Homing and engraftment potential of Sca-1+lin− cells fractionated on the basis of adhesion molecule expression and position in cell cycle

Abstract

Abstract Engraftment potential of hematopoietic stem cells (HSCs) is likely to be dependent on several factors including expression of certain adhesion molecules (AMs) and degree of mitotic quiescence. The authors investigated the functional properties and engraftment potential of Sca-1+lin− cells subfractionated on the basis of expression, or lack thereof, of CD11a, CD43, CD49d, CD49e, or CD62L and correlated that expression with cell cycle status and proliferative potential of engrafting fractions. Donor-derived chimerism in mice receiving CD49e+ or CD43+ Sca-1+lin− cells was greater than that in mice receiving cells lacking these 2 markers, while Sca-1+lin− cells positive for CD11a and CD62L and bright for CD49d expression mediated minimal engraftment. AM phenotypes enriched for engraftment potential contained the majority of high proliferative potential–colony forming cells, low proliferative potential–colony forming cells, and cells providing rapid in vitro expansion. Cell cycle analysis of AM subpopulations revealed that, regardless of their bone marrow repopulating potential, Sca-1+lin− AM− cells contained a higher percentage of cells in G0/G1 than their AM+ counterparts. Interestingly, engrafting phenotypes, regardless of the status of their AM expression, were quicker to exit G0/G1 following in vitro cytokine stimulation than their opposing phenotypes. When engrafting phenotypes of Sca-1+lin− AM+ or AM−cells were further fractionated by Hoechst 33342 into G0/G1 or S/G2+M, cells providing long-term engraftment were predominantly contained within the quiescent fraction. These results define a theoretical phenotype of a Sca-1+lin− engrafting cell as one that is mitotically quiescent, CD43+, CD49e+, CD11a−, CD49ddim, and CD62L−. Furthermore, these data suggest that kinetics of in vitro proliferation may be a good predictor of engraftment potential of candidate populations of HSCs.