Generation of a Listeria vaccine strain by enhanced caspase‐1 activation

Abstract

The immunostimulatory properties conferred by vaccine adjuvants require Caspase-1 for processing of IL-1β and IL-18. Caspase-1 is activated in response to a breach of the cytosolic compartment by microbes and the process is initiated by intracellular pattern recognition receptors within inflammasomes. Listeria monocytogenes is detected in the cytosol by the NLRC4, NLRP3 and AIM2 inflammasomes. NLRC4 is activated by flagellin, and L. monocytogenes evades this detector by repressing flagellin expression. We generated an L. monocytogenes strain that was forced to express flagellin in the host cell cytosol. This strain hyperactivated Caspase-1 and was preferentially cleared via NLRC4 detection in an IL-1β/IL-18 independent manner. We also created a strain of L. monocytogenes with forced expression of another NLRC4 agonist, PrgJ from the Type III secretion system of S. typhimurium. Forced expression of flagellin or PrgJ resulted in attenuation, yet both strains conferred protective immunity in mice against lethal challenge with L. monocytogenes. This work is the first demonstration of specific targeting of the Caspase-1 activation pathway to generate a safe and potent L. monocytogenes based vaccine. Moreover, the attenuated strains with embedded flagellin or PrgJ adjuvants, represent attractive vectors for vaccines aimed at eliciting T cell responses.

Listeria monocytogenes engineered to activate the Nlrc4 inflammasome are severely attenuated and are poor inducers of protective immunity

“…In this study we examined the role of inflammasome activation in the development of protective immunity to L. monocytogenes infection. Warren et al recently reported that L. monocytogenes strains engineered to activate the Nlrc4 inflammasome were capable of inducing protective immunity at high immunizing doses (35). In agreement with these findings, we also found that immunization with high doses of L. monocytogenes-L.p.FlaA induced protection from subsequent challenge.…”

“…Both the S. typhimurium study and the present study find attenuation of intracellular bacteria caused by activation of the Nlrc4 inflammasome; however, we find differences in the role that neutrophils play in this process. In agreement with our findings, Warren et al recently reported that L. monocytogenes that hyperactivate the Nlrc4 inflammasome were highly attenuated in vivo by a mechanism independent of IL-1β and IL-18 (35). Understanding how inflammasome activation mediates host defense and how pathogens have overcome these defenses is central to our broader understanding of both mechanisms of pathogenesis and the function of the innate immune system.…”

The Salmonella Type III Secretion System Inner Rod Protein PrgJ Is Partially Folded

“…Our purified PrgJ and MxiI triggered an increased level of IL-1␤ when transfected into mouse bone marrow-derived macrophages (Fig. 2), similar to the results shown by others that the inner rod proteins were able to increase the amount of IL-1␤ (15)(16)(17).…”

“…Despite the importance of the inner rod proteins in assembly of the needle complex (3)(4)(5)(6), pathogenesis (11)(12)(13)(14)20), and host immune response (15)(16)(17)(18), little is known about their biophysical and structural properties. Currently, no CD or NMR data has been reported for any T3SS inner rod proteins.…”

“…Recently, the inner rod proteins were shown to be potent inducers of the inflammasome (15)(16)(17)(18)(19). Miao et al (15) showed that PrgJ and other inner rod proteins (BsaK, EprJ, EscI, and PscI) interact with the NOD-like receptor NLRC4 to activate the maturation of interleukin-1␤ (IL-1␤), which triggers the host inflammatory response against microbial infection.…”