Targeting Histone Deacetylase 6 (HDAC6) as a Novel Approach to Overcome T-Cell Anergy.

Abstract 1483

The anti-inflammatory molecules IL-10 and STAT3 are major hurdles in our efforts to harness effective anti-tumor immunity¹. Previously, we have unveiled a role for histone deacetylase 11 (HDAC11) as a negative regulator of IL-10 gene transcriptional activity in antigen-presenting cells (APCs)². In an effort to better characterize the epigenetic influences upon IL-10, we screened other HDACs and found that over-expression of HDAC6 in the macrophage cell line RAW264.7 was able to transcriptionally upregulate IL-10 in response to LPS. Next, using lentiviral vectors encoding shRNA for HDAC6, we generated stable knockdown clones of HDAC6 (HDAC6KD). In contrast to HDAC6 overexpression, HDAC6KD cells produced less IL-10 both at the mRNA and protein levels. Further analysis of HDAC6KD clones revealed elevated expression of the co-stimulatory molecule B7.2. Functionally, LPS-stimulated HDAC6KD cells were better able to activate anti-HA (hemagglutinin-influenza) transgenic CD4⁺ T cells to produce IL-2 and IFN-γ. More relevant to the tumor setting, anti-HA CD4⁺ anergic T cells isolated from animals bearing HA-expressing A20 B-cell lymphoma regained their ability to produce IL-2 and IFN-γ when cultured in vitro with HDAC6KD cells in the presence of cognate HA-antigen. These same T-cells remained anergic when cultured with control APCs displaying normal levels of HDAC6. Mechanistically, we have found that APCs lacking HDAC6 display a significant abrogation of STAT3 activation in response to LPS stimulation. Given the demonstration that HDACs, other than HDAC6, can regulate STAT3 activity³, we are actively investigating whether the effect we have observed is a result of direct HDAC6-STAT3 interaction or a diminished autocrine signaling through IL-10. Taken together, through abrogation of two well-known tolerogenic mechanisms in APCs, IL-10 and STAT3, HDAC6 inhibition represents an attractive therapeutic approach to overcome tumor-induced T-cell anergy and tip the balance towards effective anti-lymphoma immunity.

1. Cheng F., et al. Immunity 2003 Sep;19(3):425-36.

2. Villagra A., et al. Nat Immunol. 2009 Jan;10(1):92-100.

3. Yuan Z., et al. Science. 2005 Jan 14;307(5707):269-73.