The Omicron variant is highly resistant against antibody-mediated neutralization: Implications for control of the COVID-19 pandemic.

The rapid spread of the SARS-CoV-2 Omicron variant suggests that the virus might become globally dominant. Further, the high number of mutations in the viral spike protein raised concerns that the virus might evade antibodies induced by infection or vaccination. Here, we report that the Omicron spike was resistant against most therapeutic antibodies but remained susceptible to inhibition by sotrovimab. Similarly, the Omicron spike evaded neutralization by antibodies from convalescent patients or individuals vaccinated with the BioNTech-Pfizer vaccine (BNT162b2) with 12- to 44-fold higher efficiency than the spike of the Delta variant. Neutralization of the Omicron spike by antibodies induced upon heterologous ChAdOx1 (Astra Zeneca-Oxford)/BNT162b2 vaccination or vaccination with three doses of BNT162b2 was more efficient, but the Omicron spike still evaded neutralization more efficiently than the Delta spike. These findings indicate that most therapeutic antibodies will be ineffective against the Omicron variant and that double immunization with BNT162b2 might not adequately protect against severe disease induced by this variant.

SARS-CoV-2 variants B.1.351 and P.1 escape from neutralizing antibodies.

The global spread of SARS-CoV-2/COVID-19 is devastating health systems and economies worldwide. Recombinant or vaccine-induced neutralizing antibodies are used to combat the COVID-19 pandemic. However, the recently emerged SARS-CoV-2 variants B.1.1.7 (UK), B.1.351 (South Africa), and P.1 (Brazil) harbor mutations in the viral spike (S) protein that may alter virus-host cell interactions and confer resistance to inhibitors and antibodies. Here, using pseudoparticles, we show that entry of all variants into human cells is susceptible to blockade by the entry inhibitors soluble ACE2, Camostat, EK-1, and EK-1-C4. In contrast, entry of the B.1.351 and P.1 variant was partially (Casirivimab) or fully (Bamlanivimab) resistant to antibodies used for COVID-19 treatment. Moreover, entry of these variants was less efficiently inhibited by plasma from convalescent COVID-19 patients and sera from BNT162b2-vaccinated individuals. These results suggest that SARS-CoV-2 may escape neutralizing antibody responses, which has important implications for efforts to contain the pandemic.

SARS-CoV-2 Cell Entry Depends on ACE2 and TMPRSS2 and Is Blocked by a Clinically Proven Protease Inhibitor.

The recent emergence of the novel, pathogenic SARS-coronavirus 2 (SARS-CoV-2) in China and its rapid national and international spread pose a global health emergency. Cell entry of coronaviruses depends on binding of the viral spike (S) proteins to cellular receptors and on S protein priming by host cell proteases. Unravelling which cellular factors are used by SARS-CoV-2 for entry might provide insights into viral transmission and reveal therapeutic targets. Here, we demonstrate that SARS-CoV-2 uses the SARS-CoV receptor ACE2 for entry and the serine protease TMPRSS2 for S protein priming. A TMPRSS2 inhibitor approved for clinical use blocked entry and might constitute a treatment option. Finally, we show that the sera from convalescent SARS patients cross-neutralized SARS-2-S-driven entry. Our results reveal important commonalities between SARS-CoV-2 and SARS-CoV infection and identify a potential target for antiviral intervention.

Chloroquine does not inhibit infection of human lung cells with SARS-CoV-2.

The coronavirus disease 2019 (COVID-19) pandemic, which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been associated with more than 780,000 deaths worldwide (as of 20 August 2020). To develop antiviral interventions quickly, drugs used for the treatment of unrelated diseases are currently being repurposed to treat COVID-19. Chloroquine is an anti-malaria drug that is used for the treatment of COVID-19 as it inhibits the spread of SARS-CoV-2 in the African green monkey kidney-derived cell line Vero1-3. Here we show that engineered expression of TMPRSS2, a cellular protease that activates SARS-CoV-2 for entry into lung cells4, renders SARS-CoV-2 infection of Vero cells insensitive to chloroquine. Moreover, we report that chloroquine does not block infection with SARS-CoV-2 in the TMPRSS2-expressing human lung cell line Calu-3. These results indicate that chloroquine targets a pathway for viral activation that is not active in lung cells and is unlikely to protect against the spread of SARS-CoV-2 in and between patients.

Influence of antiresorptive/antiangiogenic therapy on the surgical treatment outcomes of experimentally induced peri-implantitis lesions.

