Much recent attention has been given to the use of ex vivo-modified dendritic cells in tumor vaccine therapy; that is, dendritic cells modified in the laboratory. Dendritic cells are the most potent of the antigen presenting cells (APCs) and are up to 1000 times more effective in stimulating antigen-specific T cells than are other types of APCs.(1) Dendritic cell precursors can be isolated from a patient's blood, and these precursors can be stimulated in the laboratory to mature and to take up and present tumor-specific antigens. To make the dendritic cell present a tumor-specific antigen, the cells can be coincubated with dead tumor cells, tumor cell fragments, tumor proteins, tumor DNA or RNA, or bacteria and viruses that have been engineered to contain tumor antigens.(2) These tumor cells or proteins may come from the patient who will receive the vaccine, or they may come from other patients with the same type of cancer.
These mature dendritic cells can then be injected back into the original patient, where they will migrate to the patient's lymph nodes. There, they will encounter the T cell and stimulate tumor-specific T cells to recognize and fight the tumor cells in other parts of the body. Clinical trials are ongoing in various cancer types, including melanoma, myeloma, breast, and prostate. The major limitation to this type of therapy is the need to isolate and grow dendritic cells for each patient; however, if this therapy proves to be effective and becomes widespread, centers could be established for the large-scale processing of dendritic cells much in the way that bone marrow is processed for transplants.(3)
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