EFFECT OF BIOLOGICAL SEX AND AGE ON UNIVERSAL INFLUENZA VACCINE-INDUCED IMMUNITY IN MICE

BACKGROUND: Human data and murine studies demonstrate that biological sex and age impact inactivated influenza vaccine (IIV)-induced immunity, wherein the antibodies are directed towards Influenza virus glycoprotein hemagglutinin (HA) head. Post IIV in mice, females of reproductive age generated greater antibody responses leading to better protection than males. Whereas, in aged mice, where the immunity is waning, the sex-differences are lost and are associated with reduced concentrations of sex-steroids. Whether universal influenza vaccines (UIV) producing antibodies towards the highly conserved stalk region of HA protein are also influenced by biological sex and age has not been studied. We hypothesized that age-associated sex differences to influenza vaccine response will be observed regardless of target region of antibodies. METHODS: We used the chimeric hemagglutinin (cHA)-based UIV, which produces antibodies towards the stalk region of the HA protein. We vaccinated adults and aged C57BL6 mice using a prime-boost-boost strategy with a live-attenuated influenza B virus containing chimeric H9/1, recombinant H11/1 and H12/1 protein, respectively. We evaluated the antibody responses of stalk-specific IgG, IgG isotypes and avidity against H1 stalk and cross-reactive IgG response against H9N2, H6N3, H5N1 and H3N2 viruses. We challenged the mice with H1N1 virus to monitor vaccine-induced protection. We also passively transferred antibodies from adults to their sex-matched aged counterparts to evaluate protection. RESULTS: Post-vaccination antibody analysis demonstrated that adult mice developed higher quantity and quality of antibody than aged mice. Adult mice had greater stalk-specific IgG titers against multiple subtypes of group 1 influenza A viruses and had greater antibody avidity, regardless of sex. The age-associated decline in immunity was sex-specific, where aging significantly reduced antibody responses in female but not male mice. Post-challenge with H1N1 virus, aged females suffered greater morbidity and had higher viral titers than age-matched males and younger females. Passive transfer of serum from sex-matched adult mice to aged mice was not sufficient to protect aged mice from severe outcomes following infection. CONCLUSION: In conclusion, these findings suggest a fundamental difference between males and females during aging. Hence biological sex and age should be considered in pre-clinical and clinical studies involving all influenza vaccine platforms