title: CD8+ T cell epitope-flanking mutations disrupt proteasomal processing of HIV-1 Nef.
abstract: CTL play a critical role in the control of HIV and SIV. However, intrinsic genetic instability enables these immunodeficiency viruses to evade detection by CTL through mutation of targeted antigenic sites. These mutations can impair binding of viral epitopes to the presenting MHC class I molecule or disrupt TCR-mediated recognition. In certain regions of the virus, functional constraints are likely to limit the capacity for variation within epitopes. Mutations elsewhere in the protein, however, might still enable immune escape through effects on Ag processing. In this study, we describe the coincident emergence of three mutations in a highly conserved region of Nef during primary HIV-1 infection. These mutations (R69K, A81G, and H87R) flank the HLA B*35-restricted VY8 epitope and persisted to fixation as the early CTL response to this Ag waned. The variant form of Nef showed a reduced capacity to activate VY8-specific CTL, although protein stability and expression levels were unchanged. This effect was associated with altered processing by the proteasome that caused partial destruction of the VY8 epitope. Our data demonstrate that a variant HIV genotype can significantly impair proteasomal epitope processing and substantiate the concept of immune evasion through diminished Ag generation. These observations also indicate that the scale of viral escape may be significantly underestimated if only intraepitope variation is evaluated.
authors.affiliation: James Martin 21st Century School and Nuffield Department of Clinical Medicine, The Peter Medawar Building, University of Oxford, Oxford, United Kingdom. anita.milicic@medawar.ox.ac.uk
authors.forename: Anita
authors.initials: A
authors.lastname: Milicic
authors.forename: David A
authors.initials: DA
authors.lastname: Price
authors.forename: Peter
authors.initials: P
authors.lastname: Zimbwa
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Booth
authors.forename: Helen L
authors.initials: HL
authors.lastname: Brown
authors.forename: Philippa J
authors.initials: PJ
authors.lastname: Easterbrook
authors.forename: Kara
authors.initials: K
authors.lastname: Olsen
authors.forename: Nicola
authors.initials: N
authors.lastname: Robinson
authors.forename: Uzi
authors.initials: U
authors.lastname: Gileadi
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Sewell
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Cerundolo
authors.forename: Rodney E
authors.initials: RE
authors.lastname: Phillips
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D017951:Antigen Presentation / Q000235:genetics; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002460:Cell Line; D021901:DNA, Intergenic; D018984:Epitopes, T-Lymphocyte / Q000235:genetics* / Q000502:physiology; D015693:Gene Products, nef / Q000235:genetics / Q000378:metabolism*; D015658:HIV Infections / Q000276:immunology; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism*; D015235:HLA-B Antigens / Q000378:metabolism; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000502:physiology*; D011499:Protein Processing, Post-Translational; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D054311:nef Gene Products, Human Immunodeficiency Virus
chemical_list: D021901:DNA, Intergenic; D018984:Epitopes, T-Lymphocyte; D015693:Gene Products, nef; D015235:HLA-B Antigens; D054311:nef Gene Products, Human Immunodeficiency Virus; D046988:Proteasome Endopeptidase Complex