The phenotypic changes of γδ T cells in COVID-19 patients

In Silico analysis unveils rs2109069 of DPP9 as a potential catalyst for COVID-19 severity and risk of inflammatory symptoms

BACKGROUND

During the COVID-19 pandemic, the viral illness caused by SARS-CoV-2 spread through respiratory droplets, resulting in a global pandemic with a range of symptoms from mild to severe. Pathological inflammation posed a critical issue, yet the genetic mechanisms behind the excessive activation of inflammatory responses remained unclear. To uncover the genetic and regulatory basis of the pathogenesis, we first explored possible genetic mechanisms from phenome-wide association studies (PWAS) with different severity levels of COVID-19. PWAS is a genetic research approach that identifies pleiotropic risk variants that contribute to elucidating potential physiological mechanisms from different traits.

METHODS

We used the PWAS approach to link the multiple clinical symptoms to the variants. We discovered a common variant, rs2109069, in dipeptidyl peptidase 9 (DPP9), which relates to the elevated odds ratio of developing severe illness from COVID-19. Interestingly, the proxy of rs2109069 has been identified as the susceptible locus of interstitial lung disease (ILD) and idiopathic pulmonary fibrosis (IPF). We thus examined the DPP9 expression patterns in selected organs, including the lungs, blood vessels, and skin.

RESULTS

In silico analysis revealed conserved driver activation between COVID-19-induced inflammation and the association with ILD and IPF. Multi-omics analysis further verified the association of DPP9 with abnormal inflammatory responses in COVID-19. Lastly, gene homology analysis inferred a potential regulatory role of DPP9 in inhibiting inflammasome activation, which suggests that DPP9 deficiency may exacerbate inflammation observed in some COVID-19 patients.

CONCLUSIONS

Our in silico findings reveal that severe COVID-19 inflammatory responses and inflammatory lung diseases share the same genetic risk loci, helping to elucidate the underlying physiological mechanisms of severe COVID-19 inflammation. Additionally, the individual differences in immune sensitivity may contribute to the varying multi-organ inflammatory effects among patients. The rs2109069 of DPP9 could be a genetic marker to predict the risk of specific COVID-19 symptoms and severity.

γδ T-cells in human malignancies: insights from single-cell studies and analytical considerations

γδ T-cells are a rare population of T-cells with both adaptive and innate-like properties. Despite their low prevalence, they have been found to be implicated various human diseases. γδ T-cell infiltration has been associated with improved clinical outcomes in solid cancers, prompting renewed interest in understanding their biology. To date, their biology remains elusive due to their low prevalence. The introduction of high-resolution single-cell sequencing has allowed various groups to characterize key effector subsets in various contexts, as well as begin to elucidate key regulatory mechanisms directing the differentiation and activity of these cells. In this review, we will review some of insights obtained from single-cell studies of γδ T-cells across various malignancies and highlight some important questions that remain unaddressed.

Expansion of memory Vδ2 T cells following SARS-CoV-2 vaccination revealed by temporal single-cell transcriptomics

γδ T cells provide rapid cellular immunity against pathogens. Here, we conducted matched single-cell RNA-sequencing and γδ-TCR-sequencing to delineate the molecular changes in γδ T cells during a longitudinal study following mRNA SARS-CoV-2 vaccination. While the first dose of vaccine primes Vδ2 T cells, it is the second administration that significantly boosts their immune response. Specifically, the second vaccination uncovers memory features of Vδ2 T cells, shaped by the induction of AP-1 family transcription factors and characterized by a convergent central memory signature, clonal expansion, and an enhanced effector potential. This temporally distinct effector response of Vδ2 T cells was also confirmed in vitro upon stimulation with SARS-CoV-2 spike-peptides. Indeed, the second challenge triggers a significantly higher production of IFNγ by Vδ2 T cells. Collectively, our findings suggest that mRNA SARS-CoV-2 vaccination might benefit from the establishment of long-lasting central memory Vδ2 T cells to confer protection against SARS-CoV-2 infection.

NFκB and NLRP3/NLRC4 inflammasomes regulate differentiation, activation and functional properties of monocytes in response to distinct SARS-CoV-2 proteins

Increased recruitment of transitional and non-classical monocytes in the lung during SARS-CoV-2 infection is associated with COVID-19 severity. However, whether specific innate sensors mediate the activation or differentiation of monocytes in response to different SARS-CoV-2 proteins remain poorly characterized. Here, we show that SARS-CoV-2 Spike 1 but not nucleoprotein induce differentiation of monocytes into transitional or non-classical subsets from both peripheral blood and COVID-19 bronchoalveolar lavage samples in a NFκB-dependent manner, but this process does not require inflammasome activation. However, NLRP3 and NLRC4 differentially regulated CD86 expression in monocytes in response to Spike 1 and Nucleoprotein, respectively. Moreover, monocytes exposed to Spike 1 induce significantly higher proportions of Th1 and Th17 CD4 + T cells. In contrast, monocytes exposed to Nucleoprotein reduce the degranulation of CD8 + T cells from severe COVID-19 patients. Our study provides insights in the differential impact of innate sensors in regulating monocytes in response to different SARS-CoV-2 proteins, which might be useful to better understand COVID-19 immunopathology and identify therapeutic targets.

Adaptive immune cells are necessary for SARS-CoV-2-induced pathology

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is causing the ongoing global pandemic associated with morbidity and mortality in humans. Although disease severity correlates with immune dysregulation, the cellular mechanisms of inflammation and pathogenesis of COVID-19 remain relatively poorly understood. Here, we used mouse-adapted SARS-CoV-2 strain MA10 to investigate the role of adaptive immune cells in disease. We found that while infected wild-type mice lost ~10% weight by 3 to 4 days postinfection, rag-/- mice lacking B and T lymphocytes did not lose weight. Infected lungs at peak weight loss revealed lower pathology scores, fewer neutrophils, and lower interleukin-6 and tumor necrosis factor-α in rag-/- mice. Mice lacking αβ T cells also had less severe weight loss, but adoptive transfer of T and B cells into rag-/- mice did not significantly change the response. Collectively, these findings suggest that while adaptive immune cells are important for clearing SARS-CoV-2 infection, this comes at the expense of increased inflammation and pathology.

Post COVID-19 complications and follow up biomarkers

Millions of people were infected by the coronavirus disease (COVID-19) epidemic, which left a huge burden on the care of post COVID-19 survivors around the globe. The self-reported COVID-19 symptoms were experienced by an estimated 1.3 million people in the United Kingdom (2% of the population), and these symptoms persisted for about 4 weeks from the beginning of the infection. The symptoms most frequently reported were exhaustion, shortness of breath, muscular discomfort, joint pain, headache, cough, chest pain, cognitive impairment, memory loss, anxiety, sleep difficulties, diarrhea, and a decreased sense of smell and taste in post-COVID-19 affected people. The post COVID-19 complications were frequently related to the respiratory, cardiac, nervous, psychological and musculoskeletal systems. The lungs, liver, kidneys, heart, brain and other organs had been impaired by hypoxia and inflammation in post COVID-19 individuals. The upregulation of substance "P" (SP) and various cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), interleukin 10 (IL-10), interleukin 1 beta (IL-1β), angiotensin-converting enzyme 2 (ACE2) and chemokine C-C motif ligand 3 (CCL3) has muddled respiratory, cardiac, neuropsychiatric, dermatological, endocrine, musculoskeletal, gastrointestinal, renal and genitourinary complications in post COVID-19 people. To prevent these complications from worsening, it was therefore important to study how these biomarkers were upregulated and block their receptors.

