SELECTIVE ENRICHMENT IN HUMAN MEGAKARYOCYTE PROGENITORS BY THE B203.13 SURFACE DIFFERENTIATION ANTIGEN

The B203.13 monoclonal antibody specifically recognizes a subset (8-18 .5%) of human CD34(+) haemopoietic progenitors, which are significantl y (P<0.05) enriched in megakaryocyte progenitors (CFU-meg. Moreover B2 03.13 expression a as progressively lost as maturation proceeded along the megakaryocytic lineage. In fact: (i) CFU-meg derived from CD34(+) /B203.13(+) showed a greater number of cells/colony with respect to CD 34(+)/B203.13(-); (ii) after 10 d of liquid cultures with 100 ng/ml of thrombopoietin, only a minority of CD34-derived cells positive for CD 41 coexpressed B203.13; (iii) in situ immunocytochemical staining reve aled that B203.13 was expressed exclusively on immature megakaryoblast s; (iv) circulating platelets did not express B203.13.