The role of GM-CSF in enhancing immunotherapy of cancer

Evaluation of: Kanerva A, Nokisalmi P, Diaconu I et al. Antiviral and anti-tumor T-cell immunity in patients treated with GM-CSF coding oncolytic adenovirus. Clin. Cancer Res. 19(10), 2734-2744 (2013). The field of oncolytic viral therapy has been reinvigorated recently with publication of clinical data from two leading vectors, one based on HSV and one on Vaccinia, both of which express GM-CSF. Part of the reason for the improved clinical results with these vectors appears to be the enhanced immunotherapeutic mechanism of tumor destruction mediated by GM-CSF expression itself. The article by Kanerva et al. extends this work to describe early clinical use of an oncolytic adenovirus expressing GM-CSF, although the data are too preliminary to describe significant therapeutic benefits of GM-CSF expression in this backbone. However, the description of enhanced antitumor immunity in those patients that developed greater antiviral immunity after treatment provides a potent demonstration of the immunotherapeutic potential of epitope spreading after treatment with oncolytic viral therapies.