Dissecting the heterogeneity of DENV vaccine-elicited cellular immunity using single-cell RNA sequencing and metabolic profiling

Long term T cell response and safety of a tetravalent dengue vaccine in healthy children

As robust cellular responses are important for protection against dengue, this phase 2 study evaluated the kinetics and phenotype of T cell responses induced by TAK-003, a live-attenuated tetravalent dengue vaccine, in 4-16-year-old living in dengue-endemic countries (NCT02948829). Two hundred participants received TAK-003 on Days 1 and 90. Interferon-gamma (IFN-γ) enzyme-linked immunospot assay [ELISPOT] and intracellular cytokine staining were used to analyze T cell response and functionality, using peptide pools representing non-structural (NS) proteins NS3 and NS5 matching DENV-1, -2, -3, and -4 and DENV-2 NS1. One month after the second TAK-003 dose (Day 120), IFN-γ ELISPOT T cell response rates against any peptide pool were 97.1% (95% CI: 93.4% to 99.1%), and similar for baseline dengue seropositive (96.0%) and seronegative (98.6%) participants. IFN-γ ELISPOT T cell response rates at Day 120 were 79.8%, 90.2%, 77.3%, and 74.0%, against DENV-1, -2, -3, and -4, respectively, and remained elevated through 3 years post-vaccination. Multifunctional CD4 and CD8 T cell responses against DENV-2 NS peptides were observed, independent of baseline serostatus: CD8 T cells typically secreted IFN-γ and TNF-α whereas CD4 T cells secreted ≥ 2 of IFN-γ, IL-2 and TNF-α cytokines. NAb titers and seropositivity rates remained substantially elevated through 3 years post-vaccination. Overall, TAK-003 was well tolerated and elicited durable T cell responses against all four DENV serotypes irrespective of baseline serostatus in children and adolescents aged 4-16 years living in dengue-endemic countries. TAK-003-elicited CD4 and CD8 T cells were multifunctional and persisted up to 3 years post-vaccination.

MFSD7C protects hemolysis-induced lung impairments by inhibiting ferroptosis

Hemolysis drives susceptibility to lung injury and predicts poor outcomes in diseases, such as malaria and sickle cell disease (SCD). However, the underlying pathological mechanism remains elusive. Here, we report that major facilitator superfamily domain containing 7 C (MFSD7C) protects the lung from hemolytic-induced damage by preventing ferroptosis. Mechanistically, MFSD7C deficiency in HuLEC-5A cells leads to mitochondrial dysfunction, lipid remodeling and dysregulation of ACSL4 and GPX4, thereby enhancing lipid peroxidation and promoting ferroptosis. Furthermore, systemic administration of MFSD7C mRNA-loaded nanoparticles effectively prevents lung injury in hemolytic mice, such as HbSS-Townes mice and PHZ-challenged 7 C-/- mice. These findings present the detailed link between hemolytic complications and ferroptosis, providing potential therapeutic targets for patients with hemolytic disorders.

Regional Variation of the CD4 and CD8 T Cell Epitopes Conserved in Circulating Dengue Viruses and Shared with Potential Vaccine Candidates

As dengue expands globally and many vaccines are under trials, there is a growing recognition of the need for assessing T cell immunity in addition to assessing the functions of neutralizing antibodies during these endeavors. While several dengue-specific experimentally validated T cell epitopes are known, less is understood about which of these epitopes are conserved among circulating dengue viruses and also shared by potential vaccine candidates. As India emerges as the epicenter of the dengue disease burden and vaccine trials commence in this region, we have here aligned known dengue specific T cell epitopes, reported from other parts of the world with published polyprotein sequences of 107 dengue virus isolates available from India. Of the 1305 CD4 and 584 CD8 epitopes, we found that 24% and 41%, respectively, were conserved universally, whereas 27% and 13% were absent in any viral isolates. With these data, we catalogued epitopes conserved in circulating dengue viruses from India and matched them with each of the six vaccine candidates under consideration (TV003, TDEN, DPIV, CYD-TDV, DENVax and TVDV). Similar analyses with viruses from Thailand, Brazil and Mexico revealed regional overlaps and variations in these patterns. Thus, our study provides detailed and nuanced insights into regional variation that should be considered for itemization of T cell responses during dengue natural infection and vaccine design, testing and evaluation.

Transcriptional signature of durable effector T cells elicited by a replication defective HCMV vaccine

Human cytomegalovirus (HCMV) is a leading infectious cause of birth defects and the most common opportunistic infection that causes life-threatening diseases post-transplantation; however, an effective vaccine remains elusive. V160 is a live-attenuated replication defective HCMV vaccine that showed a 42.4% efficacy against primary HCMV infection among seronegative women in a phase 2b clinical trial. Here, we integrated the multicolor flow cytometry, longitudinal T cell receptor (TCR) sequencing, and single-cell RNA/TCR sequencing approaches to characterize the magnitude, phenotype, and functional quality of human T cell responses to V160. We demonstrated that V160 de novo induces IE-1 and pp65 specific durable polyfunctional effector CD8 T cells that are comparable to those induced by natural HCMV infection. We identified a variety of V160-responsive T cell clones which exhibit distinctive "transient" and "durable" expansion kinetics, and revealed a transcriptional signature that marks durable CD8 T cells post-vaccination. Our study enhances the understanding of human T-cell immune responses to V160 vaccination.

Safety and immunogenicity of a synthetic nanoparticle-based, T cell priming peptide vaccine against dengue in healthy adults in Switzerland: a double-blind, randomized, vehicle-controlled, phase 1 study

BACKGROUND

Vaccines that minimize the risk of vaccine-induced antibody-dependent enhancement and severe dengue are needed to address the global health threat posed by dengue. This study assessed the safety and immunogenicity of a gold nanoparticle (GNP)-based, multi-valent, synthetic peptide dengue vaccine candidate (PepGNP-Dengue), designed to provide protective CD8+ T cell immunity, without inducing antibodies.

