Subpopulations of Common Acute Lymphoblastic Leukemia Antigen-Positive Lymphoid Cells in Normal Bone Marrow Identified by Hematopoietic

Bone marrow samples from normal adults and children with nonhematologic malignancies not involving the marrow, acute lymphoblastic leukemia (ALL) in continued remission, and immune cytopenias were studied by twocolor immunofluorescence (IF) and flow cytometry to characterize common acute lymphoblastic leukemia antigen (CALLA)-positive marrow lymphoid cells. Marrow was separated by Ficoll/Hypaque centrifugation followed by passage over a monoclonal antibody affinity column to remove myeloid cells prior to IF staining. A higher proportion of CALLA-positive cells was found in the pediatric marrows (mean, 33.7% ± 6.3% SEM) than in the adult marrows (mean, 4.5% ± 1 .6% SEM). Two subpopulations of CALLApositive cells identified by cell sorting to be of lymphoid morphology were found in both adult and pediatric marrows. A small subpopulation comprising 1 2.3% of the total CALLA-positive cells was characterized by a high intensity of CALLA. terminal deoxynucleotidyl transferase (TdT). and MY1O expression. but low Bi . common leukocyte antigen. and peanut agglutinin receptor expression. The