The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic that originated in Wuhan, China, in December 2019 has impacted public health, society, the global economy, and the daily lives of billions of people in an unprecedented manner. There are currently no specific registered antiviral drugs to treat or prevent SARS-CoV-2 infections. Therefore, drug repurposing would be the fastest route to provide at least a temporary solution while better, more specific drugs are being developed. Here, we demonstrate that the antiparasitic drug suramin inhibits SARS-CoV-2 replication, protecting Vero E6 cells with a 50% effective concentration (EC50) of ∼20 μM, which is well below the maximum attainable level in human serum. Suramin also decreased the viral load by 2 to 3 logs when Vero E6 cells or cells of a human lung epithelial cell line (Calu-3 2B4 [referred to here as “Calu-3”]) were treated. Time-of-addition and plaque reduction assays performed on Vero E6 cells showed that suramin acts on early steps of the replication cycle, possibly preventing binding or entry of the virus. In a primary human airway epithelial cell culture model, suramin also inhibited the progression of infection. The results of our preclinical study warrant further investigation and suggest that it is worth evaluating whether suramin provides any benefit for COVID-19 patients, which obviously requires safety studies and well-designed, properly controlled randomized clinical trials.

Background Zika virus has recently spread to South-and Central America, causing congenital birth defects and neurological complications. Many people at risk are flavivirus pre-immune due to prior infections with other flaviviruses (e.g. dengue virus) or flavivirus vaccinations. Since pre-existing cross-reactive immunity can potentially modulate antibody responses to Zika virus infection and may affect the outcome of disease, we analyzed fine-specificity as well as virus-neutralizing and infection-enhancing activities of antibodies induced by a primary Zika virus infection in flavivirus-naïve as well as yellow fever-and/or tick-borne encephalitisvaccinated individuals. Methodology Antibodies in sera from convalescent Zika patients with and without vaccine-induced immunity were assessed by ELISA with respect to Zika virus-specificity and flavivirus cross-reactivity. Functional analyses included virus neutralization and infection-enhancement. The contribution of IgM and cross-reactive antibodies to these properties was determined by depletion experiments.

PIWI-interacting (pi)RNAs are small silencing RNAs that are crucial for the defense against transposable elements in germline tissues of animals. In Aedes aegypti mosquitoes, the piRNA pathway also contributes to gene regulation in somatic tissues, illustrating additional roles for piRNAs and PIWI proteins besides transposon repression. Here, we identify a highly abundant endogenous piRNA (propiR1) that associates with both Piwi4 and Piwi5. PropiR1-mediated target silencing requires base-pairing in the seed region with supplemental base-pairing at the piRNA 3′ end. Yet, propiR1 represses a limited set of targets, among which is the lncRNA AAEL027353 (lnc027353). Slicing of lnc027353 initiates production of responder and trailer piRNAs from the cleavage fragment. Expression of propiR1 commences early during embryonic development and mediates degradation of maternally provided lnc027353. Both propiR1 and its lncRNA target are conserved in the closely related Aedes albopictus mosquito, underscoring the importance of this regulatory network for mosquito development.

47The SARS-CoV-2 pandemic that originated from Wuhan, China, in December 2019 has impacted public 48 health, society and economy and the daily lives of billions of people in an unprecedented manner. 49There are currently no specific registered antiviral drugs to treat or prevent SARS-CoV-2 infections. 50Therefore, drug repurposing would be the fastest route to provide at least a temporary solution while 51 better, more specific drugs are being developed. Here we demonstrate that the antiparasitic drug 52 suramin inhibits SARS-CoV-2 replication, protecting Vero E6 cells with an EC50 of ~20 µM, which is well 53 below the maximum attainable level in human serum. Suramin also decreased the viral load by 2-3 54 logs when Vero E6 cells or cells of a human lung epithelial cell line (Calu-3) were treated. Time of 55 addition and plaque reduction assays showed that suramin acts on early steps of the replication cycle, 56possibly preventing entry of the virus. In a primary human airway epithelial cell culture model, suramin 57 also inhibited the progression of infection.

