Enhanced SARS-CoV-2 neutralization by dimeric IgA

Cross-reactive sarbecovirus antibodies induced by mosaic RBD nanoparticles

Broad immune responses are needed to mitigate viral evolution and escape. To induce antibodies against conserved receptor-binding domain (RBD) regions of SARS-like betacoronavirus (sarbecovirus) spike proteins that recognize SARS-CoV-2 variants of concern and zoonotic sarbecoviruses, we developed mosaic-8b RBD nanoparticles presenting eight sarbecovirus RBDs arranged randomly on a 60-mer nanoparticle. Mosaic-8b immunizations protected animals from challenges from viruses whose RBDs were matched or mismatched to those on nanoparticles. Here, we describe neutralizing mAbs isolated from mosaic-8b-immunized rabbits, some on par with Pemgarda, the only currently FDA-approved therapeutic mAb. Deep mutational scanning, in vitro selection of spike resistance mutations, and single-particle cryo-electron microscopy structures of spike-antibody complexes demonstrated targeting of conserved RBD epitopes. Rabbit mAbs included critical D-gene segment RBD-recognizing features in common with human anti-RBD mAbs, despite rabbit genomes lacking an equivalent human D-gene segment, thus demonstrating that the immune systems of humans and other mammals can utilize different antibody gene segments to arrive at similar modes of antigen recognition. These results suggest that animal models can be used to elicit anti-RBD mAbs with similar properties to those raised in humans, which can then be humanized for therapeutic use, and that mosaic RBD nanoparticle immunization coupled with multiplexed screening represents an efficient way to generate and select broadly cross-reactive therapeutic pan-sarbecovirus and pan-SARS-CoV-2 variant mAbs.

mRNA COVID-19 vaccines induce superior IgA titers in cancer patients compared to viral vector vaccines: Implications for immunization strategies

OBJECTIVES

IgA antibodies are involved in mucosal immunity and eliminate pathogens immediately at the point of entry. Vaccine-induced IgA antibodies could contribute to an additional layer of protection against SARS-CoV-2 for infection prone cancer patients. This might be particularly relevant for cancer patients as they mount reduced IgG antibody titers after dual-dose BNT162b2 COVID-19 vaccination and even lower responses after double-dose ChAdOx1 vaccination, compared to healthy individuals. However, data on vaccine-induced IgA antibodies are scarce, especially in cancer patients.

METHODS

This study compares SARS-CoV-2 anti-S1 IgA antibodies after dual-dose BNT162b2 vs ChAdOx1 vaccination in cancer patients. SARS-CoV-2 anti-S1 IgA antibodies were quantified in serum samples collected 7 days after second vaccination dose (N=213) (IEQ-CoVS1RBD-IgA-1-RB ELISA kit, RayBiotech) and analyzed with colorimetric detection. Additionally correlations with different aspects of humoral immunity were assessed (neutralizing and IgG antibodies).

RESULTS

Significant lower anti-S1 IgA antibody titers were reported in cancer patients after dual-dose ChAdOx1 compared to BNT162b2 vaccination. Moreover, cancer patients that received dual-dose BNT162b2 vaccination had a significant 16.44 fold increased chance to mount detectable IgA antibodies compared to patients receiving ChAdOx1 vaccination.

CONCLUSION

These findings highlight the potential role of boosters or alternative strategies to sustain mucosal immunity.

Construction of a variable fragment (Fv)-immunoglobulin A (IgA) anti-receptor binding domain (RBD) SARS-CoV-2 library based on IgA from Indonesian COVID-19 survivors

Despite entering the post-pandemic phase, SARS-CoV-2 remains a treatment challenge due to evolving mutations and immune evasion, leading to the emergence of antibody-resistant variants. This study aims to computationally construct a human Fv against various emerged variants of SARS-CoV-2 based on IgA sequences from Indonesian COVID-19 survivors. Survivor's saliva and plasma were purified using affinity chromatography to isolate anti-SARS-CoV-2 IgA. The IgA components, heavy and light chains, were isolated using SDS-PAGE and confirmed by Western Blot. They were extracted, digested with trypsin and chymotrypsin, and sequenced using LC MS/MS. Full Fvs were constructed based on IgA sequence obtained and covered with database and reference sequences to generate an Fv Library. The selection of the Fv Library was performed based on modelling, developability, and molecular docking analysis against various RBD variants. The study identified 9 potential Fvs with strong binding affinities to RBD-SARS-CoV-2 across all variants with RMSD values of CDR and Framework of Fv model structures <0.5 Å and developability scores within the safe therapeutic range. FVIGA0289, one of the top candidates, had binding affinities (ΔG) of -17.5, -16.3, -15.6, -16.6, -17.4, and -17.6 kcal/mol for the Wuhan, alpha, beta, gamma, delta, and omicron (XBB.1.5) variants, respectively. In conclusion, the use of antibody information isolated from Indonesian patients has successfully facilitated the computational construction of IgA-based Fv candidates with strong binding to multiple SARS-CoV-2 variants, supported by promising structural models and developability.

Comprehensive analysis of nasal IgA antibodies induced by intranasal administration of the SARS-CoV-2 spike protein

Intranasal vaccination is an attractive strategy for preventing COVID-19 disease as it stimulates the production of multimeric secretory immunoglobulin A (IgA), the predominant antibody isotype in the mucosal immune system, at the target site of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry. Currently, intranasal vaccine efficacy is evaluated based on the measurement of polyclonal antibody titers in nasal lavage fluid. However, how individual multimeric secretory IgA protects the mucosa from SARS-CoV-2 infection remains to be elucidated. To understand the precise contribution and molecular nature of multimeric secretory IgA induced by intranasal vaccines, we developed 99 monoclonal IgA clones from nasal mucosa and 114 monoclonal IgA or IgG clones from nonmucosal tissues of mice that were intranasally immunized with the SARS-CoV-2 spike protein. The nonmucosal IgA clones exhibited shared origins and common and unique somatic mutations with the related nasal IgA clones, indicating that the antigen-specific plasma cells in the nonmucosal tissues originated from B cells stimulated at the nasal mucosa. Comparing the spike protein binding reactivity, angiotensin-converting enzyme-2-blocking, and in vitro SARS-CoV-2 virus neutralization of monomeric and multimeric secretory IgA pairs recognizing different epitopes showed that even non-neutralizing monomeric IgAs, which represent 70% of the nasal IgA repertoire, can protect against SARS-CoV-2 infection when expressed as multimeric secretory IgAs. We also demonstrated that the intranasal administration of multimeric secretory IgA delivered as prophylaxis in the hamster model reduced infection-induced weight loss. Our investigation is the first to demonstrate the function of nasal IgA at the monoclonal level, showing that nasal immunization can provide effective immunity against SARS-CoV-2 by inducing multimeric secretory IgAs at the target site of the virus infection.

Monoclonal Antibodies for Pediatric Viral Disease Prevention and Treatment

Medical advancements over the last century have improved our ability to treat pediatric infectious diseases, significantly reducing associated morbidity and mortality worldwide. Although vaccines have been pivotal in this progress, many viral pathogens still do not currently have effective vaccines. The COVID-19 pandemic highlighted the need for rapid responses to emerging viral pathogens and introduced new tools to combat them. This review addresses human monoclonal antibodies (mAbs) as a strategy for treating and preventing viral infections in pediatric populations. We discuss previously used and currently available mAbs and advancements in mAb discovery. We address the future of mAb therapy by describing novel approaches in drug production and delivery platforms in addition to alternative antibody classes. Finally, we review the challenges and limitations of mAb therapy development for newborns and children.

An intranasal subunit vaccine induces protective systemic and mucosal antibody immunity against respiratory viruses in mouse models

Although vaccines are usually given intramuscularly, the intranasal delivery route may lead to better mucosal protection and limit the spread of respiratory virus while easing administration and improving vaccine acceptance. The challenge, however, is to achieve delivery across the selective epithelial cell barrier. Here we report on a subunit vaccine platform, in which the antigen is genetically fused to albumin to facilitate FcRn-mediated transport across the mucosal barrier in the presence of adjuvant. Intranasal delivery in conventional and transgenic mouse models induces both systemic and mucosal antigen-specific antibody responses that protect against challenge with SARS-CoV-2 or influenza A. When benchmarked against an intramuscularly administered mRNA vaccine or an intranasally administered antigen fused to an alternative carrier of similar size, only the albumin-based intranasal vaccine yields robust mucosal IgA antibody responses. Our results thus suggest that this needle-free, albumin-based vaccine platform may be suited for vaccination against respiratory pathogens.

