One of the leading OVs targeting HCC currently being investigated in clinical trials is a modified Wyeth strain of the vaccinia virus, JX‐594/pexastigmogene devacirepvec (Pexa‐Vec), which has been genetically engineered to express GM‐CSF in order to promote host antitumour activity in tumour cells typically expressing high levels of thymidine kinase following deletion of the thymidine kinase gene from its viral genome.108, 129, 131. The gene discussed is CSF2; the disease is neoplasm.