The present invention concerns therapeutic agents that, in association with stimulation of PDGFRα-positive cells such as bone marrow mesenchymal stem cells, promote their mobilization into blood and accumulation in a damaged tissue, and induce tissue regeneration in a living body. In particular, fragments of High mobility Group Box 1 (HMGB1 or amphoterin) which stimulate PDGFRalpha-positive cells and promote their mobilization into blood and accumulation in a damaged tissue. Peptide fragments of HMGB1 were identified with migration-promoting activity on PDGFR-alpha-positive bone marrow mesenchymal stem cell line (MSC-1) and skin fibroblasts.
