Antiviral CD8 Research Articles

IRFE-mediated regulation of mCMV m152 expression

Cytomegaloviruses (CMVs) have evolved genes dedicated to subvert literally all components of the host´s immune system. The host in turn has evolved mechanisms to attenuate viral immune evasion to control the virus. The model of murine CMV (mCMV) has been pivotal to the discovery of CMV immune evasion genes and made it feasible to study their roles in vivo. Two of these genes are strong MHC class-I (MHC-I) regulators, named m06 and m152. Whereas m06 is the strongest downmodulator of total cell surface MHC-I, m152 preferentially blocks trafficking of recently-loaded peptide-MHC-I complexes to the cell surface. Here we present a previous unknown host modulation of m152 by type-I interferons (IFNs). We recognized a consensus IFN regulatory factor element (IRFE) in the promoter region of the m152 gene. Conspicuously, this m152-IRFE is one of only three IRFE sequences present in the mCMV genome, and the only one that is located in a promoter region. Moreover, the m152-IRFE is conserved among a panel of sequenced mCMV genomes and showed functional properties under type-I IFN signaling. A loss-of-function motif mutation of the m152-IRFE is associated with reduced m152 transcripts and protein expression in infected cells. Analysis by flow cytometry revealed that the IRFE-mediated regulation of m152 transcription affects MHC-I cell surface expression. In addition, we could confirm the requirement of type-I IFN signaling for antiviral CD8 T cell control in C57BL/6 IFNAR-/-mice. While mCMV wildtype virus is not controlled by adoptively transferred CD8 T cells in the absence of IFNAR signaling, an mCMV recombinant lacking m152 is again controlled. These findings suggest that type-I IFN signaling is regulating m152 expression and therefore works as a direct host counter-measure to dampen viral immune evasion.

Most viral peptides displayed by class I MHC on infected cells are immunogenic

CD8+ T cells are essential effectors in antiviral immunity, recognizing short virus-derived peptides presented by MHC class I (pMHCI) on the surface of infected cells. However, the fraction of viral pMHCI on infected cells that are immunogenic has not been shown for any virus. To approach this fundamental question, we used peptide sequencing by high-resolution mass spectrometry to identify more than 170 vaccinia virus pMHCI presented on infected mouse cells. Next, we screened each peptide for immunogenicity in multiple virus-infected mice, revealing a wide range of immunogenicities. A surprisingly high fraction (>80%) of pMHCI were immunogenic in at least one infected mouse, and nearly 40% were immunogenic across more than half of the mice screened. Further, we have extended these findings to track the kinetics of epitope presentation during infection of dendritic and fibroblast cell lines, as well from splenocytes from infected mice. The high number of peptides found to be immunogenic and the distribution of responses across mice—in addition to comprehensive profiling of presentation kinetics and binding affinity for MHCI—give us insight into the specificity of antiviral CD8+ T cell responses.

MYB orchestrates T cell exhaustion and response to checkpoint inhibition

CD8+ T cells that respond to chronic viral infections or cancer are characterized by the expression of inhibitory receptors such as programmed cell death protein 1 (PD-1) and by the impaired production of cytokines. This state of restrained functionality—which is referred to as T cell exhaustion1,2—is maintained by precursors of exhausted T (TPEX) cells that express the transcription factor T cell factor 1 (TCF1), self-renew and give rise to TCF1− exhausted effector T cells3–6. Here we show that the long-term proliferative potential, multipotency and repopulation capacity of exhausted T cells during chronic infection are selectively preserved in a small population of transcriptionally distinct CD62L+ TPEX cells. The transcription factor MYB is not only essential for the development of CD62L+ TPEX cells and maintenance of the antiviral CD8+ T cell response, but also induces functional exhaustion and thereby prevents lethal immunopathology. Furthermore, the proliferative burst in response to PD-1 checkpoint inhibition originates exclusively from CD62L+ TPEX cells and depends on MYB. Our findings identify CD62L+ TPEX cells as a stem-like population that is central to the maintenance of long-term antiviral immunity and responsiveness to immunotherapy. Moreover, they show that MYB is a transcriptional orchestrator of two fundamental aspects of exhausted T cell responses: the downregulation of effector function and the long-term preservation of self-renewal capacity.

