Extracellular vesicles shed by follicular lymphoma B cells promote the polarization of bone marrow stromal cell niche.

Follicular Lymphoma (FL) originates in the lymph nodes (LN) and infiltrates bone marrow (BM) early in the course of the disease. BM FL B cells are characterized by a lower cytological grade, a decreased proliferation, and a specific phenotypic and subclonal profile. Mesenchymal stromal cells (MSC) obtained from FL BM display a specific gene expression profile (GEP), including enrichment for a lymphoid-stromal cell signature, and an increased capacity to sustain FL B-cell growth. However, the mechanisms triggering the formation of the medullar FL permissive stromal niche have not been yet identified. In the current work, we demonstrated that FL B cells produced extracellular vesicles (EVs) that could be internalized by BM-MSC, making them more efficient to support FL B-cell survival and quiescence. Accordingly, EVs purified from FL BM plasma activated TGF-b dependent and independent pathways in BM-MSC, modified their GEP, triggering an upregulation of factors classically associated with hematopoietic stem cell niche, including CXCL12 or angiopoietin-1. Moreover, we provided the first characterization of BM FL B-cell GEP, allowing the definition of the landscape of molecular interactions they could engage with EV-primed BM-MSC. This work identified FL-derived EVs as putative mediators of BM stroma polarization and supported further investigation of their clinical interest for targeting the crosstalk between BM-MSC and malignant B cells.