THE TREATMENT OPTIONS that are available for treating cancer are surgery, radiation therapy, chemotherapy, immunotherapy, hormonal therapy, laser treatment, and biological therapies. Of all these forms of treatment for cancer, vaccines seem to hold great promise because of their efficacy and minimal side-effects profile. The mechanism of action is to teach the body’s immune system to identify cancer cells and destroy them. In the U.S., the National Cancer Institute and many biotech companies are involved in the research and development of cancer vaccines. According to estimates, more than 50 vaccines are undergoing advanced trials for cancer. The major biotech companies, besides the National Cancer Institute, involved in research and trials include Cell Genesys, Biomira, Antigenics, Dendreon, Genzyme Molecular Oncology, VaxGen, and Corixa.
History Early 90s saw cancer vaccine technology come into focus with most companies starting out research with antigen-specific cancer vaccines or whole cell vaccines. Cell Genesys and Biomira were one of the earliest companies to start research into cancer vaccines.
Research on cancer vaccines has been continuing for a long time and scientists have approached it by isolating selected antigens that are differentially expressed on tumour cells and not so well expressed on normal cells. Scientists use either the whole cancer cell or synthetically manufacturing components of the transformed cell, using recombinant protein to develop tumour-associated antigen.
The technology behind cancer vaccines is the stimulation of the body’s defence mechanism “the immune system” to identify cancer cells and release antibodies and/or killer T-cells to destroy the occult or residual cancer cells.
In melanoma, there are recognised antigens like Mark-1, GP 100, TRIP1, and TRIP2. Scientists have isolated and made recombinant protein from these antigens and injected them back into the body. This activates the human immune system in the context of vaccination. The effort is to break the tolerance the body has towards these antigens and mount an immune response to it. In another approach, the therapeutic vaccine consists of (lysed) broken melanoma cell lines combined with adjuvant, which when injected back into the body activates the immune response to the tumour cells. Other companies are trying to develop cancer vaccines by taking the approach of injecting a plasmid that encodes a protein instead of the actual protein, which triggers an immune response to cancer cells.
To break the tolerance to antigens in the clinical setting, scientists require a better understanding of the immune system and the adjuvants to come up with a reliable process. Thus far, nobody has been very successful.
Products in the Pipeline
The companies that are likely to introduce cancer vaccines in the near future are Antigenics, Dendreon, Genzyme Molecular Oncology, and VaxGen. There is a strong possibility for some of these companies to successfully obtain FDA approval for products by 2005-2006. The most probable vaccines are for melanoma and prostate cancers. There are almost seven cancer vaccines that are in phase-III trials for 10 different cancer indications. The most advanced cancer vaccine is from Corixa called “Melacine” for melanoma, which has already received marketing approval in Canada. Melacine is expected to receive the FDA approval in the U.S. by 2004.
Comparison with Other Key Technologies
Monoclonal antibodies have established their efficacy and safety profile in treating cancer. The next generation of monoclonal antibodies has also evolved with the radiolabelling of monoclonal antibodies with radioactive agents. This forms a potent combination of targeted attack on the cancer cells.
On the other hand monoclonal antibodies have also started receiving approvals for multiple indications while vaccines are targeted at specific tumors and would be more narrowly focused. This limits the market opportunity for vaccines. Yet another technology which could become a potential competitor to vaccines is gene therapy. Despite the promise this technology holds, there are many hurdles that needs to be overcome before gene therapy products reach the market.
A trend similar to monoclonal antibodies can be seen with cancer vaccines. The success of the first cancer vaccine shall largely determine the fate of the future vaccines and the hopes of millions of cancer patients who long for a better quality of life.
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