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The optimal myeloablative conditioning regimen for ALL patients undergoing hematopoietic cell transplant (HCT) with an alternative donor is unknown. We analyzed HCT outcomes ALL patients (n = 269) who underwent HCT at our center from 2010 to 2020 in complete remission (CR) after FTBI-etoposide and CNI-based GvHD prophylaxis for matched donor HCT (ETOP-package; n = 196) or FTBI-Fludarabine and post-transplant cyclophosphamide (PTCy)-based prophylaxis for HLA- mismatched (related or unrelated) donors (FLU-package; n = 64). Patients in FLU-package showed a significant delay in engraftment (p < 0.001) and lower cumulative incidence (CI) of any and extensive chronic GVHD (p = 0.009 and 0.001, respectively). At the median follow up of 4.6 years (range 1-12 years); non-relapse mortality, overall or leukemia-free survival and GVHD-free/relapse-free survival were not significantly impacted by the choice of conditioning. However, in patients at CR2 or with measurable residual disease (MRD+), there was a trend towards higher relapse after FLU-package (p = 0.08 and p = 0.07, respectively), while patients at CR1 regardless of MRD status had similar outcomes despite the package/donor type (p = 0.9 and 0.7, respectively). Our data suggests that FLU-package for alternative donors offers comparable outcomes to ETOP-package for matched donor HCT to treat ALL. Disease status and depth of remission at HCT were independent predictors for better outcomes., (© 2024. The Author(s).)

A mismatch at HLA-DPB1 locus is associated with higher acute GVHD and lower relapse rate after myeloablative (MAC) allogeneic hematopoietic cell transplantation (alloHCT). Also, in MAC setting, mismatch permissiveness and expression level impact alloHCT outcomes. However, in reduced intensity conditioning (RIC), DP mismatch effect on transplant outcomes is unknown. We retrospectively evaluated DP mismatch influence (number, permissiveness, and expression) on HCT outcomes in 310 patients with high-resolution typing (HLA-A, -B, -C, -DRB1, -DQB1, and -DPB1), who underwent RIC HCT. By multivariable analysis, 11/12 had better overall survival (OS) and relapse vs. 12/12 (HR = 1.61 and 2.02; p = 0.04 and 0.01, respectively) and better OS vs. 10/12 (HR = 1.68; p = 0.02). Within the 11/12, nonpermissive (NoPR) mismatch was associated with higher risk of grade II-IV acute GVHD (HR = 1.97; p = 0.005) and nonrelapse mortality (HR = 2.13; p = 0.02) vs. permissive (PR). Grouping 11/12 based on the DP expression conferred higher mortality (HR = 3.78; p = 0.003) when low expressers received a graft from high expressers (AG) vs. low expressers (AA). Better OS was achieved in PR 11/12, when expression was low in patient and donor (AA) vs. all other combinations. Therefore, in RIC HCT, a single-DP mismatch has a protective role, especially in permissive setting, when donor and recipient are low expressers.