Rapid control of pandemic H1N1 influenza by targeting NKT-cells

Single-cell analysis of pig lung leukocytes and their response to influenza infection and oseltamivir therapy

Despite pigs being an important species in influenza A virus (IAV) epidemiology and a reliable preclinical model for human IAV infections, many aspects of the porcine pulmonary immune system remain poorly understood. Here, we characterized the single-cell landscape of lung leukocytes of healthy pigs and then compared them to pigs infected with 2009 pandemic H1N1 IAV with or without oseltamivir antiviral therapy. Our data show conserved features as well as species-specific differences in cell types and cell states compared with human and mouse lung lymphocytes. IAV infection induced a robust antiviral transcriptional response in multiple lymphoid and myeloid cell types, as well as distinct patterns of cell-cell crosstalk. Oseltamivir treatment substantially reduced these responses. Together, our findings describe key events in the pulmonary anti-IAV response of pigs that open new avenues to develop IAV vaccines and therapies. They should also enable the better use of pigs as a model for human IAV infection and immunity.

Single-Cell Antigen Receptor Sequencing in Pigs with Influenza

Understanding the pulmonary adaptive immune system of pigs is important as respiratory pathogens present a major challenge for swine producers and pigs are increasingly used to model human pulmonary diseases. Single-cell RNA sequencing (scRNAseq) has accelerated the characterization of cellular phenotypes in the pig respiratory tract under both healthy and diseased conditions. However, combining scRNAseq with recovery of paired T cell receptor (TCR) α and β chains as well as B cell receptor (BCR) heavy and light chains to interrogate their repertoires has not to our knowledge been demonstrated for pigs. Here, we developed primers to enrich porcine TCR α and β chains along with BCR κ and λ light chains and IgM, IgA, and IgG heavy chains that are compatible with the 10x Genomics VDJ sequencing protocol. Using these pig-specific assays, we sequenced the T and B cell receptors of cryopreserved lung cells from CD1D-expressing and -deficient pigs after one or two infections with influenza A virus (IAV) to examine whether natural killer T (NKT) cells alter pulmonary TCR and BCR repertoire selection. We also performed paired single-cell RNA and receptor sequencing of FACS-sorted T cells longitudinally sampled from the lungs of IAV-vaccinated and -infected pigs to track clonal expansion in response to IAV exposure. All pigs presented highly diverse repertoires. Pigs re-exposed to influenza antigens from either vaccination or infection exhibited higher numbers of expanded CD4 and CD8 T cell clonotypes with activated phenotypes, suggesting potential IAV reactive T cell populations. Our results demonstrate the utility of high throughput single-cell TCR and BCR sequencing in pigs.

Adjuvant Use of the Invariant-Natural-Killer-T-Cell Agonist α-Galactosylceramide Leads to Vaccine-Associated Enhanced Respiratory Disease in Influenza-Vaccinated Pigs

Invariant natural killer T (iNKT) cells are glycolipid-reactive T cells with potent immunoregulatory properties. iNKT cells activated with the marine-sponge-derived glycolipid, α-galactosylceramide (αGC), provide a universal source of T-cell help that has shown considerable promise for a wide array of therapeutic applications. This includes harnessing iNKT-cell-mediated immune responses to adjuvant whole inactivated influenza virus (WIV) vaccines. An important concern with WIV vaccines is that under certain circumstances, they are capable of triggering vaccine-associated enhanced respiratory disease (VAERD). This immunopathological phenomenon can arise after immunization with an oil-in-water (OIW) adjuvanted WIV vaccine, followed by infection with a hemagglutinin and neuraminidase mismatched challenge virus. This elicits antibodies (Abs) that bind immunodominant epitopes in the HA2 region of the heterologous virus, which purportedly causes enhanced virus fusion activity to the host cell and increased infection. Here, we show that αGC can induce severe VAERD in pigs. However, instead of stimulating high concentrations of HA2 Abs, αGC elicits high concentrations of interferon (IFN)-γ-secreting cells both in the lungs and systemically. Additionally, we found that VAERD mediated by iNKT cells results in distinct cytokine profiles and altered adaptation of the challenge virus following infection compared to an OIW adjuvant. Overall, these results provide a cautionary note about considering the formulation of WIV vaccines with iNKT-cell agonists as a potential strategy to modulate antigen-specific immunity.

