Cross-recognition of two middle T protein epitopes by immunodominant polyoma virus-specific CTL.
We recently identified the immunodominant epitope for polyoma virus-specific CTL as the Dk-associated peptide MT389-397 derived from the middle T (MT) viral oncoprotein. Another Dk-restricted peptide corresponding to residues 236-244 of MT was recognized by nearly all MT389-397-reactive CTL clones, but required concentrations at least 2 logs higher to sensitize syngeneic target cells for lysis. Except for identity at the three putative Dk-peptide anchor residues, MT236-244 shares no homology with MT389-397. Using a novel europium-based class I MHC-peptide binding immunoassay, we determined that MT236-244 bound Dk 2-3 logs less well than MT389-397. Infection with a mutant polyoma virus whose MT is truncated just before the MT389-397 epitope or immunization with MT389-397 or MT236-244 peptides elicited CTL that recognized both MT389-397 and MT236-244. Importantly, infection with a polyoma virus lacking MT389-397 and mutated in an MT236-244 Dk anchor position induced polyoma virus-specific CTL recognizing neither MT389-397 nor MT236-244 epitopes. Despite predominant usage of the Vbeta6 gene segment, MT389-397/MT236-244 cross-reactive CTL clones possess diverse complementarity-determining region 3beta domains; this is functionally reflected in their heterogeneous recognition patterns of alanine-monosubstituted MT389-397 peptides. Using Dk/MT389-397 tetramers, we directly visualized MT236-244 peptide-induced TCR down-modulation of virtually all MT389-397-specific CD8+ T cells freshly explanted from polyoma-infected mice, suggesting that a single TCR recognizes both Dk-restricted epitopes. The availability of immunodominant epitope-specific CTL capable of recognizing a second epitope in MT, a viral protein essential for tumorigenesis, may serve to amplify the CTL response to the immunodominant epitope and prevent the emergence of immunodominant epitope-loss viruses and virus-induced tumors.
Wilson
C S
CS
Department of Pathology, Emory Vaccine Center, Emory University School of Medicine, Atlanta, GA 30322, USA.
Moser
J M
JM
Altman
J D
JD
Jensen
P E
PE
Lukacher
A E
AE
D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D018984:Epitopes, T-Lymphocyte / Q000378:metabolism*; D016056:Immunodominant Epitopes / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D018716:Molecular Mimicry / Q000276:immunology; D010446:Peptide Fragments / Q000276:immunology; D011120:Polyomavirus / Q000235:genetics / Q000276:immunology*; D011948:Receptors, Antigen, T-Cell / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology* / Q000378:metabolism / Q000821:virology
D000952:Antigens, Polyomavirus Transforming; D018984:Epitopes, T-Lymphocyte; D016056:Immunodominant Epitopes; D010446:Peptide Fragments; D011948:Receptors, Antigen, T-Cell