IL-10 production by CLL cells is enhanced in the anergic IGHV mutated subset and associates with reduced DNA methylation of the IL10 locus.

Chronic lymphocytic leukemias (CLL) with unmutated (U-CLL) or mutated (M-CLL) IGHV have variable features of immunosuppression, possibly influenced by those CLL cells activated to produce IL-10. The two subsets differ in their levels of anergy, defined by low surface IgM levels/signaling capacity, and in their DNA methylation profile, particularly variable in M-CLL. We have now found that levels of IL-10 produced by activated CLL cells were highly variable. Levels were higher in M-CLL than in U-CLL and correlated with anergy. DNA methylation analysis of IL10 locus revealed two previously uncharacterized 'variably methylated regions' (CLL-VMRs1/2) in the gene body, but similarly low methylation in the promoter of both U-CLL and M-CLL. CLL-VMR1/2 methylation was lower in M-CLL than in U-CLL and inversely correlated with IL-10 induction. A functional STAT3 binding site in CLL-VMR2 was confirmed by proximity-ligation and luciferase assays, while inhibition of SYK-mediated STAT3 activation resulted in suppression of IL10. The data suggest epigenetic control of IL-10 production. Higher tumor load may compensate the reduced IL-10 production in U-CLL, accounting for clinical immunosuppression in both subsets. The observation that SYK inhibition also suppresses IL-10 provides a potential new rationale for therapeutic targeting and immunological rescue by SYK-inhibitors in CLL.Leukemia accepted article preview online, 28 November 2016. doi:10.1038/leu.2016.356.