Abstract: The present invention relates to methods repairing, regenerating, and reconstituting tissues by transplanting at least two stem cell populations, wherein the first and the second population of stem cells are introduced into a subject separated by a time interval of about 2 to about 24 hours. The first population comprises stem cells derived from umbilical cord. The second population comprises ALDHbr cells. These ALDHbr cells can be administered to a patient immediately after isolation or can be primed in culture using a combination of cytokines for about 2 to about 7 days prior to transplantation. The methods of the invention are useful in accelerating time to neutrophil and/or platelet engraftment and immune reconstitution following myeloablative therapy.