- Immunization with a nucleic acid vaccine (DNA vaccine) usually elicits antibody responses and T lymphocytes with a Th1 cytokine profile. In animal models of chronic hepatitis B infection, including nonhuman primates, intramuscular injection of a plasmid encoding HBV envelope proteins induces rapid, strong, and sustained humoral and cell-mediated immune responses. Clinical trials of DNA vaccines for hepatitis B conducted in healthy adult volunteers using a plasmid encoding hepatitis B surface antigen and the gene gun as a delivery system showed good tolerance.