The surveillance of viral infections by the unconventional Type I NKT cell

Type I NKT cells, also known as Invariant Natural Killer T (iNKT) cells, are a subpopulation of unconventional, innate-like T (ILT) cells which can proficiently influence downstream immune effector functions. Type I NKT cells express a semi-invariant αβ T cell receptor (TCR) that recognises lipid-based ligands specifically presented by the non-classical cluster of differentiation (CD1) protein d (CD1d) molecule. Due to their potent immunomodulatory functional capacity, type I NKT cells are being increasingly considered in prophylactic and therapeutic approaches towards various diseases, including as vaccine-adjuvants. As viruses do not encode lipid synthesis, it is surprising that many studies have shown that some viruses can directly impede type I NKT activation through downregulating CD1d expression. Therefore, in order to harness type I NKT cells for potential anti-viral therapeutic uses, it is critical that we fully appreciate how the CD1d-iNKT cell axis interacts with viral immunity. In this review, we examine clinical findings that underpin the importance of type I NKT cell function in viral infections. This review also explores how certain viruses employ immunoevasive mechanisms and directly encode functions to target CD1d expression and type I NKT cell function. Overall, we suggest that the CD1d-iNKT cell axis may hold greater gravity within viral infections than what was previously appreciated.

Sustained release system from PLGA particles co-encapsulated with inactivated influenza virus with natural killer T cell agonist α-galactosylceramide

Vaccines against influenza and many other infectious diseases require multiple boosters in addition to the primary dose to improve efficacy, but this approach is not ideal for compliance. The multiple doses could potentially be replaced by sustained or pulsatile release of antigens encapsulated in degradable microparticles (MPs). The efficacy of a vaccine is improved by adding an adjuvant, which can be co-delivered from the particles to enhance immunogenicity. Here, we developed degradable poly-lactic-co-glycolic acid (PLGA) (7-17 kDa) MPs capable of sustained release of ultraviolet killed influenza virus (A/PR/8/34) (kPR8) vaccine and the natural killer T (NKT) cell agonist alpha-galactosylceramide (α-GalCer) and tested their effectiveness at providing long-term protection against influenza virus infection in mice. Multiple formulations were developed for encapsulating the virus and adjuvant separately, and in combination. The MPs exhibited sustained release of both the virus and the adjuvant lasting more than a month. Co-encapsulation significantly increased the encapsulation efficiency (EE) of the vaccine but reduced the release duration. On the other hand, co-encapsulation led to a reduction in EE for the α-GalCer and a change in release profile to a higher initial burst followed by a linear release compared to a low initial burst and slower linear release. The α-GalCer also had considerably longer release duration compared to the vaccine. Mice injected with particle formulations co-encapsulating kPR8 and α-GalCer were protected from a lethal influenza virus infection 30 weeks after vaccination. This study demonstrates that PLGA MP based vaccines are promising for providing effective vaccination and possibly for replacing multiple doses with a single injection.

Intradermal Vaccination against Influenza with a STING-Targeted Nanoparticle Combination Adjuvant Induces Superior Cross-Protective Humoral Immunity in Swine Compared with Intranasal and Intramuscular Immunization

The development of cross-protective vaccines against the zoonotic swine influenza A virus (swIAV), a potential pandemic-causing agent, continues to be an urgent global health concern. Commercially available vaccines provide suboptimal cross-protection against circulating subtypes of swIAV, which can lead to worldwide economic losses and poor zoonosis deterrence. The limited efficacy of current swIAV vaccines demands innovative strategies for the development of next-generation vaccines. Considering that intramuscular injection is the standard route of vaccine administration in both human and veterinary medicine, the exploration of alternative strategies, such as intradermal vaccination, presents a promising avenue for vaccinology. This investigation demonstrates the first evaluation of a direct comparison between a commercially available multivalent swIAV vaccine and monovalent whole inactivated H1N2 swine influenza vaccine, delivered by intradermal, intranasal, and intramuscular routes. The monovalent vaccines were adjuvanted with NanoST, a cationic phytoglycogen-based nanoparticle that is combined with the STING agonist ADU-S100. Upon heterologous challenge, intradermal vaccination generated a stronger cross-reactive nasal and serum antibody response in pigs compared with intranasal and intramuscular vaccination. Antibodies induced by intradermal immunization also had higher avidity compared with the other routes of vaccination. Bone marrow from intradermally and intramuscularly immunized pigs had both IgG and IgA virus-specific antibody-secreting cells. These studies reveal that NanoST is a promising adjuvant system for the intradermal administration of STING-targeted influenza vaccines.