PD-1 blockade following ART interruption enhances control of pathogenic SIV in rhesus macaques

Programmed death-1 (PD-1) blockade during chronic Simian immunodeficiency virus (SIV) infection results in restoration of CD8 T-cell function and enhances viral control. Here, we tested the therapeutic benefits of PD-1 blockade administered soon after anti-retrovial therapy (ART) interruption (ATI) by treating SIV-infected and ART-suppressed macaques with either an anti-PD-1 antibody (n = 7) or saline (n = 4) at 4 wk after ATI. Following ATI, the plasma viremia increased rapidly in all animals, and the frequency of SIV-specific CD8 T cells also increased in some animals. PD-1 blockade post ATI resulted in higher proliferation of total memory CD8 and CD4 T cells and natural killer cells. PD-1 blockade also resulted in higher proliferation of SIV-specific CD8 T cells and promoted their differentiation toward better functional quality. Importantly, four out of the seven anti-PD-1 antibody-treated animals showed a rapid decline in plasma viremia by 100- to 2300-fold and this was observed only in animals that showed measurable SIV-specific CD8 T cells post PD-1 blockade. These results demonstrate that PD-1 blockade following ATI can significantly improve the function of anti-viral CD8 T cells and enhance viral control and strongly suggests its potential synergy with other immunotherapies that induce functional CD8 T-cell response under ART. These results have important implications for HIV cure research.

Allergic sensitization impairs lung resident memory CD8 T-cell response and virus clearance

Patients with asthma often suffer from frequent respiratory viral infections and reduced virus clearance. Lung resident memory T cells provide rapid protection against viral reinfections. Because the development of resident memory T cells relies on the lung microenvironment, we investigated the impact of allergen sensitization on the development of virus-specific lung resident memory T cells and viral clearance. Mice were sensitized with house dust mite extract followed by priming with X47 and a subsequent secondary influenza infection. Antiviral memory T-cell response and protection to viral infection was assessed before and after secondary influenza infection, respectively. Gene set variation analysis was performed on data sets from the U-BIOPRED asthma cohort using an IFN-γ-induced epithelial cell signature and a tissue resident memory T-cell signature. Viral loads were higher in lungs of sensitized compared with nonsensitized mice after secondary infection, indicating reduced virus clearance. X47 priming induced fewer antiviral lung resident memory CD8 T cells and resulted in lower pulmonary IFN-γ levels in the lungs of sensitized as compared with nonsensitized mice. Using data from the U-BIOPRED cohort, we found that patients with enrichment of epithelial IFN-γ-induced genes in nasal brushings and bronchial biopsies were also enriched in resident memory T-cell-associated genes, had more epithelial CD8 T cells, and reported significantly fewer exacerbations. The allergen-sensitized lung microenvironment interferes with the formation of antiviral resident memory CD8 T cells in lungs and virus clearance. Defective antiviral memory response might contribute to increased susceptibility of patients with asthma to viral exacerbations.

Specific CD4+ T Cell Responses to Ancestral SARS-CoV-2 in Children Increase With Age and Show Cross-Reactivity to Beta Variant.

