GZMB and neoplasm: Most recently, several lines of evidence have shown that polyamine blocking therapy (PBT) can improve the anti-tumor efficacy of PD-1 blockade along with an increase in tumor infiltration of granzyme B+, IFN-γ+ CD8+ T-cells and a decrease in immunosuppressive tumor infiltrating cells including Gr-1+CD11b+ myeloid derived suppressor cells (MDSCs), CD4+CD25+ Tregs, and CD206+F4/80+ M2 macrophages (231, 257, 258).