T cells are an important component of the human immune system, acting as the body's "anti-cancer army." When cancer cells proliferate in the body, T cell receptors (TCRs) recognize antigenic peptide fragments presented by major histocompatibility complex (MHC) molecules on the surface of cancer cells, identifying them as foreign invaders and immediately initiating a response to kill the cancer cells. Importantly, T cells do not harm normal cells.
At first glance, as long as this "anti-cancer army" functions normally, the body should be free from cancer. However, cunning cancer cells, after continuous "attacks," learn to evade T cell recognition by downregulating MHC expression, allowing them to thrive in the body.
