Viral Peptides for Vaccine Epitope Discovery

Viral Epitope Discovery for Vaccine Development

The fundamental challenge in modern vaccine design—whether for pandemic preparedness or chronic viral infections—is identifying which viral fragments are actually displayed to the immune system. While a viral genome contains thousands of potential sequences, only a limited subset are processed and presented as HLA-bound peptides. These peptides serve as the primary targets for CD8+ and CD4+ T cell recognition, dictating the breadth and potency of cellular immunity.

Relying solely on prediction software often leads to high false-positive rates, as algorithms cannot fully simulate the biological intricacies of viral protein degradation, protease specificity, and MHC loading competition within the endosome. Our viral peptide discovery service provides direct, mass spectrometry-based evidence of presentation, allowing vaccine researchers to focus on immunodominant epitopes that are naturally displayed on the surface of target cells.

Immunopeptidomics for Viral Peptide Identification

Viral immunopeptidomics utilizes high-resolution liquid chromatography-tandem mass spectrometry (LC-MS/MS) to sequence peptides directly eluted from purified MHC molecules. This approach bypasses the limitations of functional validation assays, which often depend on access to suitable antigen-responsive T cells or donor immune material and require prior knowledge of the epitope sequence.

By analyzing the global landscape of peptides presented by infected cells for endogenous HLA-I presentation, and APC-based uptake/pulsing workflows for HLA-II and cross-presentation studies, we provide a high-resolution map of the viral peptidome. Our Immunopeptidomics Service is optimized to detect low-abundance viral ligands that may otherwise be masked by the vast background of endogenous host "self" peptides.

HLA-Presented Viral Peptides and T Cell Epitope Mapping

Precision T cell epitope mapping is the cornerstone of designing effective subunit and mRNA vaccines. Our workflow identifies both HLA Class I (CD8+ T cell) and HLA Class II (CD4+ T cell) ligands, providing a holistic view of the immune target landscape. This dual-class analysis is critical for vaccines requiring both cytotoxic killing and long-term helper-driven memory.

Once viral peptides are identified via mass spectrometry, we integrate NetMHCpan (Class I) and NetMHCIIpan (Class II) binding predictions to support peptide ranking. This integrated approach—combining experimental identification with computational modeling—provides a rigorous foundation for selecting candidate epitopes for downstream validation, such as ELISpot, Intracellular Cytokine Staining (ICS), or targeted Peptidomics-Based Antigen Discovery.

What We Offer in Viral Peptide and Epitope Discovery

We provide modular and integrated solutions to support viral antigen discovery at various stages of vaccine research:

Advantages of Our Viral Peptide Discovery Platform

Creative Proteomics offers a best-in-class platform for viral antigen discovery, providing several key advantages over standard epitope mapping techniques:

Workflow for Viral Epitope Discovery by Immunopeptidomics

Our standardized workflow ensures reproducible and high-quality results for complex viral samples:

Technology Platform for Viral Peptide Discovery

Our platform is engineered to meet the extreme sensitivity requirements of viral research. We utilize state-of-the-art Orbitrap high-resolution platforms, achieving sub-ppm mass accuracy and deep sequencing depth. This is supported by our comprehensive Immune Peptide Mass Spectrometry Analysis workflows.

Mass Spectrometry Platform Comparison for Immunopeptidomics

Viral Epitope Discovery vs. Epitope Prediction

Sample Requirements for Viral Peptide Analysis

To ensure successful discovery, samples must be prepared according to strict biosafety and quality guidelines.

Note: Required quantities are dependent on viral titer and cell type; please consult our experts for project-specific guidelines.

Example Results from Viral Peptide Identification

Our deliverables translate raw mass spectrometry data into actionable vaccine research insights using Nature-standard visualizations.

Deliverables for Vaccine Epitope Discovery Projects

Creative Proteomics provides a structured data package ready for integration into your research reports:

• Full Analytical Report: Detailed methodology, QC metrics, and internal control performance.
• Viral Peptide Inventory: Comprehensive list including sequence, source protein, HLA allele assignment, and spectral abundance data.
• NetMHCpan/NetMHCIIpan Validation Report: Computational binding affinity predictions for all identified viral candidates.
• Epitope Prioritization Matrix: Expert analysis ranking candidates by presentation intensity and population coverage.

