Abstract
Autologous peripheral blood stem cell transplantation (PBSCT) has been demonstrated to result in rapid, stable long-term engraftment. However, there has been considerable debate concerning the cells responsible for early and late hematopoietic reconstitution after PBSCT. Recently, CD34+ hematopoietic stem and progenitor cells have been clearly divided into two subpopulations by flow cytometry; namely undifferentiated pluripotent stem cells and differentiated committed progenitor cells. However, only a few studies have defined which subset contained in graft products might be the most predictive for late hematopoietic reconstitution after PBSCT. In this review, we present updated information regarding the relationships between the number of infused CD34+ cells or their immature subsets such as CD34+CD90+ cells and the late hematopoietic reconstitution after PBSCT, and discuss the threshold dose of CD34+CD90+ cells required for sustained long-term engraftment.