title: HIV-1 envelope resistance to proteasomal cleavage: implications for vaccine induced immune responses.
abstract: BACKGROUND
  Antigen processing involves many proteolytic enzymes such as proteasomes and cathepsins. The processed antigen is then presented on the cell surface bound to either MHC class I or class II molecules and induces/interacts with antigen-specific CD8+ and CD4+ T-cells, respectively. Preliminary immunological data from the RV144 phase III trial indicated that the immune responses were biased towards the Env antigen with a dominant CD4+ T-cell response.
  
  
  METHODS
  In this study, we examined the susceptibility of HIV-1 Env-A244 gp120 protein, one of the protein boost subunits of the RV144 Phase III vaccine trial, to proteasomes and cathepsins and identified the generated peptide epitope repertoire by mass spectrometry. The peptide fragments were tested for cytokine production in CD4(+) T-cell lines derived from RV144 volunteers.
  
  
  RESULTS
  Env-A244 was resistant to proteasomes, thus diminishing the possibility of the generation of class I epitopes by the classical MHC class I pathway. However, Env-A244 was efficiently cleaved by cathepsins generating peptide arrays identified by mass spectrometry that contained both MHC class I and class II epitopes as reported in the Los Alamos database. Each of the cathepsins generated distinct degradation patterns containing regions of light and dense epitope clusters. The sequence DKKQKVHALF that is part of the V2 loop of gp120 produced by cathepsins induced a polyfunctional cytokine response including the generation of IFN-γ from CD4(+) T-cell lines-derived from RV144 vaccinees. This sequence is significant since antibodies to the V1/V2-loop region correlated inversely with HIV-1 infection in the RV144 trial.
  
  
  CONCLUSIONS
  Based on our results, the susceptibility of Env-A244 to cathepsins and not to proteasomes suggests a possible mechanism for the generation of Env-specific CD4(+)T cell and antibody responses in the RV144 vaccinees.
authors.affiliation: United States Military HIV Research Program, Walter Reed Army Institute of Research, Silver Spring, Maryland, United States of America.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Steers
authors.forename: Silvia
authors.initials: S
authors.lastname: Ratto-Kim
authors.forename: Mark S
authors.initials: MS
authors.lastname: de Souza
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Currier
authors.forename: Jerome H
authors.initials: JH
authors.lastname: Kim
authors.forename: Nelson L
authors.initials: NL
authors.lastname: Michael
authors.forename: Carl R
authors.initials: CR
authors.lastname: Alving
authors.forename: Mangala
authors.initials: M
authors.lastname: Rao
mesh_terms: D016915:AIDS Vaccines / Q000276:immunology*; D000595:Amino Acid Sequence; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D002403:Cathepsins / Q000378:metabolism; D000939:Epitopes / Q000737:chemistry / Q000276:immunology; D015699:HIV Envelope Protein gp120 / Q000737:chemistry / Q000276:immunology*; D015497:HIV-1 / Q000187:drug effects / Q000276:immunology*; D006801:Humans; D007109:Immunity / Q000187:drug effects / Q000276:immunology*; D007371:Interferon-gamma / Q000494:pharmacology; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000276:immunology; D018448:Models, Immunological; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000276:immunology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D059748:Proteolysis
chemical_list: D016915:AIDS Vaccines; D000939:Epitopes; D015699:HIV Envelope Protein gp120; D010455:Peptides; D007371:Interferon-gamma; D002403:Cathepsins; D046988:Proteasome Endopeptidase Complex