abatacept is a CTLA4-Ig (cytotoxic T lymphocyte-associated antigen-4-Ig) that acts against RA by inhibiting CD80/86-CD28 interactions (one of the co-stimulatory pathways between antigen-presenting cells and T lymphocytes); it inhibits the formation of immunological synapses. The gene discussed is CTLA4; the disease is rheumatoid arthritis.