IHC staining of Ki-67 and cleaved-caspase3 showed that tumor cell proliferation was not inhibited in no treatment group, while combination therapy significantly induced tumor cell apoptosis compared to either single treatment (Figure 6e and f), suggesting that anti-PD-1 mAb and Arg-1 inhibitor have no direct proliferative toxicity and neither single treatment was sufficient to activate the immune killing to tumor cells. The gene discussed is ARG1; the disease is neoplasm.