CD1d-restricted human natural killer T cells are highly susceptible to human immunodeficiency virus 1 infection

CD3+CD56+ and CD3-CD56+ lymphocytes in the cerebrospinal fluid of persons with HIV-1 subtypes B and C

The transactivator of transcription (Tat) is a HIV regulatory protein which promotes viral replication and chemotaxis. HIV-1 shows extensive genetic diversity, HIV-1 subtype C being the most dominant subtype in the world. Our hypothesis is the frequency of CSF CD3+CD56+ and CD3-CD56dim is reduced in HIV-1C compared to HIV-1B due to the Tat C30S31 substitution in HIV-1C. 34 CSF and paired blood samples (PWH, n = 20; PWoH, n = 14) were studied. In PWH, the percentage of CD3+CD56+ was higher in CSF than in blood (p < 0.001), comparable in both compartments in PWoH (p = 0.20). The proportion of CD3-CD56dim in CSF in PWH was higher than PWoH (p = 0.008). There was no subtype differences. These results showed CNS compartmentalization of NKT cell response in PWH.

Current Developments in the Preclinical and Clinical use of Natural Killer T cells

Natural killer T (NKT) cells play a pivotal role as a bridge between the innate and the adaptive immune response and are instrumental in the regulation of homeostasis. In this review, we discuss the potential for NKT cells to serve as biodrugs in viral infections and in cancer. NKT cells are being investigated for their use as a prognostic biomarker, an immune adjuvant, and as a form of cellular therapy. Historically, the clinical utility of NKT cells was hampered by their low frequency in the blood, discrepancies in nomenclature, and challenges with ex vivo expansion. However, recent advances in the field have permitted the development of several NKT cell-based preclinical and clinical strategies. These new developments pave the way for the successful implementation of NKT cell-based approaches for the treatment of human disease.

CXCR6 expressing T cells: Functions and role in the control of tumors

CXCR6 is a receptor for the chemokine CXCL16, which exists as a membrane or soluble form. CXCR6 is a marker for resident memory T (TRM) cells that plays a role in immunosurveillance through their interaction with epithelial cells. The interaction of CXCR6 with CXCL16 expressed at the membrane of certain subpopulations of intratumor dendritic cells (DC) called DC3, ideally positions these CXCR6+ T cells to receive a proliferation signal from IL-15 also presented by DC3. Mice deficient in cxcr6 or blocking the interaction of CXCR6 with its ligand, experience a poorer control of tumor proliferation by CD8+ T cells, but also by NKT cells especially in the liver. Intranasal vaccination induces CXCL16 production in the lungs and is associated with infiltration by TRM expressing CXCR6, which are then required for the efficacy of anti-tumor vaccination. Therapeutically, the addition of CXCR6 to specific CAR-T cells enhances their intratumoral accumulation and prolongs survival in animal models of pancreatic, ovarian and lung cancer. Finally, CXCR6 is part of immunological signatures that predict response to immunotherapy based on anti-PD-(L)1 in various cancers. In contrast, a protumoral role of CXCR6+T cells has also been reported mainly in Non-alcoholic steatohepatitis (NASH) due to a non-antigen specific mechanism. The targeting and amplification of antigen-specific TRM expressing CXCR6 and its potential use as a biomarker of response to immunotherapy opens new perspectives in cancer treatment.

ORFV infection enhances CXCL16 secretion and causes oncolysis of lung cancer cells through immunogenic apoptosis

Oncolytic viruses have been emerging as a promising therapeutic option for cancer patients, including lung cancer. Orf virus (ORFV), a DNA parapoxvirus, can infect its natural ungulate hosts and transmit into humans. Moreover, the ORFV has advantages of low toxicity, high targeted, self-amplification and can induce potent Th1-like immunity. This study explored the therapeutic potential of ORFV infection for human lung cancer therapy and investigated the molecular mechanisms. We used a previously described ORFV NA1/11 strain and tested the oncolysis of ORFV NA1/11 in two lines of lung cancer cells in vitro and in vivo. Treatment of both cell lines with ORFV NA1/11 resulted in a decrease in cell viability by inducing cell cycle arrest in G2/M phase, suppressing cyclin B1 expression and increasing their apoptosis in a caspase-dependent manner. The ORFV NA1/11-infected lung cancer cells were highly immunogenic. Evidently, ORFV NA1/11 infection of lung cancer cells induced oncolysis of tumor cells to release danger-associated molecular patterns, and promoted dendritic cell maturation, and CD8 T cell infiltration in the tumors by enhancing CXCL16 secretion. These findings may help to understand the molecular mechanisms of ORFV oncolysis and aid in the development of novel therapies for lung cancer.

Immunomodulatory potential of in vivo natural killer T (NKT) activation by NKTT320 in Mauritian-origin cynomolgus macaques

Invariant natural killer T-lymphocytes (iNKT) are unique immunomodulatory innate T cells with an invariant TCRα recognizing glycolipids presented on MHC class-I-like CD1d molecules. Activated iNKT rapidly secrete pro-and anti-inflammatory cytokines, potentiate immunity, and modulate inflammation. Here, we report the effects of in vivo iNKT activation in Mauritian-origin cynomolgus macaques by a humanized monoclonal antibody, NKTT320, that binds to the invariant region of the iNKT TCR. NKTT320 led to rapid iNKT activation, increased polyfunctionality, and elevation of multiple plasma analytes within 24 hours. Flow cytometry and RNA-Seq confirmed downstream activation of multiple immune subsets, enrichment of JAK/STAT and PI3K/AKT pathway genes, and upregulation of inflammation-modulating genes. NKTT320 also increased iNKT frequency in adipose tissue and did not cause iNKT anergy. Our data indicate that NKTT320 has a sustained effect on in vivo iNKT activation, potentiation of innate and adaptive immunity, and resolution of inflammation, which supports its future use as an immunotherapeutic.

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NKTT320 rapidly activates iNKT in vivo, modulating downstream immune function

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In vivo NKTT320 treatment modulates pro- and anti-inflammatory genes

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NKTT320 treatment results in activation of innate and adaptive immune subsets

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NKTT320 has promise as an immunotherapeutic with translational potential

Immune Response to Viruses

Viruses are essentially, obligate intracellular parasites. They require a host to replicate their genetic material, spread to other cells, and eventually to other hosts. For humans, most viral infections are not considered lethal, regardless if at the cellular level, the virus can obliterate individual cells. Constant genomic mutations, (which can alter the antigenic content of viruses such as influenza or coronaviruses), zoonosis or immunosuppression/immunocompromisation, is when viruses achieve higher host mortality. Frequent examples of the severe consequenses of viral infection can be seen in children and the elderly. In most instances, the immune system will take a multifaceted approach in defending the host against viruses. Depending on the virus, the individual, and the point of entry, the immune system will initiate a robust response which involves multiple components. In this chapter, we expand on the total immune system, breaking it down to the two principal types: Innate and Adaptive Immunity, their different roles in viral recognition and clearance. Finally, how different viruses activate and evade different arms of the immune system.

Preferential and persistent impact of acute HIV-1 infection on CD4+ iNKT cells in colonic mucosa

Evidence suggests that HIV-1 disease progression is determined in the early stages of infection. Here, preinfection invariant natural killer T (iNKT) cell levels were predictive of the peak viral load during acute HIV-1 infection (AHI). Furthermore, iNKT cells were preferentially lost in AHI. This was particularly striking in the colonic mucosa, where iNKT cells were depleted more profoundly than conventional CD4⁺ T cells. The initiation of antiretroviral therapy during AHI-prevented iNKT cell dysregulation in peripheral blood but not in the colonic mucosa. Overall, our results support a model in which iNKT cells are early and preferential targets for HIV-1 infection during AHI.

