Neutralizing antibodies that target the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein are among the most promising approaches against COVID-19 1,2 . A bispecific IgG1-like molecule (CoV-X2) has been developed on the basis of C121 and C135, two antibodies derived from donors who had recovered from COVID-19 3 . Here we show that CoV-X2 simultaneously binds two independent sites on the RBD and, unlike its parental antibodies, prevents detectable spike binding to the cellular receptor of the virus, angiotensin-converting enzyme 2 (ACE2). Furthermore, CoV-X2 neutralizes wild-type SARS-CoV-2 and its variants of concern, as well as escape mutants generated by the parental monoclonal antibodies. We also found that in a mouse model of SARS-CoV-2 infection with lung inflammation, CoV-X2 protects mice from disease and suppresses viral escape. Thus, the simultaneous targeting of non-overlapping RBD epitopes by IgG-like bispecific antibodies is feasible and effective, and combines the advantages of antibody cocktails with those of single-molecule approaches.The COVID-19 pandemic has prompted substantial efforts to develop effective countermeasures against SARS-CoV-2. Preclinical data and phase-III clinical studies indicate that monoclonal antibodies could be effectively deployed for prevention or treatment during the viral symptoms phase of the disease 1,2 . Cocktails of two or more monoclonal antibodies are preferred over a single antibody as these cocktails result in increased efficacy and the prevention of viral escape. However, this approach requires increased manufacturing costs and volumes, which are problematic at a time when the supply chain is under pressure to meet the high demand for COVID-19 therapeutic agents, vaccines and biologics in general 4 . Cocktails also complicate formulation 5,6 and hinder strategies such as antibody delivery by viral vectors or by nonvectored nucleic acids 7,8 . One alternative is to use multispecific antibodies, which have the advantages of cocktails and single-molecule strategies.To this end, we used structural information 9 and computational simulations to design bispecific antibodies that would simultaneously bind to (i) independent sites on the same RBD and (ii) distinct RBDs on a spike (S) trimer. We evaluated several designs using atomistic molecular dynamics simulations, and produced four constructs: of these, CoV-X2 was the most potent neutralizer of SARS-CoV-2 pseudovirus, and had a half-maximal inhibitory concentration (IC 50 ) of 0.04 nM (5.8 ng ml −1 ) (Extended Data Fig. 1). CoV-X2 is a human-derived IgG1-like bispecific antibody in the CrossMAb format 10 that is the result of the combination of the Fragment antigen binding (Fab) of the monoclonal antibodies C121 and C135, which are two potent neutralizers of SARS-CoV-2 3 . Structural predictions showed that CoV-X2-but not its parental monoclonal antibodies-can bind bivalently to all RBD conformations on the S trimer, which prevents the binding of ACE2 receptor 11 (Fig. 1a, Extended Data Fig. 2).CoV-X2 bou...

There is growing evidence that Zika virus (ZIKV) can cause devastating infant brain defects and other neurological disorders in humans. However, no specific antiviral therapy is available at present. We tested a series of 2'-C- or 2'-O-methyl-substituted nucleosides, 2'-C-fluoro-2'-C-methyl-substituted nucleosides, 3'-O-methyl-substituted nucleosides, 3'-deoxynucleosides, derivatives with 4'-C-azido substitution, heterobase-modified nucleosides, and neplanocins for their ability to inhibit ZIKV replication in cell culture. Antiviral activity was identified when 2'-C-methylated nucleosides were tested, suggesting that these compounds might represent promising lead candidates for further development of specific antivirals against ZIKV.

Tick-borne encephalitis (TBE), a disease caused by tick-borne encephalitis virus (TBEV), represents the most important flaviviral neural infection in Europe and north-eastern Asia. In the central nervous system (CNS), neurons are the primary target for TBEV infection; however, infection of non-neuronal CNS cells, such as astrocytes, is not well understood. In this study, we investigated the interaction between TBEV and primary human astrocytes. We report for the first time, to the best of our knowledge, that primary human astrocytes are sensitive to TBEV infection, although the infection did not affect their viability. The infection induced a marked increase in the expression of glial fibrillary acidic protein, a marker of astrocyte activation. In addition, expression of matrix metalloproteinase 9 and several key pro-inflammatory cytokines/chemokines (e.g. tumour necrosis factor a, interferon a, interleukin (IL)-1b, IL-6, IL-8, interferon c-induced protein 10, macrophage inflammatory protein, but not monocyte chemotactic protein 1) was upregulated. Moreover, we present a detailed description of morphological changes in TBEV-infected cells, as investigated using three-dimensional electron tomography. Several novel ultrastructural changes were observed, including the formation of unique tubule-like structures of 17.9 ±0.15 nm diameter with associated viral particles and/or virus-induced vesicles and located in the rough endoplasmic reticulum of the TBEV-infected cells. This is the first demonstration that TBEV infection activates primary human astrocytes. The infected astrocytes might be a potential source of pro-inflammatory cytokines in the TBEV-infected brain, and might contribute to the TBEVinduced neurotoxicity and blood-brain barrier breakdown that occurs during TBE. The neuropathological significance of our observations is also discussed.

