Blockage of BCL-XL overcomes venetoclax resistance across BCL2+ lymphoid malignancies irrespective of BIM status.

ABSTRACT: Venetoclax (VEN), a B-cell lymphoma 2 (BCL2) inhibitor, has a promising single-agent activity in mantle cell lymphoma (MCL), acute lymphoblastic leukemia (ALL), and large BCLs, but remissions were generally short, which call for rational drug combinations. Using a panel of 21 lymphoma and leukemia cell lines and 28 primary samples, we demonstrated strong synergy between VEN and A1155463, a BCL-XL inhibitor. Immunoprecipitation experiments and studies on clones with knockout of expression or transgenic expression of BCL-XL confirmed its key role in mediating inherent and acquired VEN resistance. Of note, the VEN and A1155463 combination was synthetically lethal even in the cell lines with lack of expression of the proapoptotic BCL2L11/BIM and in the derived clones with genetic knockout of BCL2L11/BIM. This is clinically important because BCL2L11/BIM deletion, downregulation, or sequestration results in VEN resistance. Immunoprecipitation experiments further suggested that the proapoptotic effector BAX belongs to principal mediators of the VEN and A1155463 mode of action in the BIM-deficient cells. Lastly, the efficacy of the new proapoptotic combination was confirmed in vivo on a panel of 9 patient-derived lymphoma xenografts models including MCL (n = 3), B-ALL (n = 2), T-ALL (n = 1), and diffuse large BCL (n = 3). Because continuous inhibition of BCL-XL causes thrombocytopenia, we proposed and tested an interrupted 4 days on/3 days off treatment regimen, which retained the desired antitumor synergy with manageable platelet toxicity. The proposed VEN and A1155463 combination represents an innovative chemotherapy-free regimen with significant preclinical activity across diverse BCL2+ hematologic malignancies irrespective of the BCL2L11/BIM status.

MHC II-EGFP Knock-in Mouse Model.

The MHC II-EGFP knock-in mouse model enables us to visualize and track MHC-II-expressing cells in vivo by expressing enhanced green fluorescent protein (EGFP) fused to the MHC class II molecule under the MHC II beta chain promoter. Using this model, we can easily identify MHC-II-expressing cells, including dendritic cells, B cells, macrophages, and ILC3s, which play a key role as antigen-presenting cells (APCs) for CD4+ T cells. In addition, we can also precisely identify and analyze APC-containing tissues and organs. Even after fixation, EGFP retains its fluorescence, so this model is suitable for immunofluorescence studies, facilitating an unbiased characterization of the histological context, especially with techniques such as light-sheet fluorescence microscopy. Furthermore, the MHC II-EGFP knock-in mouse model is valuable for studying the molecular mechanisms of MHC II gene regulation and expression by making it possible to correlate MHC II expression (MHC II-EGFP) with surface fraction through antibody detection, thereby shedding light on the intricate regulation of MHC II expression. Overall, this model is an essential asset for quantitative and systems immunological research, providing insights into immune cell dynamics and localization, with a tool for precise cell identification and with the ability to study MHC II gene regulation, thus furthering the understanding of immune responses and underlying mechanisms © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Characterization of antigen-specific MHC II loading compartment tubulation toward the immunological synapse Basic Protocol 2: Characterization of overall versus surface MHC II expression Basic Protocol 3: Identification and preparation of the lymphoid organs Basic Protocol 4: Quantification of APC content in lymphoid organs by fluorescence stereomicroscopy Basic Protocol 5: Quantification and measurement of intestinal lymphoid tissue by light-sheet fluorescence stereomicroscopy Basic Protocol 6: Visualization of corneal APCs Basic Protocol 7: Quantification of MHC II+ cells in maternal milk by flow cytometry Support Protocol 1: Cell surface staining and flow cytometry analysis of spleen mononuclear cells.

MHC II - EGFP knock-in mouse model is a suitable tool for systems and quantitative immunology.

Immunology is a rapidly evolving field of research with sophisticated models and methods. However, detailed data on total immune cell counts and population distributions remain surprisingly scarce. Nevertheless, recently established quantitative approaches could help us understand the overall complexity of the immune system. Here, we studied a major histocompatibility complexclass II - enhanced green fluorescent protein knock-in mouse model to precisely identify and manipulate lymphoid structures. By combining flow cytometry with light sheet microscopy, we quantified MHC II+ populations of the small intestine and associated individual mesenteric lymph nodes, with 36.7 × 106 cells in lamina propria, 3.0 × 105 cells in scattered lymphoid tissue and 1.1 × 106 cells in Peyer's patches. In addition to these whole-organ cell counts, we assessed approximately 1 × 106 total villi in the small intestine and 450 scattered lymphoid tissue follicles. By direct noninvasive microscopic observation of a naturally fully translucent mouse organ, the cornea, we quantified 12 ± 4 and 35 ± 7 cells/mm2 Langerhans- and macrophage-like populations, respectively. Ultimately, our findings show that flow cytometry with quantitative imaging data analysis enables us to avoid methodological discrepancies while gaining new insights into the relevance of organ-specific quantitative approaches for immunology.