The percentage of megakaryocytes differentiated from CD9+Lin−CD34+CD45RA− HSPCs was approximately threefold higher than that of the CD9− counterpart in HC; in ITP patients, the percentage decreased to only 1/4th of that in HC, comparable to that from the CD9−Lin−CD34+ CD45RA− HSPCs. Here, CD9 is linked to autoimmune thrombocytopenic purpura.