MAIT cells come to the rescue in cancer immunotherapy?

Recent progress in immunobiology has led to the observation that, among cells classically categorized as the typical representatives of the adaptive immune system, i.e., T cells, some possess the phenotype of innate cells. Invariant T cells are characterized by T cell receptors recognizing a limited range of non-peptide antigens, presented only in the context of particular molecules. Mucosal-associated invariant T cells (MAIT cells) are an example of such unconventional cells. In humans, they constitute between 1% and 8% of the peripheral blood T lymphocytes and are further enriched in mucosal tissues, mesenteric lymph nodes, and liver, where they can account for even 40% of all the T cells. MAIT cells recognize antigens in the context of major histocompatibility complex class I-related protein (MR1). Upon activation, they instantly release pro-inflammatory cytokines and mediate cytolytic function towards bacterially infected cells. As such, they have been a rapidly evolving research topic not only in the field of infectious diseases but also in the context of many chronic inflammatory diseases and, more recently, in immuno-oncology. Novel findings suggest that MAIT cells function could also be modulated by endogenous ligands and drugs, making them an attractive target for therapeutic approaches. In this review, we summarize the current understanding of MAIT cell biology, their role in health and disease and discuss their future potential in cancer immunotherapy. This is discussed through the prism of knowledge and experiences with invariant natural killer T cells (iNKT)—another prominent unconventional T cell subset that shares many features with MAIT cells

Exploring the Functional Role of Helios in Mucosal Associated Invariant T Cells using siRNA.

Mucosal associated invariant T (MAIT) cells are a fairly recently described population of innate-like T cells. In humans, MAIT cells represent an exceptionally abundant population in the blood, where they account for 1–10% of all T cells. However, compared to conventional T cells, which can display an almost unlimited T cell receptor (TCR) repertoire, the specificities of MAIT cell TCRs are limited. This evolutionarily conserved subset displays a semi-invariant TCR which recognises riboflavin metabolites, produced by a wide range of bacteria and fungi, and presented on the major histocompatibility complex (MHC)-class I related (MR1) molecule. The function and significance of MAIT cells in health and disease have only started to be unravelled, and it is becoming increasingly clear that MAIT cells are also modulated in non-microbial diseases. Interestingly, MAIT cells have been shown to exhibit a relatively high expression of the transcription factor, Helios, compared to most other T cell subsets. The function of this translational activator and repressor, encoded by the gene IKZF2, in the MAIT cell population remains obscure. This study focused on the functional role Helios may play in regulating the activation of MAIT cells. Thus, by using siRNA to silence Helios expression, and flow cytometry to analyse any potential alterations in MAIT cell activation markers, we aimed to be able to characterise the kinetics and functional role of Helios in peripheral MAIT cells of healthy individuals. Here, we clearly established a striking upregulation of Helios in MAIT cells following 24 hours of stimulation. Moreover, we were able to achieve a >50% knockdown of Helios at the protein level, in this subset of T cells. Nevertheless, no significant difference in any of the activation markers we investigated was present between the MAIT cells with reduced Helios expression and their controls. This could, however, of occurred as a result of the toxicity that the transfection had on the functionally of the T cells. From these results, it is difficult to conclude any clear role for Helios in the activation of MAIT cells, and consequently, further research needs to be performed before any clear conclusions can be drawn

Insights Into Mucosal-Associated Invariant T Cell Biology From Studies of Invariant Natural Killer T Cells

