Epstein Barr virus-positive B-cell lymphoma is highly vulnerable to MDM2 inhibitors in vivo.

Epstein-Barr virus-positive (EBV-positive) B-cell lymphomas are common in immunocompromised patients and remain an unmet medical need. Here we report that MDM2 inhibitors (MDM2is) navtemadlin and idasanutlin have potent in vivo activity in EBV-positive B-cell lymphoma established in immunocompromised mice. Tumor regression was observed in all 5 EBV-positive xenograft-associated B-cell lymphomas treated with navtemadlin or idasanutlin. Molecular characterization showed that treatment with MDM2is resulted in activation of p53 pathways and downregulation of cell cycle effectors in human lymphoma cell lines that were either EBV-positive or had undetectable expression of BCL6, a transcriptional inhibitor of the TP53 gene. Moreover, treatment with navtemadlin resulted in tumor regression and prevented systemic dissemination of EBV-positive lymphoma derived from 2 juvenile patients with posttransplant lymphoproliferative diseases, including 1 whose tumor was resistant to virus-specific T-cell therapy. These results provide proof-of-concept for targeted therapy of EBV-positive lymphoma with MDM2is and the feasibility of using EBV infection or loss of BCL6 expression to identify responders to MDM2is.

Improved CRISPR/Cas9 knock-in efficiency via the self-excising cassette (SEC) selection method in C. elegans.

Streamlined, selection-based CRISPR knock-in protocols for C. elegans were first introduced six years ago (Dickinson et al. 2015; Schwartz and Jorgensen 2016). Though these selection-based approaches are powerful, one drawback has been the requirement to inject large numbers of P0 worms (~30-60 per gene target). We have found that a combination of high-purity DNA and a lower concentration of Cas9/sgRNA plasmid dramatically improves efficiency, often resulting in multiple independent CRISPR knock-ins via as few as 10 injected worms, comparable to the efficiency of melted dsDNA templates and purified Cas9 protein (Dokshin et al. 2018; Ghanta and Mello 2020).