SUMMARY Zika virus (ZIKV) infection during pregnancy has emerged as a global public health problem because of its ability to cause severe congenital disease. Here, we developed six mouse monoclonal antibodies (mAbs) against ZIKV including four (ZV-48, ZV-54, ZV-64, and ZV-67) that were ZIKV-specific and neutralized infection of African, Asian, and American strains to varying degrees. X-ray crystallographic and competition binding analyses of Fab fragments and scFvs defined three spatially distinct epitopes in DIII of the envelope protein corresponding to the lateral ridge (ZV-54 and ZV-67), C–C′ loop (ZV-48 and ZV-64), and ABDE sheet (ZV-2) regions. In vivo passive transfer studies revealed protective activity of DIII-lateral ridge specific neutralizing mAbs in a mouse model of ZIKV infection. Our results suggest that DIII is targeted by multiple type-specific antibodies with distinct neutralizing activity, which provides a path for developing prophylactic antibodies for use in pregnancy or designing epitope-specific vaccines against ZIKV.

Zika virus (ZIKV) is an emerging mosquito-transmitted flavivirus that can cause severe disease, including congenital birth defects during pregnancy1. To develop candidate therapeutic agents against ZIKV, we isolated a panel of human monoclonal antibodies from subjects that were previously infected with ZIKV. We show that a subset of antibodies recognize diverse epitopes on the envelope (E) protein and exhibit potent neutralizing activity. One of the most inhibitory antibodies, ZIKV-117, broadly neutralized infection of ZIKV strains corresponding to African and Asian-American lineages. Epitope mapping studies revealed that ZIKV-117 recognized a unique quaternary epitope on the E protein dimer–dimer interface. We evaluated the therapeutic efficacy of ZIKV-117 in pregnant and non-pregnant mice. Monoclonal antibody treatment markedly reduced tissue pathology, placental and fetal infection, and mortality in mice. Thus, neutralizing human antibodies can protect against maternal–fetal transmission, infection and disease, and reveal important determinants for structure-based rational vaccine design efforts.

The T-cell repertoire found in the periphery is thought to be shaped by two developmental events in the thymus that involve the antigen receptors of T lymphocytes. First, interactions between T cells and major histocompatibility complex (MHC) molecules select a T-cell repertoire skewed towards recognition of antigens in the context of self-MHC molecules. In addition, T cells that react strongly to self-MHC molecules are eliminated by a process called self-tolerance. We have recently described transgenic mice expressing the alpha beta T-cell receptor from the cytotoxic T lymphocyte 2C (ref. 11). The clone 2C was derived from a BALB.B (H-2b) anti-BALB/c (H-2d) mixed lymphocyte culture and is specific for the Ld class I MHC antigen. In transgenic H-2b mice, a large fraction of T cells in the periphery expressed the 2C T-cell receptor. These T cells were predominantly CD4-CD8+ and were able to specifically lyse target cells bearing Ld. We now report that in the periphery of transgenic mice expressing Ld, functional T cells bearing the 2C T-cell receptor were deleted. This elimination of autoreactive T cells appears to take place at or before the CD4+CD8+ stage in thymocyte development. In addition, we report that in H-2s mice, a non-autoreactive target haplotype, large numbers of CD8+ T cells bearing the 2C T-cell receptor were not found, providing strong evidence for the positive selection of the 2C T-cell receptor specificity by H-2b molecules.

West Nile virus (WNV), a positive-sense RNA virus and a member of the Flaviviridae family, recently became endemic in North America, with annual outbreaks of severe encephalitis occurring mostly in immunocompromised or elderly individuals. There is currently no vaccine approved for human use, and treatment is primarily supportive. The WNV genome encodes three structural proteins (C, prM/M, and E) and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). During the course of WNV infection, antibodies are raised against prM/M and E as well as NS1, NS3, and NS5, with a majority of the protective antibody response against the E protein (12, 63).The crystal structure of the ectodomain of the E protein has been determined for dengue virus (DENV), tick-borne encephalitis virus (TBEV), and WNV (43,45,48,56,65). Flavivirus E proteins have three separate domains and form headto-tail homodimers on the surface of the virion. Domain I (DI) is the central structural domain and consists of a 10-stranded ␤-barrel. DII is formed from two extended loops that project from DI. At the end of DII is a highly conserved loop, amino acid residues 98 to 110, that has been implicated in the acidcatalyzed type II fusion event (1,7,44). In the E dimer, the fusion loop lies in a pocket at the DI-DIII interface of the adjacent E protein. DIII, located on the opposite side of DI, forms a seven-stranded immunoglobulin-like fold and has been implicated in receptor binding (5, 10, 14). Short, flexible linker regions connect the domains and allow for the conformational changes associated with virus maturation and fusion (65).The structure of the WNV virion has been defined by cryoelectron microscopy (36, 47). The mature WNV is ϳ500 Å in diameter and has a relatively smooth surface with no apparent spikes or large projections. The 180 E monomers lay flat along the virion surface as sets of three parallel dimers. The arrangement of the 180 E monomers has quasi-icosahedral symmetry such that there are three E monomers in the asymmetric unit and three distinct chemical environments available for antibody or ligand binding (47). The reduced pH in the endosome causes the E protein to convert from a homodimer to a homotrimer and exposes the fusion loop (44).Antibodies are critical for the control of flavivirus infection in vivo (4,17,18,20,23,50,59), and this protection has been correlated with neutralizing activity in vitro (32,53,58). However, there have been reports of strong and weak in vivo protection with nonneutralizing (6,11,29,31,34,58) and neutralizing (30, 32, 41) monoclonal antibodies (MAbs), respectively. Several recent studies suggest that specific epitopes elicit flavivirus-reactive MAbs with particular functional activities (3,37,38,50,57,60). Most type-specific neutralizing antibodies map to DIII of the E protein. Cross-reactive, neutralizing MAbs bind to regions outside DIII and have been mapped to

