High-affinity CD8 variants enhance the sensitivity of pMHCI antigen recognition via low-affinity TCRs

CD8+ T cell-mediated recognition of peptide-major histocompatibility complex class I (pMHCI) molecules involves cooperative binding of the T cell receptor (TCR), which confers antigen specificity, and the CD8 coreceptor, which stabilizes the TCR/pMHCI complex. Earlier work has shown that the sensitivity of antigen recognition can be regulated in vitro by altering the strength of the pMHCI/CD8 interaction. Here, we characterized two CD8 variants with moderately enhanced affinities for pMHCI, aiming to boost antigen sensitivity without inducing non-specific activation. Expression of these CD8 variants in model systems preferentially enhanced pMHCI antigen recognition in the context of low-affinity TCRs. A similar effect was observed using primary CD4+ T cells transduced with cancer-targeting TCRs. The introduction of high-affinity CD8 variants also enhanced the functional sensitivity of primary CD8+ T cells expressing cancer-targeting TCRs, but comparable results were obtained using exogenous wild-type CD8. Specificity was retained in every case, with no evidence of reactivity in the absence of cognate antigen. Collectively, these findings highlight a generically applicable mechanism to enhance the sensitivity of low-affinity pMHCI antigen recognition, which could augment the therapeutic efficacy of clinically relevant TCRs.

Immune and metabolic markers for identifying and investigating severe Coronavirus disease and Sepsis in children and young people (pSeP/COVID ChYP study): protocol for a prospective cohort study

INTRODUCTION

Early recognition and appropriate management of paediatric sepsis are known to improve outcomes. A previous system's biology investigation of the systemic immune response in neonates to sepsis identified immune and metabolic markers that showed high accuracy for detecting bacterial infection. Further gene expression markers have also been reported previously in the paediatric age group for discriminating sepsis from control cases. More recently, specific gene signatures were identified to discriminate between COVID-19 and its associated inflammatory sequelae. Through the current prospective cohort study, we aim to evaluate immune and metabolic blood markers which discriminate between sepses (including COVID-19) from other acute illnesses in critically unwell children and young persons, up to 18 years of age.

METHODS AND ANALYSIS

We describe a prospective cohort study for comparing the immune and metabolic whole-blood markers in patients with sepsis, COVID-19 and other illnesses. Clinical phenotyping and blood culture test results will provide a reference standard to evaluate the performance of blood markers from the research sample analysis. Serial sampling of whole blood (50 μL each) will be collected from children admitted to intensive care and with an acute illness to follow time dependent changes in biomarkers. An integrated lipidomics and RNASeq transcriptomics analyses will be conducted to evaluate immune-metabolic networks that discriminate sepsis and COVID-19 from other acute illnesses. This study received approval for deferred consent.

ETHICS AND DISSEMINATION

The study has received research ethics committee approval from the Yorkshire and Humber Leeds West Research Ethics Committee 2 (reference 20/YH/0214; IRAS reference 250612). Submission of study results for publication will involve making available all anonymised primary and processed data on public repository sites.

TRIAL REGISTRATION NUMBER

NCT04904523.

The superantigens SpeC and TSST-1 specifically activate TRBV12-3/12-4+ memory T cells

Severe bacterial or viral infections can induce a state of immune hyperactivation that can culminate in a potentially lethal cytokine storm. The classic example is toxic shock syndrome, a life-threatening complication of Staphylococcus aureus or Streptococcus pyogenes infection, which is driven by potent toxins known as superantigens (SAgs). SAgs are thought to promote immune evasion via the promiscuous activation of T cells, which subsequently become hyporesponsive, and act by cross-linking major histocompatibility complex class II molecules on antigen-presenting cells to particular β-chain variable (TRBV) regions of αβ T cell receptors (TCRs). Although some of these interactions have been defined previously, our knowledge of SAg-responsive TRBV regions is incomplete. In this study, we found that CD4⁺ and CD8⁺ T cells expressing TRBV12-3/12-4⁺ TCRs were highly responsive to streptococcal pyrogenic exotoxin C (SpeC) and toxic shock syndrome toxin-1 (TSST-1). In particular, SpeC and TSST-1 specifically induced effector cytokine production and the upregulation of multiple coinhibitory receptors among TRBV12-3/12-4⁺ CD4⁺ and CD8⁺ memory T cells, and importantly, these biological responses were dependent on human leukocyte antigen (HLA)-DR. Collectively, these data provided evidence of functionally determinative and therapeutically relevant interactions between SpeC and TSST-1 and CD4⁺ and CD8⁺ memory T cells expressing TRBV12-3/12-4⁺ TCRs, mediated via HLA-DR.

mSep: investigating physiological and immune-metabolic biomarkers in septic and healthy pregnant women to predict feto-maternal immune health - a prospective observational cohort study protocol

INTRODUCTION

Maternal sepsis remains a leading cause of death in pregnancy. Physiological adaptations to pregnancy obscure early signs of sepsis and can result in delays in recognition and treatment. Identifying biomarkers that can reliably diagnose sepsis will reduce morbidity and mortality and antibiotic overuse. We have previously identified an immune-metabolic biomarker network comprising three pathways with a >99% accuracy for detecting bacterial neonatal sepsis. In this prospective study, we will describe physiological parameters and novel biomarkers in two cohorts-healthy pregnant women and pregnant women with suspected sepsis-with the aim of mapping pathophysiological drivers and evaluating predictive biomarkers for diagnosing maternal sepsis.

METHODS AND ANALYSIS

Women aged over 18 with an ultrasound-confirmed pregnancy will be recruited to a pilot and two main study cohorts. The pilot will involve blood sample collection from 30 pregnant women undergoing an elective caesarean section. Cohort A will follow 100 healthy pregnant women throughout their pregnancy journey, with collection of blood samples from participants at routine time points in their pregnancy: week 12 'booking', week 28 and during labour. Cohort B will follow 100 pregnant women who present with suspected sepsis in pregnancy or labour and will have at least two blood samples taken during their care pathway. Study blood samples will be collected during routine clinical blood sampling. Detailed medical history and physiological parameters at the time of blood sampling will be recorded, along with the results of routine biochemical tests, including C reactive protein, lactate and white blood cell count. In addition, study blood samples will be processed and analysed for transcriptomic, lipidomic and metabolomic analyses and both qualitative and functional immunophenotyping.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Wales Research Ethics Committee 2 (SPON1752-19, 30 October 2019).

TRIAL REGISTRATION NUMBER

NCT05023954.

Epitope length variants balance protective immune responses and viral escape in HIV-1 infection

Cytotoxic T lymphocyte (CTL) and natural killer (NK) cell responses to a single optimal 10-mer epitope (KK10) in the human immunodeficiency virus type-1 (HIV-1) protein p24Gag are associated with enhanced immune control in patients expressing human leukocyte antigen (HLA)-B∗27:05. We find that proteasomal activity generates multiple length variants of KK10 (4-14 amino acids), which bind TAP and HLA-B∗27:05. However, only epitope forms ≥8 amino acids evoke peptide length-specific and cross-reactive CTL responses. Structural analyses reveal that all epitope forms bind HLA-B∗27:05 via a conserved N-terminal motif, and competition experiments show that the truncated epitope forms outcompete immunogenic epitope forms for binding to HLA-B∗27:05. Common viral escape mutations abolish (L136M) or impair (R132K) production of KK10 and longer epitope forms. Peptide length influences how well the inhibitory NK cell receptor KIR3DL1 binds HLA-B∗27:05 peptide complexes and how intraepitope mutations affect this interaction. These results identify a viral escape mechanism from CTL and NK responses based on differential antigen processing and peptide competition.

