Virus World

NIH researchers explore hidden, vulnerable region of influenza neuraminidase.

Researchers at the National Institutes of Health have identified antibodies targeting a hard-to-spot region of the influenza virus, shedding light on the relatively unexplored “dark side” of the neuraminidase (NA) protein head. The antibodies target a region of the NA protein that is common among many influenza viruses, including H3N2 subtype viruses, and could be a new target for countermeasures. The research, led by scientists at the National Institute of Allergy and Infectious Diseases’ Vaccine Research Center, part of NIH, was published today in Immunity. Influenza, or flu, sickens millions of people across the globe each year and can lead to severe illness and death. While vaccination against influenza reduces the burden of the disease, updated vaccines are needed each season to provide protection against the many strains and subtypes of the rapidly evolving virus. Vaccines that provide protection against a broad range of influenza viruses could prevent outbreaks of new and reemerging flu viruses without the need for yearly vaccine reformulation or vaccinations. One way to improve influenza vaccines and other countermeasures is to identify new targets on the virus’s surface proteins in “conserved” regions—portions that tend to be relatively unchanged between different strains of the virus. Influenza NA is a surface protein containing a globular head portion and a narrow stalk portion. The underside of the NA head contains a highly conserved region with targets for antibodies—known as epitopes—that make it vulnerable to antibody binding and inhibition of the virus, as well as not being impacted by mutations common in drug-resistant strains. This region is termed the “dark side” due to its partially hidden location and relatively unexplored characteristics.

The researchers isolated human antibodies that target the NA dark side from the blood of two people who had recovered from influenza type A subtype H3N2, a major subtype of seasonal flu viruses. In lab tests, the antibodies inhibited propagation of viruses from subtype H2N2, the subtype that caused pandemic influenza in 1957-58, and H3N2 viruses from humans, swine, and birds. The antibodies also protected mice from lethal infection by a subtype H3N2 virus when given to the animals either one day before or two days after infection, showing that the antibody may treat and prevent influenza in this model. The scientists analyzed the structure of two of the antibodies while bound to NA using advanced microscopy techniques known as cryogenic electron microscopy. Each antibody targeted different, nonoverlapping regions of the dark side, demonstrating that this region has multiple areas that may be useful to explore for countermeasure development. These findings show that the NA dark side has unique, previously untapped epitopes that could be applied to the development of new vaccine and therapeutic strategies. They suggest that antibodies targeting the NA dark side could be useful in combination with antivirals or other types of antibodies for interventions against influenza, as they are effective against influenza viruses with drug-resistant mutations. The researchers also note that NA dark side targets could be included in the next generation of broadly protective vaccines against influenza.

Study published in Immunity (March 24, 2024):

https://doi.org/10.1016/j.immuni.2024.02.003 

Researchers have found an antibody that protects mice against a wide range of lethal influenza viruses, according to a study from Washington University School of Medicine in St. Louis, Icahn School of Medicine at Mount Sinai in New York City, and Scripps Research in La Jolla, Calif. The antibody could serve as a template to aid in design of a universal vaccine that protects against all strains of the virus, and a drug to treat and protect against severe cases of flu, including pandemics. 

"There are many strains of influenza virus that circulate, so every year we have to design and produce a new vaccine to match the most common strains of that year," said co-senior author Ali Ellebedy, Ph.D., an assistant professor of pathology and immunology at Washington University. "Now imagine if we could have one vaccine that protected against all influenza strains, including human, swine and highly lethal avian influenza viruses. This antibody could be the key to the design of a truly universal vaccine."  Ellebedy discovered the antibody—an immune protein that recognizes and attaches to a foreign molecule—in blood taken from a patient hospitalized with flu at Barnes-Jewish Hospital in St. Louis in the winter of 2017. Ellebedy was working on a study analyzing the immune response to flu infection in humans, in collaboration with the Washington University Emergency Care and Research Core, which was sending him blood samples from consenting flu patients. He quickly noticed that this particular blood sample was unusual: In addition to containing antibodies against hemagglutinin, the major protein on the surface of the virus, it contained other antibodies that were clearly targeting something else.

"At the time we were just starting, and I was setting up my lab so we didn't have the tools to look at what else the antibodies could be targeting," said Ellebedy, who is also an assistant professor of medicine and of molecular microbiology. He sent three of the antibodies with unknown targets to co-senior author Florian Krammer, Ph.D., a microbiology professor at the Icahn School of Medicine at Mount Sinai. An expert on neuraminidase—the other protein on the surface of the influenza virus—Krammer tested the antibodies against his extensive library of neuraminidase proteins. At least one of the three antibodies blocked neuraminidase activity in all known types of neuraminidase in flu viruses, representing a variety of human and nonhuman strains. "The breadth of the antibodies really came as a surprise to us," Krammer said. "Typically, anti-neuraminidase antibodies can be broad within a subtype, like H1N1, but an antibody with potent activity across subtypes was unheard of. At first, we did not believe our results. Especially the ability of the antibodies to cross between influenza A and influenza B viruses is just mind-boggling. It is amazing what the human immune system is capable of if presented with the right antigens."....

Published on Science (Oct. 25, 2019):

https://doi.org/10.1126/science.aay0678

Researchers at Georgia State University.develop universal flu vaccine that protects against six influenza viruses in mice. The researchers developed and showed that a novel nanoparticle vaccine that combines two major influenza proteins is effective in providing broad, long-lasting protection against the influenza virus in mice, showing promise as a universal flu vaccine. Findings from the new study—performed in mice and published recently in Advanced Healthcare Materials through an article titled “Double‐Layered M2e‐NA Protein Nanoparticle Immunization Induces Broad Cross‐Protection against Different Influenza Viruses in Mice”—suggest this unique vaccine combination has potential as a universal influenza vaccine or component of such vaccines.

The double-layered nanoparticle vaccine contains the influenza virus proteins matrix protein 2 ectodomain (M2e) and neuraminidase (NA). Mice were immunized with the nanoparticle vaccine before being exposed to the influenza virus, and they were protected against six different strains of the virus. “This nanoparticle antigen combination conferred mice with strong cross-protection,” explained lead study investigator Ye Wang, a doctoral candidate at the Institute for Biomedical Sciences. “It can protect mice from different strains of influenza virus. Each season, we have different flu strains that affect us. By using this approach, we hope this nanoparticle vaccine can protect humans from different strains of the influenza virus.”

Influenza is a leading cause of death by infection. Seasonal flu vaccines are insufficient to prevent influenza outbreaks and developing a universal influenza vaccine is the ideal strategy for eliminating public health threats of influenza epidemics and pandemics. A universal influenza vaccine would eliminate the need for vaccinations each season and offers universal protection against all influenza strains. The influenza virus protein M2e is found in all influenza virus strains, with each strain having a very similar version, and the protein has mutated very slowly over time. The protein NA is found on the surface of the influenza virus and has also mutated much slower than other influenza proteins. This double-layered nanoparticle vaccine uses M2e as its core, and NA is coated on the surface. In the current study, mice were exposed to one of six influenza virus strains after receiving the nanoparticle vaccine by intramuscular injection. The vaccine proved to have long-lasting immune protection, which was unchanged against viral challenges up to four months after immunizations. 

Published in Advanced Healthcare Materials (Dec. 15, 2019):

https://doi.org/10.1002/adhm.201901176