Designer bacteria show way for better vaccines

dangerous, appear on the cell surface of a wide range of bacteria. As a result, humans have evolved over millions of years to detect and respond to them quickly. They trigger an immediate red alert.

“In some of its forms an endotoxin can kill you,” said Trent. “But the adjuvant, which is called MPL, is a very small, carefully modified piece of it, so it’s able to trigger the immune response without overdoing it.”

What Trent and his colleagues have done is expand on that basic premise. Rather than just work with an inert piece of endotoxin, they’ve engineered E. coli bacteria to express the endotoxin in many configurations on the cell surface.

“These sixty-one E. coli strains each have a different profile on their surface,” said Brittany Needham, a doctoral student in Trent’s lab and the first author on the paper. “In every case the surface structure of the endotoxin is safe, but it will interact with the immune system in a range of ways. Suddenly we have a huge potential menu of adjuvants to test out with different kinds of vaccines.”

One form might work better with cholera vaccine, another with pertussis (whooping cough) and another with a future HIV vaccine. Trent, Needham and their colleagues should be able to fine-tune the adjuvants with increasing precision as more E. coli strains are engineered and tested, and as their understanding of how they interact with the immune system deepens.

“I think we’re at the dawn of a new age of vaccine design,” said Trent. “For a long time vaccinology was really a trial-and-error field. It was a black box. We knew certain things worked. We knew certain vaccines had certain side effects. But we didn’t entirely know why. Now that’s changing.”

Trent said that an additional advantage of their system is that the E. coli can be engineered to express key viral and bacterial antigens along with the endotoxin. A single cell could deliver both parts of the one-two punch, or even a one-two-three punch, if antigens from multiple diseases were expressed in a single E. coli.

“It makes possible a vaccine that provides protection from multiple pathogens at the same time,” said Trent.

Trent and his colleagues are working on a second round of designer E. coli. They have also filed a provisional patent on their system and are working with the university to find a corporate partner to pay for clinical trials.

“This is ready to go,” said Trent. “I can’t predict whether it will actually make it to the market. But it’s very similar to the adjuvant that has already been approved, and my instinct is that if a company will undertake to do the trials, it will get approved. A company could call us tomorrow, we could send them a strain, and they could start working.”

— Read more in Brittany D. Needham et al., “Modulating the innate immune response by combinatorial engineering of endotoxin,” Proceedings of the National Academy of Sciences (7 January 2013) (doi: 10.1073/pnas.1218080110)