Regulatory cytokines modulate early isotype-specific response associated with COVID-19 survival

Identifying immune markers driving early and effective antibody response in patients with severe coronavirus disease 2019 (COVID-19) is critical due to the threat of future coronavirus pandemics, incomplete global vaccination, and suboptimal booster coverage. Patients with life-threatening severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are characterized by dysregulated thromboinflammation and cytokine storm that could influence the isotype virus-specific antibody response and the subsequent clinical outcome. We investigated the association between COVID-19-related mortality with the dynamics, magnitude, and relative avidity of nucleoprotein (N), spike (S), and receptor-binding domain (RBD)-specific IgM, IgA, and IgG in circulation. We also assessed the relationship between the virus-specific antibody responses and cytokine patterns, as well as systemic and pulmonary thromboinflammation markers. This multicenter study included COVID-19 patients hospitalized early in the pandemic, classified as survivors (n=62) and non-survivors (n=17). We developed indirect enzyme-linked immunosorbent assays (ELISAs) to evaluate each virus-specific isotype using well-characterized outpatient COVID-19 (n=180) and pre-pandemic cohorts (n=111). The pro-inflammatory interleukin (IL)-6 and tumor necrosis factor (TNF)-α, as well as the regulatory IL-10, transforming growth factor (TGF)-β1, and soluble tumor necrosis factor receptor I (sTNFRI) levels were evaluated. The ELISAs performed highly for all virus-specific isotypes, although modest for IgM-N. Non-survivors increased N-specific, but no S-specific, IgM and IgA responses throughout the disease course and, more notably, a delayed class switching to IgG-S and IgG-RBD compared to survivors. No differences were observed in the virus-specific IgG relative avidity. Survivors exhibited an antibody response proportional to the degree of systemic and pulmonary thromboinflammation, whereas non-survivors showed those dissociated because of their uncontrolled severe thromboinflammation. Only the survivors showed a dominant regulatory cytokine pattern in the early phase of infection (<10 days after symptoms onset), which strongly correlated with developing IgG-S and IgG-RBD protective antibodies. We developed easy-to-use immune assays that enable patient monitoring and identify at-risk populations in low- to middle-income regions. Non-survivors displayed an ineffective N-mediated antibody response, marked by an inability to control inflammation and a compromised time-dependent class switching toward S and RBD-specific IgG. The regulatory cytokine axis, including TGF-β1, maybe a critical immune correlate of effective antibody-mediated immunity in COVID-19.

Effect of heterologous intranasal iNCOVACC® vaccination as a booster to two-dose intramuscular Covid-19 vaccination series: a randomized phase 3 clinical trial

BACKGROUND

Due to waning immunity and emerging variants, protection following primary intramuscular Covid-19 vaccinations is decreasing, so health agencies have been proposing heterologous booster vaccinations. Here, we report immunogenicity and safety evaluation of heterologous booster vaccination with an intranasal, adenovirus vectored SARS-CoV-2 vaccine (BBV154) in healthy adults, who were previously primed with two doses of either Covaxin® or Covishield™. We compare results with use of a homologous booster vaccination combination.

METHODS

This was a randomized, open-label phase 3 trial conducted to evaluate immunogenicity and safety of a booster dose of intranasal BBV154 vaccine or intramuscular EUA approved Covid-19 vacines in India. Healthy participants of ≥18 years age with no history of SARS-CoV-2 infection, who received two doses of Covaxin® or Covishield™ at least 6 ± 1 months earlier were enrolled. The primary outcome was the neutralising antibody titers against wild-type virus using a plaque-reduction neutralization test (PRNT50). Other outcomes measured were humoral (IgG), mucosal (IgA) and cell mediated responses. The protocol was registered #NCT05567471 and approved by National Regulatory Authority (India) #CTRI/2022/02/039992.

RESULTS

In this phase 3 trial, a total of 875 participants were randomized into 5 Groups in a ratio of 2:1:2:1:1 to receive either booster dose of BBV154 or Covaxin or Covishield. Based on per-protocol population, at Day 56, neutralization antibody titres were 564.1 (479·1, 664·1), 578.1 (436·9, 764·9), 655.5 (533·3, 805·8), 625.4 (474·7, 824·0), 650.1 (519·7, 813·1) for Group 1 to 5 respectively. This study was conducted, whilst the Omicron variant was prevalent. There were varying levels of severity of infection across different study sites with varied baseline antibody titers. Consequently, the average neutralization (PRNT50) antibody titers are similar across all Groups on day 56 and exhibited large differences within the Group, depending on the study site. All booster vaccinations are well tolerated and reported no serious adverse events; in particular, study participants boosted with BBV154 had significantly fewer solicited local adverse events than those primed and boosted with Covishield.

CONCLUSIONS

These findings demonstrate that impact of booster across different cohorts is governed by infection status of the individual and geographical diversity, thus necessitating large cohorts, well distributed studies before Covid-19 booster effects are interpreted.

Intranasal spike and nucleoprotein fusion protein-based vaccine provides cross-protection and reduced transmission against SARS-CoV-2 variants

The effectiveness of intramuscular vaccines aimed at preventing severe COVID-19 remains limited due to waning immunity and the emergence of novel variants. Next-generation vaccines are needed for broader protection and blocking virus transmission. Here, we rationally designed an original nasal subunit vaccine composed of a fusion protein (SwFN) made of Wuhan spike and nucleoprotein combined with biocompatible mucosal nanocarriers (Nc). In mouse model, the nasal Nc-SwFN vaccine elicited multivalent serum and mucosal neutralizing antibodies. Robust spike and nucleoprotein cross-reactive immunity against variants was induced with a predominant phenotype of resident memory T cells in the lungs. Moreover, Nc-SwFN led to protective responses against Wuhan and Delta infection in relevant models with an absence of morbidity, mortality, and virus dissemination in the lungs and brain. Finally, Nc-SwFN drastically reduced host-to-host transmission. These promising results underscore the advantages of the nasal Nc-SwFN approach as a broad-spectrum vaccine candidate against current and emerging SARS-CoV-2 variants.

Intranasal administration of a panreactive influenza antibody reveals Fc-independent mode of protection

Monoclonal antibodies have two core mechanisms of protection: an antibody's antigen-binding fragment (Fab) can bind and neutralize viral pathogens and its fragment crystallizable domain (Fc) catalyzes effector functions. We investigated the relative contribution of Fab- versus Fc-mediated mechanisms of protection through passive administration of distinct forms of the pan-reactive anti-influenza antibody CR9114. We demonstrated that the contribution of Fc-independent (Fab-dependent) versus Fc-dependent mechanisms of protection is defined by the route of administration. We used CR9114 variants (wild-type, two Fc-silenced variants, or the bivalent antigen-binding fragment F(ab')2), administered either intravenously or intranasally. We found that intravenously-administered CR9114 requires the Fc domain to provide potent, pre-exposure protection against influenza A and B viral challenge. In contrast, when CR9114 was administered locally to the nasal mucosa, the main mode of protection was provided by F(ab')2, and was largely Fc-independent. Importantly, this mode of protection following intranasal administration also applied to non-neutralized influenza B strains. Moreover, intranasal administration resulted in an increase in potency against influenza A/H1N1, A/H5N1, A/H3N2, B/Yam and B/Vic compared to intravenous administration up to 50-fold. These results shed new light on the application of monoclonal antibodies such as CR9114 to combat viral infection locally, and will help inform clinical strategies of pre-exposure prophylaxis. More fundamentally, this study uncovers distinct modes of protection for systemic versus intranasally-administered prophylactic antibodies.

Naive and Memory B Cell BCR Repertoires in Individuals Immunized with an Inactivated SARS-CoV-2 Vaccine

BACKGROUND

The COVID-19 pandemic has spurred a global race for a preventive vaccine, with a few becoming available just one year after describing this novel coronavirus disease. Among these are inactivated virus vaccines like CoronaVac (Sinovac Biotech), which are used in several countries to reduce the pandemic's effects. However, its use was associated with low protection, particularly against novel virus variants that quickly appeared in the following months. Vaccines play a crucial role in activating the immune system to combat infections, with Memory B-cells being a key part of this mechanism, eliciting protective neutralizing antibodies. This work focused on studying B-cell memory repertoire after two consecutive doses of CoronaVac.

METHODOLOGY

Memory B-cells were isolated from five CoronaVac vaccinated and five pre-pandemic individuals and subsequently stimulated in vitro before high-throughput Illumina sequencing of the Heavy Chain Variable repertoire.

RESULTS

We observed a shift in the VH repertoire with increased HCDR3 length and enrichment of IGVH 3-23, 3-30, 3-7, 3-72, and 3-74 for IgA BCRs and IGHV 4-39 and 4-59 for IgG BCRs. A high expansion of IgA-specific clonal populations was observed in vaccinated individuals relative to pre-pandemic controls, accompanied by shared IgA variable heavy chain (VH) sequences among memory B cells across different vaccine recipients of IgA clones was also observed in vaccinated individuals compared to pre-pandemic controls, with several IgA VH sharing between memory B cells from different vaccines. Moreover, a high convergence was observed among vaccinees and SARS-CoV-2 neutralizing antibody sequences found in the CoV-abDab database.

