Unadjuvanted intranasal spike vaccine elicits protective mucosal immunity against sarbecoviruses

Enhanced antibody response to the conformational non-RBD region via DNA prime-protein boost elicits broad cross-neutralization against SARS-CoV-2 variants

Preventing immune escape of SARS-CoV-2 variants is crucial in vaccine development to ensure broad protection against the virus. Conformational epitopes beyond the RBD region are vital components of the spike protein but have received limited attention in the development of broadly protective SARS-CoV-2 vaccines. In this study, we used a DNA prime-protein boost regimen to evaluate the broad cross-neutralization potential of immune response targeting conformational non-RBD region against SARS-CoV-2 viruses in mice. Mice with enhanced antibody responses targeting conformational non-RBD region show better performance in cross-neutralization against the Wuhan-01, Delta, and Omicron subvariants. Via analyzing the distribution of conformational epitopes, and quantifying epitope-specific binding antibodies, we verified a positive correlation between the proportion of binding antibodies against the N-terminal domain (NTD) supersite (a conformational non-RBD epitope) and SARS-CoV-2 neutralization potency. The current work highlights the importance of high ratio of conformational non-RBD-specific binding antibodies in mediating viral cross-neutralization and provides new insight into overcoming the immune escape of SARS-CoV-2 variants.

Biomaterial-based drug delivery strategies for oral mucosa

Drug therapy is a key field in modern medicine, and the optimization of its delivery method is crucial. Traditional methods are inherently limited by first-pass effects, high-risk adverse reactions, and patient compliance challenges, which significantly restrict the effectiveness and application potential of drugs. Oral mucosal drug delivery has become a minimally invasive and effective drug delivery strategy. The unique anatomical structure of the oral mucosa facilitates the rapid absorption of drugs into the systemic circulation, thus producing rapid therapeutic effects. However, a complex oral microenvironment and mucosal barrier impede drug absorption. Biomaterials have become an important driving force for the innovative development of oral medicine, owing to their unique and excellent properties. They are widely used for preventing, diagnosing, treating, and rehabilitating oral diseases. This review explores recent advancements in biomaterial-enabled oral mucosal drug delivery systems, analyzing key physiological factors and absorption barriers that impact therapeutic outcomes. Focusing on innovative material engineering strategies highlights significant progress in extending drug residence time and improving delivery precision within the oral cavity. Furthermore, the study identifies critical challenges in translating these advancements from research to clinical practice, emphasizing the need for solutions to bridge this gap.

Coordinated early immune response in the lungs is required for effective control of SARS-CoV-2 replication

Despite waning of virus-neutralizing antibodies, protection against severe SARS-CoV-2 in the majority of immune individuals remains high, but the underlying immune mechanisms are incompletely understood. Here, rhesus macaques with pre-existing immunity from Novavax WA-1 and/or P.1 vaccines and WA-1 or P.1 infection are immunized with a bivalent WA-1/Omicron BA.5 Novavax vaccine ten months after the last exposure. The boost vaccination primarily increases the frequency of cross-reactive spike (S)-specific antibodies and B cells instead of inducing de novo BA.5-specific responses. Reinfection with heterologous Omicron XBB.1.5 six months after the boost vaccination results in low levels of virus replication in the respiratory tract compared with virus-naïve results from other studies. Whereas systemic S-specific immunity remains largely unchanged in all animals, the animals with complete protection from infection exhibit a stronger influx of S-specific IgG, monocytes, B cells and T cells into the bronchioalveolar space combined with expansion of CD69+CD103+ lung tissue-resident, S-specific CD8 T cells compared to actively infected animals. Our results underscore the importance of localized respiratory immune responses in mediating protection from Omicron reinfection and provide guidance for future vaccine development.

Toxic effects of emerging pollutants on mucosal organs of teleost fish: A review focusing on mucosal microbiota, physical barrier and immune barrier

The urgency of emerging pollutants driven by human activities presents an increasing threat to the health of fish. The mucosal system, serving as a primary barrier against environmental pollutants, has emerged as a central focus in toxicological research. Alterations in the mucosal microbiota can impact health at both local and systemic levels. This review explores the toxic effects of emerging pollutants on the mucosal immunity of teleost fish, reflects on the reasons behind the limited focus on adaptive immunity studies, and highlights changes in microbial composition, gene expression, histology, and overall mucosal organ function. Furthermore, we summarize the mechanisms through which these pollutants disrupt the mucosal barriers of teleosts, emphasizing interactions between the mucosal microbiota, physical barriers, and immune defenses. The relevant methodologies and potential solutions to the current challenges have been summarized. While current research predominantly centers on the intestines and gills, further studies are needed to investigate the toxic effects of emerging pollutants on other mucosal organs and to elucidate how microbiota influence host health through neuro-immune communication. This review aims to provide a comprehensive overview of mucosal immunity, serving as a theoretical foundation for the assessment of related ecological risks.

Parasite and host immune factors that impact the development of a mucosal vaccine for Cryptosporidium

The parasite Cryptosporidium is a leading cause of diarrhea and death in malnourished children and immunocompromised individuals and an important enteric pathogen of livestock. A mucosal vaccine to mitigate clinical disease and decrease transmission would address the public health impact of this organism, but current options are limited. The development of a rational strategy for vaccination requires an appreciation of the parasite life cycle, how Cryptosporidium interacts with its host cell (the enterocyte), and the immune mechanisms that act locally to control this organism. Here we review current knowledge of the adaptive immune mechanisms that mediate resistance to Cryptosporidium, their relevance to vaccine design, and how recent advances in parasite genetics inform vaccine development.

Mucosal unadjuvanted booster vaccines elicit local IgA responses by conversion of pre-existing immunity in mice

Mucosal delivery of vaccine boosters induces robust local protective immune responses even without any adjuvants. Yet, the mechanisms by which antigen alone induces mucosal immunity in the respiratory tract remain unclear. Here we show that an intranasal booster with an unadjuvanted recombinant SARS-CoV-2 spike protein, after intramuscular immunization with 1 μg of mRNA-LNP vaccine encoding the full-length SARS-CoV-2 spike protein (Pfizer/BioNTech BNT162b2), elicits protective mucosal immunity by retooling the lymph node-resident immune cells. On intranasal boosting, peripheral lymph node-primed B cells rapidly migrated to the lung through CXCR3-CXCL9 and CXCR3-CXCL10 signaling and differentiated into antigen-specific IgA-secreting plasma cells. Memory CD4+ T cells in the lung served as a natural adjuvant for developing mucosal IgA by inducing the expression of chemokines CXCL9 and CXCL10 for memory B cell recruitment. Furthermore, CD40 and TGFβ signaling had important roles in mucosal IgA development. Repeated mucosal boosting with an unadjuvanted protein amplified anamnestic IgA responses in both the upper and the lower respiratory tracts. These findings help explain why nasal boosters do not require an adjuvant to induce robust mucosal immunity at the respiratory mucosa and can be used to design safe and effective vaccines against respiratory pathogens.

