ABSTRACT
Microthrombus formation is associated with COVID-19 severity; however, the detailed mechanism remains unclear. In this study, we investigated mouse models with severe pneumonia caused by SARS-CoV-2 infection by using our in vivo two-photon imaging system. In the lungs of SARS-CoV-2-infected mice, increased expression of adhesion molecules in intravascular neutrophils prolonged adhesion time to the vessel wall, resulting in platelet aggregation and impaired lung perfusion. Re-analysis of scRNA-seq data from peripheral blood mononuclear cells from COVID-19 cases revealed increased expression levels of CD44 and SELL in neutrophils in severe COVID-19 cases compared to a healthy group, consistent with our observations in the mouse model. These findings suggest that pulmonary perfusion defects caused by neutrophil adhesion to pulmonary vessels contribute to COVID-19 severity.
Subject(s)
Lung Diseases , Pneumonia , Severe Acute Respiratory Syndrome , Blood Platelet Disorders , COVID-19ABSTRACT
EG.5.1 is a subvariant of the SARS-CoV-2 Omicron XBB variant that is rapidly increasing in prevalence worldwide. EG.5.1 has additional substitutions in its spike protein (namely, Q52H and F456L) compared with XBB.1.5. However, the pathogenicity, transmissibility, and immune evasion properties of clinical isolates of EG.5.1 are largely unknown. In this study, we used wild-type Syrian hamsters to investigate the replicative ability, pathogenicity, and transmissibility of a clinical EG.5.1 isolate. Our data show that there are no obvious differences in growth ability and pathogenicity between EG.5.1 and XBB.1.5, and both EG.5.1 and XBB.1.5 are attenuated compared to a Delta variant isolate. We also found that EG.5.1 is transmitted more efficiently between hamsters compared with XBB.1.5. In addition, unlike XBB.1.5, we detected EG.5.1 virus in the lungs of four of six exposed hamsters, suggesting that the virus tropism of EG.5.1 is different from that of XBB.1.5 after airborne transmission. Finally, we assessed the neutralizing ability of plasma from convalescent individuals and found that the neutralizing activity against EG.5.1 was slightly, but significantly, lower than that against XBB.1.5 or XBB.1.9.2. This suggests that EG.5.1 effectively evades humoral immunity and that the amino acid differences in the S protein of EG.5.1 compared with that of XBB.1.5 or XBB.1.9.2 (i.e., Q52H, R158G, and F456L) alter the antigenicity of EG.5.1. Our data suggest that the increased transmissibility and altered antigenicity of EG.5.1 may be driving its increasing prevalence over XBB.1.5 in the human population.
ABSTRACT
The prevalence of the Omicron subvariant BA.2.75 is rapidly increasing in India and Nepal. In addition, BA.2.75 has been detected in at least 34 other countries and is spreading globally. However, the virological features of BA.2.75 are largely unknown. Here, we evaluated the replicative ability and pathogenicity of BA.2.75 clinical isolates in Syrian hamsters. Although we found no substantial differences in weight change among hamsters infected with BA.2, BA.5, or BA.2.75, the replicative ability of BA.2.75 in the lungs was higher than that of BA.2 and BA.5. Of note, BA.2.75 caused focal viral pneumonia in hamsters, characterized by patchy inflammation interspersed in alveolar regions, which was not observed in BA.5-infected hamsters. Moreover, in competition assays, BA.2.75 replicated better than BA.5 in the lungs of hamsters. These results suggest that BA.2.75 can cause more severe respiratory disease than BA.5 and BA.2 and should be closely monitored.
Subject(s)
Respiratory Tract Diseases , Adenocarcinoma, Bronchiolo-Alveolar , PneumoniaABSTRACT
The BA.2 sublineage of the SARS-CoV-2 Omicron variant has become dominant in most countries around the world; however, the prevalence of BA.4 and BA.5 is increasing rapidly in several regions. BA.2 is less pathogenic in animal models than previously circulating variants of concern (VOC). Compared with BA.2, however, BA.4 and BA.5 possess additional substitutions in the spike protein, which play a key role in viral infectivity, raising concerns that the infectivity and pathogenicity of BA.4 and BA.5 are higher than those of BA.2. Here, we evaluated the replicative ability and pathogenicity of authentic BA.4 and BA.5 isolates in wild-type Syrian hamsters and human ACE2 (hACE2) transgenic hamsters. In contrast to recent data with a recombinant chimeric virus possessing the spike protein of BA.4/BA.5 in the background of a BA.2 strain, we observed no obvious differences among BA.2, BA.4, and BA.5 isolates in growth ability or pathogenicity in hamsters, and less pathogenicity compared to a previously circulating Delta (B.1.617.2 lineage) isolate. In addition, in vivo competition experiments revealed that BA.5 outcompeted BA.2 in hamsters, whereas BA.4 and BA.2 exhibited similar fitness. These findings suggest that BA.4 and BA.5 have similar pathogenicity to BA.2 in rodents and that BA.5 possesses viral fitness superior to that of BA.2. Our study highlights the importance of using authentic isolates when evaluating virological features.
