Comparison of Nonrelapse Mortality After Haploidentical Hematopoietic Stem Cell Transplantation With Post-transplant Cyclophosphamide Versus Single Umbilical Cord Blood Transplantation in Hematologic Disease.

Unrelated cord blood transplantation (UCBT) and haploidentical transplantation using posttransplant cyclophosphamide (PTCy-haplo) are alternatives for patients lacking a human leukocyte antigen-matched donor. CD34 cell counts in cord blood affect transplantation outcomes, particularly nonrelapse mortality (NRM). The primary objective of this study was to compare the transplantation outcomes after UCBT and PTCy-haplo focusing on CD34 cell counts in cord blood. This retrospective study used data from 2014 to 2020 from a Japanese nationwide database. UCBT cases were divided into those with UCBT with higher (UCB-H; ≥.84 × 10/kg) and lower (UCB-L; <.84 × 10/kg) CD34 cell counts, depending on the median CD34 cell count. The study cohort comprised cases of PTCy-haplo (n = 1142), UCB-H (n = 3185), and UCB-L (n = 3172). In the multivariate analysis, neutrophil engraftment was significantly better in the PTCy-haplo than in the UCB-H (hazard ratio [HR], .64; 95% confidence interval [CI], .57 to .70; P < .001) and UCB-L groups (HR, .45; 95% CI, .41 to .50; P < .001). The UCB-H group showed similar NRM (HR, 1.19, 95% CI, 1.00 to 1.43, P = .051) and OS (HR, 1.05, 95% CI, .94 to 1.18, P = .38) compared with PTCy-haplo, whereas UCB-L was significantly associated with poor NRM (HR, 1.35, 95% CI, 1.13 to 1.61, P = .001) and OS (HR, 1.13, 95% CI, 1.01 to 1.26, P = .038). In contrast, the UCB-H (HR, .86; 95% CI, .75 to .98; P = .027) and UCB-L groups (HR, .80; 95% CI, .70 to .92; P = .001) were associated with lower relapse rate. Regarding the graft-versus-host disease (GVHD), the UCB-H and UCB-L groups were identified as significant risk factors for the development of grade II-IV acute GVHD (UCB-H: HR, 1.73; 95% CI, 1.51 to 1.99; P < .001; UCB-L: HR, 1.55; 95% CI, 1.35 to 1.78; P < .001) and grade III-IV acute GVHD (UCB-H: HR, 2.28; 95% CI, 1.78 to 2.91; P < .001; UCB-L: HR, 1.85; 95% CI, 1.44 to 2.37; P < .001), but neither were associated with the incidence of all-grade GVHD (UCB-H: HR, 1.12; 95% CI, .95 to 1.32; P = .16; UCB-L: HR, 1.08; 95% CI, .91 to 1.27; P = .37) or extensive chronic GVHD (UCB-H: HR, .86; 95% CI, .68 to 1.09; P = .21; UCB-L: HR, .88; 95% CI, .69 to 1.12; P = .31). Furthermore, higher NRM in UCB-L was attributed to higher infection-related mortality (HR, 1.50; 95% CI, 1.15 to 1.95; P = .003) but not GVHD-related mortality (HR, 1.15; 95% CI, .82 to 1.62; P = .43), whereas UCB-H was not a significant risk factor for both infection-related mortality (HR, 1.29; 95% CI, .99 to 1.69; P = .06) and GVHD-related mortality (HR, 1.28; 95% CI, .90 to 1.80; P = .16). UCB-H offered similar NRM and OS to PTCy-haplo, whereas UCB-L had worse outcomes. Our results can provide useful information for optimal donor selection.