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Tick-borne encephalitis (TBE) is a viral infectious disease of the central nervous system caused by the tick-borne encephalitis virus (TBEV). TBE is usually a biphasic disease and in humans the virus can only be detected during the first (unspecific) phase of the disease. Pathogenesis of TBE is not well understood, but both direct viral effects and immune-mediated tissue damage of the central nervous system may contribute to the natural course of TBE. The effect of TBEV on the innate immune system has mainly been studied in vitro and in mouse models. Characterization of human immune responses to TBEV is primarily conducted in peripheral blood and cerebrospinal fluid, due to the inaccessibility of brain tissue for sample collection. Natural killer (NK) cells and T cells are activated during the second (meningo-encephalitic) phase of TBE. The potential involvement of other cell types has not been examined to date. Immune cells from peripheral blood, in particular neutrophils, T cells, B cells and NK cells, infiltrate into the cerebrospinal fluid of TBE patients.

COVID-19 affects multiple organ-systems. Recent studies have indicated perturbations in the circulating metabolome linked to COVID-19 severity. However, several questions pertain with respect to the metabolome in COVID-19. We performed an in-depth assessment of 1129 unique metabolites in 27 hospitalized COVID-19 patients and integrated results with large-scale proteomic and immunology data to capture multi-organ system perturbations. More than half of the detected metabolic alterations in COVID-19 were driven by patient-specific confounding factors ranging from comorbidities to xenobiotic substances. Systematically adjusting for this, a COVID-19 specific metabolic imprint was defined which, over time, underwent a switch in response to SARS-CoV-2 seroconversion. Integration of the COVID-19 metabolome with clinical, cellular, molecular and immunological severity scales further revealed a network of metabolic trajectories aligned with multiple pathways for immune activation, and organ damage including neurological inflammation and damage. Altogether, this resource refines our understanding of the multi organ-system perturbations in severe COVID-19 patients. This article is protected by copyright. All rights reserved.

BackgroundFlavivirus infections pose a significant global health burden underscoring the need for the development of safe and efficient vaccination strategies. Available flavivirus vaccines are from time to time concomitantly delivered to individuals in need. Co-administration of different vaccines saves time and visits to health care units and vaccine clinics. It serves to provide protection against multiple pathogens in a shorter time-span, both for individuals living in, or travelling to, endemic areas. However, safety and immunogenicity-related responses have not been appropriately evaluated upon concomitant delivery of these vaccines. Therefore, we performed an open label, non-randomized clinical trial studying the safety and immunogenicity following concomitant delivery of the Yellow fever virus (YFV) vaccine with Tick-borne encephalitis virus (TBEV) and Japanese encephalitis virus (JE) virus vaccines.Methods and findingsFollowing screening, healthy study subjects were enrolled into different cohorts receiving either TBEV and YFV vaccines, JEV and YFV vaccines, or in control groups receiving only the TBEV, JEV, or YFV vaccine. Concomitant delivery was given in the same or different upper arms for comparison in the co-vaccination cohorts. Adverse effects were recorded throughout the study period and blood samples were taken before and at multiple time-points following vaccination to evaluate immunological responses to the vaccines. Adverse events were predominantly mild in the study groups. Four serious adverse events (SAE) were reported throughout the trial, none of them deemed related to vaccination. The development of neutralizing antibodies (nAbs) against TBEV, JEV, or YFV was not affected by the concomitant vaccination strategy. Concomitant vaccination in the same or different upper arms did not significantly affect safety or immunogenicity-related outcomes. Exploratory studies on immunological effects were additionally performed and included studies of lymphocyte activation, correlates associated with germinal center activation, and plasmablast expansion.ConclusionsInactivated TBEV or JEV vaccines can be co-administered with the live attenuated YFV vaccine without an increased risk of adverse events and without reduced development of nAbs to the respective viruses. The vaccines can be delivered in the same upper arm without negative outcome.Trial registrationEudra CT 2017-002137-32Author summaryWhy was this study done?Flavivirus infections pose a significant global health burden, underscoring the need for the development of safe and efficient vaccination strategiesCo-administration of different flavivirus vaccines saves time and visits to health care units and vaccine clinics. It serves to provide protection against multiple pathogens in a shorter time-span, both for individuals living in or travelling to endemic areasSafety and immunogenicity-related responses have not been appropriately evaluated upon co-administration of many vaccines including currently used flavivirus vaccines, such as Yellow fever virus (YFV), Tick-borne encephalitis virus (TBEV), and Japanese encephalitis virus (JE) virus vaccinesBecause of this, we performed an open label, non-randomized clinical trial studying the safety and immunogenicity following co-administration of YFV vaccine with TBEV and JEV vaccinesWhat did the researchers find?Adverse events, neutralizing antibodies (nAbs) and other related immunological parameters were not adversely affected by concomitant delivery of the vaccinesConcomitant vaccination in the same versus different upper arms of study participants did not significantly affect safety or immunogenicity outcomesWhat do these findings mean?Co-administration of YFV vaccine and TBEV or JEV vaccines is feasible without increased risk of adverse events or reduced development of nAbs against the respective viruses. Furthermore, the vaccines can safely be delivered in the same upper arm without negative outcome

