Before now, ‘gene therapy’ vaccines have often delivered just one gene to stimulate the immune system. It produces a protein, called an antigen, which activates the immune system to destroy cancer cells.
It has been difficult to develop successful cancer vaccines because each tumour has specific proteins and identifying the right antigens has been a huge challenge.
Scientists have also tried to boost the effectiveness of vaccines by using several genes to increase the chances of producing successful antigens. But a worry has always been that the immune system’s response would be too strong for the body to handle.
But now researchers, working with Mayo Clinic in Rochester, have solved this problem in experiments involving mice.
The team used doses of a vaccine made from a virus that contained a ‘library’ of DNA, containing multiple fragments of genes and therefore many possible antigens. This approach did not send the immune system into overdrive, which had been a concern. Instead the range of DNA meant the vaccine was able to target the tumour through many routes.
Importantly, the DNA library was harvested from the same organ as the tumour. This meant that the immune system ‘self-selected’ the cancer antigens to respond to and did not react against other healthy parts of the body. Also, the process of self-selection was triggered when the vaccine was injected into the bloodstream, an approach to vaccination that is far more practical than injecting directly into tumours.
The researchers delivered a library of DNA taken from healthy prostate tissue in mice. When delivered in a virus, the vaccine successfully treated mice with prostate cancer.
“This is the first time we have been able to use a whole library of DNA in a viral vaccine successfully,” University of Leeds’ Professor Alan Melcher, co-author of the study, says. “The biggest challenge in immunology is developing antigens that can target the tumour without causing harm elsewhere. By using DNA from the same part of the body as the tumour, inserted into a virus, we may be able to solve that problem.”
The vaccine was made by putting the DNA library inside a vesicular stomatitis virus (VSV), which stimulates an immune response that can then track down and kill tumour cells.
Professor Peter Johnson, chief clinician, Cancer Research UK, says, “This is an interesting and significant study which could really broaden out the field of immunotherapy research.”
“Although the vaccine didn’t trigger the immune system to overreact and cause serious side effects in mice, it will need to be further developed and tested in humans before we can tell whether this technique could one day be used to treat cancer patients,” adds Professor Peter Johnson.