Protection from COVID-19 disease in hamsters vaccinated with subunit SARS-CoV-2 S1 mucosal vaccines adjuvanted with different adjuvants

Sex-biased immunogenicity of a mucosal subunit vaccine against SARS-CoV-2 in mice

Introduction

Current vaccines against COVID-19 administered via parenteral route have limited ability to induce mucosal immunity. There is a need for an effective mucosal vaccine to combat SARS-CoV-2 virus replication in the respiratory mucosa. Moreover, sex differences are known to affect systemic antibody responses against vaccines. However, their role in mucosal cellular responses against a vaccine remains unclear and is underappreciated.

Methods

We evaluated the mucosal immunogenicity of a booster vaccine regimen that is recombinant protein-based and administered intranasally in mice to explore sex differences in mucosal humoral and cellular responses.

Results

Our results showed that vaccinated mice elicited strong systemic antibody (Ab), nasal, and bronchiole alveolar lavage (BAL) IgA responses, and local T cell immune responses in the lung in a sex-biased manner irrespective of mouse genetic background. Monocytes, alveolar macrophages, and CD103+ resident dendritic cells (DCs) in the lungs are correlated with robust mucosal Ab and T cell responses induced by the mucosal vaccine.

Discussion

Our findings provide novel insights into optimizing next-generation booster vaccines against SARS-CoV-2 by inducing spike-specific lung T cell responses, as well as optimizing mucosal immunity for other respiratory infections, and a rationale for considering sex differences in future vaccine research and vaccination practice.

Adjuvanted subunit intranasal vaccine prevents SARS-CoV-2 onward transmission in hamsters

Most COVID-19 vaccine trials have focused on recipient protection, not protection of their contacts, a critical need. As a subunit intranasal COVID-19 vaccine reduced nasopharyngeal virus more than did an intramuscular (IM) vaccine, we hypothesized that this vaccine might reduce onward transmission to others. We vaccinated hamsters with either the IM-administrated Moderna mRNA vaccine twice or one dose of mRNA IM followed by adjuvanted subunit intranasal vaccine. 24 hours after SARS-CoV-2 challenge, these animals were housed with naïve recipients in a contactless chamber that allows airborne transmission. Onward airborne transmission was profoundly blocked: the donor and recipients of the intranasal vaccine-boosted group had lower oral and lung viral loads (VL), which correlated with mucosal ACE2 inhibition activity. These data strongly support the use of the intranasal vaccine as a boost to protect not only the vaccinated person, but also people exposed to the vaccinated person, a key public health goal.

Author summary

Natural transmission of SARS-CoV-2 is primarily airborne, through the respiratory mucosal route. However, current licensed COVID-19 vaccines are all intramuscular and induce more systemic than mucosal immunity. Here, we did a head-to-head comparison of COVID-19 booster vaccines on SARS-CoV-2 onward transmission. We found that compared to boosting with a Moderna mRNA systemic vaccine, a nanoparticle intranasal COVID-19 vaccine much more effectively prevents onward airborne transmission to naïve recipient hamsters. The protection was correlated with local mucosal antibody. Thus, a mucosal nanoparticle vaccine should be considered for preventing onward airborne transmission, a key public health necessity that has not been adequately studied.

The immunobiology of SARS-CoV-2 infection and vaccine responses: potential influences of cross-reactive memory responses and aging on efficacy and off-target effects

Immune responses to both SARS-CoV-2 infection and its associated vaccines have been highly variable within the general population. The increasing evidence of long-lasting symptoms after resolution of infection, called post-acute sequelae of COVID-19 (PASC) or "Long COVID," suggests that immune-mediated mechanisms are at play. Closely related endemic common human coronaviruses (hCoV) can induce pre-existing and potentially cross-reactive immunity, which can then affect primary SARS-CoV-2 infection, as well as vaccination responses. The influence of pre-existing immunity from these hCoVs, as well as responses generated from original CoV2 strains or vaccines on the development of new high-affinity responses to CoV2 antigenic viral variants, needs to be better understood given the need for continuous vaccine adaptation and application in the population. Due in part to thymic involution, normal aging is associated with reduced naïve T cell compartments and impaired primary antigen responsiveness, resulting in a reliance on the pre-existing cross-reactive memory cell pool which may be of lower affinity, restricted in diversity, or of shorter duration. These effects can also be mediated by the presence of down-regulatory anti-idiotype responses which also increase in aging. Given the tremendous heterogeneity of clinical data, utilization of preclinical models offers the greatest ability to assess immune responses under a controlled setting. These models should now involve prior antigen/viral exposure combined with incorporation of modifying factors such as age on immune responses and effects. This will also allow for mechanistic dissection and understanding of the different immune pathways involved in both SARS-CoV-2 pathogen and potential vaccine responses over time and how pre-existing memory responses, including potential anti-idiotype responses, can affect efficacy as well as potential off-target effects in different tissues as well as modeling PASC.

SARS-CoV-2 mucosal vaccine protects against clinical disease with sex bias in efficacy

Intranasal mucosal vaccines can more effectively induce mucosal immune responses against SARS-CoV-2. Here, we show in hamsters that an intranasal subunit mucosal vaccine boost with the beta variant S1 can prevent weight loss, in addition to reducing viral load, which cannot be studied in macaques that don't develop COVID-like disease. Protective efficacy against both viral load and weight loss correlated with serum antibody titers. A sex bias was detected in that immune responses and protection against viral load were greater in females than males. We also found that priming with S1 from the Wuhan strain elicited lower humoral immune responses against beta variant and led to less protection against beta viral challenge, suggesting the importance of matched antigens. The greater efficacy of mucosal vaccines in the upper respiratory tract and the need to consider sex differences in vaccine protection are important in the development of future improved COVID-19 vaccines.