779. Genetic Delivery of an Anti-RSV Antibody Protects Against Pulmonary Infection with RSV in Mice

Field: Biochemistry, Genetics and Molecular Biology (Life Sciences)

Respiratory syncytial virus (RSV) is the leading cause of severe viral respiratory disease in infants and children. The morbidity is greatest in young infants, children with underlying risk factors such as prematurity and bronchopulmonary dysplasia, and the elderly. A safe and efficient active vaccine is not available. Passive immunization with the monoclonal antibody palivizumab, a humanized murine IgG1 antibody targeted against a neutralizing epitope of the F glycoprotein of RSV, diminishes disease severity in high risk populations and is routinely used to protect premature infants during the RSV season. Because palivzumab offers only short-term protection and must be administered every 30 days, we hypothesized that genetic delivery of palivizumab with gene therapy vectors could be a means to achieve long term protection against RSV infection. To test the hypothesis, we designed a murine version of the palivizumab antibody by replacing the human sequences with the sequence from the constant region of a murine antibody, while preserving the complementarity-determining region. As a proof-of- principle to test the validity of the strategy, an adenovirus (Ad) vector was used, and to achieve long term protection, an adenoassociate virus (AAV) was used. Using an Ad vector expressing genes for the light and heavy chains of the modified palivizumab antibody separated by an internal ribosome entry site (Adanti-RSV) was constructed. The light and heavy chains were detected by Western analysis in the supernatant of 293 cells infected with Adanti- RSV, but not in cells infected with the control Ad vector AdNull, and the antibody secreted by the 293 cells bound RSV as analyzed by SDS gel electrophoresis. To determine if Adanti-RSV would mediate generation of anti-RSV antibodies in vivo, 5x1010 particle units of Adanti-RSV or AdNull., was administered to BALB/c mice intravenously. After 4 days, RSV neutralizing titers (1:160) were detected in mice receiving Adanti-RSV but not in AdNull infected or naive mice. Four days following vector administration, the mice were challenged by intranasal administration of RSV virus strain A2 (106 pfu) and the lung homogenates analyzed for RSV titers 4 days later. The mice that had received Adanti-RSV had 2.5-fold lower titers of RSV in the lung following challenge compared to the AdNull or naive group (p<0.05). To evaluate long term protection, the anti- RSV antibody construct was expressed in an serotype rh10 AAV vector. Six weeks following intrapleural administration 5x1010 genome copies, of AAVrh10.anti-RSV or the control AAVrh10.α1AT to BALB/c mice, the mice were challenged with RSV. Mice that had received AAVrh10. anti-RSV showed lower 2.5-fold RSV titers in the lung compared to the AAVrh10.α1AT group (p<0.05). Together these data demonstrate that a gene transfer strategy for delivery of an anti-RSV antibody can generate protective immunity in mice against RSV infection to the respiratory tract and may provide an alternative to the administration of the antibody itself.