Exhaustion and over-activation of immune cells in COVID-19: Challenges and therapeutic opportunities.

Exhaustion of immune cells in COVID-19 remains a serious concern for infection management and therapeutic interventions. As reported, immune cells such as T effector cells (Teff), T regulatory cells (Tregs), natural killer cells (NKs), and antigen-presenting cells (APCs) exhibit uncontrolled functions in COVID-19. Unfortunately, the mechanisms that orchestrate immune cell functionality and virus interaction are still unknown. Recent studies linked adaptive immune cell exhaustion to underlying epigenetic mechanisms that regulate the epigenetic transcription of inhibitory immune checkpoint receptors (ICs). Further to that, the over-activation of T cells accompanied by the dysfunctionality of DCs and Tregs may enhance uncontrollable alveoli inflammation and cytokine storm in COVID-19. This might explain the reasons behind the failure of DC-based vaccines in inducing sufficient anti-viral responses. This review explains the processes behind the over-activation and exhaustion of innate and adaptive immune cells in COVID-19, which may contribute to developing novel immune intervention strategies.

Promising use of immune cell-derived exosomes in the treatment of SARS-CoV-2 infections.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is persistently threatening the lives of thousands of individuals globally. It triggers pulmonary oedema, driving to dyspnoea and lung failure. Viral infectivity of coronavirus disease 2019 (COVID-19) is a genuine challenge due to the mutagenic genome and mysterious immune-pathophysiology. Early reports highlighted that extracellular vesicles (exosomes, Exos) work to enhance COVID-19 progression by mediating viral transmission, replication and mutations. Furthermore, recent studies revealed that Exos derived from immune cells play an essential role in the promotion of immune cell exhaustion by transferring regulatory lncRNAs and miRNAs from exhausted cells to the active cells. Fortunately, there are great chances to modulate the immune functions of Exos towards a sustained repression of COVID-19. Engineered Exos hold promising immunotherapeutic opportunities for remodelling cytotoxic T cells' function. Immune cell-derived Exos may trigger a stable epigenetic repression of viral infectivity, restore functional cytokine-producing T cells and rebalance immune response in severe infections by inducing functional T regulatory cells (Tregs). This review introduces a view on the current outcomes of immunopathology, and immunotherapeutic applications of immune cell-derived Exos in COVID-19, besides new perspectives to develop novel patterns of engineered Exos triggering novel anti-SARS-CoV-2 immune responses.

Role of T Regulatory Cells and Myeloid-Derived Suppressor Cells in COVID-19.

Coronavirus disease 2019 (COVID-19) has been raised as a pandemic disease since December 2019. Immunosuppressive cells including T regulatory cells (Tregs) and myeloid-derived suppressor cells (MDSCs) are key players in immunological tolerance and immunoregulation; however, they contribute to the pathogenesis of different diseases including infections. Tregs have been shown to impair the protective role of CD8+ T lymphocytes against viral infections. In COVID-19 patients, most studies reported reduction, while few other studies found elevation in Treg levels. Moreover, Tregs have a dual role, depending on the different stages of COVID-19 disease. At early stages of COVID-19, Tregs have a critical role in decreasing antiviral immune responses, and consequently reducing the viral clearance. On the other side, during late stages, Tregs reduce inflammation-induced organ damage. Therefore, inhibition of Tregs in early stages and their expansion in late stages have potentials to improve clinical outcomes. In viral infections, MDSC levels are highly increased, and they have the potential to suppress T cell proliferation and reduce viral clearance. Some subsets of MDSCs are expanded in the blood of COVID-19 patients; however, there is a controversy whether this expansion has pathogenic or protective effects in COVID-19 patients. In conclusion, further studies are required to investigate the role and function of immunosuppressive cells and their potentials as prognostic biomarkers and therapeutic targets in COVID-19 patients.

Inhibitory Immune Checkpoint Receptors and Ligands as Prognostic Biomarkers in COVID-19 Patients.

Coronavirus disease 2019 (COVID-19) is caused by SARS-CoV-2. During T-cell activation, the immune system uses different checkpoint pathways to maintain co-inhibitory and co-stimulatory signals. In COVID-19, expression of immune checkpoints (ICs) is one of the most important manifestations, in addition to lymphopenia and inflammatory cytokines, contributing to worse clinical outcomes. There is a controversy whether upregulation of ICs in COVID-19 patients might lead to T-cell exhaustion or activation. This review summarizes the available studies that investigated IC receptors and ligands in COVID-19 patients, as well as their effect on T-cell function. Several IC receptors and ligands, including CTLA-4, BTLA, TIM-3, VISTA, LAG-3, TIGIT, PD-1, CD160, 2B4, NKG2A, Galectin-9, Galectin-3, PD-L1, PD-L2, LSECtin, and CD112, were upregulated in COVID-19 patients. Based on the available studies, there is a possible relationship between disease severity and increased expression of IC receptors and ligands. Overall, the upregulation of some ICs could be used as a prognostic biomarker for disease severity.

