Tumor Cell–Intrinsic PD-1 Promotes Merkel Cell Carcinoma Growth by Activating Downstream mTOR-Mitochondrial ROS Signaling

In human Merkel cell carcinoma lines and clinical tumors, RT-PCR–based sequencing, immunoblotting, flow cytometry, and immunofluorescence analyses demonstrated PD-1 gene and protein expression by Merkel cell carcinoma cells.