SARS-CoV-2 oral vaccine candidate found to induce neutralized mucosal IgA

New research posted on medRxiv* The preprint server reported the results of a clinical trial evaluating oral vaccine candidates for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

In this study, we investigated an oral vaccine platform that promotes an adaptive immune response on the mucosal surface, which is an important gateway to respiratory infections such as SARS-CoV-2.

Background

Mucosal immunity is the largest component of the immune system that protects the mucosa, the main site of infection. Mucosal immunoglobulin (Ig) A production exceeds that of all other immunoglobulin isotypes.In addition, mucosal IgA shows increased neutralizing activity against SARS-CoV-2 In vitro With greater cross-reactivity with other virus types. The mucous membrane acts as a barrier against most foreign bodies. Most of the pathogens are destroyed and eliminated by the immune cells of the mucosa surrounding the conjunctiva of the eye, the inner ear, the gastrointestinal tract, the urogenital tract, and the exocrine ducts.

The development of mucosal vaccines against various microbial diseases such as SARS-CoV-2 is a major research area. This is because SARS-CoV-2 infection begins in the upper respiratory tract and has a significant impact on the respiratory mucosa. As a result, when mucosal vaccination against SARS-CoV-2 is developed, it provides the required level of protection at the site of infection, thereby preventing infection and inhibiting viral replication in the upper respiratory tract.

Current vaccines are ineffective because they do not provide broad-spectrum immunity and cannot combat infections caused by SARS-CoV-2 mutants such as Omicron. There is widespread agreement on the current need for new vaccine technologies.

In this regard, this study examined oral tablet vaccination of room temperature preserved foods developed by Vaxart, which contained both peplomer (S) and nucleocapsid (N) proteins. Vaxart’s vaccine platform consists of an adenovirus type 5 (Ad5) backbone and a Toll-like receptor-3 (TLR3) agonist adjuvant. These vaccines have been tested in more than 650 patients and have been shown to be well tolerated and produce a large humoral and cell-mediated immune response against those expressed. antigen In the past.

the study

Tolerance Effectiveness of Two dose levels of oral COVID-19 vaccine candidates designated as VXA-CoV2-1.

In this study, the proportion of men (65.7%) was higher than that of women (34.3%). Participants in this study received the following prophylaxis – Cohort 1 received a low-dose oral vaccine with booster immunization on day 29. Cohort 2 received a single low dose. Cohort 3 received a single high dose.

In the clinical study, 35 adult participants who met the inclusion / exclusion criteria received either one low dose (1×1010 IU) or one high dose (5×1010 IU), whereas 5 participants Received two low doses.Researchers examined nasal, saliva, and serum samples for the presence of IgA, IgG, and alternatives Neutralizing antibody.. Convalescent individuals after infection – 1 and 8 months after confirmatory test results, participated to provide analytical nasal, saliva, and serum samples.

Safety was the main goal of this study. Secondary immunogenicity endpoints were assessed during the active phase (29th or 57th day), primarily by quantifying IgA and IgG in nasal, serum, and saliva samples. The long-term durability of the available volunteers was evaluated.

Survey results

Clinical trials have shown that VXA-COV2-1, a candidate for oral tablet vaccine against SARS-CoV-2, is well tolerated and immunogenic. The majority of participants had elevated mucosal IgA responses specific for SARS-CoV-2 S and N proteins and receptor binding domains (RBDs), but minimal serum responses.

For most responders, a single injection of VXA-CoV2-1 produced cross-reactive IgA that lasted for more than 180 days. IgA specific for SARS-CoV-2 was increased in both nasal and salivary secretions. In addition, nasal IgA has been found to be secretory IgA, demonstrating more effective neutralization of SARS-CoV-2. In vitro From monomeric IgA.

Convalescent and VXA-CoV2-1 produced similar amounts of IgA in the nose and saliva. In addition, researchers pointed out that vaccine-immunized patients enhanced the mucosal neutralizing antibody response, suggesting that vaccination may enhance the quality of the antibody response on the mucosal surface. There is. Mucosal IgA produced by VXA-CoV2-1 was cross-reactive to the omicron and delta variants of SARS-CoV-2. At the same time, saliva and nasal samples collected 29 days after immunization were also cross-reactive with other human variants of concern, such as alpha and beta mutants.

There was cross-reactivity between the IgA and S proteins produced by vaccination Coronaviridae Family rather than preferential specificity for the antigen recognized by the vaccine. Vaccine surrogate neutralizing activity persisted for more than 180 days in most respondents, and their levels were still above pre-vaccination levels.

The main drawbacks of this study were the small size of the study and the small number of subjects, and the evaluation of the messenger ribonucleic acid (mRNA) vaccine before it became commercially available.

Conclusion

VXA-CoV-2 was well received and induced a cross-reactive neutralizing mucosal IgA response in most respondents, lasting up to 180 days.

VXA-CoV-2 is the first oral vaccine against SARS-CoV-2 and has shown both safety and immunity in humans. Future studies will look at dose, antigen recognition, and efficacy variability in larger human studies.

*Important Notices

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