A pentapeptide as minimal antigenic determinant for MHC class I-restricted T lymphocytes

107

Recombinant modified vaccinia Ankara- and peptide-based IFN-γ ELISPOT assays were used to detect and measure human CMV (HCMV)-specific CD8+ T cell responses to the pp65 (UL83) and immediate early protein 1 (IE1; UL123) gene products in 16 HCMV-infected infants and children. Age at study ranged from birth to 2 years. HCMV-specific CD8+ T cells were detected in 14 (88%) of 16 children at frequencies ranging from 60 to >2000 spots/million PBMC. Responses were detected as early as 1 day of age in infants with documented congenital infection. Nine children responded to both pp65 and IE1, whereas responses to pp65 or IE1 alone were detected in three and two children, respectively. Regardless of the specificity of initial responses, IE1-specific responses predominated by 1 year of age. Changes in HCMV epitopes targeted by the CD8+ T cell responses were observed over time; epitopes commonly recognized by HLA-A2+ adults with latent HCMV infection did not fully account for responses detected in early childhood. Finally, the detection of HCMV-specific CD8+ T cell responses was temporally associated with a decrease in peripheral blood HCMV load. Taken altogether, these data demonstrate that the fetus and young infant can generate virus-specific CD8+ T cell responses. Changes observed in the protein and epitope-specificity of HCMV-specific CD8+ T cells over time are consistent with those observed after other primary viral infections. The temporal association between the detection of HCMV-specific CD8+ T cell responses and the reduction in blood HCMV load supports the importance of CD8+ T cells in controlling primary HCMV viremia.

Section: Discussionsupporting

confidence: 53%

Human Cytomegalovirus Proteins pp65 and Immediate Early Protein 1 Are Common Targets for CD8+ T Cell Responses in Children with Congenital or Postnatal Human Cytomegalovirus Infection

Gibson

Piccinini²,

Lilleri³

et al. 2004

107

“…For peptide binding studies, transfected L cell lines were incubated overnight in complete DMEM and 10% FBS in the presence of either the murine CMV (MCMV) pp89 168 -176 (YPHFMPTNL) (34) or tum Ϫ P91A 14 -22 (TQNHRALDL) (10,35) peptide at the indicated concentration or in the absence of exogenous peptide. Peptides were synthesized using 9-fluorenylmethyloxycarbonyl chemistry on a PE Applied Biosystems 432A peptide synthesizer (Foster City, CA).…”

Section: Flow Cytometric Analysesmentioning

confidence: 99%

Polymorphism at Position 97 in MHC Class I Molecules Affects Peptide Specificity, Cell Surface Stability, and Affinity for β2-Microglobulin

Smith

Myers

Robinson

et al. 2002

The two mouse MHC class I alleles, Ld and Lq, share complete amino acid sequence identity except in the α2 domain, where they differ at six positions. Despite their similarity, Lq has a stronger association with β2-microglobulin (β2m), is expressed at higher levels on the cell surface, demonstrates an increased cell surface half-life, and has fewer open forms on the cell surface than Ld. To determine the basis for their phenotypic differences, Ld molecules containing chimeric Ld-Lq α2 domains were characterized, and these analyses implicated residue 97 (LdTrp and LqArg) as the polymorphic site responsible for the disparity in β2m association between the two alleles. Single substitution analysis at this site (LdW97R and LqR97W) confirmed this. Furthermore, the LdW97R mutant molecule has a longer cell surface half-life than either Lq or Ld, and fewer open forms of LdW97R are observed on the cell surface. In addition, both LdW97R and Lq possess decreased binding affinity for the Ld-restricted tum− P91A14–22 peptide compared with Ld. Collectively, these results and the known location of Trp97 in the peptide binding cleft of Ld strongly suggest that the substitution of Arg for Trp97 in Ld alters the peptide binding cleft, increasing its affinity for endogenous peptides, which results in greater cell surface stability and better retention of β2m. Furthermore, these results imply that Trp97 plays an important role in the ability of Ld to efficiently participate in alternative MHC class I Ag presentation pathways.

“…The amino acid sequence of the murine CMV (MCMV) 4 peptide corresponds to residues 168 -176 (YPHFMPTNL) of the MCMV immediate early protein pp89 (10). The amino acid sequence of the tum Ϫ peptide corresponds to residues 14 -22 (TQNHRALDL) of the mutant protein P91A (exon 4) from the tum Ϫ P815 tumor variant (11).…”

Section: Peptidesmentioning

confidence: 99%

Homology Between an Alloantigen and a Self MHC Allele Calibrates the Avidity of the Alloreactive T Cell Repertoire Independent of TCR Affinity

Hornell

Myers

Hansen

et al. 2003

The self-restricted T cell repertoire exhibits a high frequency of alloreactivity. Because these alloreactive T cells are derived from the pool of cells selected on several different self MHC alleles, it is unknown how development of the alloantigenic repertoire is influenced by homology between a self MHC allele and an alloantigen. To address this, we used the 2C transgenic TCR that is selected by Kb, is alloreactive for Ld, and cross-reacts with Lq. Lq is highly homologous to Ld and binds several of the same peptide ligands, including p2Ca, the peptide recognized by 2C. We find that Ld/p2Ca is a high avidity agonist ligand, whereas Lq/p2Ca is a low avidity agonist ligand for 2C T cells. When mice transgenic for the 2C TCR are bred to Lq-expressing mice, 2C+ T cells develop; however, they express lower levels of either the 2C TCR or CD8 and require a higher Ld/p2Ca ligand density to be activated than 2C+ T cells selected by Kb. Furthermore, the 2C T cells selected in the presence of Lq fail to detect Lq/p2Ca complexes even at high ligand density. Thus, despite possessing the identical TCR, there is a functional avidity difference between 2C+ T cells selected in the presence of Lq vs Kb. These data provide evidence that homology between the selecting ligand and an alloantigen can influence the avidity of the T cell repertoire for the alloantigen, and suggest that thymic selection can fine tune T cell avidity independent of intrinsic TCR affinity.