Bridging the Gap: Can COVID-19 Research Help Combat African Swine Fever?

African swine fever (ASF) is a highly contagious and economically devastating disease affecting domestic pigs and wild boar, caused by African swine fever virus (ASFV). Despite being harmless to humans, ASF poses significant challenges to the swine industry, due to sudden losses and trade restrictions. The ongoing COVID-19 pandemic has spurred an unparalleled global research effort, yielding remarkable advancements across scientific disciplines. In this review, we explore the potential technological spillover from COVID-19 research into ASF. Specifically, we assess the applicability of the diagnostic tools, vaccine development strategies, and biosecurity measures developed for COVID-19 for combating ASF. Additionally, we discuss the lessons learned from the pandemic in terms of surveillance systems and their implications for managing ASF. By bridging the gap between COVID-19 and ASF research, we highlight the potential for interdisciplinary collaboration and technological spillovers in the battle against ASF.

Ketogenic Diet and Ketone Bodies as Clinical Support for the Treatment of SARS-CoV-2-Review of the Evidence

One of the proposed nutritional therapies to support drug therapy in COVID-19 is the use of a ketogenic diet (KD) or ketone bodies. In this review, we summarized the evidence from tissue, animal, and human models and looked at the mechanisms of action of KD/ketone bodies against COVID-19. KD/ketone bodies were shown to be effective at the stage of virus entry into the host cell. The use of β-hydroxybutyrate (BHB), by preventing the metabolic reprogramming associated with COVID-19 infection and improving mitochondrial function, reduced glycolysis in CD4+ lymphocytes and improved respiratory chain function, and could provide an alternative carbon source for oxidative phosphorylation (OXPHOS). Through multiple mechanisms, the use of KD/ketone bodies supported the host immune response. In animal models, KD resulted in protection against weight loss and hypoxemia, faster recovery, reduced lung injury, and resulted in better survival of young mice. In humans, KD increased survival, reduced the need for hospitalization for COVID-19, and showed a protective role against metabolic abnormalities after COVID-19. It appears that the use of KD and ketone bodies may be considered as a clinical nutritional intervention to assist in the treatment of COVID-19, despite the fact that numerous studies indicate that SARS-CoV-2 infection alone may induce ketoacidosis. However, the use of such an intervention requires strong scientific validation.

Immune Dynamics Involved in Acute and Convalescent COVID-19 Patients

COVID-19 is a viral disease that has caused millions of deaths around the world since 2020. Many strategies have been developed to manage patients in critical conditions; however, comprehension of the immune system is a key factor in viral clearance, tissue repairment, and adaptive immunity stimulus. Participation of immunity has been identified as a major factor, along with biomarkers, prediction of clinical outcomes, and antibody production after infection. Immune cells have been proposed not only as a hallmark of severity, but also as a predictor of clinical outcomes, while dynamics of inflammatory molecules can also induce worse consequences for acute patients. For convalescent patients, mild disease was related to higher antibody production, although the factors related to the specific antibodies based on a diversity of antigens were not clear. COVID-19 was explored over time; however, the study of immunological predictors of outcomes is still lacking discussion, especially in convalescent patients. Here, we propose a review using previously published studies to identify immunological markers of COVID-19 outcomes and their relation to antibody production to further contribute to the clinical and laboratorial management of patients.

Immune responses in mildly versus critically ill COVID-19 patients

The current coronavirus pandemic (COVID-19), caused by SARS-CoV-2, has had devastating effects on the global health and economic system. The cellular and molecular mediators of both the innate and adaptive immune systems are critical in controlling SARS-CoV-2 infections. However, dysregulated inflammatory responses and imbalanced adaptive immunity may contribute to tissue destruction and pathogenesis of the disease. Important mechanisms in severe forms of COVID-19 include overproduction of inflammatory cytokines, impairment of type I IFN response, overactivation of neutrophils and macrophages, decreased frequencies of DC cells, NK cells and ILCs, complement activation, lymphopenia, Th1 and Treg hypoactivation, Th2 and Th17 hyperactivation, as well as decreased clonal diversity and dysregulated B lymphocyte function. Given the relationship between disease severity and an imbalanced immune system, scientists have been led to manipulate the immune system as a therapeutic approach. For example, anti-cytokine, cell, and IVIG therapies have received attention in the treatment of severe COVID-19. In this review, the role of immunity in the development and progression of COVID-19 is discussed, focusing on molecular and cellular aspects of the immune system in mild vs. severe forms of the disease. Moreover, some immune- based therapeutic approaches to COVID-19 are being investigated. Understanding key processes involved in the disease progression is critical in developing therapeutic agents and optimizing related strategies.

Circulating effector γδ T cell populations are associated with acute coronavirus disease 19 in unvaccinated individuals

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causes severe coronavirus disease 2019 (COVID-19) in a small proportion of infected individuals. The immune system plays an important role in the defense against SARS-CoV-2, but our understanding of the cellular immune parameters that contribute to severe COVID-19 disease is incomplete. Here, we show that populations of effector γδ T cells are associated with COVID-19 in unvaccinated patients with acute disease. We found that circulating CD27^neg CD45RA⁺ CX3CR1⁺ Vδ1_effector cells expressing Granzymes (Gzms) were enriched in COVID-19 patients with acute disease. Moreover, higher frequencies of GzmB⁺ Vδ2⁺ T cells were observed in acute COVID-19 patients. SARS-CoV-2 infection did not alter the γδ T cell receptor repertoire of either Vδ1⁺ or Vδ2⁺ subsets. Our work demonstrates an association between effector populations of γδ T cells and acute COVID-19 in unvaccinated individuals.

The dynamics of γδ T cell responses in nonhuman primates during SARS-CoV-2 infection

Although most SARS-CoV-2 infections are mild, some patients develop systemic inflammation and progress to acute respiratory distress syndrome (ARDS). However, the cellular mechanisms underlying this spectrum of disease remain unclear. γδT cells are T lymphocyte subsets that have key roles in systemic and mucosal immune responses during infection and inflammation. Here we show that peripheral γδT cells are rapidly activated following aerosol or intra-tracheal/intra-nasal (IT/IN) SARS-CoV-2 infection in nonhuman primates. Our results demonstrate a rapid expansion of Vδ1 γδT cells at day1 that correlate significantly with lung viral loads during the first week of infection. Furthermore, increase in levels of CCR6 and Granzyme B expression in Vδ1 T cells during viral clearance imply a role in innate-like epithelial barrier-protective and cytotoxic functions. Importantly, the early activation and mobilization of circulating HLA-DR+CXCR3+ γδT cells along with significant correlations of Vδ1 T cells with IL-1Ra and SCF levels in bronchoalveolar lavage suggest a novel role for Vδ1 T cells in regulating lung inflammation during aerosol SARS-CoV-2 infection. A deeper understanding of the immunoregulatory functions of MHC-unrestricted Vδ1 T cells in lungs during early SARS-CoV-2 infection is particularly important in the wake of emerging new variants with increased transmissibility and immune evasion potential.