Acute HIV-1 infection (AHI) results in the widespread depletion of CD4⁺ T cells in peripheral blood and gut mucosal tissue. However, the impact on the predominantly CD4⁺ immunoregulatory invariant natural killer T (iNKT) cells during AHI remains unknown. Here, iNKT cells from peripheral blood and colonic mucosa were investigated during treated and untreated AHI. iNKT cells in blood were activated and rapidly depleted in untreated AHI. At the time of peak HIV-1 viral load, these cells showed the elevated expression of cell death–associated transcripts compared to preinfection. Residual peripheral iNKT cells suffered a diminished responsiveness to in vitro stimulation early into chronic infection. Additionally, HIV-1 DNA, as well as spliced and unspliced viral RNA, were detected in iNKT cells isolated from blood, indicating the active infection of these cells in vivo. The loss of iNKT cells occurred from Fiebig stage III in the colonic mucosa, and these cells were not restored to normal levels after initiation of ART during AHI. CD4⁺ iNKT cells were depleted faster and more profoundly than conventional CD4⁺ T cells, and the preferential infection of CD4⁺ iNKT cells over conventional CD4⁺ T cells was confirmed by in vitro infection experiments. In vitro data also provided evidence of latent infection in iNKT cells. Strikingly, preinfection levels of peripheral blood CD4⁺ iNKT cells correlated directly with the peak HIV-1 load. These findings support a model in which iNKT cells are early targets for HIV-1 infection, driving their rapid loss from circulation and colonic mucosa.

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.

Brief Report: Diminished Coinhibitory Molecule 2B4 Expression Is Associated With Preserved iNKT Cell Phenotype in HIV Long-Term Nonprogressors

BACKGROUND

We have previously shown an association of elevated coinhibitory molecule 2B4 expression with iNKT cells alterations in HIV disease. Herein, we show a comparative analysis of 2B4 expression on iNKT cells of HIV long-term nonprogressors (LTNPs) and progressors.

METHODS

Antiretroviral therapy-naive HIV-seropositive individuals (progressors, n = 16) and LTNPs (n = 10) were recruited for this study. We used multicolor flow cytometry on frozen peripheral blood mononuclear cells to determine iNKT subset frequencies, the levels of coinhibitory 2B4 expression, and intracellular interferon-γ (IFN-γ) production. CD1d tetramer was used to characterize iNKT cells.

RESULTS

We report significantly lower level of 2B4 expression on bulk LTNPs iNKT cells and on their CD4 subsets compared with HIV progressors. Furthermore, the iNKT cells from LTNPs produced higher amount of IFN-γ than HIV progressors as detected by intracellular cytokine staining. Interestingly, the frequency of 2B4iNKT cells of progressors but not LTNPs significantly correlates with CD4 T-cell count, HIV viral load, and IFN-γ production by iNKT cells.

CONCLUSION

Our results suggest that in addition to suppressed HIV replication, diminished 2B4 expression and associated coinhibitory signaling, and substantial production of IFN-γ could contribute to preserved iNKT cell phenotype in LTNPs.

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.

Invariant Natural Killer T-cell Dynamics in Human Immunodeficiency Virus-associated Tuberculosis

Background

Tuberculosis (TB) is the leading cause of mortality and morbidity in people living with human immunodeficiency virus (HIV) infection (PLWH). PLWH with TB disease are at risk of the paradoxical TB-associated immune reconstitution inflammatory syndrome (TB-IRIS) when they commence antiretroviral therapy. However, the pathophysiology is incompletely understood and specific therapy is lacking. We investigated the hypothesis that invariant natural killer T (iNKT) cells contribute to innate immune dysfunction associated with TB-IRIS.

Methods

In a cross-sectional study of 101 PLWH and HIV-uninfected South African patients with active TB and controls, iNKT cells were enumerated using α-galactosylceramide-loaded CD1d tetramers and subsequently functionally characterized by flow cytometry. In a second study of 49 people with HIV type 1 (HIV-1) and active TB commencing antiretroviral therapy, iNKT cells in TB-IRIS patients and non-IRIS controls were compared longitudinally.

Results

Circulating iNKT cells were reduced in HIV-1 infection, most significantly the CD4⁺ subset, which was inversely associated with HIV-1 viral load. iNKT cells in HIV-associated TB had increased surface CD107a expression, indicating cytotoxic degranulation. Relatively increased iNKT cell frequency in patients with HIV-1 infection and active TB was associated with development of TB-IRIS following antiretroviral therapy initiation. iNKT cells in TB-IRIS were CD4⁺CD8^– subset depleted and degranulated around the time of TB-IRIS onset.

Conclusions

Reduced iNKT cell CD4⁺ subsets as a result of HIV-1 infection may skew iNKT cell functionality toward cytotoxicity. Increased CD4^– cytotoxic iNKT cells may contribute to immunopathology in TB-IRIS.

Differential skewing of donor-unrestricted and γδ T cell repertoires in tuberculosis-infected human lungs

Unconventional T cells that recognize mycobacterial antigens are of great interest as potential vaccine targets against tuberculosis (TB). This includes donor-unrestricted T cells (DURTs), such as mucosa-associated invariant T cells (MAITs), CD1-restricted T cells, and γδ T cells. We exploited the distinctive nature of DURTs and γδ T cell receptors (TCRs) to investigate the involvement of these T cells during TB in the human lung by global TCR sequencing. Making use of surgical lung resections, we investigated the distribution, frequency, and characteristics of TCRs in lung tissue and matched blood from individuals infected with TB. Despite depletion of MAITs and certain CD1-restricted T cells from the blood, we found that the DURT repertoire was well preserved in the lungs, irrespective of disease status or HIV coinfection. The TCRδ repertoire, in contrast, was highly skewed in the lungs, where it was dominated by Vδ1 and distinguished by highly localized clonal expansions, consistent with the nonrecirculating lung-resident γδ T cell population. These data show that repertoire sequencing is a powerful tool for tracking T cell subsets during disease.

Perturbation of mucosal-associated invariant T cells and iNKT cells in HIV infection

PURPOSE OF REVIEW

To analyze the possible role that the 'unconventional' T-cell populations mucosal-associated invariant T cell (MAIT) and iNKT cells play during HIV infection and following antiretroviral therapy (ART) treatment.

RECENT FINDINGS

A substantial body of evidence now demonstrates that both MAIT and iNKT cells are depleted in blood during HIV infection. The depletion and dysfunction of MAIT and iNKT cells are only partially restored by suppressive ART, potentially contributing to HIV-related comorbidities.

SUMMARY

The deficiency and dysfunction of MAIT and iNKT T-cell subsets likely impact on immunity to important coinfections including Mycobacterium tuberculosis. This underscores the importance of research on restoring these unconventional T cells during HIV infection. Future studies in this field should address the challenge of studying tissue-resident cells, particularly in the gut, and better defining the determinants of MAIT/iNKT cell dysfunction. Such studies could have a significant impact on improving the immune function of HIV-infected individuals.

