Delayed recovery from surgery causes personal suffering and substantial societal and economic costs. Whether immune mechanisms determine recovery after surgical trauma remains ill-defined. Single-cell mass cytometry was applied to serial whole blood samples from 32 patients undergoing hip replacement to comprehensively characterize the phenotypical and functional immune response to surgical trauma. The simultaneous analysis of 14,000 phosphorylation events in precisely phenotyped immune cell subsets revealed uniform signaling responses among patients, demarcating a surgical immune signature. When regressed against clinical parameters of surgical recovery, including functional impairment and pain, strong correlations were found with STAT3, CREB and NF-kB signaling responses in subsets of CD14+ monocytes (R=0.7–0.8, FDR < 0.01). These sentinel results demonstrate the capacity of mass cytometry to survey the human immune system in a relevant clinical context. The mechanistically derived immune correlates point to diagnostic signatures, and potential therapeutic targets, that could postoperatively improve patient recovery.
Generalized immune activation during HIV infection is associated with an increased risk of cardiovascular disease, neurocognitive disease, osteoporosis, metabolic disorders, and physical frailty. The mechanisms driving this immune activation are poorly understood, particularly for individuals effectively treated with antiretroviral medications. We hypothesized that viral characteristics such as sequence diversity may play a role in driving HIV-associated immune activation. We therefore sequenced proviral DNA isolated from peripheral blood mononuclear cells from HIV-infected individuals on fully suppressive antiretroviral therapy. We performed phylogenetic analyses, calculated viral diversity and divergence in the env and pol genes, and determined coreceptor tropism and the frequency of drug resistance mutations. Comprehensive immune profiling included quantification of immune cell subsets, plasma cytokine levels, and intracellular signaling responses in T cells, B cells, and monocytes. These antiretroviral therapy-treated HIV-infected individuals exhibited a wide range of diversity and divergence in both env and pol genes. However, proviral diversity and divergence in env and pol, coreceptor tropism, and the level of drug resistance did not significantly correlate with markers of immune activation. A clinical history of virologic failure was also not significantly associated with levels of immune activation, indicating that a history of virologic failure does not inexorably lead to increased immune activation as long as suppressive antiretroviral medications are provided. Overall, this study demonstrates that latent viral diversity is unlikely to be a major driver of persistent HIV-associated immune activation.
IMPORTANCE Chronic immune activation, which is associated with cardiovascular disease, neurologic disease, and early aging, is likely to be a major driver of morbidity and mortality in HIV-infected individuals. Although treatment of HIV with antiretroviral medications decreases the level of immune activation, levels do not return to normal. The factors driving this persistent immune activation, particularly during effective treatment, are poorly understood. In this study, we investigated whether characteristics of the latent, integrated HIV provirus that persists during treatment are associated with immune activation. We found no relationship between latent viral characteristics and immune activation in treated individuals, indicating that qualities of the provirus are unlikely to be a major driver of persistent inflammation. We also found that individuals who had previously failed treatment but were currently effectively treated did not have significantly increased levels of immune activation, providing hope that past treatment failures do not have a lifelong “legacy” impact.
Elderly humans show decreased humoral immunity to pathogens and vaccines, yet the effects of aging on B cells are not fully known. Chronic viral infection by cytomegalovirus (CMV) is implicated as a driver of clonal T cell proliferations in some aging humans, but whether CMV or Epstein-Barr virus (EBV) infection contributes to alterations in the B cell repertoire with age is unclear. We have used high-throughput DNA sequencing of immunoglobulin heavy chain (IGH) gene rearrangements to study the B cell receptor repertoires over two successive years in 27 individuals ranging in age from 20 to 89 years. Some features of the B cell repertoire remain stable with age, but elderly subjects show increased numbers of B cells with long CDR3 regions, a trend toward accumulation of more highly mutated IgM and IgG immunoglobulin genes, and persistent clonal B cell populations in the blood. Seropositivity for CMV or EBV infection alters B cell repertoires, regardless of the individual's age: EBV infection correlates with the presence of persistent clonal B cell expansions, while CMV infection correlates with the proportion of highly mutated antibody genes. These findings isolate effects of aging from those of chronic viral infection on B cell repertoires, and provide a baseline for understanding human B cell responses to vaccination or infectious stimuli.