Complement C5a and Clinical Markers as Predictors of COVID-19 Disease Severity and Mortality in a Multi-Ethnic Population.

Coronavirus disease-2019 (COVID-19) was declared as a pandemic by WHO in March 2020. SARS-CoV-2 causes a wide range of illness from asymptomatic to life-threatening. There is an essential need to identify biomarkers to predict disease severity and mortality during the earlier stages of the disease, aiding treatment and allocation of resources to improve survival. The aim of this study was to identify at the time of SARS-COV-2 infection patients at high risk of developing severe disease associated with low survival using blood parameters, including inflammation and coagulation mediators, vital signs, and pre-existing comorbidities. This cohort included 89 multi-ethnic COVID-19 patients recruited between July 14th and October 20th 2020 in Doha, Qatar. According to clinical severity, patients were grouped into severe (n=33), mild (n=33) and asymptomatic (n=23). Common routine tests such as complete blood count (CBC), glucose, electrolytes, liver and kidney function parameters and markers of inflammation, thrombosis and endothelial dysfunction including complement component split product C5a, Interleukin-6, ferritin and C-reactive protein were measured at the time COVID-19 infection was confirmed. Correlation tests suggest that C5a is a predictive marker of disease severity and mortality, in addition to 40 biological and physiological parameters that were found statistically significant between survivors and non-survivors. Survival analysis showed that high C5a levels, hypoalbuminemia, lymphopenia, elevated procalcitonin, neutrophilic leukocytosis, acute anemia along with increased acute kidney and hepatocellular injury markers were associated with a higher risk of death in COVID-19 patients. Altogether, we created a prognostic classification model, the CAL model (C5a, Albumin, and Lymphocyte count) to predict severity with significant accuracy. Stratification of patients using the CAL model could help in the identification of patients likely to develop severe symptoms in advance so that treatments can be targeted accordingly.

SnoRNAs and miRNAs Networks Underlying COVID-19 Disease Severity.

There is a lack of predictive markers for early and rapid identification of disease progression in COVID-19 patients. Our study aims at identifying microRNAs (miRNAs)/small nucleolar RNAs (snoRNAs) as potential biomarkers of COVID-19 severity. Using differential expression analysis of microarray data (n = 29), we identified hsa-miR-1246, ACA40, hsa-miR-4532, hsa-miR-145-5p, and ACA18 as the top five differentially expressed transcripts in severe versus asymptomatic, and ACA40, hsa-miR-3609, ENSG00000212378 (SNORD78), hsa-miR-1231, hsa-miR-885-3p as the most significant five in severe versus mild cases. Moreover, we found that white blood cell (WBC) count, absolute neutrophil count (ANC), neutrophil (%), lymphocyte (%), red blood cell (RBC) count, hemoglobin, hematocrit, D-Dimer, and albumin are significantly correlated with the identified differentially expressed miRNAs and snoRNAs. We report a unique miRNA and snoRNA profile that is associated with a higher risk of severity in a cohort of SARS-CoV-2 infected patients. Altogether, we present a differential expression analysis of COVID-19-associated microRNA (miRNA)/small nucleolar RNA (snoRNA) signature, highlighting their importance in SARS-CoV-2 infection.

Single-Cell Transcriptome Analysis Highlights a Role for Neutrophils and Inflammatory Macrophages in the Pathogenesis of Severe COVID-19.

