Lay summary
Immune therapy is showing tremendous promise against cancer, with two new drugs causing long-lasting remissions from very advanced cancer in some patients. These drugs target the immune system to "unblock" the activity of cancer-killing cells called T cells. There are many ways tumours can block T cell activity, so determining which process needs to be "unblocked" in each patient's tumour will help target the right drug to the patient. We have discovered a type of immune cell in melanoma tumours from patients that is likely to block T cell activity in their tumours. This cell type is unusual because it seems to be dividing within the patients' tumours, making more cells capable of blocking immune attack. In this project we will discover where this cell type comes from, what makes it grow, and how it blocks T cell activity. This work will lead to new diagnostics and therapy for cancer.