Joana Dias

Arming of MAIT Cell Cytolytic Antimicrobial Activity Is Induced by IL-7 and Defective in HIV-1 Infection

Mucosa-associated invariant T (MAIT) cells represent a large innate-like evolutionarily conserved antimicrobial T-cell subset in humans. MAIT cells recognize microbial riboflavin metabolites from a range of microbes presented by MR1 molecules. MAIT cells are impaired in several chronic diseases including HIV-1 infection, where they show signs of exhaustion and decline numerically. Here, we examined the broader effector functions of MAIT cells in this context and strategies to rescue their functions. Residual MAIT cells from HIV-infected patients displayed aberrant baseline levels of cytolytic proteins, and failed to mobilize cytolytic molecules in response to bacterial antigen. In particular, the induction of granzyme B (GrzB) expression was profoundly defective. The functionally impaired MAIT cell population exhibited abnormal T-bet and Eomes expression patterns that correlated with the deficiency in cytotoxic capacity and cytokine production. Effective antiretroviral therapy (ART) did not fully restore these aberrations. Interestingly, IL-7 was capable of arming resting MAIT cells from healthy donors into cytotoxic GrzB+ effector T cells capable of killing bacteria-infected cells and producing high levels of pro-inflammatory cytokines in an MR1-dependent fashion. Furthermore, IL-7 treatment enhanced the sensitivity of MAIT cells to detect low levels of bacteria. In HIV-infected patients, plasma IL-7 levels were positively correlated with MAIT cell numbers and function, and IL-7 treatment in vitro significantly restored MAIT cell effector functions even in the absence of ART. These results indicate that the cytolytic capacity in MAIT cells is severely defective in HIV-1 infected patients, and that the broad-based functional defect in these cells is associated with deficiency in critical transcription factors. Furthermore, IL-7 induces the arming of effector functions and enhances the sensitivity of MAIT cells, and may be considered in immunotherapeutic approaches to restore MAIT cells.

Multiple layers of heterogeneity and subset diversity in human MAIT cell responses to distinct microorganisms and to innate cytokines

Significance Mucosa-associated invariant T (MAIT) cells are a large subset of unconventional T cells in humans, recognizing microbial riboflavin metabolites presented by the monomorphic MR1 molecule. The extraordinary level of conservation of MR1 and the limited diversity of riboflavin-derived antigens have suggested that MAIT cells are homogeneous, and their functional specialization has not been thoroughly investigated. Here, we show that MAIT cell responses against two distinct riboflavin biosynthesis-competent microorganisms display microbe-specific response patterns with multiple layers of heterogeneity. Furthermore, a set of natural killer cell-associated receptors define a subset with enhanced capacity to respond to innate cytokine stimulus. Thus, MAIT cells harbor multiple layers of functional heterogeneity and can adapt their antimicrobial responses to the type of microbial stimuli. Mucosa-associated invariant T (MAIT) cells are a large innate-like T-cell subset in humans defined by invariant TCR Vα7.2 use and expression of CD161. MAIT cells recognize microbial riboflavin metabolites of bacterial or fungal origin presented by the monomorphic MR1 molecule. The extraordinary level of evolutionary conservation of MR1 and the limited known diversity of riboflavin metabolite antigens have suggested that MAIT cells are relatively homogeneous and uniform in responses against diverse microbes carrying the riboflavin biosynthesis pathway. The ability of MAIT cells to exhibit microbe-specific functional specialization has not been thoroughly investigated. Here, we found that MAIT cell responses against Escherichia coli and Candida albicans displayed microbe-specific polyfunctional response profiles, antigen sensitivity, and response magnitudes. MAIT cell effector responses against E. coli and C. albicans displayed differential MR1 dependency and TCR β-chain bias, consistent with possible divergent antigen subspecificities between these bacterial and fungal organisms. Finally, although the MAIT cell immunoproteome was overall relatively homogenous and consistent with an effector memory-like profile, it still revealed diversity in a set of natural killer cell-associated receptors. Among these, CD56, CD84, and CD94 defined a subset with higher expression of the transcription factors promyelocytic leukemia zinc finger (PLZF), eomesodermin, and T-bet and enhanced capacity to respond to IL-12 and IL-18 stimulation. Thus, the conserved and innate-like MAIT cells harbor multiple layers of functional heterogeneity as they respond to bacterial or fungal organisms or innate cytokines and adapt their antimicrobial response patterns in a stimulus-specific manner.

Human MAIT-cell responses to Escherichia coli: activation, cytokine production, proliferation, and cytotoxicity

Mucosa‐associated invariant T cells are a large and relatively recently described innate‐like antimicrobial T‐cell subset in humans. These cells recognize riboflavin metabolites from a range of microbes presented by evolutionarily conserved major histocompatibility complex, class I‐related molecules. Given the innate‐like characteristics of mucosa‐associated invariant T cells and the novel type of antigens they recognize, new methodology must be developed and existing methods refined to allow comprehensive studies of their role in human immune defense against microbial infection. In this study, we established protocols to examine a range of mucosa‐associated invariant T‐cell functions as they respond to antigen produced by Escherichia coli. These improved and dose‐ and time‐optimized experimental protocols allow detailed studies of MR1‐dependent mucosa‐associated invariant T‐cell responses to Escherichia coli pulsed antigen‐presenting cells, as assessed by expression of activation markers and cytokines, by proliferation, and by induction of apoptosis and death in major histocompatibility complex, class I‐related–expressing target cells. The novel and optimized protocols establish a framework of methods and open new possibilities to study mucosa‐associated invariant T‐cell immunobiology, using Escherichia coli as a model antigen. Furthermore, we propose that these robust experimental systems can also be adapted to study mucosa‐associated invariant T‐cell responses to other microbes and types of antigen‐presenting cells.

