Functional investigation of TR1 cells in TCL1 AT mice confirmed the phenotype observed in CLL patients, with an induced IL-10 expression that increased over time (Fig. 4B and Supplementary Fig. 5E), and higher levels of IFNγ, CD107a, and GzmB (Supplementary Fig. 5F, G), as markers of cytotoxicity, in these cells. Here, IL10 is linked to B-cell chronic lymphocytic leukemia.