Dendritic Cell Maturation Regulates TSPAN7 Function in HIV-1 Transfer to CD4+ T Lymphocytes

Dendritic cells (DCs) serve a key function in host defense, linking innate detection of microbes to activation of pathogen-specific adaptive immune responses. DCs express cell surface receptors for HIV-1 entry, but are relatively resistant to productive viral replication. They do, however, facilitate infection of co-cultured T-helper cells through a process referred to as trans-infection. We previously showed that tetraspanin 7 (TSPAN7), a transmembrane protein, is involved, through positive regulation of actin nucleation, in the transfer of HIV-1 from the dendrites of immature monocyte-derived DCs (iMDDCs) to activated CD4⁺ T lymphocytes. Various molecular mechanisms have been described regarding HIV-1 trans-infection and seem to depend on DC maturation status. We sought to investigate the crosstalk between DC maturation status, TSPAN7 expression and trans-infection. We followed trans-infection through co-culture of iMDDCs with CD4⁺ T lymphocytes, in the presence of CXCR4-tropic replicative-competent HIV-1 expressing GFP. T cell infection, DC maturation status and dendrite morphogenesis were assessed through time both by flow cytometry and confocal microscopy. Our previously described TSPAN7/actin nucleation-dependent mechanism of HIV-1 transfer appeared to be mostly observed during the first 20 h of co-culture experiments and to be independent of HIV replication. In the course of co-culture experiments, we observed a progressive maturation of MDDCs, correlated with a decrease in TSPAN7 expression, a drastic loss of dendrites and a change in the shape of DCs. A TSPAN7 and actin nucleation-independent mechanism of trans-infection, relying on HIV-1 replication, was then at play. We discovered that TSPAN7 expression is downregulated in response to different innate immune stimuli driving DC maturation, explaining the requirement for a TSPAN7/actin nucleation-independent mechanism of HIV transfer from mature MDDCs (mMDDCs) to T lymphocytes. As previously described, this mechanism relies on the capture of HIV-1 by the I-type lectin CD169/Siglec-1 on mMDDCs and the formation of a “big invaginated pocket” at the surface of DCs, both events being tightly regulated by DC maturation. Interestingly, in iMDDCs, although CD169/Siglec-1 can capture HIV-1, this capture does not lead to HIV-1 transfer to T lymphocytes.

Suppression of R5-type of HIV-1 in CD4+ NKT cells by Vδ1+ T cells activated by flavonoid glycosides, hesperidin and linarin

We established transfectants expressing T cell receptors (TCRs) either for Vγ1 and Vδ1 (1C116) or for Vγ2 and Vδ2 (2C21) using the TCR-deficient Jurkat T cell line J.RT3-T3.5. The amount of IL-2 secreted from these γδ T cell clones accurately indicated TCR-dependent stimulation. Clone 2C21 was specifically stimulated by previously reported ligands for Vγ2Vδ2 (Vδ2)-TCR such as isopentenyl pyrophospate (IPP), ethylamine, or risedronate. In contrast, clone 1C116 was strongly stimulated through the Vγ1Vδ1 (Vδ1)-TCR by flavonoid glycosides such as hesperidin and linarin, having both rutinose at the A ring and methoxy (-OCH3) substitution at the B ring. Additionally, hesperidin and linarin showed stimulatory activity for peripheral blood mononuclear cell (PBMC)-derived T cells expressing Vδ1-TCR; these activated Vδ1⁺ T cells also secreted IL-5, IL-13, MIP-1α, MIP-1β and RANTES. Such PBMC-derived Vδ1⁺ T cells stimulated by hesperidin and linarin suppressed R5-HIV-1-NL(AD8) viral replication in CD4⁺ NKT cells in a dose-dependent manner. To the best of our knowledge, this is the first demonstration that flavonoid glycosides activate functional Vδ1⁺ T cells.

Mucosal Immunity in HIV/SIV Infection: T Cells, B Cells and Beyond

As our understanding of mucosal immunity increases, it is becoming clear that the host response to HIV-1 is more complex and nuanced than originally believed. The mucosal landscape is populated with a variety of specialized cell types whose functions include combating infectious agents while preserving commensal microbiota, maintaining barrier integrity, and ensuring immune homeostasis. Advances in multiparameter flow cytometry, gene expression analysis and bioinformatics have allowed more detailed characterization of these cell types and their roles in host defense than was previously possible. This review provides an overview of existing literature on immunity to HIV-1 and SIVmac in mucosal tissues of the female reproductive tract and the gastrointestinal tract, focusing on major effector cell populations and briefly summarizing new information on tissue resident memory T cells, T_reg, Th17, Th22 and innate lymphocytes (ILC), subsets that have been studied primarily in the gastrointestinal mucosa.

Adipose Tissue T Cells in HIV/SIV Infection

Adipose tissue comprises one of the largest organs in the body and performs diverse functions including energy storage and release, regulation of appetite and other neuroendocrine signaling, and modulation of immuity, among others. Adipocytes reside in a complex compartment where antigen, antigen presenting cells, innate immune cells, and adaptive immune cells interact locally and exert systemic effects on inflammation, circulating immune cell profiles, and metabolic homeostasis. T lymphocytes are a major component of the adipose tissue milieu which are altered in disease states such as obesity and human immunodeficiency virus (HIV) infection. While obesity, HIV infection, and simian immunodeficiency virus (SIV; a non-human primate virus similar to HIV) infection are accompanied by enrichment of CD8⁺ T cells in the adipose tissue, major phenotypic differences in CD4⁺ T cells and other immune cell populations distinguish HIV/SIV infection from obesity. Furthermore, DNA and RNA species of HIV and SIV can be detected in the stromal vascular fraction of visceral and subcutaneous adipose tissue, and replication-competent HIV resides in local CD4⁺ T cells. Here, we review studies of adipose tissue CD4⁺ and CD8⁺ T cell populations in HIV and SIV, and contrast the findings with those reported in obesity.

Plasma levels of the proangiogenic protein CXCL16 remains elevated for 1 month after minimally invasive colorectal cancer resection

BACKGROUND

Inflammation-induced endothelial precursor cell recruitment and angiogenesis are thought to be associated with CXCL16-CXCR6 pair activity. This study's main purpose was to determine plasma CXCL16 levels after minimally invasive colorectal resection (MICR) for colorectal cancer (CRC); an adjunct study assessed wound fluid (WF) and plasma CXCL16 levels in a separate group of CRC patients.

METHODS

CRC patients who had MICR and for whom plasma was available in a tissue bank were eligible. Plasma samples were collected preoperatively from all patients. Samples were also collected on postoperative days (POD) 1 and 3 and at various late postoperative time points (POD 7-34). In a separate study, blood and intra-abdominal wound fluid (WF) samples were collected from CRC MICR patients (pts). Samples were stored at - 80 °C. CXCL16 levels were determined via ELISA. The Wilcoxon signed-rank and Mann and Whitney tests were used for analysis.

RESULTS

Main study: 86 CRC pts. were included. The mean preoperative plasma CXCL16 level was 2.36 ± 0.57 ng/ml. Elevated mean plasma levels (p <  0.0001 × first 4 time points) were noted on POD 1 (2.82 ± 0.81, n = 86), POD 3 (3.12 ± 0.77, n = 82), POD 7-13 (3.28 ± 0.88, n = 64), POD 14-20 (3.03 ± 0.62, n = 24), POD 21-27 (3.06 ± 0.67, n = 20, p = 0.0003), and POD 28-34 (3.17 ± 0.43, n = 11, p = 0.001) vs. preop levels. WF study: In the adjunct study, plasma and WF CXCL16 levels were determined for 23 CRC MICR pts. WF levels at all time points were significantly elevated over plasma levels.

CONCLUSION

Plasma CXCL16 levels were elevated for 4 weeks after minimally invasive colorectal resection for cancer. Also, WF CXCL16 levels were 3-10 times greater than the corresponding plasma concentrations. The source of the late plasma elevations may be the healing wound. Increased plasma CXCL16 levels may promote tumor angiogenesis in the first month after MICR.

