Immunotherapy treatments have proven wildly successful in treating some patients with cancer.

But despite this success, the majority of patients do not respond to the treatments.

A new study from the University of Michigan Comprehensive Cancer Center reveals molecular changes within the tumour that are preventing the immunotherapy drugs from killing off the cancer.

Clinical trials with PD-L1 and PD-1 blockade suggested that tumours with a high number of inflammation-causing T cells were more responsive to the immunotherapy-based PD-L1 and PD-1 inhibitors.

Tumours with low inflammation, or low T cells, were less responsive.

But what controls T cells in the tumour microenvironment is poorly understood.

"We defined a molecular mechanism to explain why some tumours are inflamed and others are not - and consequently why some patients will be responsive to therapy and others not," says senior author Weiping Zou, M.D., Ph.D.

"If we can re-programme this epigenetic mechanism, then the therapy might work for more patients," says Zou, Charles B. de Nancrede Professor of Surgery, Immunology and Biology at the University of Michigan Medical School.

Zou's group was the first to show PD-L1 expression, regulation and functional blockade in dendritic cells in the human cancer microenvironment.

In this study, published in Nature, researchers studied human and mouse models of ovarian cancer cells. They applied epigenetic drugs and found that the numbers of T cells in the tumour increased. They also saw that the epigenetic drugs synergised the anti-tumour effect of PD-L1 blockade in their models.

"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 non-responders into responders," Zou says.

Source: Nature, University of Michigan Health System