Oxylipin metabolism is controlled by mitochondrial β-oxidation during bacterial inflammation

Oxylipins are potent biological mediators requiring strict control, but how they are removed en masse during infection and inflammation is unknown. Here we show that lipopolysaccharide (LPS) dynamically enhances oxylipin removal via mitochondrial β-oxidation. Specifically, genetic or pharmacological targeting of carnitine palmitoyl transferase 1 (CPT1), a mitochondrial importer of fatty acids, reveal that many oxylipins are removed by this protein during inflammation in vitro and in vivo. Using stable isotope-tracing lipidomics, we find secretion-reuptake recycling for 12-HETE and its intermediate metabolites. Meanwhile, oxylipin β-oxidation is uncoupled from oxidative phosphorylation, thus not contributing to energy generation. Testing for genetic control checkpoints, transcriptional interrogation of human neonatal sepsis finds upregulation of many genes involved in mitochondrial removal of long-chain fatty acyls, such as ACSL1,3,4, ACADVL, CPT1B, CPT2 and HADHB. Also, ACSL1/Acsl1 upregulation is consistently observed following the treatment of human/murine macrophages with LPS and IFN-γ. Last, dampening oxylipin levels by β-oxidation is suggested to impact on their regulation of leukocyte functions. In summary, we propose mitochondrial β-oxidation as a regulatory metabolic checkpoint for oxylipins during inflammation.

nSeP: immune and metabolic biomarkers for early detection of neonatal sepsis-protocol for a prospective multicohort study

INTRODUCTION

Diagnosing neonatal sepsis is heavily dependent on clinical phenotyping as culture-positive body fluid has poor sensitivity, and existing blood biomarkers have poor specificity.A combination of machine learning, statistical and deep pathway biology analyses led to the identification of a tripartite panel of biologically connected immune and metabolic markers that showed greater than 99% accuracy for detecting bacterial infection with 100% sensitivity. The cohort study described here is designed as a large-scale clinical validation of this previous work.

METHODS AND ANALYSIS

This multicentre observational study will prospectively recruit a total of 1445 newborn infants (all gestations)-1084 with suspected early-or late-onset sepsis, and 361 controls-over 4 years. A small volume of whole blood will be collected from infants with suspected sepsis at the time of presentation. This sample will be used for integrated transcriptomic, lipidomic and targeted proteomics profiling. In addition, a subset of samples will be subjected to cellular phenotype and proteomic analyses. A second sample from the same patient will be collected at 24 hours, with an opportunistic sampling for stool culture. For control infants, only one set of blood and stool sample will be collected to coincide with clinical blood sampling. Along with detailed clinical information, blood and stool samples will be analysed and the information will be used to identify and validate the efficacy of immune-metabolic networks in the diagnosis of bacterial neonatal sepsis and to identify new host biomarkers for viral sepsis.

ETHICS AND DISSEMINATION

The study has received research ethics committee approval from the Wales Research Ethics Committee 2 (reference 19/WA/0008) and operational approval from Health and Care Research Wales. Submission of study results for publication will involve making available all anonymised primary and processed data on public repository sites.

TRIAL REGISTRATION NUMBER

NCT03777670.

Preexisting memory CD4+ T cells contribute to the primary response in an HIV-1 vaccine trial

Naive and memory CD4+ T cells reactive with human immunodeficiency virus type 1 (HIV-1) are detectable in unexposed, unimmunized individuals. The contribution of preexisting CD4+ T cells to a primary immune response was investigated in 20 HIV-1-seronegative volunteers vaccinated with an HIV-1 envelope (Env) plasmid DNA prime and recombinant modified vaccinia virus Ankara (MVA) boost in the HVTN 106 vaccine trial (clinicaltrials.gov NCT02296541). Prevaccination naive or memory CD4+ T cell responses directed against peptide epitopes in Env were identified in 14 individuals. After priming with DNA, 40% (8/20) of the elicited responses matched epitopes detected in the corresponding preimmunization memory repertoires, and clonotypes were shared before and after vaccination in 2 representative volunteers. In contrast, there were no shared epitope specificities between the preimmunization memory compartment and responses detected after boosting with recombinant MVA expressing a heterologous Env. Preexisting memory CD4+ T cells therefore shape the early immune response to vaccination with a previously unencountered HIV-1 antigen.

CD4+ T Follicular Helper Cells in Human Tonsils and Blood Are Clonally Convergent but Divergent from Non-Tfh CD4+ Cells

T follicular helper (Tfh) cells are fundamental for B cell selection and antibody maturation in germinal centers. Circulating Tfh (cTfh) cells constitute a minor proportion of the CD4⁺ T cells in peripheral blood, but their clonotypic relationship to Tfh populations resident in lymph nodes and the extent to which they differ from non-Tfh CD4⁺ cells have been unclear. Using donor-matched blood and tonsil samples, we investigate T cell receptor (TCR) sharing between tonsillar Tfh cells and peripheral Tfh and non-Tfh cell populations. TCR transcript sequencing reveals considerable clonal overlap between peripheral and tonsillar Tfh cell subsets as well as a clear distinction between Tfh and non-Tfh cells. Furthermore, influenza-specific cTfh cell clones derived from blood can be found in the repertoire of tonsillar Tfh cells. Therefore, human blood samples can be used to gain insight into the specificity of Tfh responses occurring in lymphoid tissues, provided that cTfh subsets are studied.

A population of proinflammatory T cells coexpresses αβ and γδ T cell receptors in mice and humans

T cells are classically recognized as distinct subsets that express αβ or γδ TCRs. We identify a novel population of T cells that coexpress αβ and γδ TCRs in mice and humans. These hybrid αβ-γδ T cells arose in the murine fetal thymus by day 16 of ontogeny, underwent αβ TCR-mediated positive selection into CD4+ or CD8+ thymocytes, and constituted up to 10% of TCRδ+ cells in lymphoid organs. They expressed high levels of IL-1R1 and IL-23R and secreted IFN-γ, IL-17, and GM-CSF in response to canonically restricted peptide antigens or stimulation with IL-1β and IL-23. Hybrid αβ-γδ T cells were transcriptomically distinct from conventional γδ T cells and displayed a hyperinflammatory phenotype enriched for chemokine receptors and homing molecules that facilitate migration to sites of inflammation. These proinflammatory T cells promoted bacterial clearance after infection with Staphylococcus aureus and, by licensing encephalitogenic Th17 cells, played a key role in the development of autoimmune disease in the central nervous system.