Cellular determinants influence the red blood cell adsorption efficiency of poly(amine-co-ester) nanoparticles

Many poly(amine-co-ester) (PACE) nanoparticles, drug delivery vehicles for nucleic acid and small molecule cargoes, accumulate in the liver and spleen following intravenous administration, limiting delivery to nonhepatosplenic tissues. Red blood cell (RBC) hitchhiking, a strategy in which nanoparticles are nonspecifically adsorbed to RBCs prior to administration, has been used to modulate nanoparticle biodistribution, enabling enrichment in organs immediately downstream from the site of vascular infusion. We find that scarcely investigated cellular determinants-namely, storage duration, membrane stiffness, and membrane-bound sialic acid quantity-substantially affect PACE nanoparticle adsorption efficiency. Following development of an optimized adsorption protocol, RBC hitchhiking was shown to enhance PACE nanoparticle cargo delivery to pulmonary tissue while also increasing exposure to other assayed organs. These findings inform future RBC hitchhiking study design, implicate cellular variables as potential obstacles or boons to clinical translation, and demonstrate the delivery of nucleic acids using this strategy with the PACE nanoparticle platform.

Nasal vaccines for respiratory infections

Beginning with Edward Jenner's discovery of the smallpox vaccine, the ever-expanding repertoire of vaccines against pathogens has saved many lives. During the COVID-19 pandemic, a revolutionary mRNA injectable vaccine emerged that effectively controlled the severity of disease caused by SARS-CoV-2. This vaccine induced potent antigen-specific neutralizing serum IgG antibodies, but was limited in its ability to prevent viral invasion at the respiratory surfaces. Nasal vaccines have attracted attention as a potential strategy to combat respiratory infections and prepare for future pandemics. Input from disciplines such as microbiology, biomaterials, bioengineering and chemistry have complemented the immunology to create innovative delivery systems. This approach to vaccine delivery has yielded nasal vaccines that induce secretory IgA as well as serum IgG antibodies, which are expected to prevent pathogen invasion, thereby diminishing transmission and disease severity. For a nasal vaccine to be successful, the complexity of the relevant anatomical, physiological and immunological properties, including the proximity of the central nervous system to the nasal cavity, must be considered. In this Review, we discuss past and current efforts as well as future directions for developing safe and effective nasal vaccines for the prevention of respiratory infections.

The intricate interplay among microbiota, mucosal immunity, and viral infection in the respiratory tract

The mucosal system serves as the primary barrier against respiratory diseases and plays a crucial role in combating viral infections through mucosal immunity. The resident microbial community constitutes the main component of the mucosal system and exerts a significant inhibitory impact on the invasion of exogenous agents. However, the precise relationship between resident microbiota, mucosal immunity, and viral infections remains incomplete. This review aims to summarize the regulatory interactions between the resident microbiota of the mucosal system and innate immune components such as mucosal immunity and trained immunity. By clarifying these complex relationships, this review seeks to identify potential targets for augmenting respiratory disease prevention strategies and developing novel vaccine formulations. Furthermore, we propose the possibility of integrating the fields of microbiome-based therapeutics and vaccine development to create multifunctional vaccine formulations capable of targeting mucosal immunity induction. Such an approach holds great potential in offering novel pathways and strategies for the prevention and treatment of respiratory diseases.

Beyond the Pandemic Era: Recent Advances and Efficacy of SARS-CoV-2 Vaccines Against Emerging Variants of Concern

Vaccination has been instrumental in curbing the transmission of SARS-CoV-2 and mitigating the severity of clinical manifestations associated with COVID-19. Numerous COVID-19 vaccines have been developed to this effect, including BioNTech-Pfizer and Moderna's mRNA vaccines, as well as adenovirus vector-based vaccines such as Oxford-AstraZeneca. However, the emergence of new variants and subvariants of SARS-CoV-2, characterized by enhanced transmissibility and immune evasion, poses significant challenges to the efficacy of current vaccination strategies. In this review, we aim to comprehensively outline the landscape of emerging SARS-CoV-2 variants of concern (VOCs) and sub-lineages that have recently surfaced in the post-pandemic years. We assess the effectiveness of existing vaccines, including their booster doses, against these emerging variants and subvariants, such as BA.2-derived sub-lineages, XBB sub-lineages, and BA.2.86 (Pirola). Furthermore, we discuss the latest advancements in vaccine technology, including multivalent and pan-coronavirus approaches, along with the development of several next-generation coronavirus vaccines, such as exosome-based, virus-like particle (VLP), mucosal, and nanomaterial-based vaccines. Finally, we highlight the key challenges and critical areas for future research to address the evolving threat of SARS-CoV-2 subvariants and to develop strategies for combating the emergence of new viral threats, thereby improving preparedness for future pandemics.

Intranasal replicon SARS-CoV-2 vaccine produces protective respiratory and systemic immunity and prevents viral transmission

While mRNA vaccines have been effective in combating SARS-CoV-2, the waning of vaccine-induced antibody responses and lack of vaccine-induced respiratory tract immunity contribute to ongoing infection and transmission. In this work, we compare and contrast intranasal (i.n.) and intramuscular (i.m.) administration of a SARS-CoV-2 replicon vaccine delivered by a nanostructured lipid carrier (NLC). Both i.m. and i.n. vaccines induce potent systemic serum neutralizing antibodies, bone marrow-resident immunoglobulin G-secreting cells, and splenic T cell responses. The i.n. vaccine additionally induces robust respiratory mucosal immune responses, including SARS-CoV-2-reactive lung-resident memory T cell populations. As a booster following previous i.m. vaccination, the i.n. vaccine also elicits the development of mucosal virus-specific T cells. Both the i.m.- and i.n.-administered vaccines durably protect hamsters from infection-associated morbidity upon viral challenge, significantly reducing viral loads and preventing challenged hamsters from transmitting virus to naive cagemates. This replicon-NLC vaccine's potent systemic immunogenicity, and additional mucosal immunogenicity when delivered i.n., may be key for combating SARS-CoV-2 and other respiratory pathogens.

