Respiratory mucosal delivery of next-generation COVID-19 vaccine provides robust protection against both ancestral and variant strains of SARS-CoV-2.

The emerging SARS-CoV-2 variants of concern (VOCs) threaten the effectiveness of current COVID-19 vaccines administered intramuscularly and designed to only target the spike protein. There is a pressing need to develop next-generation vaccine strategies for broader and long-lasting protection. Using adenoviral vectors (Ad) of human and chimpanzee origin, we evaluated Ad-vectored trivalent COVID-19 vaccines expressing spike-1, nucleocapsid, and RdRp antigens in murine models. We show that single-dose intranasal immunization, particularly with chimpanzee Ad-vectored vaccine, is superior to intramuscular immunization in induction of the tripartite protective immunity consisting of local and systemic antibody responses, mucosal tissue-resident memory T cells and mucosal trained innate immunity. We further show that intranasal immunization provides protection against both the ancestral SARS-CoV-2 and two VOC, B.1.1.7 and B.1.351. Our findings indicate that respiratory mucosal delivery of Ad-vectored multivalent vaccine represents an effective next-generation COVID-19 vaccine strategy to induce all-around mucosal immunity against current and future VOC.

Parenteral BCG vaccine induces lung-resident memory macrophages and trained immunity via the gut-lung axis.

Aside from centrally induced trained immunity in the bone marrow (BM) and peripheral blood by parenteral vaccination or infection, evidence indicates that mucosal-resident innate immune memory can develop via a local inflammatory pathway following mucosal exposure. However, whether mucosal-resident innate memory results from integrating distally generated immunological signals following parenteral vaccination/infection is unclear. Here we show that subcutaneous Bacillus Calmette-Guérin (BCG) vaccination can induce memory alveolar macrophages (AMs) and trained immunity in the lung. Although parenteral BCG vaccination trains BM progenitors and circulating monocytes, induction of memory AMs is independent of circulating monocytes. Rather, parenteral BCG vaccination, via mycobacterial dissemination, causes a time-dependent alteration in the intestinal microbiome, barrier function and microbial metabolites, and subsequent changes in circulating and lung metabolites, leading to the induction of memory macrophages and trained immunity in the lung. These data identify an intestinal microbiota-mediated pathway for innate immune memory development at distal mucosal tissues and have implications for the development of next-generation vaccine strategies against respiratory pathogens.

Induction of Autonomous Memory Alveolar Macrophages Requires T Cell Help and Is Critical to Trained Immunity.

Innate immune memory is an emerging area of research. However, innate immune memory at major mucosal sites remains poorly understood. Here, we show that respiratory viral infection induces long-lasting memory alveolar macrophages (AMs). Memory AMs are programed to express high MHC II, a defense-ready gene signature, and increased glycolytic metabolism, and produce, upon re-stimulation, neutrophil chemokines. Using a multitude of approaches, we reveal that the priming, but not maintenance, of memory AMs requires the help from effector CD8 T cells. T cells jump-start this process via IFN-γ production. We further find that formation and maintenance of memory AMs are independent of monocytes or bone marrow progenitors. Finally, we demonstrate that memory AMs are poised for robust trained immunity against bacterial infection in the lung via rapid induction of chemokines and neutrophilia. Our study thus establishes a new paradigm of immunological memory formation whereby adaptive T-lymphocytes render innate memory of mucosal-associated macrophages.

Cigarette smoke augments CSF3 expression in neutrophils to compromise alveolar-capillary barrier function during influenza infection.

BACKGROUND: Cigarette smokers are at increased risk of acquiring influenza, developing severe disease and requiring hospitalisation/intensive care unit admission following infection. However, immune mechanisms underlying this predisposition are incompletely understood, and therapeutic strategies for influenza are limited. METHODS: We used a mouse model of concurrent cigarette smoke exposure and H1N1 influenza infection, colony-stimulating factor (CSF)3 supplementation/receptor (CSF3R) blockade and single-cell RNA sequencing (scRNAseq) to investigate this relationship. RESULTS: Cigarette smoke exposure exacerbated features of viral pneumonia such as oedema, hypoxaemia and pulmonary neutrophilia. Smoke-exposed infected mice demonstrated an increase in viral (v)RNA, but not replication-competent viral particles, relative to infection-only controls. Interstitial rather than airspace neutrophilia positively predicted morbidity in smoke-exposed infected mice. Screening of pulmonary cytokines using a novel dysregulation score identified an exacerbated expression of CSF3 and interleukin-6 in the context of smoke exposure and influenza. Recombinant (r)CSF3 supplementation during influenza aggravated morbidity, hypothermia and oedema, while anti-CSF3R treatment of smoke-exposed infected mice improved alveolar-capillary barrier function. scRNAseq delineated a shift in the distribution of Csf3 + cells towards neutrophils in the context of cigarette smoke and influenza. However, although smoke-exposed lungs were enriched for infected, highly activated neutrophils, gene signatures of these cells largely reflected an exacerbated form of typical influenza with select unique regulatory features. CONCLUSION: This work provides novel insight into the mechanisms by which cigarette smoke exacerbates influenza infection, unveiling potential therapeutic targets (e.g. excess vRNA accumulation, oedematous CSF3R signalling) for use in this context, and potential limitations for clinical rCSF3 therapy during viral infectious disease.

