PMC

Interaction of immune cells with tumor cells. (a) Dendritic cells present antigen via MHC class II to T cells via the T cell receptor (TCR). Binding of co-stimulatory signaling molecules (signal 2) is required for adequate T cell activation to occur. (b) Immune checkpoints are present at several points of the immune response, which regulate T cell activity. Blocking these interactions may enhance anti-tumor T cell activity. (c) In response to activation via dendritic (or other antigen presenting) cell signaling, T cells up-regulate specific TCRs and produce interferon-gamma (IFN-γ), which induces tumor cells to express programed death receptor 1 ligand (PD-L1), perhaps making it a therapeutic target. (d) Tumor cell destruction results in debris that is engulfed by APCs (including dendritic cells), processed, and presented back to T cells. This process is the basis for an immunotherapy-induced process known as antigen-cascade/antigen spreading.