CONCLUSION

These data show the ability of CoronaVac to elicit antibodies with characteristics similar to those previously identified as neutralizing antibodies, supporting its protective efficacy. Furthermore, this analysis of the immunological repertoire in the context of viral infections reinforces the importance of immunization in generating convergent antibodies for the antiviral response.

Viral infection and antiviral immunity in the oral cavity

Individual tissues have distinct antiviral properties garnered through various mechanisms, including physical characteristics, tissue-resident immune cells and commensal organisms. Although the oral mucosa has long been appreciated as a critical barrier tissue that is exposed to a continuous barrage of pathogens, many fundamental aspects of the antiviral immune response in this tissue remain unknown. Several viral pathogens, such as herpesviruses and human papillomaviruses, have been acknowledged both historically and at present for infections in the oral cavity that result in substantial clinical burden. However, recent viral outbreaks, including those with SARS-CoV-2 and mpox, featured oral symptoms even though these viruses are not generally considered oral pathogens. Ensuing studies have shown that the oral cavity is an important locale for viral infection and potential transmission of newly emergent or re-emergent pathogens, highlighting the need for an increased understanding of the mechanisms of antiviral immunity at this site. In this Review, we provide a broad overview of antiviral immune responses in the oral cavity and discuss common viral infections and their manifestations in the oral mucosa. In addition, we present current mouse models for the study of oral viral infections.

Intranasal parainfluenza virus-vectored vaccine expressing SARS-CoV-2 spike protein of Delta or Omicron B.1.1.529 induces mucosal and systemic immunity and protects hamsters against homologous and heterologous challenge

The continuous emergence of new SARS-CoV-2 variants requires that COVID vaccines be updated to match circulating strains. We generated B/HPIV3-vectored vaccines expressing 6P-stabilized S protein of the ancestral, B.1.617.2/Delta, or B.1.1.529/Omicron variants as pediatric vaccines for intranasal immunization against HPIV3 and SARS-CoV-2 and characterized these in hamsters. Following intranasal immunization, these B/HPIV3 vectors replicated in the upper and lower respiratory tract and induced mucosal and serum anti-S IgA and IgG. B/HPIV3 expressing ancestral or B.1.617.2/Delta-derived S-6P induced serum antibodies that effectively neutralized SARS-CoV-2 of the ancestral and B.1.617.2/Delta lineages, while the cross-neutralizing potency of B.1.1.529/Omicron S-induced antibodies was lower. Despite the lower cross-neutralizing titers induced by B/HPIV3 expressing S-6P from B.1.1.529/Omicron, a single intranasal dose of all three versions of B/HPIV3 vectors was protective against matched or heterologous WA1/2020, B.1.617.2/Delta or BA.1 (B.1.1.529.1)/Omicron challenge; hamsters were protected from challenge virus replication in the lungs, while low levels of challenge virus were detectable in the upper respiratory tract of a small number of animals. Immunization also protected against lung inflammatory response after challenge, with mild inflammatory cytokine induction associated with the slightly lower level of cross-protection of WA1/2020 and B.1.617.2/Delta variants against the BA.1/Omicron variant. Serum antibodies elicited by all vaccine candidates were broadly reactive against 20 antigenic variants, but the antigenic breadth of antibodies elicited by B/HPIV3-expressed S-6P from the ancestral or B.1.617.2/Delta variant exceeded that of the S-6P B.1.1.529/Omicron expressing vector. These results will guide development of intranasal B/HPIV3 vectors with S antigens matching circulating SARS-CoV-2 variants.

Systemic and Mucosal Antibody Responses to SARS-CoV-2 Variant-Specific Prime-and-Boost and Prime-and-Spike Vaccination: A Comparison of Intramuscular and Intranasal Bivalent Vaccine Administration in a Murine Model

Background: The rapid genetic evolution of SARS-CoV-2 has led to the emergence of immune-evading, highly transmissible variants of concern (VOCs). This prompts the need for next-generation vaccines that elicit robust mucosal immunity in the airways to directly curb viral infection. Objective: Here, we investigate the impact of heterologous variant prime-boost regimens on humoral responses, focusing on intramuscular (IM) and intranasal (IN) routes of administration. Using a murine model, we assessed the immunogenicity of unadjuvanted protein boosts with Wu-1, Omicron BA.4/5, or Wu-1 + BA.4/5 spike antigens following monovalent or bivalent IM priming with mRNA-LNP vaccines. Results: IM priming induced strong systemic total and neutralizing antibody responses that were further enhanced by IN boosts with BA.4/5. IN boosting achieved the broadest serum neutralization across all VOCs tested. Notably, bivalent mRNA-LNP IM priming induced robust, cross-variant serum neutralizing antibody production, independent of subsequent IN boost combinations. Conclusions: Our findings highlight the benefit of including distinct antigenic variants in the prime vaccination followed by a variant-tailored IN boost to elicit both systemic and mucosal variant-specific responses that are potentially capable of reducing SARS-CoV-2 transmission.

IgA-driven neutrophil activation underlies post-Zika severe dengue disease in humans

The four dengue virus serotypes (DENV1-4) and the related Zika flavivirus (ZIKV) are major public health concerns worldwide. Primary immunity against ZIKV increases the risk of a subsequent severe DENV2 infection, presenting a significant challenge for developing safe and effective ZIKV vaccines. However, the mechanisms driving this phenomenon remain unclear. Leveraging our long-standing Pediatric Dengue Cohort Study in Nicaragua, we show that serum anti-NS1 IgA antibodies elicited after a primary ZIKV infection drive neutrophil activation and correlate with increased risk of subsequent severe DENV2 disease. Depletion experiments combined with ex vivo functional NETosis assays confirmed that anti-NS1 IgA antibodies drive neutrophil activation in dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Moreover, increased neutrophil degranulation in paired serum samples obtained during the acute DENV2 infection from the same individuals correlated with IgA binding to DENV2 NS1 and preceded the development of vascular leakage. This finding was corroborated in an orthogonal hospital-based study. Thus, serum anti-NS1 IgA enhances neutrophil activation in severe dengue, with implications for prognostics, therapeutics, and vaccines.

Machine Learning Reveals Distinct Immunogenic Signatures of Th1 Imprinting in ART-Treated Individuals with HIV Following Repeated SARS-CoV-2 Vaccination

The human immune system is intrinsically variable and remarkably diverse across a population. The immune response to antigens is driven by a complex interplay of time-dependent interdependencies across components of the immune system. After repeated vaccination, the humoral and cellular arms of the immune response display highly heterogeneous dynamics, further complicating the attribution of a phenotypic outcome to specific immune system components. We employ a random forest (RF) approach to classify informative differences in immunogenicity between older people living with HIV (PLWH) on ART and an age-matched control group who received up to five SARS-CoV-2 vaccinations over 104 weeks. RFs identify immunological variables of importance, interpreted as evidence for Th1 imprinting, and suggest novel distinguishing immune features, such as saliva-based antibody screening, as promising diagnostic features towards classifying responses (whereas serum IgG is not). Additionally, we implement supervised and unsupervised Machine Learning methods to produce physiologically accurate synthetic datasets that conform to the statistical distribution of the original immunological data, thus enabling further data-driven hypothesis testing and model validation. Our results highlight the effectiveness of RFs in utilizing informative immune feature interdependencies for classification tasks and suggests broad impacts of ML applications for personalized vaccination strategies among high-risk populations.

Circulating neutralizing antibodies and SARS-CoV-2 variant replication following postvaccination infections

The effect of preexisting neutralizing antibodies (NAb) on SARS-CoV-2 shedding in postvaccination infection (PVI) is not well understood. We characterized viral shedding longitudinally in nasal specimens in relation to baseline (pre/periinfection) serum NAb titers in 125 participants infected with SARS-CoV-2 variants. Among 68 vaccinated participants, we quantified the effect of baseline NAb titers on maximum viral RNA titers and infectivity duration. Baseline NAbs were higher and targeted a broader range of variants in participants with monovalent ancestral booster vaccinations compared with those with a primary vaccine series. In Delta infections, baseline NAb titers targeting Delta or Wuhan-Hu-1 correlated negatively with maximum viral RNA. Per log10 increase in Delta-targeting baseline NAb IC50, maximum viral load was reduced -2.43 (95% CI: -3.76, -1.11) log10 nucleocapsid copies, and infectious viral shedding was reduced -2.79 (95% CI: -4.99, -0.60) days. Conversely, in Omicron infections (BA.1, BA.2, BA.4, or BA.5), baseline NAb titers against Omicron lineages or Wuhan-Hu-1 did not predict viral outcomes. Our results provide robust estimates of the effect of baseline NAbs on the magnitude and duration of nasal viral replication after PVI (albeit with an unclear effect on transmission) and show how immune escape variants efficiently evade these modulating effects.

