Invariant NKT cells reduce the immunosuppressive activity of influenza A virus-induced myeloid-derived suppressor cells in mice and humans

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.

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.

Cutting Edge: Redundant Roles for MHC Class II-, CD1d-, and MR1-restricted T Cells in Clearing Bartonella Infection

The importance of unconventional T cells for mucosal immunity is firmly established but for systemic bacterial infection remains less well defined. In this study, we explored the role of various T cell subsets in murine Bartonella infection, which establishes persistent bacteremia unless controlled by antibacterial Abs. We found that αβ T cells are essential for Ab production against and clearance of B. taylorii, whereas MHC class I (MHC-I)- or MHC class II (MHC-II)-deficient mice eliminated B. taylorii infection with normal kinetics. Similarly, animals lacking either CD1d or MR1 suppressed bacteremia with normal kinetics. Interestingly, mice with a combined deficiency of either MHC-II and CD1d or MHC-II and MR1 failed to clear the infection, indicating that the combination of CD1d- and MR1-restricted T cells can compensate for the lack of MHC-II in this model. Our data document a previously underappreciated contribution of unconventional T cells to the control of systemic bacterial infection, supposedly as helper cells for antibacterial Ab production.

Intratumoral NKT cell accumulation promotes antitumor immunity in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is a potentially lethal disease lacking effective treatments. Its immunosuppressive tumor microenvironment (TME) allows it to evade host immunosurveillance and limits response to immunotherapy. Here, using the mouse KRT19-deficient (sgKRT19-edited) PDA model, we find that intratumoral accumulation of natural killer T (NKT) cells is required to establish an immunologically active TME. Mechanistically, intratumoral NKT cells facilitate type I interferon (IFN) production to initiate an antitumor adaptive immune response, and orchestrate the intratumoral infiltration of T cells, dendritic cells, natural killer cells, and myeloid-derived suppressor cells. At the molecular level, NKT cells promote the production of type I IFN through the interaction of their CD40L with CD40 on myeloid cells. To evaluate the therapeutic potential of these observations, we find that administration of folinic acid to mice bearing PDA increases NKT cells in the TME and improves their response to anti-PD-1 antibody treatment. In conclusion, NKT cells have an essential role in the immune response to mouse PDA and are potential targets for immunotherapy.

Alpha-galactosylceramide improves the potency of mRNA LNP vaccines against cancer and intracellular bacteria

Although various types of mRNA-based vaccines have been explored, the optimal conditions for induction of both humoral and cellular immunity remain rather unknown. In this study, mRNA vaccines of nucleoside-modified mRNA in lipoplexes (LPXs) or lipid nanoparticles (LNPs) were evaluated after administration in mice through different routes, assessing mRNA delivery, tolerability and immunogenicity. In addition, we investigated whether mRNA vaccines could benefit from the inclusion of the adjuvant alpha-galactosylceramide (αGC), an invariant Natural Killer T (iNKT) cell ligand. Intramuscular (IM) vaccination with ovalbumin (OVA)-encoding mRNA encapsulated in LNPs adjuvanted with αGC showed the highest antibody- and CD8+ T cell responses. Furthermore, we observed that addition of signal peptides and endocytic sorting signals of either LAMP1 or HLA-B7 in the OVA-encoding mRNA sequence further enhanced CD8+ T cell activation although reducing the induction of IgG antibody responses. Moreover, mRNA LNPs with the ionizable lipidoid C12-200 exhibited higher pro-inflammatory- and reactogenic activity compared to mRNA LNPs with SM-102, correlating with increased T cell activation and antitumor potential. We also observed that αGC could further enhance the cellular immunity of clinically relevant mRNA LNP vaccines, thereby promoting therapeutic antitumor potential. Finally, a Listeria monocytogenes mRNA LNP vaccine supplemented with αGC showed synergistic protective effects against listeriosis, highlighting a key advantage of co-activating iNKT cells in antibacterial mRNA vaccines. Taken together, our study offers multiple insights for optimizing the design of mRNA vaccines for disease applications, such as cancer and intracellular bacterial infections.

Myeloid-derived suppressor cells in influenza virus-induced asthma exacerbation

Myeloid-derived suppressor cells (MDSCs) are a phenotypically heterogenous group of cells that potently suppress the immune response. A growing body of evidence supports the important role of MDSCs in a variety of lung diseases, such as asthma. However, the role of MDSCs in asthma exacerbation has so far not been investigated. Here, we studied the role of MDSCs in a murine model of influenza virus-induced asthma exacerbation. BALB/c mice were exposed to house dust mite (HDM) three times a week for a total of five weeks to induce a chronic asthmatic phenotype, which was exacerbated by additional exposure to the A/Hamburg/5/2009 hemagglutinin 1 neuraminidase 1 (H1N1) influenza virus. Induction of lung inflammatory features, production of T helper (Th) 1- and Th2- associated inflammatory cytokines in the lavage fluid and an increased airway hyper-responsiveness were observed, establishing the asthma exacerbation model. The number and activity of pulmonary M-MDSCs increased in exacerbated asthmatic mice compared to non-exacerbated asthmatic mice. Furthermore, depletion of MDSCs aggravated airway hyper-responsiveness in exacerbated asthmatic mice. These findings further denote the role of MDSCs in asthma and provide some of the first evidence supporting a potential important role of MDSCs in asthma exacerbation.

CAR products from novel sources: a new avenue for the breakthrough in cancer immunotherapy

Chimeric antigen receptor (CAR) T cell therapy has transformed cancer immunotherapy. However, significant challenges limit its application beyond B cell-driven malignancies, including limited clinical efficacy, high toxicity, and complex autologous cell product manufacturing. Despite efforts to improve CAR T cell therapy outcomes, there is a growing interest in utilizing alternative immune cells to develop CAR cells. These immune cells offer several advantages, such as major histocompatibility complex (MHC)-independent function, tumor microenvironment (TME) modulation, and increased tissue infiltration capabilities. Currently, CAR products from various T cell subtypes, innate immune cells, hematopoietic progenitor cells, and even exosomes are being explored. These CAR products often show enhanced antitumor efficacy, diminished toxicity, and superior tumor penetration. With these benefits in mind, numerous clinical trials are underway to access the potential of these innovative CAR cells. This review aims to thoroughly examine the advantages, challenges, and existing insights on these new CAR products in cancer treatment.

Insights into the heterogeneity of iNKT cells: tissue-resident and circulating subsets shaped by local microenvironmental cues

Invariant natural killer T (iNKT) cells are a distinct subpopulation of innate-like T lymphocytes. They are characterized by semi-invariant T cell receptors (TCRs) that recognize both self and foreign lipid antigens presented by CD1d, a non-polymorphic MHC class I-like molecule. iNKT cells play a critical role in stimulating innate and adaptive immune responses, providing an effective defense against infections and cancers, while also contributing to chronic inflammation. The functions of iNKT cells are specific to their location, ranging from lymphoid to non-lymphoid tissues, such as the thymus, lung, liver, intestine, and adipose tissue. This review aims to provide insights into the heterogeneity of development and function in iNKT cells. First, we will review the expression of master transcription factors that define subsets of iNKT cells and their production of effector molecules such as cytokines and granzymes. In this article, we describe the gene expression profiles contributing to the kinetics, distribution, and cytotoxicity of iNKT cells across different tissue types. We also review the impact of cytokine production in distinct immune microenvironments on iNKT cell heterogeneity, highlighting a recently identified circulating iNKT cell subset. Additionally, we explore the potential of exploiting iNKT cell heterogeneity to create potent immunotherapies for human cancers in the future.

