Novel intranasal proteosome-based respiratory syncytial virus (RSV) vaccines elicit protection in mice without the risk of enhanced pathology or eosinophila by triggering innate immune pathways

No safe and effective vaccine exists against respiratory syncytial virus (RSV), the main viral cause of lower respiratory tract infections in young children. Proteosome-based adjuvants, derived from the outer membrane proteins (OMP) of Neisseria species are potent inducers of mucosal and systemic immunity in humans and animals. RSV subunit vaccines based on enriched RSV proteins (eRSV) were formulated with proteosomes (Pro) or its S. flexneri LPS-supplemented derivative, Protollin (Prl). Administered intranasally (IN) in BALB/c mice, the vaccines elicited systemic and mucosal RSV-specific antibodies and fully protected against RSV challenge without enhanced pulmonary pathology or evidence of a Th2-biased response (eg: eosinophil infiltation or antigen-specific 1L-5 production by restimulated splenocytes or lung cells). Restimulation of cells from Prl-eRSV immunized mice elicited F peptide-specific CD8+ T cells producing IFNgamma and supernatant IFNgamma, TNFalpha, 1L-2 and IL-10. The Prl-eRSV vaccine was also studied in C57Bl/6 mice, to exploit the TLR2, TLR4 and MyD88-deficient (-/-) animals available on this background. Protection was significantly impaired in both TLR4-/- and MyD88 -/- mice, but not in TLR2 -/- mice following Prl- eRSV immunization and challenge. These studies revealed a role for the LPS component of Protollin in both initial (innate) cytokine release as well as dendritic cell maturation and Th1 polarization. Although antibody levels were sustained in MyD88-/- mice, the IgG1/IgG2a ratio was markedly higher in the absence of this pathway. The MyD88-/- mice also displayed elevated levels of pulmonary eosinophils following challenge, with concomitant reduction of neutrophils compared to wt mice. Using CD1d-iNKT cell-deficient mice (CD1-/-) in our BALB/c model, we also identified a significant role for the lipid component of both the Pro- and Prl-based vaccines. Responses to both vaccines in CD1-/- animals elicited lower antibody titers and reduced restimulated splenocyte supernatant cytokines (IFNgamma, IL-17 and IL-10), with concomitant augmentation of neutrophil recruitment (Prl only). Pro- and Prl-eRSV vaccines may therefore exert their powerful adjuvant effects by exploiting both CD1d-iNKT and, in the case of the Prlbased formulations the TLR4-MyD88-dependant signalling pathway. These pathways not only promote stronger Th1 immune responses but also act to control pulmonary eosinophil (MyD88-dependent) and neutrophil (MyD88 and CD1d-NKT-dependent) recruitment in a murine RSV challenge model