IMMUNOGLOBULIN AND T-CELL RECEPTOR GENE REARRANGEMENTS IN ACUTE LYMPHOBLASTIC-LEUKEMIA - A HIGHER INCIDENCE OF DOUBLE REARRANGEMENTS IN PATIENTS WITH MYELOID ANTIGEN EXPRESSION

Among 160 patients who were diagnosed as having acute lymphoblastic leukemia (ALL) by French American British (FAB) criteria, 32 patients (20%) expressed myeloid-associated antigens on leukemic blasts (My+ ALL). Correlation of immunophenotype with rearrangement of immunoglobulin (Ig) heavy chain and T-cell receptor (TCR) beta chain genes was performed on 73 of these patients (21 were My+ ALL). Rearrangements of both Ig and TCR genes (double rearrangements) were detected in 24 patients, including three (19%) of 16 T-lineage ALL, 17 (33%) of 52 B-lineage ALL, and four of five ALL expressing both B and T-cell surface markers. Also a higher incidence of double rearrangements in My+ ALL was found as compared with My+ ALL (43% vs 29%). This difference was more evident when only B-lineage ALL was considered (50% in My+ patients vs 24% in My- patients). However the difference is not statistically significant yet possibly due to the small number of patients in the study. Further studies on more patients are needed to confirm this. In My-B-lineage ALL, rearrangements of TCR beta chain gene were restricted to certain subgroups (Groups III & IV) of patients who expressed CD10 surface antigens but lacked cytoplasmic Ig. In My+ B-lineage ALL, rearrangements of TCR beta chain gene could be found in various subgroups studied (Groups II through V). Cross-lineage gene rearrangement in My+ ALL may involve mechanisms different from those in My- ALL.