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 depletion 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 six 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.