OBJECTIVE: To investigate the influence of various antiresorptive and antiangiogenic medications on the resolution of experimentally induced peri-implantitis lesions after different surgical treatment approaches. MATERIALS AND METHODS: Forty-eight albino rats randomly received a dual application of the following medications: (1) amino-bisphosphonate (zoledronate (Zo)) (n = 8), (2) RANKL inhibitor (denosumab (De)) (n = 8), (3) antiangiogenic (bevacizumab (Be)) (n = 8), (4) Zo + Be (n = 8), (5) De + Be (n = 8), or (6) no medication (control (Co)) (n = 8). Ligature-induced peri-implantitis lesions were established at 2 maxillary implants over 16 weeks. Afterward, animals were randomly treated either with open flap debridement (OFD) or reconstructive therapy (RT). Treatment procedures were followed by a 12-week healing period. The histological outcomes included residual defect length (DL); defect width (DW) at the bone crest (BC-DW); 25%, 50%, and 75% of the DL; and areas of inflammatory cell infiltrate (ICT). When present, areas of bone sequester (BS) were assessed considering the animal as a statistical unit. RESULTS: A total of 21 animals were analyzed (Zo: RT = 3, OFD = 1; De: RT = 3, OFD = 2; Be: OFD = 1; Zo + Be: RT = 2, OFD = 2; Co: RT = 3, OFD = 2). Implant loss rates were comparable among the experimental groups. Except for the 25% and 75% DW values that were significantly higher in the Zo + Be group compared to the Co group (p = 0.04 and p = 0.03, respectively), no significant differences were found among the experimental groups for the DL (lowest-Be: 0.56 mm; highest-Co: 1.05 mm), BC-DW (lowest-De: 0.86 mm, highest-Co: 1.07 mm), 50% DW (lowest-De: 0.86 mm; highest-Be + Zo: 1.29 mm), and ICT (lowest-Be: 0.56 mm2; highest-Be + Zo: 1.65 mm2). All groups, except for the Zo and Be following RT, showed presence of BS. CONCLUSIONS: The present findings did not reveal a marked effect of various antiresorptive/antiangiogenic medications on the resolution of experimentally induced peri-implantitis lesions, regardless of the surgical approach employed (OFD and RT). CLINICAL RELEVANCE: Resolution of peri-implantitis lesions may not be affected by the investigated antiresorptive/antiangiogenic medications.

Alternatives to animal models and their application in the discovery of species susceptibility to SARS-CoV-2 and other respiratory infectious pathogens: A review.

The emergence of the coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) inspired rapid research efforts targeting the host range, pathogenesis and transmission mechanisms, and the development of antiviral strategies. Genetically modified mice, rhesus macaques, ferrets, and Syrian golden hamsters have been frequently used in studies of pathogenesis and efficacy of antiviral compounds and vaccines. However, alternatives to in vivo experiments, such as immortalized cell lines, primary respiratory epithelial cells cultured at an air-liquid interface, stem/progenitor cell-derived organoids, or tissue explants, have also been used for isolation of SARS-CoV-2, investigation of cytopathic effects, and pathogen-host interactions. Moreover, initial proof-of-concept studies for testing therapeutic agents can be performed with these tools, showing that animal-sparing cell culture methods could significantly reduce the need for animal models in the future, following the 3R principles of replace, reduce, and refine. So far, only few studies using animal-derived primary cells or tissues have been conducted in SARS-CoV-2 research, although natural infection has been shown to occur in several animal species. Therefore, the need for in-depth investigations on possible interspecies transmission routes and differences in susceptibility to SARS-CoV-2 is urgent. This review gives an overview of studies employing alternative culture systems like primary cell cultures, tissue explants, or organoids for investigations of the pathophysiology and reverse zoonotic potential of SARS-CoV-2 in animals. In addition, future possibilities of SARS-CoV-2 research in animals, including previously neglected methods like the use of precision-cut lung slices, will be outlined.

The Amino Acid at Position 8 of the Proteolytic Cleavage Site of the Mumps Virus Fusion Protein Affects Viral Proteolysis and Fusogenicity.