Potent NKT cell ligands overcome SARS-CoV-2 immune evasion to mitigate viral pathogenesis in mouse models

One of the major pathogenesis mechanisms of SARS-CoV-2 is its potent suppression of innate immunity, including blocking the production of type I interferons. However, it is unknown whether and how the virus interacts with different innate-like T cells, including NKT, MAIT and γδ T cells. Here we reported that upon SARS-CoV-2 infection, invariant NKT (iNKT) cells rapidly trafficked to infected lung tissues from the periphery. We discovered that the envelope (E) protein of SARS-CoV-2 efficiently down-regulated the cell surface expression of the antigen-presenting molecule, CD1d, to suppress the function of iNKT cells. E protein is a small membrane protein and a viroporin that plays important roles in virion packaging and envelopment during viral morphogenesis. We showed that the transmembrane domain of E protein was responsible for suppressing CD1d expression by specifically reducing the level of mature, post-ER forms of CD1d, suggesting that it suppressed the trafficking of CD1d proteins and led to their degradation. Point mutations demonstrated that the putative ion channel function was required for suppression of CD1d expression and inhibition of the ion channel function using small chemicals rescued the CD1d expression. Importantly, we discovered that among seven human coronaviruses, only E proteins from highly pathogenic coronaviruses including SARS-CoV-2, SARS-CoV and MERS suppressed CD1d expression, whereas the E proteins of human common cold coronaviruses, HCoV-OC43, HCoV-229E, HCoV-NL63 and HCoV-HKU1, did not. These results suggested that E protein-mediated evasion of NKT cell function was likely an important pathogenesis factor, enhancing the virulence of these highly pathogenic coronaviruses. Remarkably, activation of iNKT cells with their glycolipid ligands, both prophylactically and therapeutically, overcame the putative viral immune evasion, significantly mitigated viral pathogenesis and improved host survival in mice. Our results suggested a novel NKT cell-based anti-SARS-CoV-2 therapeutic approach.

Comparison of oseltamivir and α-galactosylceramide for reducing disease and transmission in pigs infected with 2009 H1N1 pandemic influenza virus

Influenza virus infections are a major cause of respiratory disease in humans. Neuraminidase inhibitors (NAIs) are the primary antiviral medication used to treat ongoing influenza infections. However, NAIs are not always effective for controlling virus shedding and lung inflammation. Other concerns are the emergence of NAI-resistant virus strains and the risk of side effects, which are occasionally severe. Consequently, additional anti-influenza therapies to replace or combine with NAIs are desirable. Here, we compared the efficacy of the NAI oseltamivir with the invariant natural killer T (iNKT) cell superagonist, α-galactosylceramide (α-GalCer), which induces innate immune responses that inhibit influenza virus replication in mouse models. We show that oseltamivir reduced lung lesions and lowered virus titers in the upper respiratory tract of pigs infected with A/California/04/2009 (CA04) pandemic H1N1pdm09. It also reduced virus transmission to influenza-naïve contact pigs. In contrast, α-GalCer had no impact on virus replication, lung disease, or virus transmission, even when used in combination with oseltamivir. This is significant as iNKT-cell therapy has been studied as an approach for treating humans with influenza.