Tick-borne encephalitis (TBE) is a viral infection of the CNS caused by TBE virus. With no specific treatment available, the only protection is a formalin-inactivated whole virus vaccine. Primary immunization with European TBE vaccines, as recommended by the manufacturers, consists of three vaccine doses administered within a 1-y period. Protection from vaccination is believed to be mediated by Abs, yet T cells may also have a protective role. We set out to characterize the human CD4+ T cell response throughout primary TBE immunization. The responses were evaluated before vaccination and 1 mo after each vaccine dose. A heterogeneous magnitude of CD4+ T cell–mediated memory responses was observed in regard to lymphoblast expansion and cytokine production (IFN-γ, IL-2, and TNF), with the highest median magnitude detected after the second dose of vaccine. Stimulation with an overlapping peptide library based on structural TBE virus proteins E and C revealed that CD4+ T cells concomitantly producing IL-2 and TNF dominated the responses from vaccinees after each vaccine dose, whereas a control cohort of TBE patients responded mainly with all three cytokines. CD107a expression was not upregulated upon peptide stimulation in the vaccinees. However, CD154 (CD40L) expression on cytokine-positive memory CD4+ T cells significantly increased after the second vaccine dose. Taken together, TBE vaccination induced CD4+ T cell responses dominated by IL-2 and TNF production together with CD154 upregulation and a lower IFN-γ response compared with TBE patients. This response pattern was consistent after all three doses of TBE vaccine.

Respiratory viral infections with SARS-CoV-2 and influenza viruses commonly induce a strong infiltration of immune cells into the human lung, with potential detrimental effects on the integrity of the lung tissue. Despite comprising the largest fractions of circulating lymphocytes in the lung, rather little is known about how peripheral blood natural killer (NK) cell and T cell subsets are equipped for lung-homing in COVID-19 and influenza. Here, we provide a detailed comparative analysis of NK cells and T cells in patients infected with SARS-CoV-2 or influenza virus, focusing on the protein and gene expression of chemokine receptors known to be involved in recruitment to the lung. For this, we used 28-colour flow cytometry as well as re-analysis of a publicly available single-cell RNA-seq dataset from bronchoalveolar lavage (BAL) fluid. Frequencies of NK cells and T cells expressing CXCR3, CXCR6, and CCR5 were altered in peripheral blood of COVID-19 and influenza patients, in line with increased transcript expression of

Background Southern Sweden is endemic for tick-borne encephalitis (TBE), with Stockholm County as one of the high-risk areas. Our aim in this study was to describe cases of vaccine failures and to optimize future vaccination recommendations. Methods Patients with TBE were identified in the notification database at the Department of Communicable Disease Control and Prevention in Stockholm County during 2006–2015. Vaccine failure was defined as TBE despite adherence to the recommended vaccination schedule with at least 2 doses. Clinical data were extracted from medical records. Results A total of 1004 TBE cases were identified, 53 (5%) were defined as vaccine failures. In this latter group, the median age was 62 years (6–83). Forty-three (81%) patients were aged >50 years and 2 were children. Approximately half of the patients had comorbidities, with diseases affecting the immune system accounting for 26% of all cases. Vaccine failures following the third or fourth vaccine dose accounted for 36 (68%) of the patients. Severe and moderate TBE disease affected 81% of the cases. Conclusions To our knowledge, this is the largest documented cohort of TBE vaccine failures. Vaccine failure after 5 TBE vaccine doses is rare. Our data provide rationale for adding an extra priming dose to those aged ≥50 years., This 10-year retrospective study includes 53 patients (median age 62 years, 6-83) with TBE vaccination failure. Forty-four (81%) patients were aged ≥50 years. Based on our data, we propose adding an extra priming dose for individuals aged ≥50 years.

