Cancer immunotherapy by dendritic cells.

Cancerous lesions promote tumor growth, motility, invasion, and angiogenesis via oncogene-driven immunosuppressive leukocyte infiltrates, mainly myeloid-derived suppressor cells, tumor-associated macrophages, and immature dendritic cells (DCs). In addition, many tumors express or induce immunosuppressive cytokines such as TGF-beta and IL-10. As a result, tumor-antigen crosspresentation by DCs induces T cell anergy or deletion and regulatory T cells instead of antitumor immunity. Tumoricidal effector cells can be generated after vigorous DC activation by Toll-like receptor ligands or CD40 agonists. However, no single immunotherapeutic modality is effective in established cancer. Rather, chemotherapies, causing DC activation, enhanced crosspresentation, lymphodepletion, and reduction of immunosuppressive leukocytes, act synergistically with vaccines or adoptive T cell transfer. Here, I discuss the considerations for generating promising therapeutic antitumor vaccines that use DCs.