Consequently, a number of innovative strategies have been developed to facilitate and enhance the immunogenicity of attenuated poxvirus vectors, including the use of heterologous prime-boost regiments (151) , co-administration of TLR agonists (152) , cytokines (153) (154) (155) (156) (157) , and targeting T cell co-stimulatory receptors (158) (159) (160) .