title: Enhancing efficacy of recombinant anticancer vaccines with prime/boost regimens that use two different vectors.
abstract: BACKGROUND
  The identification of tumor-associated antigens and the cloning of DNA sequences encoding them have enabled the development of anticancer vaccines. Such vaccines target tumors by stimulating an immune response against the antigens. One method of vaccination involves the delivery of antigen-encoding DNA sequences, and a number of recombinant vectors have been used for this purpose. To optimize the efficacy of recombinant vaccines, we compared primary and booster treatment regimens that used a single vector (i.e., homologous boosting) with regimens that used two different vectors (i.e., heterologous boosting).
  
  
  METHODS
  Pulmonary tumors (experimental metastases) were induced in BALB/c mice inoculated with CT26.CL25 murine colon carcinoma cells, which express recombinant bacterial beta-galactosidase (the model antigen). Protocols for subsequent vaccination used three vectors that encoded beta-galactosidase--vaccinia (cowpox) virus, fowlpox virus, naked bacterial plasmid DNA. Mouse survival was evaluated in conjunction with antibody and cytotoxic T-lymphocyte responses to beta-galactosidase.
  
  
  RESULTS
  Heterologous boosting resulted in significantly longer mouse survival than homologous boosting (all P<.0001, two-sided). Potent antigen-specific cytotoxic T lymphocytes were generated following heterologous boosting with poxvirus vectors. This response was not observed with any of the homologous boosting regimens. Mice primed with recombinant poxvirus vectors generated highly specific antibodies against viral proteins.
  
  
  CONCLUSIONS
  The poor efficacy of homologous boosting regimens with viral vectors was probably a consequence of the induction of a strong antiviral antibody response. Heterologous boosting augmented antitumor immunity by generating a strong antigen-specific cytotoxic T-lymphocyte response. These data suggest that heterologous boosting strategies may be useful in increasing the efficacy of recombinant DNA anticancer vaccines that have now entered clinical trials.
authors.affiliation: Surgery Branch, Division of Clinical Sciences, National Cancer Institute, Bethesda, MD 20892-1502, USA.
authors.forename: K R
authors.initials: KR
authors.lastname: Irvine
authors.forename: R S
authors.initials: RS
authors.lastname: Chamberlain
authors.forename: E P
authors.initials: EP
authors.lastname: Shulman
authors.forename: D R
authors.initials: DR
authors.lastname: Surman
authors.forename: S A
authors.initials: SA
authors.lastname: Rosenberg
authors.forename: N P
authors.initials: NP
authors.lastname: Restifo
mesh_terms: D000818:Animals; D015153:Blotting, Western; D019496:Cancer Vaccines / Q000008:administration & dosage* / Q000627:therapeutic use; D004269:DNA, Bacterial; D004279:DNA, Viral; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D005822:Genetic Vectors; D007115:Immunization Schedule; D008175:Lung Neoplasms / Q000517:prevention & control*; D051379:Mice; D008807:Mice, Inbred BALB C; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000627:therapeutic use; D016019:Survival Analysis
chemical_list: D019496:Cancer Vaccines; D004269:DNA, Bacterial; D004279:DNA, Viral; D011994:Recombinant Proteins