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Lysis of fresh human B‐lymphocyte‐derived leukemia cells by interferon‐activated natural killer (NK) cells

Fresh neoplastic B cells from 14 untreated patients with naturally occurring B‐cell leukemias were found to be susceptible to lysis by human natural killer (NK) cells. The observed lysis of the fresh, non‐cultured, neoplastic B cells was mediated by a population of interferon‐augmentable, FcR‐positive, non‐adherent lymphoid cells, which were also able to kill the “standard” NK target K562. A further finding was the correlation of NK susceptibility with disease activity in 11 patients with chronic lymphocytic (CLL) and one patient with lymphosarcoma cell leukemia (LSCL). Enriched neoplastic B cells from seven untreated patients with non‐progressive CLL, whose disease activity was stable throughout the 6 month period of study, exhibited persistent and essentially unchanged NK susceptibility profiles. In contrast, four untreated patients with progressive CLL also had a measurable fraction of NK‐susceptible, neoplastic targets, but these cells subsequently disappeared after successful cytoreductive therapy, and later re‐emerged when these patients again developed progressive disease. Furthermore, one patient with LSCL was found to have persistent, measurable NK susceptibility in his tumor‐enriched fraction after unsuccessful cytoreductive therapy. An additional finding in the peripheral blood of patients with chronic B‐cell leukemias was the presence of significantly lower NK effector‐cell activity against K562 as compared to normal donor peripheral blood lymphocytes (PBLs). The implications of these findings are discussed.