T cell co-stimulatory molecule

T cell co-stimulation refers to the essential secondary signaling required by T cells during their activation by antigen-presenting cells. Full activation requires two signals: one through the antigen-specific TCR recognizing peptide-MHC complexes and another through non-antigen-specific interactions between surface-expressed co-stimulatory molecules on both APCs and T cells. Without this second signal—mediated primarily via interactions like B7/CD80/CD86 on APCs with CD28 on T cells—T cells become anergic or undergo apoptosis rather than mounting an effective immune response. Multiple protein families contribute these signals; most notably members of the Immunoglobulin superfamily (such as CD28/B7) and TNF receptor superfamily (such as OX40/TNFRSF4). Therapeutically relevant targets within this system include both positive regulators ("co‑stimulatory") that enhance immunity—of interest especially in cancer—and negative regulators ("co-inhibitory," e.g., CTLA4/PD‑1) that suppress it—targeted for autoimmune disease treatment. Drugs modulating these pathways can profoundly affect immune function but carry risks including overactivation leading to cytokine storms or suppression resulting in infection susceptibility.

Other names

Co-stimulatory moleculeT cell costimulationCo-signaling moleculeImmune checkpoint stimulators

For drugs targeting this system: - Blockade of co-stimulatory signals to induce immune tolerance or treat autoimmunity/transplant rejection (e.g., CTLA4-Ig blocks CD28–B7) - Agonism of co-stimulatory receptors to enhance anti-tumor immunity by boosting T cell activity