Latent Mycobacterium tuberculosis Infection Is Associated With a Higher Frequency of Mucosal-Associated Invariant T and Invariant Natural Killer T Cells

Increasing drug resistance and the lack of an effective vaccine are the main factors contributing to Mycobacterium tuberculosis (Mtb) being a major cause of death globally. Despite intensive research efforts, it is not well understood why some individuals control Mtb infection and some others develop active disease. HIV-1 infection is associated with an increased incidence of active tuberculosis, even in virally suppressed individuals. Mucosal-associated invariant T (MAIT) and invariant natural killer T (iNKT) cells are innate T cells that can recognize Mtb-infected cells. Contradicting results regarding the frequency of MAIT cells in latent Mtb infection have been reported. In this confirmatory study, we investigated the frequency, phenotype, and IFNγ production of MAIT and iNKT cells in subjects with latent or active Mtb infection. We found that the frequency of both cell types was increased in subjects with latent Mtb infection compared with uninfected individuals or subjects with active infection. We found no change in the expression of HLA-DR, PD-1, and CCR6, as well as the production of IFNγ by MAIT and iNKT cells, among subjects with latent Mtb infection or uninfected controls. The proportion of CD4- CD8+ MAIT cells in individuals with latent Mtb infection was, however, increased. HIV-1 infection was associated with a loss of MAIT and iNKT cells, and the residual cells had elevated expression of the exhaustion marker PD-1. Altogether, the results suggest a role for MAIT and iNKT cells in immunity against Mtb and show a deleterious impact of HIV-1 infection on those cells.

Functional Invariant Natural Killer T Cells Secreting Cytokines Are Associated With Non-Progressive Human Immunodeficiency Virus-1 Infection but Not With Suppressive Anti-Retroviral Treatment

Background

CD1d restricted invariant natural killer T (iNKT) cells are important in the activation and regulation of immune responses. Limited information is available regarding the functional role of iNKT cells in the human immunodeficiency virus (HIV) disease progression.

Methodology

α-GalCer stimulated iNKT cells were characterized for their functionality in terms of cytokine production (IFN-γ, TNF-α, IL-2, IL-4, and IL-21) and CD107a expression in HIV-1 infected [23 long-term non progressors (LTNPs), 28 progressors, 18 patients before and after suppressive anti-retroviral treatment (ART)] along with 25 HIV-1 negative subjects using multicolor flow cytometry.

Results

The functional profile of α-GalCer stimulated iNKT cells was similar in LTNPs and healthy controls. The number of LTNPs showing functional response in terms of secretion of cytokines (IFN-γ/IL2/TNF-α) and CD107a expression was significantly higher than seen in the progressors. The cytokine secretion by the stimulated iNKT cells was predominantly Th1 type. The frequencies of iNKT cells showing secretion of IFN-γ or IL2 or TNF-α or expression of CD107a were higher in LTNPs (p < 0.05 for all) and also significantly associated with lower plasma viral load (p value ranged from 0.04 to 0.003) and higher CD4 count (p value ranged from 0.02 to <0.0001). The functional profile of the iNKT cells before and after ART did not differ significantly indicating absence of restoration of iNKT cells functionality after suppressive ART. The IL-4 and IL-21 secreting iNKT cells were rare in all study populations.

Conclusion

The presence of functional iNKT cells secreting number of cytokines in non-progressive HIV infection could be one of the multiple factors required to achieve HIV control and hence have relevance in understanding the immunity in HIV infection. The failure of restoration of the iNKT functionality after ART should be potential area of future research.

Immune evasion of the CD1d/NKT cell axis

Many reviews on the CD1d/NKT cell axis focus on the ability of CD1d-restricted NKT cells to serve as effector cells in a variety of disorders, be they infectious diseases, cancer or autoimmunity. In contrast, here, we discuss the ways that viruses, bacteria and tumor cells can evade the CD1d/NKT cell axis. As a result, these disease states have a better chance to establish a foothold and potentially cause problems for the subsequent adaptive immune response, as the host tries to rid itself of infections or tumors.

The Immune Response to Mycobacterium tuberculosis in HIV-1-Coinfected Persons

Globally, about 36.7 million people were living with HIV infection at the end of 2015. The most frequent infection co-occurring with HIV-1 is Mycobacterium tuberculosis-374,000 deaths per annum are attributable to HIV-tuberculosis, 75% of those occurring in Africa. HIV-1 infection increases the risk of tuberculosis by a factor of up to 26 and alters its clinical presentation, complicates diagnosis and treatment, and worsens outcome. Although HIV-1-induced depletion of CD4⁺ T cells underlies all these effects, more widespread immune deficits also contribute to susceptibility and pathogenesis. These defects present a challenge to understand and ameliorate, but also an opportunity to learn and optimize mechanisms that normally protect people against tuberculosis. The most effective means to prevent and ameliorate tuberculosis in HIV-1-infected people is antiretroviral therapy, but this may be complicated by pathological immune deterioration that in turn requires more effective host-directed anti-inflammatory therapies to be derived.

CD1-Restricted T Cells During Persistent Virus Infections: "Sympathy for the Devil"

Some of the clinically most important viruses persist in the human host after acute infection. In this situation, the host immune system and the viral pathogen attempt to establish an equilibrium. At best, overt disease is avoided. This attempt may fail, however, resulting in eventual loss of viral control or inadequate immune regulation. Consequently, direct virus-induced tissue damage or immunopathology may occur. The cluster of differentiation 1 (CD1) family of non-classical major histocompatibility complex class I molecules are known to present hydrophobic, primarily lipid antigens. There is ample evidence that both CD1-dependent and CD1-independent mechanisms activate CD1-restricted T cells during persistent virus infections. Sophisticated viral mechanisms subvert these immune responses and help the pathogens to avoid clearance from the host organism. CD1-restricted T cells are not only crucial for the antiviral host defense but may also contribute to tissue damage. This review highlights the two edged role of CD1-restricted T cells in persistent virus infections and summarizes the viral immune evasion mechanisms that target these fascinating immune cells.

Natural Killer T Cells: An Ecological Evolutionary Developmental Biology Perspective

Type I natural killer T (NKT) cells are innate-like T lymphocytes that recognize glycolipid antigens presented by the MHC class I-like protein CD1d. Agonistic activation of NKT cells leads to rapid pro-inflammatory and immune modulatory cytokine and chemokine responses. This property of NKT cells, in conjunction with their interactions with antigen-presenting cells, controls downstream innate and adaptive immune responses against cancers and infectious diseases, as well as in several inflammatory disorders. NKT cell properties are acquired during development in the thymus and by interactions with the host microbial consortium in the gut, the nature of which can be influenced by NKT cells. This latter property, together with the role of the host microbiota in cancer therapy, necessitates a new perspective. Hence, this review provides an initial approach to understanding NKT cells from an ecological evolutionary developmental biology (eco-evo-devo) perspective.

CD1d-Restricted Natural Killer T Cells Are Preserved in Indian Long-Term Nonprogressors

BACKGROUND

Natural killer T (NKT) cells act as a bridge between innate and adaptive immune responses. Limited information is available regarding the role of NKT cells in the HIV disease progression especially HIV-1 C infection.

METHODOLOGY

NKT cells were characterized for their frequency and the activation, aging, exhaustion status, and their proliferation ability in 32 long-term nonprogressors (LTNPs), 40 progressors, 18 patients before and after suppressive combination antiretroviral therapy (cART) along with 35 HIV-1-negative subjects using multicolor flow cytometry.