METHODS

In this randomized, double-blind, vehicle-controlled, phase 1 trial (NCT04935801), healthy naïve individuals aged 18-45 years recruited at the Centre for primary care and public health, Lausanne, Switzerland, were randomly assigned to receive PepGNP-Dengue or comparator (GNP without peptides [vehicle-GNP]). Randomization was stratified into four groups (low dose [LD] and high dose [HD]), allocation was double-blind from participants and investigators. Two doses were administered by intradermal microneedle injection 21 days apart. Primary outcome was safety, secondary outcome immunogenicity. Analysis was by intention-to-treat for safety, intention-to-treat and per protocol for immunogenicity.

FINDINGS

26 participants were enrolled (August-September 2021) to receive PepGNP-Dengue (LD or HD, n = 10 each) or vehicle-GNP (LD or HD, n = 3 each). No vaccine-related serious adverse events occurred. Most (90%) related adverse events were mild; injection site pain and transient discoloration were most frequently reported. Injection site erythema occurred in 58% of participants. As expected, PepGNP-Dengue did not elicit anti-DENV antibodies of significance. Significant increases were observed in specific CD8+ T cells and dengue dextramer+ memory cell subsets in the LD PepGNP-Dengue but not in the HD PepGNP-Dengue or vehicle-GNP groups, specifically PepGNP-activated CD137+CD69+CD8+ T cells (day 90, +0.0318%, 95% CI: 0.0088-0.1723, p = 0.046), differentiated effector memory (TemRA) and central memory (Tcm) CD8+ T cells (day 35, +0.8/105 CD8+, 95% CI: 0.19-5.13, p = 0.014 and +1.34/105 CD8+, 95% CI: 0.1-7.34, p = 0.024, respectively).

INTERPRETATION

Results provide proof of concept that a synthetic nanoparticle-based peptide vaccine can successfully induce virus-specific CD8+ T cells. The favourable safety profile and cellular responses observed support further development of PepGNP-Dengue.

FUNDING

Emergex Vaccines Holding Limited.

Functional and transcriptional heterogeneity within the massively expanding HLADR+CD38+ CD8 T cell population in acute febrile dengue patients

IMPORTANCE

CD8 T cells play a crucial role in protecting against intracellular pathogens such as viruses by eliminating infected cells and releasing anti-viral cytokines such as interferon gamma (IFNγ). Consequently, there is significant interest in comprehensively characterizing CD8 T cell responses in acute dengue febrile patients. Previous studies, including our own, have demonstrated that a discrete population of CD8 T cells with HLADR+ CD38+ phenotype undergoes massive expansion during the acute febrile phase of natural dengue virus infection. Although about a third of these massively expanding HLADR+ CD38+ CD8 T cells were also CD69high when examined ex vivo, only a small fraction of them produced IFNγ upon in vitro peptide stimulation. Therefore, to better understand such functional diversity of CD8 T cells responding to dengue virus infection, it is important to know the cytokines/chemokines expressed by these peptide-stimulated HLADR+CD38+ CD8 T cells and the transcriptional profiles that distinguish the CD69+IFNγ+, CD69+IFNγ-, and CD69-IFNγ- subsets.

Altered T-cell receptor β repertoire in adults with SARS CoV-2 inactivated vaccine of BBIBP-CorV

OBJECTIVE

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the prolonged and widespread epidemic of coronavirus disease 2019 (COVID-19). The inactivated BBIBP-CorV vaccine has shown safety, efficacy and immunogenicity against COVID-19 in in-vitro studies and clinical trials. However, the characteristics changes of the TCRβ repertoire in patients receiving BBIBP-CorV remain unclear.

METHODS

TCRβ repertoire difference were analyzed between 54 uninfected subjects who received a third dose of the enhanced BBIBP-CorV vaccine and the 16 healthy donors who did not receive the vaccine and 44 COVID-19 patients with different courses of disease (asymptomatic, symptomatic and convalescent). Furthermore, antibody response, anti-inflammatory and pro-inflammatory cytokines also were examined.

RESULTS

We found that the third dose inactivated coronavirus vaccine induced widespread changes including the increased TCRβ repertoire diversity, a much shorter CDR3 length and high usage of V-J genes segments. Meanwhile, the vaccine-responding clones were also predicted. The results of the antibody response showed that 90.7 % of the vaccinated individuals were positive for NAb seroconversion and 88.9 % for IgG antibody about 60 days after the third dose. The concentration of IL-2 increased significantly compared to baseline inoculation.

CONCLUSION

Altered TCRβ repertoire in adults with SARS CoV-2 inactivated vaccine of BBIBP-CorV clarified the specific immunity induced by inactivated vaccines. Our research provides insights into the adaptive immune response induced by the new inactivated SARS-CoV-2 vaccine and strengthens the development of immunotherapy.

Evolution of a functionally intact but antigenically distinct DENV fusion loop

A hallmark of dengue virus (DENV) pathogenesis is the potential for antibody-dependent enhancement, which is associated with deadly DENV secondary infection, complicates the identification of correlates of protection, and negatively impacts the safety and efficacy of DENV vaccines. Antibody-dependent enhancement is linked to antibodies targeting the fusion loop (FL) motif of the envelope protein, which is completely conserved in mosquito-borne flaviviruses and required for viral entry and fusion. In the current study, we utilized saturation mutagenesis and directed evolution to engineer a functional variant with a mutated FL (D2-FL), which is not neutralized by FL-targeting monoclonal antibodies. The FL mutations were combined with our previously evolved prM cleavage site to create a mature version of D2-FL (D2-FLM), which evades both prM- and FL-Abs but retains sensitivity to other type-specific and quaternary cross-reactive (CR) Abs. CR serum from heterotypic (DENV4)-infected non-human primates (NHP) showed lower neutralization titers against D2-FL and D2-FLM than isogenic wildtype DENV2 while similar neutralization titers were observed in serum from homotypic (DENV2)-infected NHP. We propose D2-FL and D2-FLM as valuable tools to delineate CR Ab subtypes in serum as well as an exciting platform for safer live-attenuated DENV vaccines suitable for naïve individuals and children.

