Haploidentical donor is preferred over matched sibling donor for pre-transplantation MRD positive ALL: a phase 3 genetically randomized study

Backgroun: Previous reports suggest a benefit associated with haploidentical donor transplantation (HIDT) compared to matched sibling donor transplantation (MSDT) in certain contexts, and the choice of optimal candidates warrants further investigation. Methods: We designed a prospective genetically randomized study to evaluate donor options between acute lymphoblastic leukemia (ALL) patients positive for measurable residual disease (MRD) pre-transplantation who underwent HIDT (n = 169) or MSDT (n = 39). Results: The cumulative incidence of positive MRD post-transplantation was 26% (95% CI, 19-33%) and 44% (95% CI, 28-60%) for HIDT and MSDT, respectively (P = 0.043). Compared to the HIDT cohort, the MSDT cohort had a higher 3-year cumulative incidence of relapse (CIR; 47%, 95% CI, 31-63% vs. 23%, 95% CI, 17-29%; P = 0.006) and lower 3-year probability of leukemia-free survival (LFS; 43%, 95% CI, 27-59% vs. 65%, 95% CI, 58-72%; P = 0.023) and overall survival (OS; 46%, 95% CI, 30-62% vs. 68%, 95% CI, 61-75%; P = 0.039), without a difference in non-relapse-mortality (10%, 95% CI, 1-19% vs. 11%, 95% CI, 6-16%; P = 0.845). Multivariate analysis showed that HIDT is associated with a low CIR (HR = 0.364; 95% CI, 0.202-0.655; P = 0.001) and better LFS (HR = 0.414; 95% CI, 0.246-0.695; P = 0.001) and OS (HR = 0.380; 95% CI, 0.220-0.656; P = 0.001). Conclusions: HIDT is better than MSDT in view of favorable anti-leukemia activity for patients with pre-transplantation MRD positive ALL. The current study paves the way to determine that haploidentical donors are the preferred choice regardless of available matched sibling donors in a subgroup population.