IN VIVO MODELING AND CHARACTERIZATION OF MYC/BCL2 DOUBLE HIT LYMPHOMA

Double-hit lymphoma (DHL) arises from Germinal Center (GC) B-cells that undergo chromosomal translocations activating the MYC and BCL2 oncogenes and constitutes an aggressive group of tumors that show dismal prognosis with current therapeutic regimens. Full understanding of the pathophysiology of DHL and its exploitation for pre-clinical development depend upon the availability of a mouse model that faithfully represents the physio-pathological features of the human disease, and in particular its GC origin – a characteristic trait that is missing in the models developed do far. Here, we have pursued this goal by combining conditional lox-stop-lox(lsl)-MYC and lsl-BCL2 alleles with the GC-specific transgene C1-Cre: while either oncogene alone showed limited effects, their co-activation led to the development of fully penetrant lymphomas (median onset of 213 days) that showed a Dark Zone-like GC phenotype and a number of other DHL-like features, including extensive infiltration of multiple organs (e.g. liver, spleen, kidney, lung, brain), high levels of proliferation and apoptosis, and extensive macrophage infiltration. Careful examination by expert pathologists classified these tumors as high-grade B-cell lymphomas, similar to human DHL, and transcriptional profiling confirmed their GCB cell of origin. The tumors were transplantable and expanded in immunodeficient mice while retaining their original GC phenotype. These lymphomas were also stabilized for in vitro growth, thus creating stable DHL cell lines that can be used for further experiments. This model expands the available tools to characterize DHL at the biological, pathological and pre-clinical levels, and shall provide an advanced experimental platform for pre-clinical testing of novel therapeutic combinations. Altogether, these complementary lines of investigation shall provide deep insights into the biology and molecular underpinnings of DHL, and point to new therapeutic solutions against this aggressive lymphoma subtype.