Vaccination evokes gender-dependent protection against tularemia infection in C57BL/6Tac mice

Abstract

Francisella tularensis (Ft) is a Category A biothreat agent for which there currently is no FDA-approved vaccine. Thus, there is a substantial effort underway to develop an effective tularemia vaccine. While it is well established that gender can significantly impact susceptibility to primary infection, the impact of gender on vaccine efficacy is not well established. Thus, development of a successful vaccine against tularemia will require an understanding of the impact gender has on vaccine-induced protection against this organism. In this study, a role for gender in vaccine-induced protection following Ft challenge is identified for the first time. In the present study, mucosal vaccination with inactivated Ft (iFt) LVS elicited gender-based protection in C57BL/6Tac mice against respiratory challenge with Ft LVS. Specifically, vaccinated male mice were more susceptible to subsequent Ft LVS challenge. This increased susceptibility in male mice correlated with increased bacterial burden, increased tissue inflammation, and increased proinflammatory cytokine production late in post-challenge infection. In contrast, improved survival of iFt-vaccinated female mice correlated with reduced bacterial burden and enhanced levels of Ft-specific Abs in serum and broncho-alveolar lavage (BAL) fluid post-challenge. Furthermore, vaccination with a live attenuated vaccine consisting of an Ft LVS superoxide dismutase (SodB) mutant, which has proven efficacious against the highly virulent Ft SchuS4 strain, demonstrated similar gender bias in protection post-Ft SchuS4 challenge. Of particular significance is the fact that these are the first studies to demonstrate that gender differences impact disease outcome in the case of lethal respiratory tularemia following mucosal vaccination. In addition, these studies further emphasize the fact that gender differences must be a serious consideration in any future tularemia vaccine development studies.

Tularemia vaccine development: paralysis or progress?

“…While this may reflect, in part, differences in pathogen exposure through hunting and outdoor professional activities (CDC, http://www.cdc.gov/tularemia/statistics/agesex.html ), 125 in male versus female susceptibility could also be a contributing factor. We have observed for the first time that while both naive male and female C57BL6 mice are equally susceptible to Ft LVS infection, prior immunization with i Ft or live Ft vaccine results in a sex-based immune response and protection in the case of both Ft LVS 126 and Ft SchuS4 challenge ( Figure 3 ). Specifically, vaccinated male mice develop severe clinical disease and exhibit a significantly higher mortality rate, which correlates with increased tissue destruction, a higher bacterial burden, and weight loss, as compared to immunized female mice.…”

Intranasal administration of a two-dose adjuvanted multi-antigen TMV-subunit conjugate vaccine fully protects mice against Francisella tularensis LVS challenge

“…Stimulation with either OmpA (lowest unadjuvanted responder) or SucB (highest unadjuvanted responder) induced IFNγ response levels greater than measured at day65, suggesting robust recall responses. IFNγ responses were shown to be critically important in providing protection after intranasal inactivated LVS vaccination [ 39 ], and improved gender-specific survival in male mice [ 40 ], We believe that these heightened CTL responses to subunit proteins are a result of TMV conjugation, which likely improved antigen delivery to mucosal tissue antigen retention on mucosal surfaces, subsequent recruitment of APCs, and the stimulation of TLR-mediated immunity to the plus-strand single-stranded RNA in the TMV virus, all characteristics known to improve mucosal immunity [ 41 ].…”

Differential In Vitro Cultivation of Francisella tularensis Influences Live Vaccine Protective Efficacy by Altering the Immune Response

“…Francisella tularensis holartica LVS ( Ft LVS) and Ft LVS superoxide dismutase sod B mutant were cultured in MHM or BHIM on agar plates (Becton Dickinson, Sparks, MD, USA) at 37°C for 48 h and subsequently used for vaccination. The challenge pathogen Ft SchuS4 was cultured aerobically in MHM or BHIM broth (Becton Dickinson, Sparks, Maryland) and the active mid-log phase bacteria were harvested and used for mouse infection ( 8 , 9 ). Inactivated Ft (i Ft ) was generated, as previously described ( 5 ).…”

“…injection of 100 µl of 20 mg/ml ketamine (Vedco, St. Joseph, MO, USA) and 0.4 mg/ml xylazine (Lioyd, Shenandoah, Iowa). Mice were subsequently immunized, as previously described ( 9 ). Specifically, 1 × 10 3 CFU of BHIM or MHM- Ft LVS or - Ft sodB were administered intradermally (i.d.)…”

“…One week after the second immunization, blood was collected from the sub-mandibular vein of vaccinated and unvaccinated mice. Anti- Ft Ab production in response to vaccination was measured by enzyme linked immunosorbent assay, as previously described ( 9 ).…”