Objective: To evaluate the protective efficacy of MPT64 and ESAT6 DNA vaccines from M. tuberculosis.
Methods: BALB/c mice were randomly divided into five groups and subjected to the following treatments respectively, i.e. immunized with saline (A), plasmid vector (B), M. bovis BCG (C), MPT64 DNA vaccine (D) or ESAT6 DNA vaccine (E); and then infected by intraperitoneal injection with M. tuberculosis H37Rv. The lung histopathological changes were observed 5 or 10 weeks after infection by microscopy.
Results: At 5 weeks after infection, the lung lesions in the mice of group A and B had inflammatory infiltration with epithelial cell granulomas. In the mice of group C, main pathological changes were epithelial cell granulomas with moderate granulate hyperplasia in alveolar walls. The lung lesions of 3 mice in group D and 1 mice in group E were similar to those seen in the mice in group A and B. The lung lesions of 2 mice in group D and 4 mice in group E were similar to those seen in the mice in group C. At 10 weeks after infection, their tuberculous pneumonia tended to recovery. For the mice in groups A, B and D, their lung pathology exhibited tuberculous granulomas consisted of numerous macrophages, lymphocytes and a few epithelial cells with moderate granulate hyperplasia in alveolar walls. For the mice in groups of C and E, their lung developed epithelial cell and lymphocytic granulomas with moderate to severe granulate hyperplasia in alveolar walls. Lung tissue necrosis was not observed in any mouse.
Conclusions: MPT64 and ESAT6 DNA vaccines from M. tuberculosis could enhance immunity against M. tuberculosis. The protective efficacy of ESAT6 DNA vaccine is stronger than that of MPT64 DNA vaccine, but not stronger than that of Mycobacterium bovis BCG.