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BACKGROUND The human leukocyte antigen (HLA) allele group HLA-DQA1*05 has been associated with the development of antidrug antibodies (ADA) to tumor necrosis factor antagonists (anti-TNF)1 in the inflammatory bowel disease (IBD) population, except in the setting of proactive optimization2. We performed a meta-analysis to determine the prevalence of HLADQA1*05 carriage, to define the association of HLA-DQA1*05 on immunogenicity and loss of response (LOR) to anti-TNF, and to explore the impact of therapeutic drug monitoring (TDM) on this association. METHODS A systematic search of EMBASE, MEDLINE, Web of Science, and SCOPUS was conducted and identified 49 studies. Fourteen studies were included in the meta-analysis according to our inclusion and exclusion criteria. Two reviewers independently assessed eligibility and extracted data. Data extraction focused on the prevalence of HLADQA1*05 carriage, management style of the subjects (proactive TDM vs not), use of combination therapy with immunomodulators (IMM), and association of the variant with ADA and LOR. To examine the potential mitigating effect of management style, three forest plots were generated for each outcome including: 1. all studies, 2. studies using solely proactive TDM, and 3. studies where TDM was either not defined or not performed. RESULTS The prevalence of HLADQA1*05 carriage was 43.3% across the 14 manuscripts. Ten studies used data from adult populations, 2 reported on pediatrics only, and 2 reported on a mix of pediatrics and adults. Nine studies took place in Europe, and 5 occurred in North America. A little over half (57%) were abstracts. All studies included some patients on combination therapy with IMM. Data analysis confirmed that possessing the HLADQA1*05 variant leads to an increased ADA risk (OR 1.63 [95% CI: 1.35 - 1.98]). When focusing on the studies that used proactive optimization of anti-TNF therapy, the variant was no longer a risk factor for developing ADA (OR 0.37 [95% CI: 0.19 - 0.70]). Without proactive optimization, the carriage of HLADQA1*05 appears to consistently be associated with a higher risk of immunogenicity (OR 1.93 [95% CI: 1.58 - 2.36]) (Figure 1). HLADQA1*05 was also found to be a risk factor for LOR (HR 1.84 [95% CI: 1.53 - 2.22]) (Figure 2); insufficient data were available for the studies with proactive TDM on LOR. CONCLUSION Prevalence of HLADQA1*05 carriage is consistent across studies from both North America and Europe. This variant increases the risk of ADA and LOR to anti-TNF. However, in studies that used solely proactive TDM, variant carriage no longer conferred a risk for ADA. 1. Sazonovs A, et al. Gastro. 2020;158(1):189-199. 2. Spencer EA, et al. Gastro. 2022;162(6):1746-1748.e1743.