DNA-Launched Alphavirus Replicons Encoding a Fusion of Mycobacterial Antigens Acr and Ag85B Are Immunogenic and Protective in a Murine Model of TB Infection.

Neha Dalmia,Alistair J Ramsay,William B Klimstra,Carol Mason,Anil Kumar Tyagi

doi:10.1371/journal.pone.0136635

Neha Dalmia, Alistair J Ramsay + Show 3 more

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https://doi.org/10.1371/journal.pone.0136635

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Abstract

There is an urgent need for effective prophylactic measures against Mycobacterium tuberculosis (Mtb) infection, particularly given the highly variable efficacy of Bacille Calmette-Guerin (BCG), the only licensed vaccine against tuberculosis (TB). Most studies indicate that cell-mediated immune responses involving both CD4+ and CD8+ T cells are necessary for effective immunity against Mtb. Genetic vaccination induces humoral and cellular immune responses, including CD4+ and CD8+ T-cell responses, against a variety of bacterial, viral, parasitic and tumor antigens, and this strategy may therefore hold promise for the development of more effective TB vaccines. Novel formulations and delivery strategies to improve the immunogenicity of DNA-based vaccines have recently been evaluated, and have shown varying degrees of success. In the present study, we evaluated DNA-launched Venezuelan equine encephalitis replicons (Vrep) encoding a novel fusion of the mycobacterial antigens α-crystallin (Acr) and antigen 85B (Ag85B), termed Vrep-Acr/Ag85B, for their immunogenicity and protective efficacy in a murine model of pulmonary TB. Vrep-Acr/Ag85B generated antigen-specific CD4+ and CD8+ T cell responses that persisted for at least 10 wk post-immunization. Interestingly, parenterally administered Vrep-Acr/Ag85B also induced T cell responses in the lung tissues, the primary site of infection, and inhibited bacterial growth in both the lungs and spleens following aerosol challenge with Mtb. DNA-launched Vrep may, therefore, represent an effective approach to the development of gene-based vaccines against TB, particularly as components of heterologous prime-boost strategies or as BCG boosters.

Highlights

A third of the human population is latently infected with Mycobacterium tuberculosis (Mtb), and at risk for disease reactivation [1]
The ligation product was transformed into competent TOP10 E. coli cells (Invitrogen) and positive clones were confirmed by PCR using vector-specific primers and DNA sequencing. pHis vectors without antigens α-crystallin (Acr)/antigen 85B (Ag85B) gene inserts were used as control DNA vaccines
In attempts to optimize the outcome of Venezuelan equine encephalitis replicons (Vrep) immunization, we investigated whether increasing the interval between successive doses of Vrep-Acr/Ag85B from 3 wk to 6 wk affected vaccine immunogenicity

Summary

Introduction

A third of the human population is latently infected with Mycobacterium tuberculosis (Mtb), and at risk for disease reactivation [1]. The recent development of self-amplifying replicons “launched” from DNA plasmids addresses these issues, while providing DNA-based vaccines of greatly enhanced immunogenicity [24,25,26,27,28,29] These constructs are essentially DNA vaccines where a cDNA copy of the viral replicase and the vaccine antigen are placed on a plasmid backbone under the control of a cytomegalovirus promoter [28]. They retain the immune-stimulatory qualities of VRP and have proven to be immunogenic in several murine models of infection [24,25,26,27,28,29]

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