Dissection of Richter's syndrome pathogenesis and treatment through multiplexed CRISPR-based mouse models

Richter's syndrome (RS) is a major obstacle to the management of patients with chronic lymphocytic leukemia (CLL). Its pathogenesis remains largely unknown, and presently, faithful cellular and mouse models are lacking. We report a novel congenic mouse model of RS, based on CRISPR-mediated introduction of multiplexed CLL loss-of-function lesions (i.e. Atm, Trp53, Samhd1, Mga, Birc3, Chd2) into del(13q) B cells, leading to recapitulation of disease features from CLL to transformation to RS, and exhibiting remarkable molecular and phenotypic similarity to human disease. By integrative genomic and functional analyses, we determine that mutation in Trp53, combined with Mga and Chd2, are necessary for RS transformation and for the dysregulation of E2F/MYC and interferon signaling pathways. We demonstrate that RS requires tonic PI3K signaling for survival, and shows vulnerability to MYC, CDK, mTOR and PI3K inhibitors. This model system presents a unique tool for the study of RS biology and therapy. Overall design: Highly recurrent CLL-associated loss-of-function (LOF) driver mutations (i.e. Atm, Trp53, Samhd1, Mga, Birc3, Chd2) were simultaneously introduced into a bone marrow donor line carrying homozygous MDR, a lesion recapitulating del(13q) using CRISPR-Cas9. Different normal and malignant B cells were subjected to transcriptome analysis. Splenocytes were obtained from three murine CLL models and sequenced using mtscATAC-seq on the 10x platform