Since the priming and boosting vectors are different, this strategy allows for greater expansion of the disease antigen-specific T cell populations [115] . To date, heterologous prime-boost regimens are among the most potent strategies to induce cellular immune responses. Compared to homologous prime-boost approach with the same DNA vaccine, boosting a primary response with a heterologous vector will result in 4-10-fold higher T cell responses [116] [117] [118] .