Influenza viruses are important pathogens that can cause sporadic respiratory diseases, annual epidemics, and (in the case of influenza A virus) periodic pandemics. Further innovative and continuous research is required to understand viral pathogenesis and its genomics, the body's immune response to the infection, and the epidemiology of the virus to create adequate countermeasures.
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Collaborating Centers of the World Health Organization (WHO) in Atlanta, London, Melbourne, Beijing, and Tokyo are responsible for investigating influenza viruses circulating among humans in different countries. This information can be used by WHO to make recommendations regarding which viruses should be a part of annual seasonal influenza vaccines for the northern and southern hemispheres.
Influenza researchers at five sites in the United States received funds from the American National Institute of Allergy and Infectious Diseases (NIAID) to collaborate with scientists worldwide in a network designed to advance understanding of influenza viruses, especially regarding how they cause disease. The centers are based at Icahn School of Medicine at Mount Sinai (New York City), Emory University (Atlanta), St. Jude Children’s Research Hospital (Memphis), University of Rochester Medical Center (Rochester), and Johns Hopkins University (Baltimore).
A key mission of the network created between Excellence Centers for Influenza Research and Surveillance is to foster innovative and cooperative basic research on influenza viruses, including how they evolve and adapt to both human and animal hosts. The network has a global reach, with collaborations in Asia, Southeast Asia, the Middle East, Europe, South America, and Australia. Gained information helps in understanding why influenza pandemics occur and how to avoid them in the future.
Developing therapeutics for influenza
Two classes of antiviral medications have been traditionally used for treating influenza, but each has limitations in scope and effectiveness. The antigenic diversity of the virus and the constant influx of new subtypes allow the virus to become resistant to these antiviral drugs and evade vaccines. Therefore, there is a continuing need for new anti-influenza therapeutics using novel targets and creative strategies.
Broad research efforts resulted in a new generation of neuraminidase (NA) inhibitors, showing that NA constitutes a rational target for newer agents against viruses that develop resistance against older inhibitors. Multiple drug cocktails that target several viral functions and monoclonal antibodies have also shown much promise.
An aggressive immune response known as the cytokine storm plays a significant role in causing tissue injury and mortality following human pathogenic influenza virus infection. New research has shown that dampening such a host’s immune response by using specific immunomodulatory sphingosine-1-phosphate receptor agonists can provide substantial protection from mortality over that observed by the neuraminidase inhibitor oseltamivir.
The antiviral formulations developed in the last few years to treat influenza show higher effectiveness than previous drugs. An antiviral agent called baloxavir has recently been released for treating flu in children and adults. This new drug is administered as a single dose and has shown to be very effective at reducing the duration of flu symptoms and the risk of hospitalization. Baloxavir is also safe and well-tolerated for people at high risk of suffering complications from the flu. This drug acts as an endonuclease inhibitor that blocks the activity of the cap-dependent endonuclease (CEN) enzyme, which plays a critical role during the replication of the influenza virus. This enzyme consists of two protein domains: one that binds to the cap of host mRNAs and the second one that cuts the mRNA sequence at the cap site. The virus then uses the capped mRNA fragment as a primer to synthesize its mRNA.
Is a universal flu treatment possible?
Small interfering RNAs (siRNAs) are short, double-stranded RNA molecules that can silence the expression of genes. They are typically 21-25 nucleotides long and can be synthetically produced to inhibit endogenous gene expression via a mechanism called RNA interference (RNAi). The antiviral approach based on the use of siRNAs has several advantages when compared to traditional antiviral compounds. These short nucleic acids (siRNAs) can act as a highly potent antiviral agent with both preventive and therapeutic value, which can be designed and synthesized in hours and applied in combination with other siRNAs in a multidrug regimen to reduce the odds of resistance or to target multiple co-infecting viruses.
Chitosan is a natural, biocompatible (not harmful to living organisms) compound derived from the deacetylation of chitin. It has been shown that chitosan-siRNA nanoparticle complexes can efficiently inhibit influenza virus replication in in vitro and in vivo conditions. A recent study showed that nasal delivery of siRNA with chitosan nanoparticles significantly protected mice from influenza, suggesting that the combination of these nanoparticles with siRNAs could be used for controlling viral infections.
Is a Universal Flu Shot Possible?
