BET inhibition reforms the immune microenvironment and alleviates T cell dysfunction in chronic lymphocytic leukemia
Audrey L. Smith, Sydney A. Skupa, Alexandria P. Eiken, Timothy E. Reznicek, Elizabeth Schmitz, Nolan Williams, Dalia Y. Moore, Christopher R. D’Angelo, Avyakta Kallam, Matthew A. Lunning, R. Gregory Bociek, Julie M. Vose, Eslam Mohamed, Anna R. Mahr, Paul W. Denton, Ben Powell, Gideon Bollag, M. Jordan Rowley, Dalia El-Gamal
Audrey L. Smith, Sydney A. Skupa, Alexandria P. Eiken, Timothy E. Reznicek, Elizabeth Schmitz, Nolan Williams, Dalia Y. Moore, Christopher R. D’Angelo, Avyakta Kallam, Matthew A. Lunning, R. Gregory Bociek, Julie M. Vose, Eslam Mohamed, Anna R. Mahr, Paul W. Denton, Ben Powell, Gideon Bollag, M. Jordan Rowley, Dalia El-Gamal
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Research Article Immunology Oncology

BET inhibition reforms the immune microenvironment and alleviates T cell dysfunction in chronic lymphocytic leukemia

Abstract

Redundant tumor microenvironment (TME) immunosuppressive mechanisms and epigenetic maintenance of terminal T cell exhaustion greatly hinder functional antitumor immune responses in chronic lymphocytic leukemia (CLL). Bromodomain and extraterminal (BET) proteins regulate key pathways contributing to CLL pathogenesis and TME interactions, including T cell function and differentiation. Herein, we report that blocking BET protein function alleviates immunosuppressive networks in the CLL TME and repairs inherent CLL T cell defects. The pan-BET inhibitor OPN-51107 reduced exhaustion-associated cell signatures resulting in improved T cell proliferation and effector function in the Eμ-TCL1 splenic TME. Following BET inhibition (BET-i), TME T cells coexpressed significantly fewer inhibitory receptors (IRs) (e.g., PD-1, CD160, CD244, LAG3, VISTA). Complementary results were witnessed in primary CLL cultures, wherein OPN-51107 exerted proinflammatory effects on T cells, regardless of leukemic cell burden. BET-i additionally promotes a progenitor T cell phenotype through reduced expression of transcription factors that maintain terminal differentiation and increased expression of TCF-1, at least in part through altered chromatin accessibility. Moreover, direct T cell effects of BET-i were unmatched by common targeted therapies in CLL. This study demonstrates the immunomodulatory action of BET-i on CLL T cells and supports the inclusion of BET inhibitors in the management of CLL to alleviate terminal T cell dysfunction and potentially enhance tumoricidal T cell activity.

Authors

Audrey L. Smith, Sydney A. Skupa, Alexandria P. Eiken, Timothy E. Reznicek, Elizabeth Schmitz, Nolan Williams, Dalia Y. Moore, Christopher R. D’Angelo, Avyakta Kallam, Matthew A. Lunning, R. Gregory Bociek, Julie M. Vose, Eslam Mohamed, Anna R. Mahr, Paul W. Denton, Ben Powell, Gideon Bollag, M. Jordan Rowley, Dalia El-Gamal

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Figure 2

BET inhibition improves T cell function in an aggressive murine model of CLL.

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BET inhibition improves T cell function in an aggressive murine model of...
(A) Schematic of study design. Upon disease onset, recipient mice were randomly assigned to treatment with OPN-51107 (OPN5, n = 13) or vehicle equivalent (VEH, n = 12) for 28 days. Disease burden in the peripheral blood is shown. (B) Abundances of cell types found in the spleen. CLL B cells were gated as CD45+CD19+CD5+, other B cells were gated as CD45+CD19+CD5–, T cells were gated as CD45+CD19–/CD4+ or CD8+. (C) Ki67 expression in splenic CLL B cells and T cells evaluated by flow cytometry. MFI, median fluorescent intensity. (D) Percentages of CLL B cells expressing immune inhibitory receptors, normalized to the average of VEH-treated mice. (E) Proliferation indices of Cell Trace Violet–stained splenic T cells, stimulated ex vivo with anti-CD3/anti-CD28 for 72 hours. (F and G) Splenic T cells stimulated ex vivo for 6 hours with PMA/ionomycin and then evaluated by flow cytometry for percentages of T cells expressing intracellular cytokines (F) or membrane localized CD107a (G). (H) Representative FlowSOM clustering of splenic CD8+ T cells. Clustering is based on expression of CD44, CD107a, TNF-α, IL-4, IFN-γ, and IL-2. Relative expression is illustrated as the size of colored pie slices within each cluster. The relative abundance of each cluster is represented by cluster size. (I) Percentage of antigen-experienced (CD44+) CD8+ splenic T cells expressing KLRG1. (J and K) Distribution of CD4+ (J) and CD8+ (K) splenic T cells into naive (TN; CD44–CD62L+), central memory (TCM; CD44+CD62L+), and effector memory (TEM; CD44+CD62L–) subsets with representative flow cytometry plots. Asterisks denote significant differences between VEH and OPN5 for each T cell subset. Summary data are represented as mean ± SEM. Unpaired, 2-tailed Mann-Whitney U tests were used to determine significant difference between VEH and OPN5 groups. *P < 0.05, **P < 0.01, ***P < 0.001.