SIV-specific CD8+ T cells are clonotypically distinct across lymphoid and mucosal tissues

CD8+ T cell responses are necessary for immune control of simian immunodeficiency virus (SIV). However, the key parameters that dictate antiviral potency remain elusive, conceivably because most studies to date have been restricted to analyses of circulating CD8+ T cells. We conducted a detailed clonotypic, functional, and phenotypic survey of SIV-specific CD8+ T cells across multiple anatomical sites in chronically infected rhesus macaques with high (>10,000 copies/mL plasma) or low burdens of viral RNA (<10,000 copies/mL plasma). No significant differences in response magnitude were identified across anatomical compartments. Rhesus macaques with low viral loads (VLs) harbored higher frequencies of polyfunctional CXCR5+ SIV-specific CD8+ T cells in various lymphoid tissues and higher proportions of unique Gag-specific CD8+ T cell clonotypes in the mesenteric lymph nodes relative to rhesus macaques with high VLs. In addition, public Gag-specific CD8+ T cell clonotypes were more commonly shared across distinct anatomical sites than the corresponding private clonotypes, which tended to form tissue-specific repertoires, especially in the peripheral blood and the gastrointestinal tract. Collectively, these data suggest that functionality and tissue localization are important determinants of CD8+ T cell-mediated efficacy against SIV.

The MAIT TCRβ chain contributes to discrimination of microbial ligand

Mucosal-associated invariant T (MAIT) cells are key players in the immune response against microbial infection. The MAIT T-cell receptor (TCR) recognizes a diverse array of microbial ligands, and recent reports have highlighted the variability in the MAIT TCR that could further contribute to discrimination of ligand. The MAIT TCR complementarity determining region (CDR)3β sequence displays a high level of diversity across individuals, and clonotype usage appears to be dependent on antigenic exposure. To address the relationship between the MAIT TCR and microbial ligand, we utilized a previously defined panel of MAIT cell clones that demonstrated variability in responses against different microbial infections. Sequencing of these clones revealed four pairs, each with shared (identical) CDR3α and different CDR3β sequences. These pairs demonstrated varied responses against microbially infected dendritic cells as well as against 5-(2-oxopropylideneamino)-6-d-ribitylaminouracil, a ligand abundant in Salmonella enterica serovar Typhimurium, suggesting that the CDR3β contributes to differences in ligand discrimination. Taken together, these results highlight a key role for the MAIT CDR3β region in distinguishing between MR1-bound antigens and ligands.

Human CLEC9A antibodies deliver Wilms' tumor 1 (WT1) antigen to CD141+ dendritic cells to activate naïve and memory WT1-specific CD8+ T cells

Objectives

Vaccines that prime Wilms' tumor 1 (WT1)‐specific CD8⁺ T cells are attractive cancer immunotherapies. However, immunogenicity and clinical response rates may be enhanced by delivering WT1 to CD141⁺ dendritic cells (DCs). The C‐type lectin‐like receptor CLEC9A is expressed exclusively by CD141⁺ DCs and regulates CD8⁺ T‐cell responses. We developed a new vaccine comprising a human anti‐CLEC9A antibody fused to WT1 and investigated its capacity to target human CD141⁺ DCs and activate naïve and memory WT1‐specific CD8⁺ T cells.

Methods

WT1 was genetically fused to antibodies specific for human CLEC9A, DEC‐205 or β‐galactosidase (untargeted control). Activation of WT1‐specific CD8⁺ T‐cell lines following cross‐presentation by CD141⁺ DCs was quantified by IFNγ ELISPOT. Humanised mice reconstituted with human immune cell subsets, including a repertoire of naïve WT1‐specific CD8⁺ T cells, were used to investigate naïve WT1‐specific CD8⁺ T‐cell priming.

Results

The CLEC9A‐WT1 vaccine promoted cross‐presentation of WT1 epitopes to CD8⁺ T cells and mediated priming of naïve CD8⁺ T cells more effectively than the DEC‐205‐WT1 and untargeted control‐WT1 vaccines.

Conclusions

Delivery of WT1 to CD141⁺ DCs via CLEC9A stimulates CD8⁺ T cells more potently than either untargeted delivery or widespread delivery to all Ag‐presenting cells via DEC‐205, suggesting that cross‐presentation by CD141⁺ DCs is sufficient for effective CD8⁺ T‐cell priming in humans. The CLEC9A‐WT1 vaccine is a promising candidate immunotherapy for malignancies that express WT1.

VDJdb: a curated database of T-cell receptor sequences with known antigen specificity

The ability to decode antigen specificities encapsulated in the sequences of rearranged T-cell receptor (TCR) genes is critical for our understanding of the adaptive immune system and promises significant advances in the field of translational medicine. Recent developments in high-throughput sequencing methods (immune repertoire sequencing technology, or RepSeq) and single-cell RNA sequencing technology have allowed us to obtain huge numbers of TCR sequences from donor samples and link them to T-cell phenotypes. However, our ability to annotate these TCR sequences still lags behind, owing to the enormous diversity of the TCR repertoire and the scarcity of available data on T-cell specificities. In this paper, we present VDJdb, a database that stores and aggregates the results of published T-cell specificity assays and provides a universal platform that couples antigen specificities with TCR sequences. We demonstrate that VDJdb is a versatile instrument for the annotation of TCR repertoire data, enabling a concatenated view of antigen-specific TCR sequence motifs. VDJdb can be accessed at https://vdjdb.cdr3.net and https://github.com/antigenomics/vdjdb-db.

Primary EBV Infection Induces an Acute Wave of Activated Antigen-Specific Cytotoxic CD4+ T Cells

Primary EBV infection drives highly cytotoxic virus-specific CD4⁺ T cell responses.

EBV-specific memory CD4⁺ T cells are polyfunctional but lack cytotoxic activity.

Acute EBV-specific CD4-CTLs differ transcriptionally from classical memory CD4-CTLs.

CD4⁺ T cells are essential for immune protection against viruses, yet their multiple roles remain ill-defined at the single-cell level in humans. Using HLA class II tetramers, we studied the functional properties and clonotypic architecture of EBV-specific CD4⁺ T cells in patients with infectious mononucleosis, a symptomatic manifestation of primary EBV infection, and in long-term healthy carriers of EBV. We found that primary infection elicited oligoclonal expansions of T_H1-like EBV-specific CD4⁺ T cells armed with cytotoxic proteins that responded immediately ex vivo to challenge with EBV-infected B cells. Importantly, these acutely generated cytotoxic CD4⁺ T cells were highly activated and transcriptionally distinct from classically described cytotoxic CD4⁺ memory T cells that accumulate during other persistent viral infections, including CMV and HIV. In contrast, EBV-specific memory CD4⁺ T cells displayed increased cytokine polyfunctionality but lacked cytotoxic activity. These findings suggested an important effector role for acutely generated cytotoxic CD4⁺ T cells that could potentially be harnessed to improve the efficacy of vaccines against EBV.

TRAV1-2+ CD8+ T-cells including oligoconal expansions of MAIT cells are enriched in the airways in human tuberculosis

Mucosal-associated invariant T (MAIT) cells typically express a TRAV1-2+ semi-invariant TCRα that enables recognition of bacterial, mycobacterial, and fungal riboflavin metabolites presented by MR1. MAIT cells are associated with immune control of bacterial and mycobacterial infections in murine models. Here, we report that a population of pro-inflammatory TRAV1-2+ CD8+ T cells are present in the airways and lungs of healthy individuals and are enriched in bronchoalveolar fluid of patients with active pulmonary tuberculosis (TB). High-throughput T cell receptor analysis reveals oligoclonal expansions of canonical and donor-unique TRAV1-2+ MAIT-consistent TCRα sequences within this population. Some of these cells demonstrate MR1-restricted mycobacterial reactivity and phenotypes suggestive of MAIT cell identity. These findings demonstrate enrichment of TRAV1-2+ CD8+ T cells with MAIT or MAIT-like features in the airways during active TB and suggest a role for these cells in the human pulmonary immune response to Mycobacterium tuberculosis.

