B cell maturation in chronic lymphocytic leukemia. III. Effect of recombinant cytokines on leukemic B cell proliferation.

Proliferation and differentiation of B lymphocytes is influenced by a variety of soluble mediators. The recent cloning of various cytokines has made it possible to study the effect of molecularly defined lymphokines and other cytokines on B-cell activation. In the present study, we have analyzed the effect of several cytokines on the in vitro proliferation of highly purified leukemic B cells from patients with chronic lymphocytic leukemia (CLL). The recombinant human cytokines tested included interleukins 1, 2, 3, and 4 tumor necrosis factor-alpha (TNF-alpha) and interferon-alpha (IFN alpha), all of which are known to play a role in B-cell activation. B cells from 10 of 13 patients (all with white blood cell counts greater than 100,000/ul) did not respond to any of the cytokines tested. In contrast, B cells from 3 other patients responded well to IL-2 when preactivated for 24 h with phorbolester TPA and ionomycin. Moreover, preactivated B cells from 2 of these patients also proliferated in response to TNF-alpha, and some proliferation of unactivated B cells in response to TNF-alpha was seen in one case. Together, these results stress the clonal heterogeneity of CLL B-cell populations, and demonstrate that both IL-2 and TNF-alpha may act as a B-cell growth factor on B cells from certain CLL patients.