Fig. 1

HNCs can inhibit t-cell-mediated activation of immune responses through three pathways. 1 Tumor cells can express MHC I molecules on the cell surface and form an antigenic peptide-MHC CLASS I molecular complex through the MHC I pathway, which provides the first signal for T cell activation. CD8+ T cells can initially transform into CTL after receiving the first signal 2 At the same time, tumor cells can recognize MHC class II molecules on the surface of APC cells by pattern recognition receptors (PRR). Some MHC II molecules can form the first signal through cross-presentation and participate in the initial activation of CTL cells through the endogenous antigen presentation pathway. Other MHC CLASS II molecules can form an antigenic peptide-MHC Class II molecular complex through the MHC II pathway to activate CD4+ T cells to produce costimulatory molecules, and at the same time provide a second signal for the activation of CD8+ T cells to fully activate and maintain CTL proliferation and cloning. 3 Tumor cells and APC cells can also secrete costimulatory molecules and participate in the formation of the secondary signal