Leukemic B cells from seven patients with hairy cell leukemia (HCL), six of which contained the Tac antigen, were assayed in vitro for growth factor-mediated cell proliferation. The HCL cells showed typical phenotypic profiles by monoclonal antibody analysis. The tumor cells, which do not grow spontaneously in vitro, were found to proliferate in all but one case in response to partially purified B cell growth factor (BCGF) without anti-mu or Sac activation. Recombinant interleukin 2 however produced only a marginal response and could not support leukemic cell growth in vitro. BCGF, however, did stimulate in vitro cell growth and supported the establishment of continuous (greater than 60 d in vitro) in four of the seven HCL cases.

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