Together with human data demonstrating PD-L2 and FASL enrichment within stromal zones of lung tumours, this CAF-mediated mechanism reveals new insight into the cell biology of tumour-associated fibroblasts; helping to explain why cancer associated fibroblasts are associated with poor patient prognosis, and illustrating a novel mechanism of T cell depletion and dysfunction within tumours. The gene discussed is FASLG; the disease is cancer.