CD8

CD8 is a glycoprotein primarily present in cytotoxic T lymphocytes (CTLs), including the homodimer composed of two α chains and the heterodimer composed of one α and one β chains. It can serve as a co-receptor of T cell receptors to enhance the interaction between T cells and target cells, mediating efficient immune response. In clinical practice, CD8 is associated with the good prognosis of lung cancer, breast cancer, endometrial cancer, diffuse large B cell lymphoma and other tumors, which is because CD8+ T cells can directly kill tumor cells by secreting factors such as perforin and granzyme, so the CTL counting based on CD8 staining is an important assistant measure for tumor prognosis evaluation. The absence of CD8+ T cell infiltration in oral squamous cell carcinoma and colorectal cancer is also considered as a poor prognostic factor for patients. However, continuous antigen stimulation and immunosuppressive microenvironment may induce the exhaustion of CD8+ T cells, leading to the immune effect loss and metabolic dysfunction. Therefore, improving exhaustion has become a crucial research direction in current tumor immunotherapy.