IgA class switching enhances neutralizing potency against SARS-CoV-2 by increased antibody hinge flexibility

IgA antibodies are critical components of the mucosal immune barrier, providing essential first-line defense against viral infections. In this study, we investigated the impact of antibody class switching on neutralization efficacy by engineering recombinant antibodies of different isotypes (IgA1, IgG1) with identical variable regions from SARS-CoV-2 convalescent patients. A potent, broad-spectrum neutralizing monoclonal antibody CAV-C65 exhibited a ten-fold increase in neutralization potency upon switching from IgG1 to IgA1 monomer. Structural analysis revealed that this antibody binds to two adjacent receptor binding domains on the spike protein. Enhanced neutralization by IgA1 was attributed to the combined effects of increased affinity, unique hinge region properties, and potential cross-linking of viral particles. Inhaled CAV-C65 IgA1 demonstrated prophylactic efficacy against lethal SARS-CoV-2 infection in hACE2 mice. These findings highlight the pivotal role of IgA in antiviral immunity and inform the development of IgA-based therapeutics.

Oral Ad5 Vector-Based SARS-CoV-2 Vaccine Effectively Induces Mucosal and Systemic Immune Responses in BALB/c Mice

Mucosal immunity is essential for preventing viral infections through the mucosal route. The emerging SARS-CoV-2 variants have posed additional hurdles to the efficiency of existing vaccines. The rapid development of novel vaccines that generate broad mucosal and systemic immunity could be the most effective strategy to address this issue. In this study, we developed a recombinant and replication-deficient type-5 adenoviral vaccine with a built-in double-strand RNA adjuvant and the vaccine expresses the SARS-CoV-2 Omicron BA.1 spike (S) antigen (hereinafter referred to as "the oral vaccine"). We found that two doses of the oral vaccine in BALB/c mice generated long-lasting S-specific mucosal and systemic immune responses, as well as broad neutralizing antibodies and SIgA antibodies. In addition, we found that compared to an mRNA vaccine booster, using the oral vaccine as a booster could induce both effective mucosal and systemic immunity, addressing the limitation of mRNA vaccines in eliciting mucosal immunity. Prospective oral vaccines require further investigation into development and potential applications, particularly viral challenge experiments, before clinical trials.

Enhancing the immunogenicity of lipid-nanoparticle mRNA vaccines by adjuvanting the ionizable lipid and the mRNA

To elicit optimal immune responses, messenger RNA vaccines require intracellular delivery of the mRNA and the careful use of adjuvants. Here we report a multiply adjuvanted mRNA vaccine consisting of lipid nanoparticles encapsulating an mRNA-encoded antigen, optimized for efficient mRNA delivery and for the enhanced activation of innate and adaptive responses. We optimized the vaccine by screening a library of 480 biodegradable ionizable lipids with headgroups adjuvanted with cyclic amines and by adjuvanting the mRNA-encoded antigen by fusing it with a natural adjuvant derived from the C3 complement protein. In mice, intramuscular or intranasal administration of nanoparticles with the lead ionizable lipid and with mRNA encoding for the fusion protein (either the spike protein or the receptor-binding domain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)) increased the titres of antibodies against SARS-CoV-2 tenfold with respect to the vaccine encoding for the unadjuvanted antigen. Multiply adjuvanted mRNA vaccines may improve the efficacy, safety and ease of administration of mRNA-based immunization.

State of the Art and Emerging Technologies in Vaccine Design for Respiratory Pathogens

In this review, we present the efforts made so far in developing effective solutions to prevent infections caused by seven major respiratory pathogens: influenza virus, respiratory syncytial virus (RSV), the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Bordetella pertussis, Streptococcus pneumoniae (pneumococcus), Mycobacterium tuberculosis, and Pseudomonas aeruginosa. Advancements driven by the recent coronavirus disease 2019 (COVID-19) crisis have largely focused on viruses, but effective prophylactic solutions for bacterial pathogens are also needed, especially in light of the antimicrobial resistance (AMR) phenomenon. Here, we discuss various innovative key technologies that can help address this critical need, such as (a) the development of Lung-on-Chip ex vivo models to gain a better understanding of the pathogenesis process and the host-microbe interactions; (b) a more thorough investigation of the mechanisms behind mucosal immunity as the first line of defense against pathogens; (c) the identification of correlates of protection (CoPs) which, in conjunction with the Reverse Vaccinology 2.0 approach, can push a more rational and targeted design of vaccines. By focusing on these critical areas, we expect substantial progress in the development of new vaccines against respiratory bacterial pathogens, thereby enhancing global health protection in the framework of the increasingly concerning AMR emergence.

Sequential intranasal booster triggers class switching from intramuscularly primed IgG to mucosal IgA against SARS-CoV-2

The persistent emergence of COVID-19 variants and recurrent waves of infection worldwide underscores the urgent need for vaccines that effectively reduce viral transmission and prevent infections. Current intramuscular (IM) COVID-19 vaccines inadequately protect the upper respiratory mucosa. In response, we have developed a nonadjuvanted, IFN-armed SARS-CoV-2 fusion protein vaccine with IM priming and intranasal (IN) boost sequential immunization. Our study showed that this sequential vaccination strategy of the IM+IN significantly enhanced both upper respiratory and systemic antiviral immunity in a mouse model, characterized by the rapid increase in systemic and mucosal T and B cell responses, particularly the mucosal IgA antibody response. The IN boost triggered a swift secondary immune response, rapidly inducing antigen-specific IgA+ B cells. Further B cell receptor-seq (BCR-seq) analysis indicated that these IgA+ B cells primarily arose through direct class switching from preexisting IgG+ B cells in draining lymph nodes. Notably, our clinical studies revealed that the IN boost after IM vaccination elicited a robust systemic IgA antibody response in humans, as measured in serum. Thus, we believe that our cytokine-armed protein vaccine presents a promising strategy for inducing rapid and potent mucosal protection against respiratory viral infections.

Mucosal immune response in biology, disease prevention and treatment

The mucosal immune system, as the most extensive peripheral immune network, serves as the frontline defense against a myriad of microbial and dietary antigens. It is crucial in preventing pathogen invasion and establishing immune tolerance. A comprehensive understanding of mucosal immunity is essential for developing treatments that can effectively target diseases at their entry points, thereby minimizing the overall impact on the body. Despite its importance, our knowledge of mucosal immunity remains incomplete, necessitating further research. The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has underscored the critical role of mucosal immunity in disease prevention and treatment. This systematic review focuses on the dynamic interactions between mucosa-associated lymphoid structures and related diseases. We delve into the basic structures and functions of these lymphoid tissues during disease processes and explore the intricate regulatory networks and mechanisms involved. Additionally, we summarize novel therapies and clinical research advances in the prevention of mucosal immunity-related diseases. The review also addresses the challenges in developing mucosal vaccines, which aim to induce specific immune responses while maintaining tolerance to non-pathogenic microbes. Innovative therapies, such as nanoparticle vaccines and inhalable antibodies, show promise in enhancing mucosal immunity and offer potential for improved disease prevention and treatment.

Cross-reactive sarbecovirus antibodies induced by mosaic RBD-nanoparticles

Therapeutic monoclonal antibodies (mAbs) against SARS-CoV-2 become obsolete as spike substitutions reduce antibody binding. To induce antibodies against conserved receptor-binding domain (RBD) regions for protection against SARS-CoV-2 variants of concern and zoonotic sarbecoviruses, we developed mosaic-8b RBD-nanoparticles presenting eight sarbecovirus RBDs arranged randomly on a 60-mer nanoparticle. Mosaic-8b immunizations protected animals from challenges from viruses whose RBDs were matched or mismatched to those on nanoparticles. Here, we describe neutralizing mAbs from mosaic-8b-immunized rabbits, some on par with Pemgarda (the only currently FDA-approved therapeutic mAb). Deep mutational scanning, in vitro selection of spike resistance mutations, and cryo-EM structures of spike-antibody complexes demonstrated targeting of conserved epitopes. Rabbit mAbs included critical D-gene segment features in common with human anti-RBD mAbs, despite rabbit genomes lacking an equivalent human D-gene segment. Thus, mosaic RBD-nanoparticle immunization coupled with multiplexed screening represent an efficient way to generate and select therapeutic pan-sarbecovirus and pan-SARS-2 variant mAbs.

