Risks and Benefits of Unrelated Donor Peripheral Blood Progenitor Cells (PBPC) in Children and Adolescents with Acute Leukemia.

Although PBPC is an acceptable alternative to bone marrow (BM) for transplanting children with leukemia, there are no published studies describing outcomes after unrelated donor PBPC transplants. We compared the results of 385 unrelated donor BM transplants that were allele-matched (n=186) or mismatched (n=199) at HLA A, B, C, DRB1 and 110 PBPC transplants that were matched (n=60) or mismatched (n=50) at HLA A, B, C, DRB1 in patients younger than 18 years of age. All patients had acute leukemia and were transplanted in 2000–2006. Median follow up of surviving patients was 2 years in both treatment groups. There were no significant differences in patient and disease characteristics, transplant conditioning regimen, graft-versus-host disease (GVHD) prophylaxis and donor-recipient HLA disparity by graft type. Though the early probability of neutrophil recovery (³500/ul) was faster after transplantation of PBPC (31% vs. 10% at day-14, p<0.001) the probability of recovery by day-28 was similar after PBPC and BM transplants (94% and 91%, p=0.391). In contrast, platelet recovery (³20,000/ul) was better after PBPC transplants (86% vs. 76% at day-60, p=0.022). Risks of grade 2–4 (hazard ratio [HR] 1.24, p=0.147) and grade 3–4 (HR 1.07, p=0.785) acute GVHD were similar after PBPC and BM transplants. The risk of developing chronic GVHD was significantly greater after PBPC transplants compared to BM transplants (HR 2.36, p<0.001). After adjusting for disease status, donor-recipient HLA disparity and age, the of transplant-related mortality (TRM) relapse, treatment failure (relapse or death from any cause; inverse of leukemia-free survival and overall survival were similar after PBPC and BM transplants. The Table below shows the day-100 probability of grade 2–4 acute GVHD and the 3-year probabilities of chronic GVHD, TRM, relapse, leukemiafree survival and overall survival by graft type. These results differ from transplantation of PBPC from HLA-matched siblings where higher chronic GVHD translated into higher TRM and lower LFS. It remains to be seen whether the observed higher chronic GVHD after PBPC transplants will eventually result in the long term in higher mortality or fewer leukemia recurrence.