title: Critical components of a DNA fusion vaccine able to induce protective cytotoxic T cells against a single epitope of a tumor antigen.
abstract: DNA vaccines can activate immunity against tumor Ags expressed as MHC class I-associated peptides. However, priming of CD8(+) CTL against weak tumor Ags may require adjuvant molecules. We have used a pathogen-derived sequence from tetanus toxin (fragment C (FrC)) fused to tumor Ag sequences to promote Ab and CD4(+) T cell responses. For induction of CD8(+) T cell responses, the FrC sequence has been engineered to remove potentially competitive MHC class I-binding epitopes and to improve presentation of tumor epitopes. The colon carcinoma CT26 expresses an endogenous retroviral gene product, gp70, containing a known H2-L(d)-restricted epitope (AH1). A DNA vaccine encoding gp70 alone was a poor inducer of CTL, and performance was not significantly improved by fusion of full-length FrC. However, use of a minimized domain of FrC, with the AH1 sequence fused to the 3' position, led to rapid induction of high levels of CTL. IFN-gamma-producing epitope-specific CTL were detectable ex vivo and these killed CT26 targets in vitro. The single epitope vaccine was more effective than GM-CSF-transfected CT26 tumor cells in inducing an AH1-specific CTL response and equally effective in providing protection against tumor challenge. Levels of AH1-specific CTL in vivo were increased following injection of tumor cells, and CTL expanded in vitro were able to kill CT26 cells in tumor bearers. Pre-existing immunity to tetanus toxoid had no effect on the induction of AH1-specific CTL. These data demonstrate the power of epitope-specific CTL against tumor cells and illustrate a strategy for priming immunity via a dual component DNA vaccine.
authors.affiliation: Molecular Immunology Group, Tenovus Laboratory, Southampton University Hospitals Trust, Southampton, United Kingdom. j.rice@soton.ac.uk
authors.forename: Jason
authors.initials: J
authors.lastname: Rice
authors.forename: Sarah
authors.initials: S
authors.lastname: Buchan
authors.forename: Freda K
authors.initials: FK
authors.lastname: Stevenson
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology*; D019496:Cancer Vaccines / Q000008:administration & dosage / Q000138:chemical synthesis / Q000235:genetics / Q000276:immunology*; D003110:Colonic Neoplasms / Q000276:immunology / Q000473:pathology / Q000517:prevention & control; D003602:Cytotoxicity, Immunologic / Q000235:genetics; D018984:Epitopes, T-Lymphocyte / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology*; D006131:Growth Inhibitors / Q000008:administration & dosage / Q000138:chemical synthesis / Q000235:genetics / Q000276:immunology; D007273:Injections, Intramuscular; D007371:Interferon-gamma / Q000096:biosynthesis; D008213:Lymphocyte Activation / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D009368:Neoplasm Transplantation; D011993:Recombinant Fusion Proteins / Q000008:administration & dosage / Q000138:chemical synthesis / Q000235:genetics / Q000276:immunology*; D015682:Retroviridae Proteins, Oncogenic / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology* / Q000378:metabolism / Q000637:transplantation; D013745:Tetanus Toxoid / Q000008:administration & dosage / Q000276:immunology; D019444:Vaccines, DNA / Q000008:administration & dosage / Q000138:chemical synthesis / Q000235:genetics / Q000276:immunology*; D014759:Viral Envelope Proteins / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology
chemical_list: D000951:Antigens, Neoplasm; D019496:Cancer Vaccines; D018984:Epitopes, T-Lymphocyte; D006131:Growth Inhibitors; D011993:Recombinant Fusion Proteins; D015682:Retroviridae Proteins, Oncogenic; D013745:Tetanus Toxoid; D019444:Vaccines, DNA; D014759:Viral Envelope Proteins; D007371:Interferon-gamma