Neutralizing antibodies protect mice against Venezuelan equine encephalitis virus aerosol challenge.

Venezuelan equine encephalitis virus (VEEV) remains a risk for epidemic emergence or use as an aerosolized bioweapon. To develop possible countermeasures, we isolated VEEV-specific neutralizing monoclonal antibodies (mAbs) from mice and a human immunized with attenuated VEEV strains. Functional assays and epitope mapping established that potently inhibitory anti-VEEV mAbs bind distinct antigenic sites in the A or B domains of the E2 glycoprotein and block multiple steps in the viral replication cycle including attachment, fusion, and egress. A 3.2-Å cryo-electron microscopy reconstruction of VEEV virus-like particles bound by a human Fab suggests that antibody engagement of the B domain may result in cross-linking of neighboring spikes to prevent conformational requirements for viral fusion. Prophylaxis or postexposure therapy with these mAbs protected mice against lethal aerosol challenge with VEEV. Our study defines functional and structural mechanisms of mAb protection and suggests that multiple antigenic determinants on VEEV can be targeted for vaccine or antibody-based therapeutic development.

Identification of Dengue Virus Serotype 3 Specific Antigenic Sites Targeted by Neutralizing Human Antibodies.

The rational design of dengue virus (DENV) vaccines requires a detailed understanding of the molecular basis for antibody-mediated immunity. The durably protective antibody response to DENV after primary infection is serotype specific. However, there is an incomplete understanding of the antigenic determinants for DENV type-specific (TS) antibodies, especially for DENV serotype 3, which has only one well-studied, strongly neutralizing human monoclonal antibody (mAb). Here, we investigated the human B cell response in children after natural DENV infection in the endemic area of Nicaragua and isolated 15 DENV3 TS mAbs recognizing the envelope (E) glycoprotein. Functional epitope mapping of these mAbs and small animal prophylaxis studies revealed a complex landscape with protective epitopes clustering in at least 6-7 antigenic sites. Potently neutralizing TS mAbs recognized sites principally in E glycoprotein domains I and II, and patterns suggest frequent recognition of quaternary structures on the surface of viral particles.

Severe pandemic 2009 H1N1 influenza disease due to pathogenic immune complexes.

Pandemic influenza viruses often cause severe disease in middle-aged adults without preexisting comorbidities. The mechanism of illness associated with severe disease in this age group is not well understood. Here we find preexisting serum antibodies that cross-react with, but do not protect against, 2009 H1N1 influenza virus in middle-aged adults. Nonprotective antibody is associated with immune complex-mediated disease after infection. We detected high titers of serum antibody of low avidity for H1-2009 antigen, and low-avidity pulmonary immune complexes against the same protein, in severely ill individuals. Moreover, C4d deposition--a marker of complement activation mediated by immune complexes--was present in lung sections of fatal cases. Archived lung sections from middle-aged adults with confirmed fatal influenza 1957 H2N2 infection revealed a similar mechanism of illness. These observations provide a previously unknown biological mechanism for the unusual age distribution of severe cases during influenza pandemics.

Venezuelan equine encephalitis virus replicon particles encoding respiratory syncytial virus surface glycoproteins induce protective mucosal responses in mice and cotton rats.

Respiratory syncytial virus (RSV) is an important viral pathogen that causes severe lower respiratory tract infection in infants, the elderly, and immunocompromised individuals. There are no licensed RSV vaccines to date. To prevent RSV infection, immune responses in both the upper and lower respiratory tracts are required. Previously, immunization with Venezuelan equine encephalitis virus replicon particles (VRPs) demonstrated effectiveness in inducing mucosal protection against various pathogens. In this study, we developed VRPs encoding RSV fusion (F) or attachment (G) glycoproteins and evaluated the immunogenicity and efficacy of these vaccine candidates in mice and cotton rats. VRPs, when administered intranasally, induced surface glycoprotein-specific virus neutralizing antibodies in serum and immunoglobulin A (IgA) antibodies in secretions at the respiratory mucosa. In addition, fusion protein-encoding VRPs induced gamma interferon (IFN-gamma)-secreting T cells in the lungs and spleen, as measured by reaction with an H-2K(d)-restricted CD8(+) T-cell epitope. In animals vaccinated with F protein VRPs, challenge virus replication was reduced below the level of detection in both the upper and lower respiratory tracts following intranasal RSV challenge, while in those vaccinated with G protein VRPs, challenge virus was detected in the upper but not the lower respiratory tract. Close examination of histopathology of the lungs of vaccinated animals following RSV challenge revealed no enhanced inflammation. Immunization with VRPs induced balanced Th1/Th2 immune responses, as measured by the cytokine profile in the lungs and antibody isotype of the humoral immune response. These results represent an important first step toward the use of VRPs encoding RSV proteins as a prophylactic vaccine for RSV.