Human noroviruses (NoV) are a leading cause of gastroenteritis globally, yet host factors required for NoV infection are poorly understood. We identified host molecules essential for murine NoV (MNoV) induced cell death including CD300lf as a proteinaceous receptor. CD300lf is essential for MNoV binding and replication in cell lines and primary cells. Additionally, Cd300lf−/− mice are resistant to MNoV infection. Expression of CD300lf in human cells breaks the species barrier restricting MNoV replication. The crystal structure of the CD300lf ectodomain revealed a potential ligand binding cleft composed of residues critical for MNoV infection. Therefore, the presence of a proteinaceous receptor is the primary determinant of MNoV species tropism while other components of cellular machinery required for NoV replication are conserved between humans and mice.

Antibody protection against flaviviruses is associated with the development of neutralizing antibodies against the viral envelope (E) protein. Prior studies with West Nile virus (WNV) identified therapeutic mouse and human monoclonal antibodies (MAbs) that recognized epitopes on domain III (DIII) of the E protein. To identify an analogous panel of neutralizing antibodies against DENV type-1 (DENV-1), we immunized mice with a genotype 2 strain of DENV-1 virus and generated 79 new MAbs, 16 of which strongly inhibited infection by the homologous virus and localized to DIII. Surprisingly, only two MAbs, DENV1-E105 and DENV1-E106, retained strong binding and neutralizing activity against all five DENV-1 genotypes. In an immunocompromised mouse model of infection, DENV1-E105 and DENV1-E106 exhibited therapeutic activity even when administered as a single dose four days after inoculation with a heterologous genotype 4 strain of DENV-1. Using epitope mapping and X-ray crystallographic analyses, we localized the neutralizing determinants for the strongly inhibitory MAbs to distinct regions on DIII. Interestingly, sequence variation in DIII alone failed to explain disparities in neutralizing potential of MAbs among different genotypes. Overall, our experiments define a complex structural epitope on DIII of DENV-1 that can be recognized by protective antibodies with therapeutic potential.

The interaction between B- and T-lymphocyte attenuator (BTLA), an inhibitory receptor whose extracellular domain belongs to the immunoglobulin superfamily, and herpesvirus-entry mediator (HVEM), a co-stimulatory tumour-necrosis factor receptor, is unique in that it is the only receptor-ligand interaction that directly bridges these two families of receptors. This interaction has raised many questions about how receptors from two different families could interact and what downstream signalling events might occur as a result of receptor ligation. As we discuss, recent studies show that engagement of HVEM with its endogenous ligand (LIGHT) from the tumour-necrosis factor family induces a powerful immune response, whereas HVEM interactions with BTLA negatively regulate T-cell responses.

The open reading frame (ORF) 7a of the SARS-associated coronavirus (SARS-CoV) encodes a unique type I transmembrane protein of unknown function. We have determined the 1.8 A resolution crystal structure of the N-terminal ectodomain of orf7a, revealing a compact seven-stranded beta sandwich unexpectedly similar in fold and topology to members of the Ig superfamily. We also demonstrate that, in SARS-CoV- infected cells, the orf7a protein is expressed and retained intracellularly. Confocal microscopy studies using orf7a and orf7a/CD4 chimeras implicate the short cytoplasmic tail and transmembrane domain in trafficking of the protein within the endoplasmic reticulum and Golgi network. Taken together, our findings provide a structural and cellular framework in which to explore the role of orf7a in SARS-CoV pathogenesis.