Detection of leukemic cells in the CD34+CD38- bone marrow progenitor population in children with acute lymphoblastic leukemia

Successful autologous hematopoietic stem cell (HSC) transplantation in childhood acute lymphoblastic leukemia (ALL) requires the ability to either selectively kill the leukemia cells or separate normal from leukemic HSC, Based on previous studies showing that more than 95% of childhood B-lineage ALL express CD38, this study evaluated whether normal CD34(+)CD38(-) progenitors from children with B-lineage ALL could be isolated by flow cytometry. CD34(+) cells from bone marrow samples from 10 children with B-lineage ALL were isolated at day 28 of treatment, when clinical remission had been attained. The CD34(+) progenitor cells were flow cytometrically sorted into CD34(+)CD38(+) and CD34(+)CD38(-) populations. The absolute numbers of CD34(+)CD38(-) cells that could be isolated ranged from 401 to 6245, The cells were then analyzed for the presence of clonotypic rearrangements of the T-cell receptor (TCR) V delta2-D delta3 locus. Only patients whose diagnostic marrow had an informative TCR V delta2-D delta3 rearrangement were included in this study. Detection thresholds were typically 10(-4) to 10(-5) leukemic cells in normal marrow. In 6 of 10 samples analyzed, the sorted CD34+CD38- cells had no detectable V delta2-D delta3 rearrangements. In 4 cases, the clonotypic leukemic V delta2-V delta3 rearrangement was detected in the CD34+CD38- population, indicating that the putative normal HSC population also contained leukemic cells, The data indicate that although most childhood ALL cells express CD34 and CD38, leukemic cells are also frequently present in the CD34(+)CD38(-) population. Therefore, strategies to isolate and transplant normal HSC from children with ALL will require a more stringent definition of the normal HSC than the CD34(+)CD38(-) phenotype.