Antigen Presentation by Dendritic Cells and Their Significance in Anti-Neoplastic Immunotherapy

Dendritic cells (DCs) are present in essentially every mammalian tissue, where they operate at the interface of innate and acquired immunity by recognizing pathogens and presenting pathogen-derived peptides to T lymphocytes. According to the research group of Shortman, experimental results suggest a "dual" DC differentiation model, demonstrating the existence of both myeloid-derived (with characteristic IF: CD11b+, CD11c+, CD8alpha- and DEC205+) and lymphoid-derived DCs (showing CD11b- CD11c-, CD8alpha+ and DEC205+ IF). DCs, including interdigitating cells (IDCs) and Langerhans cells (LCs), are characterized by dendritic morphology, high migratory mobility and are the most effective, "professional" cells for antigen presentation in primary immune responses. Most of the DCs express immunocytochemically detectable antigens like: S-100, CD1a, CD40 receptor, adhesion molecules (ICAM-1 or CD54, LFA-1 and LFA-3), integrins (CD11a, CD11c and CD18), CD45, CD54, co-stimulatory molecules (B7-1 or CD80, B7-2 or CD86), F418, MHC class I and II and DEC-205, multilectin receptor, immunostimulatory cytokine (IL-12) and, of course, Fc and complement receptors. Following recognition and uptake of antigens, mature dendritic cells (DCs) migrate to the T lymphocyte rich area of draining lymph nodes, display an array of antigen-derived peptides on the surface of major histocompatibility complex (MHC) molecules and acquire the cellular specialization to select and activate naive antigen-specific T lymphocytes. Immunotherapeutic ideas are based on the ability of the mammalian immune system to recognize neoplastically transformed cells. Immunotherapy of human neoplasms has always represented a very attractive fourth-modality therapeutic approach, especially in light of the many shortcomings of conventional surgical, radiation and chemotherapies in the management of neoplastically transformed cells. The cancer vaccine approach to therapy is based on the notion that the immune system could possibly mount a rejection strength response against the neoplastic cell conglomerate. The efficiency of DCs for T lymphocyte stimulation moved a number of research groups to develop DC- based immunotherapy approaches. The failure of cancer vaccines may be attributed to the relationship between host and neoplasm: through a natural selection process, the host facilitates the selective enrichment of clones with highly aggressive neoplastically transformed cells, being in various stages of differentiation and only during certain stages express neoplastic cell specific molecules.