Scientists have taken a bold step towards creating a universal flu vaccine that could work against any flu strain.
Current flu vaccines prevent millions of illnesses each year, but they are not perfect. The key issue is that they only provide protection against select strains of the virus. The vaccine requires modification each year in an ongoing arms race as the virus mutates relatively quickly, and despite the work that goes into predicting prevalent strains, there’s no certainty that the flu vaccine will necessarily match with the main strain in circulation. This is why scientists are so focused on the tricky task of developing a universal flu shot that covers all strains for a substantial span of time.
Reporting in the journal Cell Systems, a team from MIT, Massachusetts General Hospital, and Harvard Medical School have created a vaccine that uses nanoparticles coated with flu proteins that teach the body’s immune system how to respond to an invasion of influenza. The key to their work is pinpointing and closely working with an influenza protein segment that rarely mutates, but is not typically targeted by the immune system.
Typically, flu vaccines use inactivated flu viruses that contain the protein hemagglutinin (HA), an antigen on the virus surface that triggers the immune system to create antibodies that specifically target the virus. The antibodies, however, nearly always bind to the head of the HA protein, a part of the protein that mutates the most rapidly. Instead, this newly developed method focuses on the stem of the HA protein, which rarely mutates.
Annoyingly, the head of the protein is much more accessible and the immune system does not tend to target the stem, so the team sought to find ways to refocus the immune system’s attention to this key part of the protein.
“We don't understand the complete picture yet, but for many reasons, the immune system is intrinsically not good at seeing the conserved parts of these proteins, which if effectively targeted would elicit an antibody response that would neutralize multiple influenza types,” Daniel Lingwood, senior author and assistant professor at Harvard Medical School, explained in a statement.
Armed with this knowledge, they develop a special nanoparticle that carries HA stem proteins at lower density in a spaced-out layout, meaning they are easier for the immune system’s soldiers to bind to and, in turn, better at sparking the production of stem-targeting antibodies.
Once this nanoparticle was employed in a flu vaccine for mice with human immune cells, it triggered the exact response the researchers wanted: even if the mice were vaccinated with nanoparticles displaying HA stem proteins from a different strain of flu, they still produced broadly neutralizing antibodies and appeared to be protected against the virus.
“The reason we’re excited about this work is that it is a small step toward developing a flu shot that you just take once, or a few times, and the resulting antibody response is likely to protect against seasonal flu strains and pandemic strains as well,” said MIT's Arup K Chakraborty.
The researchers were quick to point out that this is a small but significant step towards a universal flu vaccine. While their research has weeded out some of the problems with current vaccines, the prospect of a viable universal flu shot being available in your local pharmacy is still some way off.