Epidemics of tick-borne encephalitis involving thousands of humans occur annually in the forested regions of Europe and Asia. Despite the importance of this disease, the underlying basis for the development of encephalitis remains undefined. Here, we prove the key role of CD8(+) T-cells in the immunopathology of tick-borne encephalitis, as demonstrated by prolonged survival of SCID or CD8(-/-) mice, following infection, when compared with immunocompetent mice or mice with adoptively transferred CD8(+) T-cells. The results imply that tick-borne encephalitis is an immunopathological disease and that the inflammatory reaction significantly contributes to the fatal outcome of the infection.

Tick-borne encephalitis virus (TBEV) causes serious, potentially fatal neurological infections that affect humans in endemic regions of Europe and Asia. Neurons are the primary target for TBEV infection in the central nervous system. However, knowledge about this viral infection and virus-induced neuronal injury is fragmental. Here, we directly examined the pathology that occurs after TBEV infection in human primary neurons. We exploited the advantages of advanced high-pressure freezing and freeze-substitution techniques to achieve optimal preservation of infected cell architecture. Electron tomographic (ET) reconstructions elucidated high-resolution 3D images of the proliferating endoplasmic reticulum, and individual tubule-like structures of different diameters in the endoplasmic reticulum cisternae of single cells. ET revealed direct connections between the tubule-like structures and viral particles in the endoplasmic reticulum. Furthermore, ET showed connections between cellular microtubules and vacuoles that harbored the TBEV virions in neuronal extensions. This study was the first to characterize the 3D topographical organization of membranous whorls and autophagic vacuoles in TBEV-infected human neurons. The functional importance of autophagy during TBEV replication was studied in human neuroblastoma cells; stimulation of autophagy resulted in significantly increased dose-dependent TBEV production, whereas the inhibition of autophagy showed a profound, dose-dependent decrease of the yield of infectious virus.

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BackgroundThe clinical course of tick-borne encephalitis (TBE), a disease caused by TBE virus, ranges from asymptomatic or mild influenza-like infection to severe debilitating encephalitis or encephalomyelitis. Despite the medical importance of this disease, some crucial steps in the development of encephalitis remain poorly understood. In particular, the basis of the disease severity is largely unknown.MethodsTBE virus growth, neutralizing antibody response, key cytokine and chemokine mRNA production and changes in mRNA levels of cell surface markers of immunocompetent cells in brain were measured in mice with different susceptibilities to TBE virus infection.ResultsAn animal model of TBE based on BALB/c-c-STS/A (CcS/Dem) recombinant congenic mouse strains showing different severities of the infection in relation to the host genetic background was developed. After subcutaneous inoculation of TBE virus, BALB/c mice showed medium susceptibility to the infection, STS mice were resistant, and CcS-11 mice were highly susceptible. The resistant STS mice showed lower and delayed viremia, lower virus production in the brain and low cytokine/chemokine mRNA production, but had a strong neutralizing antibody response. The most sensitive strain (CcS-11) failed in production of neutralizing antibodies, but exhibited strong cytokine/chemokine mRNA production in the brain. After intracerebral inoculation, all mouse strains were sensitive to the infection and had similar virus production in the brain, but STS mice survived significantly longer than CcS-11 mice. These two strains also differed in the expression of key cytokines/chemokines, particularly interferon gamma-induced protein 10 (IP-10/CXCL10) and monocyte chemotactic protein-1 (MCP-1/CCL2) in the brain.ConclusionsOur data indicate that the genetic control is an important factor influencing the clinical course of TBE. High neutralizing antibody response might be crucial for preventing host fatality, but high expression of various cytokines/chemokines during TBE can mediate immunopathology and be associated with more severe course of the infection and increased fatality.

The anti-TBEV effect of 2=-CMA in cell culture diminished gradually after day 3 posttreatment. 7-Deaza-2=-CMA showed no detectable cellular toxicity (CC 50 > 50 M), and the antiviral effect in culture was stable for >6 days posttreatment. Computational molecular analyses revealed that compared to the other two compounds, 7-deaza-2=-CMA formed a large cluster near the active site of the TBEV polymerase. High antiviral activity and low cytotoxicity suggest that 7-deaza-2=-CMA is a promising candidate for further investigation as a potential therapeutic agent in treating TBEV infection.