The inventors found that by administering an agonistic antibody (VB22B sc(Fv)2) witha reduced molecular weight against TPO receptor, human megakaryocyte-specific differentiationis induced (platelet progenitor cells are increased), hematopoietic stem cells(CD34-positive cells) derived from human cord blood are engrafted, and multilineageblood progenitor cells are significantly increased. TPO or TPO receptor agonistcan be used as a proliferation promoter of hematopoietic CD34-positive cellsor an engraftment promoter in the bone marrow, in which an effect can be expectedonly by single administration (without concomitant administration of G-CSFor erythropoietin) after engraftment of hematopoietic stem cells (particularly engraftmentof cord blood). Further, it can be used as a multilineage hematopoietic progenitorcell proliferation and/or differentiation promoter and a multilineage hematopoieticability restoration promoter.
