THE COMPOSITION OF CD34 SUBPOPULATIONS DIFFERS BETWEEN BONE-MARROW, BLOOD AND CORD-BLOOD

Our previous data obtained by flow cytometry and by clonogenic assay h ad consistently shown a lower cloning efficiency of hematopoietic prog enitor cells in bone marrow (BM) compared to those in blood (PB) or in cord blood (CB). Also, recent clinical reports have described more ra pid reconstitution after PB than after BM transplantation. We have app lied two- or three-color flow cytometric analysis using monoclonal ant ibodies directed against the stem- and progenitor cell antigen CD34, i n combination with other cell surface markers. We report significant d ifferences in the composition of progenitor cells contained in BM (238 specimens from 53 healthy donors and from patients in remission), PB (301 samples from 92 patients with or without cytokine support) and CB (n=37). Leukapheresis products (Pher, n = 69) were included in the st udy as well as positively selected CD34(+) cells obtained from BM (BMs el, n = 2), PB (PBsel, n = 28) and CB (CBsel, n = 5). We used monoclon al antibodies directed against CD7, CD19, CD34, CD38, CD45RA and glyco phorin A. The highest proportion of CD34(+) cells (in % of the MNC) wa s found in BM (mean 5.37% +/- 4.5). In the other sources, the mean val ues were 1.79% +/- 2.46 (PB), 1.48% +/- 1.81 (Pher) and 1.1% +/- 1.69 (CB). However, BM was the only source in which a considerable proporti on of the CD34(+) cells coexpressed the B cell antigen CD19 (mean 30.1 %, median 28, range 0 to 84%). The amount of earlier myeloid progenito rs as determined by their non-expression of the CD45RA antigen was low est among BM CD34(+) cells (26.7% +/- 16.6). In the other sources, the respective values were 57.5% +/- 17.9 (PB), 63.6% +/- 13.9 (Pher) and 70.4% +/- 16.1 (CB). These results were confirmed by subtype analyses of the CD34(+) cells positively selected from the three sources. Enri chment showed minor CD34(+) subpopulations to be identified. The mean proportions of B cell progenitors were 0.11% +/- 0.24 (PBsel) and 1.3% +/- 1.42 (CBsel) of the CD34(+) cells. The CD34(+) cells from all cel l sources coexpressed GPA (median 0.15%, range 0 to 1.8%) and CD7 (med ian 0.25%, range 0 to 1.2%). The proportion of CD38(-) cells ranged fr om 0.7 to 4% of the CD34(+) MNC. Thus, despite higher CD34 counts in B M, the relative proportions of myeloid progenitors are higher in PB an d in CB. This suggests that, if timely reconstitution depends on the n umber of CD34(+) cells transplanted, the mean number of 'stem cells' ( SC) required is 1.4-fold (for myeloid cells) or 2.2-fold (for earlier myeloid cells) higher for BM than for PB.