This state of local immune privilege can be reversed by blocking antibodies to PD-1 or PD-L1 and such single agent therapies are now licensed for the treatment of patients with multiple types of cancers.4–10 Response rates can be as high as 90% for some tumour types but as low as 15% with others, but selection of patients likely to respond favourably to such single agent therapy proves a challenge, as it requires an in depth understanding of immune interactions in the TME.4,5. This evidence concerns the gene PDCD1 and cancer.