Analysis of T-cell-derived factors with the use of B-prolymphocytic leukemia cells

Mononuclear cells of five patients with B-prolymphocytic leukemia were tested for their functional capacities in vitro after stimulation. Leukemic B cells from these patients have a mature phenotypic marker profile and can be obtained in high numbers from peripheral blood. B cells of all five patients proliferated in response to phorbol myristate acetate. In one patient, this proliferation was strongly enhanced by the addition of T-cell-conditioned medium. Conditioned medium by itself or interleukin 2 in the presence or absence of the phorbol ester was not active. This enabled us to develop an assay for a B-cell growth factor different from interleukin 2. Next to their proliferative capacities, we found that malignant B cells of three of the five patients secreted large amounts of IgM when stimulated with pokeweed mitogen or interleukin 2 in the presence of allogeneic T cells. In the absence of these allogeneic cells, neither pokeweed mitogen nor interleukin 2 had any effect. However, T-cell-conditioned medium as well as the supernatants of two T-cell hybridomas induced strong IgM production in the absence of T cells. Thus, neoplastic B cells of some patients with B-prolymphocytic leukemia can be stimulated to proliferation and differentiation in vitro and can be used as an assay and model system to study the effect of T cells and/or T-cell factors in human B-cell activation.