Our group has previously demonstrated that the BET inhibitor OPN-51107 (OPN5; previously known as PLX51107) alleviates CLL disease burden and reshapes the TME, including an observed reduction in circulating MDSCs in CLL models, prompting further investigation into the effects of BET inhibition on MDSC function in CLL [23,24]. Here, OPN5 is linked to B-cell chronic lymphocytic leukemia.