ABSTRACT
Harnessing the immune response to reject autologous tumor involves at least two processes: 1) activation of tumor-specific lymphocytes and 2) targeting of the activated lymphocytes to tumor cells. For lymphocytes to be successfully activated they must interact via their antigen-specific receptor (TcR for T lymphocytes; BcR for B lymphocytes) with their cognate antigen and receive additional co-stimulatory signals. This process is called antigen presentation and usually professional APC provide both the antigen signal and the co-stimulatory signal. Although the BcR of B lymphocytes can respond to intact antigen, the TcR of T lymphocytes only responds to small fragments of antigen. APC must therefore break down macromolecular antigens into smaller fragments for presentation to T lymphocytes. This process of degradation is called antigen processing and occurs in APC. Because the antigen-specific receptor of T cells only recognizes antigenic fragments bound to specialized antigen-presenting molecules encoded by the MHC, degraded antigen must associate with the antigen presentation molecules encoded by the APC’s MHC (e.g. MHC class I, class II, or CD1 molecules) for presentation to T lymphocytes. Because CD4+ Th lymphocytes are required for both T and B lymphocyte responses, appropriate processing and presentation of antigen is central to both T and B immune responses, and critical for the generation of effective antitumor immunity.
