INHIBITION OF LEUKEMIC-CELL PROLIFERATION BY FACTOR(S) RELEASED FROM IRRADIATED LYMPHOCYTES OF B-CHRONIC LYMPHOCYTIC-LEUKEMIA PATIENTS

An attempt was made to clarify the mechanism by which splenic irradiation in patients with B-chronic lymphocytic leukemia (B-CLL) can induce a reduction in lymph node size. For this purpose peripheral blood lymphocytes from B-CLL patients were exposed to cobalt irradiation and were cultured for 1-8 days. The effect of the supernatants on the proliferation capacity of normal and malignant human cells was examined. A suppression of phytohemagglutinin (PHA)-induced proliferation of autologous and heterologous B CLL lymphocytes was observed, whereas there was no effect on the proliferation of lymphocytes obtained from healthy volunteers. In addition, supernatants of irradiated B-CLL lymphocytes inhibited thymidine incorporation into blasts derived from patients with acute leukemia and the lymphoblastoid cell line Daudi, but they did not exert any effect on normal cells obtained from human embryonic liver. These results suggest the secretion of some factor(s) by irradiated B-CLL lymphocytes, which may inhibit the proliferation of malignant cells but has no effect on normal cells. (C) 1994 Wiley-Liss, Inc.