Site-directed immune responses in DNA vaccines encoding ligand-antigen fusions.

One of the key limitations to DNA vaccines is lack of efficacy. We found that the spleen was a superior injection site to the dermis or muscle for inducing immune responses. To target sites of immune induction more practicably, antigen (human IgG1) was fused with two ligands, L-selectin (L-SEL-hIg) or CTLA4 (CTLA4-hIg) the receptors of which are found on high endothelial venule cells in lymph nodes and antigen presenting cells, respectively. Antibody and lymphocyte proliferative responses were increased. We now show that dimerization is critical for this enhancement, presumably because of avidity considerations. The hinge of hIgG3 can replace that of hIgG1 as a dimerization moiety. Fusion of other antigens e.g. ovalbumin and a malaria antigen AMA-1 have confirmed that CTLA4 induces an enhanced antibody response. Notably, in a challenge model, we have shown that CTLA4 also improves efficacy.