Induction of Proliferation and Differentiation of Leukaemic B Cells from Patients with Chronic Lymphocytic Leukaemia by Anti-mu and Conditioned Medium

We investigated the growth and differentiation of leukaemic B cells from patients with B-cell chronic lymphocytic leukaemia (CLL) in response to proliferation and differentiation factors present in conditioned medium and to anti-immunoglobulin antibodies. Highly purified E-rosette negative (E) B cells from 5 out of 15 patients with CLL exhibited moderate proliferative responses to Ml or 10 or 15 μ/ml of F(ab′)2 fragments of rabbit anti-human μ-chain specific antibody. Conditioned medium (CM), derived by stimulating human peripheral blood mononuclear leucocytes with PHA. induced significant proliferative responses of purified E cells in 13 out of 14 patients examined. The extent of these proliferative responses varied substantially, and was in the range of 2.6- to 91-fold. Stimulation of purified L cells trom patients with CLL with both anti-μ and CM resulted in significant proliferative in all l5 patients examined. These responses were significantly higher than thosc induced by CM alone (P<0.02). Synergism between CM and anti-μ in inducing proliferative responses was observed in 11 out of 15 patients. Largely loukaemic B cell populations expressing on the cell surface more than one immunoglolobulin heavy chain isotype, exhibited significantly higher (P<0.009) proliferaiive response to CM and anti-μ than those expressing IgM only. Highly purified E- peripheral blood or tonsil lymphocytes from all normal donors examined responded by proliferation to anti-μ alone or to CM alone. Synergism in inducing prolifcrative responses was aiso observed when the cells were stimulated with both CM and anti-μ. In addition to inducing proliferative responses, culture with CM of purified E-rosctte negative, largely leukaemic, B cells from patients with CLL for 6 days at 37°C resulted in differentiation into immunoglobulin synthesizing and secreting cells. Synthesis and secretion of IgM were observed in 7 out of 10 patients examined. A switch to IgG production was observed in three patients. Morphological examination of E cells from patients wiih CLL after treatment wiih CM dcmonstrated thai these cells were differentiated into plasma-like cells. These results suggest that leukaemic B cells from palicnls with CLL can be induced to proliferate and differentiate in response to growth and differentiation factors derived by mononuclear Icucocytes. in a manner similar to that of normal B cells.