Hypersensitivity reactions to biologics used in rheumatology.

: Biological agents (BAs) target disease mechanisms and have modified the natural history of several immune-mediated disorders. All BAs are immunogenic, resulting in the formation of antidrug antibodies (ADAs), which can neutralize drug activity leading to loss of response and potential relapse. In addition, ADAs can also cause serious adverse events such as infusion hypersensitivity reactions (HRs).: This review discusses the recent knowledge on the effector and regulatory mechanisms involved in the immune response to BAs used in patients suffering from rheumatic diseases leading to the production of ADAs and the impact on clinical outcome. Specifically, the demonstration of the involvement of specific T cell responses underlines B cells activation, and ADAs production is discussed correlating them to the different possible clinical consequences.: Although the mechanisms of the immune response and specifically the ADAs production to BAs have been extensively clarified in the last years, as well as their capacity to impact on clinical outcomes, among clinicians today a low awareness and in some cases a rejection persists, not only of the analysis and understanding of the immunological mechanisms behind the immunogenicity of BAs, but also the possible clinical impact that this may have.