LB19. Intramuscular therapeutic immunization targeting Rel(Mtb)/MIP-3 induces immune signatures associated with better TB control in vivo compared to

BACKGROUND: Tuberculosis (TB) is one of the leading causes of death from a single infectious agent worldwide. The lengthy treatment regimen reflects the unique ability of a subpopulation of “persister” bacteria to remain in a nonreplicating state in the infected host through various adaptive strategies, including induction of the stringent response. The key stringent response enzyme, Rel(Mtb), is essential for long-term Mycobacterium tuberculosis (Mtb) survival under physiologically relevant stresses in vitro and in animal lungs. Recently, our group has generated a therapeutic, parenteral, rel(Mtb) DNA vaccine, which induces Rel(Mtb)-specific cellular immunity and augments the activity of the first-line drug isoniazid against active TB in mice and guinea pigs. Our group also has applied a novel vaccination strategy involving the fusion of an antigen of interest with the immature dendritic cell (iDC)-targeting chemokine MIP-3α/CCL20, which significantly enhances antigen-specific T-cell responses. We sought to determine if this iDC-targeting strategy improves the immunogenicity of the therapeutic rel(Mtb) DNA vaccine. METHODS: We cloned the rel(Mtb) and chemokine MIP-3α genes into the eukaryotic expression plasmid pSectag2b. We conducted an immunogenicity study using C57BL/6J mice, comparing the T-cell responses between the rel(Mtb)vs. MIP-3α/rel(Mtb) DNA intramuscular vaccination groups. RESULTS: Intramuscular administration of the DNA vaccine expressing the MIP-3α/rel(Mtb) gene fusion induced increased production of various Mtb-protective cytokines (IL-17α, IL-2, TNF-α, IFN-γ) in various mouse tissues, including the spleen, draining lymph nodes and peripheral blood mononuclear cells, relative to the vaccine expressing rel(Mtb) alone. CONCLUSION: Intramuscular immunization with a DNA vaccine expressing rel(Mtb)/MIP-3α induces robust in vivo Mtb-protective immune signatures, suggesting this may be a promising adjunctive approach in combination with standard anti-TB therapy. DISCLOSURES: All Authors: No reported disclosures