The C-type lectin CD161 is expressed by a large proportion of human T lymphocytes
of all lineages, including a novel population known as Mucosal Associated Invariant T
(MAIT) cells. To understand whether different T cell subsets expressing CD161 have
similar properties, we examined these populations in parallel using mass cytometry and
mRNA microarray approaches. The analysis identified a conserved CD161++/MAIT cell
transcriptional signature enriched in CD161+CD8+ T cells, that can be extended to CD161+
CD4+ and CD161+TCRγδ+ T cells. Further, this led to the identification of
a shared innate-like, TCR-independent response to interleukin (IL)-12 plus IL-18 by
different CD161 expressing T cell populations. This response was independent of regulation
by CD161, which acted as a costimulatory molecule in the context of T cell receptor
stimulation. Expression of CD161 hence identifies a transcriptional and functional
phenotype, shared across human T lymphocytes and independent of both TCR expression and
Adaptive immune responses often begin with the formation of a molecular complex between a T cell receptor (TCR) and a peptide antigen bound to a major histocompatibility complex (MHC) molecule. These complexes are highly variable, however, due to the polymorphism of MHC genes, the random, inexact recombination of TCR gene segments and the vast array of possible self and pathogen peptide antigens. As a result, it has been very difficult to comprehensively study the TCR repertoire or identify and track more than a few antigen-specific T cells in mice or humans. For mouse studies, this had led to a reliance on model antigens and TCR transgenes. The study of limited human clinical samples, in contrast, requires techniques that can simultaneously survey phenotype, function and reactivity to many T cell epitopes. Thanks to recent advances in single-cell and cytometry methodologies, as well as high-throughput sequencing of the TCR repertoire, we now have or will soon have the tools needed to comprehensively analyze T-cell responses during health and disease.
We have developed a single-molecule imaging technique that uses quantum dot-labeled peptide-major histocompatibility complex (pMHC) ligands to study CD4+ T cell functional sensitivity. We found that naive T cells, T cell blasts and memory T cells could all be triggered by a single pMHC to secrete tumor necrosis factor-α (TNF-α) and interleukin-2 (IL-2) cytokines with a rate of ~1,000, ~10,000 and ~10,000 molecules/min respectively and that additional pMHCs did not augment secretion, indicating a digital response pattern. We also found that a single pMHC localized to the immunological synapse induced the slow formation of a long-lasting T cell receptor (TCR) cluster, consistent with a serial engagement mechanism. These data show that scaling up CD4+ T cell cytokine responses involves increasingly efficient T cell recruitment rather than greater cytokine production per cell.
Natural Killer (NK) cells play critical roles in immune defense and reproduction, yet remain the most poorly understood major lymphocyte population. Because their activation is controlled by a variety of combinatorially expressed activating and inhibitory receptors, NK cell diversity and function are closely linked. To provide an unprecedented understanding of NK cell repertoire diversity, we used mass cytometry to simultaneously analyze 35 parameters, including 28 NK cell receptors, on peripheral blood NK cells from five sets of monozygotic twins and twelve unrelated donors of defined HLA and killer cell immunoglobulin-like receptor (KIR) genotype. This analysis revealed a remarkable degree of NK cell diversity, with an estimated 6,000-30,000 phenotypic populations within an individual and >100,000 phenotypes in this population. Genetics largely determined inhibitory receptor expression, whereas activation receptor expression was heavily environmentally influenced. Therefore, NK cells may maintain self-tolerance through strictly regulated expression of inhibitory receptors, while using adaptable expression patterns of activating and costimulatory receptors to respond to pathogens and tumors. These findings further suggest the possibility that discrete NK cell subpopulations could be harnessed for immunotherapeutic strategies in the settings of infection, reproduction, and transplantation.
