Preclinical Assessment of IgY Antibodies Against Recombinant SARS-CoV-2 RBD Protein for Prophylaxis and Post-Infection Treatment of COVID-19

Within the framework of the current COVID-19 pandemic, there is a race against time to find therapies for the outbreak to be controlled. Since vaccines are still tedious to develop and partially available for low-income countries, passive immunity based on egg-yolk antibodies (IgY) is presented as a suitable approach to preclude potential death of infected patients, based on its high specificity/avidity/production yield, cost-effective manufacture, and ease of administration. In the present study, IgY antibodies against a recombinant RBD protein of SARS-CoV-2 were produced in specific-pathogen-free chickens and purified from eggs using a biocompatible method. In vitro immunoreactivity was tested, finding high recognition and neutralization values. Safety was also demonstrated prior to efficacy evaluation, in which body weight, kinematics, and histopathological assessments of hamsters challenged with SARS-CoV-2 were performed, showing a protective effect administering IgY intranasally both as a prophylactic treatment or a post-infection treatment. The results of this study showed that intranasally delivered IgY has the potential to both aid in prevention and in overcoming COVID-19 infection, which should be very useful to control the advance of the current pandemic and the associated mortality.

Squalene in oil-based adjuvant improves the immunogenicity of SARS-CoV-2 RBD and confirms safety in animal models

COVID-19 pandemic has accelerated the development of vaccines against its etiologic agent, SARS-CoV-2. However, the emergence of new variants of the virus lead to the generation of new alternatives to improve the current sub-unit vaccines in development. In the present report, the immunogenicity of the Spike RBD of SARS-CoV-2 formulated with an oil-in-water emulsion and a water-in-oil emulsion with squalene was evaluated in mice and hamsters. The RBD protein was expressed in insect cells and purified by chromatography until >95% purity. The protein was shown to have the appropriate folding as determined by ELISA and flow cytometry binding assays to its receptor, as well as by its detection by hamster immune anti-S1 sera under non-reducing conditions. In immunization assays, although the cellular immune response elicited by both adjuvants were similar, the formulation based in water-in-oil emulsion and squalene generated an earlier humoral response as determined by ELISA. Similarly, this formulation was able to stimulate neutralizing antibodies in hamsters. The vaccine candidate was shown to be safe, as demonstrated by the histopathological analysis in lungs, liver and kidney. These results have shown the potential of this formulation vaccine to be evaluated in a challenge against SARS-CoV-2 and determine its ability to confer protection.