Mapping of functional SARS-CoV-2 receptors in human lungs establishes differences in variant binding and SLC1A5 as a viral entry modulator of hACE2.

BACKGROUND: The COVID-19 pandemic is an infectious disease caused by SARS-CoV-2. The first step of SARS-CoV-2 infection is the recognition of angiotensin-converting enzyme 2 (ACE2) receptors by the receptor-binding domain (RBD) of the viral Spike (S) glycoprotein. Although the molecular and structural bases of the SARS-CoV-2-RBD/hACE2 interaction have been thoroughly investigated in vitro, the relationship between hACE2 expression and in vivo infection is less understood. METHODS: Here, we developed an efficient SARS-CoV-2-RBD binding assay suitable for super resolution microscopy and simultaneous hACE2 immunodetection and mapped the correlation between hACE2 receptor abundance and SARS-CoV-2-RBD binding, both in vitro and in human lung biopsies. Next, we explored the specific proteome of SARS-CoV-2-RBD/hACE2 through a comparative mass spectrometry approach. FINDINGS: We found that only a minority of hACE2 positive spots are actually SARS-CoV-2-RBD binding sites, and that the relationship between SARS-CoV-2-RBD binding and hACE2 presence is variable, suggesting the existence of additional factors. Indeed, we found several interactors that are involved in receptor localization and viral entry and characterized one of them: SLC1A5, an amino acid transporter. High-resolution receptor-binding studies showed that co-expression of membrane-bound SLC1A5 with hACE2 predicted SARS-CoV-2 binding and entry better than hACE2 expression alone. SLC1A5 depletion reduces SARS-CoV-2 binding and entry. Notably, the Omicron variant is more efficient in binding hACE2 sites, but equally sensitive to SLC1A5 downregulation. INTERPRETATION: We propose a method for mapping functional SARS-CoV-2 receptors in vivo. We confirm the existence of hACE2 co-factors that may contribute to differential sensitivity of cells to infection. FUNDING: This work was supported by an unrestricted grant from "Fondazione Romeo ed Enrica Invernizzi" to Stefano Biffo and by AIRC under MFAG 2021 - ID. 26178 project - P.I. Manfrini Nicola.

Immunosuppressant Treatment in Rheumatic Musculoskeletal Diseases Does Not Inhibit Elicitation of Humoral Response to SARS-CoV-2 Infection and Preserves Effector Immune Cell Populations.

COVID-19 has proven to be particularly serious and life-threatening for patients presenting with pre-existing pathologies. Patients affected by rheumatic musculoskeletal disease (RMD) are likely to have impaired immune responses against SARS-CoV-2 infection due to their compromised immune system and the prolonged use of disease-modifying anti-rheumatic drugs (DMARDs), which include conventional synthetic (cs) DMARDs or biologic and targeted synthetic (b/ts) DMARDs. To provide an integrated analysis of the immune response following SARS-CoV-2 infection in RMD patients treated with different classes of DMARDs we carried out an immunological analysis of the antibody responses toward SARS-CoV-2 nucleocapsid and RBD proteins and an extensive immunophenotypic analysis of the major immune cell populations. We showed that RMD individuals under most DMARD treatments mount a sustained antibody response to the virus, with neutralizing activity. In addition, they displayed a sizable percentage of effector T and B lymphocytes. Among b-DMARDs, we found that anti-TNFα treatments are more favorable drugs to elicit humoral and cellular immune responses as compared to CTLA4-Ig and anti-IL6R inhibitors. This study provides a whole picture of the humoral and cellular immune responses in RMD patients by reassuring the use of DMARD treatments during COVID-19. The study points to TNF-α inhibitors as those DMARDs permitting elicitation of functional antibodies to SARS-CoV-2 and adaptive effector populations available to counteract possible re-infections.

Exosomes Recovered From the Plasma of COVID-19 Patients Expose SARS-CoV-2 Spike-Derived Fragments and Contribute to the Adaptive Immune Response.

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by beta-coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that has rapidly spread across the globe starting from February 2020. It is well established that during viral infection, extracellular vesicles become delivery/presenting vectors of viral material. However, studies regarding extracellular vesicle function in COVID-19 pathology are still scanty. Here, we performed a comparative study on exosomes recovered from the plasma of either MILD or SEVERE COVID-19 patients. We show that although both types of vesicles efficiently display SARS-CoV-2 spike-derived peptides and carry immunomodulatory molecules, only those of MILD patients are capable of efficiently regulating antigen-specific CD4+ T-cell responses. Accordingly, by mass spectrometry, we show that the proteome of exosomes of MILD patients correlates with a proper functioning of the immune system, while that of SEVERE patients is associated with increased and chronic inflammation. Overall, we show that exosomes recovered from the plasma of COVID-19 patients possess SARS-CoV-2-derived protein material, have an active role in enhancing the immune response, and possess a cargo that reflects the pathological state of patients in the acute phase of the disease.

Corrigendum: The Impact of Anti-rheumatic Drugs on the Seroprevalence of Anti-SARS-CoV-2 Antibodies in a Cohort of Patients With Inflammatory Arthritis: The MAINSTREAM Study.

[This corrects the article DOI: 10.3389/fmed.2022.850858.].

Synthetic carbohydrate-binding agents neutralize SARS-CoV-2 by inhibiting binding of the spike protein to ACE2.