• Tick-borne encephalitis (TBE) is a viral infectious disease of the central nervous system caused by the tick-borne encephalitis virus (TBEV). • TBE is usually a biphasic disease and in humans the virus can only be detected during the first (unspecific) phase of the disease. • Pathogenesis of TBE is not well understood, but both direct viral effects and immune-mediated tissue damage of the central nervous system may contribute to the natural course of TBE. • The effect of TBEV on the innate immune system has mainly been studied in vitro and in mouse models. • Characterization of human immune responses to TBEV is primarily conducted in peripheral blood and cerebrospinal fluid, due to the inaccessibility of brain tissue for sample collection. • Natural killer (NK) cells and T cells are activated during the second (meningoencephalitic) phase of TBE. The potential involvement of other cell types has not been examined to date. • Immune cells from peripheral blood, in particular neutrophils, T cells, B cells and NK cells, infiltrate into the cerebrospinal fluid of TBE patients.

Background Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a global pandemic. The understanding of the transmission and the duration of viral shedding in SARS-CoV-2 infection is still limited. Objectives To assess the timeframe and potential risk of SARS-CoV-2 transmission from hospitalized COVID-19 patients in relation to antibody response. Method We performed a cross-sectional study of 36 COVID-19 patients hospitalized at Karolinska University Hospital. Patients with more than 8 days of symptom duration were sampled from airways, for PCR analysis of SARS-CoV-2 RNA and in vitro culture of replicating virus. Serum SARS-CoV-2-specific immunoglobulin G (IgG) and neutralizing antibodies titers were assessed by immunofluorescence assay (IFA) and microneutralization assay. Results SARS-CoV-2 RNA was detected in airway samples in 23 patients (symptom duration median 15 days, range 9–53 days), whereas 13 patients were SARS-CoV-2 RNA negative (symptom duration median 21 days, range 10–37 days). Replicating virus was detected in samples from 4 patients at 9–16 days. All but two patients had detectable levels of SARS-CoV-2-specific IgG in serum, and SARS-CoV-2 neutralizing antibodies were detected in 33 out of 36 patients. Total SARS-CoV-2-specific IgG titers and neutralizing antibody titers were positively correlated. High levels of both total IgG and neutralizing antibody titers were observed in patients sampled later after symptom onset and in patients where replicating virus could not be detected. Conclusions Our data suggest that the presence of SARS-Cov-2 specific antibodies in serum may indicate a lower risk of shedding infectious SARS-CoV-2 by hospitalized COVID-19 patients.

BackgroundInsights into early, specific humoral and cellular responses to infection with SARS-CoV-2, as well as the persistence and magnitude of resulting immune memory is important amidst the ongoing pandemic. The combination of humoral and cellular immunity will most likely contribute to protection from reinfection or severe disease.MethodsHere, we conducted a longitudinal study on hospitalized moderate and severe COVID-19 patients from the acute phase of disease into convalescence at five- and nine-months post symptom onset. Utilizing flow cytometry, serological assays as well as B cell and T cell FluoroSpot assays, we assessed the magnitude and specificity of humoral and cellular immune memory during and after human SARS-CoV-2 infection.FindingsDuring acute COVID-19, we observed an increase in germinal center activity, a substantial expansion of antibodysecreting cells, and the generation of SARS-CoV-2-neutralizing antibodies. Despite gradually decreasing antibody levels, we show persistent, neutralizing antibody titers as well as robust specific memory B cell responses and polyfunctional T cell responses at five- and nine-months after symptom onset in both moderate and severe COVID-19 patients. Long-term SARS-CoV-2 specific responses were marked by preferential targeting of spike over nucleocapsid protein.ConclusionsOur findings describe the initiation and, importantly, persistence of cellular and humoral SARS-CoV-2 specific immunological memory in hospitalized COVID-19 patients long after recovery, likely contributing towards protection against reinfection.

Since the outset of the COVID-19 pandemic, increasing evidence suggests that the innate immune responses play an important role in the disease development. A dysregulated inflammatory state has been proposed as key driver of clinical complications in COVID-19, with a potential detrimental role of granulocytes. However, a comprehensive phenotypic description of circulating granulocytes in SARS-CoV-2-infected patients is lacking. In this study, we used high-dimensional flow cytometry for granulocyte immunophenotyping in peripheral blood collected from COVID-19 patients during acute and convalescent phases. Severe COVID-19 was associated with increased levels of both mature and immature neutrophils, and decreased counts of eosinophils and basophils. Distinct immunotypes were evident in COVID-19 patients, with altered expression of several receptors involved in activation, adhesion and migration of granulocytes (e.g. CD62L, CD11a/b, CD69, CD63, CXCR4). Paired sampling revealed recovery and phenotypic restoration of the granulocytic signature in the convalescent phase. The identified granulocyte immunotypes correlated with distinct sets of soluble inflammatory markers supporting pathophysiologic relevance. Furthermore, clinical features, including multi-organ dysfunction and respiratory function, could be predicted using combined laboratory measurements and immunophenotyping. This study provides a comprehensive granulocyte characterization in COVID-19 and reveals specific immunotypes with potential predictive value for key clinical features associated with COVID-19.SignificanceAccumulating evidence shows that granulocytes are key modulators of the immune response to SARS-CoV-2 infection and their dysregulation could significantly impact COVID-19 severity and patient recovery after virus clearance. In the present study, we identify selected immune traits in neutrophil, eosinophil and basophil subsets associated to severity of COVID-19 and to peripheral protein profiles. Moreover, computational modeling indicates that the combined use of phenotypic data and laboratory measurements can effectively predict key clinical outcomes in COVID-19 patients. Finally, patient-matched longitudinal analysis shows phenotypic normalization of granulocyte subsets 4 months after hospitalization. Overall, in this work we extend the current understanding of the distinct contribution of granulocyte subsets to COVID-19 pathogenesis.

