Study on the efficient induction of therapeutic immunity against Mycobacterium tuberculosis infection by DNA immunization

DoctorIdentification of antigens that provide protective immunity via prophylacticand therapeutic vaccination against Mycobacterium tuberculosis (MTB) infectionis critical for the development of subunit vaccines for tuberculosis (TB). In thefirst part of this study, a head-to-head comparison of seven well-known MTBantigens delivered by DNA vaccine and evaluation of their respectiveimmunogenicities and protective efficacies in pre- and post-exposure mousemodels were performed. All TB antigens were designed as a chimeric fusion withFlt3-L to enhance antigen-specific T cell immunity upon vaccination. Prophylacticvaccination with the Flt3L (F)-Mtb32 DNA vaccine elicited significant protectionin both the lungs and spleen against MTB challenge, comparable to the BCGvaccine. F-Ag85A and F-Mtb32 DNA vaccines, in combination withiichemotherapy, reduced bacterial burden to undetectable levels in the lungs of allmice infected with MTB. These data collectively indicate that the F-Mtb32 DNAvaccine confers the most efficient protective immunity that suppresses bacterialgrowth in the active or latent status of MTB.Although a potent protective and therapeutic TB antigen, Mtb32, were drived,search of an efficient adjuvant for DNA vaccines is crucial to overcome weakimmunogenicity of DNA vaccine in larger animal model, and eventually human.Using an aerosol MTB infection mouse model, we analyzed how concurrenttreatment of nonlytic Fc-fused IL-7 DNA (IL-7-nFc) and Flt3-ligand fused Mtb32(F-Mtb32) DNA improved the immunogenicity of DNA vaccines. Mice weresubject to conventional chemotherapy for 6 weeks starting at 4 weeks after aerosolinfection of MTB. Once chemotherapy began, DNA immunizations wereadministered 5 times at 2 week intervals. Coadministration of IL-7-nFc and FMtb32DNA during chemotherapy synergistically enhanced the effectiveness ofMtb32-specific T cell responses and was sustainable for up to one year after thelast immunization as assessed by IFN-γ ELISPOT assay. Furthermore, afterdexamethasone treatment, TB reactivation was significantly reduced in micereceiving both IL-7-nFc and F-Mtb32 DNA compared to control mice or miceadministered with F-Mtb32 DNA alone. Additionally, mice treated with IL-7-nFcand F-Mtb32 together exhibited improved lung pathology and reduced pulmonaryinflammation values relative to saline injected mice or F-Mtb32 DNA only treatediiimice. Intracellular cytokine staining demonstrated that the protective effects of thecombinatory IL-7-nFc and F-Mtb32 DNA therapy was associated with enhancedMtb32-specific IFN-γ secreting CD4+ T cell and CD8+ T cell responses stimulatedusing cytotoxic T lymphocyte epitope peptide in the lungs and spleens of mice.These data suggest that IL-7-nFc functions as a novel adjuvant by significantlyenhancing TB DNA vaccine-induced T cell immunity and may facilitate futuretherapeutic TB DNA vaccine use in clinics