A phase 1/2 clinical trial of invariant natural killer T cell therapy in moderate-severe acute respiratory distress syndrome

Invariant natural killer T (iNKT) cells, a unique T cell population, lend themselves for use as adoptive therapy due to diverse roles in orchestrating immune responses. Originally developed for use in cancer, agenT-797 is a donor-unrestricted allogeneic ex vivo expanded iNKT cell therapy. We conducted an open-label study in virally induced acute respiratory distress syndrome (ARDS) caused by the severe acute respiratory syndrome-2 virus (trial registration NCT04582201). Here we show that agenT-797 rescues exhausted T cells and rapidly activates both innate and adaptive immunity. In 21 ventilated patients including 5 individuals receiving veno-venous extracorporeal membrane oxygenation (VV-ECMO), there are no dose-limiting toxicities. We observe an anti-inflammatory systemic cytokine response and infused iNKT cells are persistent during follow-up, inducing only transient donor-specific antibodies. Clinical signals of associated survival and prevention of secondary infections are evident. Cellular therapy using off-the-shelf iNKT cells is safe, can be rapidly scaled and is associated with an anti-inflammatory response. The safety and therapeutic potential of iNKT cells across diseases including infections and cancer, warrants randomized-controlled trials.

Fc-fused IL-7 provides broad antiviral effects against respiratory virus infections through IL-17A-producing pulmonary innate-like T cells

Repeated pandemics caused by the influenza virus and severe acute respiratory syndrome coronavirus (SARS-CoV) have resulted in serious problems in global public health, emphasizing the need for broad-spectrum antiviral therapeutics against respiratory virus infections. Here, we show the protective effects of long-acting recombinant human interleukin-7 fused with hybrid Fc (rhIL-7-hyFc) against major respiratory viruses, including influenza virus, SARS-CoV-2, and respiratory syncytial virus. Administration of rhIL-7-hyFc in a therapeutic or prophylactic regimen induces substantial antiviral effects. During an influenza A virus (IAV) infection, rhIL-7-hyFc treatment increases pulmonary T cells composed of blood-derived interferon γ (IFNγ)+ conventional T cells and locally expanded IL-17A+ innate-like T cells. Single-cell RNA transcriptomics reveals that rhIL-7-hyFc upregulates antiviral genes in pulmonary T cells and induces clonal expansion of type 17 innate-like T cells. rhIL-7-hyFc-mediated disease prevention is dependent on IL-17A in both IAV- and SARS-CoV-2-infected mice. Collectively, we suggest that rhIL-7-hyFc can be used as a broadly active therapeutic for future respiratory virus pandemic.

Harnessing Chimeric Antigen Receptor-engineered Invariant Natural Killer T Cells: Therapeutic Strategies for Cancer and the Tumor Microenvironment

Chimeric antigen receptor (CAR)-engineered T (CAR-T) cell therapy has emerged as a revolutionary approach for cancer treatment, especially for hematologic cancers. However, CAR-T therapy has some limitations, including cytokine release syndrome (CRS), immune cellassociated neurologic syndrome (ICANS), and difficulty in targeting solid tumors and delivering allogeneic cell therapy due to graft-versus-host disease (GvHD). Therefore, it is important to explore other cell sources for CAR engineering. Invariant natural killer T (iNKT) cells are a potential target, as they possess powerful antitumor ability and do not recognize mismatched major histocompatibility complexes (MHCs) and protein antigens, thus avoiding the risk of GvHD. CAR-engineered iNKT (CAR-iNKT) cell therapy offers a promising new approach to cancer immunotherapy by overcoming the drawbacks of CAR-T cell therapy while retaining potent antitumor capabilities. This review summarizes the current CAR-iNKT cell products, their functions and phenotypes, and their potential for off-the-shelf cancer immunotherapy.

T Cell Receptor-Engaging Monoclonal Antibodies Mobilize the Anti-Tumor Functions of Invariant Natural Killer T Cells

Invariant natural killer T cells (iNKTs) are innate-type T lymphocytes that directly kill tumor cells or tumor-growth promoting immunosuppressive cells such astumor-associated macrophages. Additionally, iNKTs robustly transactivate the antitumor functions of T, B, natural killer, and dendritic cells as well as reinvigorate exhausted immune cells in the tumor microenvironment. As such, iNKTs make excellent candidates for inclusion in anti-cancer cellular therapies. However, to capitalize on the potential benefits of iNKT cell-based approaches, it is imperative that we develop new and clinically viable strategies to enhance their antitumor function. To that end, two novel monoclonal antibodies (mAbs) that selectively bind to the human (NKTT320) or murine (NKT14m) invariant T cell receptor have been recently developed and characterized. Studies using purified human iNKTs (in vitro) and a model of non-human primate (in vivo) reveal that NKTT320 promotes swift, vigorous and sustained iNKT cell activation that is accompanied by robust production of inflammatory mediators and bystander immune cell activation. Furthermore, NKTT320 augments expression of cytotoxic markers and human iNKT cell degranulation. Similarly, NKT14m prompts dramatic murine iNKT cell activation and functional response both in vitro and in vivo. However, antitumor efficacy of a single dose of NKT14m injection in tumor-bearing mice is limited and tumor-model dependent. In contrast, combination treatment of NKT14m with either low dose interleukin (IL)-12 or the chemotherapeutic agent, cyclophosphamide results in a superior antitumor response in vivo. This is evident by activation of both iNKTs and other immune cells, prolonged survival of the tumor-challenged mice, and long-lasting immunity. Collectively, these recent studies justify further development of anti-iTCR mAbs that can be used alone or in conjunction with immunomodulatory agents to enhance iNKT cell antitumor immunity against various cancers.

From Snoot to Tail: A Brief Review of Influenza Virus Infection and Immunity in Pigs

Pigs play an important role in influenza A virus (IAV) epidemiology because they support replication of human, avian, and swine origin viruses and act as an IAV reservoir for pigs and other species, including humans. Moreover, novel IAVs with human pandemic potential may be generated in pigs. To minimize the threat of IAVs to human and swine health, it is crucial to understand host defense mechanisms that restrict viral replication and pathology in pigs. In this article, we review IAV strains circulating in the North American swine population, as well as porcine innate and acquired immune responses to IAV, including recent advances achieved through immunological tools developed specifically for swine. Furthermore, we highlight unique aspects of the porcine pulmonary immune system, which warrant consideration when developing vaccines and therapeutics to limit IAV in swine or when using pigs to model human IAV infections.

Myeloid-derived suppressor cells exacerbate poly(I:C)-induced lung inflammation in mice with renal injury and older mice

Viral pneumonia is a global health burden with a high mortality rate, especially in the elderly and in patients with underlying diseases. Recent studies have found that myeloid-derived suppressor cells (MDSCs) are abundant in these patient groups; however, their roles in the progression of viral pneumonia remain unclear. In this study, we observed a substantial increase in MDSCs in a mouse model of renal ischemia/reperfusion (I/R) injury and in older mice. When intranasal polyinosinic-polycytidylic acid (poly(I:C)) administration was used to mimic viral pneumonia, mice with renal I/R injury exhibited more severe lung inflammation than sham mice challenged with poly(I:C). In addition, MDSC depletion attenuated lung inflammation in mice with I/R injury. Similar results were obtained in older mice compared with those in young mice. Furthermore, adoptive transfer of in vitro-differentiated MDSCs exacerbated poly(I:C)-induced lung inflammation. Taken together, these experimental results suggest that the increased proportion of MDSCs in mice with renal I/R injury and in older mice exacerbates poly(I:C)-induced lung inflammation. These findings have important implications for the treatment and prevention of severe lung inflammation caused by viral pneumonia.