Skin damage signals mediate allergic sensitization to spatially unlinked antigen

Our current understanding of immunity to pathogens suggests that anatomic coupling of antigens with danger signals is a required feature for the formation of immune memory. However, in the context of pathogen-independent inflammation, the stringency of this anatomical coupling is unclear. Here, we demonstrate that multiple modes of skin injury were sufficient to induce a humoral response to antigens introduced in the gut. Skin damage induced a narrow subset of endocrine cytokines that were necessary and sufficient for the priming of antigens introduced at various distal tissues. Thus, in addition to "local priming" of antigen entering through damaged skin, there also exists another paradigm of "remote priming" where anatomical coupling is not essential because of the dissemination of damage-associated intermediaries. Our findings have implications for understanding the fundamental mechanisms of the formation of humoral memory with wide implications for diseases such as food allergy and in vaccinology.

Broad Mucosal and Systemic Immunity in Mice Induced by Intranasal Booster With a Novel Recombinant Adenoviral Based Vaccine Protects Against Divergent Influenza A Virus

The development of broad-spectrum universal influenza vaccines and optimization of vaccination strategies to address the threats posed by pandemics and emerging influenza viruses are critical for public health. In this study, an adenovirus type 5 vector-based influenza vaccine carrying the hemagglutinin (HA) stem of H1, HA stem of H3, and neuraminidase (NA) of N1 from the influenza virus was constructed. Immune responses were evaluated in mice using various vaccination strategies: prime-only (intramuscular [IM] or intranasal [IN]) and prime-boost (IM + IN). Compared with the prime-only strategy, the prime-boost strategy significantly enhanced the systemic immune response, inducing higher levels of antigen-specific IgG, mucosal IgA, and T cell immunity in the spleen and lungs. Furthermore, the IN boosting strategy provided complete protection in mice challenged with the H1N1-PR8, rgH3N2-X31, and rgH5N1-Vietnam viruses, significantly reducing viral loads in the lungs and alleviating lung tissue pathologies. In conclusion, this study elucidates potential avenues for the development and application of universal influenza vaccines using customized mucosal boosting strategies.

Hypertonic intranasal vaccines gain nasal epithelia access to exert strong immunogenicity

Intranasal vaccines potentially offer superior protection against viral infections compared with injectable vaccines. The immunogenicity of intranasal vaccines including adenovirus vector (AdV), has room for improvement, while few options are available for safe execution. In this study, we demonstrate that modifying a basic parameter of vaccine formulation, i.e., osmolarity, can significantly enhance the immunogenicity of intranasal vaccines. Addition of glycerol to AdV intranasal vaccine solutions, unlike other viscous additives, enhanced systemic and mucosal antibodies as well as resident memory T cells in the nasal tissues, which could protect nasal tissue and the lungs against influenza virus. While viscous glycerol could not prolong intranasal retention of solutes, it promoted AdV infection of nasal epithelial cells by facilitating AdV access to the nasal epithelial cell. The enhanced immunogenicity was induced by the hypertonicity of vaccine preparations and sodium chloride, glucose, and mannitol demonstrated the capacity to enhance immunogenicity. Moreover, hypertonic glycerol enhanced the immunogenicity of adjuvanted subunit intranasal vaccines, but not subunit vaccines without adjuvant or injectable vaccines. Overall, the delivery of intranasal vaccines to nasal epithelial cells could be improved through a simple approach, potentially resulting in stronger immunogenicity for certain vaccines.

Transmucosal drug delivery: prospects, challenges, advances, and future directions

INTRODUCTION

Traditional administration routes have limitations including first-pass metabolism and gastrointestinal degradation for sensitive drugs (oral) and pain associated with parenteral injections, which also require trained personnel and refrigeration, making them expensive. This has increased interest in alternative routes, with mucosal surfaces being of high priority.

AREAS COVERED

Mucosal routes include ocular, oral (buccal/sublingual), nasal and vaginal mucosae which avoid the limitations of the oral and parenteral routes. Though mucosal routes show great potential, they are still hindered by several barriers, especially for systemic absorption, resulting in the development of more advanced novel drug delivery systems to overcome these limitations and achieve therapeutic actions both locally and systemically, similar to or exceeding the oral route. This paper systematically reviews and compares the different mucosal routes, challenges, and recent advances in advanced novel drug delivery system design for emerging clinical challenges including the advent of large biological macromolecules (proteins, peptides, and RNA) for treatment and prevention of diseases. The review also focuses on current challenges and future perspectives.

EXPERT OPINION

Among the various transmucosal routes discussed, nose-to-brain drug delivery has the greatest translational potential to go beyond the current state of the art and achieve significant clinical impact for neurological diseases.

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.

Intranasal prime-boost RNA vaccination elicits potent T cell response for lung cancer therapy

The rapid success of RNA vaccines in preventing SARS-CoV-2 has sparked interest in their use for cancer immunotherapy. Although many cancers originate in mucosal tissues, current RNA cancer vaccines are mainly administered non-mucosally. Here, we developed a non-invasive intranasal cancer vaccine utilizing circular RNA encapsulated in lipid nanoparticles to induce localized mucosal immune responses. This strategy elicited potent anti-tumor T cell responses in preclinical lung cancer models while mitigating the systemic adverse effects commonly associated with intravenous RNA vaccination. Specifically, type 1 conventional dendritic cells were indispensable for T cell priming post-vaccination, with both alveolar macrophages and type 1 conventional dendritic cells boosting antigen-specific T cell responses in lung tissues. Moreover, the vaccination facilitated the expansion of both endogenous and adoptive transferred antigen-specific T cells, resulting in robust anti-tumor efficacy. Single-cell RNA sequencing revealed that the vaccination reprograms endogenous T cells, enhancing their cytotoxicity and inducing a memory-like phenotype. Additionally, the intranasal vaccine can modulate the response of CAR-T cells to augment therapeutic efficacy against tumor cells expressing specific tumor-associated antigens. Collectively, the intranasal RNA vaccine strategy represents a novel and promising approach for developing RNA vaccines targeting mucosal malignancies.

Protection conferred by mucosal novel bivalent Klebsiella pneumoniae vaccine immunization associates with presence of lung CD4+ TRM

Klebsiella pneumoniae is the principal cause of hospital-acquired infection with a high morbidity and mortality in immunocompromised individuals, yet no vaccine is approved. Here, we developed a novel bivalent subunit vaccine for the prevention of K. pneumoniae infection based on the outer membrane protein GlnH and the fimbriae protein FimA. The survival rate of immunized mice was significantly increased compared to that of unimmunized mice, while the bacterial burden, weight loss, and lung pathology were drastically reduced. Furthermore, vaccine-elicited CD4+ TRM cells were observed in lung tissues and appeared to play a critical role in vaccine efficacy. Transcriptomic analysis of total lung tissues from mice treated by FTY720 (S1PR1 inhibitor that blocks lymphocyte egress from secondary lymphoid structures) showed that cell activation, cytokine secretion and enhancement of the killing ability of neutrophils were related to the mechanism of protection against K. pneumoniae infection. These findings indicate that GlnH and FimA are effective candidate bivalent vaccine to fight K. pneumoniae infection.