SARS-CoV-2 is still a major burden for global health despite effective vaccines. With the reduction of social distancing measures, infection rates are increasing in children, while data on the pediatric immune response to SARS-CoV-2 infection is still lacking. Although the typical disease course in children has been mild, emerging variants may present new challenges in this age group. Peripheral blood mononuclear cells (PBMC) from 51 convalescent children, 24 seronegative siblings from early 2020, and 51 unexposed controls were stimulated with SARS-CoV-2-derived peptide MegaPools from the ancestral and beta variants. Flow cytometric determination of activation-induced markers and secreted cytokines were used to quantify the CD4+ T cell response. The average time after infection was over 80 days. CD4+ T cell responses were detected in 61% of convalescent children and were markedly reduced in preschool children. Cross-reactive T cells for the SARS-CoV-2 beta variant were identified in 45% of cases after infection with an ancestral SARS-CoV-2 variant. The CD4+ T cell response was accompanied most predominantly by IFN-γ and Granzyme B secretion. An antiviral CD4+ T cell response was present in children after ancestral SARS-CoV-2 infection, which was reduced in the youngest age group. We detected significant cross-reactivity of CD4+ T cell responses to the more recently evolved immune-escaping beta variant. Our findings have epidemiologic relevance for children regarding novel viral variants of concern and vaccination efforts.

Faster cytotoxicity with age: Increased perforin and granzyme levels in cytotoxic CD8+ T cells boost cancer cell elimination.

A variety of intrinsic and extrinsic factors contribute to the altered efficiency of CTLs in elderly organisms. In particular, the efficacy of antiviral CD8+ T cells responses in the elderly has come back into focus since the COVID‐19 pandemic outbreak. However, the exact molecular mechanisms leading to alterations in T cell function and the origin of the observed impairments have not been fully explored. Therefore, we investigated whether intrinsic changes affect the cytotoxic ability of CD8+ T cells in aging. We focused on the different subpopulations and time‐resolved quantification of cytotoxicity during tumor cell elimination. We report a surprising result: Killing kinetics of CD8+ T cells from elderly mice are much faster than those of CD8+ T cells from adult mice. This is true not only in the total CD8+ T cell population but also for their effector (TEM) and central memory (TCM) T cell subpopulations. TIRF experiments reveal that CD8+ T cells from elderly mice possess comparable numbers of fusion events per cell, but significantly increased numbers of cells with granule fusion. Analysis of the cytotoxic granule (CG) content shows significantly increased perforin and granzyme levels and turns CD8+ T cells of elderly mice into very efficient killers. This highlights the importance of distinguishing between cell‐intrinsic alterations and microenvironmental changes in elderly individuals. Our results also stress the importance of analyzing the dynamics of CTL cytotoxicity against cancer cells because, with a simple endpoint lysis analysis, cytotoxic differences could have easily been overlooked.

Functional Restoration of Exhausted CD8 T Cells in Chronic HIV-1 Infection by Targeting Mitochondrial Dysfunction.

CD8 T cell exhaustion is a hallmark of HIV-1 infection, characterized by phenotypic and functional CD8 T cell abnormalities that persist despite years of effective antiretroviral treatment (ART). More recently, the importance of cellular metabolism in shaping T cell antiviral function has emerged as a crucial aspect of immunotherapeutics aimed at re-invigorating exhausted CD8 T cells but remains under-investigated in HIV-1 infection. To gain a better insight into this process and identify new targets for effective CD8 T cell restoration we examined the metabolic profile of exhausted CD8 T cells in HIV-1 infection. We show that relative to HIV-1 elite controllers (EC) and HIV-1 seronegative donors, CD8 T cells from HIV-1 viraemic individuals are skewed toward a PD-1hiEOMEShiT-betlowTIGIT+ phenotype that is maintained during ART. This exhausted signature is enriched in HIV-specific CD8 T cells, compared to CMV-specific CD8 T cell populations, and further delineated by higher expression of the glucose transporter, Glut-1, impaired mitochondrial function and biogenesis, reflecting underlying metabolic defects. A notable improvement in antiviral HIV-specific CD8 T cell function was elicited via mitochondrial antioxidant treatment in combination with pharmacological modulation of mitochondrial dynamics and IL-15 treatment. These findings identify mitochondria as promising targets for combined reconstitution therapies in HIV-1 infection.

Natural Killer Cells Induce CD8+ T Cell Dysfunction via Galectin-9/TIM-3 in Chronic Hepatitis B Virus Infection.