The mumps virus (MuV) fusion protein (F) plays a crucial role for the entry process and spread of infection by mediating fusion between viral and cellular membranes as well as between infected and neighboring cells, respectively. The fusogenicity of MuV differs depending on the strain and might correlate with the virulence; however, it is unclear which mechanisms contribute to the differentiated fusogenicity. The cleavage motif of MuV F is highly conserved among all strains, except the amino acid residue at position 8 (P8) that shows a certain variability with a total of four amino acid variants (leucine [L], proline [P], serine [S], and threonine [T]). We demonstrate that P8 affects the proteolytic processing and the fusogenicity of MuV F. The presence of L or S at P8 resulted in a slower proteolysis of MuV F by furin and a reduced ability to mediate cell-cell fusion. However, virus-cell fusion was more efficient for F proteins harboring L or S at P8, suggesting that P8 contributes to the mechanism of viral spread: P and T enable a rapid spread of infection by cell-to-cell fusion, whereas viruses harboring L or S at P8 spread preferentially by the release of infectious viral particles. Our study provides novel insights into the fusogenicity of MuV and its influence on the mechanisms of virus spread within infected tissues. Assuming a correlation between MuV fusogenicity and virulence, sequence information on the amino acid residue at P8 might be helpful to estimate the virulence of circulating and emerging strains.IMPORTANCE Mumps virus (MuV) is the causative agent of the highly infectious disease mumps. Mumps is mainly associated with mild symptoms, but severe complications such as encephalitis, meningitis, or orchitis can also occur. There is evidence that the virulence of different MuV strains and variants might correlate with the ability of the fusion protein (F) to mediate cell-to-cell fusion. However, the relation between virulence and fusogenicity or the mechanisms responsible for the varied fusogenicity of different MuV strains are incompletely understood. Here, we focused on the amino acid residue at position 8 (P8) of the proteolytic cleavage site of MuV F, because this amino acid residue shows a striking variability depending on the genotype of MuV. The P8 residue has a significant effect on the proteolytic processing and fusogenicity of MuV F and might thereby determine the route of viral spread within infected tissues.

The Upper Respiratory Tract of Felids Is Highly Susceptible to SARS-CoV-2 Infection.

Natural or experimental infection of domestic cats and virus transmission from humans to captive predatory cats suggest that felids are highly susceptible to SARS-CoV-2 infection. However, it is unclear which cells and compartments of the respiratory tract are infected. To address this question, primary cell cultures derived from the nose, trachea, and lungs of cat and lion were inoculated with SARS-CoV-2. Strong viral replication was observed for nasal mucosa explants and tracheal air-liquid interface cultures, whereas replication in lung slices was less efficient. Infection was mainly restricted to epithelial cells and did not cause major pathological changes. Detection of high ACE2 levels in the nose and trachea but not lung further suggests that susceptibility of feline tissues to SARS-CoV-2 correlates with ACE2 expression. Collectively, this study demonstrates that SARS-CoV-2 can efficiently replicate in the feline upper respiratory tract ex vivo and thus highlights the risk of SARS-CoV-2 spillover from humans to felids.

Tetherin Inhibits Nipah Virus but Not Ebola Virus Replication in Fruit Bat Cells.

Ebola virus (EBOV) and Nipah virus (NiV) infection of humans can cause fatal disease and constitutes a public health threat. In contrast, EBOV and NiV infection of fruit bats, the putative (EBOV) or proven (NiV) natural reservoir, is not associated with disease, and it is currently unknown how these animals control the virus. The human interferon (IFN)-stimulated antiviral effector protein tetherin (CD317, BST-2) blocks release of EBOV- and NiV-like particles from cells and is counteracted by the EBOV glycoprotein (GP). In contrast, it is unknown whether fruit bat tetherin restricts virus infection and is susceptible to GP-driven antagonism. Here, we report the sequence of fruit bat tetherin and show that its expression is IFN stimulated and associated with strong antiviral activity. Moreover, we demonstrate that EBOV-GP antagonizes tetherin orthologues of diverse species but fails to efficiently counteract fruit bat tetherin in virus-like particle (VLP) release assays. However, unexpectedly, tetherin was dispensable for robust IFN-mediated inhibition of EBOV spread in fruit bat cells. Thus, the VLP-based model systems mimicking tetherin-mediated inhibition of EBOV release and its counteraction by GP seem not to adequately reflect all aspects of EBOV release from IFN-stimulated fruit bat cells, potentially due to differences in tetherin expression levels that could not be resolved by the present study. In contrast, tetherin expression was essential for IFN-dependent inhibition of NiV infection, demonstrating that IFN-induced fruit bat tetherin exerts antiviral activity and may critically contribute to control of NiV and potentially other highly virulent viruses in infected animals.IMPORTANCE Ebola virus and Nipah virus (EBOV and NiV) can cause fatal disease in humans. In contrast, infected fruit bats do not develop symptoms but can transmit the virus to humans. Why fruit bats but not humans control infection is largely unknown. Tetherin is an antiviral host cell protein and is counteracted by the EBOV glycoprotein in human cells. Here, employing model systems, we show that tetherin of fruit bats displays higher antiviral activity than human tetherin and is largely resistant against counteraction by the Ebola virus glycoprotein. Moreover, we demonstrate that induction of tetherin expression is critical for interferon-mediated inhibition of NiV but, for at present unknown reasons, not EBOV spread in fruit bat cells. Collectively, our findings identify tetherin as an antiviral effector of innate immune responses in fruit bats, which might allow these animals to control infection with NiV and potentially other viruses that cause severe disease in humans.