Respiratory viral infections with SARS-CoV-2 or influenza viruses commonly induce a strong infiltration of immune cells into the lung, with potential detrimental effects on the integrity of the lung tissue. Despite comprising the largest fractions of circulating lymphocytes in the lung, little is known about how blood natural killer (NK) cells and T cell subsets are equipped for lung-homing in COVID-19 and influenza. Using 28-colour flow cytometry and re-analysis of published RNA-seq datasets, we provide a detailed comparative analysis of NK cells and T cells in peripheral blood from moderately sick COVID-19 and influenza patients, focusing on the expression of chemokine receptors known to be involved in leukocyte recruitment to the lung. The results reveal a predominant role for CXCR3, CXCR6, and CCR5 in COVID-19 and influenza patients, mirrored by scRNA-seq signatures in peripheral blood and bronchoalveolar lavage from publicly available datasets. NK cells and T cells expressing lung-homing receptors displayed stronger phenotypic signs of activation as compared to cells lacking lung-homing receptors, and activation was overall stronger in influenza as compared to COVID-19. Together, our results indicate migration of functionally competent CXCR3+, CXCR6+, and/or CCR5+ NK cells and T cells to the lungs in moderate COVID-19 and influenza patients, identifying potential common targets for future therapeutic interventions in respiratory viral infections.Author summaryThe composition of in particular CXCR3+ and/or CXCR6+ NK cells and T cells is altered in peripheral blood upon infection with SARS-CoV-2 or influenza virus in patients with moderate disease. Lung-homing receptor-expression is biased towards phenotypically activated NK cells and T cells, suggesting a functional role for these cells co-expressing in particular CXCR3 and/or CXCR6 upon homing towards the lung.

ObjectivesThe role of innate lymphoid cells (ILCs) in coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is unknown. Understanding the immune response in COVID-19 could contribute to unravel the pathogenesis and identification of treatment targets. To describe the phenotypic landscape of circulating ILCs in COVID-19 patients and to identify ILC phenotypes correlated to serum biomarkers, clinical markers, and laboratory parameters relevant in COVID-19.MethodsBlood samples collected from moderately (n=11) and severely ill (n=12) COVID-19 patients as well as healthy control donors (n=16), were analyzed with 18-parameter flow cytometry. Using supervised and unsupervised approaches, we examined the ILC activation status and homing profile. Clinical and laboratory parameters were obtained from all COVID-19 patients and serum biomarkers were analyzed with multiplex immunoassays.ResultsILCs were largely depleted from the circulation of COVID-19 patients compared with healthy controls. Remaining circulating ILCs from patients revealed increased frequencies of ILC2 in moderate COVID-19, with a concomitant decrease of ILC precursors (ILCp), as compared with controls. ILC2 and ILCp showed an activated phenotype with increased CD69 expression, whereas expression levels of the chemokine receptors CXCR3 and CCR4 were significantly altered in ILC2 and ILCp, and ILC1, respectively. The activated ILC profile of COVID-19 patients was associated with soluble inflammatory markers, while frequencies of ILC subsets were correlated with laboratory parameters that reflect the disease severity.ConclusionThis study provides insights into the potential role of ILCs in immune responses against SARS-CoV-2, particularly linked to the severity of COVID-19.

