INHIBITION OF LEUKEMIC-CELL PROLIFERATION BY ONE OR MORE FACTORS RELEASED FROM SPLENIC BCL(1) CELLS

Irradiated peripheral blood lymphocytes from patients with chronic B-l ymphocytic leukemia (B-CLL) have been shown to secrete a factor or fac tors that caused inhibition of malignant cell proliferation. In the pr esent study, we used the murine B cell leukemia (BCL(1)) model system to examine the possible secretion of inhibitory factors from irradiate d leukemic spleen cells. It was found that under culture conditions, i rradiated spleen cells obtained from leukemic mice produce factors cap able of suppressing BCL(1) cell proliferation in vitro. The release of an inhibitory factor from nonirradiated cells was also observed, albe it to a lower extent. Supernatants collected from cultured nonirradiat ed and irradiated cells derived from animals at the first week after B CL(1) cell inoculation did not affect the proliferation capacity of ce lls at any stage of the disease, whereas supernatants obtained at more advanced stages exhibited an inhibitory effect on the proliferation o f cells derived from the same stages. The suppressive effect of supern atants of irradiated cells was more pronounced when those of 7 days' c ulture were used, compared to those of nonirradiated cells. The differ ence in suppression observed between supernatants of irradiated and no nirradiated BCL(1) cells may be attributed either to the same factor p roduced in a larger amount following irradiation or to two (or more) f actors-one produced spontaneously, the other induced by irradiation.