ABSTRACT
The recent emergence of SARS-CoV-2 Omicron variants possessing large numbers of mutations has raised concerns of decreased effectiveness of current vaccines, therapeutic monoclonal antibodies, and antiviral drugs for COVID-19 against these variants1,2. While the original Omicron lineage, BA.1, has become dominant in many countries, BA.2 has been detected in at least 67 countries and has become dominant in the Philippines, India, and Denmark. Here, we evaluated the replicative ability and pathogenicity of an authentic infectious BA.2 isolate in immunocompetent and human ACE2 (hACE2)-expressing mice and hamsters. In contrast to recent data with chimeric, recombinant SARS-CoV-2 strains expressing the spike proteins of BA.1 and BA.2 on an ancestral WK-521 backbone3, we observed similar infectivity and pathogenicity in mice and hamsters between BA.2 and BA.1, and less pathogenicity compared to early SARS-CoV-2 strains. We also observed a marked and significant reduction in the neutralizing activity of plasma from COVID-19 convalescent individuals and vaccine recipients against BA.2 compared to ancestral and Delta variant strains. In addition, we found that some therapeutic monoclonal antibodies (REGN10987/REGN10933, COV2-2196/COV2-2130, and S309) and antiviral drugs (molnupiravir, nirmatrelvir, and S-217622) can restrict viral infection in the respiratory organs of hamsters infected with BA.2. These findings suggest that the replication and pathogenicity of BA.2 is comparable to that of BA.1 in rodents and that several therapeutic monoclonal antibodies and antiviral compounds are effective against Omicron/BA.2 variants.
Subject(s)
COVID-19ABSTRACT
The spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the major antigen stimulating the host's protective immune response. A new SARS-CoV-2 variant, designated Omicron, first identified in South Africa and possess many spike protein mutations. Here, we assessed the efficacy of therapeutic monoclonal antibodies (mAbs) against an Omicron variant in Syrian hamsters. Of the mAbs tested (i.e., REGN10987/REGN10933, COV2-2196/COV2-2130, and S309), only COV2-2196/COV2-2130 efficiently inhibited the replication of the Omicron variant in the lungs of hamsters. We also found that treatment of Omicron-infected hamsters with molnupiravir (an inhibitor of the RNA-dependent RNA polymerase of SARS-CoV-2) or S-217622 (an inhibitor of the main protease of SARS-CoV-2) led to a dramatic reduction of virus replication in the lungs. These findings suggest that treatment with the mAb combination COV2-2196/COV2-2130 or the antiviral compounds molnupiravir and S-217622 may be effective against the Omicron variants.
Subject(s)
Coronavirus InfectionsABSTRACT
Despite the development and deployment of antibody and vaccine countermeasures, rapidly-spreading SARS-CoV-2 variants with mutations at key antigenic sites in the spike protein jeopardize their efficacy. The recent emergence of B.1.1.529, the Omicron variant1,2, which has more than 30 mutations in the spike protein, has raised concerns for escape from protection by vaccines and therapeutic antibodies. A key test for potential countermeasures against B.1.1.529 is their activity in pre-clinical rodent models of respiratory tract disease. Here, using the collaborative network of the SARS-CoV-2 Assessment of Viral Evolution (SAVE) program of the National Institute of Allergy and Infectious Diseases (NIAID), we evaluated the ability of multiple B.1.1.529 Omicron isolates to cause infection and disease in immunocompetent and human ACE2 (hACE2) expressing mice and hamsters. Despite modeling and binding data suggesting that B.1.1.529 spike can bind more avidly to murine ACE2, we observed attenuation of infection in 129, C57BL/6, and BALB/c mice as compared with previous SARS-CoV-2 variants, with limited weight loss and lower viral burden in the upper and lower respiratory tracts. Although K18-hACE2 transgenic mice sustained infection in the lungs, these animals did not lose weight. In wild-type and hACE2 transgenic hamsters, lung infection, clinical disease, and pathology with B.1.1.529 also were milder compared to historical isolates or other SARS-CoV-2 variants of concern. Overall, experiments from multiple independent laboratories of the SAVE/NIAID network with several different B.1.1.529 isolates demonstrate attenuated lung disease in rodents, which parallels preliminary human clinical data.
