Lack of CD114 expression distinguishes bona fide HSCs from transiently reconstituting multilineage progenitors. The percentage of human engraftment (determined by expression of human CD45) in the BM of NOD/SCID/IL-2Rγ^null (NSG) mice that received a transplantation of either CD114^neg/lo or CD114^pos subfractions of the human HSC compartment is indicated at (A) 6 weeks, or (B) 14 weeks after transplantation. Engrafted mice are defined as greater than 0.1% human chimerism of BMMCs. Black line represents the average percent human chimerism in each group of mice. The difference in the level of engraftment at week 14 is statistically significant (P = .001, 2-tailed Mann-Whitney test).