PLASMID DNA EXPRESSING A SECRETED OR A NONSECRETED FORM OF HEPATITIS-C VIRUS NUCLEOCAPSID - COMPARATIVE-STUDIES OF ANTIBODY AND T-HELPER RESPONSES FOLLOWING GENETIC IMMUNIZATION

In a murine model, we have compared humoral and T-helper (Th) response s induced following genetic immunization with two hepatitis C virus (H CV) plasmid-derived immunogens: a plasmid expressing the full-length n ucleocapsid (CAP) as a nonsecreted antigen (pCMVC2) and a plasmid expr essing the amino-terminal part of CAP as a secreted antigen (pS2S,C2N) . In BALB/c mice, intramuscular injection of either plasmid induced Ig G(2a) antibodies associated with a Th1-like profile characterized by t he in vitro splenic production of interleukin-2 (IL-2) and interferon- gamma (IFN-gamma). The pS2S,C2N plasmid induced antibody titers three- to fivefold higher than those obtained with the pCMVC2 plasmid (maxim al titers 1:1,500 versus 1:500), In control experiments, immunization using purified CAP antigen induced a predominant, but not exclusive, T h2-like profile as determined by the splenic production of IL-4 and IL -10, Six putative Th determinants were identified using a panoply of o verlapping synthetic peptides in in vitro stimulation assays: amino ac ids 20-44, 39-63, 79-113, 89-113, 118-142, and 138-152, For all CAP im munogens, MHC haplotype of immunized mice was found to influence seroc onversion rates but not the type of cytokines produced in vitro, H-2(d ) mice were faster responders and displayed recall T-cell activation b y a larger number of peptides than H-2(b) mice, whereas H-2(s) mice we re overall very poor responders, Splenic stimulation by at least one d eterminant, amino acids 79-103, appeared to be highly specific of the H-2(b) background and of DNA immunization only, These data indicate th at DNA immunogens expressing different forms of HCV-CAP are not associ ated with different Th profiles but rather different seroconversion ra tes and antibody titers and that collaboration of distinct T-help epit opes can be restricted by the MHC background.