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HCMV deletion models enable the identification of physiologically relevant T-cell epitopes

ABSTRACT: In healthy individuals, immune control of persistent human cytomegalovirus (HCMV) infection is effectively mediated by virus-specific CD4+ and CD8+ T cells. However, identification of the repertoire of T-cell specificities for HCMV is hampered by the immense protein coding capacity of this betaherpesvirus. We applied a novel approach which employs HCMV deletion mutant viruses, lacking HLA class I immunoevasins. Infection of human fibroblast cell lines with those mutant viruses allowed the direct identification of naturally presented HCMV-derived HLA ligands by mass spectrometry. Using this strategy, we identified 368 unique HCMV-derived HLA class I ligands representing an unexpectedly broad panel of 123 HCMV antigens. Functional characterization revealed memory T-cell responses in seropositive individuals for a substantial proportion (28%) of these novel peptides. The unbiased identification of naturally presented viral epitopes enabled a comprehensive and systematic assessment of the physiological repertoire of anti-HCMV T-cell specificities in seropositive individuals. This approach proved to be superior to procedures applying in silico analysis to identify true viral antigens.

INSTRUMENT(S): Orbitrap Fusion Lumos, LTQ Orbitrap XL

ORGANISM(S): Cytomegalovirus Homo Sapiens (human)

TISSUE(S): Cell Culture, Mrc-5 Cell

SUBMITTER: Leon Bichmann

LAB HEAD: Prof. Hans-Georg Rammensee

PROVIDER: PXD013120 | Pride | 2019-11-20

REPOSITORIES: Pride

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			Action	DRS
	HF-99-7_AD169_deltaUS2-11_Rep1.msf	Msf
	HF-99-7_AD169_deltaUS2-11_Rep1.raw	Raw
	HF-99-7_AD169_deltaUS2-11_Rep2.msf	Msf
	HF-99-7_AD169_deltaUS2-11_Rep2.raw	Raw
	HF-99-7_AD169_deltaUS2-11_Rep3.msf	Msf

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Project description:Infection or reactivation with human cytomegalovirus (HCMV) is still a major cause of morbidity and mortality in patients undergoing solid organ transplantation or allogeneic stem cell transplantation (alloSCT). Recent studies have shown that protection against latent HCMV infection relies on a much broader antigen spectrum than previously expected. The identification of novel immunogenic HCMV-derived peptides that facilitate HCMV control is therefore essential to improve immune monitoring of HCMV-specific T cells and HCMV vaccine development. In particular, only a few HCMV-derived peptides have been described for less common HLA alleles, such as HLA-A*03:01 and HLA-B*15:01, limiting the implementation of these techniques for a substantial number of patients. Here, we identified novel HCMV-derived HLA-A*03:01- and HLA-B*15:01-restricted immunogenic peptides by an innovative combined in vitro and in silico approach. We utilized the computational tools Peptide-PRISM (1) and PRICE (2) to analyze mass spectrometric (MS) and ribosome sequencing (ribo-seq) datasets, respectively. To refine our in silico approach, we utilized machine learning to rate the identified peptide candidates based on their translational activity, binding affinity and positioning within the small open reading frames (sORFs), with the goal of assessing their likelihood to be presented on HLA-A*03:01 and HLA-B*15:01 molecules. After identifying the highest-scoring 49 canonical and 49 cryptic potentially immunogenic peptides for each HLA allele, we assessed their immunogenicity by screening HCMV-seropositive and -seronegative healthy donors, as well as alloSCT patients for their peptide-specific T-cell responses. We used a stimulation procedure in two consecutive steps: peripheral blood cells (PBMCs) were stimulated starting with peptide pools and subsequently with potentially reactive single peptides. In vitro T-cell stimulation resulted in the direct identification of three canonical and one cryptic HLA-A*03-restricted immunogenic peptides as well as five canonical and one cryptic HLA-B*15-restricted immunogenic peptide, with a specific IFNγ+/CD8+ T cell response of ≥ 0.02%. Highest T-cell responses were identified against two HLA-A*03-restricted and three HLA-B*15-restricted canonical peptides with up to 3.42% of IFNγ+/CD8+ T cells in patients 180 days post alloSCT. In conclusion, we identified specific T-cell responses against eight canonical and two cryptic HLA-A*03:01- and HLA-B*15:01-restricted peptides in healthy individuals and post-transplanted patients and which were classified as immunogenic. Of these, six peptides are novel HCMV-derived, immunogenic peptides according to the UniProt database, broadening the spectrum of immunogenic HCMV-derived peptides for personalized immune monitoring and vaccine development.

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HCMV deletion models enable the identification of physiologically relevant T-cell epitopes

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