Mucosal immune responses to infection and vaccination in the respiratory tract

The lungs are constantly exposed to inhaled debris, allergens, pollutants, commensal or pathogenic microorganisms, and respiratory viruses. As a result, innate and adaptive immune responses in the respiratory tract are tightly regulated and are in continual flux between states of enhanced pathogen clearance, immune-modulation, and tissue repair. New single-cell-sequencing techniques are expanding our knowledge of airway cellular complexity and the nuanced connections between structural and immune cell compartments. Understanding these varied interactions is critical in treatment of human pulmonary disease and infections and in next-generation vaccine design. Here, we review the innate and adaptive immune responses in the lung and airways following infection and vaccination, with particular focus on influenza virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The ongoing SARS-CoV-2 pandemic has put pulmonary research firmly into the global spotlight, challenging previously held notions of respiratory immunity and helping identify new populations at high risk for respiratory distress.

Swine unconventional T cells

Pigs are important domestic livestock and a comprehensive understanding of their immune system is critical to improve swine vaccine efficacy. Pig models represent an excellent animal model for immunological studies because of their anatomical and physiological similarities to humans. A significant portion of pig immunological studies focused on characterizing the conventional T cell (Tconv) immune responses. These cells recognize peptides presented by major histocompatibility complex (MHC) proteins. In contrast, unconventional T cells are non-MHC-restricted and profoundly regulate conventional T cells. Key subsets of unconventional T cells reviewed here include natural killer T (NKT) cells, γδ T cells, mucosal-associated invariant T (MAIT) cells, intraepithelial lymphocytes (IELs), and two potential unconventional T cell subsets expressing NKp46 or CD11b. Unlike Tconvs, most of these cells recognize lipids, small molecule metabolites, or modified peptides, and they generally show simplified patterns of T cell receptor (TCR) expression and rapid effector responses. Here, we review that unconventional T cells are an abundant and critical component of the porcine immune system, summarize the current understanding of these cells, and highlight some of the key differences among mouse, human, and porcine unconventional T cells.

Evaluating α-galactosylceramide as an adjuvant for live attenuated influenza vaccines in pigs

Natural killer T (NKT) cells activated with the glycolipid ligand α-galactosylceramide (α-GalCer) stimulate a wide variety of immune cells that enhance vaccine-mediated immune responses. Several studies have used this approach to adjuvant inactivated and subunit influenza A virus (IAV) vaccines, including to enhance cross-protective influenza immunity. However, less is known about whether α-GalCer can enhance live attenuated influenza virus (LAIV) vaccines, which usually induce superior heterologous and heterosubtypic immunity compared to non-replicating influenza vaccines. The current study used the swine influenza challenge model to assess whether α-GalCer can enhance cross-protective immune responses elicited by a recombinant H3N2 LAIV vaccine (TX98ΔNS1) encoding a truncated NS1 protein. In one study, weaning pigs were administered the H3N2 TX98ΔNS1 LAIV vaccine with 0, 10, 50, and 100 μg/kg doses of α-GalCer, and subsequently challenged with a heterologous H3N2 virus. All treatment groups were protected from infection. However, the addition of α-GalCer appeared to suppress nasal shedding of the LAIV vaccine. In another experiment, pigs vaccinated with the H3N2 LAIV, with or without 50 μg/kg of α-GalCer, were challenged with the heterosubtypic pandemic H1N1 virus. Pigs vaccinated with the LAIV alone generated cross-reactive humoral and cellular responses which blocked virus replication in the airways, and significantly decreased virus shedding. On the other hand, combining the vaccine with α-GalCer reduced cross-protective cellular and antibody responses, and resulted in higher virus titers in respiratory tissues. These findings suggest that: (i) high doses of α-GalCer impair the replication and nasal shedding of the LAIV vaccine; and (ii) α-GalCer might interfere with heterosubtypic cross-protective immune responses. This research raise concerns that should be considered before trying to use NKT cell agonists as a possible adjuvant approach for LAIV vaccines.

Supplementary Information

The online version contains supplementary material available at 10.1186/s44149-022-00051-x.

A digital health platform for assisting the diagnosis and monitoring of COVID-19 progression: An adjuvant approach for augmenting the antiviral response and mitigating the immune-mediated target organ damage

Coronavirus disease 2019 (COVID-19), which is a respiratory illness associated with high mortality, has been classified as a pandemic. The major obstacles for the clinicians to contain the disease are limited information availability, difficulty in disease diagnosis, predicting disease prognosis, and lack of disease monitoring tools. Additionally, the lack of valid therapies has further contributed to the difficulties in containing the pandemic. Recent studies have reported that the dysregulation of the immune system leads to an ineffective antiviral response and promotes pathological immune response, which manifests as ARDS, myocarditis, and hepatitis. In this study, a novel platform has been described for disseminating information to physicians for the diagnosis and monitoring of patients with COVID-19. An adjuvant approach using compounds that can potentiate antiviral immune response and mitigate COVID-19-induced immune-mediated target organ damage has been presented. A prolonged beneficial effect is achieved by implementing algorithm-based individualized variability measures in the treatment regimen.

