Enhancement of DNA vaccine potency by linkage of antigen gene to a gene encoding the extracellular domain of Fms-like tyrosine kinase 3-ligand

Recently, Flt3 (Fms-like tyrosine kinase 3)-ligand has been identified as a n important cytokine for the generation of professional antigen-presenting cells (APCs), particularly dendritic cells (DCs), A recombinant chimera of the extracellular domain of Flt3-ligand (FL) linked to a model antigen may potentially target the antigen to DCs and their precursor cells, Using huma n papillomavirus-16 E7 as a model antigen, we evaluated the effect of linka ge to FL on the potency of antigen-specific immunity generated by naked DNA vaccines administered intradermally via gene gun. We found that vaccines c ontaining chimeric FL-E7 fusion genes significantly increased the frequency of E7-specific CD8(+) T cells relative to vaccines containing the wild-typ e E7 gene. In vitro studies indicated that cells transfected with FL-E7 DNA presented E7 antigen through the MHC class I pathway more efficiently than wild-type E7 DNA, Furthermore, bone marrow-derived DCs pulsed with cell ly sates containing FL-E7 fusion protein presented E7 antigen through the MHC class I pathway more efficiently than DCs pulsed with cell lysates containi ng wild-type E7 protein. More importantly, this fusion converted a less eff ective vaccine into one with significant potency against established Ell-ex pressing metastatic tumors, The FL-E7 fusion vaccine mainly targeted CD8+ T cells, and antitumor effects were completely CD4 independent, These result s indicate that fusion of a gene encoding the extracellular domain of FL to an antigen gene may greatly enhance the potency of DNA vaccines via CDS-de pendent pathways.