Umbilical Cord Blood Produces Small Megakaryocytes After Transplantation

Representative BM megakaryocytes stained with antibody to CD61 followed by diaminobenzidine (megakaryocytes are brown). (A) Megakaryocytes in a 4-year-old patient 1 month after CB transplantation. Megakaryocytes are small and of relatively uniform size. These megakaryocytes have a single or bilobed nucleus, typical of micromegakaryocytes [40]. (B) Megakaryocytes in a 1-year-old patient 1 month after mobilized peripheral blood transplantation from an adult donor. Megakaryocytes are larger and have more size heterogeneity. (C) Mean megakaryocyte diameter is significantly smaller after CB transplantation than after transplantation of hematopoietic cells from adult sources 1–3 months posttransplantation. (Line = median; box = 25%–75% quartiles; bars = range of individual medians; n = 10 CB transplants; n = 9 BM transplants.)

Hematoxylin and eosin–stained sections showing individual megakaryocytes assigned a maturational stage based on size, nuclear lobulation, ratio of nucleus to cytoplasm, and degree of cytoplasmic maturation. CB stem and progenitor cells produced a lower percentage of stage III megakaryocytes (25% CB vs 44% BM; P = .059), which in normal adults is the largest megakaryocyte maturational class. In contrast, CB cells produced a higher percentage of stage IV mature megakaryocytes. When stage III and IV (mature) megakaryocytes are considered together, there is little difference between CB and BM transplants.