[Dendritic cells and tumor specific immunity]

Dendritic cells (DCs) are the most efficient antigen presenting cells (APCs) that initiate and modulate our internal immune responses in stimulating both B cells to produce various antibodies and T cells to control cell-mediated immunity. Such DCs can be classified into three groups based on their origin. One is the myeloid DCs originating from CD34+ stem cells that are further differentiated into CD14+ CD1a- phagocytotic, glass-adherent macrophages with the help of M-CSF, or into CD14- CD1a+, Birbeck granule containing LAG-1+ Langerhans cells by GM-CSF, TNF-alpha and TGF-beta 1 stimulation. The latter Langerhans cells appear to differentiate into DC1 as strong stimulators of T cells displaying large amounts of MHC-peptide complexes and co-stimulatory molecules, such as B7-1 and B7-2, after capturing antigens and migrating to a regional lymphoid organ. The second group is the lymphoid DCs originating from CD4+CD11c- cells, which differentiate into DC2 when cultured with IL-3. Third is the follicular dendritic cells (FDC) observed in lymphofollicules that capture foreign antigens with their Fc-receptor or complement-receptors and keep the antigens inside the follicules. DC1s secrete IL-12, which turns CD4 T cells into Th1 cells to induce cellular immunity, whereas DC2s favor production of Th2 cells to organize humoral immunity. Therefore, DCs appear to control our internal self-defense system. These unique features of DCs enable us to manipulate Th1 and Th2 activation selectively, and thus antigen-pulsed DCs are currently thought of as excellent tools to induce specific T cell immunity towards virus-infected cells or tumor cells.