Characteristics of haemopoietic progenitor cells related to CD34 epitope class expression

Haemopoietic progenitor cells (HPCs) express the CD34 molecule, a heavily g lycosylated transmembrane protein displaying three main classes of epitopes . The CD34 epitope class expression may vary between different subsets of H PCs. The aim of this study was to characterise the subsets of HPCs expressi ng CD34 class II and III epitopes. The cells were studied for coexpression of activation-, lineage- and adhesion-associated molecules, and their clono genic ability and morphological features were examined. CD34(+) HPCs expressing class III epitopes outnumbered those expressing cla ss II. Class III expressing HPCs were enriched for CFU-GM and BFU-E and cel ls coexpressing CD13, CD33, c-kit and CD71 compared to class II expressing HPCs. CD34(+) cells exclusively expressing class III epitopes uniformly dis played CD13 and CD33; they had a high clonogenic capacity and morphological characteristics of promyelocytes and myelocytes. The data show that class III epitopes are distributed more broadly on CD34( +) HPCs than are class II epitopes, and that lack of class II epitopes is c onfined to CD34(+) HPCs at a late stage of myeloid differentiation. The hig her number of class III expressing HPCs coexpressing c-kit and CD71 suggest s that these cells exhibit a higher proliferative or differential potential than do HPCs expressing class II epitopes.