Human Infections by Non-Rodent-Associated Hantaviruses in Africa.

Various hantaviruses have been discovered in unconventional hosts (shrews and bats) in Africa. Up to now, it was unknown whether these viruses pose a threat for human health. In this study, using newly established serological assays, we demonstrated evidence of shrew-borne hantavirus infections in humans from Côte d'Ivoire and Gabon.

Recombinant mumps viruses expressing the batMuV fusion glycoprotein are highly fusion active and neurovirulent.

A recent study reported the detection of a bat-derived virus (BatPV/Epo_spe/AR1/DCR/2009, batMuV) with phylogenetic relatedness to human mumps virus (hMuV). Since all efforts to isolate infectious batMuV have reportedly failed, we generated recombinant mumps viruses (rMuVs) in which the open reading frames (ORFs) of the fusion (F) and haemagglutinin-neuraminidase (HN) glycoproteins of an hMuV strain were replaced by the corresponding ORFs of batMuV. The batMuV F and HN proteins were successfully incorporated into viral particles and the resultant chimeric virus was able to mediate infection of Vero cells. Distinct differences were observed between the fusogenicity of rMuVs expressing one or both batMuV glycoproteins: viruses expressing batMuV F were highly fusogenic, regardless of the origin of HN. In contrast, rMuVs expressing human F and bat-derived HN proteins were less fusogenic compared to hMuV. The growth kinetics of chimeric MuVs expressing batMuV HN in combination with either hMuV or batMuV F were similar to that of the backbone virus, whereas a delay in virus replication was obtained for rMuVs harbouring batMuV F and hMuV HN. Replacement of the hMuV F and HN genes or the HN gene alone by the corresponding batMuV genes led to a slight reduction in neurovirulence of the highly neurovirulent backbone strain. Neutralizing antibodies inhibited infection mediated by all recombinant viruses generated. Furthermore, group IV anti-MuV antibodies inhibited the neuraminidase activity of bat-derived HN. Our study reports the successful generation of chimeric MuVs expressing the F and HN proteins of batMuV, providing a means for further examination of this novel batMuV.

Functional properties and genetic relatedness of the fusion and hemagglutinin-neuraminidase proteins of a mumps virus-like bat virus.

UNLABELLED: A bat virus with high phylogenetic relatedness to human mumps virus (MuV) was identified recently at the nucleic acid level. We analyzed the functional activities of the hemagglutinin-neuraminidase (HN) and the fusion (F) proteins of the bat virus (batMuV) and compared them to the respective proteins of a human isolate. Transfected cells expressing the F and HN proteins of batMuV were recognized by antibodies directed against these proteins of human MuV, indicating that both viruses are serologically related. Fusion, hemadsorption, and neuraminidase activities were demonstrated for batMuV, and either bat-derived protein could substitute for its human MuV counterpart in inducing syncytium formation when coexpressed in different mammalian cell lines, including chiropteran cells. Cells expressing batMuV glycoproteins were shown to have lower neuraminidase activity. The syncytia were smaller, and they were present in lower numbers than those observed after coexpression of the corresponding glycoproteins of a clinical isolate of MuV (hMuV). The phenotypic differences in the neuraminidase and fusion activity between the glycoproteins of batMuV and hMuV are explained by differences in the expression level of the HN and F proteins of the two viruses. In the case of the F protein, analysis of chimeric proteins revealed that the signal peptide of the bat MuV fusion protein is responsible for the lower surface expression. These results indicate that the surface glycoproteins of batMuV are serologically and functionally related to those of hMuV, raising the possibility of bats as a reservoir for interspecies transmission. IMPORTANCE: The recently described MuV-like bat virus is unique among other recently identified human-like bat-associated viruses because of its high sequence homology (approximately 90% in most genes) to its human counterpart. Although it is not known if humans can be infected by batMuV, the antigenic relatedness between the bat and human forms of the virus suggests that humans carrying neutralizing antibodies against MuV are protected from infection by batMuV. The close functional relationship between MuV and batMuV is demonstrated by cooperation of the respective HN and F proteins to induce syncytium formation in heterologous expression studies. An interesting feature of the glycoproteins of batMuV is the downregulation of the fusion activity by the signal peptide of F, which has not been reported for other paramyxoviruses. These results are important contributions for risk assessment and for a better understanding of the replication strategy of batMuV.