Phenotypical and Functional Alteration of γδ T Lymphocytes in COVID-19 Patients: Reversal by Statins

(1) Background: statins have been considered an attractive class of drugs in the pharmacological setting of COVID-19 due to their pleiotropic properties and their use correlates with decreased mortality in hospitalized COVID-19 patients. Furthermore, it is well known that statins, which block the mevalonate pathway, affect γδ T lymphocyte activation. As γδ T cells participate in the inflammatory process of COVID-19, we have investigated the therapeutical potential of statins as a tool to inhibit γδ T cell pro-inflammatory activities; (2) Methods: we harvested peripheral blood mononuclear cells (PBMCs) from COVID-19 patients with mild clinical manifestations, COVID-19 recovered patients, and healthy controls. We performed ex vivo flow cytometry analysis to study γδ T cell frequency, phenotype, and exhaustion status. PBMCs were treated with Atorvastatin followed by non-specific and specific stimulation, to evaluate the expression of pro-inflammatory cytokines; (3) Results: COVID-19 patients had a lower frequency of circulating Vδ2+ T lymphocytes but showed a pronounced pro-inflammatory profile, which was inhibited by in vitro treatment with statins; (4) Conclusions: the in vitro capacity of statins to inhibit Vδ2+ T lymphocytes in COVID-19 patients highlights a new potential biological function of these drugs and supports their therapeutical use in these patients.

Multi-omics personalized network analyses highlight progressive disruption of central metabolism associated with COVID-19 severity

The clinical outcome and disease severity in coronavirus disease 2019 (COVID-19) are heterogeneous, and the progression or fatality of the disease cannot be explained by a single factor like age or comorbidities. In this study, we used system-wide network-based system biology analysis using whole blood RNA sequencing, immunophenotyping by flow cytometry, plasma metabolomics, and single-cell-type metabolomics of monocytes to identify the potential determinants of COVID-19 severity at personalized and group levels. Digital cell quantification and immunophenotyping of the mononuclear phagocytes indicated a substantial role in coordinating the immune cells that mediate COVID-19 severity. Stratum-specific and personalized genome-scale metabolic modeling indicated monocarboxylate transporter family genes (e.g., SLC16A6), nucleoside transporter genes (e.g., SLC29A1), and metabolites such as α-ketoglutarate, succinate, malate, and butyrate could play a crucial role in COVID-19 severity. Metabolic perturbations targeting the central metabolic pathway (TCA cycle) can be an alternate treatment strategy in severe COVID-19.

Defying convention in the time of COVID-19: Insights into the role of γδ T cells

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 is a complex disease which immune response can be more or less potent. In severe cases, patients might experience a cytokine storm that compromises their vital functions and impedes clearance of the infection. Gamma delta (γδ) T lymphocytes have a critical role initiating innate immunity and shaping adaptive immune responses, and they are recognized for their contribution to tumor surveillance, fighting infectious diseases, and autoimmunity. γδ T cells exist as both circulating T lymphocytes and as resident cells in different mucosal tissues, including the lungs and their critical role in other respiratory viral infections has been demonstrated. In the context of SARS-CoV-2 infection, γδ T cell responses are understudied. This review summarizes the findings on the antiviral role of γδ T cells in COVID-19, providing insight into how they may contribute to the control of infection in the mild/moderate clinical outcome.

Where do T cell subsets stand in SARS-CoV-2 infection: an update

An outbreak of coronavirus disease 2019 (COVID-19) emerged in China in December 2019 and spread so rapidly all around the globe. It's continued and spreading more dangerously in India and Brazil with higher mortality rate. Understanding of the pathophysiology of COVID-19 depends on unraveling of interactional mechanism of SARS-CoV-2 and human immune response. The immune response is a complex process, which can be better understood by understanding the immunological response and pathological mechanisms of COVID-19, which will provide new treatments, increase treatment efficacy, and decrease mortality associated with the disease. In this review we present a amalgamate viewpoint based on the current available knowledge on COVID-19 which includes entry of the virus and multiplication of virus, its pathological effects on the cellular level, immunological reaction, systemic and organ presentation. T cells play a crucial role in controlling and clearing viral infections. Several studies have now shown that the severity of the COVID-19 disease is inversely correlated with the magnitude of the T cell response. Understanding SARS-CoV-2 T cell responses is of high interest because T cells are attractive vaccine targets and could help reduce COVID-19 severity. Even though there is a significant amount of literature regarding SARS-CoV-2, there are still very few studies focused on understanding the T cell response to this novel virus. Nevertheless, a majority of these studies focused on peripheral blood CD4+ and CD8+ T cells that were specific for viruses. The focus of this review is on different subtypes of T cell responses in COVID-19 patients, Th17, follicular helper T (TFH), regulatory T (Treg) cells, and less classical, invariant T cell populations, such as δγ T cells and mucosal-associated invariant T (MAIT) cells etc that could influence disease outcome.

SARS-CoV-2 Infection: Host Response, Immunity, and Therapeutic Targets

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has resulted in a global pandemic with severe socioeconomic effects. Immunopathogenesis of COVID-19 leads to acute respiratory distress syndrome (ARDS) and organ failure. Binding of SARS-CoV-2 spike protein to human angiotensin-converting enzyme 2 (hACE2) on bronchiolar and alveolar epithelial cells triggers host inflammatory pathways that lead to pathophysiological changes. Proinflammatory cytokines and type I interferon (IFN) signaling in alveolar epithelial cells counter barrier disruption, modulate host innate immune response to induce chemotaxis, and initiate the resolution of inflammation. Here, we discuss experimental models to study SARS-CoV-2 infection, molecular pathways involved in SARS-CoV-2-induced inflammation, and viral hijacking of anti-inflammatory pathways, such as delayed type-I IFN response. Mechanisms of alveolar adaptation to hypoxia, adenosinergic signaling, and regulatory microRNAs are discussed as potential therapeutic targets for COVID-19.

Recent advances in passive immunotherapies for COVID-19: The Evidence-Based approaches and clinical trials

In late 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged, causing a global pandemic called COVID-19. Currently, there is no definitive treatment for this emerging disease. Global efforts resulted in developing multiple platforms of COVID-19 vaccines, but their efficacy in humans should be wholly investigated in the long-term clinical and epidemiological follow-ups. Despite the international efforts, COVID-19 vaccination accompanies challenges, including financial and political obstacles, serious adverse effects (AEs), the impossibility of using vaccines in certain groups of people in the community, and viral evasion due to emerging novel variants of SARS-CoV-2 in many countries. For these reasons, passive immunotherapy has been considered a complementary remedy and a promising way to manage COVID-19. These approaches arebased on reduced inflammation due to inhibiting cytokine storm phenomena, immunomodulation,preventing acute respiratory distress syndrome (ARDS), viral neutralization, anddecreased viral load. This article highlights passive immunotherapy and immunomodulation approaches in managing and treating COVID-19 patients and discusses relevant clinical trials (CTs).

Non-structure protein ORF1ab (NSP8) in SARS-CoV-2 contains potential γδT cell epitopes

Upon activation by the pathogen through T-cell receptors (TCRs), γδT cells suppress the pathogenic replication and thus play important roles against viral infections. Targeting SARS-CoV-2 via γδT cells provides alternative therapeutic strategies. However, little is known about the recognition of SARS-CoV-2 antigens by γδT cells. We discovered a specific Vγ9/δ2 CDR3 by analyzing γδT cells derived from the patients infected by SARS-CoV-2. Using a cell model exogenously expressing γδ-TCR established, we further screened the structural motifs within the CDR3 responsible for binding to γδ-TCR. Importantly, these sequences were mapped to NSP8, a non-structural protein in SARS-CoV-2. Our results suggest that NSP8 mediates the recognition by γδT cells and thus could serve as a potential target for vaccines.