Invariant natural killer T cells in lung diseases

Invariant natural killer T (iNKT) cells are a subset of T cells that are characterized by a restricted T-cell receptor (TCR) repertoire and a unique ability to recognize glycolipid antigens. These cells are found in all tissues, and evidence to date suggests that they play many immunological roles in both homeostasis and inflammatory conditions. The latter include lung inflammatory diseases such as asthma and infections: the roles of lung-resident iNKT cells in these diseases have been extensively researched. Here, we provide insights into the biology of iNKT cells in health and disease, with a particular focus on the role of pulmonary iNKT cells in airway inflammation and other lung diseases.

Aging unconventionally: γδ T cells, iNKT cells, and MAIT cells in aging

Unconventional T cells include γδ T cells, invariant Natural Killer T cells (iNKT) cells and Mucosal Associated Invariant T (MAIT) cells, which are distinguished from conventional T cells by their recognition of non-peptide ligands presented by non-polymorphic antigen presenting molecules and rapid effector functions that are pre-programmed during their development. Here we review current knowledge of the effect of age on unconventional T cells, from early life to old age, in both mice and humans. We then discuss the role of unconventional T cells in age-associated diseases and infections, highlighting the similarities between members of the unconventional T cell family in the context of aging.

Primary Mouse Invariant Natural Killer T (iNKT) Cell Purification and Transduction

Invariant natural killer T (iNKT) cells are a non-conventional T-cell population expressing a conserved semi-invariant T-cell receptor (TCR) that reacts to lipid antigens, such as α-galactosyl ceramide (α-GalCer), presented by the monomorphic molecule CD1d. iNKT cells play a central role in tumor immunosurveillance and represent a powerful tool for anti-cancer treatment, notably because they can be efficiently redirected against hematological or solid malignancies by engineering with tumor-specific chimeric antigen receptors (CARs) or TCRs. However, iNKT cells are rare and require specific ex vivo pre-selection and substantial in vitro expansion to be exploited for adoptive cell therapy (ACT). This protocol describes a robust method to obtain a large number of mouse iNKT cells that can be effectually engineered by retroviral (RV) transduction. A major advantage of this protocol is that it requires neither particular instrumentation nor a high number of mice. iNKT cells are enriched from the spleens of iVα14-Jα18 transgenic mice; the rapid purification protocol yields a highly enriched iNKT cell population that is activated by anti-CD3/CD28 beads, which is more reproducible and less time consuming than using bone marrow-derived dendritic cells loaded with α-GalCer, without risks of expanding contaminant T cells. Forty-eight hours after activation, iNKT cells are transduced with the selected RV by spin inoculation. This protocol allows to obtain, in 15 days, millions of ready-to-use, highly pure, and stably transduced iNKT cells that might be exploited for in vitro assays and ACT experiments in preclinical studies.

CD1 and iNKT cells mediate immune responses against the GBS hemolytic lipid toxin induced by a non-toxic analog

Although hemolytic lipids have been discovered from many human pathogens including Group B Streptococcus (GBS), strategies that neutralize their function are lacking. GBS is a leading cause of pregnancy-associated neonatal infections, and adult GBS infections are on the rise. The GBS hemolytic lipid toxin or granadaene, is cytotoxic to many immune cells including T and B cells. We previously showed that mice immunized with a synthetic nontoxic analog of granadaene known as R-P4 had reduced bacterial dissemination during systemic infection. However, mechanisms important for R-P4 mediated immune protection was not understood. Here, we show that immune serum from R-P4-immunized mice facilitate GBS opsonophagocytic killing and protect naïve mice from GBS infection. Further, CD4+ T cells isolated from R-P4-immunized mice proliferated in response to R-P4 stimulation in a CD1d- and iNKT cell-dependent manner. Consistent with these observations, R-P4 immunized mice lacking CD1d or CD1d-restricted iNKT cells exhibit elevated bacterial burden. Additionally, adoptive transfer of iNKT cells from R-P4 vaccinated mice significantly reduced GBS dissemination compared to adjuvant controls. Finally, maternal R-P4 vaccination provided protection against ascending GBS infection during pregnancy. These findings are relevant in the development of therapeutic strategies targeting lipid cytotoxins.

CAR-NKT cell therapy: a new promising paradigm of cancer immunotherapy

Today, cancer treatment is one of the fundamental problems facing clinicians and researchers worldwide. Efforts to find an excellent way to treat this illness continue, and new therapeutic strategies are developed quickly. Adoptive cell therapy (ACT) is a practical approach that has been emerged to improve clinical outcomes in cancer patients. In the ACT, one of the best ways to arm the immune cells against tumors is by employing chimeric antigen receptors (CARs) via genetic engineering. CAR equips cells to target specific antigens on tumor cells and selectively eradicate them. Researchers have achieved promising preclinical and clinical outcomes with different cells by using CARs. One of the potent immune cells that seems to be a good candidate for CAR-immune cell therapy is the Natural Killer-T (NKT) cell. NKT cells have multiple features that make them potent cells against tumors and would be a powerful replacement for T cells and natural killer (NK) cells. NKT cells are cytotoxic immune cells with various capabilities and no notable side effects on normal cells. The current study aimed to comprehensively provide the latest advances in CAR-NKT cell therapy for cancers.

Die Kämpfe únd schláchten-the struggles and battles of innate-like effector T lymphocytes with microbes

The large majority of lymphocytes belong to the adaptive immune system, which are made up of B2 B cells and the αβ T cells; these are the effectors in an adaptive immune response. A multitudinous group of lymphoid lineage cells does not fit the conventional lymphocyte paradigm; it is the unconventional lymphocytes. Unconventional lymphocytes-here called innate/innate-like lymphocytes, include those that express rearranged antigen receptor genes and those that do not. Even though the innate/innate-like lymphocytes express rearranged, adaptive antigen-specific receptors, they behave like innate immune cells, which allows them to integrate sensory signals from the innate immune system and relay that umwelt to downstream innate and adaptive effector responses. Here, we review natural killer T cells and mucosal-associated invariant T cells-two prototypic innate-like T lymphocytes, which sense their local environment and relay that umwelt to downstream innate and adaptive effector cells to actuate an appropriate host response that confers immunity to infectious agents.

Towards a better understanding of human iNKT cell subpopulations for improved clinical outcomes

Invariant natural killer T (iNKT) cells are a unique T lymphocyte population expressing semi-invariant T cell receptors (TCRs) that recognise lipid antigens presented by CD1d. iNKT cells exhibit potent anti-tumour activity through direct killing mechanisms and indirectly through triggering the activation of other anti-tumour immune cells. Because of their ability to induce potent anti-tumour responses, particularly when activated by the strong iNKT agonist αGalCer, they have been the subject of intense research to harness iNKT cell-targeted immunotherapies for cancer treatment. However, despite potent anti-tumour efficacy in pre-clinical models, the translation of iNKT cell immunotherapy into human cancer patients has been less successful. This review provides an overview of iNKT cell biology and why they are of interest within the context of cancer immunology. We focus on the iNKT anti-tumour response, the seminal studies that first reported iNKT cytotoxicity, their anti-tumour mechanisms, and the various described subsets within the iNKT cell repertoire. Finally, we discuss several barriers to the successful utilisation of iNKT cells in human cancer immunotherapy, what is required for a better understanding of human iNKT cells, and the future perspectives facilitating their exploitation for improved clinical outcomes.

