Mobilization Of Allogeneic Stem Cells

Despite the rapid engraftment and the reduction in transplant-related mortality with mobilized PBSC, there are some concerns about the increased risk of acute and chronic graft-versus-host-disease (GVHD) due to the higher numbers of T cells in mobilized PBSC products. Korbling et al.67 compared the allograft content of G-CSF mobilized PBSC to cellular contents of BM harvest and showed that there was a three- to fourfold increase in CD34+ cells and a 10- to 20-fold increase in the number of CD3+ T cells in PBSC products compared to BM harvest. There have been several randomized trials comparing BM and PBSC in the allogeneic transplant setting, but the results were inconclusive.6869 However, most studies demonstrated a significant enhancement of neutrophil and platelet recovery with allogeneic PBSCT, but a survival benefit was observed only in patients with advanced hematologic malignancies. The risk of acute GVHD was not significantly increased with allogeneic PBSCT. However, a modest increase in chronic GVHD has been reported in several studies. A meta-analysis of 15 phase II and phase III trials assessing the risk of GVHD in allogeneic PBSC and BM demonstrated a modest increased relative risk of acute GVHD (relative risk 1.2) and a significant increased risk of chronic GVHD (relative risk 1.8) in recipients of allo geneic PBSCT.70 In addition, there was a significant reduction in risk of relapse after PBSC allografts.

Similar to autologous PBSC studies, the numbers of mobilized CD34+ cells correlate well with engraftment. Allogeneic PBSC recipients who received more than 5 X 106 CD34+ cells/kg had a 95% chance of both neutrophil and platelet recovery by day +15.71 However, infusion of allogeneic PBSC > 8 X 106 CD34+ cells/kg has been shown to result in poor survival presumably due to increased rates of chronic GVHD and its complications.

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