A polyvalent DNA vaccine expressing an ESAT6-Ag85B fusion protein protects mice against a primary infection with Mycobacterium tuberculosis and boosts BCG-induced protective immunity.

In this study, we evaluated the protective efficacy of a DNA vaccine (pE6/85) expressing an ESAT6-Ag85B fusion protein against a primary Mycobacterium tuberculosis infection in mice. In short-term studies, vaccination with pE6/85 protected as well as Mycobacterium bovis BCG immunization with similar lung pathology and bacterial burdens detected 28 days after a low dose aerogenic challenge (>1.0 log(10) reduction relative to naïves). In a survival experiment, the protection induced by pE6/85 immunization was also not significantly different than that elicited by BCG vaccination with the mean-times-to-death (+/-standard error of the mean) being 102+/-20, 271+/-32 and 299+/-14 days for naïve, pE6/85 and BCG-vaccinated mice, respectively. Furthermore, boosting with pE6/85 but not BCG or a DNA vaccine cocktail at 1 year after an initial BCG immunization (when BCG-induced protection was declining), augmented protection in the lung at 15 and 18 months to levels detected at 3 months post-BCG vaccination.