RESULTS

The frequencies of total NKT cells and their subpopulation were significantly higher in LTNPs as compared with those obtained in progressors (P < 0.0001) and were significantly associated with higher CD4 counts and with lower plasma viral loads. The percentage of activated, aged, and exhausted NKT cells were significantly lower in LTNPs as compared with the progressors and inversely correlated with CD4 count and positively with plasma viral loads. The NKT cells from the LTNPs showed higher proliferation ability. The frequency and proliferation ability of the NKT cells were partially restored after 12 months of suppressive cART but still lower than the levels in LTNPs. The degree of restoration after cART was similar in both CD4 and CD4 NKT cells.

CONCLUSION

The findings demonstrate significant association of preserved NKT cells with the nonprogressive HIV infection and also showed that exhausted NKT cells are associated with disease progression. Further characterization of their functionality and assessment of sustenance in HIV infection will help to understand the HIV pathogenesis and to develop immune therapies.

Increased plasma sCXCL16 levels may have a relationship with Th1/Th2 imbalance in primary immune thrombocytopenia

Primary immune thrombocytopenia (ITP) is a disease of autoimmunity in which there are Th1/Th2 imbalance and disordered cytokine profiles. CXC chemokine ligand 16 (CXCL16) was proved to implicate in some autoimmune diseases. Our research aimed to determine plasma soluble CXCL16 (sCXCL16) levels and its effects in ITP. We used ELISA to measure plasma sCXCL16, IFN-γ and IL-4 and flow cytometry to determine expression of CXCR6 on lymphocyte subsets. We used real-time PCR to detect the CXCL16 and CXCR6 mRNA expression. Additionally, plasma sCXCL16, CXCL16 and CXCR6 mRNA levels of 8 patients were monitored before and after treatment. We found that patients with active ITP had higher circulating sCXCL16 in plasma than healthy controls and patients in remission. Meanwhile, negative relationships between sCXCL16 and platelet count, IL-4 and positive relationships between sCXCL16 and IFN-γ, IFN-γ/IL-4 ratio were observed. Besides, expression of CXCR6 on lymphocyte subsets and mRNA levels of CXCL16 and CXCR6 were all increased in active ITP. Additionally, plasma sCXCL16 and IFN-γ levels and CXCR6 mRNA expression were down-regulated after effective treatment compared with those before treatment. Thus, increased plasma sCXCL16 might be implicated in the pathogenesis of ITP and have a relationship with Th1/Th2 imbalance.

CD4+CD8β+ double-positive T cells in skin-draining lymph nodes respond to inflammatory signals from the skin

CD4⁺CD8⁺ double-positive (DP), mature, peripheral T cells are readily detectable in a variety of species and tissues. Despite a common association with autoimmune and malignant skin disorders, however, little is understood about their role or function. Herein, we show that DP T cells are readily detectable in the blood, spleen, and peripheral lymph nodes of naïve C57BL/6 mice. DP T cells were also present in Jα18^-/- and CD1d^-/- mice, indicating that these cells are not NK-T cells. After skin administration of CASAC adjuvant, but not Quil A adjuvant, both total DP T cells and skin-infiltrating DP T cells increased in number. We explored the possibility that DP T cells could represent aggregates between CD4⁺ and CD8⁺ single-positive T cells and found strong evidence that a large proportion of apparent DP T cells were indeed aggregates. However, the existence of true CD4⁺CD8⁺ DP T cells was confirmed by Amnis ImageStream (Millipore Sigma, Billerica, MA, USA) imaging. Multiple rounds of FACS sorting separated true DP cells from aggregates and indicated that conventional analyses may lead to ∼10-fold overestimation of DP T cell numbers. The high degree of aggregate contamination and overestimation of DP abundance using conventional analysis techniques may explain discrepancies reported in the literature for DP T cell origin, phenotype, and function.

Negative Checkpoint Regulatory Molecule 2B4 (CD244) Upregulation Is Associated with Invariant Natural Killer T Cell Alterations and Human Immunodeficiency Virus Disease Progression

The CD1d-restricted invariant natural killer T (iNKT) cells are implicated in innate immune responses against human immunodeficiency virus (HIV). However, the determinants of cellular dysfunction across the iNKT cells subsets are seldom defined in HIV disease. Herein, we provide evidence for the involvement of the negative checkpoint regulator (NCR) 2B4 in iNKT cell alteration in a well-defined cohort of HIV-seropositive anti-retroviral therapy (ART) naïve, ART-treated, and elite controllers (ECs). We report on exaggerated 2B4 expression on iNKT cells of HIV-infected treatment-naïve individuals. In sharp contrast to CD4⁻iNKT cells, 2B4 expression was significantly higher on CD4⁺ iNKT cell subset. Notably, an increased level of 2B4 on iNKT cells was strongly correlated with parameters associated with HIV disease progression. Further, iNKT cells from ART-naïve individuals were defective in their ability to produce intracellular IFN-γ. Together, our results suggest that the levels of 2B4 expression and the downstream co-inhibitory signaling events may contribute to impaired iNKT cell responses.

Natural killer T cells contribute to the control of acute retroviral infection

Background

Natural killer T cells (NKT cells) play an important role in the immunity against viral infections. They produce cytokines or have direct cytolytic effects that can restrict virus replication. However, the exact function of NKT cells in retroviral immunity is not fully elucidated. Therefore, we analyzed the antiretroviral functions of NKT cells in mice infected with the Friend retrovirus (FV).

Results

After FV infection numbers of NKT cells remained unchanged but activation as well as improved effector functions of NKT cells were found. While the release of pro-inflammatory cytokines was not changed after infection, activated NKT cells revealed an elevated cytotoxic potential. Stimulation with α-Galactosylceramide significantly increased not only total NKT cell numbers and activation but also the anti-retroviral capacity of NKT cells.

Conclusion

We demonstrate a strong activation and a potent cytolytic function of NKT cells during acute retroviral infection. Therapeutic treatment with α-Galactosylceramide could further improve the reduction of early retroviral replication by NKT cells, which could be utilized for future treatment against viral infections.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-017-0327-8) contains supplementary material, which is available to authorized users.

Bacteroides are associated with GALT iNKT cell function and reduction of microbial translocation in HIV-1 infection

Invariant natural killer T (iNKT) cells are innate-like T cells that respond to lipid antigens presented by CD1d. These immunoregulatory cells have the capacity for rapid cytokine release after antigen recognition and are essential for the activation of multiple arms of the immune response. HIV-1 infection is associated with iNKT cell depletion in the peripheral blood; however, their role in the gastrointestinal-associated lymphoid tissue (GALT) is less well studied. Our results show that iNKT cells are found at a higher frequency in GALT compared with blood, particularly in HIV-1 elite controllers. The capacity of iNKT cells to produce interleukin-4 (IL-4) and IL-10 in the GALT was associated with less immune activation and lower markers of microbial translocation, whereas regulatory T cell frequency showed positive associations with immune activation. We hypothesized that the composition of the microbiota would influence iNKT cell frequency and function. We found positive associations between the abundance of several Bacteroides species and iNKT cell frequency and their capacity to produce IL-4 in the GALT but not in the blood. Overall, our results are consistent with the hypothesis that GALT iNKT cells, influenced by certain bacterial species, may have a key role in regulating immune activation in HIV-1 infection.

