Diverse Mucosal-Associated Invariant TCR Usage in HIV Infection.

Mucosal-associated invariant T (MAIT) cells are innate-like T cells that specifically target bacterial metabolites but are also identified as innate-like sensors of viral infection. Individuals with chronic HIV-1 infection have lower numbers of circulating MAIT cells compared with healthy individuals, yet the features of the MAIT TCR repertoire are not well known. We isolated and stimulated human PBMCs from healthy non-HIV-infected donors (HD), HIV-infected progressors on antiretroviral therapy, and HIV-infected elite controllers (EC). We sorted MAIT cells using flow cytometry and used a high-throughput sequencing method with bar coding to link the expression of TCRα, TCRß, and functional genes of interest at the single-cell level. We show differential patterns of MAIT TCR usage among the groups. We observed expansions of certain dominant MAIT clones in HIV-infected individuals upon Escherichia coli stimulation, which was not observed in clones of HD. We also found different patterns of CDR3 amino acid distributions among the three groups. Furthermore, we found blunted expression of phenotypic genes in HIV individuals; most notably, HD mounted a robust IFNG response to stimulation, whereas both HIV-infected progressors and EC did not. In conclusion, our study describes the diverse MAIT TCR repertoire of persons with chronic HIV-1 infection and suggest that MAIT clones of HIV-infected persons may be primed for expansion more than that of noninfected persons. Further studies are needed to examine the functional significance of unique MAIT cell TCR usage in EC.

Human mucosal-associated invariant T (MAIT) cells possess capacity for B cell help.

Mucosal-associated invariant T (MAIT) cells are an innate-like T cell subset, restricted by the nonclassic MHC class I-related protein MR1 and enriched at mucosal sites. Human studies have shown an association between MAIT cells and pathogen-specific antibody responses. In this study, we investigate the effect of human MAIT cells on B cells ex vivo. We found that supernatants from microbe- or cytokine-stimulated MAIT cells, when added to purified autologous B cells, increase frequencies of plasmablasts and promote IgA, IgG, and IgM production. We found effects to be mostly MR1-dependent and that the increases in plasmablasts are likely a result of increased differentiation from memory B cells. Furthermore, microbe-activated MAIT cell supernatant contains multiple cytokines known to stimulate B cells, including IL-6, -10, and -21. This study thus provides the first direct evidence of a newly identified role of MAIT cells in providing help to B cells.

Innate-like lymphocytes in intestinal infections.

PURPOSE OF REVIEW: The mechanisms of immunity against intestinal pathogens are not well understood. Innate-like lymphocytes are a group of recently discovered cells that do not fit into either side of the historical innate-adaptive classification. They are enriched in the intestinal mucosa and participate in gut homeostasis and defense against infections. We will review recent developments in innate-like T lymphocytes and innate lymphoid cells, specifically as they relate to responses to intestinal infections. RECENT FINDINGS: Recent studies have uncovered further details into antigen presentation to γδ T cells and mucosal-associated invariant T cells, the role of invariant natural killer T cells and mucosal-associated invariant T cells in intestinal infections, and how innate lymphoid cells maintain gut homeostasis and protection. SUMMARY: Innate-like lymphocytes play a major role in the critical early response to intestinal infections and maintaining gut homeostasis. Further studies of the roles these cells play in the human intestinal mucosa will aid in the development of therapeutics against intestinal infections.

Aging and cytomegalovirus infection differentially and jointly affect distinct circulating T cell subsets in humans.

The impact of intrinsic aging upon human peripheral blood T cell subsets remains incompletely quantified and understood. This impact must be distinguished from the influence of latent persistent microorganisms, particularly CMV, which has been associated with age-related changes in the T cell pool. In a cross-sectional cohort of 152 CMV-negative individuals, aged 21-101 y, we found that aging correlated strictly to an absolute loss of naive CD8, but not CD4, T cells but, contrary to many reports, did not lead to an increase in memory T cell numbers. The loss of naive CD8 T cells was not altered by CMV in 239 subjects (range 21-96 y), but the decline in CD4(+) naive cells showed significance in CMV(+) individuals. These individuals also exhibited an absolute increase in the effector/effector memory CD4(+) and CD8(+) cells with age. That increase was seen mainly, if not exclusively, in older subjects with elevated anti-CMV Ab titers, suggesting that efficacy of viral control over time may determine the magnitude of CMV impact upon T cell memory, and perhaps upon immune defense. These findings provide important new insights into the age-related changes in the peripheral blood pool of older adults, demonstrating that aging and CMV exert both distinct and joint influence upon blood T cell homeostasis in humans.

