Benign monoclonal B cell lymphocytosis--a benign variant of CLL: clinical, immunologic, phenotypic, and cytogenetic studies in 20 patients.

From 1951 through 1978, we have seen 20 cases of stage O chronic lymphocytic leukemia (CLL) without disease progression for 6.5-24 years. The cohort included 7 males and 13 females, aged 48-77 years at the time of diagnosis. None presented with anemia, thrombocytopenia, or neutropenia nor developed cytopenias during follow-up. Mean total lymphocyte count in these patients was 20,100/microL, with ranges from 10,000 to 43,700 at the time of diagnosis, and was 20,600, with ranges from 1,000 to 47,200, at last follow-up. Of 12 patients studied, 8 and 4 were phenotyped as heavy chain mu delta- and mu-type, respectively, with 7 kappa- and 4 gamma-type (no light chain was detectable in one patient). Of 13 patients studied, one had a slightly elevated IgG level and two had slightly depressed serum IgA and IgM levels. All patients had positive delayed hypersensitivity responses to at least one of five skin test antigens. Each of seven patients studied for an in vitro leukocyte thymidine uptake had a low level of [3H]thymidine incorporation. Nine of 12 patients studied had elevated total T cells, and the remaining 3 had normal T cell counts. In vitro unseparated lymphocyte response to phytohemagglutinin showed normal kinetics of DNA synthesis, with a peak response on day 3 or 4 of culture in 4 and slightly or moderately depressed and/or delayed kinetics in 8 patients studied. Cytogenetic analyses by Q- or G-banding techniques of polyclonal B cell mitogen-stimulated lymphocytes in all six patients studied showed normal karyotypes. These data are consistent with a previously undescribed syndrome involving a monoclonal B cell lymphocytosis, a prolonged asymptomatic or benign clinical course, and essentially normal humoral and cellular immunity and normal karyotype. Our observations indicate that these 20 patients with stage O CLL have a benign clinical course and that they may also be designated as benign monoclonal B cell lymphocytosis ( BMBL ), a benign variant of CLL.