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.

LNP-RNA-mediated antigen presentation leverages SARS-CoV-2-specific immunity for cancer treatment

Lipid nanoparticle (LNP)-mRNA vaccines have demonstrated protective capability in combating SARS-CoV-2. Their extensive deployment across the global population leads to the broad presence of T-cell immunity against the SARS-CoV-2 spike protein, presenting an opportunity to harness this immunological response as a universal antigen target for cancer treatment. Herein, we design and synthesize a series of amino alcohol- or amino acid-derived ionizable lipids (AA lipids) and develop an LNP-RNA-based antigen presentation platform to redirect spike-specific T-cell immunity against cancer in mouse models. First, in a prime-boost regimen, AA2 LNP encapsulating spike mRNA elicit stronger T-cell immunity against the spike epitopes compared to FDA-approved LNPs (ALC-0315 and SM-102), highlighting the superior delivery efficiency of AA2 LNP. Next, AA15V LNP efficiently delivers self-amplifying RNAs (saRNAs) encoding spike epitope-loaded single-chain trimer (sSE-SCT) MHC I molecules into tumor tissues, thereby inducing the presentation of spike epitopes. Our results show that a single intratumoral (i.t.) treatment of AA15V LNP-sSE-SCTs suppresses tumor growth and extends the survival of B16F10 melanoma and A20 lymphoma tumor-bearing mice vaccinated with AA2 LNP-spike mRNA. Additionally, AA15V LNP-sSE-SCTs enable SE-SCT expression in ex vivo human glioblastoma and lung cancer samples, suggesting its potential in clinical translation.

Targeting Respiratory Viruses: The Efficacy of Intranasal mRNA Vaccination in Generating Protective Mucosal and Systemic Immunity Against Influenza A (H1N1)

Four significant influenza outbreaks have occurred over the past 100 years, and the 1918 influenza pandemic is the most severe. Since influenza viruses undergo antigenic evolution, they are the pathogens most likely to trigger a new pandemic shortly. Intranasal vaccination offers a promising strategy for preventing diseases triggered by respiratory viruses by eliciting an immunoglobulin A (IgA) response, limiting virus replication and transmission from the respiratory tract more efficiently than intramuscular vaccines. Combining intranasal administration and mRNA-lipid nanoparticles can be an ideal strategy for limiting the extent of the next flu pandemic. This study explored the immunogenicity of intranasally delivered mRNA encapsulated in mannose-histidine-conjugated chitosan lipid nanoparticles (MHCS-LNPs) as a vaccine against influenza A (H1N1) in BALB/c mice. Intranasal administration of mRNA-MHCS-LNPs resulted in the generation of influenza A (H1N1) hemagglutinin-specific neutralizing antibodies in vaccinated animals. The enzyme-linked immunosorbent assay (ELISA) results indicated a notable increase in the quantity of immunoglobulin G (IgG) and IgA antibodies in serum and the bronchoalveolar lavage fluid (BALF), respectively, and exhibited influenza A-specific IFN-γ secretion in vaccinated mice, as well as a noticeable alteration in IL-5 production. Overall, this study demonstrated an effective immunogenic response against respiratory viral infections through intranasal delivery of an mRNA-MHCS-LNP vaccine.

Intranasal recombinant protein subunit vaccine targeting TLR3 induces respiratory tract IgA and CD8 T cell responses and protects against respiratory virus infection

BACKGROUND

Intranasal vaccines against respiratory viruses are desired due to ease of administration and potential to protect against virus infection of the upper respiratory tract.

METHODS

We tested a cationic liposomal adjuvant delivering the TLR3 agonist Poly (I:C) (CAF®09b) for intranasal administration, by formulating this with SARS-CoV-2 spike trimeric protein and assessing airway mucosal immune responses in mice. The vaccine was further evaluated in SARS-CoV-2 virus challenge models, using mice expressing the human ACE2 receptor and Syrian hamsters.

FINDINGS

The intranasal vaccine elicited both serum neutralising antibody responses and IgA responses in the upper respiratory tract. Uniquely, it also elicited high-magnitude CD4 and CD8 T cell responses in the lung parenchyma and nasal-associated lymphoid tissue. In contrast, parenteral administration of the same vaccine, or the mRNA-1273 (Spikevax®) vaccine, led to systemic antibody responses and vaccine-induced CD4 T cells were mainly found in circulation. The intranasal vaccine protected against homologous SARS-CoV-2 (Wuhan-Hu-1) challenge in K18-hACE2 mice, preventing weight loss and virus infection in the upper and lower airways. In Syrian hamsters, the vaccine prevented weight loss and significantly reduced virus load after challenge with the homologous strain and Omicron BA.5.

INTERPRETATION

This study demonstrates that intranasal subunit vaccines containing TLR3-stimulating cationic liposomes effectively induce airway IgA and T cell responses, which could be utilised in future viral pandemics.

FUNDING

This work was primarily supported by the European Union Horizon 2020 research and innovation program under grant agreement no. 101003653.

SARS-CoV-2 infection primes cross-protective respiratory IgA in a MyD88- and MAVS-dependent manner

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is constantly evolving mutations in the Spike protein to evade humoral immunity. Respiratory tract antiviral IgA antibodies are superior to circulating IgG antibodies in preventing SARS-CoV-2 infection. However, the role of innate immune signals required for the induction of mucosal IgA against SARS-CoV-2 infection is unknown. Here we show that hamsters recovered from ancestral SARS-CoV-2 infection are cross-protected against heterologous SARS-CoV-2 alpha, gamma, delta, and omicron BA.1 variants. Intranasal vaccination with an inactivated whole virus vaccine completely protects hamsters against heterologous SARS-CoV-2 infection. In addition, we show that intranasal boost vaccination of mice recovered from SARS-CoV-2 infection with unadjuvanted Spike protein induces robust levels of respiratory anti-Spike IgA and protects the mice from a heterologous SARS-CoV-2 infection. Furthermore, our findings suggest that MyD88 and MAVS play a role in the induction of the memory IgA response following an intranasal booster with unadjuvanted Spike protein in mice recovered from the SARS-CoV-2 infection. These findings provide a useful basis for the development of cross-protective mucosal vaccines against heterologous SARS-CoV-2 infection.