Evolution of a Functionally Intact but Antigenically Distinct DENV Fusion Loop

A hallmark of Dengue virus (DENV) pathogenesis is the potential for antibody-dependent enhancement, which is associated with deadly DENV secondary infection, complicates the identification of correlates of protection, and negatively impacts the safety and efficacy of DENV vaccines. ADE is linked to antibodies targeting the fusion loop (FL) motif of the envelope protein, which is completely conserved in mosquito-borne flaviviruses and required for viral entry and fusion. In the current study, we utilized saturation mutagenesis and directed evolution to engineer a functional variant with a mutated FL (D2-FL) which is not neutralized by FL-targeting monoclonal antibodies. The FL mutations were combined with our previously evolved prM cleavage site to create a mature version of D2-FL (D2-FLM), which evades both prM- and FL-Abs but retains sensitivity to other type-specific and quaternary cross-reactive (CR) Abs. CR serum from heterotypic (DENV4) infected non-human primates (NHP) showed lower neutralization titers against D2-FL and D2-FLM than isogenic wildtype DENV2 while similar neutralization titers were observed in serum from homotypic (DENV2) infected NHP. We propose D2-FL and D2-FLM as valuable tools to delineate CR Ab subtypes in serum as well as an exciting platform for safer live attenuated DENV vaccines suitable for naïve individuals and children.

Single-cell RNA sequencing reveals the transcriptomic characteristics of peripheral blood mononuclear cells in hepatitis B vaccine non-responders

The emergence of a vaccine against hepatitis B has proven to be an important milestone in the prevention of this disease; however, 5%-10% of vaccinated individuals do not generate an immune response to the vaccine, and its molecular mechanism has not been clarified. In this study, single-cell RNA sequencing was performed on peripheral blood mononuclear cells (PBMCs) from three volunteers with a high immune response (HR) and three with no immune response (NR) to the hepatitis B vaccine. We found that the antigen-presenting activity scores of various antigen-presenting cells, the mitogen-activated protein kinase (MAPK) pathway activity scores of naive B cells, and the cell activity scores of three types of effector T cells were significantly decreased, whereas the cytotoxicity scores of CD3highCD16lowKLRG1high natural killer T (NKT) cells were significantly increased in the NR group compared with those in the HR group. Additionally, the expression levels of some classical molecules associated with distinct signaling pathways-including HLA-B, HLA-DRB5, BLNK, BLK, IL4R, SCIMP, JUN, CEBPB, NDFIP1, and TXNIP-were significantly reduced in corresponding subsets of PBMCs from the NR group relative to those of the HR group. Furthermore, the expression of several cytotoxicity-related effector molecules, such as GNLY, NKG7, GZMB, GZMM, KLRC1, KLRD1, PRF1, CST7, and CTSW, was significantly higher in CD3highCD16lowKLRG1high NKT cells derived from non-responders. Our study provides a molecular basis for the lack of response to the hepatitis B vaccine, including defective antigen presentation, decreased T cell activity, and reduced IL-4 secretion, as well as novel insight into the role of NKT cells in the immune response to the hepatitis B vaccine.

Insights into dengue immunity from vaccine trials

The quest for an effective dengue vaccine has culminated in two approved vaccines and another that has completed phase 3 clinical trials. However, shortcomings exist in each, suggesting that the knowledge on dengue immunity used to develop these vaccines was incomplete. Vaccine trial findings could refine our understanding of dengue immunity, because these are experimentally derived, placebo-controlled data. Results from these trials suggest that neutralizing antibody titers alone are insufficient to inform protection against symptomatic infection, implicating a role for cellular immunity in protection. These findings have relevance for both future dengue vaccine development and application of current vaccines for maximal public health benefit.

Single-cell profiling of lncRNA expression during Ebola virus infection in rhesus macaques

Long non-coding RNAs (lncRNAs) are involved in numerous biological processes and are pivotal mediators of the immune response, yet little is known about their properties at the single-cell level. Here, we generate a multi-tissue bulk RNAseq dataset from Ebola virus (EBOV) infected and not-infected rhesus macaques and identified 3979 novel lncRNAs. To profile lncRNA expression dynamics in immune circulating single-cells during EBOV infection, we design a metric, Upsilon, to estimate cell-type specificity. Our analysis reveals that lncRNAs are expressed in fewer cells than protein-coding genes, but they are not expressed at lower levels nor are they more cell-type specific when expressed in the same number of cells. In addition, we observe that lncRNAs exhibit similar changes in expression patterns to those of protein-coding genes during EBOV infection, and are often co-expressed with known immune regulators. A few lncRNAs change expression specifically upon EBOV entry in the cell. This study sheds light on the differential features of lncRNAs and protein-coding genes and paves the way for future single-cell lncRNA studies.

Single-Cell Transcriptome Atlas of Newcastle Disease Virus in Chickens Both In Vitro and In Vivo

Newcastle disease virus (NDV) is an avian paramyxovirus that causes major economic losses to the poultry industry around the world, with NDV pathogenicity varying due to strain virulence differences. However, the impacts of intracellular viral replication and the heterogeneity of host responses among cell types are unknown. Here, we investigated the heterogeneity of lung tissue cells in response to NDV infection in vivo and that of the chicken embryo fibroblast cell line DF-1 in response to NDV infection in vitro using single-cell RNA sequencing. We characterized the NDV target cell types in the chicken lung at the single-cell transcriptome level and classified cells into five known and two unknown cell types. The five known cell types are the targets of NDV in the lungs with virus RNA detected. Different paths of infection in the putative trajectories of NDV infection were distinguished between in vivo and in vitro, or between virulent Herts/33 strain and nonvirulent LaSota strain. Gene expression patterns and the interferon (IFN) response in different putative trajectories were demonstrated. IFN responses were elevated in vivo, especially in myeloid and endothelial cells. We distinguished the virus-infected and non-infected cells, and the Toll-like receptor signaling pathway was the main pathway after virus infection. Cell-cell communication analysis revealed the potential cell surface receptor-ligand of NDV. Our data provide a rich resource for understanding NDV pathogenesis and open the way to interventions specifically targeting infected cells. IMPORTANCE Newcastle disease virus (NDV) is an avian paramyxovirus that causes major economic losses to the poultry industry around the world, with NDV pathogenicity varying due to strain virulence differences. However, the impacts of intracellular viral replication and the heterogeneity of host responses among cell types are unknown. Here, we investigated the heterogeneity of lung tissue cells in response to NDV infection in vivo and that of the chicken embryo fibroblast cell line DF-1 in response to NDV infection in vitro using single-cell RNA sequencing. Our results open the way to interventions specifically targeting infected cells, suggest principles of virus-host interactions applicable to NDV and other similar pathogens, and highlight the potential for simultaneous single-cell measurements of both host and viral transcriptomes for delineating a comprehensive map of infection in vitro and in vivo. Therefore, this study can be a useful resource for the further investigation and understanding of NDV.