Mucosal-associated invariant T (MAIT) cells and invariant natural killer T (iNKT) cells are innate-like T cells that function at the interface between innate and adaptive immunity. They express semi-invariant T cell receptors (TCRs) and recognize unconventional non-peptide ligands bound to the MHC Class I-like molecules MR1 and CD1d, respectively. MAIT cells and iNKT cells exhibit an effector-memory phenotype and are enriched within the liver and at mucosal sites. In humans, MAIT cell frequencies dwarf those of iNKT cells, while in laboratory mouse strains the opposite is true. Upon activation via TCR- or cytokine-dependent pathways, MAIT cells and iNKT cells rapidly produce cytokines and show direct cytotoxic activity. Consequently, they are essential for effective immunity, and alterations in their frequency and function are associated with numerous infectious, inflammatory, and malignant diseases. Due to their abundance in mice and the earlier development of reagents, iNKT cells have been more extensively studied than MAIT cells. This has led to the routine use of iNKT cells as a reference population for the study of MAIT cells, and such an approach has proven very fruitful. However, MAIT cells and iNKT cells show important phenotypic, functional, and developmental differences that are often overlooked. With the recent availability of new tools, most importantly MR1 tetramers, it is now possible to directly study MAIT cells to understand their biology. Therefore, it is timely to compare the phenotype, development, and function of MAIT cells and iNKT cells. In this review, we highlight key areas where MAIT cells show similarity or difference to iNKT cells. In addition, we discuss important avenues for future research within the MAIT cell field, especially where comparison to iNKT cells has proven less informative

THE EFFECT OF ACUTE EXERCISE ON MUCOSAL ASSOCIATED INVARIANT T-CELL ACTIVITY IN MODERATELY TRAINED YOUNG MALES

Purpose: To determine circulating mucosal associated invariant T (MAIT) cell number, frequency and activation and chemokine receptor expression in response to submaximal exercise. Methods: 20 young men performed a VO2max test and then exercised for 40 minutes at 86% of ventilatory threshold (VT). Immune cells were isolated from blood samples obtained at rest and after 0h and 1h of recovery. Results: MAIT cell counts significantly increased by 92% (p=0.003) at 0h before returning to baseline at 1h. MAIT cells were preferentially mobilized, rising from 2.9% of T-cells at baseline to 4.5% at 0h and 4.6% at 1h (p=0.002). MAIT cell chemokine and activation marker expression was not affected by exercise. Conclusion: MAIT cells follow a biphasic response and are preferentially mobilized within the T cell subsets. MAIT cell numbers expressing activation and homing markers following exercise are higher but are driven by the exercise-stimulated lymphocytosis, rather than intrinsic cellular changes.Master of Art

MAIT cells launch a rapid, robust and distinct hyperinflammatory response to bacterial superantigens and quickly acquire an anergic phenotype that impedes their cognate antimicrobial function: Defining a novel mechanism of superantigen-induced immunopathology and immunosuppression

Superantigens (SAgs) are potent exotoxins secreted by Staphylococcus aureus and Streptococcus pyogenes. They target a large fraction of T cell pools to set in motion a "cytokine storm" with severe and sometimes life-threatening consequences typically encountered in toxic shock syndrome (TSS). Given the rapidity with which TSS develops, designing timely and truly targeted therapies for this syndrome requires identification of key mediators of the cytokine storm's initial wave. Equally important, early host responses to SAgs can be accompanied or followed by a state of immunosuppression, which in turn jeopardizes the host's ability to combat and clear infections. Unlike in mouse models, the mechanisms underlying SAg-associated immunosuppression in humans are ill-defined. In this work, we have identified a population of innate-like T cells, called mucosa-associated invariant T (MAIT) cells, as the most powerful source of pro-inflammatory cytokines after exposure to SAgs. We have utilized primary human peripheral blood and hepatic mononuclear cells, mouse MAIT hybridoma lines, HLA-DR4-transgenic mice, MAIThighHLA-DR4+ bone marrow chimeras, and humanized NOD-scid IL-2Rγnull mice to demonstrate for the first time that: i) mouse and human MAIT cells are hyperresponsive to SAgs, typified by staphylococcal enterotoxin B (SEB); ii) the human MAIT cell response to SEB is rapid and far greater in magnitude than that launched by unfractionated conventional T, invariant natural killer T (iNKT) or γδ T cells, and is characterized by production of interferon (IFN)-γ, tumor necrosis factor (TNF)-α and interleukin (IL)-2, but not IL-17A; iii) high-affinity MHC class II interaction with SAgs, but not MHC-related protein 1 (MR1) participation, is required for MAIT cell activation; iv) MAIT cell responses to SEB can occur in a T cell receptor (TCR) Vβ-specific manner but are largely contributed by IL-12 and IL-18; v) as MAIT cells are primed by SAgs, they also begin to develop a molecular signature consistent with exhaustion and failure to participate in antimicrobial defense. Accordingly, they upregulate lymphocyte-activation gene 3 (LAG-3), T cell immunoglobulin and mucin-3 (TIM-3), and/or programmed cell death-1 (PD-1), and acquire an anergic phenotype that interferes with their cognate function against Klebsiella pneumoniae and Escherichia coli; vi) MAIT cell hyperactivation and anergy co-utilize a signaling pathway that is governed by p38 and MEK1/2. Collectively, our findings demonstrate a pathogenic, rather than protective, role for MAIT cells during infection. Furthermore, we propose a novel mechanism of SAg-associated immunosuppression in humans. MAIT cells may therefore provide an attractive therapeutic target for the management of both early and late phases of severe SAg-mediated illnesses