MAIT cell activation and decline in blood are associated with COVID-19 severity, features that dynamically recover in convalescence., Innate-like rapid responders Viral infections elicit host responses from conventional T cells, innate lymphoid cells, and innate-like lymphocyte subsets. Parrot et al. used blood from acute and convalescent COVID-19 patients to investigate how SARS-CoV-2 infection affects the innate-like mucosa-associated invariant T (MAIT) cells. Acute viral infection induced a profound decline in the number of blood MAIT cells and activation of the residual blood MAIT cells. The loss of circulating MAIT cells in acute COVID-19 patients coincided with enrichment of MAIT cells among T cells recovered from the respiratory tract. With convalescence, the number of blood MAIT cells and their activation status reverted toward normal. These findings indicate that circulating MAIT cells are mobilized early after SARS-CoV-2 infection and may contribute to both resolution and exacerbation of COVID-19–associated pneumonia., Severe coronavirus disease 2019 (COVID-19) is characterized by excessive inflammation of the lower airways. The balance of protective versus pathological immune responses in COVID-19 is incompletely understood. Mucosa-associated invariant T (MAIT) cells are antimicrobial T cells that recognize bacterial metabolites and can also function as innate-like sensors and mediators of antiviral responses. Here, we investigated the MAIT cell compartment in COVID-19 patients with moderate and severe disease, as well as in convalescence. We show profound and preferential decline in MAIT cells in the circulation of patients with active disease paired with strong activation. Furthermore, transcriptomic analyses indicated substantial MAIT cell enrichment and proinflammatory IL-17A bias in the airways. Unsupervised analysis identified MAIT cell CD69high and CXCR3low immunotypes associated with poor clinical outcome. MAIT cell levels normalized in the convalescent phase, consistent with dynamic recruitment to the tissues and later release back into the circulation when disease is resolved. These findings indicate that MAIT cells are engaged in the immune response against SARS-CoV-2 and suggest their possible involvement in COVID-19 immunopathogenesis.

To understand the risk of transmission of SARS-CoV-2 in hospitalized COVID-19 patients we simultaneously assessed the presence of SARS-CoV-2 RNA, live infectious virus in the airways, and virus-specific IgG and neutralizing antibodies in sera in 36 hospitalized COVID-19 patients. SARS-CoV-2 could be cultured from four patients, all with low or undetectable antibody response. Our data suggests that the level of SARS-CoV-2 antibodies may correlate to risk for shedding live SARS-CoV-2 virus in hospitalized COVID-19 patients.

SARS-CoV-2-specific memory T cells will likely prove critical for long-term immune protection against COVID-19. We systematically mapped the functional and phenotypic landscape of SARS-CoV-2-specific T cell responses in a large cohort of unexposed individuals as well as exposed family members and individuals with acute or convalescent COVID-19. Acute phase SARS-CoV-2-specific T cells displayed a highly activated cytotoxic phenotype that correlated with various clinical markers of disease severity, whereas convalescent phase SARS-CoV-2-specific T cells were polyfunctional and displayed a stem-like memory phenotype. Importantly, SARS-CoV-2-specific T cells were detectable in antibody-seronegative family members and individuals with a history of asymptomatic or mild COVID-19. Our collective dataset shows that SARS-CoV-2 elicits robust memory T cell responses akin to those observed in the context of successful vaccines, suggesting that natural exposure or infection may prevent recurrent episodes of severe COVID-19 also in seronegative individuals.

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged in late 2019 and has since become a global pandemic. Pathogen-specific Abs are typically a major predictor of protective immunity, yet human B cell and Ab responses during COVID-19 are not fully understood. In this study, we analyzed Ab-secreting cell and Ab responses in 20 hospitalized COVID-19 patients. The patients exhibited typical symptoms of COVID-19 and presented with reduced lymphocyte numbers and increased T cell and B cell activation. Importantly, we detected an expansion of SARS-CoV-2 nucleocapsid protein–specific Ab-secreting cells in all 20 COVID-19 patients using a multicolor FluoroSpot Assay. Out of the 20 patients, 16 had developed SARS-CoV-2–neutralizing Abs by the time of inclusion in the study. SARS-CoV-2–specific IgA, IgG, and IgM Ab levels positively correlated with SARS-CoV-2–neutralizing Ab titers, suggesting that SARS-CoV-2–specific Ab levels may reflect the titers of neutralizing Abs in COVID-19 patients during the acute phase of infection. Last, we showed that IL-6 and C-reactive protein serum concentrations were higher in patients who were hospitalized for longer, supporting the recent observations that IL-6 and C-reactive protein could be used as markers for COVID-19 severity. Altogether, this study constitutes a detailed description of clinical and immunological parameters in 20 COVID-19 patients, with a focus on B cell and Ab responses, and describes tools to study immune responses to SARS-CoV-2 infection and vaccination.

