Two cases of ulcerative colitis that developed while using abatacept.

Abatacept (ABT) is a recombinant fusion protein consisting of the Fc domain fragment of human IgG1 and the extracellular domain of human cytotoxic T lymphocyte antigen-4 (CTLA-4). The function of ABT is similar to that of CTLA-4, which selectively regulates T-cell activation by inhibiting the co-stimulation of CD80/CD86 on antigen-presenting cells and CD28 on T lymphocytes. ABT is used for the treatment of rheumatoid arthritis (RA) and juvenile idiopathic arthritis. We report two cases of ulcerative colitis (UC) that developed while using ABT. Case 1 is of a 58-year-old man who developed diarrhea and hematochezia 2 months after starting ABT therapy for RA. Case 2 is of a 66-year-old man who experienced hematochezia 15 months after starting ABT therapy for RA. In both cases, no obvious gastrointestinal symptoms were observed before ABT therapy was initiated. Colonoscopy after disease onset showed UC findings in both cases. The patients' condition improved following ABT withdrawal and treatment for UC. Several cases of UC development during ABT therapy have been reported. The complication of UC should be considered when diarrhea and hematochezia are observed in patients with RA being treated with CTLA-4Ig agents.