ISOLATION OF A 2ND RECOMBINANT HUMAN RESPIRATORY SYNCYTIAL VIRUS MONOCLONAL-ANTIBODY FRAGMENT (FAB RSVF2-5) THAT EXHIBITS THERAPEUTIC EFFICACY IN-VIVO

A second human respiratory syncytial virus (RSV)-neutralizing monoclon al antibody was isolated and its binding site was identified. Fab F2-5 is a broadly reactive fusion (F) protein-specific recombinant Fab gen erated by antigen selection from a random combinatorial library displa yed on the surface of filamentous phage. In an in vitro plaque-reducti on test, the Fab RSVF2-5 neutralized the infectivity of a variety of f ield isolates representing viruses of both RSV subgroups A and B. The Fab recognized an antigenic determinant that differed from the only ot her human anti-F monoclonal antibody (RSV Fab 19) described thus far. A single dose of 4.0 mg of Fab RSVF2-5/kg of body weight administered by inhalation was sufficient to achieve a 2000-fold reduction in pulmo nary virus titer in RSV-infected mice. The antigen-binding domain of F ab RSVF2-5 offers promise as part of a prophylactic regimen for RSV in fection in humans.