Efficacy and security of an RBD-based recombinant protein COVID-19 vaccine

The emergence of the coronavirus illness 2019 (COVID-19) pandemic attributable to extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2) led the scientific group and pharmaceutical business to concentrate on the event of vaccines to fight the well being emergency.

Study: Preclinical efficacy, safety, and immunogenicity of PHH-1V, a second-generation COVID-19 vaccine candidate based on a novel recombinant RBD fusion heterodimer of SARS-CoV-2. Image Credit: Tero Vesalainen/ShutterstockResearch: Preclinical efficacy, security, and immunogenicity of PHH-1V, a second-generation COVID-19 vaccine candidate primarily based on a novel recombinant RBD fusion heterodimer of SARS-CoV-2. Picture Credit score: Tero Vesalainen/Shutterstock

A number of vaccines are at the moment obtainable in opposition to COVID-19, and greater than 7.55 billion doses have been administered globally.

Nonetheless, COVID-19 circumstances proceed to emerge because of the evolution of a number of SARS-CoV-2 variants, the shortage of homogeneous distribution of the vaccines, and the decline in immunological safety by the present vaccines. Subsequently, it is very important develop second-generation vaccines which are efficient in opposition to the SARS-CoV-2 variants and may be additional used as a booster.


SARS-CoV-2 is a novel beta coronavirus belonging to the subfamily Coronovirinae throughout the household Coronaviridae. The genome of SARS-CoV-2 encodes a minimum of 4 structural proteins: spike (S) glycoprotein that promotes entry of the virus contained in the host cell, membrane (M) protein that’s chargeable for shaping the virions, nucleocapsid (N) protein that’s concerned in genome packaging and envelope (E) protein that’s chargeable for virion meeting and launch.

The S glycoprotein is the first goal of viral neutralizing antibodies and is the primary candidate for vaccine growth because it binds to the host receptor angiotensin-converting enzyme 2 (ACE2). The S glycoprotein consists of two domains S1 and S2 that enable binding of the viral particle and promotes mobile entry by fusion with the host cell membrane.

The receptor-binding area (RBD) containing a extremely immunogenic receptor binding motif (RBM) that interacts with ACE2 and neutralizes antibodies is situated within the S1 area. Subsequently, many of the key mutations happen within the RBM, resulting in the emergence of variants.

Two proline substitutions within the unique S protein sequence (S-2P) of MERS-CoV, SARS-CoV, and HKU1 coronavirus are concerned in sustaining the antigenic conformation. The mRNA-based vaccines and adenoviral vaccines are developed primarily based on this S-2P design.

Though adjuvanted protein-based vaccines are thought-about an essential kind of vaccine, their growth has lagged because of the have to optimize the manufacturing course of for every antigen. Two of the most typical subunit vaccines are the Novavax vaccine candidate and the Sanofi-GSK vaccine candidate.

Recombinant protein vaccines have a number of benefits: no danger of genome integration, an sufficient security profile, appropriate for folks with compromised immune methods, excessive productiveness, and good stability.

A brand new research revealed within the pre-print server bioRxiv* developed a protein-based subunit vaccine, PHH-1V, that consisted of a recombinant RBD fusion heterodimer of the B.1.1.7 (alpha) and B.1.351 (beta) variants of SARS-CoV-2 produced in Chinese language Hamster Ovary (CHO) cells with an oil-based adjuvant equal to MF59C.1. The research assessed the protection and efficacy of the PHH-1V vaccine in transgenic mice and characterised the RBD fusion heterodimer antigen and its immunogenicity.

In regards to the research

The research concerned the manufacturing of the viral antigen and its purification. The purified RBD fusion heterodimer was formulated with an oil in water adjuvant. The PHH-1V vaccine was examined at totally different concentrations: 0.04 µg, 0.2 µg, 1 µg, 5 µg, and 20 µg of RBD fusion heterodimer/dose for security assay in BALB/c mice. The vaccine was examined at 10 µg and 20 µg of fusion heterodimer/dose in K18-hACE2 mice for efficacy evaluation.

