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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 requires new immunization strategies in addition to the current vaccines approved for human administration. In the present report, the immunological and safety evaluation in mice and hamsters of a subunit vaccine based on the RBD sub-domain with two adjuvants of oil origin is described.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 in mice and hamsters, the purified RBD formulated with adjuvants based on oil-water emulsifications and squalene was able to stimulate specific neutralizing antibodies and confirm the secretion of IFN-γ after stimulating spleen cells with the purified RBD. The vaccine candidate was shown to be safe, as demonstrated by the histopathological analysis in lungs, liver and kidney. These results demonstrate the potential of the purified RBD administered with adjuvants through an intramuscular route, to be evaluated in a challenge against SARS-CoV-2 and determine its ability to confer protection against infection.

The COVID-19 pandemic has claimed the lives of millions of people. Vaccination is a critical tool for the control of transmission; however, the recent emergence of potentially vaccine-resistant variants renders it important to have a range of vaccines types. It is desirable that vaccines are safe, effective, easy to administer and store, and inexpensive to produce. Newcastle disease virus (NDV), responsible for respiratory disease in chickens, has no pathogenic homologue in humans. We developed two types of NDV-vectored candidate vaccines, and evaluated them in a SARS-CoV-2 challenge in hamsters. Vaccinations resulted in generation of neutralizing antibodies, prevented lung damage, and reduced viral load and viability. In conclusion, our NDV-based vaccine candidate performed well in a SARS-CoV-2 challenge and warrants evaluation in a Phase I human clinical trial. This candidate represents a promising tool in the fight against COVID-19.

The coronavirus disease-19 (COVID-19) pandemic has already claimed millions of lives and remains one of the major catastrophes in the recorded history. While mitigation and control strategies provide short term solutions, vaccines play critical roles in long term control of the disease. Recent emergence of potentially vaccine-resistant and novel variants necessitated testing and deployment of novel technologies that are safe, effective, stable, easy to administer, and inexpensive to produce. Here we developed three recombinant Newcastle disease virus (rNDV) vectored vaccines and assessed their immunogenicity, safety, and protective efficacy against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in mice and hamsters. Intranasal administration of rNDV-based vaccine candidates elicited high levels of neutralizing antibodies. Importantly, the nasally administrated vaccine prevented lung damage, and significantly reduced viral load in the respiratory tract of vaccinated animal which was compounded by profound humoral immune responses. Taken together, the presented NDV-based vaccine candidates fully protected animals against SARS-CoV-2 challenge and warrants evaluation in a Phase I human clinical trial as a promising tool in the fight against COVID-19.

El estudio tuvo por objetivo desarrollar una plataforma molecular para la cuantificación del virus de la enfermedad de Newcastle (NDV) a partir de un sistema de cultivo en huevos embrionados SPF. Primero se evaluaron cuatro pares de cebadores que amplifican diferentes regiones del genoma viral de NDV que codifican para la proteína de nucleocápside (NP), proteína matriz (M), proteína fusión (F) y la ARN polimerasa ARN dependiente (L), con la finalidad de seleccionar el más conservado a partir del cual se desarrolló una plataforma molecular basada en la transcripción reversa - reacción en cadena de polimerasa convencional (RT-PCRc) en dos pasos para la detección del NDV. Posteriormente, esta fue llevada a transcripción reversa - reacción en cadena de polimerasa en tiempo real (RT-qPCR) para la cuantificación de NDV producido a partir de un sistema de huevos embrionados. Mediante estas técnicas se determinó que los cebadores para el gen M fueron adecuados según los criterios de optimización para el desarrollo de ambos métodos. Mediante ensayos de sensibilidad se demostró que la RT-qPCR (116 copias genómicas/μl) era 10 veces más sensible que el RT-PCRc. Los cebadores fueron específicos pues no hubo amplificados en los controles negativos ni en otros patógenos aviares (virus de la laringotraqueitis infecciosa, metapneumovirus aviar, virus de la bronquitis infecciosa, Avibacterium paragallinarum, Gallibacterium anatis y Ornithobacterium rhinotracheale). Debido su sensibilidad y especificidad, se propone esta plataforma para la cuantificación de NDV vacunal cuando es producido a partir de un sistema de huevos embrionados, como una alternativa frente a métodos convencionales de titulación como hemaglutinación, ensayo en placa, TCDI50 y DIEP50., The objective of the study was to develop a molecular platform for the quantification of Newcastle disease virus (NDV) from a culture system in embryonated SPF eggs. First, four pairs of primers were evaluated that amplify different regions of the NDV viral genome that code for: nucleocapsid protein (NP), protein matrix (M), fusion protein (F) and RNA-dependent RNA polymerase (L) to select the most conserved one from which a molecular platform based on reverse transcription was developed - conventional polymerase chain reaction (RT-PCRc) in two steps for the detection of NDV. Subsequently, it was taken to reverse transcription - real-time polymerase chain reaction (RT-qPCR) for the quantification of NDV produced from a system of embryonated eggs. Through these techniques, it was determined that the primers for the M gene were adequate according to the optimization criteria for the development of both methods. Sensitivity tests showed that the RT-qPCR (116 genomic copies/μl) was 10 times more sensitive than the RT-PCRc. The primers proved to be specific since there were no amplifications in the negative controls or in other avian pathogens (infectious laryngotracheitis virus, avian metapneumovirus, infectious bronchitis virus, Avibacterium paragallinarum, Gallibacterium anatis and Ornithobacterium rhinotracheale). Due to its sensitivity and specificity, this platform is proposed for the quantification of NDV vaccine when it is produced from an embryonated egg system, as an alternative to conventional titration methods such as hemagglutination, plaque assay, TCDI50 and DIEP50.