Cancer Vaccine Information

Vaccines for Cancer Prevention

If vaccination can be used to stop infectious diseases, can it be used to prevent cancer? Some scientists are asking this question. Cancer vaccines can be divided into two categories: therapeutic and preventative. Neither exists in a serious way yet, but both are envisioned and cancer centers throughout the world are working on them.

Worldwide, there is the potential to prevent 1.8 million cases of cancer (18%) each year by fighting infections. The proportion is even larger in the third world, where an estimated one in four cancers is linked to infection. It is easier, cheaper, and more effective to vaccinate against viruses to prevent cancer than it is to treat it by conventional means or through a cancer treatment vaccine, and this is where most of the benefit from cancer vaccines is likely to come from in the very near future.

Regardless of which strategies are used to direct the immune response against the tumor or the virus that causes tumors, additives that help boost general immune response are often used. Bacteria, viruses, cytokines (molecules used by the immune system to communicate between cells), as well as various chemicals cause the immune system to increase its response and are therefore often added to vaccines.

The immune system is far more effective when it has to fight a smaller number of cells, so cancer vaccines work best when the tumor has already been removed by standard means, such as chemotherapy, radiation, or surgery. When attacking single tumor cells or small clumps of tumor cells, T cells and B cells devastate their small prey, but an entire tumor easily overwhelms the capabilities of the limited number of T and B cells. With the exception of vaccines against cancer-causing viruses, which will be given to prevent cancer, cancer vaccines show most promise for preventing the resurgence of cancer after the tumor has been removed.

Several early stage clinical trials have shown substantial results for therapeutic cancer vaccines. In one study, the average remission of 18 of 20 people who were vaccinated against non-Hodgkin’s lymphoma lasted four years. In a second study of 33 patients with advanced non-small cell lung caner, three patients experienced complete remission and were alive three years later. In both of these studies, an autologous vaccine was used. Another trial demonstrated that an antibody that interferes with immune-system regulation shrinks metastatic melanoma tumors when added to a melanoma peptide vaccine. This antibody inhibits the tumor’s attempts to interfere with the body’s immune response. Cancer treatment vaccines are under development for melanoma, kidney cancer, lymphoma, lung cancer, breast cancer, prostate cancer, colorectal cancer, cervical cancer (to treat as well as to prevent), ovarian cancer, and others.

There is also growing evidence that a universal cancer vaccine may be possible. Researchers from Duke University Medical Center in Durham, North Carolina and Geron Corp. of Menlo Park, California are targeting a protein called telomerase, which is present in all major human cancers. The telomerase vaccine will not be as effective as vaccines made from a patient’s own tumor antigens, but it may be very useful when combined with other universal antigens. So far, the vaccine has been able to stimulate immune cells to slow tumor growth in mice and kill unrelated human cancer cells in the test tube.

Most antigens used in allogenic vaccines are only specific to one type of cancer, and a few are expressed in two or more types. For example, Carcinoembryonic antigen is found on 90 percent of colon cancers and 40 percent of breast cancers but is still absent from most types. Telomerase, however, is required for cells to divide many times, as it elongates the ends of the chromosomes that are chopped off as cells undergo mitosis. Cancer cells have to divide many times rapidly in order for the tumor to grow, so they virtually always express telomerase. Scientists were initially worried that the body would not mount an immune response against telomerase, because non-cancer cells that need to divide continuously (such as the cells that create new sperm) also express telomerase, so the body may not recognize it as foreign.

To stimulate the T and B cells to recognize telomerase as foreign, the team inserted the RNA that codes for telomerase into APC’s (the cells that present antigens to the B and T cells) in order to induce them to display telomerase on their surface. Once the APC’s are displaying telomerase, the T cells and B cells will recognize it as foreign and mount an immune response. The result is a vaccine that is only moderately effective, but is effective with virtually every type of cancer cell. Once other universal cancer antigens are identified, their combined use may produce a broadly effective vaccine.

These promising early-stage studies, however, are often later proved wrong when re-tested with a larger sample size. For example, one early-stage study that indicated that a melanoma vaccine would help to prevent melanoma recurrence was later surpassed by a larger trial of 774 subjects that showed the vaccine to be less effective than the alternate treatment of high-dose interferon. All of the cancer treatment vaccines mentioned are in the earliest stages of trials, and the universal vaccine has not yet even been tested on humans – it has only been tested on human cell lines and mice.

Early success with cancer vaccines

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