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DNA vaccines based on subunits from pathogens have several advantages over other vaccine strategies. DNA vaccines can easily be modified, they show good safety profiles, are stable and inexpensive to produce, and the immune response can be focused to the antigen of interest. However, the immunogenicity of DNA vaccines which is generally quite low needs to be improved. Electroporation and co-delivery of genetically encoded immune adjuvants are two strategies aiming at increasing the efficacy of DNA vaccines. Here, we have examined whether targeting to antigen-presenting cells (APC) could increase the immune response to surface envelope glycoprotein (Env) gp120 from Human Immunodeficiency Virus type 1 (HIV-1). To target APC, we utilized a homodimeric vaccine format denoted vaccibody, which enables covalent fusion of gp120 to molecules that can target APC. Two molecules were tested for their efficiency as targeting units: the antibody-derived single chain Fragment variable (scFv) specific for the major histocompatilibility complex (MHC) class II I-E molecules, and the CC chemokine ligand 3 (CCL3). The vaccines were delivered as DNA into muscle of mice with or without electroporation. Targeting of gp120 to MHC class II molecules induced antibodies that neutralized HIV-1 and that persisted for more than a year after one single immunization with electroporation. Targeting by CCL3 significantly increased the number of HIV-1 gp120-reactive CD8+ T cells compared to non-targeted vaccines and gp120 delivered alone in the absence of electroporation. The data suggest that chemokines are promising molecular adjuvants because small amounts can attract immune cells and promote immune responses without advanced equipment such as electroporation. [ABSTRACT FROM AUTHOR]

Background: Idiotypes (Id) are antigenic determinants localized in variable (V) regions of Ig. Id-specific T and B cells (antibodies) play a role in immunotherapy of Id+ tumors. However, vaccine strategies that enhance Id-specific responses are needed. Methods: Id+ single-chain fragment variable (scFv) from multiple myelomas and B cell lymphomas were prepared in a fusion format that bivalently target surface molecules on antigen-presenting cells (APC). APC-specific targeting units were either scFv from APC-specific mAb (anti-MHC II, anti-CD40) or chemokines (MIP-1α, RANTES). Homodimeric Id-vaccines were injected intramuscularly or intradermally as plasmids in mice, combined with electroporation. Results: (i) Transfected cells secreted plasmid-encoded Id+ fusion proteins to extracellular fluid followed by binding of vaccine molecules to APC. (ii) Targeted vaccine molecules increased Id-specific B and T cell responses. (iii) Bivalency and xenogeneic sequences both contributed to enhanced responses. (iv) Targeted Id DNA vaccines induced tumor resistance against challenges with Id+ tumors. (v) Human MIP-1α targeting units enhanced Id-specific responses in mice, due to a cross reaction with murine chemokine receptors. Thus, targeted vaccines designed for humans can be quality tested in mice. (vi) Human Id+ scFv from four multiple myeloma patients were inserted into the vaccine format and were successfully tested in mice. (vii) Human MIP-1a vaccine proteins enhanced human T cell responses in vitro. (viii) A hypothetical model for how the APC-targeted vaccine molecules enhance Id-specific T and B cells is presented. Conclusion: Targeted DNA Id-vaccines show promising results in preclinical studies, paving the way for testing in patients. [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]