Exosomes from 5-aminolevulinic acid photodynamic therapy-treated squamous carcinoma cells promote dendritic cell maturation

Abstract Background 5-aminolevulinic acid photodynamic therapy (ALA-PDT) is effective in skin tumours. Studies have demonstrated that the therapy has anti-tumour immunity in squamous cell carcinoma (SCC). Exosomes play an important role in tumour microenvironment (TME) crosstalk. Nevertheless, whether exosomes mediate the ALA-PDT anti-tumour effect is unclear. This study aims to investigate whether exosomes secreted from ALA-PDT-treated squamous carcinoma cells (SCCs) demonstrate an anti-tumour effect by inducing dendritic cell (DCs) maturation. Method In this study, we used electron microscopy, nanoparticle tracking analysis and western blotting to identify exosomes. Subsequently, BCA assay and fluorescence staining were used to evaluate the biological activity of exosomes. Exosomes derived from ALA-PDT-treated SCCs were incubated with SCCs, fibroblasts and immature DCs, separately. A CCK-8 kit was used to analyse the cytotoxicity of exosomes to SCCs. ELISA was utilised to analyse IL-6, VEGF, MMP-3, and TGF-β1 secreted from fibroblasts. FACS and ELISA were used to analysed DC phenotypic maturation (CD80, MHC-II) and IL-12 secretion. Result Herein we show that exosomes secreted from SCCs after ALA-PDT cannot exert cytotoxicity towards SCCs. However, exosomes derived from ALA-PDT-treated SCCs could induce DCs maturation and IL-12 secretion. Furthermore, exosomes secreted from SCCs after ALA-PDT promote the secretion of TGF-β1 from fibroblast. Conclusion In conclusion, we found that exosomes derived from ALA-PDT-treated SCCs have the ability to stimulate DC maturation and fibroblast secretion of TGF-β1, which results in the elevation of anti-tumour immunity. These findings provide a new promising strategy of anti-tumour immune response for ALA-PDT in treating SCCs.