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged in late 2019 and has since become a global pandemic. Pathogen-specific antibodies are typically a major predictor of protective immunity, yet B cell and antibody responses during COVID-19 are not fully understood. Here, we analyzed antibody-secreting cell (ASC) and antibody responses in twenty hospitalized COVID-19 patients. The patients exhibited typical symptoms of COVID-19, and presented with reduced lymphocyte numbers and increased T cell and B cell activation. Importantly, we detected an expansion of SARS-CoV-2 nucleocapsid protein-specific ASCs in all twenty COVID-19 patients using a multicolor FluoroSpot assay. Out of the 20 patients, 16 had developed SARS-CoV-2-neutralizing antibodies by the time of inclusion in the study. SARS-CoV-2-specific IgA, IgG and IgM antibody levels positively correlated with SARS-CoV-2-neutralizing antibody titers, suggesting that SARS-CoV-2-specific antibody levels may reflect the titers of neutralizing antibodies in COVID-19 patients during the acute phase of infection. Lastly, we showed that interleukin 6 (IL-6) and C-reactive protein (CRP) concentrations were higher in serum of patients who were hospitalized for longer, supporting the recent observations that IL-6 and CRP could be used to predict COVID-19 severity. Altogether, this study constitutes a detailed description of clinical and immunological parameters in twenty COVID-19 patients, with a focus on B cell and antibody responses, and provides tools to study immune responses to SARS-CoV-2 infection and vaccination.

Tick-borne encephalitis virus (TBEV) is a leading cause of viral meningoencephalitis in many parts of Europe and eastwards in Asia, with high morbidity and often long-term neurologic sequelae. With no treatment available, studies of the immune response to TBEV are essential for the understanding of the immunopathogenesis of tick-borne encephalitis and for the development of therapeutics. We have previously demonstrated that CD8+ T cell responses in peripheral blood in patients with acute TBEV peak at around 7 d after hospitalization in the neuroinvasive phase of the disease. In this study, we identified six novel TBEV HLA-A2– and HLA-B7–restricted epitopes, all derived from the nonstructural proteins of TBEV. This identification allowed for a comprehensive phenotypic and temporal analysis of the HLA-A2– and HLA-B7–restricted Ag-specific CD8+ T cell response during the acute stages of human TBEV infection. HLA-A2– and HLA-B7–restricted TBEV epitope–specific effector cells predominantly displayed a CD45RA−CCR7−CD27+CD57− phenotype at day 7, which transitioned into separate distinct phenotypes for HLA-A2– and HLA-B7–restricted TBEV-specific CD8+ T cells, respectively. At day 21, the most prevalent phenotype in the HLA-A2–restricted CD8+ T cell populations was CD45RA−CCR7−CD27+CD57+, whereas the HLA-B7–restricted CD8+ T cell population was predominantly CD45RA+CCR7−CD27+CD57+. Almost all TBEV epitope–specific CD8+ T cells expressed α4 and β1 integrins at days 7 and 21, whereas the bulk CD8+ T cells expressed lower integrin levels. Taken together, human TBEV infection elicits broad responses to multiple epitopes, predominantly derived from the nonstructural part of the virus, establishing distinct maturation patterns for HLA-A2– and HLA-B7–restricted TBEV epitope–specific CD8+ T cells.

Tick-borne encephalitis (TBE) is a viral infection of the CNS caused by TBE virus. With no specific treatment available, the only protection is a formalin-inactivated whole virus vaccine. Primary immunization with European TBE vaccines, as recommended by the manufacturers, consists of three vaccine doses administered within a 1-y period. Protection from vaccination is believed to be mediated by Abs, yet T cells may also have a protective role. We set out to characterize the human CD4

Tick-borne encephalitis virus (TBEV) is a flavivirus that is transferred to humans by infected ticks. The virus causes tick-borne encephalitis, a severe infection of the CNS with a high risk for long-lasting sequelae. Currently, no treatment exists for the disease. Understanding the cellular immune response to this infection is important to gain further understanding into the pathogenesis, treatment, and prevention of the disease. NK cells are known to participate in the control of viral infections. We performed a longitudinal analysis of the human NK cell response to TBEV infection in a cohort of infected individuals from the onset of severe clinical symptoms to the convalescence phase. NK cell activation, as measured by expression of Ki67, was apparent at the time of hospitalization. By 3 wk after hospitalization, it decreased to levels seen in healthy controls. Concomitant with the increase in NK cell activation, augmented levels of IL-12, IL-15, IL-18, IFN-γ, and TNF were detected in patient plasma. This TBEV-induced NK cell activation was restricted predominantly to differentiated CD57+CD56dim NK cells. Functionally, CD56dim NK cells responded poorly to target cells at the time of hospitalization, but they recovered functional capacity to control levels during the convalescent phase. In contrast, the responsiveness of NK cells to cytokine stimulation remained intact throughout the disease. These findings demonstrate that NK cells respond to TBEV infection with characteristics that are distinct from those of other human viral infections and provide insights into the NK cell response to clinical TBEV infection.

