A Protective and Safe Intranasal RSV Vaccine Based on a Recombinant Prefusion-Like Form of the F Protein Bound to Bacterium-Like Particles

Abstract

Respiratory syncytial virus (RSV) is an important cause of respiratory tract disease in infants and the elderly. Currently, no licensed vaccine against RSV is available. Here we describe the development of a safe and effective intranasal subunit vaccine that is based on recombinant fusion (F) protein bound to the surface of immunostimulatory bacterium-like particles (BLPs) derived from the food-grade bacterium Lactococcus lactis. Different variants of F were analyzed with respect to their conformation and reactivity with neutralizing antibodies, assuming that F proteins mimicking the metastable prefusion form of RSV F expose a more extensive and relevant epitope repertoire than F proteins corresponding to the postfusion structure. Our results indicate that the recombinant soluble ectodomain of RSV F readily adopts a postfusion conformation, generation of which cannot be prevented by C-terminal addition of a trimerization motif, but whose formation is prevented by mutation of the two furin cleavage sites in F. While the putative postfusion form of F is recognized well by the monoclonal antibody Palivizumab, this is much less so for the more potently neutralizing, prefusion-specific antibodies D25 and AM22. Both addition of the trimerization motif and mutation of the furin cleavage sites increased the reactivity of F with D25 and AM22, with the highest reactivity being observed for F proteins in which both these features were combined. Intranasal vaccination of mice or cotton rats with BLPs loaded with this latter prefusion-like F protein (BLP-F), resulted in the potent induction of F-specific immunoglobulins and in significantly decreased virus titers in the lungs upon RSV challenge. Moreover, and in contrast to animals vaccinated with formalin-inactivated RSV, animals that received BLP-F exhibited high levels of F-specific secretory IgA in the nose and RSV-neutralizing antibodies in sera, but did not show symptoms of enhanced disease after challenge with RSV.

Updated Guidance for Palivizumab Prophylaxis Among Infants and Young Children at Increased Risk of Hospitalization for Respiratory Syncytial Virus Infection

“…Early experience with a formalininactivated whole virus vaccine resulted in enhanced RSV disease in young children in the 1960s, which has complicated development of inactivated RSV vaccines. 150,155 The demonstration of the effectiveness of passive prophylaxis with an anti-F monoclonal provides reassurance that antibody to the F protein is protective. New subunit vaccines and particularly vaccines directed against the F protein administered intramuscularly or intranasally continue to be explored.…”

“…New subunit vaccines and particularly vaccines directed against the F protein administered intramuscularly or intranasally continue to be explored. 150,155 A vaccine against a "prefusion" configuration of the F protein may offer increased efficacy with less risk of disease enhancement. 156 F protein virallike particle vaccines administered during the latter half of pregnancy might offer passive protection for young children through the first months of life.…”

Controlled human infection with RSV: The opportunities of experimental challenge

“…However, they were relatively poor producers of cytotoxic molecules such as granzyme B and perforin, and together with an observed deficiency in production of type 1 cytokines by RSV-specific CD8+ T cells in blood compared to influenza, these data again suggest that RSV-specific adaptive immune responses are relatively impaired. Several RSV vaccine candidates have been developed that can be delivered intranasally with the aim of inducing both antibodies and T cells in the respiratory tract [48,49]. However, the development of Trm cells has not been investigated using any of these.…”

Immunosilencing a Highly Immunogenic Protein Trimerization Domain

“…These include cancer therapeutics that have been tested in clinical trials, such as the TNF superfamily member CD40 ligand (6 -8), as well as therapeutics that have been tested preclinically, such as OX40 ligand (9) and TRAIL (10). Experimental protein vaccines, some, which are considered for clinical trials, also exploit IZ and/or Fd and include the spike proteins of human immunodeficiency virus (HIV-1) (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), respiratory syncytial virus (21,22), and influenza virus (4,(23)(24)(25)(26)(27)(28).…”