Immunotherapeutic effects of recombinant adenovirus encoding interleukin 12 in experimental pulmonary tuberculosis

High dose of Mycobacterium tuberculosis (Mtb) strain H37Rv administered by intratracheal injection in BALB/c mice induce progressive tuberculosis (TB). In this model, during the first month there is a temporal control of bacillary growth, in coexistence with macrophage activation, granuloma formation and Th-1 response. Then, bacterial proliferation recommences, accompanied by progressive pneumonia and decreasing expression of protective cytokines (IFN-gamma and TNF-alpha). In this model, we studied the IL-12 gene expression kinetics and cellular source. There is a rapid and progressive IL-12 expression peaking at day 14, when granulomas start their formation and numerous macrophages show strong IL-12 immunostaining, while during progressive TB there is a significant decrease of IL-12 expression and occasional macrophages showed IL-12 immunolabeling. In the second part of this study, we determined the immunotherapeutic effect of recombinant adenoviruses that codify IL-12 (AdIL-12). Intratracheal administration of only one dose of AdIL-12 one day before Mtb infection produced significant decrease of bacterial loads, lesser pneumonia and higher expression of TNF-alpha, IFN-gamma and iNOS. When only one dose of AdIL-12 was given in healthy mice cohoused with infected mice with highly virulent and transmissible Mtb, total prevention of infection was conferred. Moreover, when AdIL-12 was administered by intranasal route in animals suffering late active TB after 2 months of infection, a very low pulmonary bacilli burdens was detected. These experimental data confirm that IL-12 is a significant cytokine in the immune protection against Mtb, and gene therapy based in adenoviruses coding this cytokine increased protective immunity and prevent Mtb transmission.