JX-594, also known as pexastimogene devacirepvec or Pexa-Vec, is a genetically modified vaccinia virus that possesses an insertion of the human granulocyte-macrophage colony-stimulating factor (GM-CSF) gene to enhance the antitumor immune response and a mutation in the TK gene that confers cancer cell-selective replication. The gene discussed is CSF2; the disease is cancer.