Characterization of a leukemic cell line of the pre‐B phenotype

NALM-6-M1, 1 of 8 leukemia cell lines cultured from the blood of a 19-yr-old boy with non-T, non-B acute lymphoblastic leukemia (ALL) in relapse, was characterized. This cell line was found to be more than 90% cytoplasmic immunoglobulin positive (cIg⁺) for both mu heavy and lambda light chains, but surface immunoglobulin (sIg) and complement receptor (CR) negative. NALM-6-M1 was cIg^- for alpha, delta, and gamma heavy chains and kappa light chain. About 45% of the cells exhibited sheep erythrocyte receptors. Approximately 12% of cells were positive for Fc receptors. Approximately 90% of the cultured cells had a deleted long arm of chromosome 5 (5q^-) and a marker Y chromosome. The remaining 10% of cells were found to have some additional chromosomal material on the long arm of chromosome 12, suggesting a partial translocation. No other karyotypic abnormalities were found. The cell line was found to react strongly with anti-p23, 30, suggesting Ia-like activity, but it only weakly stimulated normal lymphocytes in mixed leukocyte culture (MLC). The cells expressed HLA antigens. NALM-6-M1 failed to react with anti-thymocyte serum (ATS), did not possess Epstein-Barr membrane or nuclear antigens, nor did it exhibit phagocytosis for zymosan. NALM-6-M1 reacted positively with oil red O and Sudan black stains. On the basis of the cIgM staining, NALM-6-M1 seems to be arrested at an early stage in B-cell development and is considered to be of the pre-B cell phenotype possessing a chromosomal abnormality.