Novel vaccine strategies to induce respiratory mucosal immunity: advances and implications

Rapid advances in vaccine technology are becoming increasingly important in tackling global health crises caused by respiratory virus infections. While traditional vaccines, primarily administered by intramuscular injection, have proven effective, they often fail to provide the broad upper respiratory tract mucosal immunity, which is urgently needed for first-line control of respiratory viral infections. Furthermore, traditional intramuscular vaccines may not adequately address the immune escape of emerging virus variants. In contrast, respiratory mucosal vaccines developed using the body's mucosal immune response mechanism can simultaneously establish both systemic and mucosal immunity. This dual action effectively allows the respiratory mucosal immune system to function as the first line of defense, preventing infections at the entry points. This review highlights the efficacy of respiratory mucosal vaccines, including innovative delivery methods such as nasal and oral formulations, in enhancing local and systemic immune barriers. Notably, respiratory mucosal vaccines offer potential advantages in protecting against emerging virus variants and maintaining long-term and multidimensional immune memory in the upper respiratory tract. In addition, a combination of intramuscular and respiratory mucosal delivery of vaccines largely improves their coverage and effectiveness, providing valuable insights for future vaccine development and public inoculation strategies.

Progress in African Swine Fever Vector Vaccine Development

African swine fever (ASF) is a highly lethal, infectious, hemorrhagic fever disease, characterized by an acute mortality rate approaching 100%. It is highly contagious, and results in significant losses to the global hog industry as it spreads. Despite incremental progress in research on the African swine fever virus (ASFV), a safe and effective commercial vaccine has yet to be developed. Vector vaccines, a promising type of vaccine, offer unique advantages, and are a primary focus in ASFV vaccine research. This paper focuses on the characteristics of viral, bacterial, and yeast vector vaccines; elucidates the immunological mechanisms associated with antigens; lists the types of antigens that have significant potential; discusses the feasibility of using exogenously expressed cytokines to enhance the protective power of vector vaccines; and, finally, discusses the types of vectors that are commonly used and the latest advances in this field.

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.

Characterization of Vaccine-Enhanced Humoral Immune Responses Against Emergent SARS-CoV-2 Variants in a Convalescent Cohort

Vaccination of COVID-19-convalescent individuals may generate 'hybrid' immunity of enhanced magnitude, durability, and cross-reactive breadth. Our primary goal was to characterize hybrid antibody (Ab) responses in a patient cohort infected with ancestral Wuhan-Hu-1 virus and vaccinated between 6 and 10 months later with the Wuhan-Hu-1-based BNT162b2 mRNA vaccine. We were particularly interested in determining the efficacy of neutralizing Ab responses against subsequently emergent SARS-CoV-2 variants. Sera collected at 3-monthly intervals over a period of 12 months were analyzed by ELISA for SARS-CoV-2 RBD-specific Ab responses, and also for neutralizing Ab activity using pseudovirus-based neutralization assays. We found that convalescent RBD-reactive IgG and IgA Ab responses did not decline significantly through 9 months post-diagnosis. These responses improved significantly following vaccination and remained elevated through at least 12-months. SARS-CoV-2 neutralizing Ab activity was detected in convalescent sera through 9 months post-diagnosis, although it trended downwards from 3 months. Neutralizing Ab activity against the Wuhan-Hu-1 strain was significantly improved by vaccination, to levels that persisted through the end of the study. However, sera collected from vaccinated convalescent subjects also had significant neutralization activity against Delta B.1.617.2 and Omicron variants that persisted for at least 2-3 months, unlike sera from unvaccinated convalescent controls. Thus, vaccination of Wuhan-Hu-1-convalescent individuals with the BNT162b2 vaccine improved and sustained protective neutralizing Ab activity against SARS-CoV-2, including cross-reactive neutralizing activity against variants that emerged months later.

Pulmonary Delivery of Nonviral Nucleic Acid-Based Vaccines With Spotlight on Gold Nanoparticles

Nucleic acid-based vaccines are leading-edge tools in developing next-generation preventative care. Much research has been done to convert vaccine gene therapy from an invasive to a noninvasive administration approach. The lung's large surface area and permeability make the pulmonary route a promising noninvasive delivery option for vaccines, with systemic and local applications. This review summarizes the challenges and the approaches that have been carried out to optimize the delivery of nucleic acids through the pulmonary route for vaccination purposes in recent years, with a spotlight on gold nanoparticles (AuNPs). Nonviral delivery systems have been widely explored, and AuNPs with their unique properties are emerging as promising tools for nucleic acid vaccines due to surface functionalization with mucus-penetrating polymers and targeting moieties that can bypass the barriers in pulmonary delivery and successfully deliver nucleic acids to the cells of interest. However, while promising, several challenges remain including selectively overcoming the lungs' immunological surveillance and adhesive mucus.

Enhanced mucosal SARS-CoV-2 immunity after heterologous intramuscular mRNA prime/intranasal protein boost vaccination with a combination adjuvant

Current COVID-19 mRNA vaccines delivered intramuscularly (IM) induce effective systemic immunity, but with suboptimal immunity at mucosal sites, limiting their ability to impart sterilizing immunity. There is strong interest in rerouting immune responses induced in the periphery by parenteral vaccination to the portal entry site of respiratory viruses, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), by mucosal vaccination. We previously demonstrated the combination adjuvant, NE/IVT, consisting of a nanoemulsion (NE) and an RNA-based RIG-I agonist (IVT) induces potent systemic and mucosal immune responses in protein-based SARS-CoV-2 vaccines administered intranasally (IN). Herein, we demonstrate priming IM with mRNA followed by heterologous IN boosting with NE/IVT adjuvanted recombinant antigen induces strong mucosal and systemic antibody responses and enhances antigen-specific T cell responses in mucosa-draining lymph nodes compared to IM/IM and IN/IN prime/boost regimens. While all regimens induced cross-neutralizing antibodies against divergent variants and sterilizing immunity in the lungs of challenged mice, mucosal vaccination, either as homologous prime/boost or heterologous IN boost after IM mRNA prime, was required to impart sterilizing immunity in the upper respiratory tract. Our data demonstrate the benefit of hybrid regimens whereby strong immune responses primed via IM vaccination are rerouted by IN vaccination to mucosal sites to provide optimal protection against SARS-CoV-2.

