Human CD34+ cell preparations contain over 100-fold greater NOD/SCID mouse engrafting capacity than do CD34- cell preparations

Objective. The CD34 cell surface marker is used widely for stem/progenitor cell isolation. Since several recent studies reported that CD34 cells also have in vivo engrafting capacity, we quantitatively compared the engraftment potential of CD34' vs CD34 cell preparations from normal human placental/umbilical cord blood (CB), bone marrow (BM), and mobilized peripheral blood (PBSC) specimens, using the nonobese diabetic/severe combined immunodeficient (NOD/SCID) mouse model, Methods. CD34(+) and CD34 cell preparations were purified by four different approaches in 14 individual experiments involving 293 transplanted NOD/SCID mice. In most experiments, CD34(+) cells were depleted twice (CD34(-)) in order to obtain efficient depiction of CD34 cells from the CD34(-) cell preparations. Results. Dose-dependent levels of human hematopoietic cells were observed after transplantation of CD34(+) cell preparations. To rigorously assess the complementary CD34(-) cell preparations, cell doses 10- to 1000-fold higher than the minimum dose of the CD34 cell preparations necessary for engraftment were transplanted. Nevertheless, of 125 NOD/SCID mice transplanted with CD34 cell preparations purified from the same starting cells, only sis mice had detectable human hematopoiesis, by flow cytometric or PCR assay. Conclusions. CD34 cells provide only a minor contribution to hematopoietic engraftment in this in vivo model system, as compared to CD34(+) cells from the same samples of noncultured human cells. Hematopoiesis derived from actual CD34 cells is difficult to distinguish from that due to CD34+ cells potentially contaminating the preparations, (C) 2001 International Society for Experimental Hematology. Published by Elsevier Science Inc.