CD8 + T cells specific to a single Yersinia pseudotuberculosis epitope restrict bacterial replication in the liver but fail to provide sterilizing immunity

Abstract

CD8+ T cells use contact-dependent cytolysis of target cells to protect the host against intracellular pathogens. We have previously shown that CD8+ T cells and perforin are required to protect against the extracellular pathogen Yersinia pseudotuberculosis. Here we establish an experimental system where CD8+ T cells specific to a single model antigen are the only memory response present at time of challenge. Using mice immunized with a vaccine strain of Listeria monocytogenes that expresses secreted ovalbumin (Lm-OVA), we show that OVA-specific CD8+ T cells are generated and provide limited protection against challenge with virulent OVA+ Y. pseudotuberculosis. Perforin expression by OVA-specific CD8+ T cells was required, as Lm-OVA-immunized perforin-deficient mice showed higher bacterial burden as compared to Lm-OVA-immunized perforin-sufficient mice. Surprisingly, antigen-specific T cell protection waned over time, as Lm-OVA-immune mice eventually succumbed to Yersinia infection. Kinetic analysis of infection in mice with and without OVA-specific CD8+ T cells revealed that bacterial numbers increased sharply in OVA-naïve mice until death, while OVA-immune mice held bacterial burden to a lower level throughout the duration of illness until death. Clonal analysis of bacterial populations in OVA-naïve and OVA-immune mice at distinct time points revealed equivalent and severe bottle-neck effects for bacteria in both sets of mice immediately after intravenous challenge, demonstrating a dominant role for other aspects of the immune system regardless of CD8+ T cell status. These studies indicate that CD8+ T cells against a single antigen can restrict Y. pseudotuberculosis colonization in a perforin-dependent manner, but ultimately are insufficient in their ability to provide sterilizing immunity and protect against death.

Checkpoint blockade inhibitors enhances the effectiveness of aListeria monocytogenes-based melanoma vaccine

“…Female and male C57BL/6 mice vaccinated with 2 × 10 4 CFU of the OVA-expressing L. monocytogenes strain developed a robust OVA specific CD8 + /TCRβ + T-cell response while those vaccinated with the parental L. monocytogenes strain did not ( Figure 1B and 1C). As previously reported by us and others [28,29], a single vaccination with increasing doses of Lm: OVA (2 × 10 5 or 2 × 10 6 CFU) vaccine failed to significantly increase the numbers of OVA specific CD8 + /TCRβ + T-cells (Supplementary Figure 1A and 1B). Importantly, the ΔactA:plcB (Lm: Parental) as well as the actA-OVA fusion (Lm: OVA) vaccine strains were completely attenuated with i. v. vaccination doses up to 2 × 10 7 CFU ( Figure 1D).…”

“…Although others have reported similar protection with oral or intra-muscular routes of vaccination [29], the safety of this specific strain [26,28] and newer phase I safety trials [45] suggest vaccination via the i.v. route is not a barrier to utilization.…”

“…We previously showed that the Lm: OVA vaccine induces a robust antigen-specific CD8 + /TCRβ + T-cell response ( Figure 1B and 1C) and [28]. However, both CD8 + T-cells and NK cells have been shown to be important in Lm vaccine-mediated immunity [36].…”

“…We previously described the Listeria monocytogenes strain deficient in both actin-assembly inducing protein (actA) and phospholipase C (plcB) [28], which was used as the vaccine platform in this study. This double mutant is completely attenuated in humans, lacking the ability to directly enter a neighboring cell or escape a secondary membrane [34], and importantly it is unable to cause neuro-invasiveness [35].…”

“…Several Lm cancer vaccination platforms have fused tumorassociated antigens (TAA) to the LLO peptide [22][23][24]. Due to its proinflammatory properties [25] and lack of pathogenesis in human subjects [26], we developed an actA:plcB double mutant with the TAA peptide fused to the first 100 amino acids of ActA [27,28]. Fusing TAAs to ActA results in the TAA being delivered directly to the cytoplasm and thus the MHC-I processing compartment.…”