Benign marrow progenitors are enriched in the CD34+/HLA-DRlo population but not in the CD34+/CD38lo population in chronic myeloid leukemia: an analysis using interphase fluorescence in situ hybridization

Fluorescence in situ hybridization (FISH) was used to discriminate between benign and malignant cells in sorted populations of chronic myelogenous leukemia (CML) marrow. FISH has the advantage of allowing for a cell by cell analysis of the breakpoint cluster region (BCR) gene rearrangement immediately after flow sorting in nondividing G0/G1 cells that are potentially transcriptionally inactive. We initially selected CD34+ cells with very low expression of the activation antigen CD38 as a candidate phenotype for an immature and hypothetically more benign cell population, but found no enrichment for Ph negativity in that subtype. In five CML samples, 55% +/- 3.3% (mean +/- SE) of CD34+/CD38hi cells had the BCR gene rearrangement, similar to 57% +/- 3.7% seen in the CD34+/CD38lo population. In contrast, subsequent experiments (n = 4) determined that the CD34+/HLA-DRlo population in CML marrow does contain an increased proportion of benign cells: 15% +/- 1% of the CD34+/DRlo cells were BCR rearranged, compared with 52% +/- 5.8% of the CD34+/DRhi cells (P = .001). Our results indicate that benign progenitors in CML are enriched within the CD34+ cells with low DR antigen expression, but not low CD38 expression. One possible interpretation of these observations is that low CD38 antigen expression is not as useful as low HLA-DR expression for isolating immature cells.