Study on the regulation of Treg cell infiltration by EZH2 through CXCR4/CXCL12 in diffuse large B-cell lymphoma

Enhancer of Zeste Homolog 2 (EZH2) is an important methyltransferase, which is overexpressed in a variety of tumors and is involved in promoting tumor growth and immune escape. Both EZH2 and C-X-C chemokine receptor type 4 (CXCR4) exhibit high-level expression in the germinal centers of lymph nodes. However, it remains unclear whether there exists a synergistic relationship between these two molecules. Our study found that approximately 90.7% of cases of diffuse large B-cell lymphoma (DLBCL) exhibited medium-to-high intensity expression of both EZH2 and CXCR4. CXCR4 and C-X-C motif chemokine ligand 12 (CXCL12) are a pair of receptor-ligands, which are related to tumor invasion and migration and immune cell infiltration in the tumor background. Our study found that the expression intensity of EZH2 and CXCR4 in CXCL12 + group DLBCL and the level of Treg cell infiltration were higher than those in CXCL12- group. In CXCL12 + DLBCL, EZH2 might regulate the infiltration level of Treg cells through CXCR4/CXCL12. In the in vitro experiment of co-culture of human Peripheral Blood Mononuclear Cells (PBMCs) and DLBCL cell lines, we also observed that under the chemotactic effect of CXCL12, the proportion of Treg cells in the oe-EZH2 group was higher than that in the oe-NC group. In DLBCL tumor cells of the oe-EZH2 group, the expression of CXCR4 could be upregulated CXCR4 through the downregulation of miR-9. Subsequently, the upregulated CXCR4 binds to the exogenous CXCL12, thereby increasing the differentiation ratio of Treg cells in PBMCs. In the subcutaneous transplanted tumor model of C-NKG mice with human T cell immune function, the sh-EZH2 group had less Treg cell infiltration in the tumor and lower tumor cell activity compared with the sh-NC group. In summary, our study found that the EZH2/miR-9/CXCR4 pathway participates in the occurrence and development of DLBCL. Specifically, high-expression EZH2 recruits the infiltration of Treg cells within the chemotactic DLBCL microenvironment via the upregulated CXCR4/CXCL12 axis. This research provides novel evidence for elucidating the immune escape mechanism of DLBCL. EZH2 and its associated signaling cascades hold the potential to serve as promising targets for the immunotherapy of DLBCL.