Fc-empowered exosomes with superior epithelial layer transmission and lung distribution ability for pulmonary vaccination

Mucosal vaccines offer potential benefits over parenteral vaccines for they can trigger both systemic immune protection and immune responses at the predominant sites of pathogen infection. However, the defense function of mucosal barrier remains a challenge for vaccines to overcome. Here, we show that surface modification of exosomes with the fragment crystallizable (Fc) part from IgG can deliver the receptor-binding domain (RBD) of SARS-CoV-2 to cross mucosal epithelial layer and permeate into peripheral lung through neonatal Fc receptor (FcRn) mediated transcytosis. The exosomes F-L-R-Exo are generated by genetically engineered dendritic cells, in which a fusion protein Fc-Lamp2b-RBD is expressed and anchored on the membrane. After intratracheally administration, F-L-R-Exo is able to induce a high level of RBD-specific IgG and IgA antibodies in the animals' lungs. Furthermore, potent Th1 immune-biased T cell responses were also observed in both systemic and mucosal immune responses. F-L-R-Exo can protect the mice from SARS-CoV-2 pseudovirus infection after a challenge. These findings hold great promise for the development of a novel respiratory mucosal vaccine approach.

Constructing the cGAMP-Aluminum Nanoparticles as a Vaccine Adjuvant-Delivery System (VADS) for Developing the Efficient Pulmonary COVID-19 Subunit Vaccines

The cGAMP-aluminum nanoparticles (CAN) are engineered as a vaccine adjuvant-delivery system to carry mixed RBD (receptor-binding domain) of the original severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its new variant for developing bivalent pulmonary coronavirus disease 2019 (COVID-19) vaccines (biRBD-CAN). High phosphophilicity/adsorptivity made intrapulmonary CAN instantly form the pulmonary ingredient-coated CAN (piCAN) to possess biomimetic features enhancing biocompatibility. In vitro biRBD-CAN sparked APCs (antigen-presenting cells) to mature and make extra reactive oxygen species, engendered lysosome escape effects and enhanced proteasome activities. Through activating the intracellular stimulator of interferon genes (STING) and nucleotide-binding domain and leucine-rich repeat and pyrin domain containing proteins 3 (NALP3) inflammasome pathways to exert synergy between cGAMP and AN, biRBD-CAN stimulated APCs to secret cytokines favoring mixed Th1/Th2 immunoresponses. Mice bearing twice intrapulmonary biRBD-CAN produced high levels of mucosal antibodies, the long-lasting systemic antibodies, and potent cytotoxic T lymphocytes which efficiently erased cells displaying cognate epitopes. Notably, biRBD-CAN existed in mouse lungs and different lymph nodes for at least 48 h, unveiling their sustained immunostimulatory activity as the main mechanism underlying the long-lasting immunity and memory. Hamsters bearing twice intrapulmonary biRBD-CAN developed high resistance to pseudoviral challenges performed using different recombinant strains including the ones with distinct SARS-CoV-2-spike mutations. Thus, biRBD-CAN as a broad-spectrum pulmonary COVID-19 vaccine candidate may provide a tool for controlling the emerging SARS-CoV-2 variants.

A Dual-Adjuvanted Parenteral-Intranasal Subunit Nanovaccine generates Robust Systemic and Mucosal Immunity Against SARS-CoV-2 in Mice

Existing parenteral SARS-CoV-2 vaccines produce only limited mucosal responses, essential for reducing transmission and achieving sterilizing immunity. Appropriately designed mucosal boosters can overcome the shortcomings of parenteral vaccines and enhance pre-existing systemic immunity. Here, a new protein subunit nanovaccine is developed by utilizing dual-adjuvanted (RIG-I: PUUC RNA and TLR-9: CpG DNA) polysaccharide-amino acid-lipid nanoparticles (PAL-NPs) along with SARS-CoV-2 S1 trimer protein, that can be delivered both intramuscularly (IM) and intranasally (IN) to generate balanced mucosal-systemic SARS-CoV-2 immunity. Mice receiving IM-Prime PUUC+CpG PAL subunit nanovaccine, followed by an IN-Boost, developed high levels of IgA, IgG, and cellular immunity in the lungs and showed robust systemic humoral immunity. Interestingly, as a purely intranasal subunit vaccine (IN-Prime/IN-Boost), PUUC+CpG PAL-NPs induced stronger lung-specific T cell immunity than IM-Prime/IN-Boost, and a comparable IgA and neutralizing antibodies, although with a lower systemic antibody response, indicating that a fully mucosal delivery route for SARS-CoV-2 vaccination may also be feasible. The data suggest that PUUC+CpG PAL subunit nanovaccine is a promising candidate for generating SARS-CoV-2 specific mucosal immunity.

Advanced technologies for the development of infectious disease vaccines

Vaccines play a critical role in the prevention of life-threatening infectious disease. However, the development of effective vaccines against many immune-evading pathogens such as HIV has proven challenging, and existing vaccines against some diseases such as tuberculosis and malaria have limited efficacy. The historically slow rate of vaccine development and limited pan-variant immune responses also limit existing vaccine utility against rapidly emerging and mutating pathogens such as influenza and SARS-CoV-2. Additionally, reactogenic effects can contribute to vaccine hesitancy, further undermining the ability of vaccination campaigns to generate herd immunity. These limitations are fuelling the development of novel vaccine technologies to more effectively combat infectious diseases. Towards this end, advances in vaccine delivery systems, adjuvants, antigens and other technologies are paving the way for the next generation of vaccines. This Review focuses on recent advances in synthetic vaccine systems and their associated challenges, highlighting innovation in the field of nano- and nucleic acid-based vaccines.

RSV Vaccine with Nanoparticle-Based Poly-Sorbitol Transporter (PST) Adjuvant Improves Respiratory Protection Against RSV Through Inducing Both Systemic and Mucosal Humoral Immunity

Background/Objectives: Respiratory syncytial virus (RSV) causes symptoms similar to a mild cold for adults, but in case of infants, it causes bronchitis and/or pneumonia, and in some cases, mortality. Mucosal immunity within the respiratory tract includes tissue-resident memory T (TRM) cells and tissue-resident memory B (BRM) cells, which provides rapid and efficient protection against RSV re-infection. Therefore, vaccine strategies should aim to generate mucosal immune responses. However, the interactions between RSV vaccines and mucosal immune responses within the respiratory tract are poorly understood. We evaluated a mucosal immune system following immunization by RSV vaccine with poly-sorbitol transporter (RSV-PST), a nanoparticle adjuvant. Methods: We intranasally immunized the RSV-PST and identified the systemic and mucosal immune responses. Furthermore, we challenged with RSV A2 strain after immunization and investigated the protective effects. Results: Consequently, antigen-specific CD8+ TRM cells were markedly elevated in the lung parenchyma, yet exhibited impaired cytokine expression. In contrast, humoral immunity, with systemic antibody production from serum, but not in the respiratory tract, was significantly increased by RSV-PST immunization. Interestingly, the production of respiratory mucosal antigen-specific IgG after RSV A2 challenge dramatically increased in the bronchoalveolar lavage fluid (BALF) of the RSV-PST immunized group in the presence of FTY720, and the lung-infected RSV titer was significantly lower in this group. Furthermore, after RSV A2 challenge, CD69+ IgG+ BRM cells were significantly increased in lung tissues in the RSV-PST group. Conclusions: The RSV-PST vaccine has protective effects against RSV infection by promoting both systemic and local humoral immunity rather than cellular immunity.

