In phase 2 multi-center open label clinical trial adenoviral p53 (Ad-p53) gene therapy is administered intratumorally in combination with immune checkpoint PD-1 and PD-L1 inhibitors in patients with recurrent or metastatic HNSCC and other solid tumors approved for anti-PD-1 or anti-PD-L1 therapy [179]. The gene discussed is PDCD1; the disease is head and neck squamous cell carcinoma.