The antiviral response of natural killer (NK) cells and CD8+ T cells is weak in patients with chronic hepatitis B (CHB) infection. However, the specific characteristics of these cells and the association between NK cells and CD8+ T cell dysfunction is not well known. In this study, higher galectin-9 (Gal-9) expression was observed in circulating NK cells from CHB patients than from healthy controls and was found to contribute to NK cell dysfunction. In addition, circulating CD8+ T cells showed obvious dysfunction and overexpressed TIM-3, the natural receptor of Gal-9, during active CHB infection. Gal-9+ and Gal-9- NK cells from active CHB patients were sorted and cocultured with autologous CD8+ T cells. The proportion of tetramer+CD8+ T cells and the cytokines production of CD8+ T cells were lower after cocultivation with Gal-9+ than with Gal-9- NK cells. We showed that in vitro depletion of NK cells increased circulating hepatitis B virus (HBV)-specific CD8+ T cell responses in patients with active CHB infection. Because Gal-9 is increased in the serum of CHB patients, CD8+ T cells were sorted and cultured with exogenous Gal-9, resulting in lower IFN-γ, TNF-α, CD107a, and granzyme B levels, decreased expression of the activation receptor CD69, increased expression of TIM-3, and a high percentage of early apoptotic CD8+ T cells. Blocking Gal-9 or TIM-3 in vitro in a culture of peripheral blood mononuclear cells (PBMCs) stimulated with HBV peptide from active CHB patients restored CD8+ T cell function. However, blocking Gal-9 in vitro after removal of NK cells from PBMCs did not rescue CD8+ T cells exhaustion. Furthermore, NK and CD8+ T cells from active CHB patients were sorted and cocultured in vitro, and the exhaustion of CD8+ T cells were alleviated after blocking Gal-9 or TIM-3. In summary, overexpression of Gal-9 on NK cells, which interacts with TIM-3+CD8+ T cells and likely contributes to antiviral CD8+ T cell dysfunction, may be a potential target for the treatment of CHB patients.

A Novel Prognostic Score Based on Artificial Intelligence in Hepatocellular Carcinoma: A Long-Term Follow-Up Analysis.

ObjectiveT cell immunity plays an important role in anti-tumor effects and immunosuppression often leads to the development and relapse of cancer. This study aimed to investigate the effect of T cell numbers on the long-term prognosis of patients with hepatocellular carcinoma (HCC) and construct an artificial neural network (ANN) model to evaluate its prognostic value.MethodsWe enrolled 3,427 patients with HCC at Beijing Ditan Hospital, Capital Medical University, and randomly divided them into two groups of 1,861 and 809 patients as the training and validation sets, respectively. Cox regression analysis was used to screen for independent risk factors of survival in patients with HCC. These factors were used to build an ANN model using Python. Concordance index, calibration curve, and decision curve analysis were used to evaluate the model performance.ResultsThe 1-year, 3-year, 5-year, and 10-year cumulative overall survival (OS) rates were 66.9%, 45.7%, 34.9%, and 22.6%, respectively. Cox multivariate regression analysis showed that age, white blood cell count, creatinine, total bilirubin, γ-GGT, LDH, tumor size ≥ 5 cm, tumor number ≥ 2, portal vein tumor thrombus, and AFP ≥ 400 ng/ml were independent risk factors for long-term survival in HCC. Antiviral therapy, albumin, T cell, and CD8 T cell counts were independent protective factors. An ANN model was developed for long-term survival. The areas under the receiver operating characteristic (ROC) curve of 1-year, 3-year, and 5-year OS rates by ANNs were 0.838, 0.833, and 0.843, respectively, which were higher than those of the Barcelona Clinic Liver Cancer (BCLC), tumor node metastasis (TNM), Okuda, Chinese University Prognostic Index (CUPI), Cancer of the Liver Italian Program (CLIP), Japan Integrated Staging (JIS), and albumin–bilirubin (ALBI) models (P < 0.0001). According to the ANN model scores, all patients were divided into high-, middle-, and low-risk groups. Compared with low-risk patients, the hazard ratios of 5-year OS of the high-risk group were 8.11 (95% CI: 7.0-9.4) and 6.13 (95% CI: 4.28-8.79) (P<0.0001) in the training and validation sets, respectively.ConclusionHigh levels of circulating T cells and CD8 + T cells in peripheral blood may benefit the long-term survival of patients with HCC. The ANN model has a good individual prediction performance, which can be used to assess the prognosis of HCC and lay the foundation for the implementation of precision treatment in the future.

