Chemokine-idiotype fusion DNA vaccines are potentiated by bivalency and xenogeneic sequences

V regions of monoclonal Ig express an exquisite B-cell tumor-specific antigen called idiotype (Id). Id is a weak antigen and it is important to improve immunogenicity of Id vaccines. Chemokine receptors are expressed on antigen-presenting cells (APCs) and are promising targets for Id vaccines. Here we compare monomeric and dimeric forms of MIP-1 alpha and RANTES that target Id to APCs in a mouse B lymphoma (A20) and a multiple myeloma model (MOPC315). MIP-1 alpha was more potent than RANTES. The dimeric proteins were more potent than monomeric equivalents in short-term assays. When delivered in vivo by intramuscular injection of plasmids followed by electroporation, dimeric proteins efficiently primed APCs in draining lymph nodes for activation and proliferation of Id-specific CD4(+) T cells. Good anti-Id antibody responses were obtained, and mice immunized only once were 60% to 80% protected in both tumor models. CD8(+) T cells contributed to the protection. Antibody responses and tumor protection were reduced when the human Ig hinge + C(H)3 dimerization motif was replaced with syngeneic mouse counterparts, indicating that tumor-protective responses were dependent on xenogeneic sequences. The results suggest that bivalency and foreign sequences combine to increase the efficiency of chemokine-Id DNA vaccines.