COVID-19: Current knowledge in clinical features, immunological responses, and vaccine development.

The COVID-19 pandemic has unfolded to be the most challenging global health crisis in a century. In 11 months since its first emergence, according to WHO, the causative infectious agent SARS-CoV-2 has infected more than 100 million people and claimed more than 2.15 million lives worldwide. Moreover, the world has raced to understand the virus and natural immunity and to develop vaccines. Thus, within a short 11 months a number of highly promising COVID-19 vaccines were developed at an unprecedented speed and are now being deployed via emergency use authorization for immunization. Although a considerable number of review contributions are being published, all of them attempt to capture only a specific aspect of COVID-19 or its therapeutic approaches based on ever-expanding information. Here, we provide a comprehensive overview to conceptually thread together the latest information on global epidemiology and mitigation strategies, clinical features, viral pathogenesis and immune responses, and the current state of vaccine development.

Airway Macrophages Mediate Mucosal Vaccine-Induced Trained Innate Immunity against Mycobacterium tuberculosis in Early Stages of Infection.

Mycobacterium tuberculosis, the causative agent of pulmonary tuberculosis (TB), is responsible for millions of infections and deaths annually. Decades of TB vaccine development have focused on adaptive T cell immunity, whereas the importance of innate immune contributions toward vaccine efficacy has only recently been recognized. Airway macrophages (AwM) are the predominant host cell during early pulmonary M. tuberculosis infection and, therefore, represent attractive targets for vaccine-mediated immunity. We have demonstrated that respiratory mucosal immunization with a viral-vectored vaccine imprints AwM, conferring enhanced protection against heterologous bacterial challenge. However, it is unknown if innate immune memory also protects against M. tuberculosis In this study, by using a murine model, we detail whether respiratory mucosal TB vaccination profoundly alters the airway innate immune landscape associated with AwM prior to M. tuberculosis exposure and whether such AwM play a critical role in host defense against M. tuberculosis infection. Our study reveals an important role of AwM in innate immune protection in early stages of M. tuberculosis infection in the lung.

New Tuberculosis Vaccine Strategies: Taking Aim at Un-Natural Immunity.

Despite some major progress made in developing tuberculosis (TB) vaccine strategies, with a dozen novel vaccines currently in the clinical pipeline, the world is still missing an effective TB vaccine. This questions whether any major breakthroughs can be achieved without making a drastic departure from the current strategy, which creates a state of 'near-natural immunity', imitating the natural immunity developed after Mycobacterium tuberculosis (Mtb) infection. Here, we argue instead that mounting evidence suggests an effective strategy ought to induce a state of all-around 'un-natural' immunity comprising trained innate immunity (TII), tissue-resident memory T cells (TRM), and anti-Mtb surface antibodies in the lung. Thus, here we summarize the latest information, thinking, and development in the field of TB and vaccines.

CD11b+ Dendritic Cell-Mediated Anti-Mycobacterium tuberculosis Th1 Activation Is Counterregulated by CD103+ Dendritic Cells via IL-10.

Mycobacterium tuberculosis, the pathogen causing pulmonary tuberculosis (TB) in humans, has evolved to delay Th1 immunity in the lung. Although conventional dendritic cells (cDCs) are known to be critical to the initiation of T cell immunity, the differential roles and molecular mechanisms of migratory CD11b+ and CD103+ cDC subsets in anti-M. tuberculosis Th1 activation remain unclear. Using a murine model of pulmonary M. tuberculosis infection, we found that slow arrival of M. tuberculosis-bearing migratory CD11b+ and CD103+ cDCs at the draining lymph nodes preceded the much-delayed Th1 immunity and protection in the lung. Contrary to their previously described general roles in Th polarization, CD11b+ cDCs, but not CD103+ cDCs, were critically required for Th1 activation in draining lymph nodes following M. tuberculosis infection. CD103+ cDCs counterregulated CD11b+ cDC-mediated Th1 activation directly by producing the immune-suppressive cytokine IL-10. Thus, our study provides new mechanistic insights into differential Th immune regulation by migratory cDC subsets and helps to develop novel vaccines and therapies.

