Optimizing engraftment--source and dose of stem cells.

In recent years, the use of antibodies to measure CD34(+) cells and the availability of peripheral blood (PB) and umbilical cord blood (CB) as additional stem cell sources other than bone marrow (BM) has increased interest in determining the impact of stem cell source and dose on the outcome of allogeneic stem cell transplantation. In addition to differences in their stem cell content, transplants from the three sources differ in the composition and state of activation of immune cells. As a consequence, BM, CB, and PB transplants have different kinetics of hematological recovery, the most rapid engraftment being observed with PB and the slowest with CB. Stem cell source also incurs different risks for developing graft-versus-host disease (GVHD): PB transplants show a possible increase in acute and a definite increase in chronic GVHD compared with BM. CB transplants have a favorably low risk of GVHD even in mismatched transplants. Stem cell dose in an independent factor in transplants from any source, determining engraftment, transplant-related mortality and risk of leukemic relapse. These findings are of clinical importance-an understanding of the impact of stem cell source and dose is essential to obtain optimum conditions for a successful outcome after transplant. Copyright 2002 by W.B. Saunders Company.