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 C(H)3 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.

New influenza A viruses with pandemic potential periodically emerge due to viral genomic reassortment. In the face of pandemic threats, production of conventional egg-based vaccines is time consuming and of limited capacity. We have developed in this study a novel DNA vaccine in which viral hemagglutinin (HA) is bivalently targeted to MHC class II (MHC II) molecules on APCs. Following DNA vaccination, transfected cells secreted vaccine proteins that bound MHC II on APCs and initiated adaptive immune responses. A single DNA immunization induced within 8 d protective levels of strain-specific Abs and also cross-reactive T cells. During the Mexican flu pandemic, a targeted DNA vaccine (HA from A/California/07/2009) was generated within 3 wk after the HA sequences were published online. These results suggest that MHC II–targeted DNA vaccines could play a role in situations of pandemic threats. The vaccine principle should be extendable to other infectious diseases.

IntroductionB lymphomas and multiple myelomas (MMs) produce monoclonal Ig, the V regions of which can serve as targets for tumor-specific immune responses. 1,2 The V region antigenic determinants (idiotype [Id]) arise as a consequence of clone-specific V(D)J rearrangements and somatic mutations. Id can be directly recognized in 3 ways: (1) by Ab, 3 (2) by CD4 ϩ , 4 and (3) by CD8 ϩ T cells. 5 Id-specific CD4 ϩ and CD8 ϩ T cells recognize V region-derived Id peptides presented on MHC class II and I molecules, respectively. While B-lymphoma cells display all 3 types of Id targets on their cell surface, MM cells often express little surface Ig and MHC class II. Nevertheless, Id-specific CD4 ϩ T cells can confer protection against MHC class II-negative MM cells because secreted myeloma protein is processed and presented by tumorinfiltrating antigen-presenting cells (APCs) to Id-specific CD4 ϩ T cells. [6][7][8] Immunization with myeloma protein in complete Freund adjuvant (CFA) induced an Id-specific resistance against tumor challenge in mice, 1 a finding that has been confirmed and extended in a number of experimental mouse studies. Id vaccination has entered clinical trials, with more promising results in B-cell lymphoma 9 than in MM 10 patients. However, Id is a weak antigen and a number of innovative strategies have been used to increase its immunogenicity. Id-pulsed dendritic cells (DCs) 11 are promising, but suffer from labor-intensive manufacture. Attractive alternatives are to fuse Ig, Fab, or single-chain fragment variable (scFv) to GM-CSF, 12 chemokines, [13][14][15] CD40Ligand, 16 tetanus toxin fragment C, and to deliver these as protein 12,13,[16][17][18] or DNA 13,17,18 vaccines. Such immunizations have generated tumorprotective responses by mechanisms that are not fully elucidated, but that most likely include targeting of Id to APCs, APC maturation, or both.Chemokines control migration of specific leukocyte populations during inflammatory responses, hematopoiesis, and routine immune surveillance. RANTES (regulated upon activation normal T-cell expressed, CCL5) and MIP-1␣ (macrophage inflammatory protein 1␣, CCL3) are inflammatory chemokines. They both have high affinity for CCR1 and CCR5 expressed on T cells, monocytes, natural killer cells, and DCs.MIP-1␣ and RANTES self-associate to form high-molecularmass aggregates. 19,20 However, the activation state of chemokine monomers versus oligomers has been a disputed field. [21][22][23] It has been shown that chemokine receptors initiate their ligand-induced signaling cascades by receptor dimerization. [24][25][26] Monomeric variants of RANTES and MIP-1␤ retain full activity in vitro, but are devoid of activity in vivo, suggesting that these chemokines require oligomerization to recruit cells in vivo. 27 It has been proposed that although chemokines are able to interact with receptors as monomers, 21 glycosaminoglycan-induced oligomerization of chemokines can achieve higher order oligomers in vivo, and they may interact with receptors differently as dime...