ABSTRACT
The most important hurdle for DNA vaccines is efficacy. Responses in humans especially antibody responses have been disappointing. Therefore. our work has principally been focused on increasing the potency of DNA immunization. As antigen is probably limiting in DNA immunisation, we opined that trapping the antigen at the sites of immune induction [eg. the secondary lymphoid organs] would enhance the immune response. Indeed we found that injecting directly into spleen was more immunogenic than into muscle even though muscle expression was IOO-fold higher. To target sites of immune induction more practicably, antigen [human IgG I] was fused with two ligands. L-selectin [L-SEL-hIg] or CTLA4 [CTLA4-hIg] whose receptors are found on high endothelial venule cells in lymph nodes and antigen presenting cells respectively Antibody responses were dramatically increased [1000-fold] and lymphocyte proliferative responses were increased 6-fold. We have further shown that dimerisation is critical for this enhancement. presumably because of avidity considerations. Fusion of other antigens eg. ovalbumin and a malaria antigen have confirmed that the enhancement by a targeting ligand is generic. Notably. in challenge models. we have shown that targeting also improves efficacy