Seventy-two of the five-week-old BALB/c mice concerned within the research have been divided into six teams for security and immunogenicity assays. Group A was the management, group B was immunized with 0.04 μg recombinant protein RBD fusion heterodimer/dose, group C was 0.2 μg dose, group D have been immunized with 1 μg dose, group E was immunized with 5 μg dose, and group F immunized with 20 μg dose.  

62 K18- humanized ACE2 (hACE2) mice which have been 4/five-week-old have been divided into 4 teams for evaluation of vaccine efficacy. All of the mice have been vaccinated and, after that, challenged with SARS-CoV-2. Group A was the management group, group B was contaminated with SARS-CoV-2 however obtained the placebo, group C was vaccinated with 10 μg/dose of recombinant protein RBD fusion heterodimer and contaminated with SARS-CoV-2, and group D was vaccinated with 20 μg/dose and contaminated with SARS-CoV-2.

Moreover, evaluation of serum binding SARS-CoV-2 particular antibodies and SARS-CoV-2 neutralizing antibodies was carried out. Following this, intracellular cytokine staining (ICS) together with mouse cytokine assay and IFN-ɣ and IL-4 ELISpot assays.

RT-qPCR was completed to find out the viral load in respiratory tissue samples, adopted by virus titration utilizing TCID50 assay. Lastly, histopathological evaluation was carried out utilizing the higher and decrease respiratory tract and mind tissues.

Research findings

The outcomes indicated that after the prime-boost immunization with the PHH-1V, greater titers of RBD antibodies have been noticed in all teams besides the management. Nonetheless, no vital distinction in IgG response was noticed among the many teams that have been immunized with greater than 1 µg of recombinant RBD fusion heterodimer antigen in BALB/c mice. Additionally, in K18-hACE2 mice, each the teams vaccinated with both 10 or 20 µg of recombinant heterodimer confirmed related antibody titers.

Prime-boost immunization of teams C to F induced greater neutralizing antibody titers in opposition to the S protein of the alpha variant. In distinction, no neutralizing antibody response was noticed in group B. Nonetheless, the imply neutralizing antibody titers noticed in teams C to E remained the identical. Vaccination with 20 µg of RBD fusion heterodimer antigen (group F) induced greater neutralizing titers as in comparison with teams C to E. Excessive neutralizing titers have been obtained in opposition to all of the SARS-CoV-2 variants (alpha, beta, gamma, delta) from the sera obtained from group F.

The outcomes additionally indicated activation of CD4+ and CD8+ T cells expressing IFN-γ and IL-2 upon stimulation with an RBD peptide pool in group F. Moreover, greater ranges of IL-2, IL-5, and TNF-α have been noticed in group E. Compared, greater ranges of IL-5 and TNF-α was noticed in group F. Additionally, a balanced Th1/Th2 was noticed in group F as in comparison with group E.

The outcomes confirmed that the PHH-1V vaccine candidate was protected in mice because it didn’t trigger any medical signs or body weight loss in both immunized BALB/c or K18-hACE2 mice. Nonetheless, gentle lesions have been noticed in just a few mice as a consequence of native innate immune response. Moreover, immunization with both 10 or 20 µg of PHH-1V was discovered to cut back the viral load detected by RT-qPCR within the mice’s lungs, nasal turbinate, and mind.

Subsequently, the present research indicated that utilizing the PHH-1V vaccine is protected in mice and results in the event of RBD-binding and neutralizing antibodies. Additionally, in addition to security and efficacy, this second-generation vaccine might be efficient in opposition to rising SARS-CoV-2 variants. On this regard, the PHH-1V vaccine candidate has proven promising preclinical information and is at the moment being evaluated in a Section I/IIa medical trial.

*Essential discover

bioRxiv publishes preliminary scientific stories that aren’t peer-reviewed and, due to this fact, shouldn’t be thought to be conclusive, information medical follow/health-related habits, or handled as established data

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