CTLA4 and rheumatoid arthritis: Abatacept is an approved therapy for RA; it is a fusion protein consisted of CTLA4 attached to the Fc region of IgG1 and acts by blocking co-stimulation signals and therefore inhibiting activation of T cells.13 On the other hand, in Oncology, CTLA4 is also targeted but in a different way; the monoclonal antibody ipilimumab blocks CTLA4 and leads to enhanced T cell activation.1,2 Taking the above into account, there is certainly a theoretical concern regarding the use of immunotherapy, especially in the form of anti-CTLA4, in patients with RA.