Promotion of hematopoiesis by endothelial cell infusion. In hematopoietic organs, the vascular endothelium interacts with the hematopoietic stem/progenitor cells either directly or indirectly via multiple soluble factor pathways. Following bone marrow damage, infusion of endothelial cells may help restore normal hematopoiesis by yet-unrecognized mechanisms. The effects may be exerted directly on hematopoietic stem cells (in the osteoblastic niche) or indirectly on bone marrow endothelium. Alternatively, infused endothelial cell–derived factors may effect survival, proliferation, or differentiation of more differentiated hematopoietic precursors. Illustration by Paulette Dennis.