Single-Dose Mucosal Immunotherapy With Chimpanzee Adenovirus-Based Vaccine Accelerates Tuberculosis Disease Control and Limits Its Rebound After Antibiotic Cessation.

BACKGROUND: The development of strategies to accelerate disease resolution and shorten antibiotic therapy is imperative in curbing the global tuberculosis epidemic. Therapeutic application of novel vaccines adjunct to antibiotics represents such a strategy. METHODS: By using a murine model of pulmonary tuberculosis (TB), we have investigated whether a single respiratory mucosal therapeutic delivery of a novel chimpanzee adenovirus-vectored vaccine expressing Ag85A (AdCh68Ag85A) accelerates TB disease control in conjunction with antibiotics and restricts pulmonary disease rebound after premature (nonsterilizing) antibiotic cessation. RESULTS: We find that immunotherapy via the respiratory mucosal, but not parenteral, route significantly accelerates pulmonary mycobacterial clearance, limits lung pathology, and restricts disease rebound after premature antibiotic cessation. We further show that vaccine-activated antigen-specific T cells, particularly CD8 T cells, in the lung play an important role in immunotherapeutic effects. CONCLUSIONS: Our results indicate that a single-dose respiratory mucosal immunotherapy with AdCh68Ag85A adjunct to antibiotic therapy has the potential to significantly accelerate disease control and shorten the duration of conventional treatment. Our study provides the proof of principle to support therapeutic applications of viral-vectored vaccines via the respiratory route.

CXCR3 Signaling Is Required for Restricted Homing of Parenteral Tuberculosis Vaccine-Induced T Cells to Both the Lung Parenchyma and Airway.

Although most novel tuberculosis (TB) vaccines are designed for delivery via the muscle or skin for enhanced protection in the lung, it has remained poorly understood whether systemic vaccine-induced memory T cells can readily home to the lung mucosa prior to and shortly after pathogen exposure. We have investigated this issue by using a model of parenteral TB immunization and intravascular immunostaining. We find that systemically induced memory T cells are restricted to the blood vessels in the lung, unable to populate either the lung parenchymal tissue or the airway under homeostatic conditions. We further find that after pulmonary TB infection, it still takes many days before such T cells can enter the lung parenchymal tissue and airway. We have identified the acquisition of CXCR3 expression by circulating T cells to be critical for their entry to these lung mucosal compartments. Our findings offer new insights into mucosal T cell biology and have important implications in vaccine strategies against pulmonary TB and other intracellular infections in the lung.

Enhancement of Antituberculosis Immunity in a Humanized Model System by a Novel Virus-Vectored Respiratory Mucosal Vaccine.

Background: The translation of preclinically promising novel tuberculosis vaccines to ultimate human applications has been challenged by the lack of animal models with an immune system equivalent to the human immune system in its genetic diversity and level of susceptibility to tuberculosis. Methods: We have developed a humanized mice (Hu-mice) tuberculosis model system to investigate the clinical relevance of a novel virus-vectored (VV) tuberculosis vaccine administered via respiratory mucosal or parenteral route. Results: We find that VV vaccine activates T cells in Hu-mice as it does in human vaccinees. The respiratory mucosal route for delivery of VV vaccine in Hu-mice, but not the parenteral route, significantly reduces the humanlike lung tuberculosis outcomes in a human T-cell-dependent manner. Conclusions: Our results suggest that the Hu-mouse can be used to predict the protective efficacy of novel tuberculosis vaccines/strategies before they proceed to large, expensive human trials. This new vaccine testing system will facilitate the global pace of clinical tuberculosis vaccine development.

Role of B Cells in Mucosal Vaccine-Induced Protective CD8+ T Cell Immunity against Pulmonary Tuberculosis.