Role of NKT Cells during Viral Infection and the Development of NKT Cell-Based Nanovaccines

Natural killer T (NKT) cells, a small population of T cells, are capable of influencing a wide range of the immune cells, including T cells, B cells, dendritic cells and macrophages. In the present review, the antiviral role of the NKT cells and the strategies of viruses to evade the functioning of NKT cell have been illustrated. The nanoparticle-based formulations have superior immunoadjuvant potential by facilitating the efficient antigen processing and presentation that favorably elicits the antigen-specific immune response. Finally, the immunoadjuvant potential of the NKT cell ligand was explored in the development of antiviral vaccines. The use of an NKT cell-activating nanoparticle-based vaccine delivery system was supported in order to avoid the NKT cell anergy. The results from the animal and preclinical studies demonstrated that nanoparticle-incorporated NKT cell ligands may have potential implications as an immunoadjuvant in the formulation of an effective antiviral vaccine that is capable of eliciting the antigen-specific activation of the cell-mediated and humoral immune responses.

New IT driven rapid manufacturing for emergency response

COVID-19, which is rampant around the world, has seriously disrupted people's normal work and living. To respond to public urgent needs such as COVID-19, emergency supplies are essential. However, due to the special requirements of supplies, when an emergency occurs, the supply reserve mostly cannot cope with the high demand. Given the importance of emergency supplies in public emergencies, rapid response manufacturing of emergency supplies is a necessity. The faster emergency supplies and facilities are manufactured, the more likely the pandemic can be controlled and the more human lives are saved. Besides, new generation information technology represented by cloud computing, IoT, big data, AI, etc. is rapidly developing and can be widely used to address such situations. Therefore, rapid response manufacturing enabled by New IT is presented to quickly meet emergency demands. And some policy suggestions are presented.

Baseline CD3+CD56+ (NKT-like) Cells and the Outcome of Influenza Vaccination in Children Undergoing Chemotherapy

Background

In children undergoing chemotherapy yearly influenza vaccination is recommended by treatment protocols. We investigated the relationship between cellular immunity and the antibody response to inactivated influenza vaccines.

Methods

25 patients (age: 2-18 years) undergoing chemotherapy for different malignancies participated in our study. Flow cytometric detection of peripheral blood lymphocyte subpopulations together with hemagglutination inhibition antibody titers were measured before and 21-28 days after vaccination. We examined the ratio and total numbers of CD3+, CD4+, CD8+ T cells, activated helper (CD3+CD4+CD25^low), regulatory (CD3+CD4+CD25^high), naive (CD3+CD45RA+) and memory (CD3+CD45RO+) T cells, CD56+NK, and CD3+CD56+ (NKT-like) cells. Relationships between specific antibody responses (seroprotection, seroconversion, geometric mean titer (GMT), geometric mean fold increase (GMFI)) and the ratios and counts of lymphocyte subpopulations were evaluated using one-way ANOVA and the paired sample t test after dichotomization according to age-related reference values.

Results

Patients with CD4+ lymphocyte levels in the normal age-specific range showed significantly better response regarding postvaccination GMT elevation for H1N1 and H3N2 strains (97.52 vs. 19.2, p=0.019, 80 vs. 14.43, p=0.021, respectively). GMFI results were significant only against B strain (2.69-fold vs. 1.23-fold, p=0.046). Prevaccination CD3+CD56+ (NKT-like) cells above predicted values according to age showed significant associations both in postvaccination GMT elevation (H1N1: 75.11 vs. 14.14, p=0.010; H3N2: 62.18 vs. 11.22, p=0.012; B: 22.69 vs. 6.67, p=0.043) and GMFI against all three strains (H1N1: 3.76-fold vs. 1.06-fold, p=0.015; H3N2: 2.74-fold vs. 1, p=0.013; B: 2.57-fold vs. 1, p=0.008). By one-way ANOVA, we found a positive relation between absolute lymphocyte cell count above 1000/µl and the postvaccination GMT elevation against H3N2 (12.81 vs. 56.56, p=0.032), and GMFI regarding H1N1 (1.22-fold vs. 3.48-fold, p=0.044).