Summary SARS-CoV-2-specific memory T cells will likely prove critical for long-term immune protection against COVID-19. We here systematically mapped the functional and phenotypic landscape of SARS-CoV-2-specific T cell responses in unexposed individuals, exposed family members, and individuals with acute or convalescent COVID-19. Acute phase SARS-CoV-2-specific T cells displayed a highly activated cytotoxic phenotype that correlated with various clinical markers of disease severity, whereas convalescent phase SARS-CoV-2-specific T cells were polyfunctional and displayed a stem-like memory phenotype. Importantly, SARS-CoV-2-specific T cells were detectable in antibody-seronegative exposed family members and convalescent individuals with a history of asymptomatic and mild COVID-19. Our collective dataset shows that SARS-CoV-2 elicits robust, broad and highly functional memory T cell responses, suggesting that natural exposure or infection may prevent recurrent episodes of severe COVID-19., Highlights 1. Acute phase SARS-CoV-2-specific T cells display an activated cytotoxic phenotype 2. Broad and polyfunctional SARS-CoV-2-specific T cell responses in convalescent phase 3. Detection of SARS-CoV-2-specific T cell responses also in seronegative individuals

Tick-borne encephalitis virus (TBEV) is a leading cause of viral meningoencephalitis in many parts of Europe and eastwards in Asia, with high morbidity and often long-term neurologic sequelae. With no treatment available, studies of the immune response to TBEV are essential for the understanding of the immunopathogenesis of tick-borne encephalitis and for the development of therapeutics. We have previously demonstrated that CD8

Human cytomegalovirus (HCMV), a member of the herpesvirus family, establishes life-long persistence and latency after primary infection and can be reactivated later in life. In immunosuppressed patients, it is an important pathogen that can cause severe disease. HCMV is also thought to play a causative role in inflammatory diseases and cancer. The virus can infect different immune cells, including dendritic cells (DCs) and can take advantage of host immune functions to avoid immune recognition. These characteristics have sparked major interest in understanding HCMV and its interaction with immune cells and their relevance to disease pathogenesis. In this review, we focus on the complex host-pathogen relationship between HCMV and DCs, including the persistence of the virus in these cells, their function in the immune response to HCMV infection and the potential clinical consequences of HCMV infection in DCs.

Rabeximod (9-chloro-2,3-dimethyl-6-(N,N-dimethylaminoethylamino-2-oxoethyl)-6H-indolo[2,3-b]quinoxaline) is a synthetic compound that is currently being developed for the treatment of rheumatoid arthritis (RA). Here, we investigated the effects of Rabeximod on the functionality of human antigen-presenting cells (APCs) of myeloid origin. Different subsets of professional APCs were generated from human monocytes in vitro and simultaneously treated with different doses of Rabeximod. Although Rabeximod had no effect on the differentiation of monocytes into anti-inflammatory macrophages (AI-Mϕs), this compound impaired monocyte differentiation into monocyte-derived dendritic cells (MDCs) and pro-inflammatory allostimulated macrophages (Allo-Mϕs). MDCs that were treated with Rabeximod resulted in a significant decrease in their ability to pinocytose antigens, while no effect was exerted by the drug on the ability of Allo-Mϕs and AI-Mϕs to phagocytose. Furthermore, we observed a significant reduction in the allostimulatory ability of MDCs and Allo-Mϕs after treatment with Rabeximod, although this compound did not affect the low immunostimulatory capacity of AI-Mϕs. Conversely, the effect of Rabeximod in influencing cytokine secretion by APCs appeared to be limited. In conclusion, Rabeximod impairs differentiation of monocytes into different pro-inflammatory APCs, leading to impaired immunostimulatory abilities of these cells. Our observations shed light on the cellular mode of action and the immunomodulatory effect of Rabeximod.