Th1 and Th17 proinflammatory profile characterizes invariant natural killer T cells in virologically suppressed HIV+ patients with low CD4+/CD8+ ratio

INTRODUCTION

Scanty data exist on the phenotype and functionality of invariant natural killer T (iNKT) cells in HIV-infected (HIV+) patients.

METHODS

By flow cytometry, we studied iNKT cells from 54 HIV+ patients who started combined antiretroviral therapy and had undetectable viral load for more than 1 year. Twenty-five maintained a CD4/CD8 ratio less than 0.4, whereas 29 reached a ratio more than 1.1; 32 age-matched and sex-matched patients were healthy controls (CTR).

RESULTS

Patients with low ratio had lower percentage of CD4 iNKT cells compared with patients with high ratio and higher CD8 iNKT cell percentage; double-negative iNKT cells were lower in HIV+ patients compared with CTR. Patients with low ratio had higher percentage of CD4 and double-negative iNKT cells expressing CD38 and HLA-DR compared with patients with high ratio. CD4 iNKT cells expressing PD-1 were higher in patients with CD4/CD8 ratio less than 0.4, whereas double-negative iNKT cells expressing PD-1 were lower compared with patients with ratio more than 1.1. Patients with low ratio had higher CD4 iNKT cells producing IL-17, CD8 iNKT cells producing IFN-γ, TNF-α or IFN-γ and TNF-α, and double-negative iNKT cells producing IL-17 or IL-17 and IFN-γ compared with CTR. Activated CD4 (or CD8) T cells correlated with activated CD4 (or CD8) iNKT cells, as well as the percentages of CD4 (or CD8) T cells expressing PD-1 was correlated to that of CD4 (or CD8) iNKT cells expressing PD-1.

CONCLUSION

Low CD4/CD8 ratio despite effective combined antiretroviral therapy is associated with altered iNKT cell subsets, enhanced activation, and prominent Th1/Th17 proinflammatory profile.

Innate Invariant NKT Cell Recognition of HIV-1-Infected Dendritic Cells Is an Early Detection Mechanism Targeted by Viral Immune Evasion

Invariant NKT (iNKT) cells are innate-like T cells that respond rapidly with a broad range of effector functions upon recognition of glycolipid Ags presented by CD1d. HIV-1 carries Nef- and Vpu-dependent mechanisms to interfere with CD1d surface expression, indirectly suggesting a role for iNKT cells in control of HIV-1 infection. In this study, we investigated whether iNKT cells can participate in the innate cell-mediated immune response to HIV-1. Infection of dendritic cells (DCs) with Nef- and Vpu-deficient HIV-1 induced upregulation of CD1d in a TLR7-dependent manner. Infection of DCs caused modulation of enzymes in the sphingolipid pathway and enhanced expression of the endogenous glucosylceramide Ag. Importantly, iNKT cells responded specifically to rare DCs productively infected with Nef- and Vpu-defective HIV-1. Transmitted founder viral isolates differed in their CD1d downregulation capacity, suggesting that diverse strains may be differentially successful in inhibiting this pathway. Furthermore, both iNKT cells and DCs expressing CD1d and HIV receptors resided in the female genital mucosa, a site where HIV-1 transmission occurs. Taken together, these findings suggest that innate iNKT cell sensing of HIV-1 infection in DCs is an early immune detection mechanism, which is independent of priming and adaptive recognition of viral Ag, and is actively targeted by Nef- and Vpu-dependent viral immune evasion mechanisms.

Elevated levels of invariant natural killer T-cell and natural killer cell activation correlate with disease progression in HIV-1 and HIV-2 infections

Objective:

In this study, we aimed to investigate the frequency and activation of invariant natural killer T (iNKT) cells and natural killer (NK) cells among HIV-1, HIV-2, or dually HIV-1/HIV-2 (HIV-D)-infected individuals, in relation to markers of disease progression.

Design:

Whole blood samples were collected from treatment-naive HIV-1 (n = 23), HIV-2 (n = 34), and HIV-D (n = 11) infected individuals, as well as HIV-seronegative controls (n = 25), belonging to an occupational cohort in Guinea-Bissau.

Methods:

Frequencies and activation levels of iNKT and NK cell subsets were analysed using multicolour flow cytometry, and results were related to HIV-status, CD4⁺ T-cell levels, viral load, and T-cell activation.

Results:

HIV-1, HIV-D, and viremic HIV-2 individuals had lower numbers of CD4⁺ iNKT cells in circulation compared with seronegative controls. Numbers of CD56^bright NK cells were also reduced in HIV-infected individuals as compared with control study participants. Notably, iNKT cell and NK cell activation levels, assessed by CD38 expression, were increased in HIV-1 and HIV-2 single, as well as dual, infections. HIV-2 viremia was associated with elevated activation levels in CD4⁺ iNKT cells, CD56^bright, and CD56^dim NK cells, as compared with aviremic HIV-2 infection. Additionally, disease markers such as CD4⁺ T-cell percentages, viral load, and CD4⁺ T-cell activation were associated with CD38 expression levels of both iNKT and NK cells, which activation levels also correlated with each other.

Conclusion:

Our data indicate that elevated levels of iNKT-cell and NK-cell activation are associated with viremia and disease progression markers in both HIV-1 and HIV-2 infections.

Human Immunodeficiency Virus Infection and Host Defense in the Lungs

Immunosuppression associated with human immunodeficiency virus (HIV) infection impacts all components of host defense against pulmonary infection. Cells within the lung have altered immune function and are important reservoirs for HIV infection. The host immune response to infected lung cells further compromises responses to a secondary pathogenic insult. In the upper respiratory tract, mucociliary function is impaired and there are decreased levels of salivary immunoglobulin A. Host defenses in the lower respiratory tract are controlled by alveolar macrophages, lymphocytes, and polymorphonuclear leukocytes. As HIV infection progresses, lung CD4 T cells are reduced in number causing a lack of activation signals from CD4 T cells and impaired defense by macrophages. CD8 T cells, on the other hand, are increased in number and cause lymphocytic alveolitis. Specific antibody responses by B-lymphocytes are decreased and opsonization of microorganisms is impaired. These observed defects in host defense of the respiratory tract explain the susceptibility of HIV-infected persons for oropharyngeal candidiasis, bacterial pneumonia, Pneumocystis pneumonia, and other opportunistic infections.

HIV Disrupts Human T Cells That Target Mycobacterial Glycolipids

Single-cell analysis captures the heterogeneity of T-cell populations that target defined antigens. Human immunodeficiency virus (HIV) infection results in defects of antimycobacterial immunity, which remain poorly defined. We therefore recruited a small number of subjects, including those with latent and active M. tuberculosis infection, with or without concomitant HIV infection, and tracked the mycobacterial glycolipid-reactive T-cell repertoire by using CD1b tetramers. Glycolipid-reactive T cells expressed memory markers and the HIV coreceptors CD4 and CCR5; they were not detected in subjects with HIV-associated active M. tuberculosis infection. HIV infection may affect T cells that recognize mycobacterial glycolipids and influence immunity.

iNKT Cells and Their Potential Lipid Ligands during Viral Infection

Invariant natural killer T (iNKT) cells are a unique population of lipid-reactive CD1d-restricted innate-like T lymphocytes. Despite being a minor population, they serve as an early source of cytokines and promote immunological crosstalk thus bridging innate and adaptive immunity. Diseases ranging from allergy, autoimmunity, and cancer, as well as infectious diseases, including viral infection, have been reported to be influenced by iNKT cells. However, it remains unclear how iNKT cells are activated during viral infection, as virus-derived lipid antigens have not been reported. Cytokines may activate iNKT cells during infections from influenza and murine cytomegalovirus, although CD1d-dependent activation is evident in other viral infections. Several viruses, such as dengue virus, induce CD1d upregulation, which correlates with iNKT cell activation. In contrast, herpes simplex virus type 1 (HSV-1), human immunodeficiency virus (HIV), Epstein–Barr virus, and human papilloma virus promote CD1d downregulation as a strategy to evade iNKT cell recognition. These observations suggest the participation of a CD1d-dependent process in the activation of iNKT cells in response to viral infection. Endogenous lipid ligands, including phospholipids as well as glycosphingolipids, such as glucosylceramide, have been proposed to mediate iNKT cell activation. Pro-inflammatory signals produced during viral infection may stimulate iNKT cells through enhanced CD1d-dependent endogenous lipid presentation. Furthermore, viral infection may alter lipid composition and inhibit endogenous lipid degradation. Recent advances in this field are reviewed.