Profiling of innate and adaptive immune cells during influenza virus infection reveals sex bias in invariant natural killer T (iNKT) cells

BACKGROUND

Influenza A virus (IAV) infection leads to significant morbidity and mortality. Biological sex influences the immune responses to IAV infection, resulting in higher mortality in women of reproductive age. Previous studies revealed increased activation of T and B cells in female mice after IAV infection, but extensive analysis of sex differences in both innate and adaptive immune cells over time is lacking. Invariant natural killer T (iNKT) cells are fast-reacting forces and modulators of immune responses that are important to IAV immunity, but it is not known if the presence and function of iNKT cells differ between females and males. The aim of this study was to determine immunological mechanisms that contribute to the increased disease severity in female mice during IAV infection.

METHODS

Female and male mice were infected with mouse-adapted IAV and monitored for weight loss and survival. Immune cell populations and cytokine expression in bronchoalveolar lavage fluid, lung, and mediastinal lymph node were determined at three time points after infection using flow cytometry and ELISA.

RESULTS

The results reveal increased severity and mortality in adult female mice compared to age-matched males. Female mice show larger increases in innate and adaptive immune cell populations and cytokine production in lung compared to mock on Day 6 postinfection. On Day 9 postinfection, female mice express higher numbers of iNKT cells in lung and liver compared to males.

CONCLUSIONS

This comprehensive analysis of immune cells and cytokines over time following IAV infection reveals increased leukocyte expansion and stronger proinflammatory cytokine responses in female mice during disease initiation. Furthermore, this is the first study to report a sex bias in iNKT cell populations after IAV infection. The data suggests that the process of recovery from IAV-induced airway inflammation is associated with increased expansion of several different iNKT cell subpopulations in female mice.

Inducible nitric oxide synthase-expressing myeloid-derived suppressor cells regulated by interleukin 35 contribute to the pathogenesis of psoriasis

Although psoriasis is classified as a T cell-mediated inflammatory disease, the contribution of myeloid cells to the pathogenesis of psoriasis is not fully understood. In the present study, we demonstrated that the expression of the anti-inflammatory cytokine interleukin-35 (IL-35) was significantly increased in patients with psoriasis with a marked increase in the number of myeloid-derived suppressor cells (MDSCs). Similar results were obtained in an imiquimod-induced psoriasis mouse model. IL-35 reduced the total number of MDSCs and their subtypes in the spleens and psoriatic skin lesions, ameliorating psoriasis. IL-35 also reduced the expression of inducible nitric oxide synthase in MDSCs, although it had no significant effect on interleukin-10 expression. Adoptive transfer of MDSCs from imiquimod-challenged mice aggravated the disease and weakened the effect of IL-35 in the recipient mice. In addition, mice transferred with MDSCs isolated from inducible nitric oxide synthase knockout mice had milder disease than those with wild-type MDSCs. Furthermore, wild-type MDSCs reversed the effects of IL-35, while MDSCs isolated from inducible nitric oxide synthase knockout mice did not affect IL-35 treatment. In summary, IL-35 may play a critical role in the regulation of iNOS-expressing MDSCs in the pathogenesis of psoriasis, highlighting IL-35 as a novel therapeutic strategy for patients with chronic psoriasis or other cutaneous inflammatory diseases.

Invariant NKT cells metabolically adapt to the acute myeloid leukaemia environment

Acute myeloid leukaemia (AML) creates an immunosuppressive environment to conventional T cells through Arginase 2 (ARG2)-induced arginine depletion. We identify that AML blasts release the acute phase protein serum amyloid A (SAA), which acts in an autocrine manner to upregulate ARG2 expression and activity, and promote AML blast viability. Following in vitro cross-talk invariant natural killer T (iNKT) cells become activated, upregulate mitochondrial capacity, and release IFN-γ. iNKT retain their ability to proliferate and be activated despite the low arginine AML environment, due to the upregulation of Large Neutral Amino Acid Transporter-1 (LAT-1) and Argininosuccinate Synthetase 1 (ASS)-dependent amino acid pathways, resulting in AML cell death. T cell proliferation is restored in vitro and in vivo. The capacity of iNKT cells to restore antigen-specific T cell immunity was similarly demonstrated against myeloid-derived suppressor cells (MDSCs) in wild-type and Jα18^-/- syngeneic lymphoma-bearing models in vivo. Thus, stimulation of iNKT cell activity has the potential as an immunotherapy against AML or as an adjunct to boost antigen-specific T cell immunotherapies in haematological or solid cancers.

Innate immune responses in pneumonia

The lungs are an immunologically unique environment; they are exposed to innumerable pathogens and particulate matter daily. Appropriate clearance of pathogens and response to pollutants is required to prevent overwhelming infection, while preventing tissue damage and maintaining efficient gas exchange. Broadly, the innate immune system is the collection of immediate, intrinsic immune responses to pathogen or tissue injury. In this review, we will examine the innate immune responses of the lung, with a particular focus on their role in pneumonia. We will discuss the anatomic barriers and antimicrobial proteins of the lung, pathogen and injury recognition, and the role of leukocytes (macrophages, neutrophils, and innate lymphocytes) and lung stromal cells in innate immunity. Throughout the review, we will focus on new findings in innate immunity as well as features that are unique to the lung.

Immune responses in mildly versus critically ill COVID-19 patients

The current coronavirus pandemic (COVID-19), caused by SARS-CoV-2, has had devastating effects on the global health and economic system. The cellular and molecular mediators of both the innate and adaptive immune systems are critical in controlling SARS-CoV-2 infections. However, dysregulated inflammatory responses and imbalanced adaptive immunity may contribute to tissue destruction and pathogenesis of the disease. Important mechanisms in severe forms of COVID-19 include overproduction of inflammatory cytokines, impairment of type I IFN response, overactivation of neutrophils and macrophages, decreased frequencies of DC cells, NK cells and ILCs, complement activation, lymphopenia, Th1 and Treg hypoactivation, Th2 and Th17 hyperactivation, as well as decreased clonal diversity and dysregulated B lymphocyte function. Given the relationship between disease severity and an imbalanced immune system, scientists have been led to manipulate the immune system as a therapeutic approach. For example, anti-cytokine, cell, and IVIG therapies have received attention in the treatment of severe COVID-19. In this review, the role of immunity in the development and progression of COVID-19 is discussed, focusing on molecular and cellular aspects of the immune system in mild vs. severe forms of the disease. Moreover, some immune- based therapeutic approaches to COVID-19 are being investigated. Understanding key processes involved in the disease progression is critical in developing therapeutic agents and optimizing related strategies.

Role of myeloid-derived suppressor cells during Trypanosoma cruzi infection

Chagas disease (CD), caused by the protozoan parasite Trypanosoma cruzi, is the third largest parasitic disease burden globally. Currently, more than 6 million people are infected, mainly in Latin America, but international migration has turned CD into an emerging health problem in many nonendemic countries. Despite intense research, a vaccine is still not available. A complex parasite life cycle, together with numerous immune system manipulation strategies, may account for the lack of a prophylactic or therapeutic vaccine. There is substantial experimental evidence supporting that T. cruzi acute infection generates a strong immunosuppression state that involves numerous immune populations with regulatory/suppressive capacity. Myeloid-derived suppressor cells (MDSCs), Foxp3+ regulatory T cells (Tregs), regulatory dendritic cells and B regulatory cells are some of the regulatory populations that have been involved in the acute immune response elicited by the parasite. The fact that, during acute infection, MDSCs increase notably in several organs, such as spleen, liver and heart, together with the observation that depletion of those cells can decrease mouse survival to 0%, strongly suggests that MDSCs play a major role during acute T. cruzi infection. Accumulating evidence gained in different settings supports the capacity of MDSCs to interact with cells from both the effector and the regulatory arms of the immune system, shaping the outcome of the response in a very wide range of scenarios that include pathological and physiological processes. In this sense, the aim of the present review is to describe the main knowledge about MDSCs acquired so far, including several crosstalk with other immune populations, which could be useful to gain insight into their role during T. cruzi infection.

