The invention provides compositions and methods useful for mobilizing populations of hematopoietic stem and progenitor cells within a donor, as well as for determining whether samples of mobilized cells are suitable for release for ex vivo expansion and/or therapeutic use. In accordance with the compositions and methods described herein, mobilized hematopoietic stem and progenitor cells can be withdrawn from a donor and administered to a patient for the treatment of various stem cell disorders, including hematopoietic diseases, metabolic disorders, cancers, and autoimmune diseases, among others. In certain embodiments, the compositions and methods described herein lead to the mobilization of a population of CD34dim cells that have immunosuppressive effects and that can reduce the incidence of graft vs. host disease.