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Many congratulations to Melissa Bedard, who won a Speakers’ Award for best presentation at the recent CD1-MR1 Conference held in Napa Valley, California.
AbstractPre-existing T cell immunity to SARS-CoV-2 in individuals without prior exposure to SARS-CoV-2 has been reported in several studies. While emerging evidence hints toward prior exposure to common-cold human coronaviruses (HCoV), the extent of- and conditions for-cross-protective immunity between SARS-CoV-2 and HCoVs remain open. Here, by leveraging a comprehensive pool of publicly available functionally evaluated SARS-CoV-2 peptides, we report 126 immunogenic SARS-CoV-2 peptides with high sequence similarity to 285 MHC-presented target peptides from at least one of four HCoV, thus providing a map describing the landscape of SARS-CoV-2 shared and private immunogenic peptides with functionally validated T cell responses. Using this map, we show that while SARS-CoV-2 immunogenic peptides in general exhibit higher level of dissimilarity to both self-proteome and -microbiomes, there exist several SARS-CoV-2 immunogenic peptides with high similarity to various human protein coding genes, some of which have been reported to have elevated expression in severe COVID-19 patients. We then combine our map with a SARS-CoV-2-specific TCR repertoire data from COVID-19 patients and healthy controls and show that whereas the public repertoire for the majority of convalescent patients are dominated by TCRs cognate to private SARS-CoV-2 peptides, for a subset of patients, more than 50% of their public repertoires that show reactivity to SARS-CoV-2, consist of TCRs cognate to shared SARS-CoV-2-HCoV peptides. Further analyses suggest that the skewed distribution of TCRs cognate to shared and private peptides in COVID-19 patients is likely to be HLA-dependent. Finally, by utilising the global prevalence of HLA alleles, we provide 10 peptides with known cognate TCRs that are conserved across SARS-CoV-2 and multiple human coronaviruses and are predicted to be recognised by a high proportion of the global population. Overall, our work indicates the potential for HCoV-SARS-CoV-2 reactive CD8+ T cells, which is likely dependent on differences in HLA-coding genes among individuals. These findings may have important implications for COVID-19 heterogeneity and vaccine-induced immune responses as well as robustness of immunity to SARS-CoV-2 and its variants.
The α- and β-globin loci harbor developmentally expressed genes, which are silenced throughout post-natal life. Reactivation of these genes may offer therapeutic approaches for the hemoglobinopathies, the most common single gene disorders. Here, we address mechanisms regulating the embryonically expressed α-like globin, termed ζ-globin. We show that in embryonic erythroid cells, the ζ-gene lies within a ~65 kb sub-TAD (topologically associating domain) of open, acetylated chromatin and interacts with the α-globin super-enhancer. By contrast, in adult erythroid cells, the ζ-gene is packaged within a small (~10 kb) sub-domain of hypoacetylated, facultative heterochromatin within the acetylated sub-TAD and that it no longer interacts with its enhancers. The ζ-gene can be partially re-activated by acetylation and inhibition of histone de-acetylases. In addition to suggesting therapies for severe α-thalassemia, these findings illustrate the general principles by which reactivation of developmental genes may rescue abnormalities arising from mutations in their adult paralogues.
Müllerian duct anomalies (MDAs) are developmental disorders of the Müllerian duct, the embryonic anlage of most of the female reproductive tract. The prevalence of MDAs is 6.7% in the general female population and 16.7% in women who exhibit recurrent miscarriages. Individuals affected by these anomalies suffer from high rates of infertility, first-trimester pregnancy losses, premature labour, placental retention, foetal growth retardation and foetal malpresentations. The aetiology of MDAs is complex and heterogeneous, displaying a range of clinical pictures that generally lack a direct genotype-phenotype correlation. De novo and familial cases sharing the same genomic lesions have been reported. The familial cases follow an autosomal-dominant inheritance, with reduced penetrance and variable expressivity. Furthermore, few genetic factors and molecular pathways underpinning Müllerian development and dysregulations causing MDAs have been identified. The current knowledge in this field predominantly derives from loss-of-function experiments in mouse and chicken models, as well as from human genetic association studies using traditional approaches, such as microarrays and Sanger sequencing, limiting the discovery of causal factors to few genetic entities from the coding genome. In this Review, we summarise the current state of the field, discuss limitations in the number of studies and patient samples that have stalled progress, and review how the development of new technologies provides a unique opportunity to overcome these limitations. Furthermore, we discuss how these new technologies can improve functional validation of potential causative alterations in MDAs.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has undergone progressive change, with variants conferring advantage rapidly becoming dominant lineages, e.g., B.1.617. With apparent increased transmissibility, variant B.1.617.2 has contributed to the current wave of infection ravaging the Indian subcontinent and has been designated a variant of concern in the United Kingdom. Here we study the ability of monoclonal antibodies and convalescent and vaccine sera to neutralize B.1.617.1 and B.1.617.2, complement this with structural analyses of Fab/receptor binding domain (RBD) complexes, and map the antigenic space of current variants. Neutralization of both viruses is reduced compared with ancestral Wuhan-related strains, but there is no evidence of widespread antibody escape as seen with B.1.351. However, B.1.351 and P.1 sera showed markedly more reduction in neutralization of B.1.617.2, suggesting that individuals infected previously by these variants may be more susceptible to reinfection by B.1.617.2. This observation provides important new insights for immunization policy with future variant vaccines in non-immune populations.