SARS-CoV-2 spike and nucleocapsid proteins fail to activate human dendritic cells or γδ T cells

γδ T cells are thought to contribute to immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but the mechanisms by which they are activated by the virus are unknown. Using flow cytometry, we investigated if the two most abundant viral structural proteins, spike and nucleocapsid, can activate human γδ T cell subsets, directly or in the presence of dendritic cells (DC). Both proteins failed to induce interferon-γ production by Vδ1 or Vδ2 T cells within fresh mononuclear cells or lines of expanded γδ T cells generated from healthy donors, but the same proteins stimulated CD3+ cells from COVID-19 patients. The nucleocapsid protein stimulated interleukin-12 production by DC and downstream interferon-γ production by co-cultured Vδ1 and Vδ2 T cells, but protease digestion and use of an alternative nucleocapsid preparation indicated that this activity was due to contaminating non-protein material. Thus, SARS-CoV-2 spike and nucleocapsid proteins do not have stimulatory activity for DC or γδ T cells. We propose that γδ T cell activation in COVID-19 patients is mediated by immune recognition of viral RNA or other structural proteins by γδ T cells, or by other immune cells, such as DC, that produce γδ T cell-stimulatory ligands or cytokines.

Role of hormones in the pregnancy and sex-specific outcomes to infections with respiratory viruses

Pregnant women infected with pathogenic respiratory viruses, such as influenza A viruses (IAV) and coronaviruses, are at higher risk for mortality, hospitalization, preterm birth, and stillbirth. Several factors are likely to contribute to the susceptibility of pregnant individuals to severe lung disease including changes in pulmonary physiology, immune defenses, and effector functions of some immune cells. Pregnancy is also a physiologic state characterized by higher levels of multiple hormones that may impact the effector functions of immune cells, such as progesterone, estrogen, human chorionic gonadotropin, prolactin, and relaxin. Each of these hormones acts to support a tolerogenic immune state of pregnancy, which helps prevent fetal rejection, but may also contribute to an impaired antiviral response. In this review, we address the unique role of adaptive and innate immune cells in the control of pathogenic respiratory viruses and how pregnancy and specific hormones can impact their effector actions. We highlight viruses with sex-specific differences in infection outcomes and why pregnancy hormones may contribute to fetal protection but aid the virus at the expense of the mother's health.

γδ T Cells in Emerging Viral Infection: An Overview

New emerging viruses belonging to the Coronaviridae, Flaviviridae, and Filoviridae families are serious threats to public health and represent a global concern. The surveillance to monitor the emergence of new viruses and their transmission is an important target for public health authorities. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is an excellent example of a pathogen able to cause a pandemic. In a few months, SARS-CoV-2 has spread globally from China, and it has become a world health problem. Gammadelta (γδ) T cell are sentinels of innate immunity and are able to protect the host from viral infections. They enrich many tissues, such as the skin, intestines, and lungs where they can sense and fight the microbes, thus contributing to the protective immune response. γδ T cells perform their direct antiviral activity by cytolytic and non-cytolytic mechanisms against a wide range of viruses, and they are able to orchestrate the cellular interplay between innate and acquired immunity. For their pleiotropic features, γδ T cells have been proposed as a target for immunotherapies in both cancer and viral infections. In this review, we analyzed the role of γδ T cells in emerging viral infections to define the profile of the response and to better depict their role in the host protection.

The BLT Humanized Mouse Model as a Tool for Studying Human Gamma Delta T Cell-HIV Interactions In Vivo

Gamma-delta (γδ) T cells recognize antigens in a major histocompatibility complex (MHC) independent and have cytotoxic capability. Human immunodeficiency virus (HIV) infection reduces the proportion of the Vδ2 cell subset compared to the Vδ1 cell subset of γδ T cells in the blood in most infected individuals, except for elite controllers. The capacity of Vδ2 T cells to kill HIV-infected targets has been demonstrated in vitro, albeit in vivo confirmatory studies are lacking. Here, we provide the first characterization of γδ T cell-HIV interactions in bone marrow-liver-thymus (BLT) humanized mice and examined the immunotherapeutic potential of Vδ2 T cells in controlling HIV replication in vivo. We demonstrate a reduced proportion of Vδ2 T cells and an increased proportion of Vδ1 T cells in HIV-infected BLT humanized mice, like in HIV-positive individuals. HIV infection in BLT humanized mice also impaired the ex vivo expansion of Vδ2 T cells, like in HIV-positive individuals. Adoptive transfer of activated Vδ2 T cells did not control HIV replication during cell-associated HIV transmission in BLT humanized mice but instead exacerbated viremia, suggesting that Vδ2 T cells may serve as early targets for HIV replication. Our findings demonstrate that BLT humanized mice can model γδ T cell-HIV interactions in vivo.

The role of unconventional T cells in COVID-19

COVID-19 is a respiratory disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It was first documented in late 2019, but within months, a worldwide pandemic was declared due to the easily transmissible nature of the virus. Research to date on the immune response to SARS-CoV-2 has focused largely on conventional B and T lymphocytes. This review examines the emerging role of unconventional T cell subsets, including γδ T cells, invariant natural killer T (iNKT) cells and mucosal associated invariant T (MAIT) cells in human SARS-CoV-2 infection.Some of these T cell subsets have been shown to play protective roles in anti-viral immunity by suppressing viral replication and opsonising virions of SARS-CoV. Here, we explore whether unconventional T cells play a protective role in SARS-CoV-2 infection as well. Unconventional T cells are already under investigation as cell-based immunotherapies for cancer. We discuss the potential use of these cells as therapeutic agents in the COVID-19 setting. Due to the rapidly evolving situation presented by COVID-19, there is an urgent need to understand the pathogenesis of this disease and the mechanisms underlying its immune response. Through this, we may be able to better help those with severe cases and lower the mortality rate by devising more effective vaccines and novel treatment strategies.

The interplay between SARS-CoV-2 infected airway epithelium and immune cells modulates regulatory/inflammatory signals

To assess the cross-talk between immune cells and respiratory tract during SARS-CoV-2 infection, we analyzed the relationships between the inflammatory response induced by SARS-CoV-2 replication and immune cells phenotype in a reconstituted organotypic human airway epithelium (HAE). The results indicated that immune cells failed to inhibit SARS-CoV-2 replication in the HAE model. In contrast, immune cells strongly affected the inflammatory profile induced by SARS-CoV-2 infection, dampening the production of several immunoregulatory/inflammatory signals (e.g., IL-35, IL-27, and IL-34). Moreover, these mediators were found inversely correlated with innate immune cell frequency (NK and γδ T cells) and directly with CD8 T cells. The enriched signals associated with NK and CD8 T cells highlighted the modulation of pathways induced by SARS-CoV-2 infected HAE. These findings are useful to depict the cell-cell communication mechanisms necessary to develop novel therapeutic strategies aimed to promote an effective immune response.