In-silico generation of high-dimensional immune response data in patients using a deep neural network

Technologies for single-cell profiling of the immune system have enabled researchers to extract rich interconnected networks of cellular abundance, phenotypical and functional cellular parameters. These studies can power machine learning approaches to understand the role of the immune system in various diseases. However, the performance of these approaches and the generalizability of the findings have been hindered by limited cohort sizes in translational studies, partially due to logistical demands and costs associated with longitudinal data collection in sufficiently large patient cohorts. An evolving challenge is the requirement for ever-increasing cohort sizes as the dimensionality of datasets grows. We propose a deep learning model derived from a novel pipeline of optimal temporal cell matching and overcomplete autoencoders that uses data from a small subset of patients to learn to forecast an entire patient's immune response in a high dimensional space from one timepoint to another. In our analysis of 1.08 million cells from patients pre- and post-surgical intervention, we demonstrate that the generated patient-specific data are qualitatively and quantitatively similar to real patient data by demonstrating fidelity, diversity, and usefulness.

Serum Metabolic Correlates of the Antibody Response in Subjects Receiving the Inactivated COVID-19 Vaccine

BACKGROUND

Metabolites are involved in biological process that govern the immune response to infection and vaccination. Knowledge of how metabolites interact with the immune system during immunization with the COVID-19 vaccine is limited. Here, we report that the serum metabolites are correlated with the magnitude of the antibody response in recipients receiving the inactivated COVID-19 vaccine, which provides critical information for studying metabolism regarding the human immune response to vaccination.

METHODS

106 healthy volunteers without history of SARS-CoV-2 infection or vaccination were prospectively enrolled to receive the primary series of two doses of inactivated whole-virion SARS-CoV-2 vaccine. The serum samples were collected 2-4 weeks after the second dose. The magnitude of the anti-RBD antibody was quantified using surrogate virus neutralization tests. The profile of metabolites in serum was identified using untargeted metabolomics analysis.

RESULTS

The level of anti-RBD antibody 14-28 days after the second dose was significantly elevated and its interpersonal variability was diverse in a wide range. Thirty-two samples at extremes of the anti-RBD antibody titer were selected to discover the metabolic correlates. Two hundred and fifteen differential metabolites associated with antibody response independent of body mass index were identified. Pregnenolone and sphingolipid metabolism might be involved in the modulation of the human antibody response to the inactivated COVID-19 vaccine.

CONCLUSION

We discovered key metabolites as well as those with a related functional significance that might modulate the human immune response to vaccination.

Innate-like bystander-activated CD38+ HLA-DR+ CD8+ T cells play a pathogenic role in patients with chronic hepatitis C

BACKGROUND AND AIMS

HCV-specific T cells are few and exhausted in patients with chronic hepatitis C (CHC). Whether these T cells are responsible for the liver damage and fibrosis is still debated. However, cluster of differentiation 38-positive (CD38⁺ ) human leukocyte antigen DR-positive (HLA-DR⁺ ) CD8⁺ T cells are regarded as bystander CD8⁺ T cells that cause liver injury in acute hepatitis. We propose that these innate CD8⁺ T cells play a pathogenic role in CHC.

METHODS

Lymphocytes from peripheral blood were obtained from 108 patients with CHC and 43 healthy subjects. Immunophenotyping, functional assays, T-cell receptor (TCR) repertoire, and cytotoxic assay of CD38⁺ HLA-DR⁺ CD8⁺ T cells were studied.

RESULTS

The percentage of CD38⁺ HLA-DR⁺ CD8⁺ T cells increased significantly in patients with CHC. These cells expressed higher levels of effector memory and proinflammatory chemokine molecules and showed higher interferon-γ production than CD38^- HLA-DR^- CD8 T cells. They were largely composed of non-HCV-specific CD8⁺ T cells as assessed by HLA-A2-restricted pentamers and next-generation sequencing analysis of the TCR repertoire. In addition, these CD38⁺ HLA-DR⁺ CD8⁺ T cells had strong cytotoxicity, which could be inhibited by anti-DNAX accessory molecule 1, anti-NKG2 family member D, and anti-natural killer NKp30 antibodies. Lastly, the percentage of CD38⁺ HLA-DR⁺ CD8⁺ T cells was significantly associated with liver injury and fibrosis and decreased significantly along with serum alanine aminotransferase normalization after successful direct-acting antiviral treatment.

CONCLUSIONS

The TCR-independent, cytokine-responsive bystander CD38⁺ HLA-DR⁺ CD8⁺ T cells are strongly cytotoxic and play a pathogenic role in patients with CHC.

Current Vaccine Platforms in Enhancing T-Cell Response

The induction of T cell-mediated immunity is crucial in vaccine development. The most effective vaccine is likely to employ both cellular and humoral immune responses. The efficacy of a vaccine depends on T cells activated by antigen-presenting cells. T cells also play a critical role in the duration and cross-reactivity of vaccines. Moreover, pre-existing T-cell immunity is associated with a decreased severity of infectious diseases. Many technical and delivery platforms have been designed to induce T cell-mediated vaccine immunity. The immunogenicity of vaccines is enhanced by controlling the kinetics and targeted delivery. Viral vectors are attractive tools that enable the intracellular expression of foreign antigens and induce robust immunity. However, it is necessary to select an appropriate viral vector considering the existing anti-vector immunity that impairs vaccine efficacy. mRNA vaccines have the advantage of rapid and low-cost manufacturing and have been approved for clinical use as COVID-19 vaccines for the first time. mRNA modification and nanomaterial encapsulation can help address mRNA instability and translation efficacy. This review summarizes the T cell responses of vaccines against various infectious diseases based on vaccine technologies and delivery platforms and discusses the future directions of these cutting-edge platforms.

