CSF2 and cancer: In 2015, the U.S. FDA approved T-VEC, an attenuated HSV-1 encoding GM-CSF for the local treatment of unresectable cutaneous, subcutaneous and nodal lesions in patients with recurrent melanoma after the initial surgery.314 It has been shown that GM-CSF may stimulate MDSCs, resulting in diminished innate and adaptive antitumor responses in numerous cancers.234,315,316 An insertion of a sole GM-CSF into the virus seems not an ideal strategy.