Streptococcus pneumoniae and influenza are the world's foremost bacterial and viral respiratory pathogens. We have previously described a γ-irradiated influenza A virus (γ-FLU) vaccine that provides cross-protective immunity against heterosubtypic infections. More recently, we reported a novel non-adjuvanted γ-irradiated S . pneumoniae (γ-PN) vaccine that elicits serotype-independent protection. Considering the clinical synergism of both pathogens, combination of a serotype-independent pneumococcal vaccine with a broad-spectrum influenza vaccine to protect against both infections would have a considerable clinical impact. In the present study, we co-immunized C57BL/6 mice intranasally (IN) with a mixture of γ-PN (whole inactivated cells) and γ-FLU (whole inactivated virions) and examined protective efficacy. Co-immunization enhanced γ-PN vaccine efficacy against virulent pneumococcal challenge, which was dependent on CD4 + T-cell responses. In contrast, vaccination with γ-PN alone, co-immunization enhanced pneumococcal-specific effector T-helper 17 cell (Th17) and Th1 memory cell, promoted development of CD4 + tissue-resident memory (TRM) cells and enhanced Pneumococcus -specific antibody responses. Furthermore, co-immunization elicited significant protection against lethal influenza challenge, as well as against co-infection with both influenza and S . pneumoniae. This is the first report showing the synergistic effect of combining whole cell and whole virion vaccines to both S . pneumoniae and influenza as a single vaccine to protect against individual and co-infection, without compromising pathogen-specific immunity.

Generating a pneumococcal vaccine that is serotype independent and cost effective remains a global challenge. γ-Irradiation has been used widely to sterilize biological products. It can also be utilized as an inactivation technique to generate whole-cell bacterial and viral vaccines with minimal impact on pathogen structure and antigenic determinants. In the present study, we utilized γ-irradiation to inactivate an un-encapsulated Streptococcus pneumoniae strain Rx1 with an unmarked deletion of the autolysin gene lytA and with the pneumolysin gene ply replaced with an allele encoding a non-toxic pneumolysoid (PdT) (designated γ-PN vaccine). Intranasal vaccination of C57BL/6 mice with γ-PN was shown to elicit serotype-independent protection in lethal challenge models of pneumococcal pneumonia and sepsis. Vaccine efficacy was shown to be reliant on B-cells and interleukin (IL)-17A responses. Interestingly, immunization promoted IL-17 production by innate cells not T helper 17 (Th17) cells. These data are the first to report the development of a non-adjuvanted intranasal γ-irradiated pneumococcal vaccine that generates effective serotype-independent protection, which is mediated by both humoral and innate IL-17 responses.