The injectable form of the polio vaccine has proven effective at preventing illness but it does not block the transmission of the virus as well as the oral version of the vaccine. That is because the virus is usually transmitted through contaminated food or water and is first exposed to the GI tract, where the oral vaccine induces a mucosal immune response. To date, several countries no longer use the oral vaccine because there is a small risk of infection. It is also possible for people who receive the injected polio vaccine to spread the virus even though they are asymptomatic. 

Now according to data from an Massachusetts Institute of Technology-led study, it may be possible to modify the injectable vaccine so that it can also promote a mucosal immune response. This way, the vaccine could support polio eradication efforts without the risks of the oral polio vaccine. Details are published in a new Science Advances paper titled “Am80-Lipid nanoparticles serve as an enteric mucosal adjuvant 3 following parenteral immunization with inactivated polio vaccine.”

In comments that shed some light on the thinking behind the work, Ana Jaklenec, PhD, a principal investigator in MIT’s Koch Institute for Integrative Cancer Research, stated that while “people who are vaccinated with the injectable vaccine are not getting sick” they may be helping spread the highly contagious virus. “Mucosal immunity could help lower that shedding and ideally eliminate it,” she said. 

Her team’s version of the vaccine comprises an injectable, inactivated polio vaccine delivered with a nanoparticle-based adjuvant that helps steer immune cells to the mucosal lining of the intestine. Digging into the details, Jaklenec and her team worked with a group at Harvard Medical School who have shown previously that using a derivative of vitamin A as a vaccine adjuvant can help stimulate immune cells to go into the GI tract. 

Though the adjuvant, known as Am80, generates a strong response, one challenge is that it needs to be injected for several days in a row, which is not feasible for most vaccine campaigns. To eliminate the need for repeated vaccinations, the scientists used a lipid nanoparticle (LNP) as a delivery vehicle that releases the adjuvant slowly over several days.

Armed with the updated vaccine, the scientists moved on to testing it in rats. For their tests, the scientists injected the standard inactivated polio vaccine along with a separate injection of Am80 encapsulated in LNPs. They also delivered boosters to the rats at four and eight weeks. 

Following injection, LNPs accumulate in the lymph nodes where they interact with B and T cells that are also exposed to the polio vaccine. The interaction stimulates the cells to produce two surface proteins that direct them to the GI tract. Additionally, the B cells produce IgA antibodies, which protect body surfaces from infection by coating the mucosal membranes. Lastly the rats produce IgG antibodies in the bloodstream, which are similar to the antibodies produced in response to the standard injected polio vaccine. 

Overall, in the rats, they found that administering the vaccine and adjuvant produced a two-fold increase in the type of antibodies needed for mucosal immunity compared to the inactivated vaccine alone. Essentially, “by adding Am80 to lipid nanoparticle as an adjuvant, we are combining the safety of IPV with an adjuvant that can produce the mucosal immunity that normally you can only get with OPV,” said Behnaz Eshaghi, PhD, a postdoctoral student at MIT and lead author of the paper. 

For their next steps, the scientists plan to test the improved vaccine in other large animal models where they will inject the vaccine and adjuvant mixed together. More broadly, Am80 and similar adjuvants could help scientists design improved vaccines for other pathogens that infect the GI tract or for diseases that infect the lungs or reproductive tract. 

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