Emerging evidence suggests a role of B cells in host defense against primary pulmonary tuberculosis (TB). However, the role of B cells in TB vaccine-induced protective T cell immunity still remains unknown. Using a viral-vectored model TB vaccine and a number of experimental approaches, we have investigated the role of B cells in respiratory mucosal vaccine-induced T cell responses and protection against pulmonary TB. We found that respiratory mucosal vaccination activated Ag-specific B cell responses. Whereas respiratory mucosal vaccination elicited Ag-specific T cell responses in the airway and lung interstitium of genetic B cell-deficient (Jh(-/-) knockout [KO]) mice, the levels of airway T cell responses were lower than in wild-type hosts, which were associated with suboptimal protection against pulmonary Mycobacterium tuberculosis challenge. However, mucosal vaccination induced T cell responses in the airway and lung interstitium and protection in B cell-depleted wild-type mice to a similar extent as in B cell-competent hosts. Furthermore, by using an adoptive cell transfer approach, reconstitution of B cells in vaccinated Jh(-/-) KO mice did not enhance anti-TB protection. Moreover, respiratory mucosal vaccine-activated T cells alone were able to enhance anti-TB protection in SCID mice, and the transfer of vaccine-primed B cells alongside T cells did not further enhance such protection. Alternatively, adoptively transferring vaccine-primed T cells from Jh(-/-) KO mice into SCID mice only provided suboptimal protection. These data together suggest that B cells play a minimal role, and highlight a central role by T cells, in respiratory mucosal vaccine-induced protective immunity against M. tuberculosis.

LPS-induced lung tissue-resident trained innate immunity provides differential protection against pneumococci and SARS-CoV-2.

Recent evidence indicates that tissue-resident innate immune memory and trained innate immunity (TII) can be induced centrally in myeloid cells within the bone marrow and locally in tissue-resident macrophages in respiratory mucosal tissues. However, it remains unclear whether acute exposure to airborne microbial components like lipopolysaccharide (LPS) induces lasting innate immune memory in airway macrophages and TII capable of protection against heterologous pathogens. Using a murine model, we demonstrate that acute LPS exposure leads to dynamic changes in the immune phenotype of airway macrophages that persist long after the acute inflammatory response has subsided. The original airway-resident alveolar macrophage pool remains stable in size despite these changes and the earlier transient acute inflammatory responses, including monocytic recruitment in the lung. We further demonstrate that the induction of innate immune memory in airway macrophages is accompanied by TII capable of robust protection against acute pneumococcal infection, whereas it provides minimal protection against acute SARS-CoV-2 infection.

Viral-vectored respiratory mucosal vaccine strategies.

Increasing global concerns of pandemic respiratory viruses highlight the importance of developing optimal vaccination strategies that encompass vaccine platform, delivery route, and regimens. The decades-long effort to develop vaccines to combat respiratory infections such as influenza, respiratory syncytial virus, and tuberculosis has met with challenges, including the inability of systemically administered vaccines to induce respiratory mucosal (RM) immunity. In this regard, ample preclinical and available clinical studies have demonstrated the superiority of RM vaccination to induce RM immunity over parenteral route of vaccination. A great stride has been made in developing vaccines for RM delivery against respiratory pathogens, including M. tuberculosis and SARS-CoV-2. In particular, inhaled aerosol delivery of adenoviral-vectored vaccines has shown significant promise.

Adenoviral-vectored next-generation respiratory mucosal vaccines against COVID-19.

The world is in need of next-generation COVID-19 vaccines. Although first-generation injectable COVID-19 vaccines continue to be critical tools in controlling the current global health crisis, continuous emergence of SARS-CoV-2 variants of concern has eroded the efficacy of these vaccines, leading to staggering breakthrough infections and posing threats to poor vaccine responders. This is partly because the humoral and T-cell responses generated following intramuscular injection of spike-centric monovalent vaccines are mostly confined to the periphery, failing to either access or be maintained at the portal of infection, the respiratory mucosa (RM). In contrast, respiratory mucosal-delivered vaccine can induce immunity encompassing humoral, cellular, and trained innate immunity positioned at the respiratory mucosa that may act quickly to prevent the establishment of an infection. Viral vectors, especially adenoviruses, represent the most promising platform for RM delivery that can be designed to express both structural and nonstructural antigens of SARS-CoV-2. Boosting RM immunity via the respiratory route using multivalent adenoviral-vectored vaccines would be a viable next-generation vaccine strategy.

Corrigendum: Differential biodistribution of adenoviral-vectored vaccine following intranasal and endotracheal deliveries leads to different immune outcomes.

[This corrects the article DOI: 10.3389/fimmu.2022.860399.].

Subcutaneous BCG vaccination protects against streptococcal pneumonia via regulating innate immune responses in the lung.