Altered populations of unconventional T Cell lineages in patients with Langerhans Cell Histiocytosis

Langerhans cell histiocytosis (LCH) lesions are defined by the presence of CD1a+/CD207+ myeloid cells, but many other immune cells are present including unconventional T cells, which have powerful immunoregulatory functions. Unconventional T cell lineages include mucosal-associated invariant T (MAIT) cells, type I natural killer T (NKT) cells and gamma-delta (γδ) T cells, which are associated with many inflammatory conditions, although their importance has not been studied in LCH. We characterized their phenotype and function in blood and lesions from patients with LCH, and identified a deficiency in MAIT cell frequency and abnormalities in the subset distributions of γδ T cells and NKT cells. Such abnormalities are associated with immune dysregulation in other disease settings and are therefore potentially important in LCH. Our study is the first to recognize alterations to MAIT cell proportions in patients with LCH. This finding along with other abnormalities identified amongst unconventional T cells could potentially influence the onset and progression of LCH, thereby highlighting potential targets for new immune based therapies

Investigation of unconventional T cells in patients with haematological malignancies

Haematological malignancies involve the uncontrolled division of white blood cells, which can lead to an accumulation of these cells in lymphoid organs and cause the disruption of normal immune function. Multiple Myeloma (MM) and Myelodysplastic syndromes (MDS) are the most common haematological disorders among the elderly (Elidrissi Errahhali et al, 2016), but despite recent advances in treatment options, most individuals with MM or MDS eventually relapse and succumb to the disease (Rjkumar 2020 and Schurch 2018 and Kumar et al, 2012). The association of immune defects with MM and MDS may be a factor in disease progression, therefore it is important to develop a comprehensive understanding of how the immune system changes throughout the progression of these diseases, so that more effective treatment options can be developed. This thesis presents a detailed analysis of the frequency, phenotype and function of conventional T cells, unconventional T cells and antigen presenting cells (APC) throughout the progression of MM and MDS. This analysis has identified a range of immune abnormalities within these patient groups, including novel findings that provide new insights into disease progression and potential new targets for immune therapies. Some of the abnormalities we identified in patients with MM and MDS include; a reduction in the frequency of unconventional T cell (Natural Killer T (NKT) cells and Mucosal Associated Invariant T (MAIT) cells), as well as reduced frequencies of various APC populations. We also reported an increased expression of chronic activation and exhaustion markers on CD8+ T cells and MAIT cells, despite their retention of functional capacity. Importantly, the abnormalities we observed in patients with MM were consistent from the pre-malignant disease stage to active disease, which has not been shown previously suggesting that many of these defects are present from very early in disease development. We also identified key differences in the frequency and phenotype of conventional T cells, unconventional T cells and APC between patients with MM and those with MDS. Together highlighting the many different immune changes that are occurring within these patients groups and the importance of analysing haematological malignancies as individual diseases rather than as a collective. One of the most significant findings in this thesis was the alteration in frequency and phenotype of MAIT cells within the blood of patients with MM and MDS. MAIT cells may have important roles in anti-tumour immunity, so we explored the potential causes of these changes, including soluble factors and cell-to-cell interactions between MAIT cells and APC. Interestingly, we found MM patient plasma contained increased levels of IL-18, which is a cytokine known to influence MAIT cell function. This led us to establishing a long term in vitro culture of sorted MAIT cells supplemented with IL-18, finding that culturing MAIT cells with IL-18 lead to rapid expansion of MAIT cells without otherwise alternating their phenotype or function. We next established a novel mixed-donor MAIT cell co-culture system to examine the interactions between sorted healthy MAIT cells and APC from patients. This system uniquely allowed us to investigate whether abnormal patient APC were capable of stimulating MAIT cells and whether MAIT cell responses were altered as a result of this interaction. Whilst this was conducted as a pilot study to look for potentially important interactions rather than significance, we did conclude that culturing healthy donor MAIT cells with APC from monoclonal gammopathy of undetermined significance (MGUS) and MM patients did not lead to alterations in phenotype. The development and application of these long term MAIT cell cultures shed new light on how MAIT cell defects emerge in MM and MDS, and has also provided valuable insights into optimal MAIT cell growth conditions, which could be applied in the future to analyse other complex disease settings and for the use in therapeutic approaches. Our research was the first comprehensive study to characterise immune system alterations at both the individual cell population level and to examine their functional interactions throughout all stages of MM and in MDS. We discovered a range of novel findings which have greatly improved our understanding of the role that these various immune cells populations might play in MM and MDS, and identified new areas of study that could lead to improved disease management.Doctor of Philosoph

