S842 MODELING MANTLE CELL LYMPHOMA IN MICE

Abstract

Background:Mantle cell lymphoma (MCL) is a highly aggressive subtype of B‐cell lymphoma that is characterized by a poor response to current treatment regimens. Most MCLs carry a prototypical translocation, t(11;14), which juxtaposes the CCND1 gene towards the immunoglobulin heavy chain (IGH) locus, resulting in cyclin D1 overexpression. Notably, a subset of MCL patients are cyclin D1 negative but instead overexpress cyclin D2 (encoded by CCND2)as a consequence of recurrent genomic rearrangements involving the CCND2locus. These CCND2rearrangements were acknowledged in the revised 2016 WHO classification of lymphoid neoplasms and hints towards a putative role for Cyclin D2 in the etiology of MCL. In addition, the transcription factor SOX11 highly expressed in MCL, hinting that it might act as an oncogene in MCL.Aims:We wanted to evaluate if cyclin D2 and SOX11 are true oncogenic drivers of MCL. Furthermore, we aimed to model MCL in mice and use them as a preclinical tool to identify novel therapeutic options for MCL patients.Methods:To unravel the role of Cyclin D2 and SOX11 in the formation of MCL in vivo, we generated R26‐KI mice that allow conditional overexpression of either Ccnd2 or SOX11. For this, we used a targeting vector that contained a floxed stop cassette followed by cDNA (from Ccnd2 or SOX11) and a EGFP/luciferase reporter, which was subsequently targeted in mESCs using recombinase‐mediated cassette exchange (RMCE, Fig. A).Results:We found that hematopoietic‐specific Ccnd2 activation (using Vav‐iCre) is sufficient to drive MCL formation in mice (Fig. B, top). Moreover, we could show that this murine model recapitulates several clinical features of MCL patients, including CD19+, CD5+, CD23‐ immunophenotype, clonal tumor expansion, lack of somatic hypermutation, high expression of Sox11 and Bcl‐2, and infiltration in spleen, liver and GI tract. Furthermore, these murine MLC tumors were transplantable and homed to sites within the lymphatic system, but unfortunately did not show aggressive growth in vivo.Finally, we tested putative synergism between Ccnd2 and SOX11 overexpression and other cooperating genetic lesions that occur in human MCL, such as loss of p53. To this end, we generated mice with B‐cell specific overexpression of Cyclin D2 or SOX11 in combination with deletion of p53 (Fig. B, middle). These mice also formed MCL‐like tumors and developed “full blown” MCL within weeks upon their transplantation into immunocompromised mice (Fig. B, bottom). Importantly, the transplanted tumor cells are luciferase‐positive and are therefore suitable for in vivodrug testing using bioluminescence. As proof‐of‐principle, we tested the efficacy of known MCL drugs, such as the anti‐BCL2 inhibitor Venetoclax in our model system. In conclusion, we generated novel cyclin‐D2 and SOX11‐driven MCL mouse models that can be used for preclinical drug screening and will hopefully lead to a better outcome for MCL patients.Summary/Conclusion:Using novel R26‐KI mice with conditional expression of Ccnd2 or SOX11, we demonstrated that both Ccnd2 and SOX11 are bona fide drivers of MCL.image