Importance of CD34(+) cell subsets in autologous PBSC transplantation: theMulhouse experience using CD34(+)CD38(-) cells as predictive tool for hematopoietic engraftment

Over the years, various biological parameters have been proposed for predic ting rapidity and long term maintenance of hematopoietic engraftment after peripheral blood stem cell transplantation (PBSCT), Determination of the gr aft content in CFU-GM was the only one available until the end of the eight ies. But, for technical reasons, and also because it does not actually eval uate 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 f requent discrepancy still exists between the number of CD34(+) cells reinfu sed and the engraftment efficiency. We have recently demonstrated a higher accuracy of the numbers of CD34(+)38(-) cells contained in graft products t o predict rapidity of trilineage engraftment, which has further been confir med by other investigators. Furthermore, we and others, have proposed a thr eshold dose of 5 x 10(4) CD34(+)38(-) cells/kg b.w. below which the triline age engraftment kinetics are significantly slower and unpredictible. This " cut-off" value also appears to be a realistic clinical tool to decide if he matopoietic 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 cos ts, enough to make it fully justified in this situation, it is absolutely n ot the case when it is administered after reinfusion of CD34(+)38(-) cell a mounts > 5 x 10(4) /kg. In this case, posttransplant rh-G-CSF administratio n could even result in a decrease in stem cells with self-renewal potential of the graft, which should still raise more concerns for its indiscriminat e and costly use.