Single-cell RNA sequencing reveals immunological rewiring at the maternal-fetal interface following asymptomatic/mild SARS-CoV-2 infection.

While severe coronavirus 2019 (COVID-19) is associated with immune activation at the maternal-fetal interface, responses to asymptomatic/mild severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during pregnancy remain unknown. Here, we assess immunological adaptations in blood and term decidua in response to asymptomatic/mild disease in pregnant women. We report attenuated antigen presentation and type I interferon (IFN) signaling pathways, loss of tissue-resident decidual macrophages, and upregulated cytokine/chemokine signaling in monocyte-derived decidual macrophages. Furthermore, we describe increased frequencies of activated tissue-resident T cells and decreased abundance of regulatory T cells with infection while frequencies of cytotoxic CD4/CD8 T cells are increased in the blood. In contrast to decidual macrophages, type I IFN signaling is higher in decidual T cells. Finally, infection leads to a narrowing of T cell receptor diversity in both blood and decidua. Collectively, these observations indicate that asymptomatic/mild COVID-19 during pregnancy results in remodeling of the immunological landscape of the maternal-fetal interface, with a potential for long-term adverse outcomes for the offspring.

Helpless CD8 T cell memory explained: prolonged antigen presentation drives a temporal rather than terminal defect

Abstract CD4 T cell help is critical for long-term antiviral CD8 T cell immunity. Despite seemingly normal effector properties, “helpless” CD8 memory T cells (TM) generated in the absence of CD4 T cells during initial priming exhibit a substantially blunted recall response. Yet, how lack of CD4 help specifically impairs CD8 TM formation in the context of acute viral infections remains elusive. Here, we demonstrate that in transiently and constitutively CD4 T cell-deficient mice “helpless” antiviral CD8 TM to acute lymphocytic choriomeningitis virus (LCMV) exhibit a wide array of homeostatic, phenotypic, and functional defects that are broadly consistent with delayed CD8 TM maturation. Mechanistically, “helpless” CD8 T cell memory is not grounded in altered CD8 effector T (TE) cell differentiation in the absence of CD4 T cells but in exposure of post-effector CD8 T cells to protracted viral antigen presentation. Conversely, efficient generation of “helped” CD8 T cell memory is contingent on CD40L-mediated activities by LCMV-specific CD4 T cells that promote timely clearance of viral antigen. Importantly, we show that “helpless” memory-precursor CD8 TE display comparable memory potential to their “helped” counterparts, and that, once viral antigen is cleared, complete resolution of “helpless” CD8 memory is achieved over a period of ~1.5 years during which “helpless” CD8 TM eventually acquire mature TM properties including fully restored recall capacities. Collectively, our data redefine “helpless” CD8 T cell memory as a temporal rather than terminal defect, with implications for our general conceptualization of CD8 T cell memory as well as for the development of preventive and therapeutic strategies to improve protective CD8 TM function. Supported by grant NIH R01AI093637.