Abstract B007: Identification of prostate cancer stem cell antigens for T-cell immunotherapy by HLA ligandome analysis

Introduction: Localized prostate cancer (PCa) can be successfully treated by androgen deprivation, radiotherapy and surgery, however these may not be sufficient to eradicate cancer stem cells (CSCs). CSCs are more resistant to such treatments than the bulk of the tumor; and can contribute to disease relapse. PCa patients who relapse have a poor prognosis. We hypothesize that CSCs could be killed by T-cells in an antigen specific way, thus preventing the possibility of relapse. In this study we identified novel PCa CSC antigens by HLA ligandome analysis and isolated antigen specific CD8+ T-cells. Methods: We identified CSCs using aldehyde dehydrogenase (ALDH) activity as a CSC marker. ALDH high and low cells from the DU145 PCa cell line and from prostate adenocarcinoma primary tissue were characterized in vitro; DU145 CSCs and non-CSCs were additionally characterized in vivo. We isolated peptide-HLA complexes from DU145 cells by immunoprecipitation and analyzed the eluted peptides by mass spectrometry. We identified CSC antigens based on the gene expression in ALDH high and low DU145 cells (measured by qPCR). To select antigens for further analysis we performed homology modelling of the HLA-peptide interface using COOT software and the YASARA server for energy minimization. The interface interactions were quantified using PISA software. We additionally confirmed antigen expression in the primary cells by fluorescence microscopy and PCR. Tetramers were produced to isolate T-cells which recognized a selection of these antigens. Results: The ligandome analysis identified over 1900 peptides. We selected antigens with low gene expression in healthy tissues (www.GTexportal.org) and high predicted binding to DU145 HLA alleles (http://tools.immuneepitope.org/mhci/). ALDH high DU145 cells were more tumorigenic in vivo than ALDH low cells. ALDH high DU145 and primary prostate cancer cells grew larger colonies and spheres in vitro. We identified 11 CSC antigens by qPCR; 6 upregulated in ALDH high DU145 cells (e.g., TACSTD2) and 5 abundant in both ALDH high and ALDH low DU145 cells (e.g., XPO1). Relevant 9-mer epitopes from three antigens* induced CD8+ T-cell responses in vitro. Antigen-specific CD8+ T-cells were identified by tetramer staining at a frequency of approx. 15 per 100000 cells. These cells are currently being expanded to use in CTL assays. Conclusion: We have identified CSC antigens which could lead to specific targeting by T-cells and prevention of PCa relapse. Further epitopes restricted to the more frequent HLA alleles could additionally be predicted in silico from the novel antigens we identified. We are also investigating prediction of viral epitopes highly aligned with the self-peptides (determined in silico) to boost the immune response against CSCs. *Subject of an ongoing patent application.

Citation Format: Amy S. Codd, Saly Al-Taei, Serina Tokita, Emi Mizushima, Pierre J. Rizkallah, Tom Whalley, Barbara Szomolay, Kristin Ladell, James E. McLaren, Sian Llewellyn-Lacey, David A. Price, Takayuki Kanaseki, Toshihiko Torigoe, Stephen Man, Zsuzsanna Tabi. Identification of prostate cancer stem cell antigens for T-cell immunotherapy by HLA ligandome analysis [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B007.

IL-33 Augments Virus-Specific Memory T Cell Inflation and Potentiates the Efficacy of an Attenuated Cytomegalovirus-Based Vaccine

Candidate vaccines designed to generate T cell-based immunity are typically vectored by nonpersistent viruses, which largely fail to elicit durable effector memory T cell responses. This limitation can be overcome using recombinant strains of CMV. Proof-of-principle studies have demonstrated the potential benefits of this approach, most notably in the SIV model, but safety concerns require the development of nonreplicating alternatives with comparable immunogenicity. In this study, we show that IL-33 promotes the accumulation and recall kinetics of circulating and tissue-resident memory T cells in mice infected with murine CMV. Using a replication-deficient murine CMV vector, we further show that exogenous IL-33 boosts vaccine-induced memory T cell responses, which protect against subsequent heterologous viral challenge. These data suggest that IL-33 could serve as a useful adjuvant to improve the efficacy of vaccines based on attenuated derivatives of CMV.

Memory CD4+ T cells are generated in the human fetal intestine

The fetus is thought to be protected from exposure to foreign antigens, yet CD45RO⁺ T cells reside in the fetal intestine. Here we combined functional assays with mass cytometry, single-cell RNA-sequencing and high-throughput T cell antigen receptor (TCR) sequencing to characterize the CD4⁺ T cell compartment in the human fetal intestine. We identified 22 CD4⁺ T cell clusters, including naive-like, regulatory-like and memory-like subpopulations, which were confirmed and further characterized at the transcriptional level. Memory-like CD4⁺ T cells had high expression of Ki-67, indicative of cell division, and CD5, a surrogate marker of TCR avidity, and produced the cytokines IFN-γ and IL-2. Pathway analysis revealed a differentiation trajectory associated with cellular activation and proinflammatory effector functions, and TCR repertoire analysis indicated clonal expansions, distinct repertoire characteristics and interconnections between subpopulations of memory-like CD4⁺ T cells. Imaging-mass cytometry indicated that memory-like CD4⁺ T cells colocalized with antigen-presenting cells. Collectively, these results provide evidence for the generation of memory-like CD4⁺ T cells in the human fetal intestine that is consistent with exposure to foreign antigens.

Islet-reactive CD8+ T cell frequencies in the pancreas, but not in blood, distinguish type 1 diabetic patients from healthy donors

The human leukocyte antigen-A2 (HLA-A2)-restricted zinc transporter 8_186-194 (ZnT8_186-194) and other islet epitopes elicit interferon-γ secretion by CD8⁺ T cells preferentially in type 1 diabetes (T1D) patients compared with controls. We show that clonal ZnT8_186-194-reactive CD8⁺ T cells express private T cell receptors and display equivalent functional properties in T1D and healthy individuals. Ex vivo analyses further revealed that CD8⁺ T cells reactive to ZnT8_186-194 and other islet epitopes circulate at similar frequencies and exhibit a predominantly naïve phenotype in age-matched T1D and healthy donors. Higher frequencies of ZnT8_186-194-reactive CD8⁺ T cells with a more antigen-experienced phenotype were detected in children versus adults, irrespective of disease status. Moreover, some ZnT8_186-194-reactive CD8⁺ T cell clonotypes were found to cross-recognize a Bacteroides stercoris mimotope. Whereas ZnT8 was poorly expressed in thymic medullary epithelial cells, variable thymic expression levels of islet antigens did not modulate the peripheral frequency of their cognate CD8⁺ T cells. In contrast, ZnT8_186-194-reactive cells were enriched in the pancreata of T1D patients versus nondiabetic and type 2 diabetic individuals. Thus, islet-reactive CD8⁺ T cells circulate in most individuals but home to the pancreas preferentially in T1D patients. We conclude that the activation of this common islet-reactive T cell repertoire and progression to T1D likely require defective peripheral immunoregulation and/or a proinflammatory islet microenvironment.