Current Development and Challenges of Tetravalent Live-Attenuated Dengue Vaccines

Dengue is the most common arboviral disease caused by one of four distinct but closely related dengue viruses (DENV) and places significant economic and public health burdens in the endemic areas. A dengue vaccine will be important in advancing disease control. However, the effort has been challenged by the requirement to induce effective protection against all four DENV serotypes and the potential adverse effect due to the phenomenon that partial immunity to DENV may worsen the symptoms upon subsequent heterotypic infection. Currently, the most advanced dengue vaccines are all tetravalent and based on recombinant live attenuated viruses. CYD-TDV, developed by Sanofi Pasteur, has been approved but is limited for use in individuals with prior dengue infection. Two other tetravalent live attenuated vaccine candidates: TAK-003 by Takeda and TV003 by National Institute of Allergy and Infectious Diseases, have completed phase 3 and phase 2 clinical trials, respectively. This review focuses on the designs and evaluation of TAK-003 and TV003 vaccine candidates in humans in comparison to the licensed CYD-TDV vaccine. We highlight specific lessons from existing studies and challenges that must be overcome in order to develop a dengue vaccine that confers effective and balanced protection against all four DENV serotypes but with minimal adverse effects.

Transcriptomics of Acute DENV-Specific CD8+ T Cells Does Not Support Qualitative Differences as Drivers of Disease Severity

While several lines of evidence suggest a protective role of T cells against disease associated with Dengue virus (DENV) infection, their potential contribution to immunopathology in the acute phase of DENV infection remains controversial, and it has been hypothesized that the more severe form of the disease (dengue hemorrhagic fever, DHF) is associated with altered T cell responses. To address this question, we determined the transcriptomic profiles of DENV-specific CD8+ T cells in a cohort of 40 hospitalized dengue patients with either a milder form of the disease (dengue fever, DF) or a more severe disease form (dengue hemorrhagic fever, DHF). We found multiple transcriptomic signatures, one associated with DENV-specific interferon-gamma responding cells and two other gene signatures, one specifically associated with the acute phase and the other with the early convalescent phase. Additionally, we found no differences in quantity and quality of DENV-specific CD8+ T cells based on disease severity. Taken together with previous findings that did not detect altered DENV-specific CD4 T cell responses, the current analysis argues against alteration in DENV-specific T cell responses as being a correlate of immunopathology.

Single-cell Temporal Analysis of Natural Dengue Infection Reveals Skin-Homing Lymphocyte Expansion One Day before Defervescence

Effective clinical management of acute dengue virus (DENV) infection relies on the timing of suitable treatments during the disease progression. We analyzed single-cell transcriptomic profiles of the peripheral blood mononuclear cell samples from two DENV patients, collected daily during acute phase and also at convalescence. Key immune cell types demonstrated different dynamic responses over the course of the infection. On the day before defervescence (Day −1), we observed the peak expression of several prominent genes in the adaptive immunological pathways. We also characterized unique effector T cell clusters that expressed skin-homing signature genes at Day −1, whereas upregulation of skin and gut homing genes was also observed in plasma cells and plasmablasts during the febrile period. This work provides an overview of unique molecular dynamics that signify the entry of the critical phase, and the findings could improve the patient management of DENV infection.

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Time-course scRNA-seq reveals immune response dynamics during acute dengue infection

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Rapid transcriptional switching was observed one day before fever subsided (Day -1)

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Skin-homing signatures were observed in specific T cells during the febrile phase

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Expansion of skin-homing CD69⁺ PD-1⁺ T cells at Day -1 was confirmed with FACS

Reinvestigation of Classic T Cell Subsets and Identification of Novel Cell Subpopulations by Single-Cell RNA Sequencing

Classic T cell subsets are defined by a small set of cell surface markers, while single-cell RNA sequencing (scRNA-seq) clusters cells using genome-wide gene expression profiles. The relationship between scRNA-seq clustered populations (scCPops) and cell surface marker-defined classic T cell subsets remains unclear. In this article, we integrated six bead-enriched T cell subsets with 62,235 single-cell transcriptomes from human PBMCs and clustered them into nine scCPops. Bead-enriched CD4⁺/CD45RA⁺/CD25^- naive T and CD8⁺/CD45RA⁺ naive T cells were mainly clustered into their scCPop counterparts, while cells from the other T cell subsets were assigned to multiple scCPops, including mucosal-associated invariant T cells and NKT cells. The multiple T cell subsets forming one scCPop exhibit similar expression patterns, but not vice versa, indicating scCPop is a more homogeneous cell population with similar cell states. Interestingly, we discovered and named IFN signaling-associated gene (ISAG) high T (ISAG^hi T) cells, a T cell subpopulation that highly expressed ISAGs. We further enriched ISAG^hi T cells from human PBMCs by FACS of BST2 for scRNA-seq analyses. The ISAG^hi T cell cluster disappeared on t-distributed stochastic neighbor embedding plot after removing ISAGs, whereas the ISAG^hi T cell cluster showed up by analysis of ISAGs alone, indicating ISAGs are the major contributor of the ISAG^hi T cell cluster. BST2⁺ and BST2^- T cells showing different efficiencies of T cell activation indicate that a high level of ISAGs may contribute to quick immune responses.

Tetravalent formulation of Polymeric nanoparticle-based vaccine induces a potent immune response against Dengue virus

Dengue is a mosquito-borne disease caused by the four serotypes of dengue virus (DENV 1-4). It is growing at an alarming rate globally, which could be partly attributed to the...