Conclusions

In addition to verifying the predictive value of absolute lymphocyte count above 1000/µl, our results suggest an association between NKT-like cell counts and the specific antibody response against all three investigated influenza strains in highly immunosuppressed patients. Furthermore, prevaccination CD4+ lymphocyte levels in the normal age-specific range may influence seroresponse.

Ceramide and Related Molecules in Viral Infections

Ceramide is a lipid messenger at the heart of sphingolipid metabolism. In concert with its metabolizing enzymes, particularly sphingomyelinases, it has key roles in regulating the physical properties of biological membranes, including the formation of membrane microdomains. Thus, ceramide and its related molecules have been attributed significant roles in nearly all steps of the viral life cycle: they may serve directly as receptors or co-receptors for viral entry, form microdomains that cluster entry receptors and/or enable them to adopt the required conformation or regulate their cell surface expression. Sphingolipids can regulate all forms of viral uptake, often through sphingomyelinase activation, and mediate endosomal escape and intracellular trafficking. Ceramide can be key for the formation of viral replication sites. Sphingomyelinases often mediate the release of new virions from infected cells. Moreover, sphingolipids can contribute to viral-induced apoptosis and morbidity in viral diseases, as well as virus immune evasion. Alpha-galactosylceramide, in particular, also plays a significant role in immune modulation in response to viral infections. This review will discuss the roles of ceramide and its related molecules in the different steps of the viral life cycle. We will also discuss how novel strategies could exploit these for therapeutic benefit.

Type I Natural Killer T Cells as Key Regulators of the Immune Response to Infectious Diseases

The immune system must work in an orchestrated way to achieve an optimal response upon detection of antigens. The cells comprising the immune response are traditionally divided into two major subsets, innate and adaptive, with particular characteristics for each type. Type I natural killer T (iNKT) cells are defined as innate-like T cells sharing features with both traditional adaptive and innate cells, such as the expression of an invariant T cell receptor (TCR) and several NK receptors. The invariant TCR in iNKT cells interacts with CD1d, a major histocompatibility complex class I (MHC-I)-like molecule. CD1d can bind and present antigens of lipid nature and induce the activation of iNKT cells, leading to the secretion of various cytokines, such as gamma interferon (IFN-γ) and interleukin 4 (IL-4). These cytokines will aid in the activation of other immune cells following stimulation of iNKT cells. Several molecules with the capacity to bind to CD1d have been discovered, including α-galactosylceramide. Likewise, several molecules have been synthesized that are capable of polarizing iNKT cells into different profiles, either pro- or anti-inflammatory. This versatility allows NKT cells to either aid or impair the clearance of pathogens or to even control or increase the symptoms associated with pathogenic infections. Such diverse contributions of NKT cells to infectious diseases are supported by several publications showing either a beneficial or detrimental role of these cells during diseases. In this article, we discuss current data relative to iNKT cells and their features, with an emphasis on their driving role in diseases produced by pathogenic agents in an organ-oriented fashion.

Unaltered influenza disease outcomes in swine prophylactically treated with α-galactosylceramide

Influenza A viruses (IAV) are a major cause of respiratory diseases in pigs. Invariant natural killer T (iNKT) cells are an innate-like T cell subset that contribute significantly to IAV resistance in mice. In the current work, we explored whether expanding and activating iNKT cells with the iNKT cell superagonist α-galactosylceramide (α-GalCer) would change the course of an IAV infection in pigs. In one study, α-GalCer was administered to pigs intramuscularly (i.m.) 9 days before infection, which systemically expanded iNKT cells. In another study, α-GalCer was administered intranasally (i.n.) 2 days before virus infection to activate mucosal iNKT cells. Despite a synergistic increase in iNKT cells when α-GalCer i.m. treated pigs were infected with IAV, neither approach reduced disease signs, lung pathology, or virus replication. Our results indicate that prophylactic use of iNKT cell agonists to prevent IAV infection is ineffective in pigs. This is significant because this type of approach has been considered for humans whose iNKT cell levels and IAV infections are more similar to those of pigs than mice.

