Bioinformatic Evaluation of Molecular Differences in HLA-B and Their Effect on Graft-Versus-Host Disease in Patients Receiving Haploidentical Hematopoietic Stem Cell Transplantation from Related Donors
Authors: Morcos Michelle , Gonzalez Alexia , Vaquera Alfaro Héctor Alejandro , Alvarado-Navarro Dalila Marisol , Colunga-Pedraza Perla R. Rocio , Gomez-De Leon Andres , Salazar-Riojas Rosario , Aguilar-Escobedo Maria Luisa , Ugarte Pelaez Luis Paulo , Rubio Macias Francisco Javier , Cantu Olga , Gomez-Almaguer David , Moncada Saucedo Nidia Karina 
Published: December 2024

Background
Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) from related donors has become more accessible due to difficulties in finding matched related donors, the high cost of matched unrelated donors (MUD), and the use of post-transplant cyclophosphamide (PTcy) to reduce acute graft-versus-host disease (aGVHD). Key factors in selecting a haploidentical donor include age, gender, donor-specific antibodies, ABO blood group, and HLA mismatch degree. HLA-B is the most polymorphic locus, prompting the development of bioinformatics tools to evaluate the dissimilarity score (DS) of mismatched HLA alleles, providing predictive data on alloimmune responses. A dimorphism at position -21 of exon 1 in the B-leader chain (BLC) results in peptides translating to methionine (M) or threonine (T), which have been linked to GVHD, relapse, and mortality. Translation to M is linked to HLA-E gene expression and improved recognition by T and NK cells, showing clinical relevance. However, bioinformatic tools still need to be explored in related donor transplant cohorts.
Objective
Main objective: To analyze dimorphisms and molecular dissimilarities of HLA-B and their relationship with GVHD in related haplo-HSCT.
Methods
This was a single-center retrospective study that included 120 pediatric and adult patients who received related haplo-HSCT between 2019-2024, using peripheral blood as a cell source. GVHD prophylaxis was based on PTcy, calcineurin inhibitor, and mycophenolate mofetil. High-resolution HLA typing (A, B, C, DRB1) was performed by Sanger/NGS. The BLC dimorphism and HLA-B DS were evaluated using BLEAT and HistoCheck, respectively. Statistical analyses included Fisher's test, Tukey's test, T-Student test, and descriptive statistics (R). Statistical significance was set at p&lt;0.05.
Results
A total of 120 patients (78 males and 42 females) were evaluated, with a median age of 23 years (range: 1-61). The predominant diagnoses were acute lymphoblastic leukemia (52, 43%), acute myeloblastic leukemia (35, 29%), aplastic anemia (10, 8.3%), chronic myeloid leukemia (4, 3.3%), myelodysplastic syndrome (3, 2.5%), and other conditions (16, 13.4%). HLA mismatches included 4/8 (93, 78%), 5/8 (22, 18%), 6/8 (4, 3.3%), and 7/8 (1, 0.8%). BLC genotypes were: MMM (4, 3.3%), MMT (10, 8.3%), MTM (7, 5.8%), MTT (12, 10%), TMM (6, 5%), TMT (27, 23%), TTM (11, 9.2%), and TTT (43, 36%). The TMT genotype showed the highest incidence (35%) with a B-leader mismatch in patients with aGVHD. HLA-B DS was not statistically significant between patients with and without GVHD. However, the DS was significantly higher (&gt;18) in patients with a BLC mismatch who developed GVHD compared to those without GVHD and with a BLC match (p&lt;0.005, Tukey's test).
Conclusion
The presence of a BLC mismatch, a TMT genotype, and an HLA-B DS &gt;18 increases the likelihood of developing GVHD. Incorporating these evaluations of the BLC and DS into haploidentical donor selection criteria, following this algorithm, could improve transplant success and identify patients at higher risk of developing GVHD.