abatacept

Abatacept is a fusion protein that acts as a selective costimulation blocker of T cells. It combines the extracellular domain of CTLA-4 with the modified Fc region of IgG1, and binds to CD80 and CD86 on antigen-presenting cells, preventing interaction with CD28 on T cells. This reduces T-cell activation and downstream inflammatory cytokine production.

Abatacept is approved for the treatment of rheumatoid arthritis in adults, particularly in patients with inadequate response to one or more TNF inhibitors. It is also approved for moderate to severe polyarticular juvenile idiopathic arthritis in pediatric patients; beyond RA, it has been studied in psoriatic arthritis and other inflammatory conditions.

Administration: available as an intravenous infusion and as a subcutaneous injection. IV dosing is given on specific days (initial loading doses), then every 4 weeks, with dose adjusted by body weight. Subcutaneous abatacept provides a fixed 125 mg weekly regimen after an IV loading phase in eligible patients. The subcutaneous form offers an at-home option for some patients after initial dosing in clinic.

Safety: abatacept can increase the risk of infections, including serious bacterial, viral, and opportunistic infections; screen for latent tuberculosis and provide vaccination as appropriate before starting. Live vaccines should be avoided during therapy. Concurrent use with other biologics or high-dose steroids may increase infection risk. Common adverse events include headache, nausea, cough, and infusion or injection-site reactions. Rare cases of malignancy have been reported. Monitor for symptoms of infection or organ toxicity.

Brand name Orencia is the best-known product; abatacept has been developed and reviewed by regulatory agencies worldwide for these indications.