Clonal chromosome changes in stimulated lymphocytes of untreated human B-cell leukemias

The chromosome constitution of peripheral blood lymphocytes from nine cases of B-cell chronic lymphocytic leukemia and one case of B-cell prolymphocytic leukemia were studied at diagnosis following stimulation by B- and T-cell activators. Chromosome analysis with banding techniques revealed an extra chromosome 12 (trisomy 12) in 4 B-cell chronic lymphocytic leukemia cases and complicated abnormalities, i.e., trisomy 12, 6q-, 14q+, and a translocation between chromosomes 6 and 12, [t(6; 12)] in the prolymphocytic leukemia case. These findings suggest that trisomy 12 is a prototypic change in B-cell leukemia, particularly in B-cell chronic lymphocytic leukemia. Based on sister chromatid exchange studies of unstimulated lymphocytes, it appears that some leukemia cells with a normal karyotype not only divide but also proliferate in vitro.