Getting closer to the haemopoietic stem cell utilising internal CD34 expression

Abstract

CD34 surface molecules has been exhaustively used as surrogate markers for primitive haemopoietic cells, but, increasing immunophenotyping combined with SCID mice / sheep repopulation evidence since 1997 suggests extremely primitive haemopoietic cells exist that do not express external (e)CD34. CD38 is expressed in increasing amounts on (e)CD34+ cells as they mature. Most primitive (≅10%) (e)CD34+ cells, are also characterized by lack of CD38. AC133 (a novel 5-transmembrane glycoprotein), is expressed on early (e)CD34+ subsets. CD34 can be quickly upregulated (1 min) independently of transcription / translation, probably from preformed intracellular stores. Our study investigated internal CD34, determining its significance in haemopoietic hierarchy, via triple flow cytometry examining (i)CD34 & (e)CD34, with one other haemopoietic cell marker CD38 or AC133).Such statistically different staining patterns suggests the CD34 molecule translocates from internal stores to surface during haemopoietic cell development. (i)CD34+/(e)CD34neg cell expression profiles are markedly different to (e)CD34+ cells indicating they are a separate distinct subset. Although (i)CD34 is not a feasible “positive” marked for harvest/selection, it's analysis allows a new haemopoietic developmental stage to be determined. Further immunophenotyping of these (i)CD34+ cells is being performed to elucidate the significance of internal CD34 expression, and its relationship to reversible CD34 expression.