Humoral and Cellular Immunity to an Encoded Protein Induced by Direct DNA Injection

Abstract

An immunization procedure with naked DNA that generates both humoral and cellular immune responses is described. A mammalian expression vector encoding human factor IX as an example of immunogen was injected into mice three times at 10-day intervals. Three of the 4 mice in which the DNA was injected intramuscularly and 5 of the 9 mice injected subcutaneously produced antibodies to human factor IX. Spleen cells from inoculated mice also showed significant cytotoxic T lymphocyte response to target cells expressing human factor IX. The titers of anti-single-stranded (ss)DNA antibodies were significantly higher in the subsets of genetically inoculated mice than in the control mice, but anti-double-stranded (ds)DNA antibodies were not detected in any serum samples. Thus, intramuscular and subcutaneous injection of plasmid DNA can induce immune responses against the encoded protein without an exposure to virus particles, and this approach may serve as the basis for immunotherapy in the treatment of cancer and infectious diseases in humans. An immunization procedure for the intramuscular and subcutaneous injection of naked DNA has now developed with the use of a mammalian expression vector that encodes human factor IX. The subcutaneous injection of plasmid DNA resulted in both humoral and cellular immune responses to human factor IX in mice. Antibodies to vector DNA were measured with enzyme-linked immunosorbent assay. Direct injection of DNA in vivo thus offers a new approach to vaccination with potential implications for the treatment of cancer and infectious diseases.