Proviral role of human respiratory epithelial cell-derived small extracellular vesicles in SARS-CoV-2 infection

Small Extracellular Vesicles (sEVs) are 50-200 nm in diameter vesicles delimited by a lipid bilayer, formed within the endosomal network or derived from the plasma membrane. They are secreted in various biological fluids, including airway nasal mucus. The goal of this work was to understand the role of sEVs present in the mucus (mu-sEVs) produced by human nasal epithelial cells (HNECs) in SARS-CoV-2 infection. We show that uninfected HNECs produce mu-sEVs containing SARS-CoV-2 receptor ACE2 and activated protease TMPRSS2. mu-sEVs cleave prefusion viral Spike proteins at the S1/S2 boundary, resulting in higher proportions of prefusion S proteins exposing their receptor binding domain in an 'open' conformation, thereby facilitating receptor binding at the cell surface. We show that the role of nasal mu-sEVs is to complete prefusion Spike priming performed by intracellular furin during viral egress from infected cells. This effect is mediated by vesicular TMPRSS2 activity, rendering SARS-CoV-2 virions prone to entry into target cells using the 'early', TMPRSS2-dependent pathway instead of the 'late', cathepsin-dependent route. These results indicate that prefusion Spike priming by mu-sEVs in the nasal cavity plays a role in viral tropism. They also show that nasal mucus does not protect from SARS-CoV-2 infection, but instead facilitates it.

Régulation de TMPRSS2 par la voie des androgènes et implications dans l’infection SARS-CoV-2

Objectifs

TMPRSS2 est une protéase cellulaire régulée par les androgènes dans les cellules prostatiques. L’entrée de SARS-CoV2 par fusion membranaire dans les cellules pulmonaires nécessite le clivage de Spike par TMPRSS2. Notre hypothèse est que le niveau des androgènes et la présence du récepteur des androgènes (RA) dans les cellules pulmonaires pourrait réguler l’expression de TMPRSS2 et influencerait l’entrée de SARS-CoV-2.

Méthodes

Les régulations de TMPRSS2 et du RA ont été étudiées dans deux lignées cellulaires pulmonaires (A549 et Calu-3) et dans des lignées de cellules prostatiques contrôles (LNCaP ou VCaP) grâce à des expériences de privation et de supplémentation en androgènes ainsi que par utilisation d’un siRNA ciblant le RA. La régulation de l’expression de ces deux gènes a été étudiée par RT-qPCR et Western blot. L’infection de SARS-CoV2 dans les cellules Calu-3 a été étudiée en condition de blocage du RA.

Résultats

Les études cliniques semblent montrer que les patients atteints de cancer de la prostate sous hormonothérapie ont une incidence plus faible d’infection par le SARS-CoV2 suggérant le rôle du RA dans l’infection du virus. Nos résultats montrent que les deux lignées de cellules pulmonaires utilisées (A549 et Calu-3) expriment TMPRSS2 et le RA au niveau ARNm et protéique. Dans ces lignées, il existe également une régulation de l’expression de TMPRSS2 et du RA par les androgènes. Cet effet est connu et bien retrouvé pour les lignées prostatiques. Enfin, nous avons pu montrer qu’au niveau des cellules pulmonaires, le taux d’infection par le SARS-CoV2 était moins important lorsque la voie du RA a été au préalable bloquée.

Conclusion

Le blocage de TMPRSS2 permettrait de limiter l’infection du virus. Nos résultats suggèrent que l’expression de TMPRSS2 est régulée par les androgènes dans des cellules pulmonaires et que la testostérone pourrait jouer un rôle dans l’infection du SARS-CoV2. Le blocage du RA serait donc une option thérapeutique envisagée pour limiter la COVID-19.

Evolutionary Pathways to Persistence of Highly Fit and Resistant Hepatitis C Virus Protease Inhibitor Escape Variants

Protease inhibitors (PIs) are important components of treatment regimens for patients with chronic hepatitis C virus (HCV) infection. However, emergence and persistence of antiviral resistance could reduce their efficacy. Thus, defining resistance determinants is highly relevant for efforts to control HCV. Here, we investigated patterns of PI resistance-associated substitutions (RASs) for the major HCV genotypes and viral determinants for persistence of key RASs. We identified protease position 156 as a RAS hotspot for genotype 1-4, but not 5 and 6, escape variants by resistance profiling using PIs grazoprevir and paritaprevir in infectious cell culture systems. However, except for genotype 3, engineered 156-RASs were not maintained. For genotypes 1 and 2, persistence of 156-RASs depended on genome-wide substitution networks, co-selected under continued PI treatment and identified by next-generation sequencing with substitution linkage and haplotype reconstruction. Persistence of A156T for genotype 1 relied on compensatory substitutions increasing replication and assembly. For genotype 2, initial selection of A156V facilitated transition to 156L, persisting without compensatory substitutions. The developed genotype 1, 2, and 3 variants with persistent 156-RASs had exceptionally high fitness and resistance to grazoprevir, paritaprevir, glecaprevir, and voxilaprevir. A156T dominated in genotype 1 glecaprevir and voxilaprevir escape variants, and pre-existing A156T facilitated genotype 1 escape from clinically relevant combination treatments with grazoprevir/elbasvir and glecaprevir/pibrentasvir. In genotype 1 infected patients with treatment failure and 156-RASs, we observed genome-wide selection of substitutions under treatment. Conclusion: Comprehensive PI resistance profiling for HCV genotypes 1-6 revealed 156-RASs as key determinants of high-level resistance across clinically relevant PIs. We obtained in vitro proof of concept for persistence of highly fit genotype 1-3 156-variants, which might pose a threat to clinically relevant combination treatments.

Ribavirin revisited in the era of direct-acting antiviral therapy for hepatitis C virus infection

Over the past two decades, ribavirin has been an integral component of treatment for hepatitis C virus (HCV) infection, where it has been shown to improve the efficacy of (pegylated) interferon. However, because of treatment-limiting side effects and its additive toxicity with interferon, the search for interferon- and ribavirin-free regimens has been underway. The recent approvals of all-oral direct acting antivirals (DAAs) have revolutionized the HCV therapeutic landscape, and initially it was expected that the role of ribavirin with DAA regimens would be eliminated. On the contrary, what we have witnessed is that ribavirin retains an important role in the optimal treatment of some subgroups of patients, particularly those that historically have been considered the most difficult to cure. Fortunately, it has also been recognized that the safety profile of ribavirin is improved when co-administered with all-oral DAA combinations in the absence of interferon. Despite the antiviral mechanism of action of ribavirin being poorly understood, we now have a range of novel insights into the potential role of ribavirin in all-oral DAA HCV treatment and greater insight into the antiviral mechanism by which it continues to provide clinical benefit for defined patient groups.