ELUCIDATION OF THE MECHANISM OF ACTION OF A RESPIRATORY SYNCYTIAL VIRUS SUBUNIT VACCINE CANDIDATE CONTAINING A POLYMER-BASED COMBINATION ADJUVANT

Abstract

Human respiratory syncytial virus (RSV) is the primary cause of respiratory illnesses in infants, young children, elderly and immunocompromised individuals. Supportive care is the mainstay of RSV treatment. Currently no licensed vaccine against RSV is available. We have developed a subunit RSV vaccine candidate (ΔF/TriAdj) consisting of a truncated version of the RSV fusion protein (ΔF) formulated with a combination adjuvant (TriAdj) comprised of low molecular weight (LMW) polyinosinic:polycytidylic acid [poly(I:C)], an innate defense regulator (IDR) peptide and poly[di(sodium carboxylatoethylphenoxy)]-phosphazene (PCEP). We previously demonstrated the safety and protective efficacy of ΔF/TriAdj in several animal models. The overall objective of this thesis was to elucidate the mechanism of action of ΔF/TriAdj in BALB/c mice. First, we determined that ΔF/TriAdj when delivered intranasally plays a crucial role in stimulating innate immune responses in both upper and lower respiratory tracts of immunized mice as demonstrated by local production of cytokines, chemokines and interferons, as well as infiltration and activation of immune cells. Innate activation subsequently led to robust adaptive immunity and protection against RSV. Next, we elucidated the mechanisms of action of ΔF/TriAdj at the cell-signaling level in macrophages. Macrophages responded directly to in vitro stimulation with ΔF/TriAdj with induction of both endosomal and cytosolic pattern recognition receptors (PRRs). Based on inhibition studies, we determined that multiple signal transduction pathways are involved in ΔF/TriAdj-mediated activation of macrophages. Finally, we conducted a comprehensive chemical isotope labeling liquid chromatography-mass spectrometry (CIL LC-MS) analysis of the lung tissues from vaccinated and unvaccinated, RSV-infected mice as well as healthy controls, to understand the underlying mechanisms of action of ΔF/TriAdj at the further downstream metabolomic level. Metabolomic profiling revealed alterations of tryptophan metabolism (including kynurenine pathway), biosynthesis of amino acids (including arginine biosynthesis), urea cycle and tyrosine metabolism due to RSV infection. Interestingly, ΔF/TriAdj was found to a play a critical role in modulating alterations in the concentrations of the metabolites of the above-mentioned pathways in response to RSV infection. Ultimately, information on the mechanism of action of this RSV vaccine candidate may serve to identify potential biomarkers for immunogenicity and protective efficacy of ΔF/TriAdj in future.