title: Induction of human T cell-mediated immune responses after primary and secondary smallpox vaccination.
abstract: BACKGROUND
  Postexposure vaccination strategies rely on a rapid induction of poxvirus-specific immune responses. Postvaccination cell-mediated immune (CMI) responses have not been compared by use of controlled trials in previously vaccinated (vaccinia-nonnaive) and nonvaccinated (vaccinia-naive) individuals.
  
  
  METHODS
  To assess the time course of vaccinia-specific CMI responses, 20 previously vaccinated and 10 vaccinia-naive individuals were vaccinated with Dryvax, and serial blood samples were drawn.
  
  
  RESULTS
  Both groups developed peak levels of vaccinia-specific interferon (IFN)- gamma -producing T cells by day 14 after vaccination. In vaccinia-nonnaive individuals, vaccinia-specific CMI responses were detected by day 7 after vaccination and preceded the increase in antibody titers. IFN- gamma enzyme-linked immunospot responses were significantly different between the 2 groups on days 7 (greater in vaccinia-nonnaive than in vaccinia-naive individuals) and 14 (greater in vaccinia-naive than in vaccinia-nonnaive individuals). Lymphoproliferation responses in vaccinia-nonnaive individuals were significantly higher on days 3 and 7, but cytotoxic T cell lysis activity was not statistically different at any time point. Antibody responses conformed to expected primary and secondary patterns of induction.
  
  
  CONCLUSIONS
  This study demonstrates that the kinetics of CMI responses are different after primary vaccination versus after revaccination and indicates that memory can exist in individuals vaccinated >/=30 years ago. These data support the epidemiological observation in smallpox outbreaks that successful revaccination within 4 days of exposure is partially protective. In vaccinia-nonnaive individuals, protection against smallpox during the postexposure revaccination period may require T cell memory as an essential component for the rapid induction of protective cellular and humoral responses.
authors.affiliation: Center for Infectious Disease and Vaccine Research, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA. jeff.kennedy@umassmed.edu.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Kennedy
authors.forename: Sharon E
authors.initials: SE
authors.lastname: Frey
authors.forename: Lihan
authors.initials: L
authors.lastname: Yan
authors.forename: Alan L
authors.initials: AL
authors.lastname: Rothman
authors.forename: John
authors.initials: J
authors.lastname: Cruz
authors.forename: Frances K
authors.initials: FK
authors.lastname: Newman
authors.forename: Laura
authors.initials: L
authors.lastname: Orphin
authors.forename: Robert B
authors.initials: RB
authors.lastname: Belshe
authors.forename: Francis A
authors.initials: FA
authors.lastname: Ennis
mesh_terms: D000328:Adult; D000914:Antibodies, Viral / Q000097:blood; D006801:Humans; D007117:Immunization, Secondary; D007156:Immunologic Memory; D007371:Interferon-gamma / Q000096:biosynthesis; D008213:Lymphocyte Activation; D008875:Middle Aged; D012900:Smallpox Vaccine / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D014611:Vaccination; D014616:Vaccinia virus / Q000276:immunology*
chemical_list: D000914:Antibodies, Viral; D012900:Smallpox Vaccine; D007371:Interferon-gamma