Several series[66-68] have demonstrated a potential role for the PD-1 /PD-L1 and PD-L2 pathway, including a nationwide study of 81 cases with 67% of PTLD diagnosed after SOT expressing PD-1 (on tumor-associated macrophages) and PD-L1/PD-L2 (on malignant cells)[66]. This evidence concerns the gene PDCD1 and neoplasm.