EZH2 plays a mind games with tumor and CD8 T cells, and to scientists too

Few days ago I reviewed new Nature article where the authors found a negative correlation between EZH2^hi tumor phenotype (EZH2 is a methyltransferase involved in epigenetic modification at H3K27me3) and progression-free survival of ovarian cancer patients. 

Now, it appears that the same group had another paper in Nature immunology showing exactly opposite effect of EZH2 in tumor infiltrating CD8 T cells (TIL). Namely, the authors found a positive correlation between frequency of EZH2-positive CD8 TILs and progression-free survival of ovarian cancer patients. 

First, the authors showed that in human CD8 T cells, EZH2⁺ subset displayed increased polyfunctionality.

Indeed, inhibition of EZH2 by GSK126 in in vitro CD8 T cells reduced their polyfunctionality.

Next, the authors found that, like GSK126, tumor tissue environment suppressed EZH2 level and TIL functionality by reducing access to glucose.

In another set of experiments, the authors showed that adoptive transfer of EZH2 inhibitor (drug or shRNA) pre-treated tumor-specific CD8 T cells failed to control melanoma metastases in lung.

Finally, analysis of clinical samples from ovarian cancer patients revealed positive correlation between frequency of EZH2⁺CD8⁺ subset and disease-free survival.

In summary, this paper indicates that glucose deprivation in tumor environment reduces EZH2 expression in TIL CD8 T cells and reduces their functionality, implying that increasing of EZH2 expression would benefit cancer patients.

Now these results are exactly opposite from the results provided in Nature paper. There, EZH2 expression in tumor cells inhibited TIL infiltration and EZH2^hi tumor phenotype showed reduced progression-free survival in ovarian cancer patients implying that decreasing of EZH2 expression would benefit cancer patients.

The only difference between these two papers is that one mostly deals with cancer cells and another with CD8 T cells. But this separation in vivo is hardly feasible suggesting more difficult path for medical application of discoveries in epigenetics [it is not clear how the same tumor environment reduces EZH2 expression in TIL CD8 T cells and at the same time increasing it in cancer cells]. 

David Usharauli

Epigenetic modification silence cancer responsiveness to IFN-γ and immunotherapy

Epigenetics is a study of modulation of gene function through non-heritable mechanisms such as histone modification and DNA methylation. These mechanisms are so potent that observed phenotypes could be mistaken for genomic mutations. In clinics, epigenetics plays especially important role during therapeutic treatment where drug effectiveness varies widely among pool of patients, for example, during immunotherapy in cancer patients.      

For example, a new paper recently in Nature showed that both (a) EZH2-mediated histone H3 lysine 27 trimethylation (H3K27me3) and (b) DNA methyltransferase 1-mediated DNA methylation independently silence cancer cells' responsiveness to IFN-γ/T cells and their activity inversely correlated with patients outcome.

The authors have used EZH2 inhibitor GSK126 or DNMT1 inhibitor 5-AZA-dC. Using humanized mouse model of ovarian cancer, the authors showed that combination of GSK126 and 5-AZA-dC synergized with tumor-specific T cells in tumor protection (inhibitors alone or in absence of T cells had no/minimal effect).

Interestingly, combination of GSK126 and 5-AZA-dC specifically enhanced tumor expression of Th1 chemokines CXCL9 and CXCL10 in response to IFN-γ.

Further experiments showed that both inhibitors could independently enhanced cancer CXCL10 expression in response to IFN-γ (here, primary ovarian cancer cells were pre-treated with shEZH2 or shDNMT and exposed to 5-AZA-dC and GSK126 respectively).

As an additional control, the authors showed that GSK126 had no effect on DNMT1 and 5-AZA-dC had no effect on H3K27me3. 

Finally, the authors found negative correlation between expression level of EZH2 and DNMT1 and cancer patients survival.

In summary, this study expands our understanding of cancer tissue sensitivity to immunotherapy (including to anti-PD1 therapy). It appears that in some patients EZH2 and DNMT1 selectively silence TH1 chemokine locus and inhibit cancer cell responsiveness to IFN-γ derived from tumor infiltrated T cells thus blocking positive loop for attracting and recruiting additional tumor-specific T cells. Accordingly, application of selective inhibitors of EZH2 and DNMT1 could improve cancer patients survival.

Of note: it is not clear why would cancer cells silence only Th1 chemokine locus. While it is true that Th1 play important role in cancer protection, several other cancer models have shown protective role for Th17 and even Th2 cells. Since we don't know whether cancer protection in this paper is dependent of IFN-γ, we have no way to make any conclusion in this matter.      

David Usharauli