The molecular basis of antibody protection against West Nile virus.

West Nile virus (WNV) infection of mosquitoes, birds, and vertebrates continues to spread in the Western Hemisphere. In humans, WNV infects the central nervous system and causes severe disease, primarily in the immunocompromised and elderly. In this review we discuss the mechanisms by which antibody controls WNV infection. Recent virologic, immunologic, and structural experiments have enhanced our understanding on how antibodies neutralize WNV and protect against disease. These advances have significant implications for the development of novel antibody-based therapies and targeted vaccines.

Macaque dendritic cells infected with SIV-recombinant canarypox ex vivo induce SIV-specific immune responses in vivo.

Dendritic cells (DCs) infected with recombinant avipox vectors express the introduced genes and activate antigen-specific T cells. DCs exhibit distinct differentiation-dependent immune functions. Moreover, immature DCs are readily infected by canarypox vectors, but undergo tumor necrosis factor (TNF)-alpha-dependent death, while fewer mature DCs get infected and resist dying. A pilot study was performed using the rhesus macaque system to explore whether immature and mature DCs infected with SIV-recombinant canarypox (vCP180) ex vivo could induce primary virus-specific immune responses in vivo. After subcutaneous (sc) reinjection, functional monocyte-derived DCs migrated to lymph nodes (LNs) within 1-2 days and primed T cells in vivo. This was observed by monitoring dye-labeled DCs in the draining LNs and tetanus toxoid (TT)-specific T cell responses after injection of TT-loaded DCs. DCs from simian immunodeficiency virus (SIV)-naïve rhesus macaques were infected with vCP180 (SIVmac142 gag, pol, and env genes), and sc reinjected into donor animals. Low-level SIV-specific T cell proliferation, but little if any interferon (IFN)-gamma production was detected. DCs pulsed with vCP180 in combination with TT and keyhole limpet hemocyanin (KLH) (to activate additional T cells and provide "helper" cytokines) induced SIV-, TT-, and KLH-specific T cell responses, including IFN-gamma responses not seen when vCP180-carrying DCs were used alone. Interleukin (IL)-10 and low-level antibody responses were also observed. This pilot study provides the proof of principle that sc injected ex vivo SIV-recombinant canarypox-infected DCs safely induce low-level SIV-specific immune responses in vivo.

Canarypox virus-induced maturation of dendritic cells is mediated by apoptotic cell death and tumor necrosis factor alpha secretion.

Recombinant avipox viruses are being widely evaluated as vaccines. To address how these viruses, which replicate poorly in mammalian cells, might be immunogenic, we studied how canarypox virus (ALVAC) interacts with primate antigen-presenting dendritic cells (DCs). When human and rhesus macaque monocyte-derived DCs were exposed to recombinant ALVAC, immature DCs were most susceptible to infection. However, many of the infected cells underwent apoptotic cell death, and dying infected cells were engulfed by uninfected DCs. Furthermore, a subset of DCs matured in the ALVAC-exposed DC cultures. DC maturation coincided with tumor necrosis factor alpha (TNF-alpha) secretion and was significantly blocked in the presence of anti-TNF-alpha antibodies. Interestingly, inhibition of apoptosis with a caspase 3 inhibitor also reduced some of the maturation induced by exposure to ALVAC. This indicates that both TNF-alpha and the presence of primarily apoptotic cells contributed to DC maturation. Therefore, infection of immature primate DCs with ALVAC results in apoptotic death of infected cells, which can be internalized by noninfected DCs driving DC maturation in the presence of the TNF-alpha secreted concomitantly by exposed cells. This suggests an important mechanism that may influence the immunogenicity of avipox virus vectors.