The receptor EP4 is identified as the PGE2 receptor that is most responsible enhancing the homing and engraftment of hematopoietic stem and progenitor cells. Treatment of graft sources and graft recipients with compounds that preferentially target the EP4 receptor provide effective methods of increasing engraftment success while minimizing adverse side effects that may be associated with therapies that include the use of less selective molecules such as PGE2 and dmPGE2. One effective molecule used in such therapies is 5-[(1E,3R)-4,4-difluoro-3-hydroxy-4-phenyl-1-buten-1-yl]-1-[6-(2H-tetrazol-5R-yl)hexyl]-2-pyrrolidinone or a pharmaceutically acceptable salt thereof (L-902, 688).