Subject(s)
Respiratory Tract Diseases , Lung Diseases , Communicable DiseasesABSTRACT
Despite various attempts to treat SARS-CoV-2-infected patients with COVID-19-convalescent plasmas, neither appropriate approach nor clinical utility has been established. We examined the efficacy of administration of highly-neutralizing COVID-19-convalescent plasma (hn-plasmas) and such plasma-derived IgG administration using the Syrian hamster COVID-19 model. Two hn-plasmas, which were in the best 1% of 340 neutralizing-activity-determined convalescent plasma samples, were intraperitoneally administered to SARS-CoV-2-infected hamsters, resulting in significant reduction of viral titers in lungs by up to 32-fold as compared to the viral titers in hamsters receiving control non-neutralizing plasma, while with two moderately neutralizing plasmas (mn-plasmas) administered, viral titer reduction was by up to 6-fold. IgG fractions purified from the two hn-plasmas also reduced viral titers in lungs than those from the two mn-plasmas. The severity of lung lesions seen in hamsters receiving hn-plasmas was minimal to moderate as assessed using micro-computerized tomography, which histological examination confirmed. Western blotting revealed that all four COVID-19-convalescent-plasmas variably contained antibodies against SARS-CoV-2 components including the receptor-binding domain and S1 domain. The present data strongly suggest that administering potent-neutralizing-activity-confirmed COVID-19-convalescent plasmas would be efficacious in treating patients with COVID-19.
Subject(s)
COVID-19 , Severe Acute Respiratory Syndrome , Lung DiseasesABSTRACT
In 2020, two mRNA-based vaccines, encoding the full length of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein, have been introduced for control of the coronavirus disease (COVID-19) pandemic1,2. However, reactogenicity, such as fever, caused by innate immune responses to the vaccine formulation remains to be improved. Here, we optimized a lipid nanoparticle (LNP)-based mRNA vaccine candidate, encoding the SARS-CoV-2 spike protein receptor-binding domain (LNP-mRNA-RBD), which showed improved immunogenicity by removing reactogenic materials from the vaccine formulation and protective potential against SARS-CoV-2 infection in cynomolgus macaques. LNP-mRNA-RBD induced robust antigen-specific B cells and follicular helper T cells in the BALB/c strain but not in the C57BL/6 strain; the two strains have contrasting abilities to induce type I interferon production by dendritic cells. Removal of reactogenic materials from original synthesized mRNA by HPLC reduced type I interferon (IFN) production by dendritic cells, which improved immunogenicity. Immunization of cynomolgus macaques with an LNP encapsulating HPLC-purified mRNA induced robust anti-RBD IgG in the plasma and in various mucosal areas, including airways, thereby conferring protection against SARS-CoV-2 infection. Therefore, fine-tuning the balance between the immunogenic and reactogenic activity of mRNA-based vaccine formulations may offer safer and more efficacious outcomes.
Subject(s)
Coronavirus Infections , Fever , COVID-19ABSTRACT
Although infection by SARS-CoV-2, the causative agent of COVID-19, is spreading rapidly worldwide, no drug has been shown to be sufficiently effective for treating COVID-19. We previously found that nafamostat mesylate, an existing drug used for disseminated intravascular coagulation (DIC), effectively blocked MERS-CoV S protein-initiated cell fusion by targeting TMPRSS2, and inhibited MERS-CoV infection of human lung epithelium-derived Calu-3 cells. Here we established a quantitative fusion assay dependent on SARS-CoV-2 S protein, ACE2 and TMPRSS2, and found that nafamostat mesylate potently inhibited the fusion while camostat mesylate was about 10-fold less active. Furthermore, nafamostat mesylate blocked SARS-CoV-2 infection of Calu-3 cells with an EC50 around 10 nM, which is below its average blood concentration after intravenous administration through continuous infusion. These findings, together with accumulated clinical data regarding its safety, make nafamostat a likely candidate drug to treat COVID-19.