Human Endogenous Retroviruses As Epigenetic Therapeutic Targets in TP53-mutated Diffuse Large B-cell Lymphoma

TP53 mutation (TP53) occurs in 10-20% of diffuse large B-cell lymphoma (DLBCL) cases and serves as an unfavorable biomarker of DLBCL progression. It confers resistance to immunochemotherapy, high-dose chemotherapy, autologous stem cell transplantation, and anti-CD19 chimeric antigen receptor T-cell therapy. Therapeutic targeting of TP53 remains a significant challenge in DLBCL treatment. Here we assessed TP53 in 667 patients with newly diagnosed DLBCL, including 576 patients treated with immunochemotherapy rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) and 91 patients with decitabine plus R-CHOP (DR-CHOP, NCT02951728 and NCT04025593). TP53 independently predicted an inferior prognosis in R-CHOP-treated DLBCL, although this could be mitigated by DR-CHOP treatment. In TP53 patients, multiple viral regulation pathways were repressed, resulting in the inhibition of immune modulation, as revealed by gene set enrichment analysis. TP53 DLBCL exhibited increased methyltransferase SUV39H1 expression and H3K9 trimethylation (H3K9me3), contributing to repression of endogenous retroviruses (ERVs) and immunosuppressive tumor microenvironment. In TP53 DLBCL cell lines, decitabine down-regulated SUV39H1, inhibited H3K9me3 occupancy on ERVs, and triggered ERV expression, thereby unleashing interferons program and CD4T/CD8T cell activation. Molecular silencing of SUV39H1 significantly abrogated decitabine-induced H3K9me3 inhibition and ERV expression. In TP53 patient-derived xenograft models and TP53 patients, the anti-tumor effect was improved upon the use of combined treatment of decitabine and doxorubicin via SUV39H1-H3K9me3-ERVs axis. Collectively, our findings highlight an ERV regulatory circuitry in TP53 DLBCL and the crucial roles ERVs for epigenetically reprogramming tumor microenvironment for treating TP53-driven cancers.