Exploring the pre-immune landscape of antigen-specific T cells

Background

Adaptive immune responses to newly encountered pathogens depend on the mobilization of antigen-specific clonotypes from a vastly diverse pool of naive T cells. Using recent advances in immune repertoire sequencing technologies, models of the immune receptor rearrangement process, and a database of annotated T cell receptor (TCR) sequences with known specificities, we explored the baseline frequencies of T cells specific for defined human leukocyte antigen (HLA) class I-restricted epitopes in healthy individuals.

Methods

We used a database of TCR sequences with known antigen specificities and a probabilistic TCR rearrangement model to estimate the baseline frequencies of TCRs specific to distinct antigens epitopespecificT-cells. We verified our estimates using a publicly available collection of TCR repertoires from healthy individuals. We also interrogated a database of immunogenic and non-immunogenic peptides is used to link baseline T-cell frequencies with epitope immunogenicity.

Results

Our findings revealed a high degree of variability in the prevalence of T cells specific for different antigens that could be explained by the physicochemical properties of the corresponding HLA class I-bound peptides. The occurrence of certain rearrangements was influenced by ancestry and HLA class I restriction, and umbilical cord blood samples contained higher frequencies of common pathogen-specific TCRs. We also identified a quantitative link between specific T cell frequencies and the immunogenicity of cognate epitopes presented by defined HLA class I molecules.

Conclusions

Our results suggest that the population frequencies of specific T cells are strikingly non-uniform across epitopes that are known to elicit immune responses. This inference leads to a new definition of epitope immunogenicity based on specific TCR frequencies, which can be estimated with a high degree of accuracy in silico, thereby providing a novel framework to integrate computational and experimental genomics with basic and translational research efforts in the field of T cell immunology.

Electronic supplementary material

The online version of this article (10.1186/s13073-018-0577-7) contains supplementary material, which is available to authorized users.

Divergent roles for antigenic drive in the aetiology of primary versus dasatinib-associated CD8+ TCR-Vβ+ expansions

CD8+ T-cell expansions are the primary manifestation of T-cell large granular lymphocytic leukemia (T-LGLL), which is frequently accompanied by neutropenia and rheumatoid arthritis, and also occur as a secondary phenomenon in leukemia patients treated with dasatinib, notably in association with various drug-induced side-effects. However, the mechanisms that underlie the genesis and maintenance of expanded CD8+ T-cell receptor (TCR)-Vβ+ populations in these patient groups have yet to be fully defined. In this study, we performed a comprehensive phenotypic and clonotypic assessment of expanded (TCR-Vβ+) and residual (TCR-Vβ-) CD8+ T-cell populations in T-LGLL and dasatinib-treated chronic myelogenous leukemia (CML) patients. The dominant CD8+ TCR-Vβ+ expansions in T-LGLL patients were largely monoclonal and highly differentiated, whereas the dominant CD8+ TCR-Vβ+ expansions in dasatinib-treated CML patients were oligoclonal or polyclonal, and displayed a broad range of memory phenotypes. These contrasting features suggest divergent roles for antigenic drive in the immunopathogenesis of primary versus dasatinib-associated CD8+ TCR-Vβ+ expansions.

Autoreactive CD8+ T-cells are highly dependent on CD8 for activation and as such targeting CD8 is an effective way of blocking autoreactive CD8+ T-cell activation

Autoimmune diseases such as type I diabetes (TID) and multiple sclerosis (MS) are chronic conditions that have a significant impact on quality of life. CD8+ T-cells play an important role in the pathogenesis of these diseases. However, drugs that target the entire CD8+ T-cell population are not desirable because this population provides protection against infection. Accordingly, there is an urgent requirement to develop novel treatment strategies that exclusively target the autoreactive CD8+ T-cell population. CD8+ T-cells express a molecule called CD8 at their cell surface which assists with activation. We have demonstrated that autoreactive CD8+ T-cells are entirely dependent on CD8 for activation. In stark contrast, pathogen specific CD8+ T-cells are characterized by higher functional sensitivity and are relatively CD8 independent. This represents an intrinsic difference that can be exploited for therapeutic benefit. Our data suggests that “blocking anti-CD8 antibodies” can be used to block autoreactive CD8+ T-cell attack without affecting pathogen specific immunity, a key goal in the treatment of autoimmunity. The generation of “blocking anti-CD8 antibodies” offers an opportunity to develop a novel therapeutic approach that can be used to treat CD8+ T-cell mediated autoimmunity. In order to conduct a further assessment, we are currently developing a strategy for in vivo validation of the approach.

Clonal selection in the human Vδ1 T cell repertoire indicates γδ TCR-dependent adaptive immune surveillance

γδ T cells are considered to be innate-like lymphocytes that respond rapidly to stress without clonal selection and differentiation. Here we use next-generation sequencing to probe how this paradigm relates to human Vδ2^neg T cells, implicated in responses to viral infection and cancer. The prevalent Vδ1 T cell receptor (TCR) repertoire is private and initially unfocused in cord blood, typically becoming strongly focused on a few high-frequency clonotypes by adulthood. Clonal expansions have differentiated from a naive to effector phenotype associated with CD27 downregulation, retaining proliferative capacity and TCR sensitivity, displaying increased cytotoxic markers and altered homing capabilities, and remaining relatively stable over time. Contrastingly, Vδ2⁺ T cells express semi-invariant TCRs, which are present at birth and shared between individuals. Human Vδ1⁺ T cells have therefore evolved a distinct biology from the Vδ2⁺ subset, involving a central, personalized role for the γδ TCR in directing a highly adaptive yet unconventional form of immune surveillance.

γδ T cells are generally considered innate-like lymphocytes. Here the authors sequence human γδ T cell receptors (TCR) to show focusing of the private Vδ1 TCR repertoire, suggesting that, unlike Vδ2 T cells, the Vδ1 T cell compartment has adaptive attributes.

CD8+ T-cell specificity is compromised at a defined MHCI/CD8 affinity threshold

The CD8 co-receptor engages peptide-major histocompatibility complex class I (pMHCI) molecules at a largely invariant site distinct from the T-cell receptor (TCR)-binding platform and enhances the sensitivity of antigen-driven activation to promote effective CD8+ T-cell immunity. A small increase in the strength of the pMHCI/CD8 interaction (~1.5-fold) can disproportionately amplify this effect, boosting antigen sensitivity by up to two orders of magnitude. However, recognition specificity is lost altogether with more substantial increases in pMHCI/CD8 affinity (~10-fold). In this study, we used a panel of MHCI mutants with altered CD8-binding properties to show that TCR-mediated antigen specificity is delimited by a pMHCI/CD8 affinity threshold. Our findings suggest that CD8 can be engineered within certain biophysical parameters to enhance the therapeutic efficacy of adoptive T-cell transfer irrespective of antigen specificity.