The vast majority of currently licensed human vaccines work on the basis of long-term protective antibody responses. It is now conceivable that an antibody-dependent HIV vaccine might be possible, given the discovery of HIV broadly neutralizing antibodies (bnAbs) in some HIV-infected individuals. However, these antibodies are difficult to develop and have characteristics indicative of a high degree of affinity maturation in germinal centers (GCs). CD4+ T follicular helper (Tfh) cells are specialized for B cell help and necessary for GCs. Therefore, the development of HIV bnAbs might depend on Tfh cells. Here, we identified in normal individuals a subpopulation of circulating memory PD-1+CXCR5+ CD4+ T cells that are resting memory cells most related to bona fide GC Tfh cells by gene expression profile, cytokine profile, and functional properties. Importantly, the frequency of these cells correlated with the development of bnAbs against HIV in a large cohort of HIV+ individuals.
Flow cytometry is used increasingly in clinical research for cancer, immunology and vaccines. Technological advances in cytometry instrumentation are increasing the size and dimensionality of data sets, posing a challenge for traditional data management and analysis. Automated analysis methods, despite a general consensus of their importance to the future of the field, have been slow to gain widespread adoption. Here we present OpenCyto, a new BioConductor infrastructure and data analysis framework designed to lower the barrier of entry to automated flow data analysis algorithms by addressing key areas that we believe have held back wider adoption of automated approaches. OpenCyto supports end-to-end data analysis that is robust and reproducible while generating results that are easy to interpret. We have improved the existing, widely used core BioConductor flow cytometry infrastructure by allowing analysis to scale in a memory efficient manner to the large flow data sets that arise in clinical trials, and integrating domain-specific knowledge as part of the pipeline through the hierarchical relationships among cell populations. Pipelines are defined through a text-based csv file, limiting the need to write data-specific code, and are data agnostic to simplify repetitive analysis for core facilities. We demonstrate how to analyze two large cytometry data sets: an intracellular cytokine staining (ICS) data set from a published HIV vaccine trial focused on detecting rare, antigen-specific T-cell populations, where we identify a new subset of CD8 T-cells with a vaccine-regimen specific response that could not be identified through manual analysis, and a CyTOF T-cell phenotyping data set where a large staining panel and many cell populations are a challenge for traditional analysis. The substantial improvements to the core BioConductor flow cytometry packages give OpenCyto the potential for wide adoption. It can rapidly leverage new developments in computational cytometry and facilitate reproducible analysis in a unified environment.
Using an elaborately evolved language of cytokines and chemokines as well as cell-cell interactions, the different components of the immune system communicate with each other and orchestrate a response (or wind one down). Immunological synapses are a key feature of the system in the ways in which they can facilitate and direct these responses. Studies analyzing the structure of an immune synapse as it forms between two cells have provided insight into how the stability and kinetics of this interaction ultimately affect the sensitivity, potency, and magnitude of a given response. Furthermore, we have gained an appreciation of how the immunological synapse provides directionality and contextual cues for downstream signaling and cellular decision-making. In this review, we discuss how using a variety of techniques, developed over the last decade, have allowed us to visualize and quantify key aspects of the dynamic synaptic interface and have furthered our understanding of their function. We describe some of the many characteristics of the immunological synapse that make it a vital part of intercellular communication and some of the questions that remain to be answered.
T-cell receptor; peptide–major histocompatibility complex; immunological synapse; central supramolecular activation cluster; cytokines
T cells specific for the cytochrome c Ag are widely used to investigate many aspects of TCR specificity and interactions with peptide-MHC, but structural information has long been elusive. In this study, we present structures for the well-studied 2B4 TCR, as well as a naturally occurring variant of the 5c.c7 TCR, 226, which is cross-reactive with more than half of possible substitutions at all three TCR-sensitive residues on the peptide Ag. These structures alone and in complex with peptide-MHC ligands allow us to reassess many prior mutagenesis results. In addition, the structure of 226 bound to one peptide variant, p5E, shows major changes in the CDR3 contacts compared with wild-type, yet the TCR V-region contacts with MHC are conserved. These and other data illustrate the ability of TCRs to accommodate large variations in CDR3 structure and peptide contacts within the constraints of highly conserved TCR–MHC interactions.
