# Design and in vitro validation of Brome mosaic –virus-like particles for gene delivery and immunomodulation of melanoma

## TL;DR

Researchers tested plant-based virus-like particles for delivering RNA to silence a cancer immune checkpoint, showing safe and effective gene silencing in melanoma cells and immune cells.

## Contribution

BMV-VLPs are proposed as a biocompatible, scalable alternative to synthetic systems for RNA-based immunotherapy.

## Key findings

- BMV-VLPs efficiently encapsulate and deliver siRNA to knockdown PD-L1 in melanoma and immune cells.
- PD-L1 silencing via BMV-VLPs enhances T-cell-mediated cytotoxicity and T-cell proliferation in tumor models.
- BMV-VLPs show high biocompatibility and no cytotoxicity in vitro.

## Abstract

RNA interference (RNAi) is a powerful tool for post-transcriptional gene silencing, yet its clinical translation remains limited by the lack of safe and efficient delivery systems. In this study, we evaluated the potential of plant virus-like particles (VLPs), derived from Brome Mosaic Virus (BMV), as a biodegradable and biocompatible nanocarrier for small interfering RNA (siRNA) delivery aimed at modulating immune checkpoints in melanoma. Recombinant BMV capsid proteins were expressed in E. coli and self-assembled in vitro into uniform VLPs encapsulating siRNA directed against the programmed death-ligand 1 (PD-L1). The VLPs displayed high structural stability, efficient siRNA encapsulation, and excellent biocompatibility. In vitro, A high cellular uptake was confirmed by confocal microscopy and flow cytometry. Besides, no cytotoxicity was observed and functional siRNA delivery was demonstrated in vitro by knockdown of eGFP in macrophages and PD-L1 in B16F10 melanoma and JAWS II dendritic cells, with significant knockdown efficiencies comparable to controls. Beyond molecular knockdown, PD-L1 silencing mediated by BMV-VLPs induced functional immunomodulation, increasing CD8⁺ T-cell–mediated cytotoxicity in melanoma and CMT64 tumor models and enhancing allogeneic T-cell proliferation in dendritic cell–based mixed leukocyte reactions. Overall, these findings indicate that plant-derived BMV-VLPs can safely mediate RNA-based checkpoint modulation and could complement antibody-based PD-1/PD-L1 blockade strategies. Owing to their intrinsic biocompatibility, scalability, and modular design, BMV-VLPs represent a sustainable and versatile alternative to synthetic lipid systems for RNA immunotherapy.

In this study, we demonstrate the potential of Brome mosaic virus-derived virus like particles (BMV-VLPs), as a biocompatible siRNA carrier for silencing PD-L1, a key immune checkpoint, in melanoma cells. The BMV-VLPs exhibited efficient siRNA encapsulation, cellular uptake, and gene knockdown across tumor and immune cells, highlighting their potential as a versatile platform for RNA-based immunomodulation in cancer therapy.Image 1