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HAE as a model to study the cross-talk between infected epithelium and immune cells

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Immune cells failed to inhibit SARS-CoV-2 replication

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Immune cells dampen the production of several signals induced by SARS-CoV-2 infection

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Decrease of NK/γδ T and increase of CD8 T cells in SARS-CoV-2 infected HAE co-culture

Single-Cell RNAseq Profiling of Human γδ T Lymphocytes in Virus-Related Cancers and COVID-19 Disease

The detailed characterization of human γδ T lymphocyte differentiation at the single-cell transcriptomic (scRNAseq) level in tumors and patients with coronavirus disease 2019 (COVID-19) requires both a reference differentiation trajectory of γδ T cells and a robust mapping method for additional γδ T lymphocytes. Here, we incepted such a method to characterize thousands of γδ T lymphocytes from (n = 95) patients with cancer or adult and pediatric COVID-19 disease. We found that cancer patients with human papillomavirus-positive head and neck squamous cell carcinoma and Epstein-Barr virus-positive Hodgkin's lymphoma have γδ tumor-infiltrating T lymphocytes that are more prone to recirculate from the tumor and avoid exhaustion. In COVID-19, both TCRVγ9 and TCRVγnon9 subsets of γδ T lymphocytes relocalize from peripheral blood mononuclear cells (PBMC) to the infected lung tissue, where their advanced differentiation, tissue residency, and exhaustion reflect T cell activation. Although severe COVID-19 disease increases both recruitment and exhaustion of γδ T lymphocytes in infected lung lesions but not blood, the anti-IL6R therapy with Tocilizumab promotes γδ T lymphocyte differentiation in patients with COVID-19. PBMC from pediatric patients with acute COVID-19 disease display similar γδ T cell lymphopenia to that seen in adult patients. However, blood γδ T cells from children with the COVID-19-related multisystem inflammatory syndrome are not lymphodepleted, but they are differentiated as in healthy PBMC. These findings suggest that some virus-induced memory γδ T lymphocytes durably persist in the blood of adults and could subsequently infiltrate and recirculate in tumors.

Gamma Delta T Cells and Their Involvement in COVID-19 Virus Infections

The global outbreak of the SARS-Cov-2 virus in 2020 has killed millions of people worldwide and forced large parts of the world into lockdowns. While multiple vaccine programs are starting to immunize the global population, there is no direct cure for COVID-19, the disease caused by the SARS-Cov-2 infection. A common symptom in patients is a decrease in T cells, called lymphopenia. It is as of yet unclear what the exact role of T cells are in the immune response to COVID-19. The research so far has mainly focused on the involvement of classical αβ T cells. However, another subset of T cells called γδ T cells could have an important role to play. As part of the innate immune system, γδ T cells respond to inflammation and stressed or infected cells. The γδ T cell subset appears to be particularly affected by lymphopenia in COVID-19 patients and commonly express activation and exhaustion markers. Particularly in children, this subset of T cells seems to be most affected. This is interesting and relevant because γδ T cells are more prominent and active in early life. Their specific involvement in this group of patients could indicate a significant role for γδ T cells in this disease. Furthermore, they seem to be involved in other viral infections and were able to kill SARS infected cells in vitro. γδ T cells can take up, process and present antigens from microbes and human cells. As e.g. tumour-associated antigens are presented by MHC on γδ T cells to classical T-cells, we argue here that it stands to reason that also viral antigens, such as SARS-Cov-2-derived peptides, can be presented in the same way. γδ T cells are already used for medical purposes in oncology and have potential in cancer therapy. As γδ T cells are not necessarily able to distinguish between a transformed and a virally infected cell it could therefore be of great interest to investigate further the relationship between COVID-19 and γδ T cells.

Cheap and Commonplace: Making the Case for BCG and γδ T Cells in COVID-19

Antigen-specific vaccines developed for the COVID-19 pandemic demonstrate a remarkable achievement and are currently being used in high income countries with much success. However, new SARS-CoV-2 variants are threatening this success via mutations that lessen the efficacy of antigen-specific antibodies. One simple approach to assisting with this issue is focusing on strategies that build on the non-specific protection afforded by the innate immune response. The BCG vaccine has been shown to provide broad protection beyond tuberculosis disease, including against respiratory viruses, and ongoing studies are investigating its efficacy as a tool against SARS-CoV-2. Gamma delta (γδ) T cells, particularly the Vδ2 subtype, undergo rapid expansion after BCG vaccination due to MHC-independent mechanisms. Consequently, γδ T cells can produce diverse defenses against virally infected cells, including direct cytotoxicity, death receptor ligands, and pro-inflammatory cytokines. They can also assist in stimulating the adaptive immune system. BCG is affordable, commonplace and non-specific, and therefore could be a useful tool to initiate innate protection against new SARS-CoV-2 variants. However, considerations must also be made to BCG vaccine supply and the prioritization of countries where it is most needed to combat tuberculosis first and foremost.

Immunomodulation and immunotherapeutics of COVID-19

Severe acute respiratory syndrome coronavirus-2 causes coronavirus disease 2019, a pandemic which was originated from Wuhan city of China. The pandemic has affected millions of people worldwide. The pathogenesis of SARS-CoV-2 is characterized by a cytokine storm in the blood (cytokinemia) and tissues, especially the lungs. One of the major repercussions of this inflammatory process is the endothelial injury-causing intestinal bleeding, coagulopathy, and thromboembolism which result in various sudden and unexpected post-COVID complications including kidney failure, myocardial infarction, or multiorgan failure. In this review, we have summarized the immune responses, biochemical changes, and inflammatory responses in the human body after infection with the SARS-CoV-2 virus. The increased amount of inflammatory cytokines, chemokines, and involvement of complement proteins in inflammatory reaction increase the risk of occurrence of disease.

Endogenous control of inflammation characterizes pregnant women with asymptomatic or paucisymptomatic SARS-CoV-2 infection

SARS-CoV-2 infection can affect all human beings, including pregnant women. Thus, understanding the immunological changes induced by the virus during pregnancy is nowadays of pivotal importance. Here, using peripheral blood from 14 pregnant women with asymptomatic or mild SARS-CoV-2 infection, we investigate cell proliferation and cytokine production, measure plasma levels of 62 cytokines, and perform a 38-parameter mass cytometry analysis. Our results show an increase in low density neutrophils but no lymphopenia or gross alterations of white blood cells, which display normal levels of differentiation, activation or exhaustion markers and show well preserved functionality. Meanwhile, the plasma levels of anti-inflammatory cytokines such as interleukin (IL)-1RA, IL-10 and IL-19 are increased, those of IL-17, PD-L1 and D-dimer are decreased, but IL-6 and other inflammatory molecules remain unchanged. Our profiling of antiviral immune responses may thus help develop therapeutic strategies to avoid virus-induced damages during pregnancy.

