Cytotoxic T cell

A cytotoxic T cell is a specialized T cell that identifies and eliminates cells displaying abnormal peptides on MHC class I molecules — typically cells infected by viruses or transformed by cancer. Upon recognition, the cytotoxic T cell releases perforin and granzymes that induce apoptosis in the target cell, a mechanism of lethal precision that spares adjacent healthy tissue. This targeted killing is the central execution mechanism of cell-mediated immunity.

The cytotoxic T cell is also a site of immunological control and failure. In chronic infections and tumors, persistent antigen exposure can render cytotoxic T cells dysfunctional through a state called T-cell exhaustion, characterized by the upregulation of inhibitory receptors such as PD-1 and CTLA-4. The discovery of this exhaustion pathway and its pharmacological blockade — checkpoint inhibition — represents one of the most significant advances in cancer therapy, transforming lethal malignancies into manageable chronic conditions.