Combined DNA vaccine encapsulated in microspheres enhanced protection efficacy against Mycobacterium tuberculosis infection of mice

In a study to develop novel vaccination strategies against tuberculosis, we encapsulated DNA encoding Ag85B, MPT-64 and MPT-83 antigens mixed with dimethyldioctyldecyl ammonium bromide (DDA) into biodegradable poly(dl-lactide-co-glycolide, PLGA) microspheres. Scanning electron microscopy (SEM) analysis demonstrated a uniform microsphere population with a mean diameter of <5 μm. Using RT-PCR we were able to demonstrate antigen gene expression in selected tissue. Moreover, in mice injected with PLGA encapsulated DNA, the levels of expression appeared to be higher comparing to those injected with non-encapsulated DNA. Also, C57BL/6 mice immunized with a single dose of PLGA encapsulated DNA produced increased levels of IFN-γ in the supernatant of spleen cells when cultured in the presence of the recombinant antigens. High levels of specific IgG antibody against the three antigens were also observed. In vaccine/challenge experiments, mice receiving a single dose of PLGA encapsulated DNA were protected against Mycobacterium tuberculosis challenge at levels comparable to groups of mice immunized with three doses of non-encapsulated DNA vaccine or with Mycobacterium bovis BCG.