LAUSR

Background In recent years, haploidentical related donor (haplo) transplantation has markedly increased, accounting for 17% of allogeneic transplantations in adults compared to 5% with UCB and 18% and 20% respectively, in children with hematological malignancy. As prior studies comparing these two hematopoietic stem cell (HSC) sources were largely limited to patients receiving reduced dose conditioning, the current analyses compared outcomes with these HSC sources after myeloablative conditioning. Patients Between 2012 and 2017, there were 375 transplants with haplo HSC (BM, n=126; PB, n=249), and 333 with UCB (188 matched at ≤5/8 HLA alleles and 145 matched at 6-8/8 HLA alleles). All haplo recipients had PTCy, calcineurin inhibitor (CNI) and mycophenylate mofetil (MMF) as GVHD prophylaxis and all UCB recipients were conditioned with TBI 1320 cGy, fludarabine and Cy and received CNI/MMF. The median infused total nucleated dose for ≤5/8 and 6-8/8 UCB transplants were 4.7 and 4.4 × 107/kg, respectively. Recipients of 6-8/8 UCB transplants were younger (14 years vs. 21 and 29 years) and more likely to have lower co-morbidity scores (81% vs. 69% and 63%) compared to recipients of ≤5/8 UCB and haplo transplants. UCB recipients were more likely to have ALL and transplanted in second CR and haploidentical related donor transplants were more likely to have AML and transplanted in first CR. Cytogenetic risk did not differ between HSC groups. Results Compared to haplo transplants, relapse was lower in recipients of ≤5/8 UCB and similar to that in recipients of 6/8 UCB. Non-relapse mortality (NRM), however, was higher after UCB regardless of HLA match group (Table 1). While overall survival was higher 1-year after haploidentical transplant (81% vs 68% and 72% after ≤5/8 [p Conclusion Three-year LFS and overall survival were comparable in recipients of Haplo with PTCy and UCB. While greater HLA mismatch is associated with less relapse after UCB transplant, NRM counters this beneficial effect. Strategies that address the early mortality risk after UCB transplant could further enhance success with this HSC source.