# A New Strategy to Identify Naturally Presenting SLA-I Bound Peptides Derived from the O Serotype of Foot-and-Mouth Disease Virus, by Mild Acid Elution in a VP1 Stably Expressed PK15 Cell Line

## TL;DR

This study creates a cell line to identify peptides from foot-and-mouth disease virus that bind to swine immune proteins, which could help in developing new vaccines.

## Contribution

The first known cell line for screening naturally presenting FMDV O serotype peptides bound to SLA-I is constructed.

## Key findings

- A VP1-stably expressed PK15 cell line was successfully established using pEGFP-N1-VP1.
- 37 peptides derived from O-VP1 were identified as binding to SLA-I through mild acid elution.
- Flow cytometry and ELISA confirmed the association of eluted peptides with SLA-I.

## Abstract

The naturally presented antigenic peptides bound with swine leukocyte antigen class I (SLA-I) are crucial in developing multi-epitope vaccines in foot-and-mouth disease virus (FMDV). In this article, a transient expression plasmid, pEGFP-N1-VP1, was used to establish a VP1-stably expressed PK15 cell line. Using mild acid elution, 37 peptides that bound to SLA-I were separated and identified. These peptides will be used as candidates for a multi-epitope vaccine in FMDV.

Multi-epitopes of FMDV can be used to develop a novel vaccine. Determining how to screen naturally presenting epitope peptides derived from FMDV is crucial for advancing progress in this area. In this study, a transient expression plasmid named pEGFP-N1-VP1 was transfected into Porcine Kidney Epithelial cells 15 (PK15). The positive cells that stably expressed the O-VP1 gene of FMDV were screened with gradient concentrations of G418 (Geneticin). The constructed pEGFP-N1-VP1/PK15 cell line was eluted by pH 3.3 phosphate buffer to isolate the eluted peptides, followed by desalting, liquid chromatography–tandem mass spectrometry (LC–MS/MS), a flow cytometric analysis of SLA-I expression, and an ELISA detection of SLA-I bound peptides. It was demonstrated that a PK15 cell line stably expressing the VP1 gene was initially screened out at 500 μg/mL of G418, followed by culturing at 300 μg/mL. The O-VP1 expression was identified using an image analysis system, RT-PCR, and Western blot analysis. Thirty-seven peptides derived from O-VP1 were eluted from the constructed cell line. The flow cytometric analysis and ELISA detection results showed that the eluted peptides were associated with SLA-I and bound. This is the first known study to construct a cell line for screening naturally presenting antigenic peptides derived from the O serotype of FMDV.