New COVID-19 protein component vaccine induces lasting immune responses in rodents

In a recent study posted on bioRxiv* Preprint server, researchers describe novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). spike protein A component vaccine called MT-001 induced long-lasting and very high levels of anti-spike immunoglobulin G (IgG) antibodies in rodents.

study: A SARS-CoV-2 vaccine designed for manufacturability offers unexpected potency and a persistent humoral response. Image credit: siam.pukkato / Shutterstock.com

Important Considerations for New COVID-19 Vaccines

The original coronavirus disease 2019 (COVID-19) vaccine was effective against the ancestral strain of SARS-CoV-2 and successfully reduced disease severity by more than 90%. However, the decline of immunity due to vaccines and the emergence of new virus variants with mutations in the spike protein that enable immune evasion are threatening. efficacy of these vaccines.

Therefore, the development of more effective booster vaccines and pan-coronavirus or variant-specific vaccines is urgently needed. Moreover, protection of immunocompromised patients remains a challenge.

In April 2022, the World Health Organization (WHO) revised its COVID-19 vaccine target product profile to address shortcomings of current vaccines in light of emerging SARS-CoV-2 variants. Desirable properties of next-generation vaccines include broader protection against different variants, durable vaccine protection, and ease of manufacture and distribution. Existing messenger ribonucleic acid (mRNA) and viral vector vaccines meet only one of these criteria.

About research

In the current study, researchers designed a protein component vaccine consisting of the SARS-CoV-2 spike protein receptor-binding domain (RBD) and sequences flanking the RBD, as previous studies have reported higher values. Did. Neutralizing antibody Titers of RBD-based COVID-19 vaccines. Additionally, the vaccine is designed to be highly soluble, stable, expressed at high levels, and amenable to purification protocols, all of which make it easier to manufacture and distribute.

We analyzed the spike protein sequence of the ancestral SARS-CoV-2, the Wuhan Hu-1 strain, to determine the biophysical, structural, and biochemical properties of the vaccine. A final codon-optimized RBD construct spanning spike residues 316–594 was then expressed using a secretory vector.

Details of the SARS-CoV-2 spike protein in region 300-600 and MT-001 construct design. A) Structures of MT-001 constructs derived from PDB IDs 7BYR and 7KNE. RBD constructs are color-coded by annotated blocks of amino acid sequence (see ‘Regions’, panel C and ref. 45). Cysteines are shown as yellow balls. The ligand for RBM, ACE2 (from 7KNE), is shown as a gray molecular surface (left). B) The MT-001 construct (ribbon) is shown in the context of a full-length spike trimer (space-filling model). C) Schematic of the area shown in (A). Top: Color-coded region keys of the MT-001 construct in (A). NT: N-terminal region (residues 316-332, red). CD1: “core domain 1” region (333-436, magenta). RBM: receptor binding motif (437-508, green). CD2: “core domain 2” region (509-527, cyan). CTD1: “C-terminal domain 1” region (528-594, blue). Red arrows indicate the 538-590 disulfide bond that stabilizes CTD1. Middle: Black bars—residue-by-residue sequence identities between the SARS-CoV-2 spike and representative members of the coronavirus superfamily. Highly conserved regions at the N- and C-termini of RBM are shown (Table 1). Orange bars – sites and frequencies of mutations in characterized SARS-CoV-2 variants (3). Bottom: Schematic showing secondary structure and post-translational modifications in the region of residues 300–600 of the SARS-CoV-2 spike protein. Alpha helices are shown as blue cylinders, beta sheets as red arrows, and turns as orange loops. Disulfide bonds are indicated by purple bridges and N-linked glycosylation sites are indicated by green circles. Bottom: Alignment of the MT-001 construct with the visualized region.

The antigenicity and persistence of the vaccine were tested in BALB/cJ mice and Syrian golden hamsters. Mice were immunized intramuscularly with different concentrations of her MT-001 vaccine and boosted on day 21.

Serum samples were taken 3 days before vaccination and at various time points after immunization. Anti-RBD IgG levels were measured using a sandwich enzyme-linked immunosorbent assay (ELISA).

One group of Syrian golden hamsters was inoculated intramuscularly with the adjuvanted MT-001 vaccine, and another group, used as a control group, was inoculated with phosphate-buffered saline (PBS). Both groups received a booster dose of his MT-001 vaccine or PBS on day 21. Blood samples were taken before vaccination and at 2, 3, 4, 5, and 6 weeks after vaccination.

On day 42, all hamsters were challenged with the USA-WA-1 strain of SARS-CoV-2, after which all animals were weighed daily and finally euthanized on day 4 to remove the virus. Blood and lungs were collected for stress assessment.

A quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assay was performed on total ribonucleic acid (RNA) extracted from lungs to determine viral load, whereas a SARS-CoV-2 neutralization assay was performed on serum performed on the sample. Additionally, lung sections were stained with hematoxylin-eosin for histopathological analysis.

Investigation result

Two pre-challenges of MT-001 vaccine in BALB/cJ mice induced anti-RBD IgG titers comparable to Pfizer/BioNTech and Moderna mRNA vaccines. In addition, the adjuvanted MT-001 vaccine also demonstrated a balance of type 1 T helper cell (Th1) and type 2 T helper cell (Th2) responses.

Syrian golden hamsters immunized with the adjuvanted MT-001 vaccine and challenged with SARS-CoV-2 6 weeks later had an undetectable viral load in lung tissue after 4 days.

Half maximal effective concentration of IgG titer against SARS-CoV-2 spike protein RBD in serum of immunized mice is 10^Five-Ten⁶ Range, even 12 months after vaccination.

Addition of the Toll-like receptor-9 (TLR-9) agonist CpG oligonucleotide (ODN) 1826 significantly increased antispike IgG titers. Inclusion of CpG ODN 1826 also generated broad cross-reactive immune responses against SARS-CoV-2 Delta and Omicron variants, and neutralizing antibody levels against Omicron BA.1 variants were induced by variant-specific mRNA vaccine mRNA. was equivalent to -1273.529.

Conclusion

The results of this study indicate that the SARS-CoV-2 protein component vaccine MT-001 is a promising candidate for the next generation vaccine against COVID-19. MT-001 elicited high and durable anti-spike IgG titers in mouse and hamster models when combined with CpG ODN 1826, and broadly cross-reactive immune responses against SARS-CoV-2 variants. bottom.

*Important Notices

Bio Rxiv We publish a non-peer-reviewed, preliminary scientific report and should not be taken as conclusive, to guide clinical practice/health-related actions, or to be treated as established information.