A multi-antigen vaccinia vaccine broadly protected mice against SARS-CoV-2 and influenza A virus while also targeting SARS-CoV-1 and MERS-CoV

Introduction

Coronaviruses and influenza viruses are significant respiratory pathogens that cause severe disease burdens and economic losses for society. Due to their diversity and evolution, vaccines typically require periodic updating to remain effective. An additional challenge is imposed by the possible coinfection of SARS-CoV-2 and influenza, which could increase disease severity.

Methods

We developed a vaccinia vaccine, named rTTV-RBD-HA2, broadly targeting coronaviruses and influenza viruses. This vaccine expresses three fusion proteins, each comprising the receptor-binding domain (RBD) from one of the three highly pathogenic coronaviruses (SARS-CoV-2, SARS-CoV, and MERS-CoV) and the conserved HA stalk region from two influenza viruses (pdmH1N1 and nH7N9) belonging to groups 1 and 2, respectively.

Results

The multi-targeting nature of this vaccine was validated by its success in inducing antibody responses to the three RBDs and both group 1 and 2 HAs in mice. Importantly, it also generated robust T cell responses to all the immunogens, which could be mobilized to the lung through intranasal vaccination. Consistent with this broad immunogenicity profile, when administered via intramuscular priming and two intranasal boosts, rTTV-RBD-HA2 effectively protected vaccinated mice against challenges of the wild-type SARS-CoV-2 virus, the Omicron XBB variant, and the influenza A H1N1 and H3N2 viruses.

Discussion

Our results collectively support the candidacy of recombinant rTTV-RBD-HA2 as a novel respiratory virus vaccine that provides cross-protection against coronaviruses and influenza viruses, surpassing the breadth of previous vaccines. Additionally, they underscore the importance of establishing a strong mucosal T cell response in the development of a universal respiratory virus vaccine.

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.

A B cell screen against endogenous retroviruses identifies glycan-reactive IgM that recognizes a broad array of enveloped viruses

Endogenous retroviruses (ERVs), comprising a substantial portion of the vertebrate genome, are remnants of ancient genetic invaders. ERVs with near-intact coding potential reactivate in B cell-deficient mice. To study how B cells contribute to host anti-ERV immunity, we used an antigen-baiting strategy to enrich B cells reactive to ERV surface antigens. We identified ERV-reactive B-1 cells expressing germline-encoded natural IgM antibodies in naïve mice, the level of which further increases upon innate immune sensor stimulation. B cell receptor repertoire profiling of ERV-reactive B-1 cells revealed increased usage of the Igh VH gene that gives rise to glycan-specific antibodies targeting terminal N-acetylglucosamine moieties on ERV glycoproteins, which further engage the complement pathway to mediate anti-ERV responses. These same antibodies also recognize glycoproteins of other enveloped viruses but not self-proteins. These results reveal an innate antiviral mechanism of germline-encoded antibodies with broad reactivity to enveloped viruses, which constitutes a natural antibody repertoire capable of preventing the emergence of infectious ERVs.

STAR LIGHT Study: XBB.1.5 COVID-19 mRNA Vaccines Boost Systemic but Not Mucosal Immunity Against the SARS-CoV-2 JN.1 Variant in Patients with Chronic Liver Disease

BACKGROUND

Patients with chronic liver disease (CLD) have impaired vaccine immunogenicity and an excess risk of severe COVID-19. While variant-adapted COVID-19 mRNA vaccines are recommended for vulnerable individuals, their efficacy in patients with CLD has not been studied.

METHODS

We present the first evaluation of XBB.1.5 COVID-19 vaccine immunogenicity against the SARS-CoV-2 JN.1 variant in patients with CLD. Serum anti-receptor binding domain (RBD) IgG, neutralization, and saliva anti-RBD IgG and IgA against wild-type SARS-CoV-2 (WT) and the XBB.1.5, EG.5.1, BA.2.86, and JN.1 variants were quantified before and 2-4 weeks following a fourth dose of XBB.1.5 mRNA vaccines.

RESULTS

Vaccination boosted anti-RBD IgG and neutralization against all tested variants including JN.1 (each p < 0.001). Following immunization, neutralization was lower against JN.1 compared to WT, XBB.1.5, and EG.5.1 (p < 0.001, p < 0.001, and p < 0.01, respectively). Vaccination reduced neutralization failure rates against BA.2.86 and JN.1 (each p < 0.05). The evasion of vaccine-induced antibodies by the tested variants was low, indicated by the positive correlation between anti-RBD IgG and neutralization. At mucosal sites, vaccination boosted anti-RBD IgG (each p < 0.01) but failed to induce infection-blocking IgA (each p > 0.05).

CONCLUSION

XBB.1.5 vaccines protect CLD patients against recent SARS-CoV-2 variants, but developing vaccines with optimized mucosal immunogenicity is required to prevent SARS-CoV-2 transmission and recurrent seasonal COVID-19 outbreaks.

Immunity to fungi and vaccine considerations

Fungal disease poses a growing threat to public health that our current antifungal therapies are not well equipped to meet. As the population of immunocompromised hosts expands, and ecological changes favor the emergence of fungal pathogens, the development of new antifungal agents, including vaccines, becomes a global priority. Here, we summarize recent advancements in the understanding of fungal pathogenesis, key features of the host antifungal immune response, and how these findings could be leveraged to design novel approaches to deadly fungal disease.

