DNA vaccine constructs expressing Mycobacterium tuberculosis-specific genes induce immune responses

RD1 PE35, PPE68, EsxA, EsxB and RD9 EsxV genes are present in Mycobacterium tuberculosis genome but deleted in Mycobacterium bovis BCG. The aim of this study was to clone these genes into DNA vaccine vectors capable of expressing them in eukaryotic cells as fusion proteins, fused with immunostimulatory signal peptides of human interleukin-2 (hIL-2) and tissue plasminogen activator (tPA), and evaluate the recombinant DNA vaccine constructs for induction of antigen-specific cellular immune responses in mice. DNA corresponding to the aforementioned RD1 and RD9 genes was cloned into DNA vaccine plasmid vectors pUMVC6 and pUMVC7 (with hIL-2 and tPA signal peptides, respectively), and a total of 10 recombinant DNA vaccine constructs were obtained. BALB/c mice were immunized with the parent and recombinant plasmids and their spleen cells were tested for antigen-induced proliferation with antigens of M. tuberculosis and pure proteins corresponding to the cloned genes. The results showed that antigen-specific proliferation responses were observed for a given antigen only with spleen cells of mice immunized with the homologous recombinant DNA vaccine construct. The mice immunized with the parent plasmids did not show positive immune responses to any of the antigens of the cloned genes. The ability of the DNA vaccine constructs to elicit cellular immune responses makes them an attractive weapon as a safer vaccine candidate for preventive and therapeutic applications against tuberculosis.