Several studies have described a two- to 34-fold increase in intratumoral transduction efficiency (Rancourt et al, 1998; Doukas et al, 1999; Qin et al, 2005) and a two-fold increased transduction efficiency of adenoviral TK gene was observed for human HNSCC (Saito et al, 2009). This evidence concerns the gene TKT and head and neck squamous cell carcinoma.