Attachment protein G of an African bat henipavirus is differentially restricted in chiropteran and nonchiropteran cells.

Henipaviruses are associated with pteropodid reservoir hosts. The glycoproteins G and F of an African henipavirus (strain M74) have been reported to induce syncytium formation in kidney cells derived from a Hypsignathus monstrosus bat (HypNi/1.1) but not in nonchiropteran BHK-21 and Vero76 cells. Here, we show that syncytia are also induced in two other pteropodid cell lines from Hypsignathus monstrosus and Eidolon helvum bats upon coexpression of the M74 glycoproteins. The G protein was transported to the surface of transfected chiropteran cells, whereas surface expression in the nonchiropteran cells was detectable only in a fraction of cells. In contrast, the G protein of Nipah virus is transported efficiently to the surface of both chiropteran and nonchiropteran cells. Even in chiropteran cells, M74-G was predominantly expressed in the endoplasmic reticulum (ER), as indicated by colocalization with marker proteins. This result is consistent with the finding that all N-glycans of the M74-G proteins are of the mannose-rich type, as indicated by sensitivity to endo H treatment. These data indicate that the surface transport of M74-G is impaired in available cell culture systems, with larger amounts of viral glycoprotein present on chiropteran cells than on nonchiropteran cells. The restricted surface expression of M74-G explains the reduced fusion activity of the glycoproteins of the African henipavirus. Our results suggest strategies for the isolation of infectious viruses, which is necessary to assess the risk of zoonotic virus transmission. Importance: Henipaviruses are highly pathogenic zoonotic viruses associated with pteropodid bat hosts. Whether the recently described African bat henipaviruses have a zoonotic potential as high as that of their Asian and Australian relatives is unknown. We show that surface expression of the attachment protein G of an African henipavirus, M74, is restricted in comparison to the G protein expression of the highly pathogenic Nipah virus. Transport to the cell surface is more restricted in nonchiropteran cells than it is in chiropteran cells, explaining the differential fusion activity of the M74 surface proteins in these cells. Our results imply that surface expression of viral glycoproteins may serve as a major marker to assess the zoonotic risk of emerging henipaviruses.

Characterization of African bat henipavirus GH-M74a glycoproteins.

In recent years, novel henipavirus-related sequences have been identified in bats in Africa. To evaluate the potential of African bat henipaviruses to spread in non-bat mammalian cells, we compared the biological functions of the surface glycoproteins G and F of the prototype African henipavirus GH-M74a with those of the glycoproteins of Nipah virus (NiV), a well-characterized pathogenic member of the henipavirus genus. Glycoproteins are central determinants for virus tropism, as efficient binding of henipavirus G proteins to cellular ephrin receptors and functional expression of fusion-competent F proteins are indispensable prerequisites for virus entry and cell-to-cell spread. In this study, we analysed the ability of the GH-M74a G and F proteins to cause cell-to-cell fusion in mammalian cell types readily permissive to NiV or Hendra virus infections. Except for limited syncytium formation in a bat cell line derived from Hypsignathus monstrosus, HypNi/1.1 cells, we did not observe any fusion. The highly restricted fusion activity was predominantly due to the F protein. Whilst GH-M74a G protein was found to interact with the main henipavirus receptor ephrin-B2 and induced syncytia upon co-expression with heterotypic NiV F protein, GH-M74a F protein did not cause evident fusion in the presence of heterotypic NiV G protein. Pulse-chase and surface biotinylation analyses revealed delayed F cleavage kinetics with a reduced expression of cleaved and fusion-active GH-M74a F protein on the cell surface. Thus, the F protein of GH-M74a showed a functional defect that is most likely caused by impaired trafficking leading to less efficient proteolytic activation and surface expression.

Surface glycoproteins of an African henipavirus induce syncytium formation in a cell line derived from an African fruit bat, Hypsignathus monstrosus.

