What is the T cell receptor and why is it critical?

T cells are the effector arm of the adaptive immune system, responsible for eliminating foreign pathogens, infected cells, or senescent/cancerous cells. They determine which cells to eliminate via a recognition system mediated by the T cell receptor (TCR, on the T cell) and major immunohistocompatibility complex (MHCs, on the antigenic cell). T cell activation requires antigen presenting cells (APCs) to deliver two interactions. First, the APC presents an antigen as part of an MHC, which binds to the TCR. Second, APC-expressed B7.1 and B7.2 bind CD28 on the T cell, providing a co-stimulatory signal. When the activated T cell interacts with other cells expressing MHC containing the same antigen initially presented to it, T cell-mediated cytotoxic killing ensues.¹ For expanded information on CAR-T cells please visit our resource center here.

Reference:
C.A. Janeway Jr., et al., Immunobiology: The Immune System in Health and Disease. 6th edition. New York: Garland Science; 2005.