Enhancement of vaccine efficacy by expression of a TLR5 ligand in the defined live attenuated Francisella tularensis subsp. novicida strain U112ΔiglB::fljB

Abstract

Oral vaccination with the defined live attenuated Francisella novicida vaccine strain U112▲iglB has been demonstrated to induce protective immunity against pulmonary challenge with the highly human virulent F. tularensis strain SCHU S4. However, this vaccination regimen requires a booster dose in mice and exhibits 50% protective efficacy in the Fischer 344 rat model. To enhance the efficacy of this vaccine strain, we engineered U112▲iglB to express the Salmonella typhimurium FljB flagellin D1 domain, a TLR5 agonist. The U112▲iglB::fljB strain was highly attenuated for intracellular macrophage replication, and although the FljB protein was expressed within the cytosol, it exhibited TLR5 activation in a TLR5-expressing HEK cell line. Additionally, infection of splenocytes and lymphocytes with U112▲iglB::fljB induced significantly greater TNF-α production than infection with U112▲iglB. Oral vaccination with U112▲iglB::fljB also induced significantly greater protection than U112ΔiglB against pulmonary SCHU S4 challenge in rats. The enhanced protection was accompanied by higher IgG2a production and serum-mediated reduction of Francisella infectivity. Thus, the U112▲iglB::fljB strain may serve as a potential vaccine candidate against pneumonic tularemia.

Live Attenuated Tularemia Vaccines for Protection Against Respiratory Challenge With Virulent F. tularensis subsp. tularensis

“…This has been accompanied by a substantial increase in publications on development of tularemia vaccines, mostly on live attenuated vaccine candidates, including defined mutants of F. tularensis subsp. holarctica (Bakshi et al, 2006 , 2008 ; Pechous et al, 2006 , 2008 ; Li et al, 2007 ; Sebastian et al, 2007 , 2009 ; Meibom et al, 2008 ; Sammons-Jackson et al, 2008 ; Santiago et al, 2009 ; Jia et al, 2010 ; Zarrella et al, 2011 ; Kim et al, 2012 ; Schmitt et al, 2012 ; Barrigan et al, 2013 ; Golovliov et al, 2013 ; Mahawar et al, 2013 ; Straskova et al, 2015 ; Suresh et al, 2015 ), F. novicida (Pammit et al, 2006 ; Tempel et al, 2006 ; Mohapatra et al, 2007 ; Quarry et al, 2007 ; Kanistanon et al, 2008 ; West et al, 2008 ; Cong et al, 2009 ; Sanapala et al, 2012 ; Signarovitz et al, 2012 ; Chu et al, 2014 ; Cunningham et al, 2014 ), and subsp. tularensis (Twine et al, 2005 , 2012 ; Qin et al, 2008 , 2009 ; Conlan et al, 2010 ; Michell et al, 2010 ; Shen et al, 2010 ; Ireland et al, 2011 ; Rockx-Brouwer et al, 2012 ; Reed et al, 2014 ; Santiago et al, 2015 ), but also on live attenuated heterologous vaccines expressing F. tularensis proteins (Jia et al, 2009 ; Kaur et al, 2012 ; Banik et al, 2015 ) and recombinant LVS vaccines expressing F. tularensis proteins (Jia et al, 2013 , 2016 ).…”

Genetic engineering ofFrancisella tularensisLVS for use as a novel live vaccine platform againstPseudomonas aeruginosainfections

“…A recent study indicated that a mutant of F. novicida U112 expressing flagellin of Salmonella typhimurium could activate TLR5 resulting in increased inflammation, and therefore, this strain may be a potent tularemia vaccine candidate. 22 The possibility exists that F. tularensis LVS / pGFLI may also provide increased protection against F. tularensis for similarly stimulating TLR5, however this remains to be determined.…”

Immunomodulation as a Novel Strategy for Prevention and Treatment of Bordetella spp. Infections

“…leads to faster clearance of the infection (132), and it was later revealed that TLR5 activates antigen-presenting cells, increasing T cell response (133) (manuscript in preparation), and may ultimately contribute to the more rapid clearance previously reported. In several other microorganisms, the addition of TLR5 agonists have resulted in an increased performance of the vaccine (134)(135)(136)(137)(138)(139)(140)(141). Altogether these data suggest that TLR5 agonists could significantly increase the performance of the current acellular pertussis vaccine.…”