Tumor cells can upregulate PD1 ligands to induce T cell exhaustion and mold the TME towards a supportive niche; blocking the PD1 axis with PD1 inhibitors (e.g. pembrolizumab and nivolumab) has been shown to have substantial anti-tumour activity in relapsed or refractory Hodgkin lymphoma (16, 17), primary mediastinal B cell lymphoma (18) and also in T cell (19, 20) and NK/T cell lymphoma (21). This evidence concerns the gene PDCD1 and Hodgkins lymphoma.