Revisiting the dimensions of universal vaccine with special focus on COVID-19: Efficacy versus methods of designing

Even though the use of SARS-CoV-2 vaccines during the COVID-19 pandemic showed unprecedented success in a short time, it also exposed a flaw in the current vaccine design strategy to offer broad protection against emerging variants of concern. However, developing broad-spectrum vaccines is still a challenge for immunologists. The development of universal vaccines against emerging pathogens and their variants appears to be a practical solution to mitigate the economic and physical effects of the pandemic on society. Very few reports are available to explain the basic concept of universal vaccine design and development. This review provides an overview of the innate and adaptive immune responses generated against vaccination and essential insight into immune mechanisms helpful in designing universal vaccines targeting influenza viruses and coronaviruses. In addition, the characteristics, safety, and factors affecting the efficacy of universal vaccines have been discussed. Furthermore, several advancements in methods worthy of designing universal vaccines are described, including chimeric immunogens, heterologous prime-boost vaccines, reverse vaccinology, structure-based antigen design, pan-reactive antibody vaccines, conserved neutralizing epitope-based vaccines, mosaic nanoparticle-based vaccines, etc. In addition to the several advantages, significant potential constraints, such as defocusing the immune response and subdominance, are also discussed.

Mucosal adenovirus vaccine boosting elicits IgA and durably prevents XBB.1.16 infection in nonhuman primates

A mucosal route of vaccination could prevent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication at the site of infection and limit transmission. We compared protection against heterologous XBB.1.16 challenge in nonhuman primates (NHPs) ~5 months following intramuscular boosting with bivalent mRNA encoding WA1 and BA.5 spike proteins or mucosal boosting with a WA1-BA.5 bivalent chimpanzee adenoviral-vectored vaccine delivered by intranasal or aerosol device. NHPs boosted by either mucosal route had minimal virus replication in the nose and lungs, respectively. By contrast, protection by intramuscular mRNA was limited to the lower airways. The mucosally delivered vaccine elicited durable airway IgG and IgA responses and, unlike the intramuscular mRNA vaccine, induced spike-specific B cells in the lungs. IgG, IgA and T cell responses correlated with protection in the lungs, whereas mucosal IgA alone correlated with upper airway protection. This study highlights differential mucosal and serum correlates of protection and how mucosal vaccines can durably prevent infection against SARS-CoV-2.

Intranasal Multiepitope PD-L1-siRNA-Based Nanovaccine: The Next-Gen COVID-19 Immunotherapy

The first approved vaccines for human use against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are nanotechnology-based. Although they are modular, rapidly produced, and can reduce disease severity, the currently available vaccines are restricted in preventing infection, stressing the global demand for novel preventive vaccine technologies. Bearing this in mind, we set out to develop a flexible nanovaccine platform for nasal administration to induce mucosal immunity, which is fundamental for optimal protection against respiratory virus infection. The next-generation multiepitope nanovaccines co-deliver immunogenic peptides, selected by an immunoinformatic workflow, along with adjuvants and regulators of the PD-L1 expression. As a case study, we focused on SARS-CoV-2 peptides as relevant antigens to validate the approach. This platform can evoke both local and systemic cellular- and humoral-specific responses against SARS-CoV-2. This led to the secretion of immunoglobulin A (IgA), capable of neutralizing SARS-CoV-2, including variants of concern, following a heterologous immunization strategy. Considering the limitations of the required cold chain distribution for current nanotechnology-based vaccines, it is shown that the lyophilized nanovaccine is stable for long-term at room temperature and retains its in vivo efficacy upon reconstitution. This makes it particularly relevant for developing countries and offers a modular system adaptable to future viral threats.

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.

Beta Spike-Presenting SARS-CoV-2 Virus-like Particle Vaccine Confers Broad Protection against Other VOCs in Mice

Virus-like particles (VLPs) are non-infectious and serve as promising vaccine platforms because they mimic the membrane-embedded conformations of fusion glycoproteins on native viruses. Here, we employed SARS-CoV-2 VLPs (SMEN) presenting ancestral, Beta, or Omicron spikes to identify the variant spike that elicits potent and cross-protective immune responses in the highly sensitive K18-hACE2 challenge mouse model. A combined intranasal and intramuscular SMEN vaccine regimen generated the most effective immune responses to significantly reduce disease burden. Protection was primarily mediated by antibodies, with minor but distinct contributions from T cells in reducing virus spread and inflammation. Immunization with SMEN carrying ancestral spike resulted in 100, 75, or 0% protection against ancestral, Delta, or Beta variant-induced mortality, respectively. However, SMEN with an Omicron spike provided only limited protection against ancestral (50%), Delta (0%), and Beta (25%) challenges. By contrast, SMEN with Beta spikes offered 100% protection against the variants used in this study. Thus, the Beta variant not only overcame the immunity produced by other variants, but the Beta spike also elicited diverse and effective humoral immune responses. Our findings suggest that leveraging the Beta variant spike protein can enhance SARS-CoV-2 immunity, potentially leading to a more comprehensive vaccine against emerging variants.

Harnessing the potential of the NALT and BALT as targets for immunomodulation using engineering strategies to enhance mucosal uptake

Mucosal barrier tissues and their mucosal associated lymphoid tissues (MALT) are attractive targets for vaccines and immunotherapies due to their roles in both priming and regulating adaptive immune responses. The upper and lower respiratory mucosae, in particular, possess unique properties: a vast surface area responsible for frontline protection against inhaled pathogens but also simultaneous tight regulation of homeostasis against a continuous backdrop of non-pathogenic antigen exposure. Within the upper and lower respiratory tract, the nasal and bronchial associated lymphoid tissues (NALT and BALT, respectively) are key sites where antigen-specific immune responses are orchestrated against inhaled antigens, serving as critical training grounds for adaptive immunity. Many infectious diseases are transmitted via respiratory mucosal sites, highlighting the need for vaccines that can activate resident frontline immune protection in these tissues to block infection. While traditional parenteral vaccines that are injected tend to elicit weak immunity in mucosal tissues, mucosal vaccines (i.e., that are administered intranasally) are capable of eliciting both systemic and mucosal immunity in tandem by initiating immune responses in the MALT. In contrast, administering antigen to mucosal tissues in the absence of adjuvant or costimulatory signals can instead induce antigen-specific tolerance by exploiting regulatory mechanisms inherent to MALT, holding potential for mucosal immunotherapies to treat autoimmunity. Yet despite being well motivated by mucosal biology, development of both mucosal subunit vaccines and immunotherapies has historically been plagued by poor drug delivery across mucosal barriers, resulting in weak efficacy, short-lived responses, and to-date a lack of clinical translation. Development of engineering strategies that can overcome barriers to mucosal delivery are thus critical for translation of mucosal subunit vaccines and immunotherapies. This review covers engineering strategies to enhance mucosal uptake via active targeting and passive transport mechanisms, with a parallel focus on mechanisms of immune activation and regulation in the respiratory mucosa. By combining engineering strategies for enhanced mucosal delivery with a better understanding of immune mechanisms in the NALT and BALT, we hope to illustrate the potential of these mucosal sites as targets for immunomodulation.

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.