Gemcitabine has been shown to cause tumor cell death that stimulates an immune response. It also can decrease regulatory cells, such as Tregs and MDSCs. An article published by Zhao, et al. (Immunology Lett. 2017 Jan; 181:36-44), demonstrated that Gemcitabine could decrease Tregs, reduce suppressive cytokines, such as TGF-B, and increase stimulatory cytokines like Interferon-gamma. This was in low dose therapy in mice. As mentioned, the immune-stimulating aspects of chemotherapy seem to occur when it is used with frequent low dosing (metronomic). This certainly requires further study, but this goes against the typical chemotherapy dosing scheme that uses a maximum tolerated dose therapy, which is intermittent, but high dosing.
Reference: Jason R. Williams, 15 Oct 2019, The Immunotherapy Revolution: The Best New Hope For Saving Cancer Patients’ Lives, https://williamscancerinstitute.com/the-immunotherapy-revolution