A Machine-Generated View of the Role of Blood Glucose Levels in the Severity of COVID-19

SARS-CoV-2 started spreading toward the end of 2019 causing COVID-19, a disease that reached pandemic proportions among the human population within months. The reasons for the spectrum of differences in the severity of the disease across the population, and in particular why the disease affects more severely the aging population and those with specific preconditions are unclear. We developed machine learning models to mine 240,000 scientific articles openly accessible in the CORD-19 database, and constructed knowledge graphs to synthesize the extracted information and navigate the collective knowledge in an attempt to search for a potential common underlying reason for disease severity. The machine-driven framework we developed repeatedly pointed to elevated blood glucose as a key facilitator in the progression of COVID-19. Indeed, when we systematically retraced the steps of the SARS-CoV-2 infection, we found evidence linking elevated glucose to each major step of the life-cycle of the virus, progression of the disease, and presentation of symptoms. Specifically, elevations of glucose provide ideal conditions for the virus to evade and weaken the first level of the immune defense system in the lungs, gain access to deep alveolar cells, bind to the ACE2 receptor and enter the pulmonary cells, accelerate replication of the virus within cells increasing cell death and inducing an pulmonary inflammatory response, which overwhelms an already weakened innate immune system to trigger an avalanche of systemic infections, inflammation and cell damage, a cytokine storm and thrombotic events. We tested the feasibility of the hypothesis by manually reviewing the literature referenced by the machine-generated synthesis, reconstructing atomistically the virus at the surface of the pulmonary airways, and performing quantitative computational modeling of the effects of glucose levels on the infection process. We conclude that elevation in glucose levels can facilitate the progression of the disease through multiple mechanisms and can explain much of the differences in disease severity seen across the population. The study provides diagnostic considerations, new areas of research and potential treatments, and cautions on treatment strategies and critical care conditions that induce elevations in blood glucose levels.

Neutrophils at the crossroads of acute viral infections and severity

Neutrophils are versatile immune effector cells essential for mounting a first-line defense against invading pathogens. However, uncontrolled activation can lead to severe life-threatening complications. Neutrophils exist as a heterogeneous population, and their interaction with pathogens and other immune cells may shape the outcome of the host immune response. Diverse classes of viruses, including the recently identified novel SARS-CoV-2, have shown to alter the various aspects of neutrophil biology, offering possibilities for selective intervention. Here, we review heterogeneity within the neutrophil population, highlighting the functional consequences of circulating phenotypes and their critical involvement in exaggerating protective and pathological immune responses against the viruses. We discuss the recent findings of neutrophil extracellular traps (NETs) in COVID-19 pathology and cover other viruses, where neutrophil biology and NETs are crucial for developing disease severity. In the end, we have also pointed out the areas where neutrophil-mediated responses can be finely tuned to outline opportunities for therapeutic manipulation in controlling inflammation against viral infection.

Immunological Approaches to the Treatment of New Coronavirus Infection (Review)

The pandemic of the new coronavirus infection (COVID-19) caused by the SARS-CoV-2 virus has spread all over the world. The large amount of information that appears every day requires comprehension and systematization. The immunological aspects of the virus-host interaction are the core issues in the effective treatment and prevention of COVID-19' development. The review analyzes the known pathways of the viral invasion and evasion, the mechanisms of the cytokine storm, endothelial damage, and hypercoagulability associated with SARS-CoV-2 infection. Clinical data from previous SARS and MERS epidemics is discussed here. We also address the therapeutic approaches based on the basic knowledge of immune response and the blood cells' immune functions, as well as the ways to reduce their hyperactivation. The use of interferon therapy, anti-inflammatory therapy, anti-cytokine therapy, neutralizing antibodies, convalescent plasma, and mesenchymal stem cells, as well as prophylactic vaccines, is discussed.

Ketogenic diet restrains aging-induced exacerbation of coronavirus infection in mice

Increasing age is the strongest predictor of risk of COVID-19 severity and mortality. Immunometabolic switch from glycolysis to ketolysis protects against inflammatory damage and influenza infection in adults. To investigate how age compromises defense against coronavirus infection, and whether a pro-longevity ketogenic diet (KD) impacts immune surveillance, we developed an aging model of natural murine beta coronavirus (mCoV) infection with mouse hepatitis virus strain-A59 (MHV-A59). When inoculated intranasally, mCoV is pneumotropic and recapitulates several clinical hallmarks of COVID-19 infection. Aged mCoV-A59-infected mice have increased mortality and higher systemic inflammation in the heart, adipose tissue, and hypothalamus, including neutrophilia and loss of γδ T cells in lungs. Activation of ketogenesis in aged mice expands tissue protective γδ T cells, deactivates the NLRP3 inflammasome, and decreases pathogenic monocytes in lungs of infected aged mice. These data establish harnessing of the ketogenic immunometabolic checkpoint as a potential treatment against coronavirus infection in the aged.

Cytokine Overproduction and Immune System Dysregulation in alloHSCT and COVID-19 Patients

The COVID-19 pathomechanism depends on (i) the pathogenicity of the virus, (ii) ability of the immune system to respond to the cytopathic effect of the virus infection, (iii) co-morbidities. Inflammatory cytokine production constitutes a hallmark of COVID-19 that is facilitated by inability of adaptive immunity to control virus invasion. The effect of cytokine release syndrome is deleterious, but the severity of it depends on other confounding factors: age and comorbidities. In this study, we analyze the literature data on the post-transplant course of allogeneic hematopoietic stem cell transplanted (alloHSCT) patients, which is affected by generated inflammatory cytokines. The sequence of events boosting cytokine production was analyzed in relation to clinical and laboratory data highlighting the impact of cytokine generation on the post-transplant course. The collected data were compared to those from studies on COVID-19 patients. The similarities are: (i) the damage/pathogen-associated molecular pattern (DAMP/PAMP) stage is similar except for the initiation hit being sterile in alloHSCT (toxic damage of conditioning regimen) and viral in COVID-19; (ii) genetic host-derived factors play a role; (iii) adaptive immunity fails, DAMP signal(s) increases, over-production of cytokines occurs; (iv) monocytes lacking HLADR expression emerge, being suppressor cells hampering adaptive immunity; (v) immune system homeostasis is broken, the patient's status deteriorates to bed dependency, leading to hypo-oxygenation and malnutrition, which in turn stimulates the intracellular alert pathways with vigorous transcription of cytokine genes. All starts with the interaction between DAMPs with appropriate receptors, which leads to the production of pro-inflammatory cytokines, the inflammatory process spreads, tissue is damaged, DAMPs are released and a vicious cycle occurs. Attempts to modify intracellular signaling pathways in patients with post-alloHSCT graft vs host disease have already been undertaken. The similarities documented in this study show that this approach may also be used in COVID-19 patients for tuning signal transduction processes to interrupt the cycle that powers the cytokine overproduction.

Lymphopenia in COVID-19: γδ T Cells-Based Therapeutic Opportunities

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection dysregulates the immune system by lymphopenia of B cells, monocytes, eosinophils, basophils, and cytotoxic cells such as CD8, γδ T cells, and natural killer (NK) cells. Despite many studies being conducted to better understand the effects of SARS-CoV-2 on the immune system, many mechanisms still remain unclear, hindering the development of novel therapeutic approaches and strategies to improve the host’s immune defense. This mini-review summarizes the findings on the role of γδ T cells in coronavirus disease 2019 (COVID-19), providing an overview of the excellent anti-viral therapeutic potential of γδ T cells, that had not yet been exploited in depth.

Delivery Routes for COVID-19 Vaccines

The novel coronavirus, SARS-CoV-2, which causes COVID-19, has resulted in a pandemic with millions of deaths. To eradicate SARS-CoV-2 and prevent further infections, many vaccine candidates have been developed. These vaccines include not only traditional subunit vaccines and attenuated or inactivated viral vaccines but also nucleic acid and viral vector vaccines. In contrast to the diversity in the platform technology, the delivery of vaccines is limited to intramuscular vaccination. Although intramuscular vaccination is safe and effective, mucosal vaccination could improve the local immune responses that block the spread of pathogens. However, a lack of understanding of mucosal immunity combined with the urgent need for a COVID-19 vaccine has resulted in only intramuscular vaccinations. In this review, we summarize the history of vaccines, current progress in COVID-19 vaccine technology, and the status of intranasal COVID-19 vaccines. Future research should determine the most effective route for vaccine delivery based on the platform and determine the mechanisms that underlie the efficacy of different delivery routes.