Cytomegalovirus (CMV) is associated with atherosclerosis and transplant vascular sclerosis. The aim of this study was to explore the hypothesis that active CMV infection in the vessel wall could be associated with abdominal aortic aneurysm (AAA). We examined the prevalence of CMV in AAA specimens from 22 patients undergoing surgery and, in five cases, characterized the function of smooth muscle cells (SMCs) from the aneurysm in vitro. Twenty-one (95%) of the 22 AAA specimens were CMV positive by a polymerase chain reaction assay, in situ hybridization, or a highly sensitive immunohistochemical staining technique. No positive cells were found in aortas from three CMV-seronegative organ donor cadavers. CMV immediate-early and late antigens were expressed in SMCs in the lesions and were associated with 5-lipoxygenase (5-LO) expression. CMV-positive intimal SMCs migrated 6.6 +/- 1.5 times more efficiently than CMV-negative medial SMCs (p < 0.05). In vitro CMV infection of medial SMCs resulted in a 3.2 +/- 1.2 times increase in migration (p < 0.05). The intimal migration was significantly inhibited by antibodies against basic fibroblast growth factor (bFGF; p < 0.05) in a dose-dependent fashion. Antibodies against platelet-derived growth factor (PDGF)-AB, insulin-like growth factor 1, vascular endothelial growth factor (VEGF), RANTES, monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory protein (MIP)-1alpha, or interleukin-1beta did not significantly affect intimal SMC migration. However, intimal and medial SMCs secreted similar amounts of bFGF, MCP-1, MIP-1alpha, RANTES, PDGF-AB, PDGF-BB, epidermal growth factor, and VEGF. CMV infection in vitro of intimal and medial cells did not result in significant changes of bFGF or MCP-1 secretion. Since CMV infection can affect several functional parameters in SMCs, including several key factors in infected SMCs, our findings provide support for the hypothesis that CMV contributes to the pathogenesis of abdominal aortic aneurysm.

Infection of mice with murine gammaherpesvirus 68 (MHV-68) robustly activates CD8 T cells, but only six class I major histocompatibility complex (MHC)-restricted epitopes have been described to date for the widely usedH-2bhaplotype mice. To explore the specificity and kinetics of the cytotoxic T-lymphocyte response in MHV-68-infected C57BL/6 mice, we screened for H-2Kb- and H-2Db-restricted epitopes using a set of 384 candidate epitopes in an MHC tetramer-based approach and identified 19 new epitopes in 16 different open reading frames. Of the six known H-2Kb- and H-2Db-restricted epitopes, we confirmed a response against three and did not detect CD8 T-cell-specific responses for the remaining three. The peak of the CD8 T-cell response to most peptides occurs between 6 and 10 days postinfection. The respective MHC tetramer-positive CD8 T cells display an activated/effector phenotype (CD62Lloand CD44hi) and produce gamma interferon upon peptide stimulation ex vivo. MHV-68 infection in vivo elicits a response to multiple viral epitopes, derived from both early and late viral antigens, illustrating a far broader T-cell repertoire and more-rapid activation than those previously recorded.

Murine gammaherpesvirus 68 (MHV-68) contains a ubiquitin (Ub)-specific cysteine protease (USP) domain embedded within the large tegument protein ORF64, as do all other herpesviruses. The biological role of this protease is still unclear, but for the alphaherpesvirus Marek's disease virus, its USP is involved in T-cell lymphoma formation. We here study the role of the MHV-68 USP, encoded by ORF64. By constructing a mutant virus with a single cysteine-to-alanine replacement in the active site of ORF64, we demonstrate that the USP activity of ORF64 is abolished. The mutant virus replicates less efficiently in vitro, and plaque size is reduced compared to that of a revertant virus. Electron microscopy of infected cells did not reveal any obvious differences in virion morphogenesis or differences in egress for the mutant and revertant viruses. Intraperitoneal infection of C57/BL6 mice demonstrates that the mutant virus is generally cleared by day 7, indicating a role for the USP in the persistence of MHV-68 infection or efficient replication. However, the USP activity in MHV-68 is unlikely to be involved in the establishment of latency or reactivation, since we observed no significant difference in viral DNA genome copy number in the spleen or in the number of cells that reactivate MHV-68 from latency. Our results for MHV-68 ORF64 are consistent with an enzymatic function of the tegument protein that is beneficial to the virus during acute infection, particularly in vivo.

Tick-borne encephalitis virus (TBEV) is a flavivirus that belongs to the Flaviviridae family. TBEV is transmitted to humans primarily from infected ticks. The virus causes tick-borne encephalitis (TBE), an acute viral disease that affects the central nervous system (CNS). Infection can lead to acute neurological symptoms of significant severity due to meningitis or meningo(myelo)encephalitis. TBE can cause long-term suffering and has been recognized as an increasing public health problem. TBEV-affected areas currently include large parts of central and northern Europe as well as northern Asia. Infection with TBEV triggers a humoral as well as a cell-mediated immune response. In contrast to the well-characterized humoral antibody-mediated response, the cell-mediated immune responses elicited to natural TBEV-infection have been poorly characterized until recently. Here, we review recent progress in our understanding of the cell-mediated immune response to human TBEV-infection. A particular emphasis is devoted to studies of the response mediated by natural killer (NK) cells and CD8 T cells. The studies described include results revealing the temporal dynamics of the T cell- as well as NK cell-responses in relation to disease state and functional characterization of these cells. Additionally, we discuss specific immunopathological aspects of TBEV-infection in the CNS.