In vivo antiviral efficacy of LCTG-002, a pooled, purified human milk secretory IgA product, against SARS-CoV-2 in a murine model of COVID-19

Immunoglobulin A (IgA) is the most abundant antibody (Ab) in human mucosae, with secretory form (sIgA) being dominant and uniquely stable. sIgA is challenging to produce recombinantly but is naturally found in human milk, which could be considered a global resource for this biologic, justifying its development as a mucosal therapeutic. Presently, SARS-CoV-2 was utilized as a model mucosal pathogen, and methods were developed to efficiently extract human milk sIgA from donors who were naïve to SARS-CoV-2 or had recovered from infection that elicited high-titer anti-SARS-CoV-2 Spike sIgA in their milk (pooled to make LCTG-002). Mass spectrometry determined that proteins with a relative abundance of 1% or greater were all associated with sIgA. Western blot demonstrated that all batches consisted predominantly of sIgA. Compared to control IgA, LCTG-002 demonstrated significantly higher Spike binding (mean endpoint of 0.87 versus 5.87). LCTG-002 was capable of blocking the Spike receptor-binding domain - angiotensin-converting enzyme 2 (ACE2) interaction with significantly greater potency compared to control (mean LCTG-002 IC50 154ug/mL versus 50% inhibition not achieved for control), and exhibited significant neutralization activity against Spike-pseudotyped virus infection (mean LCTG-002 IC50 49.8ug/mL versus 114.5ug/mL for control). LCTG-002 was tested for its capacity to reduce viral lung burden in K18+hACE2 transgenic mice inoculated with SARS-CoV-2. LCTG-002 significantly reduced SARS-CoV-2 titers compared to control when administered at 0.25 mg/day or 1 mg/day, with a maximum TCID50 reduction of 4.9 logs. This innovative study demonstrates that LCTG-002 is highly pure and efficacious in vivo, supporting further development of milk-derived, polyclonal sIgA therapeutics.

Induction of Tier 2 HIV-Neutralizing IgA Antibodies in Rhesus Macaques Vaccinated with BG505.664 SOSIP

BACKGROUND

A goal of mucosal human immunodeficiency virus type 1 (HIV-1) vaccines is to generate mucosal plasma cells producing polymeric IgA (pIgA)-neutralizing antibodies at sites of viral entry. However, vaccine immunogens capable of eliciting IgA neutralizing antibodies (nAbs) that recognize tier 2 viral isolates have not yet been identified.

METHODS

To determine if stabilized native-like HIV-1 envelope (Env) trimers could generate IgA nAbs, we purified total IgA and IgG from the banked sera of six rhesus macaques that had been found in a previous study to develop serum nAbs after subcutaneous immunization with BG505.664 SOSIP and 3M-052 adjuvant, which is a TLR7/8 agonist. The neutralization of autologous tier 2 BG505 T332N pseudovirus by the IgA and IgG preparations was measured using the TZM-bl assay. Anti-SOSIP binding antibodies (bAbs) were measured by ELISA.

RESULTS

The IgG samples were found to have significantly greater levels of both nAb and bAb. However, after normalizing the nAb titer relative to the concentration of bAb, SOSIP-specific IgA purified from 2/6 animals was found to neutralize just as effectively as SOSIP-specific IgG, and in 3/6 animals, neutralization by the specific IgA was significantly greater. The more potent neutralization by IgA in these three animals was associated with a higher percentage of anti-SOSIP J chain-bound (polymeric) antibody.

CONCLUSIONS

The parenteral vaccination of nonhuman primates with BG505.664 SOSIP generates HIV-1 tier 2 IgA nAbs in serum, including SOSIP-specific polymeric IgA, which appears to neutralize more efficiently than monomeric IgA or IgG. Mucosal delivery of this SOSIP or other stable Env trimers could generate locally synthesized polymeric IgA nAbs in mucosal tissues and secretions.

The Circulating Proteome─Technological Developments, Current Challenges, and Future Trends

Recent improvements in proteomics technologies have fundamentally altered our capacities to characterize human biology. There is an ever-growing interest in using these novel methods for studying the circulating proteome, as blood offers an accessible window into human health. However, every methodological innovation and analytical progress calls for reassessing our existing approaches and routines to ensure that the new data will add value to the greater biomedical research community and avoid previous errors. As representatives of HUPO's Human Plasma Proteome Project (HPPP), we present our 2024 survey of the current progress in our community, including the latest build of the Human Plasma Proteome PeptideAtlas that now comprises 4608 proteins detected in 113 data sets. We then discuss the updates of established proteomics methods, emerging technologies, and investigations of proteoforms, protein networks, extracellualr vesicles, circulating antibodies and microsamples. Finally, we provide a prospective view of using the current and emerging proteomics tools in studies of circulating proteins.

Impaired mucosal IgA response in patients with severe COVID-19

Several studies have investigated the antibody response to SARS-CoV-2, focusing particularly on the systemic humoral immune response and the production of immunoglobulin G (IgG) antibodies. IgA antibodies play a crucial role in protecting against respiratory viral infections but have also been associated with the pathophysiology of COVID-19. We performed a prospective study of 169 COVID-19 patients - 50 with critical/severe (ICU), 47 with moderate (Non-ICU), and 72 with asymptomatic COVID-19 - to explore the humoral immune response to SARS-CoV-2 infection. We found that the early systemic IgA response strongly induced in patients with severe disease did not block IgG neutralization functions and activated FcRs more effectively than IgG. However, even if SIgA levels were high, mucosal IgA antibodies could not control the infection effectively in patients with severe disease. Our findings highlight the complexity of the immune response to SARS-CoV-2 exhibiting high systemic levels of IgA with strong neutralizing capacity in severe cases, together with higher levels of IgA-FcR activation than in asymptomatic patients. They also suggest the need for further research to fully understand the role of IgA and its structural alterations in mucosal tissues in cases of severe disease and the impact of these antibodies on disease progression.

A Possible Protective Effect of IgA Against Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) in Bronchoalveolar Lavage in COVID-19 Patients Admitted to Intensive Care Unit

SARS-CoV-2 infection induces a humoral immune response, producing virus-specific antibodies such as IgM, IgG, and IgA. IgA antibodies are present at mucosal sites, protecting against respiratory and other mucosal infections, including SARS-CoV-2, by neutralizing viruses or impeding attachment to epithelial cells. Since SARS-CoV-2 spreads through the nasopharynx, the specific IgAs of SARS-CoV-2 are produced quickly after infection, effectively contributing to virus neutralization. Dimeric IgA has been reported to be 10 to 15 times more potent than its equivalent IgG, suggesting that this isotype may be particularly interesting in developing new monoclonal antibodies and/or new vaccines efficiently neutralizing the virus at the mucosal sites. It is still unclear whether IgA antibodies in BAL might play a role in the disease course and if their presence may have a prognostic significance. However, a harmful effect on diseases with high IgA titers has been reported. This study evaluated mucosal-specific IgA and IgG profiles in BAL of patients with COVID-19 acute respiratory failure admitted to the ICU. We included 57 patients (41 males and 16 females), admitted to the ICU of the University of Foggia. We used a commercially available ELISA assay to evaluate the presence of SARS-CoV-2 IgG and IgA antibodies in plasma and BAL of the 57 hospitalized patients with severe COVID-19 respiratory failure. However, 40/57 BAL and plasma from infected patients were available for the ELISA test; the remaining specimens were unsuitable. IgG and IgA antibodies against SARS-CoV-2 were detectable in 37 (92.5%) and 40 (100%) plasma specimens, respectively. IgG antibodies were found in a single sample, while IgAs were detected in 19 of 40 BAL samples analyzed. Correlations between these parameters and patient outcomes reveal a signature associated with survival. Interestingly, a statistically significant inverse correlation was found between the mortality rate and the presence of IgA to SARS-CoV-2 in BAL specimens. None of the 19 patients with a positive IgA died, compared to 7 out of 12 patients with a negative IgA-BAL (p: <0.0004). Despite being limited in size, this study suggests a significant protective effect of mucosal immunity in COVID-19 patients, even in advanced disease stages, and a role of IgA in the defense against the virus, as well as the possible use of effective vaccines and therapeutic strategies based on IgA antibodies.

Immune evasion after SARS-CoV-2 Omicron BA.5 and XBB.1.9 endemic observed from Guangdong Province, China from 2022 to 2023

BACKGROUND

From 2022 to 2023, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused by Omicron variants spread rapidly in Guangdong Province, resulting in over 80% of the population being infected.

RESULTS

To investigate the levels of neutralizing antibodies (NAbs) in individuals following the rapid pandemic and to evaluate the cross-protection against currently circulating variants of SARS-CoV-2 in China, neutralization assay and magnetic particle chemiluminescence method were used to test the 117 serum samples from individuals who had recovered 4 weeks post-infection. The results indicated that the levels of NAbs against prototype and Omicron variants BA.5 were significantly higher than those against Omicron variants BQ.1, XBB.1.1, XBB.1.9, XBB.1.16 and EG.5, regardless of whether the infection was primary or secondary.

