Respiratory Syncytial Virus (RSV) is the leading cause of severe lower respiratory disease in young children and is the second most important viral cause of respiratory disease in adulthood, after influenza virus. Currently, no vaccines and no antivirals are available to control RSV infections. Recent advances in RSV research have shown that the F protein is a major target for development of novel therapy and prophylaxis. F-specific antibodies, such as Palivizumab, are available, but were shown not to be fully effective, since hospitalization rates are reduced only by 55%. In addition, vaccines may also not fully protect against infection. This is exemplified by the fact that even after natural infection(s) and induction of F-specific neutralizing antibodies, RSV is able to reinfect. Since re-infection occurs without considerable antigenic change, there must be a different immune evasive mechanism than that influenza A virus reinfections, which is dependent on antigenic drift/shift.
Our understanding of RSV F protein functionality, besides its role in fusion, is however insufficient to explain the immune evasive mechanisms involved. Currently there is a great risk that newly developed monoclonal antibodies and vaccines will suffer from constrained effectiveness.
Very recently, preliminary studies in our research group have shown that upon binding of RSV-specific antibodies to RSV F protein expressed on the surface of infected cells, internalization occurs of RSV protein-antibody complexes. As a result, infected cells will most likely no longer be efficiently detected and eliminated by antibody-based immunity. In addition, a reduction in the expression of RSV proteins on the surface of infected cells may interfere with the immunogenicity and hamper the induction of strong immune responses. This novel finding may have profound effects on (1) our understanding of RSV pathogenesis and the occurrence of frequent RSV reinfections and (2) the development of new RSV vaccines and monoclonal antibodies. It is therefore the aim of this project to fully characterize this endocytosis process up to the molecular level, both in vitro and in vivo. We will (A) characterize the endocytic process and the consequences for RSV immune evasion, (B) identify amino acids of the F protein involved and create F proteins that show no internalization, (C) generate recombinant viruses with mutant F proteins lacking endocytic properties and (D) evaluate the recombinant viruses in vivo.