Targeted suppression of autoreactive CD8+ T-cell activation using blocking anti-CD8 antibodies

CD8⁺ T-cells play a role in the pathogenesis of autoimmune diseases such as multiple sclerosis and type 1 diabetes. However, drugs that target the entire CD8⁺ T-cell population are not desirable because the associated lack of specificity can lead to unwanted consequences, most notably an enhanced susceptibility to infection. Here, we show that autoreactive CD8⁺ T-cells are highly dependent on CD8 for ligand-induced activation via the T-cell receptor (TCR). In contrast, pathogen-specific CD8⁺ T-cells are relatively CD8-independent. These generic differences relate to an intrinsic dichotomy that segregates self-derived and exogenous antigen-specific TCRs according to the monomeric interaction affinity with cognate peptide-major histocompatibility complex class I (pMHCI). As a consequence, “blocking” anti-CD8 antibodies can suppress autoreactive CD8⁺ T-cell activation in a relatively selective manner. These findings provide a rational basis for the development and in vivo assessment of novel therapeutic strategies that preferentially target disease-relevant autoimmune responses within the CD8⁺ T-cell compartment.

Proinsulin Expression Shapes the TCR Repertoire but Fails to Control the Development of Low-Avidity Insulin-Reactive CD8+ T Cells

NOD mice, a model strain for human type 1 diabetes, express proinsulin (PI) in the thymus. However, insulin-reactive T cells escape negative selection, and subsequent activation of the CD8(+) T-cell clonotype G9C8, which recognizes insulin B15-23 via an αβ T-cell receptor (TCR) incorporating TRAV8-1/TRAJ9 and TRBV19/TRBJ2-3 gene rearrangements, contributes to the development of diabetes. In this study, we used fixed TRAV8-1/TRAJ9 TCRα-chain transgenic mice to assess the impact of PI isoform expression on the insulin-reactive CD8(+) T-cell repertoire. The key findings were: 1) PI2 deficiency increases the frequency of insulin B15-23-reactive TRBV19(+)CD8(+) T cells and causes diabetes; 2) insulin B15-23-reactive TRBV19(+)CD8(+) T cells are more abundant in the pancreatic lymph nodes of mice lacking PI1 and/or PI2; 3) overexpression of PI2 decreases TRBV19 usage in the global CD8(+) T-cell compartment; 4) a biased repertoire of insulin-reactive CD8(+) T cells emerges in the periphery regardless of antigen exposure; and 5) low-avidity insulin-reactive CD8(+) T cells are less affected by antigen exposure in the thymus than in the periphery. These findings inform our understanding of the diabetogenic process and reveal new avenues for therapeutic exploitation in type 1 diabetes.

Early innate responses to pathogens: pattern recognition by unconventional human T-cells

Although typically viewed as a feature of innate immune responses, microbial pattern recognition is increasingly acknowledged as a function of particular cells nominally categorized within the adaptive immune system. Groundbreaking research over the past three years has shown how unconventional human T-cells carrying invariant or semi-invariant TCRs that are not restricted by classical MHC molecules sense microbial compounds via entirely novel antigen presenting pathways. This review will focus on the innate-like recognition of non-self metabolites by Vγ9/Vδ2 T-cells, mucosal-associated invariant T (MAIT) cells and germline-encoded mycolyl-reactive (GEM) T-cells, with an emphasis on early immune responses in acute infection.

Determinants of gliadin-specific T cell selection in celiac disease

In HLA-DQ8-associated celiac disease (CD), the pathogenic T cell response is directed toward an immunodominant α-gliadin-derived peptide (DQ8-glia-α1). However, our knowledge of TCR gene usage within the primary intestinal tissue of HLA-DQ8 (+) CD patients is limited. We identified two populations of HLA-DQ8-glia-α1 tetramer(+) CD4(+) T cells that were essentially undetectable in biopsy samples from patients on a gluten-free diet but expanded rapidly and specifically after antigenic stimulation. Distinguished by expression of TRBV9, both T cell populations displayed biased clonotypic repertoires and reacted similarly against HLA-DQ8-glia-α1. In particular, TRBV9 paired most often with TRAV26-2, whereas the majority of TRBV9(-) TCRs used TRBV6-1 with no clear TRAV gene preference. Strikingly, both tetramer(+)/TRBV9(+) and tetramer(+)/TRBV9(-) T cells possessed a non-germline-encoded arginine residue in their CDR3α and CDR3β loops, respectively. Comparison of the crystal structures of three TRBV9(+) TCRs and a TRBV9(-) TCR revealed that, as a result of distinct TCR docking modes, the HLA-DQ8-glia-α1 contacts mediated by the CDR3-encoded arginine were almost identical between TRBV9(+) and TRBV9(-) TCRs. In all cases, this interaction centered on two hydrogen bonds with a specific serine residue in the bound peptide. Replacement of serine with alanine at this position abrogated TRBV9(+) and TRBV9(-) clonal T cell proliferation in response to HLA-DQ8-glia-α1. Gluten-specific memory CD4(+) T cells with structurally and functionally conserved TCRs therefore predominate in the disease-affected tissue of patients with HLA-DQ8-mediated CD.

Determinants of gliadin-specific T cell selection in celiac disease

In HLA-DQ8-associated celiac disease (CD), the pathogenic T cell response is directed toward an immunodominant α-gliadin-derived peptide (DQ8-glia-α1). However, our knowledge of TCR gene usage within the primary intestinal tissue of HLA-DQ8 (+) CD patients is limited. We identified two populations of HLA-DQ8-glia-α1 tetramer(+) CD4(+) T cells that were essentially undetectable in biopsy samples from patients on a gluten-free diet but expanded rapidly and specifically after antigenic stimulation. Distinguished by expression of TRBV9, both T cell populations displayed biased clonotypic repertoires and reacted similarly against HLA-DQ8-glia-α1. In particular, TRBV9 paired most often with TRAV26-2, whereas the majority of TRBV9(-) TCRs used TRBV6-1 with no clear TRAV gene preference. Strikingly, both tetramer(+)/TRBV9(+) and tetramer(+)/TRBV9(-) T cells possessed a non-germline-encoded arginine residue in their CDR3α and CDR3β loops, respectively. Comparison of the crystal structures of three TRBV9(+) TCRs and a TRBV9(-) TCR revealed that, as a result of distinct TCR docking modes, the HLA-DQ8-glia-α1 contacts mediated by the CDR3-encoded arginine were almost identical between TRBV9(+) and TRBV9(-) TCRs. In all cases, this interaction centered on two hydrogen bonds with a specific serine residue in the bound peptide. Replacement of serine with alanine at this position abrogated TRBV9(+) and TRBV9(-) clonal T cell proliferation in response to HLA-DQ8-glia-α1. Gluten-specific memory CD4(+) T cells with structurally and functionally conserved TCRs therefore predominate in the disease-affected tissue of patients with HLA-DQ8-mediated CD.

