# Genetically engineered CD80–pMHC-harboring extracellular vesicles for antigen-specific CD4+ T-cell engagement

## TL;DR

This paper introduces a new method using genetically engineered extracellular vesicles to efficiently detect and expand antigen-specific CD4+ T cells, which is important for immunomonitoring.

## Contribution

The novel approach uses extracellular vesicles with CD80 and pMHC-II complexes to stimulate and expand CD4+ T cells.

## Key findings

- EVs derived from modified HeLa cells effectively activate human CD4+ T cells.
- The method successfully expands low-frequency influenza-specific CD4+ T cells from healthy individuals.
- The technique offers a streamlined alternative to current T-cell expansion protocols.

## Abstract

The identification of low-frequency antigen-specific CD4+ T cells is crucial for effective immunomonitoring across various diseases. However, this task still encounters experimental challenges necessitating the implementation of enrichment procedures. While existing antigen-specific expansion technologies predominantly concentrate on the enrichment of CD8+ T cells, advancements in methods targeting CD4+ T cells have been limited. In this study, we report a technique that harnesses antigen-presenting extracellular vesicles (EVs) for stimulation and expansion of antigen-specific CD4+ T cells. EVs are derived from a genetically modified HeLa cell line designed to emulate professional antigen-presenting cells (APCs) by expressing key costimulatory molecules CD80 and specific peptide–MHC-II complexes (pMHCs). Our results demonstrate the beneficial potent stimulatory capacity of EVs in activating both immortalized and isolated human CD4+ T cells from peripheral blood mononuclear cells (PBMCs). Our technique successfully expands low-frequency influenza-specific CD4+ T cells from healthy individuals. In summary, the elaborated methodology represents a streamlined and efficient approach for the detection and expansion of antigen-specific CD4+ T cells, presenting a valuable alternative to existing antigen-specific T-cell expansion protocols.