Single-Cell Genomics: Enabling the Functional Elucidation of Infectious Diseases in Multi-Cell Genomes

Since the time when detection of gene expression in single cells by microarrays to the Next Generation Sequencing (NGS) enabled Single Cell Genomics (SCG), it has played a pivotal role to understand and elucidate the functional role of cellular heterogeneity. Along this journey to becoming a key player in the capture of the individuality of cells, SCG overcame many milestones, including scale, speed, sensitivity and sample costs (4S). There have been many important experimental and computational innovations in the efficient analysis and interpretation of SCG data. The increasing role of AI in SCG data analysis has further enhanced its applicability in building models for clinical intervention. Furthermore, SCG has been instrumental in the delineation of the role of cellular heterogeneity in specific diseases, including cancer and infectious diseases. The understanding of the role of differential immune responses in driving coronavirus disease-2019 (COVID-19) disease severity and clinical outcomes has been greatly aided by SCG. With many variants of concern (VOC) in sight, it would be of great importance to further understand the immune response specificity vis-a-vis the immune cell repertoire, the identification of novel cell types, and antibody response. Given the potential of SCG to play an integral part in the multi-omics approach to the study of the host-pathogen interaction and its outcomes, our review attempts to highlight its strengths, its implications for infectious disease biology, and its current limitations. We conclude that the application of SCG would be a critical step towards future pandemic preparedness.

Single-Cell Analysis of Antigen-Specific CD8+ T-Cell Transcripts Reveals Profiles Specific to mRNA or Adjuvanted Protein Vaccines

CD8+ T cells play a key role in mediating protective immunity after immune challenges such as infection or vaccination. Several subsets of differentiated CD8+ T cells have been identified, however, a deeper understanding of the molecular mechanism that underlies T-cell differentiation is lacking. Conventional approaches to the study of immune responses are typically limited to the analysis of bulk groups of cells that mask the cells' heterogeneity (RNA-seq, microarray) and to the assessment of a relatively limited number of biomarkers that can be evaluated simultaneously at the population level (flow and mass cytometry). Single-cell analysis, on the other hand, represents a possible alternative that enables a deeper characterization of the underlying cellular heterogeneity. In this study, a murine model was used to characterize immunodominant hemagglutinin (HA533-541)-specific CD8+ T-cell responses to nucleic- and protein-based influenza vaccine candidates, using single-cell sorting followed by transcriptomic analysis. Investigation of single-cell gene expression profiles enabled the discovery of unique subsets of CD8+ T cells that co-expressed cytotoxic genes after vaccination. Moreover, this method enabled the characterization of antigen specific CD8+ T cells that were previously undetected. Single-cell transcriptome profiling has the potential to allow for qualitative discrimination of cells, which could lead to novel insights on biological pathways involved in cellular responses. This approach could be further validated and allow for more informed decision making in preclinical and clinical settings.

In Vitro Characterization of the Innate Immune Pathways Engaged by Live and Inactivated Tick-Borne Encephalitis Virus

Tick-borne encephalitis virus (TBEV) infection can lead to inflammation of the central nervous system. The disease can be effectively prevented by whole inactivated virus vaccines. Here, we investigated the innate immune profile induced in vitro by the antigen component of the vaccines, inactivated TBEV (I-TBEV), to gain insights into the mechanism of action of the TBE vaccine as compared to the live virus. To this end, we exposed human peripheral blood mononuclear cells (PBMCs) to inactivated and live TBEV and assessed cellular responses by RNA sequencing. Both inactivated and live TBEV significantly induced an interferon-dominated gene signature and an increased RIG-I-like receptor (RLR) expression. Using pathway-specific inhibitors, we assessed the involvement of pattern recognition receptors in the sensing of inactivated or live TBEV. Only RLR pathway inhibition significantly suppressed the downstream cascade induced by I-TBEV, while responses to the replicating virus were impacted by the inhibition of RIG-I-like, as well as Toll-like, receptors. Our results show that inactivated and live TBEV predominantly engaged an interferon response in our in vitro PBMC platform, and indicate RLRs as the main pattern recognition receptors involved in I-TBEV sensing.

Prospective Artificial Intelligence to Dissect the Dengue Immune Response and Discover Therapeutics

Dengue virus (DENV) poses a serious threat to global health as the causative agent of dengue fever. The virus is endemic in more than 128 countries resulting in approximately 390 million infection cases each year. Currently, there is no approved therapeutic for treatment nor a fully efficacious vaccine. The development of therapeutics is confounded and hampered by the complexity of the immune response to DENV, in particular to sequential infection with different DENV serotypes (DENV1-5). Researchers have shown that the DENV envelope (E) antigen is primarily responsible for the interaction and subsequent invasion of host cells for all serotypes and can elicit neutralizing antibodies in humans. The advent of high-throughput sequencing and the rapid advancements in computational analysis of complex data, has provided tools for the deconvolution of the DENV immune response. Several types of complex statistical analyses, machine learning models and complex visualizations can be applied to begin answering questions about the B- and T-cell immune responses to multiple infections, antibody-dependent enhancement, identification of novel therapeutics and advance vaccine research.

Predictive Markers of Immunogenicity and Efficacy for Human Vaccines

Vaccines represent one of the major advances of modern medicine. Despite the many successes of vaccination, continuous efforts to design new vaccines are needed to fight "old" pandemics, such as tuberculosis and malaria, as well as emerging pathogens, such as Zika virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Vaccination aims at reaching sterilizing immunity, however assessing vaccine efficacy is still challenging and underscores the need for a better understanding of immune protective responses. Identifying reliable predictive markers of immunogenicity can help to select and develop promising vaccine candidates during early preclinical studies and can lead to improved, personalized, vaccination strategies. A systems biology approach is increasingly being adopted to address these major challenges using multiple high-dimensional technologies combined with in silico models. Although the goal is to develop predictive models of vaccine efficacy in humans, applying this approach to animal models empowers basic and translational vaccine research. In this review, we provide an overview of vaccine immune signatures in preclinical models, as well as in target human populations. We also discuss high-throughput technologies used to probe vaccine-induced responses, along with data analysis and computational methodologies applied to the predictive modeling of vaccine efficacy.