Aggregation and partial immobilisation of membrane proteins interplay with local lipid order in the plasma membrane of T cells.
To disentangle the elusive lipid-protein interactions in T-cell activation, we investigate how externally imposed variations in mobility of key membrane proteins (T-cell receptor [TCR], kinase Lck, and phosphatase CD45) affect the local lipid order and protein co-localisation. Using spectral imaging with polarity-sensitive membrane probes in model membranes and live Jurkat T cells, we find that partial immobilisation of proteins (including TCR) by aggregation or ligand binding changes their preference towards a more ordered lipid environment, which can recruit Lck. Our data suggest that the cellular membrane is poised to modulate the frequency of protein encounters upon alterations of their mobility, e.g. in ligand binding, which offers new mechanistic insight into the involvement of lipid-mediated interactions in membrane-hosted signalling events.
AbstractAlthough we can now measure single-cell signaling responses with multivariate, high-throughput techniques our ability to interpret such measurements is still limited. Even interpretation of dose–response based on single-cell data is not straightforward: signaling responses can differ significantly between cells, encompass multiple signaling effectors, and have dynamic character. Here, we use probabilistic modeling and information-theory to introduce fractional response analysis (FRA), which quantifies changes in fractions of cells with given response levels. FRA can be universally performed for heterogeneous, multivariate, and dynamic measurements and, as we demonstrate, quantifies otherwise hidden patterns in single-cell data. In particular, we show that fractional responses to type I interferon in human peripheral blood mononuclear cells are very similar across different cell types, despite significant differences in mean or median responses and degrees of cell-to-cell heterogeneity. Further, we demonstrate that fractional responses to cytokines scale linearly with the log of the cytokine dose, which uncovers that heterogeneous cellular populations are sensitive to fold-changes in the dose, as opposed to additive changes.
Natural History of Epstein-Barr Virus Replication and Viral Load Dynamics after Alemtuzumab-Based Allogeneic Stem Cell Transplantation
Epstein-Barr virus (EBV) load monitoring after allogeneic hematopoietic stem cell transplantation (HSCT) enables earlier detection of EBV replication and often serves as a trigger for preemptive therapies aimed at reducing EBV-related diseases. Our institutional strategy is to treat patients with clinical signs of EBV-related disease accompanied by a rising viral load, rather than to intervene based solely on viral load. This affords an opportunity to study the natural history of EBV replication and to assess whether our strategy reduces overtreatment without compromising outcomes. The objectives of the present study were to assess the natural history of untreated EBV replication in patients who underwent an alemtuzumab-based allogeneic HSCT and to examine whether our clinical strategy reduced overtreatment without compromising patient outcomes. In this retrospective single-center observational study of 515 consecutive patients (age ≥18 years) undergoing T cell-depleted allogeneic HSCT incorporating alemtuzumab, patients underwent surveillance monitoring for EBV by quantitative PCR in the peripheral blood at least weekly up to 100 days post-transplantation and longer if they remained on immunosuppressive therapy. The cumulative incidence of EBV detection and EBV-related disease were assessed. Among the 515 patients, 192 had EBV DNA detectable on ≥1 occasion, with a cumulative incidence of 35.8% (31.8% to 40.4%), although this remained below the limit of quantification in 93 patients. The median time to first detection was 89.5 days (range, 0 to 2254 days). The incidence was higher in recipients of sibling donor transplants (45.4% versus 30%; P = .00021) compared with recipients of unrelated donor transplants. Twenty patients developed EBV-related disease (cumulative incidence, 3.9%). Two patients had immunosuppression reduction alone, 18 received rituximab, and 5 required additional therapies. Five patients died from post-transplantation lymphoproliferative disorder, all of whom had received rituximab. The positive predictive value of EBV load for disease was higher in the unrelated donor cohort but remained <75% regardless of EBV threshold (57.1% to 72.7%). The cumulative incidence of EBV-related disease in our study (3.9%) is comparable to that reported in other studies incorporating alemtuzumab, and our clinical strategy reduced overtreatment in this patient population. PCR-based surveillance strategies have limitations, as reflected in the relatively low sensitivity of the assay coupled with the low positive predictive value, which may influence the potential choice of a threshold for preemptive intervention. We conclude that it remains unclear whether treatment based on a rising EBV viral load alone provides superior overall results to treatment based on the development of clinical signs of EBV-related disease in the context of a rising viral load.
