The Kinetics of Antidrug Antibodies, Drug Levels, and Clinical Outcomes in Infliximab-Exposed Patients with Immune-Mediated Disorders

Background Hypersensitivity reactions (HRs) and loss of response (LOR) to infliximab (IFX) are related to drug immunogenicity characterized by antidrug antibodies (ADAs). Objective To analyze the timing of ADA appearance and its relationship with drug levels and clinical outcomes in IFX-treated patients with different diseases. Methods Samples were longitudinally collected before each infusion from 91 IFX-treated patients and were assayed for ADA and drug levels by enzyme-linked immunosorbent assay and for IgE by ImmunoCAP system. Clinical data regarding efficacy and safety of therapy were also monitored. Results The ADA onset occured quite early, irrespective of the type of disease, during the first year and more frequently and earlier during the second cycle of therapy. Patients with HR were more frequently ADA-positive and with higher ADA titers compared with other patient groups. ADA onset tends to precede HRs and LOR; all HRs that occur after a period of drug interruption are preceded by ADA development. Before ADA detection, a progressive decline in IFX levels until a complete disappearance was observed. The ADA titer was maintained for years both in patients with ongoing therapy and in those who interrupted it. IgE ADAs are more frequently developed in patients with higher ADA levels and earlier ADA onset, but their rate of negativization is faster. Conclusion The present data suggest that most IFX-exposed patients develop ADAs within the first year of treatment irrespective of disease type. The clinical outcome to the treatment is preceded by ADA development, which in turn is associated with the reduction in drug serum levels. Both ADA evaluation and therapeutic drug monitoring may have a relevant impact on clinical practice, giving new insights to predict LOR and HRs.