Single-Cell TCR Sequencing Reveals the Dynamics of T Cell Repertoire Profiling During Pneumocystis Infection

T cell responses play critical roles in host adaptive immunity against Pneumocystis. However, the dynamics and diversity of the T cell immune repertoire in human immunodeficiency virus (HIV)-negative Pneumocystis pneumonia (PCP) remains unclear. In this study, single-cell RNA and single-cell T cell receptor (TCR) sequencing were applied to cells sorted from lung tissues of mice infected with Pneumocystis. Our findings demonstrated the clonal cells were mainly composed of CD4⁺ T cells in response to Pneumocystis, which were marked by highly expressed genes associated with T cell activation. Mice infected with Pneumocystis showed reduced TCR diversity in CD4⁺ T cells and increased diversity in CD8⁺ T cells compared with uninfected controls. Furthermore, Th17 cells were mostly clonal CD4⁺ T cells, which exhibited the phenotype of tissue-resident memory-like Th17 cells. In addition, Pneumocystis-infected mice showed biased usage of TCRβ VDJ genes. Taken together, we characterized the transcriptome and TCR immune repertoires profiles of expanded T cell clones, which demonstrate a skewed TCR repertoire after Pneumocystis infection.

Conserved epitopes with high HLA-I population coverage are targets of CD8+ T cells associated with high IFN-γ responses against all dengue virus serotypes

Cytotoxic CD8⁺ T cells are key for immune protection against viral infections. The breadth and cross-reactivity of these responses are important against rapidly mutating RNA viruses, such as dengue (DENV), yet how viral diversity affect T cell responses and their cross-reactivity against multiple variants of the virus remains poorly defined. In this study, an integrated analysis was performed to map experimentally validated CD8⁺ T cell epitopes onto the distribution of DENV genome sequences across the 4 serotypes worldwide. Despite the higher viral diversity observed within HLA-I restricted epitopes, mapping of 609 experimentally validated epitopes sequences on 3985 full-length viral genomes revealed 19 highly conserved epitopes across the four serotypes within the immunogenic regions of NS3, NS4B and NS5. These conserved epitopes were associated with a higher magnitude of IFN-γ response when compared to non-conserved epitopes and were restricted to 13 HLA class I genotypes, hence providing high coverage among human populations. Phylogeographic analyses showed that these epitopes are largely conserved in most of the endemic regions of the world, and with only some of these epitopes presenting distinct mutated variants circulating in South America and Asia.This study provides evidence for the existence of highly immunogenic and conserved epitopes across serotypes, which may impact design of new universal T-cell-inducing vaccine candidates that minimise detrimental effects of viral diversification and at the same time induce responses to a broad human population.

Probing infectious disease by single-cell RNA sequencing: Progresses and perspectives

The increasing application of single-cell RNA sequencing (scRNA-seq) technology in life science and biomedical research has significantly increased our understanding of the cellular heterogeneities in immunology, oncology and developmental biology. This review will summarize the development of various scRNA-seq technologies; primarily discussing the application of scRNA-seq on infectious diseases, and exploring the current development, challenges, and potential applications of scRNA-seq technology in the future.

Transcriptome dynamics of CD4+ T cells during malaria maps gradual transit from effector to memory

The dynamics of CD4⁺ T cell memory development remain to be examined at genome scale. In malaria-endemic regions, antimalarial chemoprevention protects long after its cessation and associates with effects on CD4⁺ T cells. We applied single-cell RNA sequencing and computational modelling to track memory development during Plasmodium infection and treatment. In the absence of central memory precursors, two trajectories developed as T helper 1 (T_H1) and follicular helper T (T_FH) transcriptomes contracted and partially coalesced over three weeks. Progeny of single clones populated T_H1 and T_FH trajectories, and fate-mapping suggested that there was minimal lineage plasticity. Relationships between T_FH and central memory were revealed, with antimalarials modulating these responses and boosting T_H1 recall. Finally, single-cell epigenomics confirmed that heterogeneity among effectors was partially reset in memory. Thus, the effector-to-memory transition in CD4⁺ T cells is gradual during malaria and is modulated by antiparasitic drugs. Graphical user interfaces are presented for examining gene-expression dynamics and gene-gene correlations ( http://haquelab.mdhs.unimelb.edu.au/cd4_memory/ ).

A Department of Defense Laboratory Consortium Approach to Next Generation Sequencing and Bioinformatics Training for Infectious Disease Surveillance in Kenya

Epidemics of emerging and re-emerging infectious diseases are a danger to civilian and military populations worldwide. Health security and mitigation of infectious disease threats is a priority of the United States Government and the Department of Defense (DoD). Next generation sequencing (NGS) and Bioinformatics (BI) enhances traditional biosurveillance by providing additional data to understand transmission, identify resistance and virulence factors, make predictions, and update risk assessments. As more and more laboratories adopt NGS and BI technologies they encounter challenges in building local capacity. In addition to choosing the right sequencing platform and approach, considerations must also be made for the complexity of bioinformatics analyses, data storage, as well as personnel and computational requirements. To address these needs, a comprehensive training program was developed covering wet lab and bioinformatics approaches to NGS. The program is meant to be modular and adaptive to meet both common and individualized needs of medical research and public health laboratories across the DoD. The training program was first deployed internationally to the Basic Science Laboratory of the US Army Medical Research Directorate-Africa in Kisumu, Kenya, which is an overseas Lab of the Walter Reed Army Institute of Research (WRAIR). A week-long workshop with intensive focus on targeted sequencing and the bioinformatics of genome assembly (n = 24 participants) was held. Post-workshop self-assessment (completed by 21 participants) noted significant median gains in knowledge domains related to NGS targeted sequencing, bioinformatics for genome assembly, and sequence quality assessment. The participants also reported that the information on study design, sample preparation, sequencing quality control, data quality assessment, reporting, and basic and advanced bioinformatics analysis were the most useful information presented in the training. While longer-term evaluations are planned, the training resulted in significant short-term improvement of a laboratory’s self-reported wet lab and bioinformatics capabilities. This framework can be used for future DoD laboratory development in the area of NGS and BI for infectious disease surveillance, ultimately enhancing this global DoD capability.

T lymphocyte responses to flaviviruses - diverse cell populations affect tendency toward protection and disease

Dengue virus (DENV), Yellow Fever virus, West Nile virus, Japanese encephalitis virus and Zika virus are medically important flaviviruses transmitted to humans by mosquitoes and circulate in overlapping geographic areas. Cross-reactive immune responses have been demonstrated among the flaviviruses, particularly the four DENV serotypes. The immunological imprint left by a flavivirus infection can therefore have profound effects on the responses to subsequent infections. In this review we summarize recent research focusing on T cell responses to DENV using clinical samples from prospective cohort studies in Asia. These data suggest that durability of different T cell populations after natural infection or vaccination is an important consideration for the outcome of subsequent flavivirus exposures and we argue for continued investigation in the context of longitudinal cohort studies.

