title: Identification and localization of minimal MHC-restricted CD8+ T cell epitopes within the Plasmodium falciparum AMA1 protein.
abstract: BACKGROUND
  Plasmodium falciparum apical membrane antigen-1 (AMA1) is a leading malaria vaccine candidate antigen that is expressed by sporozoite, liver and blood stage parasites. Since CD8+ T cell responses have been implicated in protection against pre-erythrocytic stage malaria, this study was designed to identify MHC class I-restricted epitopes within AMA1.
  
  
  METHODS
  A recombinant adenovirus serotype 5 vector expressing P. falciparum AMA1 was highly immunogenic when administered to healthy, malaria-naive adult volunteers as determined by IFN-γ ELISpot responses to peptide pools containing overlapping 15-mer peptides spanning full-length AMA1. Computerized algorithms (NetMHC software) were used to predict minimal MHC-restricted 8-10-mer epitope sequences within AMA1 15-mer peptides active in ELISpot. A subset of epitopes was synthesized and tested for induction of CD8+ T cell IFN-γ responses by ELISpot depletion and ICS assays. A 3-dimensional model combining Domains I + II of P. falciparum AMA1 and Domain III of P. vivax AMA1 was used to map these epitopes.
  
  
  RESULTS
  Fourteen 8-10-mer epitopes were predicted to bind to HLA supertypes A01 (3 epitopes), A02 (4 epitopes), B08 (2 epitopes) and B44 (5 epitopes). Nine of the 14 predicted epitopes were recognized in ELISpot or ELISpot and ICS assays by one or more volunteers. Depletion of T cell subsets confirmed that these epitopes were CD8+ T cell-dependent. A mixture of the 14 minimal epitopes was capable of recalling CD8+ T cell IFN-γ responses from PBMC of immunized volunteers. Thirteen of the 14 predicted epitopes were polymorphic and the majority localized to the more conserved front surface of the AMA1 model structure.
  
  
  CONCLUSIONS
  This study predicted 14 and confirmed nine MHC class I-restricted CD8+ T cell epitopes on AMA1 recognized in the context of seven HLA alleles. These HLA alleles belong to four HLA supertypes that have a phenotypic frequency between 23% - 100% in different human populations.
authors.affiliation: USMMVP, Malaria Department, NMRC, Silver Spring, MD 20910, USA.
authors.forename: Martha
authors.initials: M
authors.lastname: Sedegah
authors.forename: Yohan
authors.initials: Y
authors.lastname: Kim
authors.forename: Bjoern
authors.initials: B
authors.lastname: Peters
authors.forename: Shannon
authors.initials: S
authors.lastname: McGrath
authors.forename: Harini
authors.initials: H
authors.lastname: Ganeshan
authors.forename: Jennylynn
authors.initials: J
authors.lastname: Lejano
authors.forename: Esteban
authors.initials: E
authors.lastname: Abot
authors.forename: Glenna
authors.initials: G
authors.lastname: Banania
authors.forename: Maria
authors.initials: M
authors.lastname: Belmonte
authors.forename: Renato
authors.initials: R
authors.lastname: Sayo
authors.forename: Fouzia
authors.initials: F
authors.lastname: Farooq
authors.forename: Denise L
authors.initials: DL
authors.lastname: Doolan
authors.forename: David
authors.initials: D
authors.lastname: Regis
authors.forename: Cindy
authors.initials: C
authors.lastname: Tamminga
authors.forename: Ilin
authors.initials: I
authors.lastname: Chuang
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Bruder
authors.forename: C Richter
authors.initials: CR
authors.lastname: King
authors.forename: Christian F
authors.initials: CF
authors.lastname: Ockenhouse
authors.forename: Bart
authors.initials: B
authors.lastname: Faber
authors.forename: Edmond
authors.initials: E
authors.lastname: Remarque
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hollingdale
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Richie
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sette
mesh_terms: D000260:Adenoviruses, Human / Q000235:genetics; D000328:Adult; D000953:Antigens, Protozoan / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D018604:Epitope Mapping; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D005822:Genetic Vectors; D006805:Human Experimentation; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism; D017780:Malaria Vaccines / Q000235:genetics / Q000276:immunology; D008565:Membrane Proteins / Q000276:immunology*; D015800:Protozoan Proteins / Q000276:immunology*
chemical_list: D000953:Antigens, Protozoan; D018984:Epitopes, T-Lymphocyte; D017780:Malaria Vaccines; D008565:Membrane Proteins; D015800:Protozoan Proteins; C090077:apical membrane antigen I, Plasmodium; D007371:Interferon-gamma