Immunoglobulin and T-cell receptor gene rearrangement in blast crisis of chronic myelocytic leukemia

Chronic myelocytic leukemia (CML) displays a wide repertoire in its terminal phase, with blast cells showing characteristics of myeloid, B-lymphoid, or T-lymphoid cells in some patients. Blast crisis (BC) cells from 14 patients were studied for immunoglobulin (Ig)- and T-cell-associated gene rearrangements. Five myeloid BC patients had no Ig- or T-cell-associated gene rearrangement. In contrast, all eight patients with pure lymphoid BC displayed Cμ rearrangement and two also showed κ-light chain rearrangement. One patient with mixed (lymphoid and erythroid) BC, however, showed neither Ig- nor T-cell-associated rearrangements. One patient displayed both Ig- (Cμ) and T-cell-associated (Tβ and Tγ) rearrangements. These cells expressed CD9, CD10, and CD24 surface antigens, but no T-cell antigens. Although most lymphoid blast crises appear to represent an early stage in B-cell differentiation, some cells have undergone apparently inappropriate gene rearrangements during differentiation. Such cells may have been immortalized while undergoing normally occurring nonproductive rearrangement or may, due to their malignant nature, display abnormal genotypic characteristics.