BACKGROUND: Molecular typing before hematopoietic stem cell transplantation (HSCT) at the eplet level is an emerging method to optimize HLA matching.

MATERIAL AND METHODS: Patients who received outpatient haploidentical HSCT (Haplo-HSCT) from a sibling after reduced intensity conditioning (RIC) were studied. HLA class I and II mismatched eplets (MEs) load was determined using HLAMatchmaker software. A cutoff > or < 10 MEs was used to assess outcomes.

RESULTS: 114 patients were studied. A locus B MEs load > 10 was associated with decreased overall survival (OS), (p = 0.049), increased graft failure (GF) (p = 0.004). Mortality was higher with > 10 MEs in HLA-I locus B (p = 0.025), and HLA-II DRB1 (p = 0.026); chronic GVHD was higher with > 10 MEs in DRB1 (p = 0.009). Anti-HLA donor-specific antibodies (DSA) were more frequent in recipients with > 10 MEs load at locus C (p = 0.021) and DRB1 (p = 0.002). MEs load > 10 at locus C and DRB1 were associated with anti-HLA DSA. Infection (p = 0.012), DSA (p = 0.014), and relapse (p = 0.001) were associated with lower OS, while multitransfusion (p = 0.035), aGVHD (p = 0.035) and infection (p = 0.021) with reduced event-free survival (EFS).

CONCLUSION: HLA MEs load > 10 in locus B was associated with reduced OS, and in locus DRB1 with higher death rate and cGVHD after outpatient sibling haplo-HSCT using RIC.