title: Quantitative and qualitative analyses of the immune responses induced by a multivalent minigene DNA vaccine.
abstract: Vaccines containing minigenes - isolated antigenic epitopes encoded by short open reading frames - can, under certain circumstances, confer protective immunity upon the vaccinee. Here we evaluate the efficacy of the minigene vaccine approach using DNA immunization and find that, to be immunogenic, a minigene-encoded epitope requires a perfect "Kozak" translational initiation region. In addition, using intracellular cytokine staining, we show that immunization with a plasmid encoding a full-length protein induces epitope-specific CD8(+) T cells which are detectable directly ex vivo, and constitute approximately 2% of the vaccinee's splenic CD8(+) T cells. In contrast, such cells are undetectable directly ex vivo in recipients of a minigene vaccine. Nevertheless, the minigene plasmid does induce a low number of epitope-specific CD8(+) T cells, which can be amplified to detectable levels by in vivo stimulation. Indeed, 4 days after in vivo stimulation (by virus infection), all vaccinated mice - regardless of whether they had been vaccinated with the minigene or with the full-length gene - had similar numbers of epitope-specific CD8(+) T cells. However, despite these strong responses at 4 days post-infection, recipients of the minigene vaccine showed no enhanced ability to limit virus replication and dissemination. We therefore observe a dichotomy; minigene vaccinees are not protected, despite the presence of strong virus-specific immune responses at 4 days post-challenge. We suggest that the protective benefits of vaccination exert themselves very soon - perhaps within minutes or hours - after virus challenge. If the vaccine-induced immune response is too low to achieve this early protective effect, virus-specific T cells will expand rapidly, but ineffectually, leading to the strong but non-protective response measured at 4 days post-infection. Thus, vaccine-induced immunity should be monitored very early in infection, since the extent to which these responses may later be amplified is largely irrelevant to the protection observed.
authors.affiliation: Department of Neuropharmacology, CVN-9, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: L L
authors.initials: LL
authors.lastname: An
authors.forename: F
authors.initials: F
authors.lastname: Rodriguez
authors.forename: S
authors.initials: S
authors.lastname: Harkins
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.forename: J L
authors.initials: JL
authors.lastname: Whitton
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000914:Antibodies, Viral / Q000096:biosynthesis / Q000276:immunology; D000956:Antigens, Viral / Q000235:genetics / Q000276:immunology*; D001483:Base Sequence; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D003062:Codon / Q000235:genetics; D016207:Cytokines / Q000096:biosynthesis; D000939:Epitopes / Q000235:genetics / Q000276:immunology*; D005813:Genes, Synthetic; D007111:Immunity, Cellular; D018655:Lymphocyte Count; D008217:Lymphocytic choriomeningitis virus / Q000235:genetics / Q000276:immunology* / Q000502:physiology; D008574:Mengovirus / Q000235:genetics / Q000276:immunology* / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010957:Plasmids / Q000235:genetics / Q000276:immunology; D012045:Regulatory Sequences, Nucleic Acid; D012136:Respiratory Syncytial Viruses / Q000235:genetics / Q000276:immunology*; D018108:Respirovirus / Q000235:genetics / Q000276:immunology*; D013154:Spleen / Q000276:immunology; D013997:Time Factors; D014611:Vaccination; D019444:Vaccines, DNA / Q000276:immunology*; D014721:Vesicular stomatitis Indiana virus / Q000235:genetics / Q000276:immunology*; D014765:Viral Vaccines / Q000276:immunology*; D014779:Virus Replication
chemical_list: D000914:Antibodies, Viral; D000956:Antigens, Viral; D003062:Codon; D016207:Cytokines; D000939:Epitopes; D019444:Vaccines, DNA; D014765:Viral Vaccines