Detection of SARS-coronavirus-2 (SARS-CoV-2) specific CD4+ and CD8+ T cells in SARS-CoV-2-unexposed donors has been explained by the presence of T cells primed by other coronaviruses. However, based on the relative high frequency and prevalence of cross-reactive T cells, we hypothesized CMV may induce these cross-reactive T cells. Stimulation of pre-pandemic cryo-preserved PBMCs with SARS-CoV-2 peptides revealed that frequencies of SARS-CoV-2-specific T cells were higher in CMV-seropositive donors. Characterization of these T cells demonstrated that membrane-specific CD4+ and spike-specific CD8+ T cells originate from cross-reactive CMV-specific T cells. Spike-specific CD8+ T cells recognize SARS-CoV-2 spike peptide FVSNGTHWF (FVS) and dissimilar CMV pp65 peptide IPSINVHHY (IPS) presented by HLA-B*35:01. These dual IPS/FVS-reactive CD8+ T cells were found in multiple donors as well as severe COVID-19 patients and shared a common T cell receptor (TCR), illustrating that IPS/FVS-cross-reactivity is caused by a public TCR. In conclusion, CMV-specific T cells cross-react with SARS-CoV-2, despite low sequence homology between the two viruses, and may contribute to the pre-existing immunity against SARS-CoV-2.

PIWI-interacting (pi)RNAs are small silencing RNAs that are crucial for the defense against transposable elements in germline tissues of animals. In the mosquito Aedes aegypti, the piRNA pathway also contributes to gene regulation in somatic tissues, illustrating additional roles for piRNAs and PIWI proteins besides transposon repression. Here, we identify a highly abundant, endogenous piRNA (propiR1) that associates with both Piwi4 and Piwi5. PropiR1-mediated target silencing requires base pairing in the seed region with supplemental base pairing at the piRNA 3' end. Yet, propiR1 strongly represses a single target, the lncRNA AAEL027353 (lnc027353). Slicing of this target initiates the production of responder and trailer piRNAs from the 3' cleavage fragment. Expression of propiR1 commences early during embryonic development and mediates degradation of maternally provided lnc027353. Both propiR1 and its lncRNA target display a high degree of sequence conservation in the closely related Aedes albopictus, underscoring the importance of this regulatory network for mosquito development.

Infection biology and pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the coronavirus disease 2019 (COVID-19), are incompletely understood. Here, we assessed the impact of airway epithelial cellular composition on infection in air-liquid interface (ALI) cultures of differentiated primary human tracheal (PTEC) and bronchial epithelial cells (PBEC). We first compared SARS-CoV-2 infection kinetics, related antiviral and inflammatory responses, and viral entry factors in PTEC and PBEC. Next, the contribution of differentiation time was investigated by differentiating ALI-PTEC/PBEC for 3-5 weeks and comparing dynamics of viral replication/spread, cellular composition and epithelial responses. We observed a gradual increase in viral load with prolonged culture duration. Ciliated and goblet cells were predominantly infected in both PTEC and PBEC. Immunofluorescence analysis and RT-qPCR showed that compared to other cell types mainly ciliated and goblet cell numbers were affected by increased culture duration. An increased proportion of these two target cell types was associated with increased viral load. Furthermore, modulation of cellular composition using IL-13 and the Notch signaling inhibitor DAPT, underlined the importance of both ciliated and goblet cells for infection. DAPT treatment resulted in a lower viral load and a relative increase in ciliated cells at the expense of goblet cells, compared to IL-13 treated cultures in which both cell types were present and viral load was higher. In conclusion, our results identify cellular composition as a contributing factor to airway epithelial susceptibility to SARS-CoV-2.

The SARS-CoV-2 pandemic highlighted the need for broad-spectrum antivirals to increase our preparedness. Patients often require treatment by the time that blocking virus replication is less effective. Therefore, therapy should not only aim to inhibit the virus, but also to suppress pathogenic host responses, e.g., leading to microvascular changes and pulmonary damage. Clinical studies have previously linked SARS-CoV-2 infection to pathogenic intussusceptive angiogenesis in the lungs, involving the upregulation of angiogenic factors such as ANGPTL4. The β-blocker propranolol is used to suppress aberrant ANGPTL4 expression in the treatment of hemangiomas. Therefore, we investigated the effect of propranolol on SARS-CoV-2 infection and the expression of ANGPTL4. SARS-CoV-2 upregulated ANGPTL4 in endothelial and other cells, which could be suppressed with R-propranolol. The compound also inhibited the replication of SARS-CoV-2 in Vero-E6 cells and reduced the viral load by up to ~2 logs in various cell lines and primary human airway epithelial cultures. R-propranolol was as effective as S-propranolol but lacks the latter’s undesired β-blocker activity. R-propranolol also inhibited SARS-CoV and MERS-CoV. It inhibited a post-entry step of the replication cycle, likely via host factors. The broad-spectrum antiviral effect and suppression of factors involved in pathogenic angiogenesis make R-propranolol an interesting molecule to further explore for the treatment of coronavirus infections.