Development of a novel co-vaccination approach for pneumococcal and influenza infections

Abstract

Streptococcus pneumoniae and influenza are the world’s foremost bacterial and viral respiratory pathogens. In addition to their individual clinical significance, co-infection with these pathogens enhances disease progression and is associated with substantially increased mortality rates. Vaccination is the best preventative method to control disease caused by individual pathogens as well as co-infection. Gamma-irradiation is considered a safe sterilization method, used routinely to sterilize medical devices, pharmaceuticals and most commonly food products. It can also be utilised as an inactivation technique to generate whole cell bacterial and viral vaccines with minimal impact on pathogen structure and antigenic determinants. This study presents the first evidence illustrating the use of this inactivation technique for development of a mucosal S. pneumoniae whole cell vaccine (γ- PN). Gamma-irradiation was utilised to inactivate an unencapsulated S. pneumoniae strain Rx1 with an unmarked deletion of the autolysin gene and with the pneumolysin gene replaced with an allele encoding a non-toxic pneumolysoid. Intranasal administration of mice with γ-PN without an adjuvant was shown to elicit serotype-independent protection against pneumococcal challenge in models of sepsis and pneumonia. In particular, vaccine efficacy was shown to be reliant on B cells and IL-17 responses. Importantly, immunisation promoted IL-17 production by γδ T cells, as opposed to conventional Th17 cells commonly reported with other pneumococcal whole cell vaccines. Moreover, this study also illustrated that the immunogenicity and protective efficacy of the γ-PN vaccine can be enhanced in the presence of the mucosal adjuvant, cholera toxin. In addition, this study describes a novel combination vaccine approach comprising inactivated whole bacterial cells and whole virions to S. pneumoniae and influenza respectively. In this study mice were co-immunised intranasally with the un-adjuvanted γ-PN vaccine and a gamma-irradiated influenza vaccine (γ-FLU). Interestingly, co-immunisation was shown to enhance γ-PN vaccine efficacy and immunogenicity against virulent pneumococcal challenge, which was dependent on CD4+ T cell responses. In contrast to vaccination with γ-PN alone, co-immunisation enhanced pneumococcal-specific effector Th17 and Th1 memory cells, promoted development of CD4+ tissue-resident memory cells, and enhanced pneumococcus-specific antibody responses. In addition, this combination approach was shown to elicit significant protection against lethal influenza challenge, as well as against co-infection with both influenza and S. pneumoniae. These data support the notion that γ-FLU exhibits adjuvant-like properties to enhance immunogenicity of a co-administered vaccine without compromising pathogen-specific immune responses. Future work will be focused on clinical development of individual and combination vaccines.