A circulating subset of iNKT cells mediates antitumor and antiviral immunity

Invariant natural killer T (iNKT) cells are a group of innate-like T lymphocytes that recognize lipid antigens. They are supposed to be tissue resident and important for systemic and local immune regulation. To investigate the heterogeneity of iNKT cells, we recharacterized iNKT cells in the thymus and peripheral tissues. iNKT cells in the thymus were divided into three subpopulations by the expression of the natural killer cell receptor CD244 and the chemokine receptor CXCR6 and designated as C0 (CD244 − CXCR6 − ), C1 (CD244 − CXCR6 + ), or C2 (CD244 + CXCR6 + ) iNKT cells. The development and maturation of C2 iNKT cells from C0 iNKT cells strictly depended on IL-15 produced by thymic epithelial cells. C2 iNKT cells expressed high levels of IFN-γ and granzymes and exhibited more NK cell–like features, whereas C1 iNKT cells showed more T cell–like characteristics. C2 iNKT cells were influenced by the microbiome and aging and suppressed the expression of the autoimmune regulator AIRE in the thymus. In peripheral tissues, C2 iNKT cells were circulating that were distinct from conventional tissue-resident C1 iNKT cells. Functionally, C2 iNKT cells protected mice from the tumor metastasis of melanoma cells by enhancing antitumor immunity and promoted antiviral immune responses against influenza virus infection. Furthermore, we identified human CD244 + CXCR6 + iNKT cells with high cytotoxic properties as a counterpart of mouse C2 iNKT cells. Thus, this study reveals a circulating subset of iNKT cells with NK cell–like properties distinct from conventional tissue-resident iNKT cells.

Diagnostic Value of Natural Killer Cells, CD56+ CD16+ Natural Killer Cells, NLRP3, and Lactate Dehydrogenase in Severe/Critical COVID-19: A Prospective Longitudinal Study According to the Severe/Critical COVID-19 Definitions

Innate immunity, as the first line of defense of our immune system, plays a crucial role in defending against SARS-CoV-2 infection and also its immunopathogenesis. We aim to investigate the immune status of natural killer (NK) cells, natural killer T (NKT) cells, and NLRP3 gene expression in COVID-19 patient blood samples. The immunophenotype of NK cell subsets and NKT cells was detected by flow cytometry and the expression of NLRP3 gene assessed by reverse transcriptase real-time polymerase chain reaction in 44 COVID-19 patients and 20 healthy individuals. The percentage of most of NK cell subpopulation and NKT cells was significantly decreased in COVID-19 patients. The percentage of CD56dim CD16- NK cell subsets, and NLRP3 gene expression increased. The percentage of total NK cells, CD56+ CD16+ NK cells, and NLRP3 gene expression had acceptable sensitivity and specificity for assisting diagnosis of severe/critical COVID-19. O₂ saturation% and lactate dehydrogenase levels showed valuable diagnostic value to identify critical cases. The declined NK and NKT cells in COVID-19 patients and enhanced NLRP3 gene expression were associated with disease severity. Total NK cells, CD56+ CD16+ NK cells, and NLRP3 gene expression might be used as meaningful indicators for assisting diagnosis of severe/critical COVID-19.

TCR-engineered iNKT cells induce robust antitumor response by dual targeting cancer and suppressive myeloid cells

Adoptive immunotherapy with T cells engineered with tumor-specific T cell receptors (TCRs) holds promise for cancer treatment. However, suppressive cues generated in the tumor microenvironment (TME) can hinder the efficacy of these therapies, prompting the search for strategies to overcome these detrimental conditions and improve cellular therapeutic approaches. CD1d-restricted invariant natural killer T (iNKT) cells actively participate in tumor immunosurveillance by restricting suppressive myeloid populations in the TME. Here, we showed that harnessing iNKT cells with a second TCR specific for a tumor-associated peptide generated bispecific effectors for CD1d- and major histocompatibility complex (MHC)-restricted antigens in vitro. Upon in vivo transfer, TCR-engineered iNKT (TCR-iNKT) cells showed the highest efficacy in restraining the progression of multiple tumors that expressed the cognate antigen compared with nontransduced iNKT cells or CD8+ T cells engineered with the same TCR. TCR-iNKT cells achieved robust cancer control by simultaneously modulating intratumoral suppressive myeloid populations and killing malignant cells. This dual antitumor function was further enhanced when the iNKT cell agonist α-galactosyl ceramide (α-GalCer) was administered as a therapeutic booster through a platform that ensured controlled delivery at the tumor site, named multistage vector (MSV). These preclinical results support the combination of tumor-redirected TCR-iNKT cells and local α-GalCer boosting as a potential therapy for patients with cancer.

Invariant natural killer T cells minimally influence gut microbiota composition in mice

Invariant Natural Killer T (iNKT) cells are unconventional T cells that respond to glycolipid antigens found in microbes in a CD1d-dependent manner. iNKT cells exert innate-like functions and produce copious amounts of cytokines, chemokines and cytotoxic molecules within only minutes of activation. As such, iNKT cells can fuel or dampen inflammation in a context-dependent manner. In addition, iNKT cells provide potent immunity against bacteria, viruses, parasites and fungi. Although microbiota-iNKT cell interactions are not well-characterized, mounting evidence suggests that microbiota colonization early in life impacts iNKT cell homeostasis and functions in disease. In this study, we showed that CD1d^-/- and Vα14 Tg mice, which lack and have increased numbers of iNKT cells, respectively, had no significant alterations in gut microbiota composition compared to their littermate controls. Furthermore, specific iNKT cell activation by glycolipid antigens only resulted in a transient and minimal shift in microbiota composition when compared to the natural drift found in our colony. Our findings demonstrate that iNKT cells have little to no influence in regulating commensal bacteria at steady state.Abbreviations: iNKT: invariant Natural Killer T cell; αGC: α-galactosylceramide.

Immature granulocytes: Innovative biomarker for SARS‑CoV‑2 infection

Immature granulocytes (IGs) include metamyelocytes, myelocytes and promyelocytes, and are the precursors of neutrophils. Increased IG counts found in peripheral blood indicate an enhanced bone marrow activity. In addition, IGs have been evaluated in numerous clinical conditions, such as severe acute pancreatitis, systemic inflammatory response syndrome and infectious complications following open‑heart surgery under cardiopulmonary bypass. Neutrophils are considered to play a crucial role in the host defense during bacterial and fungal infections, and are involved in the antiviral immune response. Numerous studies have reported the role of neutrophils in coronavirus disease 2019 (COVID‑19) infection, concluding that the percentage of neutrophils may be a predictor of the severity of COVID‑19 infection. There has been limited research regarding the role of neutrophil precursors in viral infections, including severe acute respiratory syndrome coronavirus 2 infection. The present thus aimed to evaluate the role of the IG count in patients hospitalized due to COVID‑19 infection. The patients were predominantly infected with the alpha variant and were all unvaccinated. The IG count was measured and was found to be associated with disease severity, with patient outcomes, with the duration of hospitalization and with the development of complications. The IG count was a significantly associated with the severity of COVID‑19 infection, with greater IG count values being detected in severe and critical cases. In addition, greater IG count values were associated with a longer duration of hospitalization. Furthermore, the IG count was found to be an independent prognostic biomarker of intubation and mortality in patients with COVID‑19, according to multivariate logistic regression analysis, including age, the male sex and the presence of comorbidities as confounders.