Differential localization and kinetics of antiviral CD8 T cell responses to chronic and acute murine norovirus infections from initiation onwards

Abstract Recent global events have highlighted the need to better understand mucosal antiviral immunity. Murine Norovirus (MNV) is small non-enveloped positive sense RNA virus that can be used as a model of intestinal viral infection. In this work we use two highly related MNV strains with distinct biological behaviors; CR6 establishes chronic colonic infection, while CW3 establishes systemic infection initiated in the small intestine and is cleared by day 8, correlating with the peak of cell-mediated adaptive immunity. Using flow cytometry and quantitative immunofluorescent microscopy (QIM) of transgenic P14 CD8 T cells specific to recombinant CR6gp33 and CW3gp33, we characterized CD8 T cell responses to CR6 and CW3 from initiation to clearance of CW3. Our data indicate that initiation of CD8 T cell division in response to CR6 infection is delayed, less robust, and largely limited to the mesenteric lymph nodes (MLNs) with less splenic division compared to CW3 infection. Further, the biogeography of P14 T cell priming differs, as early T cell expansion was restricted to distinct nodes of the MLN complex. These early differences propagate out to the time of CW3 clearance. By day 8, there is differential localization of P14 cells in the GI tract to the site of highest viral load and a larger systemic population of P14 cells following CW3 infection. Infection of MLN-deficient mice revealed a critical role for MLN surveillance in targeting P14 T cells to the GI tract following CR6 infection while the spleen plays a compensatory role in response to CW3. These results show how distinct infectious locations of a continuous mucosal surface influence the responses of antiviral CD8 T cells without confounding effects of antigenicity. This work is supported by the Canadian Institutes for Health Research (CIHR) and a UBC 4 Year Fellowship awarded to Blair K Hardman

DEC-205-expressing dendritic cells inhibit T cell responses during West Nile Virus encephalitis in the central nervous system

Abstract West Nile Virus (WNV), a neurotropic flavivirus, is the leading cause of mosquito-borne neuroinvasive disease in the U.S. Recent studies show that dysfunctional T cell responses correlate with severe disease in both humans and mice. Dendritic cells (DCs) are critical for reactivating antiviral CD8+ T cell responses in the CNS that are required to mitigate viral encephalitis. Previous reports have shown that CNS-localized DEC-205+ DCs accumulate within the CNS during WNV encephalitis; however, their specific role in programming T cell immunity remains poorly understood. DEC-205, an endocytic receptor expressed by DC subsets can promote either antigen-specific effector T cell activation or immunological T cell tolerance. Using a mouse model of WNV encephalitis, we demonstrate that DEC-205−/− mice exhibit enhanced clinical signs of disease and increased mortality compared to WT controls. The enhanced susceptibility in DEC-205−/− mice arose from an increased viral burden with the CNS; however, this was associated with increased inflammatory myeloid, CD4+, and CD8+ T cell infiltrates. In addition, expression of activation markers CD25 and CD44 increased while CD69 levels decreased within the DEC-205−/− mice compared with their WT counterparts. CD69 expression has been shown to be associated with regulatory T cells. To confirm the immunomodulatory role of DEC-205, we will measure CD4+ regulatory T cell frequencies within the CNS of DEC-205−/− and WT animals following WNV infection. Taken together, these data suggest that DEC-205 critically regulates WNV pathogenesis and neuroinvasive disease by limiting immune-mediated pathology in the CNS following WNV infection. Supported by grants from NIH (SC3GM130472).

CMV drives phenotypic changes in CD4 T cells prior to but not during the first year after solid organ transplantation

Abstract Cytomegalovirus (CMV) infection is a major complication after solid organ transplantation. The virus establishes latency after immune clearance of the primary infection. Immunosuppression impairs immune control in transplant recipients. We have previously shown that CMV drives accelerated immune aging of CD8 T cells in the first year after transplant. CMV-specific CD4 T cells also contribute to resolution of post-transplant viremia and reduce severity of disease at least in part by promoting maintenance of anti-viral CD8 T cell populations. Thus, we investigated the impact of CMV on CD4 T cell differentiation in the first year after transplant. Compared to CMV seronegative (CMV−) recipients, CMV+ recipients had an elevated frequency of aged (CD57+) CD4 T cells, with trends towards elevated PD-1+ and skewing toward memory rather than naïve phenotype. Unlike CMV-specific CD8 T cells, these phenotypes were stable over the first year after transplant, indicating these differences demonstrate a pre-established differentiation state. To correlate these findings to T cell receptor repertoire at a single cell level, we conducted single cell sequencing of TCR coupled to gene expression in CMV-responsive CD4 T cells from 6 transplant recipients from pre- to one-year post-transplant. Cell phenotypes were stable over time, and clonally expanded cells predominantly had an aged cytotoxic phenotype. Thus, CMV-responsive CD4 T cells in transplant recipients display evidence of immune aging and cytotoxicity. This is consistent with similar phenotypes in CD8 T cells, but striking in stability. Further study of this population will be important to determine whether this pre-existing phenotype is protective or pathogenic after transplant. This work was supported by funding from the NIH to LEH (NIDDK 5K01DK123196) and AAA (Stanford PreRenal Initiative, NIDDK KUH 1R25DK122957) and the Department of Veterans Affairs to JSM (CSR&amp;D 1I01CX001971).

