Importance of CD34+ cell subsets in autologous PBSC transplantation: the mulhouse experience using CD34+CD38- cells as predictive tool for hematopoietic engraftment.

Over the years, various biological parameters have been proposed for predicting rapidity and long term maintenance of hematopoietic engraftment after peripheral blood stem cell transplantation (PBSCT). Determination of the graft content in CFU-GM was the only one available until the end of the eighties. But, for technical reasons, and also because it does not actually evaluate the self-renewal potential of the cell products reinfused, it has now been commonly replaced by the determination of CD34+ cell amounts, which are known to contain the pluripotent hematopoietic stem cells. However, a frequent discrepancy still exists between the number of CD34+ cells reinfused and the engraftment efficiency. We have recently demonstrated a higher accuracy of the numbers of CD34+38- cells contained in graft products to predict rapidity of trilineage engraftment, which has further been confirmed by other investigators. Furthermore, we and others, have proposed a threshold dose of 5 x 10(4) CD34+38- cells/kg b.w. below which the trilineage engraftment kinetics are significantly slower and unpredictible. This "cut-off" value also appears to be a realistic clinical tool to decide if hematopoietic growth factor(s) must be administered or not after PBSCT. Indeed, when for example, rh-G-CSF administration after transplant of CD34+38- amounts < 5 x 10(4) kg has indisputable positive effects on the rapidity of neutrophil engraftment, length of hospitalization and posttransplant costs, enough to make it fully justified in this situation, it is absolutely not the case when it is administered after reinfusion of CD34+38- cell amounts > 5 x 10(4) /kg. In this case, posttransplant rh-G-CSF administration could even result in a decrease in stem cells with self-renewal potential of the graft, which should still raise more concerns for its indiscriminate and costly use.