CONCLUSIONS

The cross-protection provided by NAbs induced by prototype and Omicron BA.5 variants was limited when challenged by BQ.1, XBB.1.1, XBB.1.9, XBB.1.16 and EG.5 variants. This indicates that we should pay more attention to the risk of multiple infection from any novel Omicron variants that may emerge in the near future.

Intranasal delivery of a subunit protein vaccine provides protective immunity against JN.1 and XBB-lineage variants

The mucosal immune response plays a crucial role in the prevention of respiratory viruses. Given the risk of recurrent SARS-CoV-2 infections in the population, the rapid development of next-generation intranasal COVID-19 vaccines with high safety and efficacy is paramount. In the current study, we developed a protein-based intranasal vaccine comprising the XBB.1.5 receptor binding domain (RBD)-derived trimeric recombinant protein (RBDXBB.1.5-HR) and an MF59-like oil-in-water adjuvant. Intranasal administration of RBDXBB.1.5-HR vaccine elicited robust and sustained humoral immune responses in mice and rats, resulting in high levels of neutralizing antibodies against XBB-lineage subvariants, with protection lasting for at least six months. The intranasal RBDXBB.1.5-HR vaccine generated potent mucosal immune responses, characterized by the inductions of tissue-resident T (TRM) cells, local cellular immunity, germinal center, and memory B cell responses in the respiratory tract. The combination of intramuscular and intranasal delivery of the RBDXBB.1.5-HR vaccine demonstrated exceptional systemic and mucosal protective immunity. Furthermore, intranasal delivery of RBDXBB.1.5-HR vaccine as a heterologous booster shot showed more effective boosting effects after mRNA administration compared to homologous vaccination, as evidenced by the induction of superior systemic and extra mucosal immune response. Importantly, the intranasal RBDXBB.1.5-HR vaccine conferred efficient protection against the challenge with authentic EG.5.1 viruses in vivo. These findings identify the intranasal RBDXBB.1.5-HR vaccine as a potential mucosal vaccine candidate for the prevention of SARS-CoV-2 infection.

Role of mucosal IgA antibodies as novel therapies to enhance mucosal barriers

To prevent infection, the experience of the recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) pandemic has led to recognition of the importance of not only vaccines but also the strengthening of mucosal barriers by secretory immunoglobulin A (IgA). Strong mucosal barrier provided by IgA is also possible to prevent allergies and chronic inflammatory conditions in the intestinal tract, since it can protect foreign enemies or antigens at the first line of defense before their invasion. Therefore, it is important to understand the role of IgA antibodies secreted by the mucosa of the body. In this section, we discuss the role of mucosal IgA antibodies in relation to three disease states: control of intestinal microbiota, protection against infection, and allergy. In addition, we provide the evidence in which the quality as well as the quantity of IgA is critical for disease prevention. Therefore, we discuss about novel strategies to enhance mucosal barriers by induction of high-quality IgA.

Identification of potential antigenic proteins and epitopes for the development of a monkeypox virus vaccine: an in silico approach

Virus assembly, budding, or surface proteins play important roles such as viral attachment to cells, fusion, and entry into cells. The present study aimed to identify potential antigenic proteins and epitopes that could be used to develop a vaccine or diagnostic assay against the Monkeypox virus (MPXV) which may cause a potential epidemic. To do this, 39 MPXV proteins (including assembly, budding, and surface proteins) were analyzed using an in silico approach. Of these 39 proteins, the F5L virus protein was found to be the best vaccine candidate due to its signal peptide properties, negative GRAVY value, low transmembrane helix content, moderate aliphatic index, large molecular weight, long-estimated half-life, beta wrap motifs, and being stable, soluble, and containing non-allergic features. Moreover, the F5L protein exhibited alpha-helical secondary structures, making it a potential "structural antigen" recognized by antibodies. The other viral protein candidates were A9 and A43, but A9 lacked beta wrap motifs, while A43 had a positive GRAVY value and was insoluble. These two proteins were not as suitable candidates as the F5L protein. The KRVNISLTCL epitope from the F5L protein demonstrated the highest antigen score (2.4684) for MHC-I, while the GRFGYVPYVGYKCI epitope from the A9 protein exhibited the highest antigenicity (1.754) for MHC-II. Both epitopes met the criteria for high antigenicity, non-toxicity, solubility, non-allergenicity, and the presence of cleavage sites. Molecular docking and dynamics (MD) simulations further validated their potential, revealing stable and energetically favorable interactions with MHC molecules. The immunogenicity assessment showed that GRFGYVPYVGYKCI could strongly induce immune responses through both IFN-γ and IL-4 pathways, suggesting its capacity to provoke a balanced Th1 and Th2 response. In contrast, KRVNISLTCL exhibited limited immunostimulatory potential. Overall, these findings lay the groundwork for future vaccine development, indicating that F5L, particularly the GRFGYVPYVGYKCI epitope, may serve as an effective candidate for peptide-based vaccine design against MPXV.

Spatial Engineering of Heterotypic Antigens on a DNA Framework for the Preparation of Mosaic Nanoparticle Vaccines with Enhanced Immune Activation against SARS-CoV-2 Variants

Mosaic nanoparticle vaccines with heterotypic antigens exhibit broad-spectrum antiviral capabilities, but the impact of antigen proportions and distribution patterns on vaccine-induced immunity remains largely unexplored. Here, we present a DNA nanotechnology-based strategy for spatially assembling heterotypic antigens to guide the rational design of mosaic nanoparticle vaccines. By utilizing two aptamers with orthogonal selectivity for the original SARS-CoV-2 spike trimer and Omicron receptor-binding domain (RBD), along with a DNA soccer-ball framework, we precisely manipulate the spacing, stoichiometry, and overall distribution of heterotypic antigens to create mosaic nanoparticles with average, bipolar, and unipolar antigen distributions. Systematic in vitro and in vivo immunological investigations demonstrate that 30 heterotypic antigens in equivalent proportions, with an average distribution, lead to higher production of broad-spectrum neutralizing antibodies compared to the bipolar and unipolar distributions. Furthermore, the precise assembly utilizing our developed methodology reveals that a mere increment of five Omicron RBD antigens on a nanoparticle (from 15 to 20) not only diminishes neutralization against the Omicron variant but also triggers excessive inflammation. This work provides a unique perspective on the rational design of mosaic vaccines by highlighting the significance of the spatial placement and proportion of heterotypic antigens in their structure-activity mechanisms.

Protective role of antibodies in enteric virus infections: Lessons from primary and secondary immune deficiencies

Enteric viruses are the main cause of acute gastroenteritis worldwide with a significant morbidity and mortality, especially among children and aged adults. Some enteric viruses also cause disseminated infections and severe neurological manifestations such as poliomyelitis. Protective immunity against these viruses is not well understood in humans, with most knowledge coming from animal models, although the development of poliovirus and rotavirus vaccines has extended our knowledge. In a classical view, innate immunity involves the recognition of foreign DNA or RNA by pathogen recognition receptors leading to the production of interferons and other inflammatory cytokines. Antigen uptake and presentation to T cells and B cells then activate adaptive immunity and, in the case of the mucosal immunity, induce the secretion of dimeric IgA, the more potent immunoglobulins in viral neutralization. The study of Inborn errors of immunity (IEIs) offers a natural opportunity to study nonredundant immunity toward pathogens. In the case of enteric viruses, patients with a defective production of antibodies are at risk of developing neurological complications. Moreover, a recent description of patients with low or absent antibody production with protracted enteric viral infections associated with hepatitis reinforces the prominent role of B cells and immunoglobulins in the control of enteric virus.

Antibodies in breast milk: Pro-bodies designed for healthy newborn development

This manuscript sheds light on the impact of maternal breast milk antibodies on infant health. Milk antibodies prepare and protect the newborn against environmental exposure, guide and regulate the offspring's immune system, and promote transgenerational adaptation of the immune system to its environment. While the transfer of IgG across the placenta ceases at birth, milk antibodies are continuously replenished by the maternal immune system. They reflect the mother's real-time adaptation to the environment to which the infant is exposed. They cover the infant's upper respiratory and digestive mucosa and are perfectly positioned to control responses to environmental antigens and might also reach their circulation. Maternal antibodies in breast milk play a key role in the immune defense of the developing child, with a major impact on infectious disease susceptibility in both HIC and LMIC. They also influence the development of another major health burden in children-allergies. Finally, emerging evidence shows that milk antibodies also actively shape immune development. Much of this is likely to be mediated by their effect on the seeding, composition and function of the microbiota, but not only. Further understanding of the bridge that maternal antibodies provide between the child and its environment should enable the best interventions to promote healthy development.

