DNA vaccination against tuberculosis: Expression of a ubiquitin-conjugatedtuberculosis protein enhances antimycobacterial immunity

Genetic immunization is a promising new technology for developing vaccines against tuberculosis that are more effective. In the present study, we eval uated the effects of intracellular turnover of antigens expressed by DNA va ccines on the immune response induced by these vaccines in a mouse model of pulmonary tuberculosis. The mycobacterial culture filtrate protein MPT64 w as expressed as a chimeric protein fused to one of three variants of the ub iquitin protein (UbG, UbA, and UbGR) known to differentially affect the int racellular processing of the coexpressed antigens, Immunoblot analysis of c ell lysates of in vitro-transfected cells showed substantial differences in the degradation rate of ubiquinated MPT64 (i.e., UbG64 < UbA64 < UbGR64). The specific immune response generated in mice correlated with the stabilit y of the ubiquitin-conjugated antigen. The UbA64 DNA vaccine induced a weak humoral response compared to UbG64, and a mixed population of interleukin- 4 (IL-4)- and gamma interferon (IFN-gamma)-secreting tells, Vaccination wit h the UbGR64 plasmid generated a strong Th1 cell response (high IFN-gamma, low IL-4) in the absence of a detectable humoral response, Aerogenic challe nge of vaccinated mice with Mycobacterium tuberculosis indicated that immun ization with both the UbA64- and UbGR64-expressing plasmids evoked an enhan ced protective response compared to the vector control. The expression of m ycobacterial antigens from DNA vaccines as fusion proteins with a destabili zing ubiquitin molecule (UbA or UbGR) shifted the host response toward a st ronger Th1-type immunity which was characterized by low specific antibody l evels, high numbers of IFN-gamma-secreting cells, and significant resistanc e to a tuberculous challenge.