While T cell memory is generally thought to require direct antigen exposure, we find an abundance of memory phenotype cells (20–90%, averaging over 50%) of CD4+ T cells specific for viral antigens in adults that have never been infected. These cells express the appropriate memory markers and genes, rapidly produce cytokines, and have clonally expanded. This contrasts with newborns where the same T cell receptor (TCR) specificities are almost entirely naïve, which may explain the vulnerability of young children to infections. One mechanism for this phenomenon is TCR cross-reactivity to environmental antigens and in support of this we find extensive cross-recognition by HIV-1 and influenza-reactive T lymphocytes to other microbial peptides and the expansion of one of these following influenza vaccination. Thus the presence of these memory phenotype T cells has significant implications for immunity to novel pathogens, child and adult health, and the influence of pathogen-rich versus hygienic environments.
It is currently not possible to predict which epitopes will be recognized by T cells in different individuals. This is a barrier to the thorough analysis and understanding of T-cell responses after vaccination or infection. Here, by combining mass cytometry with combinatorial peptide–MHC tetramer staining, we have developed a method allowing the rapid and simultaneous identification and characterization of T cells specific for many epitopes. We use this to screen up to 109 different peptide–MHC tetramers in a single human blood sample, while still retaining at least 23 labels to analyze other markers of T-cell phenotype and function. Among 77 candidate rotavirus epitopes, we identified six T-cell epitopes restricted to human leukocyte antigen (HLA)-A*0201 in the blood of healthy individuals. T cells specific for epitopes in the rotavirus VP3 protein displayed a distinct phenotype and were present at high frequencies in intestinal epithelium. This approach should be useful for the comprehensive analysis of T-cell responses to infectious diseases or vaccines.
γδ T cells contribute uniquely to host immune defense. However, how they function remains an enigma. Although it is unclear what most γδ T cells recognize, common dogma asserts that they recognize self-antigens. While they are the major initial Interleukin-17 (IL-17) producers in infections, it is unclear what is required to trigger these cells to act. Here, we report that a noted B cell antigen, the algae protein-phycoerythrin (PE) is an antigen for murine and human γδ T cells. PE also stained specific bovine γδ T cells. Employing this specificity, we demonstrated that antigen recognition, but not extensive clonal expansion, was required to activate naïve γδ T cells to make IL-17. In this activated state, γδ T cells gained the ability to respond to cytokine signals that perpetuated the IL-17 production. These results underscore the adaptability of lymphocyte antigen receptors and suggest a previously unrecognized antigen-driven rapid response in protective immunity prior to the maturation of classical adaptive immunity.
Thymic positive selection is based on the interactions of T cell antigen receptors (TCRs) with self peptide–major histocompatibility complex (MHC) ligands, but the identity of selecting peptides for MHC class II–restricted TCRs and the functional consequences of this peptide specificity are not clear. Here we identify several endogenous self peptides that positively selected the MHC class II–restricted 5C.C7 TCR. The most potent of these also enhanced mature T cell activation, which supports the hypothesis that one function of positive selection is to produce T cells that can use particular self peptide–MHC complexes for activation and/or homeostasis. We also show that inhibiting the microRNA miR-181a resulted in maturation of T cells that overtly reacted toward these erstwhile positively selecting peptides. Therefore, miR-181a helps to guarantee the clonal deletion of particular moderate-affinity clones by modulating the TCR signaling threshold of thymocytes.
Immature double-positive (CD4+CD8+) thymocytes respond to negatively selecting peptide-MHC ligands by forming an immune synapse that sustains contact with the antigen-presenting cell (APC). Using fluorescently labeled peptides, we showed that as few as two agonist ligands could promote APC contact and subsequent apoptosis in reactive thymocytes. Furthermore, we showed that productive signaling for positive selection, as gauged by nuclear translocation of a green fluorescent protein (GFP)-labeled NFATc construct, did not involve formation of a synapse between thymocytes and selecting epithelial cells in reaggregate thymus cultures. Antibody blockade of endogenous positively selecting ligands prevented NFAT nuclear accumulation in such cultures and reversed NFAT accumulation in previously stimulated thymocytes. Together, these data suggest a “gauntlet” model in which thymocytes mature by continually acquiring and reacquiring positively selecting signals without sustained contact with epithelial cells, thereby allowing them to sample many cell surfaces for potentially negatively selecting ligands.