Bacillus Calmette-Guérin (BCG) still remains the only licensed vaccine for TB and has been shown to provide nonspecific protection against unrelated pathogens. This has been attributed to the ability of BCG to modulate the innate immune system, known as trained innate immunity (TII). Trained innate immunity is associated with innate immune cells being in a hyperresponsive state leading to enhanced host defense against heterologous infections. Both epidemiological evidence and prospective studies demonstrate cutaneous BCG vaccine-induced TII provides enhanced innate protection against heterologous pathogens. Regardless of the extensive progress made thus far, the effect of cutaneous BCG vaccination against heterologous respiratory bacterial infections and the underlying mechanisms still remain unknown. Here, we show that s.c. BCG vaccine-induced TII provides enhanced heterologous innate protection against pulmonary Streptococcus pneumoniae infection. We further demonstrate that this enhanced innate protection is mediated by enhanced neutrophilia in the lung and is independent of centrally trained circulating monocytes. New insight from this study will help design novel effective vaccination strategies against unrelated respiratory bacterial pathogens.

Cannabis smoke suppresses antiviral immune responses to influenza A in mice.

Rationale: Despite its increasingly widespread use, little is known about the impact of cannabis smoking on the response to viral infections like influenza A virus (IAV). Many assume that cannabis smoking will disrupt antiviral responses in a manner similar to cigarette smoking; however, since cannabinoids exhibit anti-inflammatory effects, cannabis smoke exposure may impact viral infection in distinct ways. Methods: Male and female BALB/c mice were exposed daily to cannabis smoke and concurrently intranasally instilled with IAV. Viral burden, inflammatory mediator levels (multiplex ELISA), lung immune cells populations (flow cytometry) and gene expression patterns (RNA sequencing) were assessed in the lungs. Plasma IAV-specific antibodies were measured via ELISA. Results: We found that cannabis smoke exposure increased pulmonary viral burden while decreasing total leukocytes, including macrophages, monocytes and dendritic cell populations in the lungs. Furthermore, infection-induced upregulation of certain inflammatory mediators (interferon-γ and C-C motif chemokine ligand 5) was blunted by cannabis smoke exposure, which in females was linked to the transcriptional downregulation of pathways involved in innate and adaptive immune responses. Finally, plasma levels of IAV-specific IgM and IgG1 were significantly decreased in cannabis smoke-exposed, infected mice compared to infected controls, only in female mice. Conclusions: Overall, cannabis smoke exposure disrupted host-defence processes, leading to increased viral burden and dampened inflammatory signalling. These results suggest that cannabis smoking is detrimental to the maintenance of pulmonary homeostasis during viral infection and highlight the need for data regarding the impact on immune competency in humans.

Intranasal multivalent adenoviral-vectored vaccine protects against replicating and dormant M.tb in conventional and humanized mice.

Viral-vectored vaccines are highly amenable for respiratory mucosal delivery as a means of inducing much-needed mucosal immunity at the point of pathogen entry. Unfortunately, current monovalent viral-vectored tuberculosis (TB) vaccine candidates have failed to demonstrate satisfactory clinical protective efficacy. As such, there is a need to develop next-generation viral-vectored TB vaccine strategies which incorporate both vaccine antigen design and delivery route. In this study, we have developed a trivalent chimpanzee adenoviral-vectored vaccine to provide protective immunity against pulmonary TB through targeting antigens linked to the three different growth phases (acute/chronic/dormancy) of Mycobacterium tuberculosis (M.tb) by expressing an acute replication-associated antigen, Ag85A, a chronically expressed virulence-associated antigen, TB10.4, and a dormancy/resuscitation-associated antigen, RpfB. Single-dose respiratory mucosal immunization with our trivalent vaccine induced robust, sustained tissue-resident multifunctional CD4+ and CD8+ T-cell responses within the lung tissues and airways, which were further quantitatively and qualitatively improved following boosting of subcutaneously BCG-primed hosts. Prophylactic and therapeutic immunization with this multivalent trivalent vaccine in conventional BALB/c mice provided significant protection against not only actively replicating M.tb bacilli but also dormant, non-replicating persisters. Importantly, when used as a booster, it also provided marked protection in the highly susceptible C3HeB/FeJ mice, and a single respiratory mucosal inoculation was capable of significant protection in a humanized mouse model. Our findings indicate the great potential of this next-generation TB vaccine strategy and support its further clinical development for both prophylactic and therapeutic applications.