COMPARATIVE-STUDY OF DNA-BASED IMMUNIZATION VECTORS - EFFECT OF SECRETION SIGNALS ON THE ANTIBODY-RESPONSES IN MICE

The presence of a signal sequence preceding the gene encoding a target antigen in a DNA vaccine should facilitate secretion of the in vivo t ranslated antigen. The immune responses elicited upon injection with s uch a vector could differ from those induced by the same vector lackin g a signal sequence. In the present study, the humoral responses elici ted in mice immunized with two plasmids, either containing or lacking the human tissue plasminogen activator signal sequence, were compared. Both plasmids encode the chimeric antigen ZZN4, containing a malaria antigen Pf332-derived sequence (N4) linked to a bacterial fusion partn er (ZZ). In vitro transfection of COS cells with each plasmid and trea tment of the transfectants with brefeldin A confirmed that secretion o f ZZN4 via the endoplasmic reticulum and Golgi pathway only occurred i n cells transfected with the signal peptide-encoding plasmid. Repeated intramuscular injections of mice with either of the plasmids elicited comparable antibody responses to ZZN4 with regard to kinetics, specif ic IgG levels and persistence. These results indicate that in vivo tra nsfection of muscle cells by either of these two plasmids generated co mparable levels of antigen available for B-cell recognition and for up take by antigen-presenting cells, despite the differential intracellul ar targeting of the encoded antigen. The relevance of these findings f or the design of DNA vaccine vectors is discussed.