Mitogen-induced maturation of chronic lymphocytic leukemia B lymphocytes.

Peripheral blood lymphocytes from eight patients with untreated B-derived chronic lymphocytic leukemia (CLL) (only one had a serum monoclonal immunoglobulin) were stimulated by Nocardia, phytohemagglutinin, and pokeweed mitogen. This stimulation resulted in the occurrence in all but one case of large cytoplasmic immunoglobulin-containing cells with a predominantly lymphoblastic (six cases) or plasmacytic (one case) appearance. These blast cells contained the same immunoglobulin chains as those of the surface immunoglobulins on fresh lymphocytes except for delta chains that were not found by cytoplasmic immunofluorescence. In three cases, intracytoplasmic immunoglobulin inclusions that were present in both small lymphocytes and stimulated blast cells provided further evidence of the differentiation of the leukemic clone. In another case, both small leukemic B lymphocytes and large B blast cells expressed in vitro a receptor for sheep erythrocytes. A switch from IgM to IgG synthesis was observed in this patients, whose cells showed the strongest response to the activators. The most effective activator was Nocardia, then phytohemagglutinin, whereas an effect of pokeweed mitogen was observed only when the fresh lymphocytes contained a fair percentage of T cells. Leukemic cells, in most patients, were able to differentiate without appreciable B-cell proliferation.