JQ 1, a Selective Bromodomain Inhibitor, Decreased the Expression of the Tolerogenic Molecule PDL1 in Antigen-Presenting Cells (APCs) and Restores the Responsiveness of Anergic CD4+ T Cells

Bromodomain and extraterminal (BET) is a protein domain that recognizes acetylated lysine residues such as those on the N-terminal tails of histones. This recognition is often a prerequisite for protein-histone association, chromatin remodeling and gene transcription. The role of BET proteins in regulating the response of inflammatory cytokine genes through translation of histone marks is poorly understood.

Given that the inflammatory status of the APC is critical in determining T-cell activation versus T-cell tolerance and that epigenetic modifications of specific genes in the APC play a key role in this process, we recently determined the functional consequences of inhibiting BET in APCs.

First, we evaluated the effects of JQ 1, a selective small-molecule BET bromodomain inhibitor on APC’s function and its regulation of antigen-specific CD4+ T-cells response. In vitro treatment of peritoneal elicited macrophages (PEM) or bone marrow derived dendritic cells (DCs) with increasing concentrations of JQ 1 resulted in decreased expression and protein production of the anti-inflammatory cytokine IL-10 and IL-6 in response to LPS stimulation. At the concentration used, JQ 1 did not affect the viability of treated APCs. Second, analysis of the expression of MHC class molecules and co-stimulatory molecules revealed a decreased expression of the tolerogenic PDL1 molecule in JQ 1- treated APCs as compared to untreated APCs. Third, we evaluated the ability of JQ 1 treated APCs to present cognate antigen to naïve or tolerant antigen-specific CD4+ T-cells. We found that treatment of either PEM or DC with JQ 1 enhanced their antigen-presenting capabilities leading to effective priming of naïve CD4+ T-cells confirmed by their increased production of IL-2 and IFN-gamma in response to cognate antigen. More importantly, JQ 1- treated APCs were able to restore the responsiveness of tolerant CD4+ T-cells isolated from lymphoma bearing hosts.

Taken together, we have found that APCs treated with the Bromodomain specific inhibitor JQ 1 are more inflammatory, display lower expression of the immunosuppressive molecule PDL1 and more importantly, are capable of restoring the responsiveness of tolerant T-cells. Our studies therefore have unveiled a previously unknown immunological effect of BET inhibitors and have broadened their clinical scope as promising adjuvants in cancer immunotherapy.