Adoptive Immunotherapy With Engineered iNKT Cells to Target Cancer Cells and the Suppressive Microenvironment

Invariant Natural Killer T (iNKT) cells are T lymphocytes expressing a conserved semi-invariant TCR specific for lipid antigens (Ags) restricted for the monomorphic MHC class I-related molecule CD1d. iNKT cells infiltrate mouse and human tumors and play an important role in the immune surveillance against solid and hematological malignancies. Because of unique functional features, they are attractive platforms for adoptive cells immunotherapy of cancer compared to conventional T cells. iNKT cells can directly kill CD1d-expressing cancer cells, but also restrict immunosuppressive myelomonocytic populations in the tumor microenvironment (TME) via CD1d-cognate recognition, promoting anti-tumor responses irrespective of the CD1d expression by cancer cells. Moreover, iNKT cells can be adoptively transferred across MHC barriers without risk of alloreaction because CD1d molecules are identical in all individuals, in addition to their ability to suppress graft vs. host disease (GvHD) without impairing the anti-tumor responses. Within this functional framework, iNKT cells are successfully engineered to acquire a second antigen-specificity by expressing recombinant TCRs or Chimeric Antigen Receptor (CAR) specific for tumor-associated antigens, enabling the direct targeting of antigen-expressing cancer cells, while maintaining their CD1d-dependent functions. These new evidences support the exploitation of iNKT cells for donor unrestricted, and possibly off the shelf, adoptive cell therapies enabling the concurrent targeting of cancer cells and suppressive microenvironment.

Delivery of MERS antigen encapsulated in α-GalCer-bearing liposomes elicits stronger antigen-specific immune responses

Alpha-Galactosylceramide (α-GalCer) effectively activates the natural killer T (NKT) cells to secrete remarkable amounts of Th1 and Th2 cytokines and therefore, acts as a potential immunoadjuvant in vaccine formulation. In the present study, we prepared α-GalCer-bearing or α-GalCer-free liposomes and loaded them with Middle East Respiratory Syndrome Corona virus papain-like protease (α-GalCer-Lip-MERS-CoV PLpro or Lip- MERS-CoV PLpro). These formulations were injected in mice to investigate the antigen-specific humoral and cell-mediated immune responses. The immunization with α-GalCer-Lip-MERS-CoV PLpro or Lip- MERS-CoV PLpro did not induce any notable toxicity in immunized mice. The results demonstrated that mice immunized with α-GalCer-Lip-MERS-CoV PLpro showed greater antigen-specific antibody titer, switching of IgG isotyping to IgG2a subclass and higher lymphocyte proliferation. Moreover, the splenocytes from α-GalCer-Lip-MERS-CoV PLpro immunized mice secreted greater levels of IFN-γ, IL-4, IL-2 and IL-12. Interestingly, a booster dose induced stronger memory immune responses in mice previously immunized with α-GalCer-Lip-MERS-CoV PLpro. In summary, α-GalCer-Lip-MERS-CoV PLpro may prove to be a promising vaccine formulation to protect the individuals against MERS-CoV infection.

Cross Talk Between Natural Killer T and Dendritic Cells and Its Impact on T Cell Responses in Infections

Both innate and adaptive immunity is vital for host defense against infections. Dendritic cells (DCs) are critical for initiating and modulating adaptive immunity, especially for T-cell responses. Natural killer T (NKT) cells are a small population of innate-like T cells distributed in multiple organs. Many studies have suggested that the cross-talk between these two immune cells is critical for immunobiology and host defense mechanisms. Not only can DCs influence the activation/function of NKT cells, but NKT cells can feedback on DCs also, thus modulating the phenotype and function of DCs and DC subsets. This functional feedback of NKT cells on DCs, especially the preferential promoting effect on CD8α+ and CD103+ DC subsets in lymphoid and non-lymphoid tissues, significantly impacts the systemic and local adaptive CD4 and CD8 T cell responses in infections. This review focuses on the two-way interaction between NKT cells and DCs, emphasizing the importance of NKT cell feedback on DCs in bridging innate and adaptive immune responses for host defense purposes.

Development of off-the-shelf hematopoietic stem cell-engineered invariant natural killer T cells for COVID-19 therapeutic intervention

BACKGROUND

New COVID-19 treatments are desperately needed as case numbers continue to rise and emergent strains threaten vaccine efficacy. Cell therapy has revolutionized cancer treatment and holds much promise in combatting infectious disease, including COVID-19. Invariant natural killer T (iNKT) cells are a rare subset of T cells with potent antiviral and immunoregulatory functions and an excellent safety profile. Current iNKT cell strategies are hindered by the extremely low presence of iNKT cells, and we have developed a platform to overcome this critical limitation.

METHODS

We produced allogeneic HSC-engineered iNKT (AlloHSC-iNKT) cells through TCR engineering of human cord blood CD34+ hematopoietic stem cells (HSCs) and differentiation of these HSCs into iNKT cells in an Ex Vivo HSC-Derived iNKT Cell Culture. We then established in vitro SARS-CoV-2 infection assays to assess AlloHSC-iNKT cell antiviral and anti-hyperinflammation functions. Lastly, using in vitro and in vivo preclinical models, we evaluated AlloHSC-iNKT cell safety and immunogenicity for off-the-shelf application.

RESULTS

We reliably generated AlloHSC-iNKT cells at high-yield and of high-purity; these resulting cells closely resembled endogenous human iNKT cells in phenotypes and functionalities. In cell culture, AlloHSC-iNKT cells directly killed SARS-CoV-2 infected cells and also selectively eliminated SARS-CoV-2 infection-stimulated inflammatory monocytes. In an in vitro mixed lymphocyte reaction (MLR) assay and an NSG mouse xenograft model, AlloHSC-iNKT cells were resistant to T cell-mediated alloreaction and did not cause GvHD.

CONCLUSIONS

Here, we report a method to robustly produce therapeutic levels of AlloHSC-iNKT cells. Preclinical studies showed that these AlloHSC-iNKT cells closely resembled endogenous human iNKT cells, could reduce SARS-CoV-2 virus infection load and mitigate virus infection-induced hyperinflammation, and meanwhile were free of GvHD-risk and resistant to T cell-mediated allorejection. These results support the development of AlloHSC-iNKT cells as a promising off-the-shelf cell product for treating COVID-19; such a cell product has the potential to target the new emerging SARS-CoV-2 variants as well as the future new emerging viruses.

Natural killer T cell immunotherapy combined with IL-15-expressing oncolytic virotherapy and PD-1 blockade mediates pancreatic tumor regression

BACKGROUND

Pancreatic cancer is one of the leading causes of cancer death, with a 5-year -year survival rate of less than 10%. This results from late detection, high rates of metastasis, and resistance to standard chemotherapies. Furthermore, chemotherapy and radiation are associated with significant morbidity, underscoring the need for novel therapies. Recent clinical studies have shown that immunotherapies can provide durable outcomes in cancer patients, but successes in pancreatic cancer have been limited. It is likely that novel and combined therapies will be needed to achieve clinical benefits.