Porcine Invariant Natural Killer T Cells: Functional Profiling and Dynamics in Steady State and Viral Infections

Pigs are important livestock and comprehensive understanding of their immune responses in infections is critical to improve vaccines and therapies. Moreover, similarities between human and swine physiology suggest that pigs are a superior animal model for immunological studies. However, paucity of experimental tools for a systematic analysis of the immune responses in pigs represent a major disadvantage. To evaluate the pig as a biomedical model and additionally expand the knowledge of rare immune cell populations in swine, we established a multicolor flow cytometry analysis platform of surface marker expression and cellular responses for porcine invariant Natural Killer T cells (iNKT). In humans, iNKT cells are among the first line defenders in various tissues, respond to CD1d-restricted antigens and become rapidly activated. Naïve porcine iNKT cells were CD3⁺/CD4⁻/CD8⁺ or CD3⁺/CD4⁻/CD8⁻ and displayed an effector- or memory-like phenotype (CD25⁺/ICOS⁺/CD5^hi/CD45RA⁻/CCR7 ^± /CD27⁺). Based on their expression of the transcription factors T bet and the iNKT cell-specific promyelocytic leukemia zinc finger protein (PLZF), porcine iNKT cells were differentiated into functional subsets. Analogous to human iNKT cells, in vitro stimulation of porcine leukocytes with the CD1d ligand α-galactosylceramide resulted in rapid iNKT cell proliferation, evidenced by an increase in frequency and Ki-67 expression. Moreover, this approach revealed CD25, CD5, ICOS, and the major histocompatibility complex class II (MHC II) as activation markers on porcine iNKT cells. Activated iNKT cells also expressed interferon-γ, upregulated perforin expression, and displayed degranulation. In steady state, iNKT cell frequency was highest in newborn piglets and decreased with age. Upon infection with two viruses of high relevance to swine and humans, iNKT cells expanded. Animals infected with African swine fever virus displayed an increase of iNKT cell frequency in peripheral blood, regional lymph nodes, and lungs. During Influenza A virus infection, iNKT cell percentage increased in blood, lung lymph nodes, and broncho-alveolar lavage. Our in-depth characterization of porcine iNKT cells contributes to a better understanding of porcine immune responses, thereby facilitating the design of innovative interventions against infectious diseases. Moreover, we provide new evidence that endorses the suitability of the pig as a biomedical model for iNKT cell research.

Next Generation Sequencing of the Pig αβ TCR Repertoire Identifies the Porcine Invariant NKT Cell Receptor

Swine represent the only livestock with an established invariant NKT (iNKT) cell-CD1d system. In this study, we exploited the fact that pig iNKT cells can be purified using a mouse CD1d tetramer reagent to establish their TCR repertoire by next generation sequencing. CD1d tetramer-positive pig cells predominantly expressed an invariant Vα-Jα rearrangement, without nontemplate nucleotide diversity, homologous to the Vα24-Jα18 and Vα14-Jα18 rearrangements of human and murine iNKT cells. The coexpressed β-chain used a Vβ segment homologous to the semivariant Vβ11 and Vβ8.2 segments of human and murine iNKT cell receptors. Molecular modeling found that contacts within CD1d and CDR1α that underlie fine specificity differences between mouse and human iNKT cells are conserved between pigs and humans, indicating that the response of porcine and human iNKT cells to CD1d-restricted Ags may be similar. Accordingly, pigs, which are an important species for diverse fields of biomedical research, may be useful for developing human-based iNKT cell therapies for cancer, infectious diseases, and other disorders. Our study also sequenced the expressed TCR repertoire of conventional porcine αβ T cells, which identified 48 Vα, 50 Jα, 18 Vβ, and 18 Jβ sequences, most of which correspond to human gene segments. These findings provide information on the αβ TCR usage of pigs, which is understudied and deserves further attention.

