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 engraftmen t 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 immunodefici ent (NOD/SCID) mouse model, Methods. CD34(+) and CD34 cell preparations were purified by four different approaches in 14 individual experiments involving 293 transplanted NOD/SCI D mice. In most experiments, CD34(+) cells were depleted twice (CD34(-)) in order to obtain efficient depiction of CD34 cells from the CD34(-) cell pr eparations. Results. Dose-dependent levels of human hematopoietic cells were observed a fter transplantation of CD34(+) cell preparations. To rigorously assess the complementary CD34(-) cell preparations, cell doses 10- to 1000-fold highe r than the minimum dose of the CD34 cell preparations necessary for engraft ment were transplanted. Nevertheless, of 125 NOD/SCID mice transplanted wit h CD34 cell preparations purified from the same starting cells, only sis mi ce 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 ac tual CD34 cells is difficult to distinguish from that due to CD34+ cells po tentially contaminating the preparations, (C) 2001 International Society fo r Experimental Hematology. Published by Elsevier Science Inc.