Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported in late December 2019 in Wuhan, China, and is the causative agent of the coronavirus disease 2019 (COVID-19) pandemic. In progress. To date, SARS-CoV-2 has infected more than 557 million people and claimed more than 6.35 million lives worldwide.
Several effective vaccines and treatments for COVID-19 have been successfully developed and shown to protect individuals against the virus. However, the continued emergence of new SARS-CoV-2 variants has reduced their effectiveness, as current COVID-19 vaccines are primarily based on the spike protein from the original SARS-CoV-2 strain.
As a result, scientists are looking to develop new antiviral drugs, vaccines, and antibody therapies to protect individuals from contracting COVID-19.
Study: Hyperimmunized chickens produce neutralizing antibodies against SARS-CoV-2. Image Credit: ustas7777777 / Shutterstock.com
SARS-CoV-2 is a betacoronavirus that contains a single-stranded, positive-sense ribonucleic acid (RNA) genome, which ranges from 27 to 30 kilobase (kb) pairs. In addition to betacoronaviruses, other coronaviruses, including alphacoronaviruses, gammacoronaviruses and deltacoronaviruses, can infect a wide range of species, such as mammals and birds, causing respiratory and gastrointestinal illnesses. For instance. most commercial hens are immune to infectious bronchitis virus (IBV), which is a gammacoronavirus.
The SARS-CoV-2 spike protein mediates the invasion of the virus into the host. During viral infection, the S1 subunit of the spike protein, which contains the receptor binding domain (RBD), binds to the human angiotensin converting enzyme 2 (ACE2) receptor. on host cells, while the S2 domain promotes membrane fusion. Subsequently, the viral RNA genome enters the host cell.
In coronaviruses, the RBD is the most antigenic site of the S1 domain and, therefore, is used as a target in current COVID-19 vaccines and most therapeutics. The S1 domain of the protein induces the production of neutralizing antibodies.
A new COVID-19 therapy that was recently approved for emergency use by the United States Food and Drug Administration (FDA) is convalescent plasma. This treatment involves the administration of SARS-CoV-2 specific antibodies that have been isolated from recovered COVID-19 patients to newly infected patients. The researchers also generated SARS-CoV-2-specific antibodies in animals for the passive immunization of humans against the virus.
A previous study reported an attractive model for harvesting antibodies from eggs of hens immunized against the SARS-CoV-2 spike protein. Some of the benefits of this strategy include its scalability, cost effectiveness, and convenience. Notably, chickens produce immunoglobulin Y (IgY), which is analogous to mammalian IgG.
Studies have shown that one egg yolk typically produces 50-100mg of IgY, which contains between 2-10% specific antibodies. However, the amount of antigen-specific IgY produced by hyperimmunized hens depends on the age of the hen, the dose, the antigenicity, the molecular weight of the antigen and the route of administration.
About the study
A new Virus log reports the production of neutralizing antibodies against SARS-CoV-2 in hyperimmunized hens. Here, researchers immunized hens with several different vaccine formulations, which included vaccine A twice (A/A), vaccine B twice (B/B), vaccine C twice (C/C) and vaccine C followed by vaccine B (C/B).
The hens vaccinated with the adjuvant only served as a negative control. Each treatment group was divided into several subgroups based on different doses.
In this study, all vaccines had a volume of 0.5 µl and were administered intramuscularly into the pectoral muscle. Blood samples were taken 21 days after the second immunization and at the end of the experiment, six weeks after the second dose.
One month after the second immunization, eggs were collected for IgY extraction. These samples were tested for neutralizing antibodies against SARS-CoV-2 using the plaque reduction neutralization assay (PRNA) and enzyme immunoassay (ELISA).
Laying hens hyperimmunized against three different recombinant SARS-CoV-2 spike proteins produced specific antibodies in sera. Additionally, low levels of SARS-CoV-2 specific IgY titers were produced in egg yolk, while a significant level of antibody was detected in sera.
The dose and type of antigen were the two most important factors that influenced the number of antibodies produced. Although all vaccines produced antibodies against SARS-CoV-2, vaccines targeting the glycosylated S1 (C/C) protein and a combination of glycosylated S1 and non-glycosylated RBD of S1 (C/B) showed a better neutralization capacity. Notably, antibodies generated from Vaccine C could be administered as a fraction of the dose required for effective seroconversion.
Compared to the control group, hens immunized with full-length and labeled S1 protein induced higher IgY titer in serum and egg yolk at all doses. However, hens immunized with RBD fragments at the highest dose of 50 µg elicited more antibodies than the negative control group.
Importantly, no virus neutralization was observed in hens vaccinated against IBV, which does not suggest any cross-reaction between anti-IBV antibodies and SARS-CoV-2.
Antibody production in hyperimmunized hens depends on the dose and type of antigen. Researchers believe that neutralizing antibodies purified from the egg yolk of hyperimmunized chickens can be used effectively as immunoprophylaxis in humans.
- Aston, EJ, Wallach, MG, Narayanan, A., et al. (2022) Hyperimmunized chickens produce neutralizing antibodies against SARS-CoV-2. Virus 14(7):1510. doi:10.3390/v14071510.