T cell receptor and co-stimulatory molecule (TCR and co-stimulatory molecule)

The **T cell receptor (TCR)** is a multisubunit complex on T lymphocytes responsible for recognizing antigen peptides presented by major histocompatibility complex (MHC) molecules on antigen-presenting cells, initiating a signal transduction cascade that leads to T cell activation, proliferation, and differentiation. However, TCR stimulation alone is insufficient for full activation: **co-stimulatory molecules** (such as CD28, 4-1BB, OX40, and ICOS) provide secondary signals required for T cell survival, expansion, and effective immune function, while co-inhibitory molecules (such as PD1 and CTLA4) modulate or dampen the immune response. This dual-signal paradigm ensures that T cells respond robustly to pathogens and tumors, while limiting autoimmunity. Both TCR and its co-stimulatory/inhibitory partners are central to current immunotherapeutic strategies, including immune checkpoint inhibition and chimeric antigen receptor (CAR) T cell therapy, but can present serious safety risks if dysregulated or over-stimulated.

Other names

TCR and costimulatory receptorT cell receptor complexT-cell antigen receptor and co-signaling molecules

Immune activation (via agonist/antagonist modulation of signaling); Immune checkpoint blockade (inhibition of negative co-stimulatory/inhibitory pathways); Suppression of autoimmune reactions (by blocking co-stimulation); Enhanced cytotoxic response (especially in CAR T cells)