Tumor-associated antigen vaccines are made from defined antigens isolated from specific tumor cells, or produced by chemical or genetic synthesis. The antigens are combined with substances or organisms that carry them to the immune system. An ability to activate an immune response against a single tumor-associated antigen whose protein and DNA sequences are known enables researchers to develop potentially more powerful vaccines.

Vaccines currently under investigation include:

• Peptide vaccines. Peptides are combinations of amino acids, the building blocks of proteins, including antigens. Researchers have identified peptide sequences of some tumor-specific antigens that activate a cytotoxic T cell response. This has led to the production of the antigen using synthetic peptides, which have been well tolerated by patients in early clinical trials. In peptide vaccines, the synthetic antigen is transported by a protein-containing substance called an adjuvant. It is expected that the immune system, in responding to the antigen-carrying adjuvant, also will respond to the original tumor that expresses that antigen.
• Dendritic cell vaccines. Dendritic cells are powerful and effective antigen-presenting cells. They are especially efficient at alerting resting helper T cells to the presence of foreign tissue. Dendritic cells get their name from the Greek word dendron ("tree") because they resemble trees, with roots and branches spreading out from the main body of the cell. Dendritic cell vaccines use dendritic cells to carry and present melanoma antigens to the immune system, activating an immune response. The source for the dendritic cells is a patient's own blood or bone marrow stem cells, although the use of allogeneic cells is also being investigated. Tumor cells are the source for most melanoma antigens. Some recent studies are also looking at the use of antigen peptides. Clinical trials have shown encouraging evidence that dendritic cell vaccines stimulate the immune response in patients with high-risk and advanced melanoma.
• Recombinant viral vaccines. Viruses are skilled at infecting cells and stimulating an immune response. Through recombinant DNA technology – techniques used to take apart and recombine a cell's genetic information –a number of viruses have been genetically altered to carry tumor-associated antigens. It is hoped that the viral carrier will prompt the immune system to recognize the antigens on the altered cells as foreign substances, and transfer that recognition to antigens on the unaltered cancer cells remaining in the patient. Clinical trials are testing melanoma vaccines made from melanoma-associated antigens attached to a form of adenovirus, the virus that causes respiratory tract and eye infections. At this time, results are not conclusive.

For more information on these types of investigations, see Clinical Trials.