METHODS

Using experimental mouse models of pancreatic ductal adenocarcinoma, we examined natural killer T (NKT) cell activation therapy in combination with a recombinant oncolytic vesicular stomatitis virus (VSVΔM51) engineered to express the cytokine IL-15 (VSV-IL-15). Panc02 pancreatic ductal carcinoma cells were implanted subcutaneously or orthotopically into syngeneic C57BL/6 mice. Mice were then treated with VSV expressing green fluorescent protein (VSV-GFP) or VSV-IL-15 and/or NKT cell activation therapy via delivery of α-GalCer-loaded DCs. We further assessed whether the addition of PD-1 blockade could increase the therapeutic benefit of our combination treatment. Three days after NKT cell activation, some groups of mice were treated with anti-PD-1 antibodies weekly for 3 weeks.

RESULTS

VSV-GFP and VSV-IL-15 mediated equal killing of human and mouse pancreatic cancer lines in vitro. In vivo, VSV-IL-15 combined with NKT cell activation therapy to enhance tumor regression and increase survival time over individual treatments, and was also superior to NKT cell therapy combined with VSV-GFP. Enhanced tumor control was associated with increased immune cell infiltration and anti-tumor effector functions (cytotoxicity and cytokine production). While ineffective as a monotherapy, the addition of blocking PD-1 antibodies to the combined protocol sustained immune cell activation and effector functions, resulting in prolonged tumor regression and complete tumor clearance in 20% of mice. Mice who cleared the initial tumor challenge exhibited reduced tumor growth uponon rechallenge, consistent with the formation of immune memory.

CONCLUSION

TThese results demonstrate that NKT cell immunotherapy combined with oncolytic VSV-IL-15 virotherapy and PD-1 blockade enhances tumor control and presents a promising treatment strategy for targeting pancreatic cancer.

Ingestion, Immunity, and Infection: Nutrition and Viral Respiratory Tract Infections

Respiratory infections place a heavy burden on the health care system, particularly in the winter months. Individuals with a vulnerable immune system, such as very young children and the elderly, and those with an immune deficiency, are at increased risk of contracting a respiratory infection. Most respiratory infections are relatively mild and affect the upper respiratory tract only, but other infections can be more serious. These can lead to pneumonia and be life-threatening in vulnerable groups. Rather than focus entirely on treating the symptoms of infectious disease, optimizing immune responsiveness to the pathogens causing these infections may help steer towards a more favorable outcome. Nutrition may have a role in such prevention through different immune supporting mechanisms. Nutrition contributes to the normal functioning of the immune system, with various nutrients acting as energy sources and building blocks during the immune response. Many micronutrients (vitamins and minerals) act as regulators of molecular responses of immune cells to infection. It is well described that chronic undernutrition as well as specific micronutrient deficiencies impair many aspects of the immune response and make individuals more susceptible to infectious diseases, especially in the respiratory and gastrointestinal tracts. In addition, other dietary components such as proteins, pre-, pro- and synbiotics, and also animal- and plant-derived bioactive components can further support the immune system. Both the innate and adaptive defense systems contribute to active antiviral respiratory tract immunity. The initial response to viral airway infections is through recognition by the innate immune system of viral components leading to activation of adaptive immune cells in the form of cytotoxic T cells, the production of neutralizing antibodies and the induction of memory T and B cell responses. The aim of this review is to describe the effects of a range different dietary components on anti-infective innate as well as adaptive immune responses and to propose mechanisms by which they may interact with the immune system in the respiratory tract.

Blocking the human common beta subunit of the GM-CSF, IL-5 and IL-3 receptors markedly reduces hyperinflammation in ARDS models

Acute respiratory distress syndrome (ARDS) is triggered by various aetiological factors such as trauma, sepsis and respiratory viruses including SARS-CoV-2 and influenza A virus. Immune profiling of severe COVID-19 patients has identified a complex pattern of cytokines including granulocyte macrophage-colony stimulating factor (GM-CSF) and interleukin (IL)-5, which are significant mediators of viral-induced hyperinflammation. This strong response has prompted the development of therapies that block GM-CSF and other cytokines individually to limit inflammation related pathology. The common cytokine binding site of the human common beta (β_c) receptor signals for three inflammatory cytokines: GM-CSF, IL-5 and IL-3. In this study, β_c was targeted with the monoclonal antibody (mAb) CSL311 in engineered mice devoid of mouse β_c and β_IL-3 and expressing human β_c (hβ_cTg mice). Direct pulmonary administration of lipopolysaccharide (LPS) caused ARDS-like lung injury, and CSL311 markedly reduced lung inflammation and oedema, resulting in improved oxygen saturation levels in hβ_cTg mice. In a separate model, influenza (HKx31) lung infection caused viral pneumonia associated with a large influx of myeloid cells into the lungs of hβ_cTg mice. The therapeutic application of CSL311 potently decreased accumulation of monocytes/macrophages, neutrophils, and eosinophils without altering lung viral loads. Furthermore, CSL311 treatment did not limit the viral-induced expansion of NK and NKT cells, or the tissue expression of type I/II/III interferons needed for efficient viral clearance. Simultaneously blocking GM-CSF, IL-5 and IL-3 signalling with CSL311 may represent an improved and clinically applicable strategy to reducing hyperinflammation in the ARDS setting.

Mast Cell Activation Triggered by Retrovirus Promotes Acute Viral Infection

Mast cells (MCs) are strategically located at the host-environment interface and their non-allergic roles in the immune-surveillance of pathogens have recently gained more attention. However, MC-caused detrimental regulation of immune inflammations can promote viral invasion. Currently, the role of MCs in retroviral infection remains elusive. We have recently proved that human gut MCs could capture and transfer HIV-1 to CD4⁺ T cells for promoting viral spread; MC-released histamine augments HIV-1-induced functional polarization of dendritic cells to cause immunosuppression via stimulating the differentiation of regulatory T cells. In this study, we used a murine model of MuLV/Friend virus infection to address MC role in acute retroviral infection in vivo. The acute infection of MuLV/Friend virus could be established in C57BL/6 wild type mice, but viral acquisition showed low efficiency in C57BL/6-Kit ^W - ^sh/W - ^sh (Sash) mice which lack MCs. In mechanism, we found that MuLV/Friend virus triggered MC activation for degranulation; MC degranulation subsequently activated the granulocyte-like myeloid derived suppressive cells (G-MDSCs) to inhibit CD8⁺ T cells- and NK cells-mediated antiviral immune responses. The reconstruction of MCs in Sash mice promoted acute retroviral infection by regulating G-MDSCs functions and antiviral immune responses. Importantly, the administration of MC stabilizers to block cell degranulation elevated antiviral immune response and consequently suppressed retrovirus infection. This study uncovers a specific role of MCs in acute retroviral infection and elucidates the underlying immune-mechanisms. Targeting MCs may provide a novel approach for controlling acute infection by retroviruses.

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.

Role of myeloid-derived suppressor cells in viral respiratory infections; Hints for discovering therapeutic targets for COVID-19

The expansion of myeloid-derived suppressor cells (MDSCs), known as heterogeneous population of immature myeloid cells, is enhanced during several pathological conditions such as inflammatory or viral respiratory infections. It seems that the way MDSCs behave in infection depends on the type and the virulence mechanisms of the invader pathogen, the disease stage, and the infection-related pathology. Increasing evidence showing that in correlation with the severity of the disease, MDSCs are accumulated in COVID-19 patients, in particular in those at severe stages of the disease or ICU patients, contributing to pathogenesis of SARS-CoV2 infection. Based on the involved subsets, MDSCs delay the clearance of the virus through inhibiting T-cell proliferation and responses by employing various mechanisms such as inducing the secretion of anti-inflammatory cytokines, inducible nitric oxide synthase (iNOS)-mediated hampering of IFN-γ production, or forcing arginine shortage. While the immunosuppressive characteristic of MDSCs may help to preserve the tissue homeostasis and prevent hyperinflammation at early stages of the infection, hampering of efficient immune responses proved to exert significant pathogenic effects on severe forms of COVID-19, suggesting the targeting of MDSCs as a potential intervention to reactivate T-cell immunity and thereby prevent the infection from developing into severe stages of the disease. This review tried to compile evidence on the roles of different subsets of MDSCs during viral respiratory infections, which is far from being totally understood, and introduce the promising potential of MDSCs for developing novel diagnostic and therapeutic approaches, especially against COVID-19 disease.

