Extracellular vesicle secretion by leukemia cells in vivo promotes CLL progression by hampering antitumor T-cell responses

Small extracellular vesicles (sEV, or exosomes) communication among cells in the tumor microenvironment has been modeled mainly in cell culture, while their relevance in cancer pathogenesis and progression in vivo is less characterized. Here, researchers at the Luxembourg Institute of Health have investigated cancer-microenvironment interactions in vivo using mouse models of chronic lymphocytic leukemia (CLL). sEV isolated directly from CLL tissue were enriched in specific miRNA and immune checkpoint ligands. Distinct molecular components of tumor-derived sEV altered CD8+ T-cell transcriptome, proteome and metabolome leading to decreased functions and cell exhaustion ex vivo and in vivo. Using antagomiRs and blocking antibodies, the researchers defined specific cargo-mediated alterations on CD8+ T-cells. Abrogating sEV biogenesis by Rab27a/b knockout dramatically delayed CLL pathogenesis. This phenotype was rescued by exogenous leukemic sEV or CD8+ T-cell depletion. Finally, high expression of sEV-related genes correlated with poor outcomes in CLL patients, suggesting sEV profiling as prognostic tool. In conclusion, sEV shape the immune microenvironment during CLL progression.

Small EV are enriched in the human and murine leukemic microenvironments

(A) Relative mRNA expression of selected genes involved in sEV biogenesis and secretion in B-cells from peripheral blood of healthy donors (HC, n=9) and CLL patients (CLL, n=15; from GSE67640). (B) Score based on sEV-related mRNA levels from panel A. (C) mRNA levels of selected genes extracted from panel A. (D) mRNA expression of selected genes according to IGHV mutational status. (E) Score combining the expression of Rab10, Rab35, and Rab40C according to IGHV mutational status (F) Relative mRNA expression of selected genes involved in sEV biogenesis and secretion in B-cells from C57BL/6 (WT) and Eµ-TCL1 mice (TCL1; from GSE175564). (G) Score based on sEV-related RNA levels from panel F. (H) Rab3b mRNA level extracted from panel F. (I) Detailed protocol to isolate and purify sEV from murine spleen. (J) Amount of proteins (in mg) recovered from LME- (n=18) or HCME-sEV (n=10), normalized per gram of spleen. (K) Representative TRPS analysis of ME-sEV for size and concentration. (L) Electron microscopy images of MEsEV. (M) Western-blot analysis of ME-sEV. (N) HSNE clustering analysis of MB488+ LME-sEV based on CD63, CD81 and CD9 expression measured by bead-free FC (left panel) and relative percentages of combined expression (right panel).