IMMUNOPHENOTYPIC DIFFERENCES BETWEEN PUTATIVE HEMATOPOIETIC STEM-CELLS AND CHILDHOOD B-CELL PRECURSOR ACUTE LYMPHOBLASTIC-LEUKEMIA CELLS

Acute leukemia cells express myeloid, B-lymphoid and T-lymphoid lineag e specific antigens. Many acute leukemias express the hematopoietic pr ogenitor cell antigen CD34. Three proposed models of the normal human hematopoietic stem cell include CD34+ Thy-1(low) Lin-, CD34+ CD38-, an d CD34+ HLA-DR-. The patterns of expression of CD34, Thy-1, CD38, HLA- DR, and multiple lineage-specific antigens on 49 consecutive pediatric B-cell precursor acute lymphoblastic leukemia (ALL) cases submitted f or immunophenotyping (36 at first diagnosis, 13 at relapse) were analy zed. CD34+ expression was observed in 67% of the cases. CD34+ expressi on correlated with Thy-1(low) expression and expression of myeloid ant igens (p < 0.001 and < 0.025, respectively). The CD34+ Thy-1(low) phen otype was observed in 65% of the cases; the CD34+ CD38- or CD34+ HLA-D R- phenotypes were observed in only three cases. Examples of heterogen eous expression of CD34 and Thy-1 were found in six cases, but CD38 ex pression was always bright and homogeneous in all positive cases. The data from this analysis indicates that the CD34+ CD38- or CD34+ HLA-DR - phenotypes would be more useful than the CD34+ Thy-1(low) phenotype for distinguishing normal hematopoietic stem cells from leukemic cells in childhood B-cell precursor ALL.