GENETICALLY modified 鈥渟mart鈥� bacteria injected into tumours can shrink growths and trigger an immune response that stops cancer spreading, tests in animals show.
The engineered bacteria exploit the vulnerability of solid tumours to infections. This vulnerability comes about because tumours evolve all kinds of tricks for evading immune system attack, from physically keeping out immune cells to releasing chemicals that tell the cells not to attack. But this leaves tumours open to infection by bacteria and viruses that would be rapidly wiped out elsewhere in the body.
The smart bacteria, created by Sreyan Chowdhury at Columbia University in New York and his colleagues take advantage of this, infecting a tumour and multiplying.
Advertisement
Once the number of bacteria reaches a聽critical level, they are designed to self-destruct and release an antibody in the heart of the cancerous growth. This antibody then聽encourages the immune system to attack the tumour.
The team started with a harmless strain of E. coli. This was engineered to produce an antibody, which binds to聽a protein called CD47 found on the聽surface of some cancer cells, triggering their destruction.
However, CD47 is also found on the surface of healthy red blood cells, so injecting high levels of the antibody straight into the blood would be dangerous. By instead injecting the bacteria directly into tumours, high levels of the antibody are produced only where needed.
In tests in mice, several kinds of tumours shrank after being injected with the smart bacteria. What鈥檚 more, the growth of tumours elsewhere in聽the body of the mice also slowed, while the chances of cancer spreading to new sites in the body was greatly reduced (bioRxiv, ).
The research shows that the modified bacteria can be used to trigger body-wide immune system targeting of untreated tumours, says cancer biologist Graham Dellaire of Dalhousie University in Canada.
鈥淗arnessing this effect could well聽be the key to curing metastatic disease 鈥� the major cause of cancer-related death,鈥� he says.
Whether this approach will work in聽people remains to be seen, but Dellaire points out that the live bacteria used to immunise against TB,聽in the BCG vaccine, have long been used to treat bladder cancer. This is also thought to work by triggering an immune response.