Characterisation of Mucosal Associated Invariant T cells function and metabolism in health and obesity

Obesity has developed into a worldwide pandemic, affecting individuals regardless of their socio-economic status, gender or age. It is associated with development of multiple co-morbidities including type 2 diabetes mellitus, which have been shown to be underpinned by inflammation. Indeed, excessive adiposity has been shown to be associated with a large dysregulation of immune cell function, including altered phenotype of mucosal-associated invariant T (MAIT) cells. MAIT cells from people with obesity were shown to have enhanced IL-17 production, accompanied by impaired IFNγ expression. As of now, very little is known about the control of MAIT cell function, therefore more research is required to understand their biology in order to identify the altered process, which leads to their dysfunction in obesity. Immunometabolism of MAIT cells became the focus of this thesis as previous data indicated it as a key biological process that controls immune cell function. Here we confirmed previously published data, showing that MAIT cells are potent producers of IFNγ and IL-17 cytokines and that MAIT cells can proliferate and expand upon stimulation. In addition, we reported that MAIT cells enhance glycolysis upon activation, which in turn is controlled by the influx of amino acids into the cells via LAT1 amino acid transporters. Glycolytic metabolism was required for successful IFNγ production as well as proliferation and expansion of MAIT cells. People with obesity have impaired IFNγ expression and MAIT cell expansion that was accompanied by impaired glycolytic metabolism. Collectively our data indicates that MAIT cells effector functions are in part controlled by the intrinsic metabolic pathways including the glycolytic metabolism. Defect in glycolysis or glycolysis-associated pathways as observed in obesity, leads to their dysfunction and altered immune cells responses

MAIT cells altered phenotype and cytotoxicity in lupus patients are linked to renal disease severity and outcome

IntroductionSystemic lupus erythematosus (SLE) is an autoimmune disease in which circulating immune complexes can cause different types of glomerulonephritis, according to immune deposits and to the type of glomerular cell injury. Proliferative lesions represent the most severe form of lupus nephritis (LN) and often lead to kidney failure and death. Mucosal-associated invariant T (MAIT) cells are a subset of innate-like T cells that recognize microbial-derived ligands from the riboflavin synthesis pathway. Although abundant in peripheral blood, MAIT cells are enriched in mucosal and inflamed tissues. While previous studies have reported concordant results concerning lower MAIT cell frequencies in the blood of SLE patients, no information is known about MAIT cell function and LN severity and outcome.MethodsIn the current study, we analyzed the baseline phenotype and function of peripheral blood MAIT cells by flow cytometry in 26 patients with LN and in a control group of 16 healthy individuals.ResultsWe observe that MAIT cell frequencies are markedly reduced in blood of LN patients. MAIT cells from patients have an altered phenotype in terms of migration, proliferation and differentiation markers, notably in most severe forms of LN. Frequencies of PMA/ionomycin stimulated MAIT cells secreting effector molecules, such as proinflammatory IL-17 and cytotoxic protein granzyme B, are higher in LN patients. Patients undergoing a complete renal remission after immunosuppressive therapy had higher MAIT cell frequency, lower expression of proliferation marker Ki-67 and granzyme B (GzB) at inclusion. Remarkably, GzB production defines a predictive model for complete remission.DiscussionWe report here that blood MAIT cells display proinflammatory and cytotoxic function in severe lupus nephritis which may play a pathogenesis role, but without association with systemic lupus activity. Finally, low cytotoxic profile of MAIT cells may represent a promising prognostic factor of lupus nephritis remission one year after induction therapy

