Anti-RSV F protein (Nirsevimab) – Fc Muted™ (R215-500ug)

Respiratory syncytial virus (RSV) is a major cause of acute lower respiratory tract infection and hospitalization in infants1. RSV F protein is a type I integral membrane protein essential for viral membrane fusion that is highly conserved among isolates of RSV A and B subgroups2. F protein has been investigated as a target for neutralizing antibodies, small molecular antiviral drug development, as a vaccine antigen, and as an antibody target for passive prophylaxis. F protein is synthesized as an inactive, palmitoylated precursor (F0) and is decorated with N-linked glycans2. Three F0 monomers form a trimer and become activated by a furin-like host protease as they pass through the Golgi. The protease cleaves twice, generating three polypeptides: F2 and F1, which are covalently linked, and pep27, an intervening peptide that dissociates after cleavage. When functional F protein trimer in the virion membrane is triggered, it undergoes a major conformational change from a prefusion to postfusion form. Approximately 25% of isolate specific variability for F protein is found within an antigenic site at the apex of the prefusion trimer (antigenic site Ø), composed of an α-helix from F1 (aa 196–210) and a strand from F2 (aa 62–69). Nirsevimab is a long-acting, neutralizing recombinant human monoclonal antibody that binds the F1 and F2 subunits of F protein at a highly conserved epitope in antigenic site Ø and locks the RSV F protein in the prefusion conformation, blocking viral entry into the host cell1, 3, 4. In vitro, nirsevimab binds to immobilized human FcγRs (FcγRI, FcγRIIA, FcγRIIB and FcγRIII)3. Protection from infection is thought to be dependent on neutralization activity rather than Fc-mediated effector function based on data from a cotton rat model of RSV infection3. Nirsevimab has been modified with a triple amino acid substitution (YTE) in the Fc region to extend the serum half-life3. Nirsevimab originates from the D25 antibody developed by AIMM Therapeutics and was jointly developed and commercialized by AstraZeneca and Sanofi for the prevention of RSV infection in neonates and infants.