Abstract
Active immunotherapy based on live attenuated bacterial vectors has matured in terms of industrial development and develops through a combination of three phenomena. First, active immunotherapy that stimulates an antigen-specific cytotoxic T-cell immune response has become a reality after several years of work. Second, there is still a need to identify vectors that can deliver antigens to the cytosol of antigen-presenting cells in vivo. Third, the recent progress in the understanding of bacterial lifestyle and in developing genetic engineering tools has enabled the design of bioengineered bugs that are capable of delivering antigens. Here, we review the mechanisms by which clinical bacterial vectors deliver antigens into the cytosol of antigen-presenting cells and summarize the development strategy of the three identified firms in this field.