Anti-Infliximab Antibody Formation Leading to Loss of Therapeutic Response in Severe Sarcoidosis: A Case Report

Sarcoidosis is a multisystem granulomatous disorder that can become refractory to conventional immunosuppressive therapies in its severe forms. Tumor necrosis factor-alpha (TNF-α) inhibitors such as infliximab have demonstrated efficacy in managing advanced or treatment-resistant disease. However, the development of anti-drug antibodies may compromise therapeutic outcomes. We report a case of severe sarcoidosis with initial clinical improvement following infliximab therapy, followed by secondary loss of response associated with the formation of anti-infliximab antibodies. The patient presented with progressive pulmonary and extrapulmonary involvement despite corticosteroids and immunomodulatory agents. Infliximab induction resulted in marked symptomatic and radiographic improvement, but relapse occurred after several months. Therapeutic drug monitoring revealed subtherapeutic infliximab levels and high titers of anti-drug antibodies, confirming immunogenicity as the underlying cause of treatment failure. Adjustment of therapy, including discontinuation of infliximab and initiation of an alternative biologic agent, led to subsequent disease stabilization. This case highlights the clinical significance of immunogenicity in biologic therapy for sarcoidosis and underscores the importance of early recognition, therapeutic monitoring, and individualized treatment strategies to optimize long-term outcomes.