Role of naive-derived T memory stem cells in T-cell reconstitution following allogeneic transplantation

Early T-cell reconstitution following allogeneic transplantation depends on the persistence and function of T cells that are adoptively transferred with the graft. Posttransplant cyclophosphamide (pt-Cy) effectively prevents alloreactive responses from unmanipulated grafts, but its effect on subsequent immune reconstitution remains undetermined. Here, we show that T memory stem cells (TSCM), which demonstrated superior reconstitution capacity in preclinical models, are the most abundant circulating T-cell population in the early days following haploidentical transplantation combined with pt-Cy and precede the expansion of effector cells. Transferred naive, but not TSCM or conventional memory cells preferentially survive cyclophosphamide, thus suggesting that posttransplant TSCM originate from naive precursors. Moreover, donor naive T cells specific for exogenous and self/tumor antigens persist in the host and contribute to peripheral reconstitution by differentiating into effectors. Similarly, pathogen-specific memory T cells generate detectable recall responses, but only in the presence of the cognate antigen. We thus define the cellular basis of T-cell reconstitution following pt-Cy at the antigen-specific level and propose to explore naive-derived TSCM in the clinical setting to overcome immunodeficiency. These trials were registered at www.clinicaltrials.gov as #NCT02049424 and #NCT02049580.

CD8+ TCR Bias and Immunodominance in HIV-1 Infection

Immunodominance describes a phenomenon whereby the immune system consistently targets only a fraction of the available Ag pool derived from a given pathogen. In the case of CD8(+) T cells, these constrained epitope-targeting patterns are linked to HLA class I expression and determine disease progression. Despite the biological importance of these predetermined response hierarchies, little is known about the factors that control immunodominance in vivo. In this study, we conducted an extensive analysis of CD8(+) T cell responses restricted by a single HLA class I molecule to evaluate the mechanisms that contribute to epitope-targeting frequency and antiviral efficacy in HIV-1 infection. A clear immunodominance hierarchy was observed across 20 epitopes restricted by HLA-B*42:01, which is highly prevalent in populations of African origin. Moreover, in line with previous studies, Gag-specific responses and targeting breadth were associated with lower viral load set-points. However, peptide-HLA-B*42:01 binding affinity and stability were not significantly linked with targeting frequencies. Instead, immunodominance correlated with epitope-specific usage of public TCRs, defined as amino acid residue-identical TRB sequences that occur in multiple individuals. Collectively, these results provide important insights into a potential link between shared TCR recruitment, immunodominance, and antiviral efficacy in a major human infection.

Naive CD8⁺ T-cell precursors display structured TCR repertoires and composite antigen-driven selection dynamics

Basic parameters of the naive antigen (Ag)-specific T-cell repertoire in humans remain poorly defined. Systematic characterization of this ‘ground state' immunity in comparison with memory will allow a better understanding of clonal selection during immune challenge. Here, we used high-definition cell isolation from umbilical cord blood samples to establish the baseline frequency, phenotype and T-cell antigen receptor (TCR) repertoire of CD8⁺ T-cell precursor populations specific for a range of viral and self-derived Ags. Across the board, these precursor populations were phenotypically naive and occurred with hierarchical frequencies clustered by Ag specificity. The corresponding patterns of TCR architecture were highly ordered and displayed partial overlap with adult memory, indicating biased structuring of the T-cell repertoire during Ag-driven selection. Collectively, these results provide new insights into the complex nature and dynamics of the naive T-cell compartment.

β-cell-specific CD8 T cell phenotype in type 1 diabetes reflects chronic autoantigen exposure

Autoreactive CD8 T cells play a central role in the destruction of pancreatic islet β-cells that leads to type 1 diabetes, yet the key features of this immune-mediated process remain poorly defined. In this study, we combined high-definition polychromatic flow cytometry with ultrasensitive peptide-human leukocyte antigen class I tetramer staining to quantify and characterize β-cell-specific CD8 T cell populations in patients with recent-onset type 1 diabetes and healthy control subjects. Remarkably, we found that β-cell-specific CD8 T cell frequencies in peripheral blood were similar between subject groups. In contrast to healthy control subjects, however, patients with newly diagnosed type 1 diabetes displayed hallmarks of antigen-driven expansion uniquely within the β-cell-specific CD8 T cell compartment. Molecular analysis of selected β-cell-specific CD8 T cell populations further revealed highly skewed oligoclonal T cell receptor repertoires comprising exclusively private clonotypes. Collectively, these data identify novel and distinctive features of disease-relevant CD8 T cells that inform the immunopathogenesis of type 1 diabetes.

Programmed death-1 expression on HIV-1-specific CD8+ T cells is shaped by epitope specificity, T-cell receptor clonotype usage and antigen load

OBJECTIVES

Although CD8+ T cells play a critical role in the control of HIV-1 infection,their antiviral efficacy can be limited by antigenic variation and immune exhaustion.The latter phenomenon is characterized by the upregulation of multiple inhibitory receptors, such as programmed death-1 (PD-1), CD244 and lymphocyte activation gene-3 (LAG-3), which modulate the functional capabilities of CD8+ T cells.

DESIGN AND METHODS

Here, we used an array of different human leukocyte antigen(HLA)-B*15:03 and HLA-B*42:01 tetramers to characterize inhibitory receptor expression as a function of differentiation on HIV-1-specific CD8+ T-cell populations(n = 128) spanning 11 different epitope targets.

RESULTS

Expression levels of PD-1, but not CD244 or LAG-3, varied substantially across epitope specificities both within and between individuals. Differential expression of PD-1 on T-cell receptor (TCR) clonotypes within individual HIV-1-specific CD8+ T-cell populations was also apparent, independent of clonal dominance hierarchies. Positive correlations were detected between PD-1 expression and plasma viral load, which were reinforced by stratification for epitope sequence stability and dictated by effector memory CD8+ T cells.

CONCLUSION

Collectively, these data suggest that PD-1 expression on HIV-1-specific CD8+ T cells tracks antigen load at the level of epitope specificity and TCR clonotype usage. These findings are important because they provide evidence that PD-1 expression levels are influenced by peptide/HLA class I antigen exposure.

MR1-restricted MAIT cells display ligand discrimination and pathogen selectivity through distinct T cell receptor usage

MAIT cells can discriminate between pathogen-derived ligands in a clonotype-dependent manner, and the TCR repertoire is distinct within individuals, indicating that the MAIT cell repertoire is shaped by prior microbial exposure.

Mucosal-associated invariant T (MAIT) cells express a semi-invariant T cell receptor (TCR) that detects microbial metabolites presented by the nonpolymorphic major histocompatibility complex (MHC)–like molecule MR1. The highly conserved nature of MR1 in conjunction with biased MAIT TCRα chain usage is widely thought to indicate limited ligand presentation and discrimination within a pattern-like recognition system. Here, we evaluated the TCR repertoire of MAIT cells responsive to three classes of microbes. Substantial diversity and heterogeneity were apparent across the functional MAIT cell repertoire as a whole, especially for TCRβ chain sequences. Moreover, different pathogen-specific responses were characterized by distinct TCR usage, both between and within individuals, suggesting that MAIT cell adaptation was a direct consequence of exposure to various exogenous MR1-restricted epitopes. In line with this interpretation, MAIT cell clones with distinct TCRs responded differentially to a riboflavin metabolite. These results suggest that MAIT cells can discriminate between pathogen-derived ligands in a clonotype-dependent manner, providing a basis for adaptive memory via recruitment of specific repertoires shaped by microbial exposure.