Repeated COVID-19 mRNA-based vaccination contributes to SARS-CoV-2 neutralizing antibody responses in the mucosa

To prevent infection by respiratory viruses and consequently limit virus circulation, vaccines need to promote mucosal immunity. The extent to which the currently used messenger RNA (mRNA)-based COVID-19 vaccines induce mucosal immunity remains poorly characterized. We evaluated mucosal neutralizing antibody responses in a cohort of 183 individuals. Participants were sampled at several time points after primary adenovirus vector-based or mRNA-based COVID-19 vaccination and after mRNA-based booster vaccinations. Our findings revealed that repeated vaccination with mRNA boosters promoted severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) neutralizing antibodies in nasal secretions. Nasal and serum neutralizing antibody titers of both IgG and IgA isotypes correlated to one another. We investigated the source of these mucosal antibodies in a mouse model wherein mice received repeated mRNA vaccines for SARS-CoV-2. These experiments indicated that neutralizing antibody-producing cells reside in the spleen and bone marrow, whereas no proof of tissue homing to the respiratory mucosa was observed, despite the detection of mucosal antibodies. Serum transfer experiments confirmed that circulating antibodies were able to migrate to the respiratory mucosa. Collectively, these results demonstrate that, especially upon repeated vaccination, the currently used COVID-19 mRNA vaccines can elicit mucosal neutralizing antibodies and that vaccination might also stimulate mucosal immunity induced by previous SARS-CoV-2 infection. Moreover, migration of circulating antibodies to the respiratory mucosa might be a main mechanism. These findings advance our understanding of mRNA vaccine-induced immunity and have implications for the design of vaccine strategies to combat respiratory infections.

SARS-CoV-2 XBB.1.5 mRNA booster vaccination elicits limited mucosal immunity

Current COVID-19 vaccines provide robust protection against severe disease but minimal protection against acquisition of infection. Intramuscularly administered COVID-19 vaccines induce robust serum neutralizing antibodies (NAbs), but their ability to boost mucosal immune responses remains to be determined. In this study, we show that the XBB.1.5 messenger RNA (mRNA) boosters result in increased serum neutralization to multiple severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants in humans, including the dominant circulating variant JN.1. In contrast, we found that the XBB.1.5 mRNA booster did not augment mucosal NAbs or mucosal IgA responses, although acute SARS-CoV-2 XBB infection substantially increased mucosal antibody responses. These data demonstrate that current XBB.1.5 mRNA boosters substantially enhance peripheral antibody responses but do not robustly increase mucosal antibody responses. Our data highlight a separation between the peripheral and mucosal immune systems in humans and emphasize the importance of developing next-generation vaccines to augment mucosal immunity to protect against respiratory virus infections.

Role of IgA1 protease-producing bacteria in SARS-CoV-2 infection and transmission: a hypothesis

Secretory (S) IgA antibodies against severe acute respiratory syndrome (SARS)-CoV-2 are induced in saliva and upper respiratory tract (URT) secretions by natural infection and may be critical in determining the outcome of initial infection. Secretory IgA1 (SIgA1) is the predominant isotype of antibodies in these secretions. Neutralization of SARS-CoV-2 is most effectively accomplished by polymeric antibodies such as SIgA. We hypothesize that cleavage of SIgA1 antibodies against SARS-CoV-2 by unique bacterial IgA1 proteases to univalent Fabα antibody fragments with diminished virus neutralizing activity would facilitate the descent of the virus into the lungs to cause serious disease and also enhance its airborne transmission to others. Recent studies of the nasopharyngeal microbiota of patients with SARS-CoV-2 infection have revealed significant increases in the proportions of IgA1 protease-producing bacteria in comparison with healthy subjects. Similar considerations might apply also to other respiratory viral infections including influenza, possibly explaining the original attribution of influenza to Haemophilus influenzae, which produces IgA1 protease.

Unravelling the role of secretory Immnuoglobulin-A in COVID-19: a multicentre study in nursing homes during the first wave

BACKGROUND

The function of mucosal secretory IgA (SIgA) seems to be paramount in the immune response against SARS-CoV-2 however, there are few studies addressing this issue specifically in the institutionalized older population. This study aims to determine the levels of secretory IgA against the S1 domain of the SARS-CoV-2 spike (SIgA-S1) in older people living in nursing homes (NH) and to investigate the differences in baseline characteristics, severity of COVID-19, duration of symptoms, 30-day mortality, and reinfection according to the levels of SIgA-S1.

METHODS

In this multicentre longitudinal study, conducted in two NHs attended in coordination with a hospital-based Geriatric team, 305 residents (87.3 years, 74.4% female) were included. A massive collection of nasopharyngeal samples was carried out after the first wave of COVID-19 in May 2020 and an ELISA analysis of SIgA-S1 was performed on frozen samples in May 2023. Values of SIgA-S1 ≥ 57.6 U/mL ("cut-off point") were considered "induced". Resident medical records were reviewed to assess symptoms, comprehensive geriatric assessment (CGA), reinfection, and overall 30-day mortality.

RESULTS

At the time of sample collection, 274 residents (89.8%) exhibited "induced" SIgA-S1 levels (≥ 57.6 U/mL), 46 (15.1%) tested positive for PCR SARS-CoV-2, and 170 (57%) had experienced COVID-19 symptoms. "Induced" SIgA-S1 patients were more likely to be symptomatic (60.3% vs. 29%; p < 0.001) and exhibited upper respiratory tract symptoms more frequently (25.1% vs. 6.5%; p = 0.020) compared to "non-induced" patients. Patients with severe disease and duration of symptoms > 10 days had higher levels of SIgA-S1 than those with mild disease (252 vs.192.6 U/mL; p = 0.012) or duration ≤ 10 days (270.5 vs. 208.1 U/mL; p = 0.043), respectively. No significant differences were observed in age, sex, CGA, duration of symptoms, disease severity, overall 30-day-mortality, or reinfection between "induced" and "non-induced" residents.

CONCLUSIONS

Levels of SIgA-S1 are associated with the duration and type of COVID-19 symptoms, along with the severity of infection. While these findings shed light on the knowledge of SIgA-S1, further interdisciplinary studies are warranted to better understand the immune response to SARS-CoV-2 infection.

Navigating the Landscape of B Cell Mediated Immunity and Antibody Monitoring in SARS-CoV-2 Vaccine Efficacy: Tools, Strategies and Clinical Trial Insights

Correlates of Protection (CoP) are biomarkers above a defined threshold that can replace clinical outcomes as primary endpoints, predicting vaccine effectiveness to support the approval of new vaccines or follow up studies. In the context of COVID-19 vaccination, CoPs can help address challenges such as demonstrating vaccine effectiveness in special populations, against emerging SARS-CoV-2 variants or determining the durability of vaccine-elicited immunity. While anti-spike IgG titres and viral neutralising capacity have been characterised as CoPs for COVID-19 vaccination, the contribution of other components of the humoral immune response to immediate and long-term protective immunity is less well characterised. This review examines the evidence supporting the use of CoPs in COVID-19 clinical vaccine trials, and how they can be used to define a protective threshold of immunity. It also highlights alternative humoral immune biomarkers, including Fc effector function, mucosal immunity, and the generation of long-lived plasma and memory B cells and discuss how these can be applied to clinical studies and the tools available to study them.

Formulation Attributes Impact Immune Profile of an Oral and Thermostable COVID-19 Subunit Vaccine

While approved vaccines for COVID-19 provide protection against severe disease and death, they have limited efficacy in the prevention of infection and virus transmission. Mucosal immunity is preferred over systemic immunity to provide protection at the point of entry against pathogens such as SARS-CoV-2. VaxForm has developed an oral vaccine delivery platform that elicits mucosal and systemic immune responses by targeting immune cells in the gut through C-type lectin receptors. The technology consists of microencapsulating the vaccine with an enteric polymer, which also results in enhanced thermostability. This article describes the formulation development and in vivo testing of a novel protein-based oral COVID-19 vaccine using this technology. Results demonstrate successful induction of immune response in mice and showed that the particle size of the vaccines following administration can impact the ratio of mucosal to systemic response. Immunogenicity and thermostability of liquid suspension and dry powder versions of the vaccine were compared in mice. The liquid suspension vaccine showed excellent heat resistance by maintaining immunogenicity after 14 days of storage at 60 °C. While further investigation is needed to determine correlates of protection and duration of response for mucosal immunity, this study demonstrates the vaccine's potential as a COVID-19 booster to enhance mucosal protection in humans and improve global access by lowering the cost of production, removing cold-chain requirements, and allowing self-administration.

Compartment-specific antibody correlates of protection to SARS-CoV-2 Omicron in macaques

Antibodies represent a primary mediator of protection against respiratory viruses. Serum neutralizing antibodies (NAbs) are often considered a primary correlate of protection. However, detailed antibody profiles including characterization of antibody functions in different anatomic compartments are poorly understood. Here we show that antibody correlates of protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) challenge are different in systemic versus mucosal compartments in rhesus macaques. In serum, NAbs were the strongest correlate of protection and linked to spike-specific binding antibodies and other extra-NAb functions that create a larger protective network. In bronchiolar lavage (BAL), antibody-dependent cellular phagocytosis (ADCP) proved the strongest correlate of protection rather than NAbs. Within BAL, ADCP was linked to mucosal spike-specific immunoglobulin (Ig)G, IgA/secretory IgA, and Fcγ-receptor binding antibodies. Our results support a model in which antibodies with different functions mediate protection at different anatomic sites.

