CD80/CD86 (B7-1/B7-2) on antigen-presenting cells

Class

T-cell costimulation modulator (CTLA-4-Ig fusion protein)

Pathway

Blocks CD28-mediated T-cell costimulation (abatacept, open-label arm)

CD80 (B7-1) and CD86 (B7-2) are proteins displayed on antigen-presenting cells, such as dendritic cells and macrophages, that provide a second, confirmatory signal required for full T-cell activation. A T cell first recognizes an antigen fragment through its T-cell receptor, but this recognition alone is insufficient; the T cell must also receive costimulation delivered when CD80/CD86 engage the CD28 receptor on its surface. This two-signal requirement helps prevent inappropriate immune responses against the body's own tissues. In autoimmune disease, this costimulatory step becomes a therapeutic target: blocking CD80/CD86 from binding CD28 prevents T cells from becoming fully activated, dampening the self-directed immune response. This is achieved with a fusion protein that combines the extracellular portion of CTLA-4, a natural inhibitory receptor, with an antibody fragment that extends its circulating half-life. Because CTLA-4 binds CD80/CD86 with greater affinity than CD28 does, the fusion protein effectively competes for and occupies these ligands, interrupting costimulatory signaling. This mechanism broadly matters in autoimmune and inflammatory conditions where excessive T-cell activation drives tissue damage, and it illustrates a general principle in immunopharmacology: modulating costimulation rather than blocking antigen recognition itself allows for more selective dampening of pathogenic immune activity.