Immunogenicity and Protective Capacity of a Virosomal Respiratory Syncytial Virus Vaccine Adjuvanted with Monophosphoryl Lipid A in Mice

Respiratory Syncytial Virus (RSV) is a major cause of viral brochiolitis in infants and young children and is also a significant problem in elderly and immuno-compromised adults. To date there is no efficacious and safe RSV vaccine, partially because of the outcome of a clinical trial in the 1960s with a formalin-inactivated RSV vaccine (FI-RSV). This vaccine caused enhanced respiratory disease upon exposure to the live virus, leading to increased morbidity and the death of two children. Subsequent analyses of this incident showed that FI-RSV induces a Th2-skewed immune response together with poorly neutralizing antibodies. As a new approach, we used reconstituted RSV viral envelopes, i.e. virosomes, with incorporated monophosphoryl lipid A (MPLA) adjuvant to enhance immunogenicity and to skew the immune response towards a Th1 phenotype. Incorporation of MPLA stimulated the overall immunogenicity of the virosomes compared to non-adjuvanted virosomes in mice. Intramuscular administration of the vaccine led to the induction of RSV-specific IgG2a levels similar to those induced by inoculation of the animals with live RSV. These antibodies were able to neutralize RSV in vitro. Furthermore, MPLA-adjuvanted RSV virosomes induced high amounts of IFNγ and low amounts of IL5 in both spleens and lungs of immunized and subsequently challenged animals, compared to levels of these cytokines in animals vaccinated with FI-RSV, indicating a Th1-skewed response. Mice vaccinated with RSV-MPLA virosomes were protected from live RSV challenge, clearing the inoculated virus without showing signs of lung pathology. Taken together, these data demonstrate that RSV-MPLA virosomes represent a safe and efficacious vaccine candidate which warrants further evaluation

Enhanced antiviral activity of human surfactant protein d by site-specific engineering of the carbohydrate recognition domain

Innate immunity is critical in the early containment of influenza A virus (IAV) infection and surfactant protein D (SP-D) plays a crucial role in innate defense against IAV in the lungs. Multivalent lectin-mediated interactions of SP-D with IAVs result in viral aggregation, reduced epithelial infection, and enhanced IAV clearance by phagocytic cells. Previous studies showed that porcine SP-D (pSP-D) exhibits distinct antiviral activity against IAV as compared to human SP-D (hSP-D), mainly due to key residues in the lectin domain of pSP-D that contribute to its profound neutralizing activity. These observations provided the basis for the design of a full-length recombinant mutant form of hSP-D, designated as “improved SP-D” (iSP-D). Inspired by pSP-D, the lectin domain of iSP-D has 5 amino acids replaced (Asp324Asn, Asp330Asn, Val251Glu, Lys287Gln, Glu289Lys) and 3 amino acids inserted (326Gly-Ser-Ser). Characterization of iSP-D revealed no major differences in protein assembly and saccharide binding selectivity as compared to hSP-D. However, hemagglutination inhibition measurements showed that iSP-D expressed strongly enhanced activity compared to hSP-D against 31 different IAV strains tested, including (pandemic) IAVs that were resistant for neutralization by hSP-D. Furthermore, iSP-D showed increased viral aggregation and enhanced protection of MDCK cells against infection by IAV. Importantly, prophylactic or therapeutic application of iSP-D decreased weight loss and reduced viral lung titers in a murine model of IAV infection using a clinical isolate of H1N1pdm09 virus. These studies demonstrate the potential of iSP-D as a novel human-based antiviral inhalation drug that may provide immediate protection against or recovery from respiratory (pandemic) IAV infections in humans