The Tuberculosis Vaccine Candidate Bacillus Calmette-Guérin ΔureC::hly Coexpressing Human Interleukin-7 or -18 Enhances Antigen-Specific T Cell Responses in Mice

Bacillus Calmette–Guérin (BCG), the only approved tuberculosis vaccine, provides only limited protection. Previously, we generated a recombinant derivative (BCG Δ ureC :: hly ), which secretes the pore-forming toxin listeriolysin O (LLO) of Listeria monocytogenes . This vaccine shows superior protection against tuberculosis in preclinical models and is safe in humans. Here we describe two new vaccine strains which express human interleukin-7 (hIL)-7 or hIL-18 in the genetic background of BCG Δ ureC :: hly to modulate specific T cell immunity. Both strains exhibited an uncompromised in vitro growth pattern, while inducing a proinflammatory cytokine profile in human dendritic cells (DCs). Human DCs harbouring either strain efficiently promoted secretion of IL-2 by autologous T cells in a coculture system, suggesting superior immunogenicity. BALB/c mice vaccinated with BCG Δ ureC :: hly , BCG Δ ureC :: hly_hIL7 or BCG Δ ureC :: hly _ hIL18 developed a more robust Th1 response than after vaccination with parental BCG. Both strains provided significantly better protection than BCG in a murine Mycobacterium tuberculosis challenge model but efficacy remained comparable to that afforded by BCG Δ ureC :: hly . We conclude that expression of hIL-7 or hIL-18 enhanced specific T cell responses but failed to improve protection over BCG Δ ureC :: hly in mice.