HDAC7 is an actionable driver of therapeutic antibody resistance by macrophages from CLL patients

Resistance, to therapeutic antibodies used to treat chronic lymphocytic leukemia (CLL) patients is common. Monocyte-derived macrophages (MDMs) are a major effector of antitumour responses to therapeutic antibodies and we have previously reported that resistance to therapeutic antibodies, by MDMs, increases as CLL disease progresses. In this study, we examine the effect of a Class IIa-selective HDAC inhibitor (TMP195) on the phagocytic response to opsonised tumor cells or non-opsonised targets by MDMs derived from CLL patients. We report that TMP195 enhances phagocytic responses to antibody-opsonised CLL cells and E. coli within 30 min of treatment. The enhanced response is phenocopied by knockdown of the Class IIa HDAC, HDAC7, or by low concentrations of the pan-HDAC inhibitor, vorinostat. HDAC7 knockdown and inhibition induces hyperacetylation and hyperphosphorylation of Bruton's tyrosine kinase (BTK). Moreover, BTK inhibitors abrogated the enhanced response to HDAC7 inhibition. Our data show that HDAC7 is an actionable driver of resistance to therapeutic antibodies by MDMs derived from CLL patients.