Innovative vaccine models
Despite advances in the field, most vaccine formulations for influenza are still produced by rather old-fashioned techniques that have been in use for over 60 years. Such methods involve the growth and passaging of the vaccine strains in embryonated chicken eggs. Therefore, production and subsequent formulation can take several months and rely upon the availability of the eggs.
Increasing demands for influenza vaccines, especially during pandemics where there is a need for rapid production of pandemic influenza vaccines, necessitates new research approaches that will result in the development of new egg-independent manufacturing platforms. The first egg-free recombinant influenza vaccine (produced in an insect cell line) was approved by the US Food and Drug Administration in January 2013 and available for the influenza season of 2013-2014, demonstrating the proof of principle.
Cell-based vaccines are produced in cell cultures rather than eggs, which makes them less susceptible to contamination and easier to design under normal conditions. Universal vaccines target conserved regions of the influenza virus that are less likely to mutate, which means they could protect against a broader range of flu strains. In addition, many T cell-based vaccines have been developed and tested in animals and humans, offering additional avenues for heterosubtypic immunity stimulation. Conserved internal proteins of the virus represent targeted antigens in this approach.
With the next generation of vaccines, researchers aim to induce more broadly reactive, long-lasting immunity against diverse influenza virus types and subtypes. The end goal is a universal influenza vaccine that would protect from unexpected epidemics and pandemics in the future.
CRISPR-Cas gene editing: a promising tool for fighting influenza?
The CRISPR-Cas gene editing system is a powerful new tool that allows scientists to make precise changes to DNA. It is based on a naturally occurring immune system through which bacteria defend themselves against viruses. The CRISPR-Cas gene editing system consists of a guide RNA to target a specific location in the genome.
A guide RNA is a short RNA piece complementary to the DNA sequence desired to edit. Once the guide RNA has bound to the DNA, a CRISPR-associated protein (Cas) cuts the DNA at that location. The cell then tries to repair the cut in the DNA. This can lead to different outcomes, depending on how the cell repairs the excised DNA elements.
For example, the cell may insert or delete a few base pairs or a new piece of DNA. Researchers have employed this gene editing technology to identify or modify viral genomes to make them less harmful or even harmless. In this regard, a CRISPR-Cas DNA endonuclease-targeted CRISPR trans-reporter assay has been recently developed to rapidly and sensitively detect influenza A and B viruses, a fundamental step for preventing the spread of viral strains.
References
- http://www.cdc.gov/flu/professionals/index.htm
- https://www.who.int/
- http://www.niaid.nih.gov/labsandresources/resources/ceirs/Pages/default.aspx
- http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4047948/
- http://www.biomedcentral.com/1741-7015/10/104
- Nicholson KG, Webster RG, Hay AJ. Textbook of Influenza. Blackwell Science, Oxford, 1998.
- Lamb RA, Krug RM. Orthomyxoviridae: The viruses and their Replication. In: Fields Virology fourth edition, Knipe DM, Howley PM eds, Lippincott, Philadelphia 2001, pp 1487-1531.
- Nicholson KG, Webster RG, Hay AJ. Textbook of Influenza. Blackwell Science, Oxford, 1998.
- Lamb RA, Krug RM. Orthomyxoviridae: The viruses and their Replication. In: Fields Virology fourth edition, Knipe DM, Howley PM eds, Lippincott, Philadelphia 2001, pp 1487-1531.
- Baker, Jeffrey, et al. "Baloxavir marboxil single-dose treatment in influenza-infected children: a randomized, double-blind, active controlled phase 3 safety and efficacy trial (miniSTONE-2)." The Pediatric infectious disease journal 39.8 (2020): 700.
- Jamali, Abbas, et al. "Inhibiting influenza virus replication and inducing protection against lethal influenza virus challenge through chitosan nanoparticles loaded by siRNA." Drug Delivery and Translational Research 8 (2018): 12-20.
- Rajan, Aishwarya, et al. "CRISPR-Cas system: from diagnostic tool to potential antiviral treatment." Applied Microbiology and Biotechnology 106.18 (2022): 5863-5877.
- Park, Bum Ju, et al. "Specific detection of influenza A and B viruses by CRISPR-Cas12a-based assay." Biosensors 11.3 (2021): 88.
Further Reading
Study confirms flu vaccine effectiveness against A H1N1 in young children