Regulation of NKT Cell Localization in Homeostasis and Infection

Natural killer T (NKT) cells are a specialized subset of T lymphocytes that regulate immune responses in the context of autoimmunity, cancer, and microbial infection. Lipid antigens derived from bacteria, parasites, and fungi can be presented by CD1d molecules and recognized by the canonical T cell receptors on NKT cells. Alternatively, NKT cells can be activated through recognition of self-lipids and/or pro-inflammatory cytokines generated during infection. Unlike conventional T cells, only a small subset of NKT cells traffic through the lymph nodes under homeostatic conditions, with the largest NKT cell populations localizing to the liver, lungs, spleen, and bone marrow. This is thought to be mediated by differences in chemokine receptor expression profiles. However, the impact of infection on the tissue localization and function of NKT remains largely unstudied. This review focuses on the mechanisms mediating the establishment of peripheral NKT cell populations during homeostasis and how tissue localization of NKT cells is affected during infection.

The Response of CD1d-Restricted Invariant NKT Cells to Microbial Pathogens and Their Products

Invariant natural killer T (iNKT) cells become activated during a wide variety of infections. This includes organisms lacking cognate CD1d-binding glycolipid antigens recognized by the semi-invariant T cell receptor of iNKT cells. Additional studies have shown that iNKT cells also become activated in vivo in response to microbial products such as bacterial lipopolysaccharide, a potent inducer of cytokine production in antigen-presenting cells (APCs). Other studies have shown that iNKT cells are highly responsive to stimulation by cytokines such as interleukin-12. These findings have led to the concept that microbial pathogens can activate iNKT cells either directly via glycolipids or indirectly by inducing cytokine production in APCs. iNKT cells activated in this manner produce multiple cytokines that can influence the outcome of infection, usually in favor of the host, although potent iNKT cell activation may contribute to an uncontrolled cytokine storm and sepsis. One aspect of the response of iNKT cells to microbial pathogens is that it is short-lived and followed by an extended time period of unresponsiveness to reactivation. This refractory period may represent a means to avoid chronic activation and cytokine production by iNKT cells, thus protecting the host against some of the negative effects of iNKT cell activation, but potentially putting the host at risk for secondary infections. These effects of microbial pathogens and their products on iNKT cells are not only important for understanding the role of these cells in immune responses against infections but also for the development of iNKT cell-based therapies.

Activation and Function of iNKT and MAIT Cells

Over the last two decades, it has been established that peptides are not the only antigens recognized by T lymphocytes. Here, we review information on two T lymphocyte populations that recognize nonpeptide antigens: invariant natural killer T cells (iNKT cells), which respond to glycolipids, and mucosal associated invariant T cells (MAIT cells), which recognize microbial metabolites. These two populations have a number of striking properties that distinguish them from the majority of T cells. First, their cognate antigens are presented by nonclassical class I antigen-presenting molecules; CD1d for iNKT cells and MR1 for MAIT cells. Second, these T lymphocyte populations have a highly restricted diversity of their T cell antigen receptor α chains. Third, these cells respond rapidly to antigen or cytokine stimulation by producing copious amounts of cytokines, such as IFNγ, which normally are only made by highly differentiated effector T lymphocytes. Because of their response characteristics, iNKT and MAIT cells act at the interface of innate and adaptive immunity, participating in both types of responses. In this review, we will compare these two subsets of innate-like T cells, with an emphasis on the various ways that lead to their activation and their participation in antimicrobial responses.

CD4+/CD8+ double-positive T cells: more than just a developmental stage?

CD4(+)/CD8(+) DP thymocytes are a well-described T cell developmental stage within the thymus. However, once differentiated, the CD4(+) lineage or the CD8(+) lineage is generally considered to be fixed. Nevertheless, mature CD4(+)/CD8(+) DP T cells have been described in the blood and peripheral lymphoid tissues of numerous species, as well as in numerous disease settings, including cancer. The expression of CD4 and CD8 is regulated by a very strict transcriptional program involving the transcription factors Runx3 and ThPOK. Initially thought to be mutually exclusive within CD4(+) and CD8(+) T cells, CD4(+)/CD8(+) T cell populations, outside of the thymus, have recently been described to express concurrently ThPOK and Runx3. Considerable heterogeneity exists within the CD4(+)/CD8(+) DP T cell pool, and the function of CD4(+)/CD8(+) T cell populations remains controversial, with conflicting reports describing cytotoxic or suppressive roles for these cells. In this review, we describe how transcriptional regulation, lineage of origin, heterogeneity of CD4 and CD8 expression, age, species, and specific disease settings influence the functionality of this rarely studied T cell population.

A possible origin of emerged HIV-1 after interrupting anti-retroviral therapy

Although HIV-1 can be successfully eradicated from the circulating blood of HIV-1-infected individuals using anti-retroviral therapy (ART), HIV-1 virions emerge immediately after the interruption of ART. This study was aimed to investigate the origin of the emerged HIV-1. After obtaining informed consent, blood samples from nine HIV-1-infected individuals and endoscopic ileum samples from five of the individuals were obtained. Purified peripheral mononuclear cells (PBMCs)and ileum cells were analyzed by flow-cytometry, and the V3 loop sequences of the HIV-1 envelope protein were determined. By comparing the V3 loop sequences of the samples, we confirmed that the provirus hidden in the CD4(+) PBMCs was not the source of the HIV-1 that emerged after the interruption of ART. Although free virus and HIV-1-p24 antigen (p24)-positive cells were not seen in the blood of patients receiving ART, proviral DNA and p24 could be detected in the ileum from the same patient. Among the HIV-1-infected CD4(+) cells in the ileum samples, Vα24(+) natural killer T (NKT) cells were the major p24-positive cells. These results suggest that the innate NKTcells in the mucosal compartment are the most likely candidates for the origin of the HIV-1 that emerged after ART was interrupted.

Invariant natural killer T (iNKT) cells in HAART-treated, HIV-positive patients with bone and cardiovascular impairment

Background

Invariant Natural Killer T (iNKT) cells represent a determinant in the course of infections and diseases, however, their role in the pathogenesis of non-infectious co-morbidities in HIV-positive patients is unknown.

Methods

Flow cytometry was used to investigate iNKT cell frequency, phenotype and function in HIV-infected patients on HAART with bone and/or cardiovascular disorders and in HIV-positive controls free from co-morbidities.

Results

iNKT cells from subjects with bone and cardiovascular impairment expressed high levels of CD161 and predominantly secreted TNF. iNKT cells from individuals with bone disease alone did not show any distinctive phenotypical or functional characteristics. The functional capacity of iNKT cells in patients with cardiovascular disorder was impaired with no cytokine release upon stimulation.

