CXCR4 and osteoporosis: At the same time, we are aware that toxic irradiation used in HSC transplantation as a preconditioning regimen can not be used in non-life-threatening diseases like osteoporosis, and we are addressing this issue by exploiting integrin and SDF-1/CXCR4 signaling pathways (Meng, Baylink, Lau, and Zhang: unpublished).