Analysis of the Immunogenicity from Abatacept‐Treated Pediatric Patients With Polyarticular‐Course Juvenile Idiopathic Arthritis: Findings From Two Phase III Clinical Trials

OBJECTIVE: The goal of this article is to present the analysis of anti‐abatacept antibody data from children with polyarticular‐course juvenile idiopathic arthritis (pJIA), treated with abatacept. The data are from 395 participants with pJIA from two abatacept registrational trials. METHODS: We analyzed immunogenicity data according to age groups, administration route (intravenous [IV] or subcutaneous [SC]), drug treatment interruption, and co‐medications (with or without methotrexate [MTX]) to assess impact on the incidence of anti‐abatacept antibodies. RESULTS: The overall immunogenicity incidences observed in both JIA trials ranged between 4.7% and 23.3%. There was a slightly higher immunogenicity incidence in the 2–5‐year‐old participants (15.2%) compared with 6–17‐year‐old participants (4.7%). In the study with SC dosing, the overall incidence on treatment was 2.3% (3% if co‐dosed with MTX), similar to the incidence for Period A of the IV study (similar duration of treatment as the SC study), which was 2.1% (1.4% if co‐dosed with MTX). In the IV study, the period following a 6‐month interruption in treatment had comparable immunogenicity incidences (22.9% with interruption vs. 18.2% without interruption, both co‐dosed with MTX and 0% for both not co‐dosed with MTX). In most cases, participants co‐dosed with MTX had higher immunogenicity incidences than those on abatacept alone. CONCLUSION: Although some trends were noted in terms of incidence according to age and MTX co‐dosing, none where conclusive owing to differences in population size. Drug holiday had no impact on immunogenicity incidence once treatment was resumed, and incidences across SC and IV dosing were comparable. There was no impact of immunogenicity on pharmacokinetics, safety, and efficacy.