author
Sang-Moo Kang, PhD, a professor at the Institute for Biomedical Sciences at Georgia State University, is the senior author of the study.

A team of scientists led by Sang-Moo Kang, PhD, a professor at the Institute for Biomedical Sciences at Georgia State University, has designed a universal flu vaccine that protects against both influenza A and B virus types and successfully tested its efficacy in mouse models.

The vaccine consists of a virus-like particle (VLP) that displays several subtypes of neuraminidase—an enzyme commonly found in pathogens that breaks down sugars containing neuraminic acid, and tandem repeats of a highly conserved, extracellular segment of an influenza virus protein (M2e) that stimulates the host’s immune system. Neuraminidase subtypes are prominent antiviral drug targets.

Employing these conserved influenza A and B viral proteins, enabled the researchers to generate a broad-spectrum cross-protective flu vaccine. The study, published in PLoS Pathogens (“Universal protection against influenza viruses by multi-subtype neuraminidase and M2 ectodomain virus-like particle”), was funded by the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health (NIH).

candidate vaccine
Multi-component candidate universal flu vaccine (m-cNA-M2e VLP) expressing M1, multi subtype cNA (cN1, cN2, and B-cNA), and five M2e genes. [adapted from Kim K-H, et al, PLoS Pathogens, 2022]
Kang, the senior author of the study said, “We developed a single, universal vaccine entity that induced immunity to conserved M2 ectodomain and multi subtype neuraminidase proteins and was found to be effective in conferring broad cross-protection against antigenically diverse influenza A and B viruses in young and aged mice. This study provides impactful insight into developing a universal influenza vaccine inducing broad immunity against both flu A and B variants in young and aged populations.”

“The manuscript by Ki-Hye Kim, et al., on universal multi-subtype neuraminidase and M2e is exciting. It shows a baculovirus influenza vaccine that includes neuraminidase is effective against a wide range of influenza types. Neuraminidase is often considered a secondary target in influenza vaccines, where hemagglutinin is the primary target,” said Eric Weaver, PhD, associate professor and director at the Nebraska Center for Virology at the University of Nebraska in Lincoln. (Weaver was not involved in the current study.)

“This paper describes the importance of neuraminidase and will hopefully guide the field back to the importance of neuraminidase in vaccine design and efficacy. These data should have a significant impact on the field of vaccinology,” added Weaver.

VLPs
Transmission Electron Microscopy images of virus-like particles. [Kang]
The investigators demonstrated that mice administered the candidate vaccine were protected against seasonal variants of influenza A, potential pandemic viruses (H1N1, H5N1, H3N2, H9N2, and H7N9), and influenza B viruses (Yamagata and Victoria lineage) that bore significant variations in surface antigens. The authors showed that the universal vaccine candidate induced broad neuraminidase inhibition, the generation of M2e-specific antibodies, and T cell immune responses in both young and aged mice.

“Neuraminidase is a desirable target for a cross-protective vaccine as it is for antiviral drugs (such as Tamiflu),” said Kang. “However, some variations in the neuraminidase proteins have been a barrier. We tried to overcome this barrier by incorporating multiple subtypes of consensus neuraminidase and universally conserved M2 protein fragment into a single entity of virus-like particulate form.”

The team utilized a vector capable of expressing multiple genes to design the universal flu vaccine candidate. “This novel technique was originally developed by Dr. Peter Pushko, a co-author of this article from Medigen,” said Kang.

Available influenza vaccines neutralize strain-specific forms of hemagglutinin, a glycoprotein found on the surface of influenza viruses that is essential for its infectivity because it binds to receptor molecules in the host. Hemagglutinin changes constantly. Seasonal variants of influenza viruses emerge as a consequence of accumulating changes in the HA protein. Adequate variations in hemagglutinin enable the virus to evade the host’s immune system and establish disease.

At present, influenza vaccinations are recommended annually but their effectiveness remains hit or miss due to the constant changes that occur in the structure of surface hemagglutinin. The effectiveness of the seasonal vaccine can be less than 20% based on the differences between hemagglutinin that the vaccine is designed to target and the real-time status of the evolved antigen. Therefore, influenza remains a global threat to public health.

Kang emphasized that the significance of these findings is that a single vaccine construct can be designed to induce immunity against multiple neuraminidase subtypes and M2 proteins. “This universal vaccine [candidate] protects against both flu A and B and potential future pandemic virus variants, and works even in an aged mouse model,” said Kang.

The study suggests that the novel strategy of using conserved instead of highly variable protein domains to generate a vaccine could offer broad protection in humans against sickness and mortality associated with seasonal flu strains. The mouse model data support the continued testing of the cross-protective efficacy of the candidate vaccine in ferrets with pre-existing immunity. The respiratory tracts of ferrets are a closer match to humans, compared to that of mice, and thereby provide a more relevant model prior to translational studies, explained Kang.