Abatacept (trade name Orencia), a fusion protein containing the extracellular domain (ECD) of CTLA-4 and a Fc fragment of human IgG1, is used to extend graft survival by limiting the toxicity generated by standard immune suppressing regimens such as calcineurin inhibitor treatment. The CTLA-4 protein is important for T cell costimulation and selectively blocks the process of T cell activation. Abatacept binds to the CTLA-4 ligand CD80 (B7-1) with more avidity than to CD86 (B7-2), inhibiting T cell activation. Abatacept differs from Belatacept (trade name Nulojix) by only 2 amino acids. This Abatacept biosimilar is a chimeric protein composed of the CTLA-4 ECD fused to the Fc region of human IgG1.