IFN-γ promotes TH1 at the expense of TFH differentiation during viral infections

Abstract Although humoral and cellular immunity upon viral infections usually co-exist, sometimes one of the two responses emerges and is responsible for most of the antiviral activity. For example, vescicular stomatitis virus (VSV) infection induces early and potent neutralizing antibody (nAb) responses, whereas lymphocytic choriomeningitis virus (LCMV) infection induces strong cellular responses, but weak nAb responses. Recent work from our laboratory has shown that unbalance is observed also at the level of CD4 T cells responses, with VSV inducing strong TFH polarization that support nAb responses, and LCMV in contrast promoting TH1 differentiation. Analysis of the VSV and LCMV priming niches led to identification of the spatiotemporal regulation of type I IFN expression as a critical regulator of antiviral CD4+ T cell polarization, with early type I IFN sensing leading to TFH polarization. Notably, this mechanism did not explain the strong TH1 differentiation observed during LCMV infection. In this study we aimed to elucidate the role of known TH1-polarizing cytokines in CD4+ T cell differentiation upon LCMV infection. We found that IFN-γ, but not IL-12, plays a key role in early CD4+ T cell differentiation upon LCMV infection, inducing TH1 cell polarization and suppressing TFH cell development, thus resulting in a shift in the equilibrium towards TFH and humoral responses. Future studies will determine the cellular source for this TH1-polarizing cytokine and the mechanism by which IFN-γ exerts its function, possibly unveiling the mechanisms underlying the reduced humoral response in the context of viral infections like LCMV.

Combinatorial Herpes Simplex Vaccine Strategies: From Bedside to Bench and Back.

The development of vaccines against herpes simplex virus type 1 and type 2 (HSV1 and HSV-2) is an important goal for global health. In this review we reexamined (i) the status of ocular herpes vaccines in clinical trials; and (ii) discusses the recent scientific advances in the understanding of differential immune response between HSV infected asymptomatic and symptomatic individuals that form the basis for the new combinatorial vaccine strategies targeting HSV; and (iii) shed light on our novel “asymptomatic” herpes approach based on protective immune mechanisms in seropositive asymptomatic individuals who are “naturally” protected from recurrent herpetic diseases. We previously reported that phenotypically and functionally distinct HSV-specific memory CD8+ T cell subsets in asymptomatic and symptomatic HSV-infected individuals. Moreover, a better protection induced following a prime/pull vaccine approach that consists of first priming anti-viral effector memory T cells systemically and then pulling them to the sites of virus reactivation (e.g., sensory ganglia) and replication (e.g., eyes and vaginal mucosa), following mucosal administration of vectors expressing T cell-attracting chemokines. In addition, we reported that a combination of prime/pull vaccine approach with approaches to reverse T cell exhaustion led to even better protection against herpes infection and disease. Blocking PD-1, LAG-3, TIGIT and/or TIM-3 immune checkpoint pathways helped in restoring the function of antiviral HSV-specific CD8+ T cells in latently infected ganglia and increased efficacy and longevity of the prime/pull herpes vaccine. We discussed that a prime/pull vaccine strategy that use of asymptomatic epitopes, combined with immune checkpoint blockade would prove to be a successful herpes vaccine approach.