ABSTRACTChromosome conformation capture (3C) provides an adaptable tool for studying diverse biological questions. Current 3C methods provide either low-resolution interaction profiles across the entire genome, or high-resolution interaction profiles at up to several hundred loci. All 3C methods are affected to varying degrees by inefficiency, bias and noise. As such, generation of reproducible high-resolution interaction profiles has not been achieved at scale. To overcome this barrier, we systematically tested and improved upon current methods. We show that isolation of 3C libraries from intact nuclei, as well as shortening and titration of enrichment oligonucleotides used in high-resolution methods reduces noise and increases on-target sequencing. We combined these technical modifications into a new method Nuclear-Titrated (NuTi) Capture-C, which provides a >3-fold increase in informative sequencing content over current Capture-C protocols. Using NuTi Capture-C we target 8,061 promoters in triplicate, demonstrating that this method generates reproducible high-resolution genome-wide 3C interaction profiles at scale.
Distinct epicardial gene regulatory programmes drive development and regeneration of the zebrafish heart
SummaryUnlike the adult mammalian heart, which has limited regenerative capacity, the zebrafish heart can fully regenerate following injury. Reactivation of cardiac developmental programmes is considered key to successfully regenerating the heart, yet the regulatory elements underlying the response triggered upon injury and during development remain elusive. Organ-wide activation of the epicardium is essential for zebrafish heart regeneration and is considered a potential regenerative source to target in the mammalian heart. Here we compared the transcriptome and epigenome of the developing and regenerating zebrafish epicardium by integrating gene expression profiles with open chromatin ATAC-seq data. By generating gene regulatory networks associated with epicardial development and regeneration, we inferred genetic programmes driving each of these processes, which were largely distinct. We identified wt1a, wt1b, and the AP-1 subunits junbb, fosab and fosb as central regulators of the developing network, whereas hif1ab, zbtb7a, tbx2b and nrf1 featured as putative central regulators of the regenerating epicardial network. By interrogating developmental gene regulatory networks that drive cell-specific transcriptional heterogeneity, we tested novel subpopulation-related epicardial enhancers in vivo. Taken together, our work revealed striking differences between the regulatory blueprint deployed during epicardial development and regeneration. These findings challenge the dogma that heart regeneration is essentially a reactivation of developmental programmes, and provide important insights into epicardial regulation that can assist in developing therapeutic approaches to enable tissue regeneration in the adult mammalian heart.
Indispensable epigenetic control of thymic epithelial cell development and function by polycomb repressive complex 2.
Thymic T cell development and T cell receptor repertoire selection are dependent on essential molecular cues provided by thymic epithelial cells (TEC). TEC development and function are regulated by their epigenetic landscape, in which the repressive H3K27me3 epigenetic marks are catalyzed by polycomb repressive complex 2 (PRC2). Here we show that a TEC-targeted deficiency of PRC2 function results in a hypoplastic thymus with reduced ability to express antigens and select a normal repertoire of T cells. The absence of PRC2 activity reveals a transcriptomically distinct medullary TEC lineage that incompletely off-sets the shortage of canonically-derived medullary TEC whereas cortical TEC numbers remain unchanged. This alternative TEC development is associated with the generation of reduced TCR diversity. Hence, normal PRC2 activity and placement of H3K27me3 marks are required for TEC lineage differentiation and function and, in their absence, the thymus is unable to compensate for the loss of a normal TEC scaffold.
The epicardium is essential during cardiac development, homeostasis, and repair, and yet fundamental insights into its underlying cell biology, notably epicardium formation, lineage heterogeneity, and functional cross-talk with other cell types in the heart, are currently lacking. In this study, we investigated epicardial heterogeneity and the functional diversity of discrete epicardial subpopulations in the developing zebrafish heart. Single-cell RNA sequencing uncovered three epicardial subpopulations with specific genetic programs and distinctive spatial distribution. Perturbation of unique gene signatures uncovered specific functions associated with each subpopulation and established epicardial roles in cell adhesion, migration, and chemotaxis as a mechanism for recruitment of leukocytes into the heart. Understanding which mechanisms epicardial cells employ to establish a functional epicardium and how they communicate with other cardiovascular cell types during development will bring us closer to repairing cellular relationships that are disrupted during cardiovascular disease.
The epicardium is essential during cardiac development, homeostasis and repair and yet fundamental insights into its underlying cell biology, notably epicardium formation, lineage heterogeneity and functional cross-talk with other cell types in the heart, are currently lacking. In this study, we investigated epicardial heterogeneity and the functional diversity of discrete epicardial subpopulations in the developing zebrafish heart. Single-cell RNA-sequencing uncovered three epicardial subpopulations with specific genetic programmes and distinctive spatial distribution within the developing heart. Perturbation of unique gene signatures uncovered distinct functions associated with each subpopulation and established novel epicardial roles in cell adhesion, migration, and chemotaxis as a mechanism for recruitment of leukocytes into the heart. This work elucidates the mutual spatiotemporal relationships between different epicardial subpopulations and assigns unique function to each during cardiac development. Understanding which mechanisms cells employ to establish a functional epicardium and to communicate with other cardiovascular cell types during development will bring us closer to repairing cellular relationships that are disrupted during cardiovascular disease.