Needle-free and adjuvant-free vaccination with non-infectious T4-COVID nanoparticles induces strong immunity in mice

In a recent study posted on bioRxiv* Preprint server, researchers have developed a mucosal vaccine for coronavirus disease 2019 (COVID-19) based on bacteriophage.

Background

Vaccines against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) have been developed on a variety of platforms including nucleic acids, adenoviral vectors, protein subunits, and inactivated viral particles. These intramuscularly administered vaccines continue to be the primary source of vaccines for unvaccinated people. Many other vaccines are at various stages of development, but intranasal (internal) vaccines have not yet been approved for humans.

Injectable vaccines effectively protect against serious illnesses such as hospitalization and death, but do not effectively prevent the acquisition (invasion) or release (exit) of viral particles from infected individuals. There are concerns about the risk of SARS-CoV-2 infection from vaccinated but susceptible individuals.

Currently available vaccines target the SARS-CoV-2 spike (S) protein based on its ancestor Wuhan-Hu-1 strain, resulting in an urgent SARS containing a substantially mutated S protein. Less effective against CoV-2 mutants. Earlier, the authors of this study reported the development of a new intramuscular (im) vaccine based on T4 bacteriophage (T4-CoV-2).

About research

In this study, researchers tested the T4-CoV-2 vaccine in mice receiving treatment. They evaluated the immunogenicity of BALB / c mice by im or 2 dose controls (T4 vector only) or vaccination with T4-CoV-2 vaccine. The vaccine was coated with 20 µg (high dose) S-ectodomain (Secto) trimer, 4.8 µg (medium dose), or 0.8 µg (low dose). Serum collected 21 days after the second dose from (in or im) vaccinated mice showed high immunoglobulin G (IgG) levels, but lacked control mice. antigen-Specific antibody.

Investigation result

High levels of IgG1 and IgG2a subtypes were apparent during or during inoculation. Antibodies derived from T helper cells 1 (Th1) and Th2 were induced approximately equally with medium or high dose vaccination, but a 5-25 fold lower response was observed with low dose courses or single doses. rice field. In particular, higher serum IgA levels were detected regardless of the inoculation route. This is interesting given that IgA stimulation is not commonly observed with conventional vaccines, including vaccines against SARS-CoV-2.

In a virus neutralization assay for Vero E6 cells using the SARS-CoV-2 WA-1 / 2020 strain, the researchers observed a strong neutralizing effect on serum from vaccinated mice. In addition, the neutralizing titers for SARS-CoV-2 WA-1, beta, and delta variants were comparable. Three-fold higher neutralizing activity was detected at high doses compared to vaccination against SARS-CoV-2 and the mutants tested.

Researchers collected splenocytes from mice 26 days after the last dose. Clusters of differentiation 8 (CD8) and CD4 T lymphocytes that secrete tumor necrosis factor (TNF) -α, interleukin (IL) -17A, or interferon (IFN) -γ were compared with controls when stimulated ex vivo. In comparison, it increased significantly in vaccinated mice. Sect or S- and nucleoprotein (NP) peptides.

Systemic and mucosal responses are higher with vaccination, which is in contrast to the general notion that administration results in stronger and lower systemic responses, or vice versa. Bronchoalveolar lavage fluid samples (BALF) detected 25-fold higher IgG levels in intranasally vaccinated mice than in intramuscularly injected mice. In addition, control mice challenged with the SARS-CoV-2 (MA10) mouse-adapted strain showed rapid weight loss, while vaccinated mice showed moderate or no weight loss. In addition, vaccination by either route protected mice against the SARS-CoV-2 challenge.

The vaccine was then designed to display Secto (secto-β) from the beta mutant on T4 phage (T4-CoV-2-β) and inoculate AC70 mice at two high doses. it was done. Mice contained human angiotensin converting enzyme-2 (hACE2) knock-in. Overall, transgenic mice vaccinated with T4-CoV-2-β had stronger systemic and mucosal humoral immunity, consistent with findings in BALB / c mice.

The neutralizing titers for the WA-1 strain and the Delta mutant strain were similar, and the serum showed an omicron neutralizing titer, but was almost 6 times lower than that for the WA-1 strain. Th1-biased cell-mediated immunity was observed with the administration of the T4-CoV-2-β vaccine. When mice were challenged with WA-1 or delta mutants, they noticed a rapid weight loss in control mice, as opposed to a minimal to weightless loss. Pulmonary SARS-CoV-2 loading was higher in control mice, but no detectable virus in vaccinated mice.

The T4-CoV-2-β vaccine was stored at 4 ° C and 22 ° C and was tested for stability and functionality at various time points. Functionality was assessed by the ability of Secto-β to bind to hACE2, and stability was assessed by loss of intact S protein bound to phage or degradation into protein fragments. Researchers have stated that the vaccine is functioning steadily for 10 weeks, regardless of storage temperature.

Conclusion

The authors of this study reported successful establishment of a bacteriophage-based vaccine displaying SARS-CoV-2Secto, which may complement existing vaccines. Systemic and mucosal immune responses were prominent with vaccination. The authors believe that the T4-CoV-2 vaccine may block viral entry and exit due to its ability to induce cell-mediated, protective, and sterile immunity. In addition, further research in other animals and phase 1 clinical trials in humans are needed for the vaccine to be available to the general public.

*Important Notices

bioRxiv publishes unpeer-reviewed preliminary scientific reports and should not be considered definitive, guide clinical / health-related behaviors, or be treated as established information.