The Role of Autophagy in iNKT Cell Development

CD1d-restricted invariant natural killer T (iNKT) cells are innate-like T cells that express an invariant T cell receptor (TCR) α-chain and recognize self and foreign glycolipid antigens. They can rapidly respond to agonist activation and stimulate an extensive array of immune responses. Thymic development and function of iNKT cells are regulated by many different cellular processes, including autophagy, a self-degradation mechanism. In this mini review, we discuss the current understanding of how autophagy regulates iNKT cell development and effector lineage differentiation. Importantly, we propose that iNKT cell development is tightly controlled by metabolic reprogramming.

The Influence of Invariant Natural Killer T Cells on Humoral Immunity to T-Dependent and -Independent Antigens

Vaccination with CD1d-binding glycolipid adjuvants and co-administered protein, lipid, and carbohydrate antigens leads to invariant natural killer T (NKT) cell-dependent enhancement of protective B cell responses. NKT cell activation boosts the establishment of protein antigen-specific B cell memory and long-lived plasma cell (LLPC) compartments. NKT cells may exert a similar effect on some carbohydrate-specific B cells, but not lipid-specific B cells. The mechanisms of action of NKT cells on B cell responsiveness and subsequent differentiation into memory B cells and LLPC is dependent on CD1d expression by dendritic cells and B cells that can co-present glycolipids on CD1d and antigen-derived peptide on MHCII. CD1d/glycolipid-activated NKT cells are able to provide help to B cells in a manner dependent on cognate and non-cognate interactions. More recently, a glycolipid-expanded subset of IL-21-secreting NKT cells known as NKT follicular helper cells has been suggested to be a driver of NKT-enhanced humoral immunity. This review summarizes established and recent findings on how NKT cells impact humoral immunity and suggests possible areas of investigation that may allow the incorporation of NKT-activating agents into vaccine adjuvant platforms.

Harnessing Invariant NKT Cells to Improve Influenza Vaccines: A Pig Perspective

Invariant natural killer T (iNKT) cells are an "innate-like" T cell lineage that recognize glycolipid rather than peptide antigens by their semi-invariant T cell receptors. Because iNKT cells can stimulate an extensive array of immune responses, there is considerable interest in targeting these cells to enhance human vaccines against a wide range of microbial pathogens. However, long overlooked is the potential to harness iNKT cell antigens as vaccine adjuvants for domestic animal species that express the iNKT cell-CD1d system. In this review, we discuss the prospect of targeting porcine iNKT cells as a strategy to enhance the efficiency of swine influenza vaccines. In addition, we compare the phenotype and tissue distribution of porcine iNKT cells. Finally, we discuss the challenges that must be overcome before iNKT cell agonists can be contemplated for veterinary use in livestock.

Characterizing porcine invariant natural killer T cells: A comparative study with NK cells and T cells

CD1d-restricted invariant natural killer T (iNKT) cells are innate-like T cells that share phenotypic characteristics of both NK and conventional T cells (Tconv). Although iNKT cells have been well characterized in mice and humans, functional CD1d and CD1d-restricted iNKT cells are not universally expressed in mammals. Swine express iNKT cells that can be detected using α-galactosylceramide (α-GalCer)-loaded CD1d tetramers. In the present study, we characterized iNKT cells from the blood, spleen, lymph node, lung and liver of commercial mixed-breed pigs, and compared their phenotype to NK cells and Tconv. The principal findings are that pig iNKT cells are CD8α and CD44 positive and CD11b and Nkp46 negative. Most are also negative for the CD4 co-receptor, which is used to distinguish functionally distinct mouse and human iNKT cells subsets. The frequency of IFN-γ-producing CD8αbright iNKT cells was 3-4-fold higher than CD8αdull iNKT cells, suggesting that CD8α expression identifies iNKT cells with a unique functional role in immune responses. Finally, large variability was detected among pigs in interactions between iNKT cells and monocytes when iNKT cells were activated with α-GalCer, which raises a cautionary note about manipulating iNKT cells for immunotherapy. Collectively, our study provides important phenotypic and functional information about porcine iNKT cells that will be useful for understanding how iNKT cells contribute to immune responses in swine, with potential implications for human health.