Conclusion

iNKT cells may have a role in non-infectious co-morbidities in treated HIV disease, possibly through the exacerbation of inflammation. Further studies are needed to investigate iNKT cells in the pathogenesis of non-communicable disorders in HIV infection.

Inhibition of R5-tropic HIV type-1 replication in CD4⁺ natural killer T cells by γδ T lymphocytes

After the development of highly active anti-retroviral therapy, it became clear that the majority of emergent HIV-1 is macrophage-tropic and infects CD4⁺, CCR5-expressing cells (R5-tropic). There are three distinct cell populations, R5-tropic, HIV-1-susceptible CD4⁺ cells: (i) natural killer T (NKT) cells, (ii) dendritic cells and macrophages, and (iii) tissue-associated T cells residing primarily at mucosal surfaces. We have confirmed that CD4⁺ NKT cells derived from peripheral blood mononuclear cells (PBMCs) predominantly express CCR5 rather than CXCR4, whereas the reverse is true for CD4⁺ T cells derived from circulating PBMCs, and that R5-tropic HIV-1 expands efficiently in the CD4⁺ NKT cells. Moreover, when PBMCs depleted of CD8α⁺ cells were stimulated in the presence of α-galactosylceramide (α-GalCer) and R5-tropic HIV-1 [NL(AD8)], the production of HIV-1 virions was not suppressed, whereas, similar to the untreated PBMCs, depletion of CD8β⁺ cells from PBMCs significantly inhibited virion production. These findings suggest that CD8αα⁺ but not CD8αβ⁺ cells may have the ability to inhibit R5-tropic HIV-1 replication in CD4⁺ NKT cells. Here, we show that co-culturing R5-tropic HIV-1-infected CD4⁺ NKT cells with CD8αα⁺ γδ T cells, in particular Vγ1Vδ1 cells, but not with CD8αα⁺ NKT cells or CD8αα⁺ dendritic cells, inhibits HIV-1 replication mainly by secreting chemokines, such as macrophage inflammatory proteins 1α and 1β and RANTES. Collectively, these results indicate the importance of CD8αα⁺ γδ T cells in the control of R5-tropic HIV-1 replication and persistence in CD4⁺ NKT cells.

NKT cell depletion in humans during early HIV infection

Natural killer T (NKT) cells bridge across innate and adaptive immune responses and have an important role in chronic viral infections such as human immunodeficiency virus (HIV). NKT cells are depleted during chronic HIV infection, but the timing, drivers and implications of this NKT cell depletion are poorly understood. We studied human peripheral blood NKT cell levels, phenotype and function in 31 HIV-infected subjects not on antiretroviral treatment from a mean of 4 months to 2 years after HIV infection. We found that peripheral CD4(+) NKT cells were substantially depleted and dysfunctional by 4 months after HIV infection. The depletion of CD4(+) NKT cells was more marked than the depletion of total CD4(+) T cells. Further, the early depletion of NKT cells correlated with CD4(+) T-cell decline, but not HIV viral levels. Levels of activated CD4(+) T cells correlated with the loss of NKT cells. Our studies suggest that the early loss of NKT cells is associated with subsequent immune destruction during HIV infection.

Interleukins 15 and 12 in combination expand the selective loss of natural killer T cells in HIV infection in vitro

The present study evaluated the frequency and receptor expression pattern of invariant natural killer T (iNKT) cells in human immunodeficiency virus (HIV)-infected individuals. Further, the effect of IL-15 + IL-12 stimulation on iNKT cells was also assessed. The study included 15 individuals each from normal healthy subjects, pulmonary tuberculosis patients, HIV-infected individuals, and patients with HIV and tuberculosis coinfection (HIV-TB). The frequency of iNKT cells and the expression of phenotype, cytotoxic and chemokine receptors were studied by flow cytometry. The number of iNKT cells was significantly depleted in HIV and HIV-TB patients, which upon IL-15 + IL-12 stimulation expanded in HIV. The constitutively expressed natural cytotoxicity receptor, NKp46 was increased in HIV and HIV-TB, which might be the host's response to HIV replication. The distinct expression patterns of chemokine and adhesion receptors suggest that iNKT subsets might traffic to different microenvironment and tissues. High expression of chemokine receptor CCR5 by most iNKT cells suggests that these cells might be more favorable targets of HIV infection. Our results show that IL-15 and IL-12 combination has the ability to expand the selective depletion of iNKT cells in vitro in HIV-infected individuals, but of limited value when coinfected with TB.

In-vivo stimulation of macaque natural killer T cells with α-galactosylceramide

Natural killer T cells are a potent mediator of anti-viral immunity in mice, but little is known about the effects of manipulating NKT cells in non-human primates. We evaluated the delivery of the NKT cell ligand, α-galactosylceramide (α-GalCer), in 27 macaques by studying the effects of different dosing (1-100 μg), and delivery modes [directly intravenously (i.v.) or pulsed onto blood or peripheral blood mononuclear cells]. We found that peripheral NKT cells were depleted transiently from the periphery following α-GalCer administration across all delivery modes, particularly in doses of ≥10 μg. Furthermore, NKT cell numbers frequently remained depressed at i.v. α-GalCer doses of >10 μg. Levels of cytokine expression were also not enhanced after α-GalCer delivery to macaques. To evaluate the effects of α-GalCer administration on anti-viral immunity, we administered α-GalCer either together with live attenuated influenza virus infection or prior to simian immunodeficiency virus (SIV) infection of two macaques. There was no clear enhancement of influenza-specific T or B cell immunity following α-GalCer delivery. Further, there was no modulation of pathogenic SIVmac251 infection following α-GalCer delivery to a further two macaques in a pilot study. Accordingly, although macaque peripheral NKT cells are modulated by α-GalCer in vivo, at least for the dosing regimens tested in this study, this does not appear to have a significant impact on anti-viral immunity in macaque models.

IVIg immune reconstitution treatment alleviates the state of persistent immune activation and suppressed CD4 T cell counts in CVID

Common variable immunodeficiency (CVID) is characterized by defective B cell function, impaired antibody production, and increased susceptibility to bacterial infections. Here, we addressed the hypothesis that poor antibody-mediated immune control of infections may result in substantial perturbations in the T cell compartment. Newly diagnosed CVID patients were sampled before, and 6-12 months after, initiation of intravenous immunoglobulin (IVIg) therapy. Treatment-naïve CVID patients displayed suppressed CD4 T cell counts and myeloid dendritic cell (mDC) levels, as well as high levels of immune activation in CD8 T cells, CD4 T cells, and invariant natural killer T (iNKT) cells. Expression of co-stimulatory receptors CD80 and CD83 was elevated in mDCs and correlated with T cell activation. Levels of both FoxP3+ T regulatory (Treg) cells and iNKT cells were low, whereas soluble CD14 (sCD14), indicative of monocyte activation, was elevated. Importantly, immune reconstitution treatment with IVIg partially restored the CD4 T cell and mDC compartments. Treatment furthermore reduced the levels of CD8 T cell activation and mDC activation, whereas levels of Treg cells and iNKT cells remained low. Thus, primary deficiency in humoral immunity with impaired control of microbial infections is associated with significant pathological changes in cell-mediated immunity. Furthermore, therapeutic enhancement of humoral immunity with IVIg infusions alleviates several of these defects, indicating a relationship between poor antibody-mediated immune control of infections and the occurrence of abnormalities in the T cell and mDC compartments. These findings help our understanding of the immunopathogenesis of primary immunodeficiency, as well as acquired immunodeficiency caused by HIV-1 infection.