In support of this viewpoint, GM-CSF alone is sufficient to induce the generation of immunosuppressive MDSCs in vitro, which is consistent with previous observations in a spontaneous model of pancreatic ductal adenocarcinoma.33 It should be noted that CSF2−/− mice have relatively normal hematopoiesis in bone marrow.34,35 So, the decrease in MDSC number in lesions of CSF2−/− mice appears to be due to the impairment of differentiation of progenitors into MDSCs and/or the inhibition of MDSC recruitment into lesions. The gene discussed is CSF2; the disease is pancreatic ductal adenocarcinoma.