxycyclophosphamide (4HC) at 60 micrograms/ml for 30 min in vitro. In all cases studied, lytic activity against the K562 cell line was either significantly decreased or abolished following 4HC purge. Although NK activity was significantly affected by 4HC treatment, no major differences in the phenotype between the purged and unpurged population were seen. Further, while in vitro culture of BM with IL2 resulted in a significant increment of NK activity, no IL-2 responsive cells were found in the 4HC purged BM after 14 days of culture. This study demonstrates that pharmacological purging of bone marrow results in a persistent functional decline of NK cell activity and may serve as a useful model for the study of the ontogeny of NK cells.