Recombinant attenuated Listeria monocytogenes vaccine expressing Francisella tularensis IglC induces protection in mice against aerosolized Type A F. tularensis

Abstract

Fransicella tularensis, the causative agent of tularemia, is in the top category (Category A) of potential agents of bioterrorism. To develop a safer vaccine against aerosolized F. tularensis, we have employed an attenuated Listeria monocytogenes, which shares with F. tularensis an intracellular and extraphagosomal lifestyle, as a delivery vehicle for F. tularensis antigens. We constructed recombinant L. monocytogenes (rLm) vaccines stably expressing 7 F. tularensis proteins including IglC (rLm/iglC), and tested their immunogenicity and protective efficacy against lethal F. tularensis challenge in mice. Mice immunized intradermally with rLm/iglC developed significant cellular immune responses to F. tularensis IglC as evidenced by lymphocyte proliferation and CD4 + and CD8+ T-cell intracellular expression of interferon gamma. Moreover, mice immunized with rLm/iglC were protected against lethal challenge with F. tularensis LVS administered by the intranasal route, a route chosen to mimic airborne infection, and, most importantly, against aerosol challenge with the highly virulent Type A F. tularensis SchuS4 strain.

A Heterologous Prime-Boost Vaccination Strategy Comprising the Francisella tularensis Live Vaccine StraincapBMutant and Recombinant Attenuated Listeria monocytogenes Expressing F. tularensis IglC Induces Potent Protective Immunity in Mice against Virulent F. tularensis Aerosol Challenge

“…F. tularensis LVS and Schu S4 strains were obtained from the Centers for Disease Control and Prevention (Atlanta, GA). LVS ⌬capB, LVS ⌬wbtDEF (LVS ⌬LPS), and rLm/iglC were constructed in our laboratory as described previously (16,21,29). To prepare the LVS stocks, we passaged the bacteria once on phorbol-12-myristate-13-acetate (PMA)-differentiated monolayers of THP-1 cells, amplified them on chocolate II agar (BD BBL, Sparks, MD) for 2 to 3 days, scraped the colonies into sterile phosphate-buffered saline (PBS), resuspended the bacteria in the presence of 20% glycerol, and stored them frozen at Ϫ80°C.…”

“…L. monocytogenes is known to induce innate and adaptive immune responses (19) and has been developed as a cancer vaccine vector (20). In a previous study, we chose a highly attenuated L. monocytogenes mutant with a deletion in actA, L. monocytogenes ⌬actA, as a vector, and constructed a recombinant L. monocytogenes vaccine expressing F. tularensis IglC (rLm/iglC) (21). IglC (intracellular growth locus subunit C) is encoded by genes (FTT1712 and FTT1357) on the Francisella pathogenicity island (FPI), which is highly upregulated during macrophage intracellular infection, required for intracellular survival, growth, and phagosome escape (22)(23)(24), and essential for virulence (25).…”

“…IglC (intracellular growth locus subunit C) is encoded by genes (FTT1712 and FTT1357) on the Francisella pathogenicity island (FPI), which is highly upregulated during macrophage intracellular infection, required for intracellular survival, growth, and phagosome escape (22)(23)(24), and essential for virulence (25). It is highly immunogenic (21,(26)(27)(28) and was previously identified by our group as an immunoprotective antigen (21). Our previous study showed that mice immunized i.d.…”

Current biodefense vaccine programs and challenges

“…One such platform, a Listeria monocytogenes-based approach, showed promising efficacy in a rat model of inhalational tularemia. 20 The backbone consists of an ActA-deficient strain of L. monocytogenes. ActA is critical for intracellular movement, and intercellular spread of L. monocytogenes, and strains deficient in this protein are cleared from the body within about seven days.…”

Working toward the Future: Insights intoFrancisella tularensisPathogenesis and Vaccine Development

“…Heterologous hosts. The inherent problems with the use of live attenuated Francisella vaccines, as well as the limitations of subunit/component vaccines, have led some groups to explore the use of heterologous bacteria to express Francisella antigens (73,97,186) (Table 7). Of the various outer membrane protein, lipoprotein, and virulence factor genes studied to date, only iglC expressed in a Listeria monocytogenes ⌬actA mutant confers protection against challenge with type A or B F. tularensis (97).…”