Developing strategies against the SARS-CoV-2 is currently a main research subject. SARS-CoV-2 infects host cells by binding to human ACE2 receptors. Both, virus and ACE2, are highly glycosylated, and exploiting glycans of the SARS-CoV-2 envelope as binding sites for ACE2 represents a virus strategy for attacking the human host. We report here that a family of mannose-binding synthetic carbohydrate-binding agents (CBAs) inhibits SARS-CoV-2 infection, showing broad neutralizing activity vs. several variants of the spike protein. Preliminary tests indicated that the investigated CBAs interact with the spike protein rather than with ACE2. For a lead compound (IDS060), which has been selected among others for its lack of cytotoxicity, evidence of binding to the RBD of the spike protein has been found by NMR experiments, while competitive binding assays in the presence of IDS060 showed inhibition of binding of RBD to hACE2, although neutralizing activity was also observed with variants showing reduced or depleted binding.

The Impact of Anti-rheumatic Drugs on the Seroprevalence of Anti-SARS-CoV-2 Antibodies in a Cohort of Patients With Inflammatory Arthritis: The MAINSTREAM Study.

Objectives: Given the high occurrence of asymptomatic subsets, the true prevalence of SARS-CoV-2 infection in rheumatic patients is still underestimated. This study aims to evaluate the seroprevalence of SARS-CoV-2 antibodies in rheumatic musculoskeletal diseases (RMD) patients receiving immunomodulatory drugs. Methods: All consecutive patients with rheumatoid arthritis or spondyloarthritis receiving disease-modifying antirheumatic drugs (DMARDs) evaluated between 4th May and 16th June 2020 were included. All participants were tested for anti-SARS-CoV-2 antibodies (IgG, IgM, IgA) by ELISA and were questioned about previous COVID-19 symptoms and clinical course. Results were compared with healthy population from the same region and with a control group of healthy subjects diagnosed with confirmed COVID-19. Results: The study population includes 358 patients. The overall prevalence of anti-SARS-CoV-2 antibodies (18.4%) was higher than prevalence rate based on swab-positivity (1.12%) or clinically suspected cases (10.6%), but consistent with seroprevalence observed in the healthy population. Among seropositive patients 58% were asymptomatic. Mean anti-SARS-CoV-2 titer was comparable with the control group. No differences in seroprevalence were observed according to age, sex, rheumatic disease and treatment with conventional, biologic or targeted synthetic DMARDs, whereas glucocorticoids and comorbidities resulted in higher seroprevalence rate. Conclusions: The results of this study are reassuring about the low impact of RMDs and immunomodulatory therapies on the risk and clinical course of COVID-19 and on humoral immune response to SARS-CoV-2 infection.

Production of anti-PF4 antibodies in antiphospholipid antibody-positive patients is not affected by COVID-19 vaccination.

BACKGROUND: Antibodies against cationic platelet chemokine, platelet factor 4 (PF4/CXCL4), have been described in heparin-induced thrombocytopenia (HIT), but also in patients positive for antiphospholipid antibodies (aPL) even in the absence of heparin treatment and HIT-related clinical manifestations. Anti-PF4 antibodies have been recently described also in subjects who developed thrombosis with thrombocytopenia syndrome (TTS) in association with adenoviral vector-based, but not with mRNA-based, COVID-19 vaccines. OBJECTIVE: To investigate whether COVID-19 vaccination affects the production of anti-PF4 antibodies in aPL-positive patients and in control groups. METHODS: Anti-PF4 immunoglobulins were detected in patients' and controls' serum samples by ELISA and their ability to activate normal platelets was assessed by the platelet aggregation test. RESULTS: Anti-PF4 were found in 9 of 126 aPL-positive patients, 4 of 50 patients with COVID-19, 9 of 49 with other infections, and 1 of 50 aPL-negative patients with systemic lupus erythematosus. Clinical manifestations of TTS were not observed in any aPL patient positive for anti-PF4, whose serum failed to cause platelet aggregation. The administration of COVID-19 vaccines did not affect the production of anti-PF4 immunoglobulins or their ability to cause platelet aggregation in 44 aPL-positive patients tested before and after vaccination. CONCLUSIONS: Heparin treatment-independent anti-PF4 antibodies can be found in aPL-positive patients and asymptomatic carriers, but their presence, titre as well as in vitro effect on platelet activation are not affected by COVID-19 vaccination.

Integrated longitudinal immunophenotypic, transcriptional and repertoire analyses delineate immune responses in COVID-19 patients.

To understand how a protective immune response against SARS-CoV-2 develops over time, we integrated phenotypic, transcriptional and repertoire analyses on PBMCs from mild and severe COVID-19 patients during and after infection, and compared them to healthy donors (HD). A type I IFN-response signature marked all the immune populations from severe patients during the infection. Humoral immunity was dominated by IgG production primarily against the RBD and N proteins, with neutralizing antibody titers increasing post infection and with disease severity. Memory B cells, including an atypical FCRL5+ T-BET+ memory subset, increased during the infection, especially in patients with mild disease. A significant reduction of effector memory, CD8+ T cells frequency characterized patients with severe disease. Despite such impairment, we observed robust clonal expansion of CD8+ T lymphocytes, while CD4+ T cells were less expanded and skewed toward TCM and TH2-like phenotypes. MAIT cells were also expanded, but only in patients with mild disease. Terminally differentiated CD8+ GZMB+ effector cells were clonally expanded both during the infection and post-infection, while CD8+ GZMK+ lymphocytes were more expanded post-infection and represented bona fide memory precursor effector cells. TCR repertoire analysis revealed that only highly proliferating T cell clonotypes, which included SARS-CoV-2-specific cells, were maintained post-infection and shared between the CD8+ GZMB+ and GZMK+ subsets. Overall, this study describes the development of immunity against SARS-CoV-2 and identifies an effector CD8+ T cell population with memory precursor-like features.