How to Train Your Dragon: Harnessing Gamma Delta T Cells Antiviral Functions and Trained Immunity in a Pandemic Era

The emergence of viruses with pandemic potential such as the SARS-CoV-2 coronavirus causing COVID-19 poses a global health challenge. There is remarkable progress in vaccine technology in response to this threat, but their design often overlooks the innate arm of immunity. Gamma Delta (γδ) T cells are a subset of T cells with unique features that gives them a key role in the innate immune response to a variety of homeostatic alterations, from cancer to microbial infections. In the context of viral infection, a growing body of evidence shows that γδ T cells are particularly equipped for early virus detection, which triggers their subsequent activation, expansion and the fast deployment of antiviral functions such as direct cytotoxic pathways, secretion of cytokines, recruitment and activation of other immune cells and mobilization of a trained immunity memory program. As such, γδ T cells represent an attractive target to stimulate for a rapid and effective resolution of viral infections. Here, we review the known aspects of γδ T cells that make them crucial component of the immune response to viruses, and the ways that their antiviral potential can be harnessed to prevent or treat viral infection.

Cellular and Humoral Immune Responses in Covid-19 and Immunotherapeutic Approaches

Coronavirus disease 2019 (Covid-19), caused by the novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can range in severity from asymptomatic to severe/critical disease. SARS-CoV-2 uses angiotensin-converting enzyme 2 to infect cells leading to a strong inflammatory response, which is most profound in patients who progress to severe Covid-19. Recent studies have begun to unravel some of the differences in the innate and adaptive immune response to SARS-CoV-2 in patients with different degrees of disease severity. These studies have attributed the severe form of Covid-19 to a dysfunctional innate immune response, such as a delayed and/or deficient type I interferon response, coupled with an exaggerated and/or a dysfunctional adaptive immunity. Differences in T-cell (including CD4+ T-cells, CD8+ T-cells, T follicular helper cells, γδ-T-cells, and regulatory T-cells) and B-cell (transitional cells, double-negative 2 cells, antibody-secreting cells) responses have been identified in patients with severe disease compared to mild cases. Moreover, differences in the kinetic/titer of neutralizing antibody responses have been described in severe disease, which may be confounded by antibody-dependent enhancement. Importantly, the presence of preexisting autoantibodies against type I interferon has been described as a major cause of severe/critical disease. Additionally, priorVaccine and multiple vaccine exposure, trained innate immunity, cross-reactive immunity, and serological immune imprinting may all contribute towards disease severity and outcome. Several therapeutic and preventative approaches have been under intense investigations; these include vaccines (three of which have passed Phase 3 clinical trials), therapeutic antibodies, and immunosuppressants.

COVID-19: Immunology, Immunopathogenesis and Potential Therapies

The Coronavirus Disease-2019 (COVID-19) imposed public health emergency and affected millions of people around the globe. As of January 2021, 100 million confirmed cases of COVID-19 along with more than 2 million deaths were reported worldwide. SARS-CoV-2 infection causes excessive production of pro-inflammatory cytokines thereby leading to the development of "Cytokine Storm Syndrome." This condition results in uncontrollable inflammation that further imposes multiple-organ-failure eventually leading to death. SARS-CoV-2 induces unrestrained innate immune response and impairs adaptive immune responses thereby causing tissue damage. Thus, understanding the foremost features and evolution of innate and adaptive immunity to SARS-CoV-2 is crucial in anticipating COVID-19 outcomes and in developing effective strategies to control the viral spread. In the present review, we exhaustively discuss the sequential key immunological events that occur during SARS-CoV-2 infection and are involved in the immunopathogenesis of COVID-19. In addition to this, we also highlight various therapeutic options already in use such as immunosuppressive drugs, plasma therapy and intravenous immunoglobulins along with various novel potent therapeutic options that should be considered in managing COVID-19 infection such as traditional medicines and probiotics.

Understanding the Host Innate Immune Responses against SARS-CoV-2 Infection and COVID-19 Pathogenesis

The emergence of a new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has become a significant health concern worldwide. Undoubtedly, a better understanding of the innate and adaptive immune responses against SARS-CoV-2 and its relationship with the coronavirus disease 2019 (COVID-19) pathogenesis will be the sole basis for developing and applying therapeutics. This review will summarize the published results that relate to innate immune responses against infections with human coronaviruses including SARS-CoV-1 and SARS-CoV-2 in both humans and animal models. The topics encompass the innate immune sensing of the virus to the dysregulation of various innate immune cells during infection and disease progression.

Role of the Immune Microenvironment in SARS-CoV-2 Infection

Severe acute respiratory syndrome coronavirus (SARS-CoV-2) first emerged in December 2019 in Wuhan, China, and has since spread rapidly worldwide. As researchers seek to learn more about COVID-19, the disease it causes, this novel virus continues to infect and kill. Despite the socioeconomic impacts of SARS-CoV-2 infections and likelihood of future outbreaks of other pathogenic coronaviruses, options to prevent or treat coronavirus infections remain limited. In current clinical trials, potential coronavirus treatments focusing on killing the virus or on preventing infection using vaccines largely ignore the host immune response. The relatively small body of current research on the virus indicates pathological responses by the immune system as the leading cause for much of the morbidity and mortality caused by COVID-19. In this review, we investigated the host innate and adaptive immune responses against COVID-19, collated information on recent COVID-19 experimental data, and summarized the systemic immune responses to and histopathology of SARS-CoV-2 infection. Finally, we summarized the immune-related biomarkers to define patients with high-risk and worst-case outcomes, and identified the possible usefulness of inflammatory markers as potential immunotherapeutic targets. This review provides an overview of current knowledge on COVID-19 and the symptomatological differences between healthy, convalescent, and severe cohorts, while offering research directions for alternative immunoregulation therapeutic targets.

T cell phenotypes in COVID-19 - a living review

COVID-19 is characterized by profound lymphopenia in the peripheral blood, and the remaining T cells display altered phenotypes, characterized by a spectrum of activation and exhaustion. However, antigen-specific T cell responses are emerging as a crucial mechanism for both clearance of the virus and as the most likely route to long-lasting immune memory that would protect against re-infection. Therefore, T cell responses are also of considerable interest in vaccine development. Furthermore, persistent alterations in T cell subset composition and function post-infection have important implications for patients' long-term immune function. In this review, we examine T cell phenotypes, including those of innate T cells, in both peripheral blood and lungs, and consider how key markers of activation and exhaustion correlate with, and may be able to predict, disease severity. We focus on SARS-CoV-2-specific T cells to elucidate markers that may indicate formation of antigen-specific T cell memory. We also examine peripheral T cell phenotypes in recovery and the likelihood of long-lasting immune disruption. Finally, we discuss T cell phenotypes in the lung as important drivers of both virus clearance and tissue damage. As our knowledge of the adaptive immune response to COVID-19 rapidly evolves, it has become clear that while some areas of the T cell response have been investigated in some detail, others, such as the T cell response in children remain largely unexplored. Therefore, this review will also highlight areas where T cell phenotypes require urgent characterisation.