Avidity of influenza-specific memory CD8+ T-cell populations decays over time compromising antiviral immunity

Decline of cell-mediated immunity is often attributed to decaying T-cell numbers and their distribution in peripheral organs. This study examined the hypothesis that qualitative as well as quantitative changes contribute to the declining efficacy of CD8(+) T-cell memory. Using a model of influenza virus infection, where loss of protective CD8(+) T-cell immunity was observed 6 months postinfection, we found no decline in antigen-specific T-cell numbers or migration to the site of secondary infection. There was, however, a large reduction in antigen-specific CD8(+) T-cell degranulation, cytokine secretion, and polyfunctionality. A profound loss of high-avidity T cells over time indicated that failure to confer protective immunity resulted from the inferior functional capacity of remaining low avidity cells. These data imply that high-avidity central memory T cells wane with declining antigen levels, leaving lower avidity T cells with reduced functional capabilities.

A T cell-inducing influenza vaccine for the elderly: safety and immunogenicity of MVA-NP+M1 in adults aged over 50 years

BACKGROUND

Current influenza vaccines have reduced immunogenicity and are of uncertain efficacy in older adults. We assessed the safety and immunogenicity of MVA-NP+M1, a viral-vectored influenza vaccine designed to boost memory T cell responses, in a group of older adults.

METHODS

Thirty volunteers (aged 50-85) received a single intramuscular injection of MVA-NP+M1 at a dose of 1·5×10(8) plaque forming units (pfu). Safety and immunogenicity were assessed over a period of one year. The frequency of T cells specific for nucleoprotein (NP) and matrix protein 1 (M1) was determined by interferon-gamma (IFN-γ) ELISpot, and their phenotypic and functional properties were characterized by polychromatic flow cytometry. In a subset of M1-specific CD8(+) T cells, T cell receptor (TCR) gene expression was evaluated using an unbiased molecular approach.

RESULTS

Vaccination with MVA-NP+M1 was well tolerated. ELISpot responses were boosted significantly above baseline following vaccination. Increases were detected in both CD4(+) and CD8(+) T cell subsets. Clonality studies indicated that MVA-NP+M1 expanded pre-existing memory CD8(+) T cells, which displayed a predominant CD27(+)CD45RO(+)CD57(-)CCR7(-) phenotype both before and after vaccination.

CONCLUSIONS

MVA-NP+M1 is safe and immunogenic in older adults. Unlike seasonal influenza vaccination, the immune responses generated by MVA-NP+M1 are similar between younger and older individuals. A T cell-inducing vaccine such as MVA-NP+M1 may therefore provide a way to circumvent the immunosenescence that impairs routine influenza vaccination.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00942071.

Cytokines, macrophage lipid metabolism and foam cells: implications for cardiovascular disease therapy

Cardiovascular disease is the biggest killer globally and the principal contributing factor to the pathology is atherosclerosis; a chronic, inflammatory disorder characterized by lipid and cholesterol accumulation and the development of fibrotic plaques within the walls of large and medium arteries. Macrophages are fundamental to the immune response directed to the site of inflammation and their normal, protective function is harnessed, detrimentally, in atherosclerosis. Macrophages contribute to plaque development by internalizing native and modified lipoproteins to convert them into cholesterol-rich foam cells. Foam cells not only help to bridge the innate and adaptive immune response to atherosclerosis but also accumulate to create fatty streaks, which help shape the architecture of advanced plaques. Foam cell formation involves the disruption of normal macrophage cholesterol metabolism, which is governed by a homeostatic mechanism that controls the uptake, intracellular metabolism, and efflux of cholesterol. It has emerged over the last 20 years that an array of cytokines, including interferon-γ, transforming growth factor-β1, interleukin-1β, and interleukin-10, are able to manipulate these processes. Foam cell targeting, anti-inflammatory therapies, such as agonists of nuclear receptors and statins, are known to regulate the actions of pro- and anti-atherogenic cytokines indirectly of their primary pharmacological function. A clear understanding of macrophage foam cell biology will hopefully enable novel foam cell targeting therapies to be developed for use in the clinical intervention of atherosclerosis.

ERK is integral to the IFN-γ-mediated activation of STAT1, the expression of key genes implicated in atherosclerosis, and the uptake of modified lipoproteins by human macrophages

The proinflammatory cytokine IFN-gamma is a master regulator of atherosclerosis and mediates its cellular actions mainly through STAT1. Unfortunately, the impact of other IFN-gamma inducible pathways on STAT1 activation and the regulation of downstream responses associated with atherosclerosis in human macrophages are poorly understood and were therefore investigated. In this study, we demonstrate that the IFN-gamma-mediated phosphorylation of STAT1 on Ser(727), crucial for its maximal activity, was attenuated in human macrophages by pharmacological inhibition of ERK. In these cells, IFN-gamma induced changes in the expression of several key genes implicated in atherosclerosis, such as MCP-1, through an ERK-dependent mechanism. Additionally, the IFN-gamma-induced activity of STAT1-responsive promoters was attenuated by transfection of dominant-negative forms of ERK and other key components of this pathway. Furthermore, the IFN-gamma-induced uptake of acetylated and oxidized low-density lipoprotein by human macrophages was attenuated by pharmacological inhibition or RNA interference-mediated knockdown of ERK. These studies suggest a critical role for ERK signaling in the IFN-gamma-mediated changes in macrophage cholesterol homeostasis and gene expression during atherosclerosis.

The TNF-like protein 1A-death receptor 3 pathway promotes macrophage foam cell formation in vitro

TNF-like protein 1A (TL1A), a TNF superfamily cytokine that binds to death receptor 3 (DR3), is highly expressed in macrophage foam cell-rich regions of atherosclerotic plaques, although its role in foam cell formation has yet to be elucidated. We investigated whether TL1A can directly stimulate macrophage foam cell formation in both THP-1 and primary human monocyte-derived macrophages with the underlying mechanisms involved. We demonstrated that TL1A promotes foam cell formation in human macrophages in vitro by increasing both acetylated and oxidized low-density lipoprotein uptake, by enhancing intracellular total and esterified cholesterol levels and reducing cholesterol efflux. This imbalance in cholesterol homeostasis is orchestrated by TL1A-mediated changes in the mRNA and protein expression of several genes implicated in the uptake and efflux of cholesterol, such as scavenger receptor A and ATP-binding cassette transporter A1. Furthermore, through the use of virally delivered DR3 short-hairpin RNA and bone marrow-derived macrophages from DR3 knockout mice, we demonstrate that DR3 can regulate foam cell formation and contributes significantly to the action of TL1A in this process in vitro. We show, for the first time, a novel proatherogenic role for both TL1A and DR3 that implicates this pathway as a target for the therapeutic intervention of atherosclerosis.

Interferon gamma: a master regulator of atherosclerosis

Atherosclerosis is a chronic inflammatory disease that is characterized by the development of fibrotic plaques in the arterial wall. The disease exhibits a complex aetiology and its progression is influenced by a number of environmental and genetic risk factors. The cytokine interferon-gamma (IFN-gamma), a key regulator of immune function, is highly expressed in atherosclerotic lesions and has emerged as a significant factor in atherogenesis. Evidence from both mouse models of atherosclerosis and in vitro cell culture has suggested that the role of IFN-gamma is complex since both pro- and anti-atherogenic actions have been affiliated to it. This review will focus on evaluating the contribution of IFN-gamma to atherosclerosis and, in particular, how it regulates immune responses to the disease.