Mentor: Pavan Reddy, MD
CD8+ cytotoxic T cells kill infected or transformed cells in an antigen-specific manner, playing an essential role in the adaptive immune response. To develop cytotoxic capabilities, a naïve CD8+ T cell must be activated through an interaction between its T cell receptor (TCR) and an MHC I molecule on an antigen presenting cell (APC) loaded with the TCR’s cognate peptide. This process is known as antigen presentation. Classically, peptide loaded on MHC I molecules is derived from endogenous protein. However, there are instances where exogenously-derived peptide is presented on MHC I molecules to activate CD8+ T cells in a process called antigen crosspresentation. Crosspresentation is critical for initiating a cytotoxic response against viruses that do not infect APCs and for the immune response to tumors.