Correlates of protection associated with Yersinia pestis F1-LicKM and LcrV-LicKM vaccinations : protection against lethal challenge and potential t cell specific immunity
Date
2012
Authors
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Publisher
University of Delaware
Abstract
Yersinia pestis is a Gram-negative, facultative anaerobe that is the etiological agent of pneumonic plague. Y. pestis is categorized a category A select agent by the CDC, and despite over a hundred years of research an effective, safe vaccine protecting against the pneumonic form of infection has yet to be developed. Previous live vaccines using attenuated Y. pestis have been deemed unsafe for general use as it is highly reactogenic in healthy adults, and formalin killed whole-cell vaccines fail to protect against the pneumonic form of infection. Here, we investigate a novel plague vaccine using F1 and LcrV antigens fused to the carrier protein lichenase (LicKM), a thermostable enzyme from Clostridium thermocellum in a BALB/c mouse challenge model using the attenuated Y. pestis KIM D27 strain. Using this model, we determined the vaccine-generated parameters of protective efficacy against an intranasal challenge of Y. pestis KIM D27. Serum from vaccinated mice, adoptively transferred into naïve mice, conferred protection against lethal challenge. Removal of effector antibodies through Protein G column treatment eliminated this protection. Additionally, IL-2 was produced from vaccine-generated memory CD4+ T cells upon restimulation in vitro with vaccine proteins. Finally, adoptive transfer of F1 and LcrV specific T cells from vaccinated mice to naïve mice protected against lethal challenge. Taken together, we have demonstrated vaccine-generated humoral and cell-mediated protection against lethal challenge. Also, we developed a novel tool to specifically study the T cell response to Yersinia pestis infection. This immunological tool, a pKKOVA plasmid which encodes full length ovalbumin, was transformed into two attenuated strains of Y. pestis KIM D27 and KIM 10. Using transgenic mice with T cell receptors specific for peptide residues within ovalbumin (OT-I and OT-II), we were able to evaluate the ability of Y. pestis transformed with plasmid to stimulate T cells. We determined through this model that Y. pestis KIM D27pKKOVA was able to stimulate OT-I, MHC I restricted, CD8+ T cells in vitro through upregulation of memory T cell surface markers CD44, CD25, and CD27. KIM D27pKKOVA was also able to stimulate OT-II, MHC II restricted, CD4+ T cells but to a much lesser extent. KIM 10pKKOVA was able to stimulate OT-I, CD8+ T cells which showed upregulation of CD44 and CD27, but was unable to stimulate any OT-II, CD4+ T cells. These results confirm the development of a novel tool allowing us to track T cell populations that change specifically in response to Yersinia pestis infection.