Mechanisms of Dysregulated Humoral and Cellular Immunity by SARS-CoV-2

The current coronavirus disease 2019 (COVID-19) pandemic, a disease caused by severe acute respiratory syndrome corona virus 2 (SARS-CoV-2), was first identified in December 2019 in China, and has led to thousands of mortalities globally each day. While the innate immune response serves as the first line of defense, viral clearance requires activation of adaptive immunity, which employs B and T cells to provide sanitizing immunity. SARS-CoV-2 has a potent arsenal of mechanisms used to counter this adaptive immune response through processes, such as T cells depletion and T cell exhaustion. These phenomena are most often observed in severe SARS-CoV-2 patients, pointing towards a link between T cell function and disease severity. Moreover, neutralizing antibody titers and memory B cell responses may be short lived in many SARS-CoV-2 patients, potentially exposing these patients to re-infection. In this review, we discuss our current understanding of B and T cells immune responses and activity in SARS-CoV-2 pathogenesis.

Lymphocyte Changes in Severe COVID-19: Delayed Over-Activation of STING?

Upon recognition of microbial DNA or self-DNA, the cyclic-GMP-AMP synthase (cGAS) of the host catalyzes the production of the cyclic dinucleotide cGAMP. cGAMP is the main activator of STING, stimulator of interferon genes, leading to interferon synthesis through the STING-TBK1-IRF3 pathway. STING is also a hub for activation of NF-κB and autophagy. The present review details the striking similarities between T and B cell responses in severe coronavirus disease 2019 (COVID-19) and both animal or human models of STING gain of function (SAVI syndromes: STING-associated vasculopathy with onset in infancy). Those similarities may be further clues for a delayed activation of STING in severe COVID-19 patients, due to DNA damages following severe acute respiratory syndrome coronaviruses (SARS-CoV-2) infection and unusual role of STING in SARS-CoV-2 control. In early stages, Th2 differentiation are noticed in both severe COVID-19 and SAVI syndromes; then, CD4+ and CD8+ T cells functional exhaustion/senescent patterns due to TCR hyper-responsiveness are observed. T cell delayed over-responses can contribute to pneumonitis and delayed cytokine secretion with over-production of IL-6. Last, STING over-activation induces progressive CD4+ and CD8+ T lymphopenia in SAVI syndromes, which parallels what is observed in severe COVID-19. ACE2, the main receptor of SARS-CoV-2, is rarely expressed in immune cells, and it has not been yet proven that some human lymphocytes could be infected by SARS-CoV-2 through CD147 or CD26. However, STING, expressed in humans T cells, might be triggered following excessive transfer of cGAMP from infected antigen presenting cells into activated CD4+ and CD8+ T cells lymphocytes. Indeed, those lymphocytes highly express the cGAMP importer SLC19A1. Whereas STING is not expressed in human B cells, B cells counts are much less affected, either in COVID-19 or SAVI syndromes. The recognition of delayed STING over-activation in severe COVID-19 patients could prompt to target STING with specific small molecules inhibitors already designed and/or aspirin, which inhibits cGAS.

A Cell for the Ages: Human γδ T Cells across the Lifespan

The complexity of the human immune system is exacerbated by age-related changes to immune cell functionality. Many of these age-related effects remain undescribed or driven by mechanisms that are poorly understood. γδ T cells, while considered an adaptive subset based on immunological ontogeny, retain both innate-like and adaptive-like characteristics. This T cell population is small but mighty, and has been implicated in both homeostatic and disease-induced immunity within tissues and throughout the periphery. In this review, we outline what is known about the effect of age on human peripheral γδ T cells, and call attention to areas of the field where further research is needed.

Lymphocyte subsets in haematological patients with COVID-19: Multicentre prospective study

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Patients with haematological malignancies and COVID-19 are characterized by T lymphopenia and reduction in NK cell numbers.

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T lymphopenia in haematological patients with COVID-19 include reduction in CD4+ T cells numbers and lowered CD4/CD8 ratio.

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Increase in activated T cells with low CD4/CD8 ratio are crucial for the early stages of COVID-19 in haematological patients.

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Low levels of both TCRγ/δ and CD3+CD25+ T cells may indicate impaired cellular response to COVID-19 in haematological patients.

The role of immune dysregulation in the course and prognosis of COVID-19 is not clearly established. In particular, immune status in specific populations such as haematological patients, who have an impaired immunological system, has not been described so far. Here, we performed a comprehensive analysis of peripheral blood lymphocyte subsets in 27 SARS-CoV-2-infected patients, including 16 patients with haematological malignancies. We identified T cell subpopulations, B cells, NK cells and TCR α/ß and ɣ/ƍ-expressing T cells during COVID-19 infection, with significant changes observed in immune profiles during the course of disease, especially in haematological patients. We observed an increase in activated T lymphocytes (CD3+HLA-DR+ and CD3+CD8+HLA-DR+) in the early stages of SARS-CoV-2 infection with a concomitant decrease in the CD4/CD8 ratio in haematological patients compared to non-haematological patients affected by COVID-19. We also found a decrease in ɣ/ƍ T cells in both studied groups of patients, with lower numbers of CD25+ T cells and CD16+CD56+ NK cells in haematological patients compared to non-haematological patients with COVID-19. Our findings demonstrate, for the first time, impaired adaptive immunity in patients with haematological malignancies infected with COVID-19, resulting in impaired cellular immune responses to SARS-CoV-2. This warrants further investigation of this disease group in COVID-19 patient cohorts

Making a case for using γδ T cells against SARS-CoV-2

Intensive worldwide efforts are underway to determine both the pathogenesis of SARS-CoV-2 infection and the immune responses in COVID-19 patients in order to develop effective therapeutics and vaccines. One type of cell that may contribute to these immune responses is the γδ T lymphocyte, which plays a key role in immunosurveillance of the mucosal and epithelial barriers by rapidly responding to pathogens. Although found in low numbers in blood, γδ T cells consist the majority of tissue-resident T cells and participate in the front line of the host immune defense. Previous studies have demonstrated the critical protective role of γδ T cells in immune responses to other respiratory viruses, including SARS-CoV-1. However, no studies have profoundly investigated these cells in COVID-19 patients to date. γδ T cells can be safely expanded in vivo using existing inexpensive FDA-approved drugs such as bisphosphonate, in order to test its protective immune response to SARS-CoV-2. To support this line of research, we review insights gained from previous coronavirus research, along with recent findings, discussing the potential role of γδ T cells in controlling SARS-CoV-2. We conclude by proposing several strategies to enhance γδ T cell's antiviral function, which may be used in developing therapies for COVID-19.

The phenotypic changes of γδ T cells in COVID-19 patients

A novel pneumonia-associated respiratory syndrome named coronavirus disease-2019 (COVID-19), which was caused by SARS-CoV-2，broke out in Wuhan, China, in the end of 2019. Unfortunately, there is no specific antiviral agent or vaccine available to treat SARS-CoV-2 infections. The information regarding the immunological characteristics in COVID-19 patients remains limited. Here, we collected the blood samples from 18 healthy donors (HD) and 38 COVID-19 patients to analyze changes on γδ T cell population. In comparison with HD, the γδ T cell percentage decreased, while the activation marker CD25 expression increased in response to SARS-CoV-2 infection. Interestingly, the CD4 expression was upregulated in γδ T cells reflecting the occurrence of a specific effector cell population, which may serve as a biomarker for the assessment of SARS-CoV-2 infection.