doi:10.1093/ecco-jcc/jjae178engLópez De-La-Cruz, JuliaGomollón, FernandoLouro, JavierLópez Pérez, JuanNocito Colon, María MercedesGallego Llera, BeatrizGarcía-Mateo, SandraMartínez-Domínguez, Samuel JAso Gonzalvo, María ConcepciónGargallo-Puyuelo, Carla JImpact of HLADQA1*05 and HLADQA1*03 on Safety and Loss of Response to Anti-Tumor Necrosis Factor in Patients With Inflammatory Bowel DiseaseART-2024-142601Background: HLADQA1*05 is recently associated with heightened immunogenicity to anti-tumor necrosis factor (TNFα). We aimed to determine whether HLADQ1*05 is a risk factor for primary non-response, loss of response (LOR), or adverse events (AE) to first-line anti-TNFα in patients with inflammatory bowel disease. Methods: We performed a retrospective observational study enrolling biologic naïve patients with Crohn’s disease and ulcerative colitis who initiated adalimumab or infliximab from 2000 to 2021. HLA-DQA1 genotype was determined in all patients and immunogenicity in 98 patients. Results: We enrolled 408 patients who started first-line infliximab (n = 211) and adalimumab (n = 197), with a mean follow-up of 7.6 years. Primary response at Week 24 occurred in 347 (85.0%), LOR in 133 (38.3%), and AE in 93 (22.8%). The HLADQA1*05 was identified in 185 (43.3%) patients. In multivariate analyses, no risk factors were identified for primary response. HLADQA1*05 was an independent risk factor for LOR (adjusted hazard ratio [aHR] = 1.80, 95% CI = 1.21-2.67) and immunogenicity (aOR = 3.44, 95% CI = 1.12-11.92). HLADQA1*03 was a protective factor against LOR (aHR = 0.42, 95% CI = 0.20-0.88). Stratified analysis by anti-TNF type showed that HLADQA1*05 increased the risk of LOR to infliximab but not to adalimumab and HLADQA1*03 decreased the risk of LOR to adalimumab but not to infliximab. Female sex, infliximab, and the co-presentation of at least one allele of the HLADQA1*03 and HLADQA1*05 were risk factors for AE. Conclusions: HLADQA1*05 is associated with a higher risk of LOR and immunogenicity, particularly to infliximab. HLADQA1*03 seems to play a protective role against LOR, particularly adalimumab. Female sex and infliximab are risk factors for AE.2024http://zaguan.unizar.es/record/15054310.1093/ecco-jcc/jjae178http://zaguan.unizar.es/record/150543oai:zaguan.unizar.es:150543Journal of Crohn's & colitis 20 (2024), 1-10All rights reservedhttp://www.europeana.eu/rights/rr-f/info:eu-repo/semantics/openAccess