A highly potent extended half-life antibody as a potential RSV vaccine surrogate for all infants.

Prevention of respiratory syncytial virus (RSV) illness in all infants is a major public health priority. However, no vaccine is currently available to protect this vulnerable population. Palivizumab, the only approved agent for RSV prophylaxis, is limited to high-risk infants, and the cost associated with the requirement for dosing throughout the RSV season makes its use impractical for all infants. We describe the development of a monoclonal antibody as potential RSV prophylaxis for all infants with a single intramuscular dose. MEDI8897*, a highly potent human antibody, was optimized from antibody D25, which targets the prefusion conformation of the RSV fusion (F) protein. Crystallographic analysis of Fab in complex with RSV F from subtypes A and B reveals that MEDI8897* binds a highly conserved epitope. MEDI8897* neutralizes a diverse panel of RSV A and B strains with >50-fold higher activity than palivizumab. At similar serum concentrations, prophylactic administration of MEDI8897* was ninefold more potent than palivizumab at reducing pulmonary viral loads by >3 logs in cotton rats infected with either RSV A or B subtypes. MEDI8897 was generated by the introduction of triple amino acid substitutions (YTE) into the Fc domain of MEDI8897*, which led to more than threefold increased half-life in cynomolgus monkeys compared to non-YTE antibody. Considering the pharmacokinetics of palivizumab in infants, which necessitates five monthly doses for protection during an RSV season, the high potency and extended half-life of MEDI8897 support its development as a cost-effective option to protect all infants from RSV disease with once-per-RSV-season dosing in the clinic.

Distinct cellular immune responses following primary and secondary influenza virus challenge in cotton rats.

To evaluate cell-mediated immunity in influenza-infected cotton rats, we compared the cellular composition of spleen, mediastinal lymph nodes (MLN) and bronchoalveolar lavage (BAL) after primary and secondary infection. There was an increase in cellularity in the MLN after primary infection that was further expanded upon rechallenge. CD4(+) T cells expanded after primary infection, but there was preferential increase in the number of CD4-negative T cells following secondary challenge. After primary infection, a large proportion of the monocytes and NK cells were present in the BAL while a T cell population dominated after secondary infection. CD4(+) T cells were predominant in this population unless the animals had been challenged with heterosubtypic influenza A virus. These studies are the first to show evidence of a memory T cell response to influenza infection in cotton rats and show quantitative and qualitative differences between the recall response to homosubtypic and heterosubtypic viruses.

Antigen-dependent proliferation and cytokine induction in respiratory syncytial virus-infected cotton rats reflect the presence of effector-memory T cells.

Respiratory syncytial virus (RSV) is a major cause of lower airway disease in infants and children. Immunity to RSV is not long lasting, resulting in re-occurring infections throughout life. Effective long-lived immunity results when central-memory T cells that proliferate vigorously and secrete IL-2 are present. In contrast, effector-memory T cells that mainly produce IFN-gamma, facilitate virus clearance but are not long lived. To identify the type of memory response induced after RSV-A (Long) infection, we characterized the kinetics of the antigen-specific immune response and identified the types of cytokines induced. RSV-specific lymphocytic proliferation following primary and secondary infection was similar, and in both cases responses waned within a short period of time. In addition, mRNA for IFN-gamma but not IL-2 was induced in RSV-specific CD4(+) T cells. This supports the idea that the presence of effector-memory rather than central-memory T cells contributes to the ineffectiveness of the immune response to RSV.

VIAF, a conserved inhibitor of apoptosis (IAP)-interacting factor that modulates caspase activation.

Inhibitor of apoptosis (IAP) proteins are involved in the suppression of apoptosis, signal transduction, cell cycle control and gene regulation. Here we describe the cloning and characterization of viral IAP-associated factor (VIAF), a highly conserved, ubiquitously expressed phosphoprotein with limited homology to members of the phosducin family that associates with baculovirus Op-IAP. VIAF bound Op-IAP both in vitro and in intact cells, with each protein displaying a predominantly cytoplasmic localization. VIAF lacks a consensus IAP binding motif, and overexpression of VIAF failed to prevent Op-IAP from protecting human cells from a variety of apoptotic stimuli, suggesting that VIAF does not function as an IAP antagonist. VIAF was unable to directly inhibit caspase activation in vitro and a reduction of VIAF protein levels by RNA interference led to a decrease in Bax-mediated caspase activation, suggesting that VIAF functions to co-regulate the apoptotic cascade. Finally, VIAF is a substrate for ubiquitination mediated by Op-IAP. Thus, VIAF is a novel IAP-interacting factor that functions in caspase activation during apoptosis.