Cell adhesion molecule expression in cord blood CD34+ cells.

Self-renewal, proliferation, differentiation, homing, and mobilization of hematopoietic progenitor cells (HPCs) are regulated by a complex mechanism that involves the bone marrow (BM) microenvironment. Cell adhesion molecules (CAMs) expressed on HPCs and on endothelial and stromal cells play a pivotal role in this process. In this study, we have used three-color cytofluorometric analysis to compare CAM expression in the subsets of cord blood (CB) and BM HPCs and examined the effect of a short exposure to various cytokines on L-selectin expression. The study was carried out on unseparated samples to avoid any possible bias from positive CD34 selection. CAMs were highly expressed in both CB and BM CD34+CD38+ cells. In this population, L-selectin, H-CAM, and LFA-1 were significantly more expressed in BM than in CB. With regard to the more immature progenitors, the subsets of CD34+/CD38-/L-selectin+ and CD34+/CD38-/LFA1+ cells were significantly larger in CB than in BM. Since the expression of such CAMs has been related to the repopulating capacity of HPCs, our results suggest a possible advantage in homing and engraftment of more undifferentiated CB as opposed to BM HPCs. A 4/24-h exposure to various cytokines significantly increased the percentage of CB CD34+/CD38+/L-selectin+ cells, while HPCs were differentiated since the percentage of CD34+/CD38-/L-selectin+ cells was reduced. These data show that a short exposure to cytokines increases L-selectin expression in the more differentiated CB HPCs. This could improve their homing in a transplant setting.