The Application of Single-Cell RNA Sequencing in Vaccinology

Single-cell RNA sequencing allows highly detailed profiling of cellular immune responses from limited-volume samples, advancing prospects of a new era of systems immunology. The power of single-cell RNA sequencing offers various opportunities to decipher the immune response to infectious diseases and vaccines. Here, we describe the potential uses of single-cell RNA sequencing methods in prophylactic vaccine development, concentrating on infectious diseases including COVID-19. Using examples from several diseases, we review how single-cell RNA sequencing has been used to evaluate the immunological response to different vaccine platforms and regimens. By highlighting published and unpublished single-cell RNA sequencing studies relevant to vaccinology, we discuss some general considerations how the field could be enriched with the widespread adoption of this technology.

Protection against dengue virus requires a sustained balance of antibody and T cell responses

Pre-existing immunity to dengue virus (DENV) can either protect against or exacerbate, a phenomenon known as antibody dependent enhancement (ADE), a secondary DENV infection. DENV, as an escalating health problem worldwide, has increased the urgency to understand the precise parameters shaping the anti-DENV antibody (Ab) and T cell responses, thereby tipping the balance towards protection versus pathogenesis. Herein, we present the current state of knowledge of about the interplay between the Ab and T cell responses that dictate the outcome of DENV infection and discuss how this newfound knowledge is reshaping strategies for developing safe and effective DENV vaccines.

The Role of Single-Cell Technology in the Study and Control of Infectious Diseases

The advent of single-cell research in the recent decade has allowed biological studies at an unprecedented resolution and scale. In particular, single-cell analysis techniques such as Next-Generation Sequencing (NGS) and Fluorescence-Activated Cell Sorting (FACS) have helped show substantial links between cellular heterogeneity and infectious disease progression. The extensive characterization of genomic and phenotypic biomarkers, in addition to host-pathogen interactions at the single-cell level, has resulted in the discovery of previously unknown infection mechanisms as well as potential treatment options. In this article, we review the various single-cell technologies and their applications in the ongoing fight against infectious diseases, as well as discuss the potential opportunities for future development.

Emerging technologies for systems vaccinology - multi-omics integration and single-cell (epi)genomic profiling

Systems vaccinology leverages high-throughput 'omics' technologies, such as transcriptomics, metabolomics, and mass cytometry, coupled with computational approaches to construct a global map of the complex processes that occur during an immune response to vaccination. Its goal is to define the mechanisms of protective immunity and to identify cellular and molecular correlates of vaccine efficacy. Emerging technological advances including integration of multi-omics datasets, and single-cell genomic and epigenomic profiling of immune responses, have invigorated systems vaccinology, and provide new insights into the mechanisms by which the cellular and molecular information underlying immune memory is stored in the innate and adaptive immune systems. Here, we will review these emerging directions in systems vaccinology, with a particular focus on the epigenome, and its impact on modulating vaccination induced memory in the innate and adaptive immune systems.

Complex human adenoid tissue-based ex vivo culture systems reveal anti-inflammatory drug effects on germinal center T and B cells

BACKGROUND

Human immunology research is often limited to peripheral blood. However, there are important differences between blood immune cells and their counterparts residing in secondary lymphoid organs, such as in the case of germinal center (GC) T follicular helper (Tfh) cells and GC B cells.

METHODS

We developed a versatile ex vivo lymphoid organ culture platform that is based on human pharyngeal tonsils (adenoids) and allows for drug testing. We systematically phenotyped Tfh and GC B cell subsets in explant- and suspension cultures using multicolor flow cytometry and cytokine multiplex analysis.

FINDINGS

Phenotypic changes of certain ex vivo cultured immune cell subsets could be modulated by cytokine addition. Furthermore, we optimized an activation-induced marker assay to evaluate the response to T cell stimulation. We provide proof-of-concept that Tfh and GC B cells could be modulated in these cultures by different anti-inflammatory drugs in unstimulated states and upon activation with vaccine-derived antigens. For example, GC B cells were lost upon CD40L blockade, and clinically approved JAK inhibitors impacted Tfh and GC B cells, including down-regulation of their key transcription factor BCL6. BCL6 regulation was affected by IL-6 signaling in T cells and IL-4 in B cells, respectively. Furthermore, we demonstrated that JAK signaling and TNF signaling contributed to the stimulation-induced activation of tonsil-derived T cells.

INTERPRETATION

Our optimized methods, assays, and mechanistic findings can contribute to a better understanding of human GC responses. These insights may be relevant for improving autoimmune disease therapy and vaccination efficacy.

FUNDING

This work was supported by a project grant under the joint research cooperation agreement of LMU Munich, LMU University Hospital, and Sanofi-Aventis Deutschland GmbH, as well as by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Emmy Noether Programme BA 5132/1-1 and BA 5132/1-2 (252623821), SFB 1054 Project B12 (210592381), and SFB 914 Project B03 (165054336).

Transcriptomic immune profiles of human flavivirus-specific T-cell responses

The Flavivirus genus of viruses includes dengue (DENV), Zika (ZIKV), yellow fever (YFV), Japanese encephalitis (JEV), and West Nile (WNV) viruses. Infections with these species combined are prevalent in tropical and sub-tropical areas, affecting millions of people and ranging from asymptomatic to severe forms of the disease. They therefore pose a serious threat to global public health. Several studies imply a role for T cells in the protection but also pathogenesis against the different flavivirus species. Identifying flavivirus-specific T-cell immune profiles and determining how pre-exposure of one species might affect the immune response against subsequent infections from other species is important to further define the role of T cells in the immune response against infection. Understanding the immune profiles of the flavivirus-specific T-cell response in natural infection is important to understand the T-cell response in the context of vaccination. In this review, we summarize the current knowledge on human immune profiles of flavivirus-specific T-cell reactivity, comparing natural infection with the acute form of the disease and vaccination in different flavivirus infections.