Cumulative data link cytokine storms with coronavirus disease 2019 (COVID-19) severity. The precise identification of immune cell subsets in bronchoalveolar lavage (BAL) and their correlation with COVID-19 disease severity are currently being unraveled. Herein, we employed iterative clustering and guide-gene selection 2 (ICGS2) as well as uniform manifold approximation and projection (UMAP) dimensionality reduction computational algorithms to decipher the complex immune and cellular composition of BAL, using publicly available datasets from a total of 68,873 single cells derived from two healthy subjects, three patients with mild COVID-19, and five patients with severe COVID-19. Our analysis revealed the presence of neutrophils and macrophage cluster-1 as a hallmark of severe COVID-19. Among the identified gene signatures, IFITM2, IFITM1, H3F3B, SAT1, and S100A8 gene signatures were highly associated with neutrophils, while CCL8, CCL3, CCL2, KLF6, and SPP1 were associated with macrophage cluster-1 in severe-COVID-19 patients. Interestingly, although macrophages were also present in healthy subjects and patients with mild COVID-19, they had different gene signatures, indicative of interstitial and cluster-0 macrophage (i.e., FABP4, APOC1, APOE, C1QB, and NURP1). Additionally, MALAT1, NEAT1, and SNGH25 were downregulated in patients with mild and severe COVID-19. Interferon signaling, FCγ receptor-mediated phagocytosis, IL17, and Tec kinase canonical pathways were enriched in patients with severe COVID-19, while PD-1 and PDL-1 pathways were suppressed. A number of upstream regulators (IFNG, PRL, TLR7, PRL, TGM2, TLR9, IL1B, TNF, NFkB, IL1A, STAT3, CCL5, and others) were also enriched in BAL cells from severe COVID-19-affected patients compared to those from patients with mild COVID-19. Further analyses revealed genes associated with the inflammatory response and chemotaxis of myeloid cells, phagocytes, and granulocytes, among the top activated functional categories in BAL from severe COVID-19-affected patients. Transcriptome data from another cohort of COVID-19-derived peripheral blood mononuclear cells (PBMCs) revealed the presence of several genes common to those found in BAL from patients with severe and mild COVID-19 (IFI27, IFITM3, IFI6, IFIT3, MX1, IFIT1, OASL, IFI30, OAS1) or to those seen only in BAL from severe-COVID-19 patients (S100A8, IFI44, IFI44L, CXCL8, CCR1, PLSCR1, EPSTI1, FPR1, OAS2, OAS3, IL1RN, TYMP, BCL2A1). Taken together, our data reveal the presence of neutrophils and macrophage cluster-1 as the main immune cell subsets associated with severe COVID-19 and identify their inflammatory and chemotactic gene signatures, also partially reflected systemically in the circulation, for possible diagnostic and therapeutic interventions.

T-cell responses and therapies against SARS-CoV-2 infection.

Coronavirus disease 2019 (COVID-19) is caused by SARS-CoV-2, a novel coronavirus strain. Some studies suggest that COVID-19 could be an immune-related disease, and failure of effective immune responses in initial stages of viral infection could contribute to systemic inflammation and tissue damage, leading to worse disease outcomes. T cells can act as a double-edge sword with both pro- and anti-roles in the progression of COVID-19. Thus, better understanding of their roles in immune responses to SARS-CoV-2 infection is crucial. T cells primarily react to the spike protein on the coronavirus to initiate antiviral immunity; however, T-cell responses can be suboptimal, impaired or excessive in severe COVID-19 patients. This review focuses on the multifaceted roles of T cells in COVID-19 pathogenesis and rationalizes their significance in eliciting appropriate antiviral immune responses in COVID-19 patients and unexposed individuals. In addition, we summarize the potential therapeutic approaches related to T cells to treat COVID-19 patients. These include adoptive T-cell therapies, vaccines activating T-cell responses, recombinant cytokines, Th1 activators and Th17 blockers, and potential utilization of immune checkpoint inhibitors alone or in combination with anti-inflammatory drugs to improve antiviral T-cell responses against SARS-CoV-2.

SARS-CoV-2 Infection and Lung Cancer: Potential Therapeutic Modalities.

Human coronaviruses, especially SARS-CoV-2, are emerging pandemic infectious diseases with high morbidity and mortality in certain group of patients. In general, SARS-CoV-2 causes symptoms ranging from the common cold to severe conditions accompanied by lung injury, acute respiratory distress syndrome in addition to other organs' destruction. The main impact upon SARS-CoV-2 infection is damage to alveolar and acute respiratory failure. Thus, lung cancer patients are identified as a particularly high-risk group for SARS-CoV-2 infection and its complications. On the other hand, it has been reported that SARS-CoV-2 spike (S) protein binds to angiotensin-converting enzyme 2 (ACE-2), that promotes cellular entry of this virus in concert with host proteases, principally transmembrane serine protease 2 (TMPRSS2). Today, there are no vaccines and/or effective drugs against the SARS-CoV-2 coronavirus. Thus, manipulation of key entry genes of this virus especially in lung cancer patients could be one of the best approaches to manage SARS-CoV-2 infection in this group of patients. We herein provide a comprehensive and up-to-date overview of the role of ACE-2 and TMPRSS2 genes, as key entry elements as well as therapeutic targets for SARS-CoV-2 infection, which can help to better understand the applications and capacities of various remedial approaches for infected individuals, especially those with lung cancer.