Evolution of cultured leukemic cell lines monitored by chromosomal and immunologic analysis

The authors have investigated the karyotypes and markers of B lymphocyte differentiation in 2 leukemic cell lines, NALM-6-B and NALM-6-Ml, both derived from a patient with non-T, non-B acute lymphoblastic leukemia. Both possess characteristics of thymus-independent, bursal-equivalent (B) lymphocytes. By means of immunofluorescence techniques, NALM-6-B was shown to possess 47% surface membrane immunoglobulin-positive (SIg ⁺) cells, while NALM-6-MP is surface membrane immunoglobulin-negative (SIg ^-), but does possess cytoplasmic immunoglobulin M (CIgM ⁺) in more than 90% of the cells. The SIg ^- CIgM ⁺ phenotype, coupled with morphologic features, is consistent with NALM-6-MP being arrested at a stage early in B-lymphocyte differentiation (a 'pre-B' cell). The predominant banded chromosome karyotype of NALM-6-B is pseudodiploid with a translocation of chromosomal material from the long arm of a chromosome 5 to the short arm of a chromosome 12 (5q ^-/12p ⁺) and a marker Y chromosome. NALM-6-MP possesses the same marker Y chromosome and a deletion of the long arm of chromosome 5 (5q ^-) since in most cells material missing from chromosome 5 does not appear on the short arm of chromosome 12. Within the limits of resolution available with the banding technique, no other karyotypic differences are observed in the 2 cell lines. The history of the 2 cell lines, the karyotypic analysis, and the pattern of immunoglobulin markers indicate the possible clonal evolution of NALM-6-MP from NALM-6-B and implicate a portion of the long arm of chromosome 5 in lymphoid differentiation of these leukemic cell lines.