SARS-CoV-2 escapes direct NK cell killing through Nsp1-mediated downregulation of ligands for NKG2D.

Natural killer (NK) cells are cytotoxic effector cells that target and lyse virally infected cells; many viruses therefore encode mechanisms to escape such NK cell killing. Here, we interrogate the ability of SARS-CoV-2 to modulate NK cell recognition and lysis of infected cells. We find that NK cells exhibit poor cytotoxic responses against SARS-CoV-2-infected targets, preferentially killing uninfected bystander cells. We demonstrate that this escape is driven by downregulation of ligands for the activating receptor NKG2D (NKG2D-L). Indeed, early in viral infection, prior to NKG2D-L downregulation, NK cells are able to target and kill infected cells; however, this ability is lost as viral proteins are expressed. Finally, we find that SARS-CoV-2 non-structural protein 1 (Nsp1) mediates downregulation of NKG2D-L and that Nsp1 alone is sufficient to confer resistance to NK cell killing. Collectively, our work demonstrates that SARS-CoV-2 evades direct NK cell cytotoxicity and describes a mechanism by which this occurs.

IMMUNE SYSTEM PROFILE and CYTOKINE LEVELS of SARS-CoV-2 in PREGNANCY and NEWBORNS

Background: Knowledge about SARS-CoV2 infection in pregnancy and exposed newborns is deficient. We performed a longitudinal analysis of innate immune system status and determined soluble cytokines of women infected with SARS-CoV2 during pregnancy and their newborns Methods: Women with confirmed SARS-CoV2 infection (RT-PCR+ or SARS-CoV2 anti-IgM/IgG+) (COVID MOTHER group, CM n=29, median age of 31 years) and their SARS-CoV2 exposed uninfected newborns were recruited from Hospital Gregorio Marañón, Spain. Peripheral blood mononuclear cells (PBMCs), cord cells and plasma were collected at birth and 6 months later (n=15). The immunophenotyping of innate components (natural killer cells [NK] and monocytes) was studied on cryopreserved PBMCs and cord cells by multiparametric flow cytometry. Up to 4 soluble pro/anti-inflammatory cytokines were assessed in plasma and cord plasma by ELISA assay. CM was compared to a healthy non-SARS-CoV2 infected mothers' group matched by age (SARS-CoV2 PCR-and SARS-CoV2 anti-IgM/IgG-)(Uninfected Mothers, UM n=16) and their newborns (n=16) Results: On NK cell assays, CM show at baseline lower percentage of CD16++ subset, higher NKG2D and lower NKG2A expression on CD16++ and CD56++ subsets and reduced CD57 expression compared to UM;proportion of CD16++ subset and percentage of NKG2D reverted after 6 months(A). Regarding monocytes, CM show increased levels of CD62L and decreased CD49d expression on classical subset, elevated intermediate monocytes proportion and decreased CD40 expression on patrolling subset(B). No differences were found 6 months later. No newborn was infected by SARS-CoV2 and the phenotype analyzed on cord cells shows lower frequency of NK subsets compared with unexposed children and increased CD16++ subset after 6 months(C). In monocytes distribution, exposed children present lower frequency of total monocytes and its subsets than unexposed. Classical monocytes show significant changes at follow-up time-point(D). Increased TNFα and IL10 levels were found on CM compared to UM. Strong and direct correlations were observed between the age and IL6(E). No differences were observed in soluble cytokine levels comparing both groups of newborns Conclusion: SARS-CoV2 infection during pregnancy shows differences in activation, maturation and endothelial markers on innate immune system that could lead newborns clinical implications at birth. However, altered cell proportions and phenotypes found at SARS-CoV2 at birth time and on their exposed newborns is later reverted.

Prognostic Value of Serum MICA Levels as a Marker of Severity in COVID-19 Patients.

The COVID-19 global pandemic and high mortality rates necessitate the development of diagnostic and prognostic tools, as well as expanding testing capacity. Existing methods for detecting and characterizing SARS-CoV-2 infection are typically based on viral genome detection or measuring COVID-19-specific antibody levels. Despite their value, these methods are unable to predict disease outcomes in patients. Given the critical role of innate immune cells, particularly natural killer (NK) cells, in antiviral defense, this study sought to determine the prognostic value of serum secretory MHC class I polypeptide-related sequence A (sMICA) levels as an essential ligand for the NKG2D receptor, the master regulator of NK cell development and responsiveness. Serum MICA levels were measured by ELISA assay. Sera (n = 60) from SARS-CoV-2 positive patients were collected, and disease severity was determined using clinical criteria. The patient group included 30 patients with mild disease and 30 severely ill patients, as well as 30 healthy controls. Our findings revealed that serum MICA levels were significantly higher in patients than in controls, especially in cases with severe complications (P < .0001). Higher serum MICA levels may be associated with respiratory failure in COVID-19 and may serve as a marker of clinical severity in patients infected with SARS-CoV-2, particularly when clinical manifestations are insufficient to make a confident prediction.

Higher MICA levels may be associated with respiratory failure in COVID-19 infection.SMICA levels change with age, particularly for patients with severe COVID-19 disease.NKG2D ligands may have prognostic and therapeutic value for COVID-19 patients.

SARS-CoV-2 peptides bind to NKG2D and increase NK cell activity.

Immune dysregulation is commonly observed in patients with coronavirus disease 2019 (COVID-19). Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) induces severe lung inflammation and innate immune cell dysregulation. However, the precise interaction between SARS-CoV-2 and the innate immune system is currently unknown. To understand the interaction between SARS-CoV-2 and natural killer (NK) cells, several SARS-CoV-2 S protein peptides capable of binding to the NKG2D receptor were screened by in silico analysis. Among them, two peptides, cov1 and cov2, bound to NK cells and NKG2D receptors. These cov peptides increased NK cytotoxicity toward lung cancer cells, stimulated interferon gamma (IFN-γ) production by NK cells, and likely mediated these responses through the phosphorylation of Vav1, a key downstream-signaling molecule of NKG2D and NK activation genes. The direct interaction between SARS-CoV-2 and NK cells is a novel finding, and modulation of this interaction has potential clinical application as a therapeutic target for COVID-19.

Manipulating the NKG2D Receptor-Ligand Axis Using CRISPR: Novel Technologies for Improved Host Immunity.

The activating immune receptor natural killer group member D (NKG2D) and its cognate ligands represent a fundamental surveillance system of cellular distress, damage or transformation. Signaling through the NKG2D receptor-ligand axis is critical for early detection of viral infection or oncogenic transformation and the presence of functional NKG2D ligands (NKG2D-L) is associated with tumor rejection and viral clearance. Many viruses and tumors have developed mechanisms to evade NKG2D recognition via transcriptional, post-transcriptional or post-translational interference with NKG2D-L, supporting the concept that circumventing immune evasion of the NKG2D receptor-ligand axis may be an attractive therapeutic avenue for antiviral therapy or cancer immunotherapy. To date, the complexity of the NKG2D receptor-ligand axis and the lack of specificity of current NKG2D-targeting therapies has not allowed for the precise manipulation required to optimally harness NKG2D-mediated immunity. However, with the discovery of clustered regularly interspaced short palindromic repeats (CRISPRs) and CRISPR-associated (Cas) proteins, novel opportunities have arisen in the realm of locus-specific gene editing and regulation. Here, we give a brief overview of the NKG2D receptor-ligand axis in humans and discuss the levels at which NKG2D-L are regulated and dysregulated during viral infection and oncogenesis. Moreover, we explore the potential for CRISPR-based technologies to provide novel therapeutic avenues to improve and maximize NKG2D-mediated immunity.