Identification of an atypical CD8 T cell epitope encoded by murine cytomegalovirus ORF-M54 gaining dominance after deletion of the immunodominant antiviral CD8 T cell specificities.

Abstract

Control of murine cytomegalovirus (mCMV) infection is mediated primarily by CD8 T cells, with four specificities dominating in BALB/c mice. Functional deletion of the respective immunodominant epitopes (IDEs) in mutant virus Δ4IDE revealed a still efficient control of infection. In a murine model of hematopoietic cell transplantation and infection with Δ4IDE, an mCMV-specific open reading frame (ORF) library screening assay indicated a strong CD8 T cell reactivity against the ORF-M54 product, the highly conserved and essential mCMV homolog of human CMV DNA polymerase UL54, which is a known inducer of in vivo protection against mCMV by DNA immunization. Applying bioinformatic algorithms for CD8 T cell epitope prediction, the top-scoring peptides were used to stimulate ex vivo-isolated CD8 T cells and to generate cytolytic T cell lines; yet, this approach failed to identify M54 epitope(s). As an alternative, a peptide library consisting of 549 10-mers with an offset of two amino acids (aa), covering the complete aa-sequence of the M54 protein, was synthesized and used for the stimulation. A region of 12 aa proved to encompass an epitope. An 'alanine walk' over this antigenic 12-mer and all possible 11-, 10- and 9-mers derived thereof revealed aa-residues critical for antigenicity, and terminal truncations identified the H-2D(d) presented 8-mer M5483-90 as the optimal epitope. An increased frequency of the corresponding CD8 T cells in the absence of the 4 IDEs indicated immunodomination by the IDE-specific CD8 T cells as a mechanism by which the generation of M54-specific CD8 T cells is inhibited after infection with wild-type mCMV.

• Authors: Rafaela Holtappels, Niels A W Lemmermann, Doris Thomas, Angélique Renzaho, Matthias J Reddehase
• Journal: Medical microbiology and immunology (Med Microbiol Immunol) Vol. 204 Issue 3 Pg. 317-26 (Jun 2015) ISSN: 1432-1831 [Electronic] Germany
• PMID: 25805564 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antigens, Viral
• Epitopes, T-Lymphocyte
• Histocompatibility Antigen H-2D
• Immunodominant Epitopes
• Peptide Library
• Peptides

Topics

• Amino Acid Sequence
• Animals
• Antigens, Viral (chemistry, immunology)
• CD8-Positive T-Lymphocytes (immunology)
• Computational Biology
• Cytotoxicity, Immunologic
• Epitope Mapping
• Epitopes, T-Lymphocyte (chemistry, immunology)
• Female
• Genome, Viral
• Herpesviridae Infections (immunology, virology)
• Histocompatibility Antigen H-2D (immunology)
• Immunodominant Epitopes (chemistry, immunology)
• Mice
• Muromegalovirus (genetics, immunology)
• Mutation
• Open Reading Frames (genetics, immunology)
• Peptide Library
• Peptides (chemistry, immunology)