Enhanced expression of Programmed cell death 1 (PD-1) protein in benign vascular anomalies

Programmed cell death 1 (PD-1) and its ligands have been shown to play a significant role in evasion of malignant tumour cells from the immune system. Last year, the United States Food and Drug Administration (FDA) approved anti-PD-1 inhibitors for treatment of non-small cell lung carcinoma and recently has approved anti-PD-L1 blocker for treatment of metastatic urothelial cell carcinoma. However, the role that the immune system might have on benign tumours including vascular anomalies has received less attention. In this study, we evaluated PD-1 and PD-L1 expression on two benign vascular anomalies: infantile haemangiomas and venous malformations. Tissue microarrays (TMAs) from these two entities were stained for PD-1 and PD-L1 antibodies. Blood vessels from normal tissue were used as control. The endothelial cells in both infantile haemangioma and venous malformation showed high expression of PD-1 but were negative for PD-L1. Endothelial cells within the blood vessels in normal tissues were negative for both PD-1 and PD-L1. Our results showed over-expression of PD-1 in subsets of vascular anomalies, while PD-L1 was negative. This would raise the possibility of immunotherapy in benign vascular tumour when other options are exhausted.