Memory CD4+ T-Cell Lymphocytic Angiopathy in Fatal Forms of COVID-19 Pulmonary Infection.

The immunopathological pulmonary mechanisms leading to Coronavirus Disease (COVID-19)-related death in adults remain poorly understood. Bronchoalveolar lavage (BAL) and peripheral blood sampling were performed in 74 steroid and non-steroid-treated intensive care unit (ICU) patients (23–75 years; 44 survivors). Peripheral effector SARS-CoV-2-specific T cells were detected in 34/58 cases, mainly directed against the S1 portion of the spike protein. The BAL lymphocytosis consisted of T cells, while the mean CD4/CD8 ratio was 1.80 in non-steroid- treated patients and 1.14 in steroid-treated patients. Moreover, strong BAL SARS-CoV-2 specific T-cell responses were detected in 4/4 surviving and 3/3 non-surviving patients. Serum IFN-γ and IL-6 levels were decreased in steroid-treated patients when compared to non-steroid treated patients. In the lung samples from 3 (1 non-ICU and 2 ICU) additional deceased cases, a lymphocytic memory CD4 T-cell angiopathy colocalizing with SARS-CoV-2 was also observed. Taken together, these data show that disease severity occurs despite strong antiviral CD4 T cell-specific responses migrating to the lung, which could suggest a pathogenic role for perivascular memory CD4 T cells upon fatal COVID-19 pneumonia.

Mast Cells Meet Cytomegalovirus: A New Example of Protective Mast Cell Involvement in an Infectious Disease.

Cytomegaloviruses (CMVs) belong to the β-subfamily of herpesviruses. Their host-to-host transmission involves the airways. As primary infection of an immunocompetent host causes only mild feverish symptoms, human CMV (hCMV) is usually not considered in routine differential diagnostics of common airway infections. Medical relevance results from unrestricted tissue infection in an immunocompromised host. One risk group of concern are patients who receive hematopoietic cell transplantation (HCT) for immune reconstitution following hematoablative therapy of hematopoietic malignancies. In HCT patients, interstitial pneumonia is a frequent cause of death from hCMV strains that have developed resistance against antiviral drugs. Prevention of CMV pneumonia requires efficient reconstitution of antiviral CD8 T cells that infiltrate lung tissue. A role for mast cells (MC) in the immune control of lung infection by a CMV was discovered only recently in a mouse model. MC were shown to be susceptible for productive infection and to secrete the chemokine CCL-5, which recruits antiviral CD8 T cells to the lungs and thereby improves the immune control of pulmonary infection. Here, we review recent data on the mechanism of MC-CMV interaction, a field of science that is new for CMV virologists as well as for immunologists who have specialized in MC.

Infection-induced lymphatic zippering restricts fluid transport and viral dissemination from skin.

Lymphatic vessels are often considered passive conduits that flush antigenic material, pathogens, and cells to draining lymph nodes. Recent evidence, however, suggests that lymphatic vessels actively regulate diverse processes from antigen transport to leukocyte trafficking and dietary lipid absorption. Here we tested the hypothesis that infection-induced changes in lymphatic transport actively contribute to innate host defense. We demonstrate that cutaneous vaccinia virus infection by scarification activates dermal lymphatic capillary junction tightening (zippering) and lymph node lymphangiogenesis, which are associated with reduced fluid transport and cutaneous viral sequestration. Lymphatic-specific deletion of VEGFR2 prevented infection-induced lymphatic capillary zippering, increased fluid flux out of tissue, and allowed lymphatic dissemination of virus. Further, a reduction in dendritic cell migration to lymph nodes in the absence of lymphatic VEGFR2 associated with reduced antiviral CD8+ T cell expansion. These data indicate that VEGFR2-driven lymphatic remodeling is a context-dependent, active mechanism of innate host defense that limits viral dissemination and facilitates protective, antiviral CD8+ T cell responses.