P398 The early appearance of anti-drug antibodies during the induction phase predicts the clinical response of adalimumab and infliximab in IBD

Background Several studies have shown a link between circulating anti-TNF levels during induction and clinical progression during IBD. There are less data on the detection of anti-drug antibodies at induction because it requires the use of so-called ‘drug-tolerant’ techniques. The purpose of our study was to investigate in two distinct cohorts (IBD patients on IFX or ADA) whether the early appearance of anti-drug antibodies measured using a drug-tolerant test was associated with clinical progression. Methods In a retrospective study, we included all patients followed in our department for at least 3 months and having had an anti-TNF dosage from W2 of induction under ADA or IFX. At follow-up, therapeutic failure was defined by the obligation to optimise, a change in biotherapy, the use of corticosteroids or surgery. IFX and ADA levels were measured routinely (Lisa-Tracker; Theradiag) and anti-medicine antibodies were detected by ‘drug-sensitive’ ELISA technique (Lisa-Tracker; Theradiag) or ‘drug-tolerant’ as previously described [1]. Patients with a positive rheumatoid factor were excluded. Results 54 patients were included in ADA (mean age: 36 years, sex ratio M/F = 54%, CD: 65%, combotherapy: 10%) and 54 treated with IFX (mean age: 35 years, sex ratio M/F: 46%, CD: 62%, combotherapy: 65%). The search for anti-drug antibodies to W2 using a ‘drug-sensitive’ technique did not reveal any antibodies, whereas 74% of patients on ADA (AAA > or = 2.5 µg/ml eq) and 55% of patients on IFX (ATI > or = 4µg/ml eq). Under ADA, the duration of treatment until loss of response was significantly shorter in the presence of AAA at W2: 6 months vs. 24 months (HR = 18.51; 95CI = 4.35–78.11; p < 0.001). In multivariate analysis, the only independent factor associated with failure was the rate of ADA antibodies to W2 (HR = 18.17; 95CI: 4.27–77.45; p < 0.001). Under IFX, the treatment time to loss of response was significantly shorter in the presence of ATI to W2 (ATI > or = 4µg/ml eq): 5.5 months vs. >24 months (HR = 13.89; 95CI = 4.08–47.31; p < 0.001). In multivariate analysis, the only independent factor associated with failure was the level of anti-IFX antibodies to W2 (> or = 4 µg/ml eq) (HR = 8.07; 95CI: 3.13–20.82; p < 0.001). The higher quartiles of ATI and AAA were significantly associated with poor outcomes (p < 0.001 for each anti-TNF). Conclusion The early onset of anti-drug antibodies in the induction phase as early as W2 is the only isolated independent factor associated with loss of response. Anti-drug antibody frequencies are very high when measured with a drug-tolerant test and these Abs may be more neutralising with ADA than with IFX.