Abatacept is an FDA-approved CTLA-4-Ig fusion protein that robustly inhibits co-stimulatory signals critical for T cell activation.12 Abatacept is used clinically as an effective and extremely well characterized T cell inhibitor in the setting of autoimmunity, and remains a prototypical pre-clinical tool for the precise inhibition of T cell responses.19,31,32 As such, we used abatacept to simultaneously gain mechanistic insights into the importance of co-stimulation dependent T cell responses in CIRI and assess the therapeutic value of T cell inhibition. This evidence concerns the gene CTLA4 and Autoimmunity.