Liver cirrhosis : epidemiology, prognosis, and cancer

Liver cirrhosis is a major risk factor for hepatocellular carcinoma (HCC). Patients with liver cirrhosis also have a high risk to develop infections leading to deterioration of liver function and increased mortality. In this PhD-thesis, our aim was to improve the ability to predict risk of developing liver cancer and infections in patients with cirrhosis. In study I, all patients diagnosed with HCC at the Karolinska University Hospital between 2004 and 2018 were included. Patients with HCC and underlying non-alcoholic fatty liver disease (NAFLD) were characterized in detail to investigate their prognosis compared to that of other patients with HCC. In study II, we included randomly selected patients with an international classification of disease (ICD)-code corresponding to cirrhosis and cirrhosis complications registered in the national patient registry (NPR) between 2000 and 2016 to investigate the positive predictive value (PPV) of liver-related ICD-codes. In study III, all patients with cirrhosis registered in the outpatient part of the NPR were included to investigate rate and risk of HCC in cirrhosis. In study IV, we included patients with cirrhosis seen at the Hepatology clinic at the Karolinska University Hospital and obtained a blood test from the participants analyzed for fractions of mucosal-associated invariant T (MAIT) cells. Patient were followed prospectively for risk of bacterial infection and hepatic decompensation. In study I, we included 1,562 patients with HCC, and 225 (14%) of these had NAFLD. We report that NAFLD is a growing cause of HCC. One third of the patients with NAFLD-HCC had no clinical signs of cirrhosis. NAFLD patients were older than non-NAFLD patients, and non-cirrhotic NAFLD patients were even older than NAFLD patients with cirrhosis. Survival was similar between patients with NAFLD and non-NAFLD and between patients with cirrhotic and non-cirrhotic NAFLD. In study II, we found that ICD-10 codes for cirrhosis and esophageal varices had a PPV above 90%, whereas HCC had a PPV of 84%. Ascites had an unsatisfactorily low PPV of 43% for liver-related ascites, but when combined with a code indicating chronic liver disease, the PPV increased to 91%. In study III we included 15,215 individuals with cirrhosis and report that the rate of HCC in cirrhosis is 23/1,000 person-years with a lower-than-expected cumulative risk at five and ten years of 8.3% and 12.2% respectively. The cancer risk varied significantly depending on sex, age, and etiology of liver disease. In study IV, we included 106 patients with cirrhosis and found that relatively preserved MAIT cell fractions were associated with a higher risk of bacterial infections in patients with cirrhosis. In conclusion, we describe NAFLD HCC-patients with and without cirrhosis and found that patients with non-cirrhotic NAFLD are older. We suggest that any surveillance attempts in this patient group should take age into account. ICD-codes for cirrhosis and esophageal varices have a high PPV, but when using ICD-10 code for ascites to identify patients with cirrhosis, we recommend adding another code for chronic liver disease to obtain a PPV above 90%. In study III, we report that the incidence for HCC in cirrhosis and the cumulative risk at five and ten years highly depends on sex, age, and type of liver disease, indicating that HCC-surveillance should be individually tailored. In study IV, the association of bacterial infections and a relatively preserved MAIT cell fraction is an interesting finding that needs to be investigated further