Gene therapy strategies for HIV/AIDS: preclinical modeling in humanized mice.

In the absence of an effective vaccine and lack of a complete cure, gene therapy approaches to control HIV infection offer feasible alternatives. Due to the chronic nature of infection, a wide window of opportunity exists to gene modify the HIV susceptible cells that continuously arise from the bone marrow source. To evaluate promising gene therapy approaches that employ various anti-HIV therapeutic molecules, an ideal animal model is necessary to generate important efficacy and preclinical data. In this regard, the humanized mouse models that harbor human hematopoietic cells susceptible to HIV infection provide a suitable in vivo system. This review summarizes the currently used humanized mouse models and different anti-HIV molecules utilized for conferring HIV resistance. Humanized mouse models are compared for their utility in this context and provide perspectives for new directions.

Receptor binding by an H7N9 influenza virus from humans.

Of the 132 people known to have been infected with H7N9 influenza viruses in China, 37 died, and many were severely ill. Infection seems to have involved contact with infected poultry. We have examined the receptor-binding properties of this H7N9 virus and compared them with those of an avian H7N3 virus. We find that the human H7 virus has significantly higher affinity for α-2,6-linked sialic acid analogues ('human receptor') than avian H7 while retaining the strong binding to α-2,3-linked sialic acid analogues ('avian receptor') characteristic of avian viruses. The human H7 virus does not, therefore, have the preference for human versus avian receptors characteristic of pandemic viruses. X-ray crystallography of the receptor-binding protein, haemagglutinin (HA), in complex with receptor analogues indicates that both human and avian receptors adopt different conformations when bound to human H7 HA than they do when bound to avian H7 HA. Human receptor bound to human H7 HA exits the binding site in a different direction to that seen in complexes formed by HAs from pandemic viruses and from an aerosol-transmissible H5 mutant. The human-receptor-binding properties of human H7 probably arise from the introduction of two bulky hydrophobic residues by the substitutions Gln226Leu and Gly186Val. The former is shared with the 1957 H2 and 1968 H3 pandemic viruses and with the aerosol-transmissible H5 mutant. We conclude that the human H7 virus has acquired some of the receptor-binding characteristics that are typical of pandemic viruses, but its retained preference for avian receptor may restrict its further evolution towards a virus that could transmit efficiently between humans, perhaps by binding to avian-receptor-rich mucins in the human respiratory tract rather than to cellular receptors.

Fine-tuning of T-cell receptor avidity to increase HIV epitope variant recognition by cytotoxic T lymphocytes.

OBJECTIVE: T-cell receptor (TCR) gene therapy is an approach being considered for HIV-1, but epitope mutation is a significant barrier. We assessed whether HIV-specific TCR can be modified to have broader coverage of epitope variants by recombining polymorphisms between public clonotype TCR sequences. DESIGN: Public clonotype TCRs recognizing the same epitope often differ by polymorphisms in their third complementarity determining regions (CDR3). We assessed whether novel combinations of such polymorphisms could improve TCR recognition of epitope variation. METHODS: A TCR recognizing the HLA A*0201-restricted epitope SLYNTVATL (Gag 77-85, SL9) was engineered to have combinations of four polymorphisms in the CDR3 regions compared to another SL9-specific TCR. These novel TCRs were screened for functional avidities against SL9 epitope variants and abilities to mediate cytotoxic T-lymphocyte suppression of HIV-1 containing the same epitope variants. RESULTS: The TCRs varied modestly in functional avidities for SL9 variants, due to alterations in affinity. This translated to differences in antiviral activities against HIV-1 when functional avidity changes crossed the previously defined threshold required for efficient recognition of HIV-1-infected cells. Higher avidity TCR mutants had generally broader recognition of SL9 variants. CONCLUSION: These results indicate that rationally targeted increases in functional avidities can be utilized to maximize the antiviral breadth of transgenic TCRs. In contrast to previously reported random mutagenesis to markedly increase functional avidities, tuning through recombining naturally occurring polymorphisms may offer a more physiologic approach that minimizes the risk of deleterious TCR reactivities.

