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.