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Naked DNA vaccines have a number of advantages over conventional vaccines, but induce only weak immune responses. We have here investigated if this inadequacy may be overcome by inducing muscle to secrete fusion proteins with the ability to target antigen-presenting cells (APC). The novel targeted vaccines are homodimers with (i) two identical single-chain fragment variable (scFv) targeting units specific for MHC class II molecules on mouse APC, (ii) a human Ig hinge and CH3 dimerization unit, and (iii) two identical scFv tumor antigenic units (idiotypes) from B cell cancers. After plasmid injection and electroporation of mouse muscle, secreted vaccine proteins (vaccibodies) delivered idiotypic tumor antigen to APC in draining lymph nodes for induction of T and B cell responses that protected mice against tumor challenges with a multiple myeloma (MOPC315) and a B cell lymphoma (A20). Targeting to APC was essential for these effects. The results show that immunogenicity of plasmid DNA vaccines can be increased by inducing muscle to secrete proteins that target antigen to APC.Molecular Therapy (2006) 13, 776–785; doi: 10.1016/j.ymthe.2005.10.019 [ABSTRACT FROM AUTHOR]

Abstract: Efficacy of DNA vaccination has been improved in mice by fusion vaccines targeting antigen to antigen-presenting cells (APC) via chemokine receptors. Here, we aimed at extending this strategy to large animals and humans. Fusion proteins equipped with human MIP1α (LD78β isoform) retained functional activity and conformational correctness of targeting and antigenic units, respectively. Fusion proteins improved responses of cloned human CD4+ T cells, and a two amino acid NH2-truncated version of LD78β outperformed full length LD78β-vaccine proteins in vitro. LD78β DNA fusion vaccines induced improved T cell (both CD4+ and CD8+) and antibody responses in mice following plasmid injection and skin electroporation. Finally, LD78β-vaccine proteins bound Rhesus macaque CCR5, setting the stage for targeted DNA immunization in non-human primates. [ABSTRACT FROM AUTHOR]

Abstract: Experiments in mice have suggested that engagement of receptors of innate immunity has an adjuvant effect on adaptive immune responses. Such studies need to be extended to humans. We have here constructed recombinant scFv-based vaccine candidate proteins (vaccibodies) that target human TLR2 and CD14 for delivery of large antigens. Vaccibodies are homodimers, each chain consisting of scFv specific for surface molecules on antigen-presenting cells (APC), a homodimerization motif, and an antigenic unit. The TLR2- and CD14-specific vaccibodies bound their respective target receptors expressed on transfected CHO cells and PBMC. Large proteins such as paired mouse Cκ-domains (229 aa) and fragment C of tetanus toxin (TetC, 451 aa) could be expressed as antigenic units with intact serological determinants detected by mAb or polyclonal antisera. In the presence of monocytes, TLR2- and CD14-specific vaccibodies having either Cκ or TetC as antigenic unit were 100–10,000 more efficient at stimulating T cell clones in vitro compared to non-targeted vaccibodies expressing the same antigens. The results show that TLR2 and CD14 are efficient targets for delivery of antigen to APC for stimulation of HLA class II-restricted CD4+ T cells. Thus, receptors of innate immunity should be further explored as targets for vaccines. [Copyright &y& Elsevier]