Frequently Asked Questions

Summary

Using HLA peptidomics, Nagler et al. directly identified naturally presented SARS-CoV-2 peptides from both HLA class I and HLA class II molecules. Rather than relying on prediction alone, the study combined infected-cell and viral gene expression models with LC-MS/MS-based immunopeptidomics to capture viral antigens that were genuinely processed and presented. In total, the authors identified 26 HLA-I peptides and 36 HLA-II peptides, including peptides derived from both canonical and non-canonical open reading frames (ORFs). Several peptides were shared across different cell types, and multiple identified ligands showed immunogenicity, supporting their value as experimentally grounded candidates for T cell epitope discovery and next-generation vaccine design.

Methods

This study used a combined HLA peptidomics + bioinformatics workflow to identify naturally presented SARS-CoV-2 ligands across prevalent HLA backgrounds.

Key Technical Features:

• Experimental systems: Cells infected with SARS-CoV-2 as well as cells transduced to express SARS-CoV-2 genes
• HLA context: Highly prevalent HLA class I alleles were prioritized to improve population relevance; both HLA-I and HLA-II peptidomes were analyzed
• Discovery platform: HLA-bound peptides were isolated and analyzed by LC-MS/MS-based HLA peptidomics
• Antigen scope: Analysis included peptides derived from both canonical viral proteins and out-of-frame / non-canonical ORFs
• Cross-cell comparison: Shared peptides presented across different cell types were identified to strengthen confidence in biological relevance
• Immunogenicity follow-up: HLA multimer staining was used to identify additional immunoreactive peptides beyond those already reported in prior studies

Creative Proteomics can support and extend this type of workflow through:

• High-sensitivity HLA class I and HLA class II immunopeptidomics by LC-MS/MS
• Viral peptide discovery from infected cell lysates or antigen-expression systems
• Canonical and non-canonical viral ORF-aware database searching
• Comparative ligandome analysis across cell types, infection conditions, or HLA backgrounds
• Experimental viral epitope prioritization supported by peptide annotation and binding prediction
• Custom bioinformatics for viral source mapping, hotspot analysis, and candidate ranking

These capabilities support vaccine epitope discovery, T cell target prioritization, and deeper characterization of viral antigen presentation landscapes.

Results

The study identified dozens of SARS-CoV-2-derived HLA-I and HLA-II peptides. A substantial portion of these peptides originated from viral proteins beyond Spike, and some were derived from non-canonical or out-of-frame open reading frames (ORFs).

Figure 1. Distribution of SARS-CoV-2 peptide lengths confirms standard HLA Class I and Class II presentation characteristics.

Naturally Presented SARS-CoV-2 Ligands Were Directly Identified
The authors identified 26 SARS-CoV-2-derived HLA-I peptides and 36 SARS-CoV-2-derived HLA-II peptides, providing direct evidence of viral antigen presentation.

Presented Peptides Originated from Multiple Viral Regions
Identified ligands were not limited to a single structural protein. Peptides were derived from both canonical viral proteins and non-canonical / out-of-frame ORFs, expanding the set of potential T cell targets beyond standard prediction-first approaches.

Shared Peptides Were Observed Across Different Cells
Some viral peptides were shared between distinct cell systems, strengthening confidence that these ligands reflect reproducible processing and presentation rather than a cell-line-specific artifact.

Immunogenic Peptides Were Identified
Among the detected ligands, seven peptides had been previously shown to be immunogenic, and the study identified two additional immunoreactive peptides using HLA multimer staining. This supports the translational relevance of direct HLA peptidomics for downstream T cell epitope validation.

Implications for Vaccine Design
Because the identified peptides span several viral genes and include naturally presented antigens beyond a spike-only focus, the results provide a stronger experimental basis for selecting T cell epitope candidates for next-generation SARS-CoV-2 vaccines.