BENIGN MARROW PROGENITORS ARE ENRICHED IN THE CD34(+) HLA-DR(LO) POPULATION BUT NOT IN THE CD34(+)/CD38(LO) POPULATION IN CHRONIC MYELOID-LEUKEMIA - AN ANALYSIS USING INTERPHASE FLUORESCENCE IN-SITU HYBRIDIZATION/

Fluorescence in situ hybridization (FISH) was used to discriminate bet ween benign and malignant cells in sorted populations of chronic myelo genous leukemia (CML) marrow. FISH has the advantage of allowing for a cell by cell analysis of the breakpoint cluster region (BCR) gene rea rrangement immediately after flow sorting in nondividing G(0)/G(1) cel ls that are potentially transcriptionally inactive., We initially sele cted 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 t hat subtype. In five CML samples, 55% +/- 3.3% (mean +/- SE) of CD34()/CD38h(hi) cells had the BCR gene rearrangement, similar to 57% +/- 3 .7% seen in the CD34(+)/CD381(lo) population. In contrast, subsequent experiments (n = 4) determined that the CD34(+)/HLA-DR(lo) population in CML marrow does contain an increased proportion of benign cells: 15 % +/- 1% of the CD34(+)/DR(lo) cells were BCR rearranged, compared wit h 52% +/- 5.8% of the CD34(+)/DR(hi) cells (P =.001). Our results indi cate that benign progenitors in CML are enriched within the CD34(+) ce lls with low DR antigen expression, but not low CD38 expression, One p ossible interpretation of these observations is that low CD38 antigen expression is not as useful as low HLA-DR expression for isolating imm ature cells. (C) 1995 by The American Society of Hematology.