Cross-clade detection of HIV-1-specific cytotoxic T lymphocytes does not reflect cross-clade antiviral activity.

The genetic divergence of human immunodeficiency virus (HIV)-1 into distinct clades is a serious consideration for cytotoxic T lymphocyte (CTL)-based vaccine development. Demonstrations that CTLs can cross-recognize epitope sequences from different clades has been proposed as offering hope for a single vaccine. Cross-clade CTL data, however, have been generated by assessing recognition of exogenous peptides. The present study compares HIV-1-specific CTL cross-clade epitope recognition of exogenously loaded peptides with suppression of HIV-1-infected cells. Despite apparently broad cross-clade reactivity of CTLs against the former, CTL suppression of HIV-1 strains with corresponding epitope sequences is significantly impaired. The functional avidity of CTLs for nonautologous clade epitope sequences is diminished, suggesting that CTLs can fail to recognize levels of infected endogenously derived cell-surface epitopes despite recognizing supraphysiologic exogenously added epitopes. These data strongly support clade-specific antiviral activity of CTLs and call into question the validity of standard methods for assessing cross-clade CTL activity or CTL antiviral activity in general.

Epitope-dependent avidity thresholds for cytotoxic T-lymphocyte clearance of virus-infected cells.

Cytotoxic T lymphocytes (CTLs) are crucial for immune control of viral infections. "Functional avidity," defined by the sensitizing dose of exogenously added epitope yielding half-maximal CTL triggering against uninfected target cells (SD(50)), has been utilized extensively as a measure of antiviral efficiency. However, CTLs recognize infected cells via endogenously produced epitopes, and the relationship of SD(50) to antiviral activity has never been directly revealed. We elucidate this relationship by comparing CTL killing of cells infected with panels of epitope-variant viruses to the corresponding SD(50) for the variant epitopes. This reveals a steeply sigmoid relationship between avidity and infected cell killing, with avidity thresholds (defined as the SD(50) required for CTL to achieve 50% efficiency of infected cell killing [KE(50)]), below which infected cell killing rapidly drops to none and above which killing efficiency rapidly plateaus. Three CTL clones recognizing the same viral epitope show the same KE(50) despite differential recognition of individual epitope variants, while CTLs recognizing another epitope show a 10-fold-higher KE(50), demonstrating epitope dependence of KE(50). Finally, the ability of CTLs to suppress viral replication depends on the same threshold KE(50). Thus, defining KE(50) values is required to interpret the significance of functional avidity measurements and predict CTL efficacy against virus-infected cells in pathogenesis and vaccine studies.

Nef interference with HIV-1-specific CTL antiviral activity is epitope specific.

HIV-1 Nef and HIV-1-specific cytotoxic T lymphocytes (CTLs) have important and opposing roles in the immunopathogenesis of HIV-1 infection. Nef-mediated down-modulation of HLA class I on infected cells can confer resistance to CTL clearance, but the factors determining the efficiency of this process are unknown. This study examines the impact of Nef on the antiviral activity of several CTL clones recognizing epitopes from early and late HIV-1 proteins, restricted by HLA-A, -B, and -C molecules. CTL-targeting epitopes in early proteins remained susceptible to the effects of Nef, although possibly to a lesser degree than CTL-targeting late protein epitopes, indicating that significant Nef-mediated HLA down-regulation can precede even the presentation of early protein-derived epitopes. However, HLA-C-restricted CTLs were unaffected by Nef, consistent with down-regulation of cell-surface HLA-A and -B but not HLA-C molecules. Thus, CTLs vary dramatically in their susceptibility to Nef interference, suggesting differences in the relative importance of HLA-A- and HLA-B- versus HLA-C-restricted CTLs in vivo. The data thus indicate that HLA-C-restricted CTLs may have an under-appreciated antiviral role in the setting of Nef in vivo and suggest a benefit of promoting HLA-C-restricted CTLs for immunotherapy or vaccine development.