Immunologic and ultrastructural heterogeneity of acute lymphoblastic leukemia-associated antigen-positive human leukemias.

To further examine the heterogeneity of human acute lymphoblastic leukemia, an immunologic and ultrastructural study was undertaken on 14 patients positive for the acute lymphoblastic leukemia-associated antigen (ALLA). In malignant cells from 7 of the patients studied, cytoplasmic granular inclusions that resembled those seen in leukemia mast cells and basophils (M-B granules) were evident. Four patients had malignant cells expressing the pre-B-cell phenotype (i.e., cytoplasmic IgM-positive and surface immunoglobulin-negative), and 3 patients had malignant cells that lacked both M-B granules and cytoplasmic IgM. These results support the existence of distinct phenotypic subgroups within the ALLA+ leukemias.