Will loss of your MAITs weaken your HAART

Mucosa-associated Invariant T (MAIT) cells are an evolutionarily conserved innate-like T cell subset that recognizes antigens presented by MR1 molecules. These antigens include vitamin B derivatives shared by many potentially pathogenic microbes, including Mycobacterium tuberculosis and Candida albicans. It was recently discovered that MAIT cells decay numerically and functionally in HIV-1 infection, and that they fail to recover despite several years of effective suppression of viral replication by antiretroviral therapy (ART). Here, we briefly discuss the roles of MAIT cells and their loss in HIV immunopathogenesis. We furthermore propose that the persistence of MAIT cell loss on ART needs to be taken into account when assessing the immunological response to treatment, and when treatment should commence. The importance of this T cell subset in HIV-1 infection needs further study, and interventions to restore the MAIT cell compartment should be considered.

Extensive Phenotypic Analysis, Transcription Factor Profiling, and Effector Cytokine Production of Human MAIT Cells by Flow Cytometry.

The mucosa-associated invariant T (MAIT) cells are a large and relatively recently described innate-like antimicrobial T cell subset in humans. The study of human MAIT cells is still in its infancy, and many aspects of MAIT cell immunobiology in health and disease remain unexplored. Here, we describe methodological approaches and protocols to investigate the expression of a broad spectrum of surface receptors on human MAIT cells, and to examine their unique transcription factor profile, as well as their antimicrobial effector function using multicolor flow cytometry-based techniques. We provide specific guidance on protocols and describe potential pitfalls for each of the presented methodologies. Finally, we discuss future prospects and current limitations of multicolor flow cytometry-based approaches to the study of human MAIT cells.

Will loss of your MAITs weaken your HAART [corrected]?

Mucosa-associated Invariant T (MAIT) cells are an evolutionarily conserved innate-like T cell subset that recognizes antigens presented by MR1 molecules. These antigens include vitamin B derivatives shared by many potentially pathogenic microbes, including Mycobacterium tuberculosis and Candida albicans. It was recently discovered that MAIT cells decay numerically and functionally in HIV-1 infection, and that they fail to recover despite several years of effective suppression of viral replication by antiretroviral therapy (ART). Here, we briefly discuss the roles of MAIT cells and their loss in HIV immunopathogenesis. We furthermore propose that the persistence of MAIT cell loss on ART needs to be taken into account when assessing the immunological response to treatment, and when treatment should commence. The importance of this T cell subset in HIV-1 infection needs further study, and interventions to restore the MAIT cell compartment should be considered.

Factors Influencing Functional Heterogeneity in Human Mucosa-Associated Invariant T Cells

Mucosa-associated invariant T (MAIT) cells are unconventional innate-like T cells that recognize microbial riboflavin metabolites presented by the monomorphic MHC class I-related (MR1) molecule. Despite the high level of evolutionary conservation of MR1 and the limited diversity of known antigens, human MAIT cells and their responses may not be as homogeneous as previously thought. Here, we review recent findings indicating that MAIT cells display microbe-specific response patterns with multiple layers of heterogeneity. The natural killer cell receptor CD56 marks a MAIT cell subset with distinct response profile, and the T cell receptor β-chain diversity influences responsiveness at the single cell level. The MAIT cell tissue localization also influences their response profiles with higher IL-17 in tissue-resident MAIT cells. Furthermore, there is emerging evidence that the type of antigen-presenting cells, and innate cytokines produced by such cells, influence the quality of the ensuing MAIT cell response. On the microbial side, the expression patterns of MR1-presented antigenic and non-antigenic compounds, expression of other bioactive microbial products, and of innate pattern recognition ligands all influence downstream MAIT cell responses. These recent findings deepen our understanding of MAIT cell functional diversity and adaptation to the type and location of microbial challenge.

Proteome analysis of human CD56neg NK cells reveals a homogeneous phenotype surprisingly similar to CD56dim NK cells

NK cells lacking CD56 (CD56neg) were first identified in chronic HIV‐1 infection. However, CD56neg NK cells also exist in healthy individuals, albeit in significantly lower numbers. Here, we provide an extensive proteomic characterisation of human CD56neg peripheral blood NK cells of healthy donors and compare them to their CD56dim and CD56bright counterparts. Unbiased large‐scale surface receptor profiling clustered CD56neg cells as part of the main NK cell compartment and indicated an overall CD56dim‐like phenotype. Total proteome analyses of CD56neg NK cells further confirmed their similarity with CD56dim NK cells, and revealed a complete cytolytic inventory with high levels of perforin and granzyme H and M. In the present study, twelve proteins discriminated CD56neg NK cells from CD56dim NK cells with nine up‐regulated and three down‐regulated proteins in the CD56neg NK cell population. Those proteins were functionally related to lytic granule composition and transport, interaction with the extracellular matrix, DNA transcription or repair, and proliferation. Corroborating these results, CD56neg NK cells showed modest cytotoxicity, degranulation, and IFN‐ɣ secretion as compared to CD56dim NK cells. In conclusion, CD56neg NK cells constitute functionally competent cells sharing many features of bona fide CD56dim NK cells in healthy individuals, but with some distinct characteristics.