A paper recently published online by a group at the University of Michigan details a mechanism by which epigenetic modulation can increase the number of tumor infiltrating CD8+ T cells and could potentially lead to increased immunotherapy response.
Weiping Zou, MD
While cancer immunotherapy generally leads to therapeutic responses, patient response does vary.1A paper recently published online inNatureby a group at the University of Michigan details a mechanism by which epigenetic modulation can increase the number of tumor infiltrating CD8+ T cells and could potentially lead to increased immunotherapy response.
“Clinical trials with PD-L1 and PD-1 blockade suggested that tumors with a high number of inflammation-causing T cells were more responsive to the immunotherapy-based PD-L1 and PD-1 inhibitors. Tumors with low inflammation, or low T cells, were less responsive,” a University of Michigan press release stated.2
Clinical trials in melanoma with antiPD-1 agents, such as pembrolizumab and nivolumab, have reported varying response rates. Data from a phase I expansion study of pembrolizumab in patients with advanced melanoma indicated a response rate of 38% across all dose cohorts, with 52% response rates in the patients administered 10 mg/kg every 2 weeks.3In a follow-up open-label randomized expansion cohort, the overall response rate was 26% in both arms of the study (2 mg/kg or 10 mg/kg every 3 weeks).4Data from a phase III trial showed objective responses in 31.7% of patients with advanced melanoma receiving 3 mg/kg of nivolumab every 2 weeks versus 10.6% in patients treated with investigators choice of chemotherapy.5
Research to identify agents to combine with immunotherapy and potentially increase response rates in patients with cancer is actively under way, with two recent papers describing the potential of RRx001 and COX inhibitors in this role.6,7
The University of Michigan group led by Weiping Zou, MD, PhD, Charles B. de Nancrede professor of Surgery, Immunology and Biology at the University of Michigan Medical School, have revealed a novel mechanism. They show that the invasion of the tumor microenvironment by T cells is impeded by the activity of enhancer of zeste homologue 2 (EZH2)-mediated histone H3 lysine 27 trimethylation (H3K27me3) and DNA methyltransferase 1 (DNMT1)-mediated DNA methylation. The resulting epigenetic histone modification and DNA methylation inhibits the production of T helper (Th1)-type chemokines CXCL9 and CXCL10 that would normally attract T cells into the tumor. The group explored manipulating the activity of EZH2 and DNMT1 with epigenetic modulators and found that when their activities are repressed, there is an increase in infiltration of effector T cells, a reduction in tumor growth, and an increase in the therapeutic efficacy of PD-L1 checkpoint blockade and adoptive T-cell transfusion in a mouse tumor model.1
“We defined a molecular mechanism to explain why some tumors are inflamed and others are not and consequently why some patients will be responsive to therapy and others not,” said Zou in a press release. “We hope this could be developed into a clinical trial, testing a combination of PD-L1 and PD-1 blockade with epigenetic therapy. We want to see if we can make the responders more responsive and turn the nonresponders into responders.”2
The research was driven by the hypothesis that possible epigenetic silencing of immune protective signature genes results in progressive malignancy and downregulates responses to immunotherapy. The researchers tested this idea using drugs that inhibited EZH2 (DZNep and EPZ6348) and DNMT1, (5-aza-2/-deoxycytidine [5-AZA-dC]) to reprogram the epigenetic pathways.1
Using a mouse model of ovarian cancer, namely ID8 ovarian cancer in C57/BL6 mice, it was shown that while the drugs had a weak impact as single agents, in combination, they reduced tumor growth, increased the expression of the Th1-type chemokines and increased the number of T cells entering the tumor (P< .05 for combination versus control or group treated with either DZNep or 5-AZA-dC).1
Expecting the addition of DZNep and 5-AZA-dc would potentiate the efficacy of an antiPD-L1 agent in the ID8-bearing mice; they treated mice with either anti–PD-L1 alone or in combination with DZNep and 5-AZA-dC. The combination demonstrated greater antitumor activity inducing larger decreases in tumor volume, increased tumor entry by CD8+ T cells, and increased expression of Th1-type chemokines (P<.5, combination versus control). The authors stated that, “Selective epigenetic reprogramming alters the T-cell landscape in cancer and may enhance the clinical efficacy of cancer therapy.”1
Given that activities of EZH2 and DNMT1 resulted in a blunted antitumor immune response, the team examined samples of human ovarian cancer tissue and quantified nuclear levels of EZH2 and DNMT1 by immunohistochemical methods to assess the impact on patient survival. Guided by staining intensity, patients were divided into low and high groups. Overall survival (OS) and disease-free interval (DFI) were significantly lower in patients with high versus low levels of either EZH2 or DNMT1 (P<.0001), and high levels of both versus just one had a bigger negative impact on OS and DFI (P<.0001). Uni- and multivariate analyses confirmed that tumor EZH2 and DNMT1 were positive predictors of risk of death.1
The group also performed a time-dependent receiver operating characteristic (ROC) curve analysis to calculate the ability of EZH2, DNMT1, and intratumoral CD8+ T cells to predict survival. The areas under the curves AUCs (± standard error) for DNMT1, EZH2, and CD8+ T cells were similar in predicting OS, at 82.66 ± 3.34, 83.63 ± 3.53, and 75.13 ± 4.18, respectively. Values of AUCs for predicting disease-free survival were also similar for DNMT1, EZH2, and CD8+ T cells at 81.06 ± 3.91, 71.98 ± 6.28, and 76.53 ± 5.86, respectively. Researchers also found that patients with high levels of both EZH2 and DNMT1 (n = 57) experienced shorter OS and DFI than patients with low levels of both EZH2 and DNMT1 (n = 50) in univariate and multivariate analyses (P<.0001). In contrast, patients with mixed levels (high + low) experienced similar and moderate survival. The authors stated, “Thus, the combination of EZH2 and DNMT1 allows for improved prognostic stratification of ovarian cancer survival compared to EZH2 or DNMT1 alone.”1
In agreement with the mechanisms revealed, the increasing levels of EZH2 and DNMT1 were negatively correlated with the number of intratumoral CD8+ T cells (P< .0001).
Concluding their paper, and speaking to the potential of their findings for oncology, the authors state, “Applicably, our work suggests that epigenetic reprogramming may condition tumors from poor T-cell infiltration to rich T-cell infiltration, and ultimately potentiate cancer therapy.”1