Serological screening and detection of genomic RNA indicates that members of the genus Henipavirus are present not only in Southeast Asia but also in African fruit bats. We demonstrate that the surface glycoproteins F and G of an African henipavirus (M74) induce syncytium formation in a kidney cell line derived from an African fruit bat, Hypsignathus monstrosus. Despite a less broad cell tropism, the M74 glycoproteins show functional similarities to glycoproteins of Nipah virus.

SARS-CoV-2 infection induces adaptive NK cell responses by spike protein-mediated induction of HLA-E expression.

HLA-E expression plays a central role for modulation of NK cell function by interaction with inhibitory NKG2A and stimulatory NKG2C receptors on canonical and adaptive NK cells, respectively. Here, we demonstrate that infection of human primary lung tissue with SARS-CoV-2 leads to increased HLA-E expression and show that processing of the peptide YLQPRTFLL from the spike protein is primarily responsible for the strong, dose-dependent increase of HLA-E. Targeting the peptide site within the spike protein revealed that a single point mutation was sufficient to abrogate the increase in HLA-E expression. Spike-mediated induction of HLA-E differentially affected NK cell function: whereas degranulation, IFN-γ production, and target cell cytotoxicity were enhanced in NKG2C+ adaptive NK cells, effector functions were inhibited in NKG2A+ canonical NK cells. Analysis of a cohort of COVID-19 patients in the acute phase of infection revealed that adaptive NK cells were induced irrespective of the HCMV status, challenging the paradigm that adaptive NK cells are only generated during HCMV infection. During the first week of hospitalization, patients exhibited a selective increase of early NKG2C+CD57- adaptive NK cells whereas mature NKG2C+CD57+ cells remained unchanged. Further analysis of recovered patients suggested that the adaptive NK cell response is primarily driven by a wave of early adaptive NK cells during acute infection that wanes once the infection is cleared. Together, this study suggests that NK cell responses to SARS-CoV-2 infection are majorly influenced by the balance between canonical and adaptive NK cells via the HLA-E/NKG2A/C axis.

Correction to "Cathepsin-Targeting SARS-CoV-2 Inhibitors: Design, Synthesis, and Biological Activity".

[This corrects the article DOI: 10.1021/acsptsci.3c00313.].

Cathepsin-Targeting SARS-CoV-2 Inhibitors: Design, Synthesis, and Biological Activity.

Cathepsins (Cats) are proteases that mediate the successful entry of SARS-CoV-2 into host cells. We designed and synthesized a tailored series of 21 peptidomimetics and evaluated their inhibitory activity against human cathepsins L, B, and S. Structural diversity was realized by combinations of different C-terminal warhead functions and N-terminal capping groups, while a central Leu-Phe fragment was maintained. Several compounds were identified as promising cathepsin L and S inhibitors with Ki values in the low nanomolar to subnanomolar range, for example, the peptide aldehydes 9a and 9b (9a, 2.67 nM, CatL; 0.455 nM, CatS; 9b, 1.76 nM, CatL; 0.512 nM, CatS). The compounds' inhibitory activity against the main protease of SARS-CoV-2 (Mpro) was additionally investigated. Based on the results at CatL, CatS, and Mpro, selected inhibitors were subjected to investigations of their antiviral activity in cell-based assays. In particular, the peptide nitrile 11e exhibited promising antiviral activity with an EC50 value of 38.4 nM in Calu-3 cells without showing cytotoxicity. High metabolic stability and favorable pharmacokinetic properties make 11e suitable for further preclinical development.

Filamentous fungus-produced human monoclonal antibody provides protection against SARS-CoV-2 in hamster and non-human primate models.

Monoclonal antibodies are an increasingly important tool for prophylaxis and treatment of acute virus infections like SARS-CoV-2 infection. However, their use is often restricted due to the time required for development, variable yields and high production costs, as well as the need for adaptation to newly emerging virus variants. Here we use the genetically modified filamentous fungus expression system Thermothelomyces heterothallica (C1), which has a naturally high biosynthesis capacity for secretory enzymes and other proteins, to produce a human monoclonal IgG1 antibody (HuMab 87G7) that neutralises the SARS-CoV-2 variants of concern (VOCs) Alpha, Beta, Gamma, Delta, and Omicron. Both the mammalian cell and C1 produced HuMab 87G7 broadly neutralise SARS-CoV-2 VOCs in vitro and also provide protection against VOC Omicron in hamsters. The C1 produced HuMab 87G7 is also able to protect against the Delta VOC in non-human primates. In summary, these findings show that the C1 expression system is a promising technology platform for the development of HuMabs in preventive and therapeutic medicine.