ADAM10 partially protects mice against influenza pneumonia by suppressing specific myeloid cell population

The influenza virus infection poses a serious health threat worldwide. Myeloid cells play pivotal roles in regulating innate and adaptive immune defense. A disintegrin and metalloproteinase (ADAM) family of proteins contributes to various immune responses; however, the role of a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) in influenza virus infection remains largely unknown. Herein, we investigated its role, focusing on myeloid cells, during influenza virus infection in mice. ADAM10 gene (Adam10)^flox/flox/Lyz2-Cre (Adam10^ΔLyz2) and control Adam10^flox/flox mice were intranasally infected with 200 plaque-forming units of influenza virus A/H1N1/PR8/34. Adam10^ΔLyz2 mice exhibited a significantly higher mortality rate, stronger lung inflammation, and a higher virus titer in the lungs than control mice. Macrophages and inflammatory cytokines, such as TNF-α, IL-1β, and CCL2, were increased in bronchoalveolar lavage fluid from Adam10^ΔLyz2 mice following infection. CD11b⁺Ly6G^-F4/80⁺ myeloid cells, which had an inflammatory monocyte/macrophage-like phenotype, were significantly increased in the lungs of Adam10^ΔLyz2 mice. Adoptive transfer experiments suggested that these cells likely contributed to the poorer prognosis in Adam10^ΔLyz2 mice. Seven days after infection, CD11b⁺Ly6G^-F4/80⁺ lung cells exhibited significantly higher arginase-1 expression levels in Adam10^ΔLyz2 mice than in control mice, whereas an arginase-1 inhibitor improved the prognosis of Adam10^ΔLyz2 mice. Enhanced granulocyte-macrophage colony-stimulating factor (GM-CSF)/GM-CSF receptor signaling likely contributed to this process. Collectively, these results indicate that myeloid ADAM10 protects against influenza virus pneumonia and may be a promising therapeutic target.

LIGHT of pulmonary NKT cells annihilates tissue protective alveolar macrophages in augmenting severe influenza pneumonia

CD1d-restricted natural killer T (NKT) cells are innate-like T lymphocytes with protective or pathogenic roles in the development of influenza pneumonia. Here, we show that lung-infiltrated and activated NKT cells are the major cellular source of LIGHT/TNFSF14, which determines the severity of pulmonary pneumonia by highly deteriorative influenza A virus (IAV) infection. Compared to wild-type mice, LIGHT^-/- mice exhibit much lower morbidity and mortality to IAV, due to alleviated lung damage and reduced apoptosis of alveolar macrophages (AMs). LIGHT preferentially promotes cell death of lymphotoxin β receptors positive (LTβR⁺) AMs but not herpesvirus entry mediator positive (HVEM⁺) AMs. Therefore, these results suggest that NKT-derived LIGHT augments cell death of the tissue protective AMs in exacerbating lung pathology and susceptibility to fatal influenza infection. Suppression of LIGHT signaling might be a viable option in the treatment of influenza-associated acute respiratory distress syndrome.

The Current Landscape of NKT Cell Immunotherapy and the Hills Ahead

Simple Summary

Natural killer T (NKT) cells are a subset of lipid-reactive T cells that enhance anti-tumor immunity. While preclinical studies have shown NKT cell immunotherapy to be safe and effective, clinical studies lack predictable therapeutic efficacy and no approved treatments exist. In this review, we outline the current strategies, challenges, and outlook for NKT cell immunotherapy.

Abstract

NKT cells are a specialized subset of lipid-reactive T lymphocytes that play direct and indirect roles in immunosurveillance and anti-tumor immunity. Preclinical studies have shown that NKT cell activation via delivery of exogenous glycolipids elicits a significant anti-tumor immune response. Furthermore, infiltration of NKT cells is associated with a good prognosis in several cancers. In this review, we aim to summarize the role of NKT cells in cancer as well as the current strategies and status of NKT cell immunotherapy. This review also examines challenges and future directions for improving the therapy.

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.

The Role of NKT Cells in Glioblastoma

Glioblastoma is an aggressive and deadly cancer, but to date, immunotherapies have failed to make significant strides in improving prognoses for glioblastoma patients. One of the current challenges to developing immunological interventions for glioblastoma is our incomplete understanding of the numerous immunoregulatory mechanisms at play in the glioblastoma tumor microenvironment. We propose that Natural Killer T (NKT) cells, which are unconventional T lymphocytes that recognize lipid antigens presented by CD1d molecules, may play a key immunoregulatory role in glioblastoma. For example, evidence suggests that the activation of type I NKT cells can facilitate anti-glioblastoma immune responses. On the other hand, type II NKT cells are known to play an immunosuppressive role in other cancers, as well as to cross-regulate type I NKT cell activity, although their specific role in glioblastoma remains largely unclear. This review provides a summary of our current understanding of NKT cells in the immunoregulation of glioblastoma as well as highlights the involvement of NKT cells in other cancers and central nervous system diseases.

Harnessing NKT cells for vaccination

Natural killer T (NKT) cells are innate-like T cells capable of enhancing both innate and adaptive immune responses. When NKT cells are stimulated in close temporal association with co-administered antigens, strong antigen-specific immune responses can be induced, prompting the study of NKT cell agonists as novel immune adjuvants. This activity has been attributed to the capacity of activated NKT cells to act as universal helper cells, with the ability to provide molecular signals to dendritic cells and B cells that facilitate T cell and antibody responses, respectively. These signals can override the requirement for conventional CD4⁺ T cell help, so that vaccines can be designed without need to consider CD4⁺ T cell repertoire and major histocompatibility complex Class II diversity. Animal studies have highlighted some drawbacks of the approach, namely, concerns around induction of NKT cell hyporesponsiveness, which may limit vaccine boosting, and potential for toxicity. Here we highlight studies that suggest these obstacles can be overcome by targeted delivery in vivo. We also feature new studies that suggest activating NKT cells can help encourage differentiation of T cells into tissue-resident memory cells that play an important role in prophylaxis against infection, and may be required in cancer therapy.

Viral Respiratory Pathogens and Lung Injury

Several viruses target the human respiratory tract, causing different clinical manifestations spanning from mild upper airway involvement to life-threatening acute respiratory distress syndrome (ARDS). As dramatically evident in the ongoing SARS-CoV-2 pandemic, the clinical picture is not always easily predictable due to the combined effect of direct viral and indirect patient-specific immune-mediated damage. In this review, we discuss the main RNA (orthomyxoviruses, paramyxoviruses, and coronaviruses) and DNA (adenoviruses, herpesviruses, and bocaviruses) viruses with respiratory tropism and their mechanisms of direct and indirect cell damage. We analyze the thin line existing between a protective immune response, capable of limiting viral replication, and an unbalanced, dysregulated immune activation often leading to the most severe complication. Our comprehension of the molecular mechanisms involved is increasing and this should pave the way for the development and clinical use of new tailored immune-based antiviral strategies.