SAT0277 Immunogenicity and loss of response to tnf inhibitors in axial spondyloarthritis: results from an observational cohort study

Objectives We aimed to evaluate the immunogenicity of TNF-α inhibitors and to assess potential influence on serum drug levels and clinical efficacy in patients with axial spondyloarthritis (axSpA). Methods We performed a cross sectional observational cohort study in 87 consecutive axSpA receiving anti-TNFs (either for the first time or switched), followed-up in a single outpatient rheumatology department. Treatment with anti-TNF agents was recommended in accordance with the local regulations on the initiation and continuation of biologics, as well as ASAS/EULAR guidelines. Disease activity scores were assessed at baseline (V1) and study visit (V2), while drug trough levels and anti-drug antibodies were measured in serum samples (ELISA, Progenika) and collected before the next administration as a single-point data. Serum drug levels were considered positive if >0.035 µg/mL IFX,>0.024 µg/mL ADL and >0.035 µg/mL ETN, while the cut-offs for anti-IFX was 5AU/mL, anti-ADL 10AU/mL, anti-ETN 142 AU/mL. Statistical analysis was performed using SSPS version 19.0, p Results Among 150 axSpA treated with TNF inhibitors in our centre, 28 (32.18%) receiving adalimumab (ADL), 19 (21.83%) infliximab (IFX) and 40 (45.97%) etanercept (ETN) were included in the immunogenicity analysis. Only 11 patients (12.64%) developed anti-drug antibodies, 8 under ADL (28.57%) and 3 under IFX (15.78%), with significant decrease in drug levels (3.97 µg/mL vs. 0.07 µg/mL ADL, p Higher disease activity scores (BASDAI, ASDAS-CRP) were reported in anti-drug positive axSpA irrespective of the background therapy (p Furthermore, a relation between clinical improvement (change in ASDAS) and immunogenicity was reported: positive anti-drug antibodies axSpA achieved worse clinical response than negative anti-drug antibodies cases, with a significant association between ADL respectively IFX levels and ASDAS (p No anti-drug antibodies were found in patients treated with ETN; significant higher persistence on ETA than under monoclonal antibodies was registered in our axSpA (p Conclusions Immunogenicity may impact disease outcomes and drug survival, particularly in the adalimumab and infliximab treated axSpA. Measuring anti-drug antibodies and serum drug levels may help to optimise therapeutic strategies in selected patients. Disclosure of Interest None declared