Intranasal Self-Adjuvanted Lipopeptide Vaccines Elicit High Antibody Titers and Strong Cellular Responses against SARS-CoV-2

Despite concerted efforts to tackle the COVID-19 pandemic, the persistent transmission of SARS-CoV-2 demands continued research into novel vaccination strategies to combat the virus. In light of this, intranasally administered peptide vaccines, particularly those conjugated to an immune adjuvant to afford so-called "self-adjuvanted vaccines", remain underexplored. Here, we describe the synthesis and immunological evaluation of self-adjuvanting peptide vaccines derived from epitopes of the spike glycoprotein of SARS-CoV-2 covalently fused to the potent adjuvant, Pam2Cys, that targets toll-like receptor 2 (TLR2). When administered intranasally, these vaccines elicited a strong antigen-specific CD4+ and CD8+ T-cell response in the lungs as well as high titers of IgG and IgA specific to the native spike protein of SARS-CoV-2. Unfortunately, serum and lung fluid from mice immunized with these vaccines failed to inhibit viral entry in spike-expressing pseudovirus assays. Following this, we designed and synthesized fusion vaccines composed of the T-cell epitope discovered in this work, covalently fused to epitopes of the receptor-binding domain of the spike protein reported to be neutralizing. While antibodies elicited against these fusion vaccines were not neutralizing, the T-cell epitope retained its ability to stimulate strong antigen-specific CD4+ lymphocyte responses within the lungs. Given the Spike(883-909) region is still completely conserved in SARS-CoV-2 variants of concern and variants of interest, we envision the self-adjuvanting vaccine platform reported here may inform future vaccine efforts.

Nanoplatform Based Intranasal Vaccines: Current Progress and Clinical Challenges

Multiple vaccine platforms have been employed to develop the nasal SARS-CoV-2 vaccines in preclinical studies, and the dominating pipelines are viral vectored as protein-based vaccines. Among them, several viral vectored-based vaccines have entered clinical development. Nevertheless, some unsatisfactory results were reported in these clinical studies. In the face of such urgent situations, it is imperative to rapidly develop the next-generation intranasal COVID-19 vaccine utilizing other technologies. Nanobased intranasal vaccines have emerged as an approach against respiratory infectious diseases. Harnessing the power of nanotechnology, these vaccines offer a noninvasive yet potent defense against pathogens, including the threat of COVID-19. The improvements made in vaccine mucosal delivery technologies based on nanoparticles, such as lipid nanoparticles, polymeric nanoparticles, inorganic nanoparticles etc., not only provide stability and controlled release but also enhance mucosal adhesion, effectively overcoming the limitations of conventional vaccines. Hence, in this review, we overview the evaluation of intranasal vaccine and highlight the current barriers. Next, the modern delivery systems based on nanoplatforms are summarized. The challenges in clinical application of nanoplatform based intranasal vaccine are finally discussed.

A mouse protozoan boosts antigen-specific mucosal IgA responses in a specific lipid metabolism- and signaling-dependent manner

IgA antibodies play an important role in mucosal immunity. However, there is still no effective way to consistently boost mucosal IgA responses, and the factors influencing these responses are not fully understood. We observed that colonization with the murine intestinal symbiotic protozoan Tritrichomonas musculis (T.mu) boosted antigen-specific mucosal IgA responses in wild-type C57BL/6 mice. This enhancement was attributed to the accumulation of free arachidonic acid (ARA) in the intestinal lumen, which served as a signal to stimulate the production of antigen-specific mucosal IgA. When ARA was prevented from undergoing its downstream metabolic transformation using the 5-lipoxygenase inhibitor zileuton or by blocking its downstream biological signaling through genetic deletion of the Leukotriene B4 receptor 1 (Blt1), the T.mu-mediated enhancement of antigen-specific mucosal IgA production was suppressed. Moreover, both T.mu transfer and dietary supplementation of ARA augmented the efficacy of an oral vaccine against Salmonella infection, with this effect being dependent on Blt1. Our findings elucidate a tripartite circuit linking nutrients from the diet or intestinal microbiota, host lipid metabolism, and the mucosal humoral immune response.

Bacteriophage T4 as a Protein-Based, Adjuvant- and Needle-Free, Mucosal Pandemic Vaccine Design Platform

The COVID-19 pandemic has transformed vaccinology. Rapid deployment of mRNA vaccines has saved countless lives. However, these platforms have inherent limitations including lack of durability of immune responses and mucosal immunity, high cost, and thermal instability. These and uncertainties about the nature of future pandemics underscore the need for exploring next-generation vaccine platforms. Here, we present a novel protein-based, bacteriophage T4 platform for rapid design of efficacious vaccines against bacterial and viral pathogens. Full-length antigens can be displayed at high density on a 120 × 86 nm phage capsid through nonessential capsid binding proteins Soc and Hoc. Such nanoparticles, without any adjuvant, induce robust humoral, cellular, and mucosal responses when administered intranasally and confer sterilizing immunity. Combined with structural stability and ease of manufacture, T4 phage provides an excellent needle-free, mucosal pandemic vaccine platform and allows equitable vaccine access to low- and middle-income communities across the globe.

Beyond COVID-19: the promise of next-generation coronavirus vaccines

Coronaviruses (CoVs) have caused three global outbreaks: severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1) in 2003, Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012, and SARS-CoV-2 in 2019, with significant mortality and morbidity. The impact of coronavirus disease 2019 (COVID-19) raised serious concerns about the global preparedness for a pandemic. Furthermore, the changing antigenic landscape of SARS-CoV-2 led to new variants with increased transmissibility and immune evasion. Thus, the development of broad-spectrum vaccines against current and future emerging variants of CoVs will be an essential tool in pandemic preparedness. Distinct phylogenetic features within CoVs complicate and limit the process of generating a pan-CoV vaccine capable of targeting the entire Coronaviridae family. In this review, we aim to provide a detailed overview of the features of CoVs, their phylogeny, current vaccines against various CoVs, the efforts in developing broad-spectrum coronavirus vaccines, and the future.

The impact of vaccine type and booster dose on the magnitude and breadth of SARS-CoV-2-specific systemic and mucosal antibodies among COVID-19 vaccine recipients

The COVID-19 pandemic has had a major impact on global health and economy, which was significantly mitigated by the availability of COVID-19 vaccines. The levels of systemic and mucosal antibodies against SARS-CoV-2 correlated with protection. However, there is limited data on how vaccine type and booster doses affect mucosal antibody response, and how the breadth of mucosal and systemic antibodies compares. In this cross-sectional study, we compared the magnitude and breadth of mucosal and systemic antibodies in 108 individuals who received either the BNT162b2 (Pfizer) or CoronaVac (SinoVac) vaccine. We found that BNT162b2 (vs CoronaVac) or booster doses (vs two doses) were significantly associated with higher serum IgG levels, but were not significantly associated with salivary IgA levels, regardless of prior infection status. Among non-infected individuals, serum IgG, serum IgA and salivary IgG levels were significantly higher against the ancestral strain than the Omicron BA.2 sublineage, but salivary IgA levels did not differ between the strains. Salivary IgA had the weakest correlation with serum IgG (r = 0.34) compared with salivary IgG (r = 0.63) and serum IgA (r = 0.60). Our findings suggest that intramuscular COVID-19 vaccines elicit a distinct mucosal IgA response that differs from the systemic IgG response. As mucosal IgA independently correlates with protection, vaccine trials should include mucosal IgA as an outcome measure.

Germinal Center Response to mRNA Vaccination and Impact of Immunological Imprinting on Subsequent Vaccination

Vaccines are the most effective intervention currently available, offering protective immunity against targeted pathogens. The emergence of the coronavirus disease 2019 pandemic has prompted rapid development and deployment of lipid nanoparticle encapsulated, mRNA-based vaccines. While these vaccines have demonstrated remarkable immunogenicity, concerns persist regarding their ability to confer durable protective immunity to continuously evolving severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. This review focuses on human B cell responses induced by SARS-CoV-2 mRNA vaccination, with particular emphasis on the crucial role of germinal center reactions in shaping enduring protective immunity. Additionally, we explored observations of immunological imprinting and dynamics of recalled pre-existing immunity following variants of concern-based booster vaccination. Insights from this review contribute to comprehensive understanding B cell responses to mRNA vaccination in humans, thereby refining vaccination strategies for optimal and sustained protection against evolving coronavirus variants.