In the study, which appears online on November 16 in advance of publication in the December print issue of the Journal of Clinical Investigation, Martin Friedlander and colleagues from The Scripps Research Institute, La Jolla, show that the abnormal blood vessels that grow in the retina of mice exposed to a stimulus that induces retinopathy can be converted to normal blood vessels if the mice are transplanted with adult bone marrow–derived myeloid progenitor cells. Blood vessel repair occurred when the transplanted cells migrated to the eye and became cells known as microglial cells, it also required that the transplanted cells express a protein known as HIF-1-alpha.This study has clinical relevance because it suggests that transplantation of autologous bone marrow–derived progenitor cells might be a viable therapy for the treatment of human diseases that resemble this mouse model of retinopathy, such as ROP.