After a half-century of mouse-dominated research, human immunology is making a comeback. Informed by mouse studies and powered by new techniques, human immune research is both advancing disease treatment and providing new insights into basic biology.
This chapter describes a method to generate plasma membrane sheets that are large enough to visualize the membrane architecture and perform quantitative analyses of protein distributions. This procedure places the sheets on electron microscopy grids, parallel to the imaging plane of the microscope, where they can be characterized by transmission electron microscopy. The basic principle of the technique is that cells are broken open (“ripped”) through mechanical forces applied by the separation of two opposing surfaces sandwiching the cell, with one of the surfaces coated onto an EM grid. The exposed inner membrane surfaces can then be visualized with electron dense stains and specific proteins can be detected with gold conjugated probes.
Plasma membrane; Transmission electron microscopy; Protein distribution
The physiological basis and mechanistic requirement for the high immunoreceptor tyrosine activation motifs (ITAM) multiplicity of the T cell receptor (TCR)-CD3 complex remains obscure. Here we show that while low TCR-CD3 ITAM multiplicity is sufficient to engage canonical TCR-induced signaling events that lead to cytokine secretion, high TCR-CD3 ITAM multiplicity is required for TCR-driven proliferation. This is dependent on compact immunological synapse formation, interaction of the adaptor Vav1 with phosphorylated CD3 ITAMs to mediate Notch1 recruitment and activation and ultimately c-Myc-induced proliferation. Analogous mechanistic events are also required to drive proliferation in response to weak peptide agonists. Thus, the TCR-driven pathways that initiate cytokine secretion and proliferation are separable and co-ordinated by the multiplicity of phosphorylated TCR-CD3 ITAMs.
Cytotoxic CD8+ T lymphocytes directly kill infected or aberrant cells and secrete proinflammatory cytokines. By using metal-labeled probes and mass spectrometric analysis (cytometry by time-of-flight, or CyTOF) of human CD8+ T cells, we analyzed the expression of many more proteins than previously possible with fluorescent labels, including surface markers, cytokines, and antigen specificity with modified peptide-MHC tetramers. With 3-dimensional principal component analysis (3D-PCA) to display phenotypic diversity, we observed a relatively uniform pattern of variation in all subjects tested, highlighting the interrelatedness of previously described subsets and the continuous nature of CD8+ T cell differentiation. These data also showed much greater complexity in the CD8+ T cell compartment than previously appreciated, including a nearly combinatorial pattern of cytokine expression, with distinct niches occupied by virus-specific cells. This large degree of functional diversity even between cells with the same specificity gives CD8+ T cells a remarkable degree of flexibility in responding to pathogens.
The human antibody repertoire is one of the most important defenses against infectious disease, and the development of vaccines has enabled the conferral of targeted protection to specific pathogens. However, there are many challenges to measuring and analyzing the immunoglobulin sequence repertoire, such as the fact that each B cell contains a distinct antibody sequence encoded in its genome, that the antibody repertoire is not constant but changes over time, and the high similarity between antibody sequences. We have addressed this challenge by using high-throughput long read sequencing to perform immunogenomic characterization of expressed human antibody repertoires in the context of influenza vaccination. Informatic analysis of 5 million antibody heavy chain sequences from healthy individuals allowed us to perform global characterizations of isotype distributions, determine the lineage structure of the repertoire and measure age and antigen related mutational activity. Our analysis of the clonal structure and mutational distribution of individuals’ repertoires shows that elderly subjects have a decreased number of lineages but an increased pre-vaccination mutation load in their repertoire and that some of these subjects have an oligoclonal character to their repertoire in which the diversity of the lineages is greatly reduced relative to younger subjects. We have thus shown that global analysis of the immune system’s clonal structure provides direct insight into the effects of vaccination and provides a detailed molecular portrait of age-related effects.
Labelling antigen-specific T cells with peptide–MHC multimers has provided an invaluable way to monitor T cell-mediated immune responses. A number of recent developments in this technology have made these multimers much easier to make and use in large numbers. Furthermore, enrichment techniques have provided a greatly increased sensitivity that allows the analysis of the naive T cell repertoire directly. Thus, we can expect a flood of new information to emerge in the coming years.