Modulation of Immune Responses Induced by Vaccination Against Bovine Respiratory Syncytial Virus

Abstract

As respiratory syncytial virus (RSV) is a respiratory pathogen that causes significant morbidity and mortality in infants, there has always been great interest in the development of a vaccine. In the 1960s, children were immunized with formalin-inactivated (FI)-RSV vaccines. Not only did these vaccines fail to prevent infection, but in most cases they resulted in enhanced disease upon subsequent exposure to the virus. In the intervening years, studies in mice have led to the hypothesis that the enhanced disease is due to an aberrant Th2-biased immune response. Thus, we hypothesized that formulating FI-RSV vaccines with a Th1 promoting adjuvant, such as CpG oligoeoxynucleotides (ODN), would result in the induction of protective immunity against RSV without risk of deleterious effects. We observed in calves that parenterally delivered FI-bovine RSV (BRSV) formulated with CpG ODN resulted in a shift towards a Th1-biased or more balanced immune response that was protective against BRSV.

As RSV infects the lung mucosa, vaccines that induce mucosal immunity are desirable. Parenterally delivered vaccines typically induce systemic immunity with low mucosal immune response levels, whereas mucosally delivered vaccines induce systemic and mucosal immunity. However, upon mucosal delivery there is an increased chance of vaccine components being degraded or washed away prior to the induction of immunity. Thus, we added polyphosphazenes (PP) to our mucosal vaccine formulations. PP are synthetic polymers that form non-covalent complexes with other vaccine components, increasing their stability. Intranasally delivered FI-BRSV co-formulated with CpG ODN and PP performed better than FI-BRSV alone, or FI-BRSV formulated with either adjuvant individually, in terms of inducing protective immunity against BRSV in mice. Furthermore, mice that received intranasally-delivered FI-BRSV or BRSV F protein co-formulated with CpG ODN and PP developed higher levels of immunity and protection than mice that received parenterally delivered vaccines. Because of the similarities between BRSV and HRSV, co-formulation of intranasally delivered HRSV vaccines with CpG ODN and PP could prove important in the development of a safe vaccine against HRSV in humans.