Therefore, we decided to use CB-1158 (named as the ref. ARGi) in our studies for comparison purposes, since—similarly to other known arginase inhibitors [62]—this molecule lacks the intracellular activity essential to effectively target not only the extracellular myeloid cell-derived ARG1 [24], but also the intracellular ARG2 that regulates the fitness of immune cells [19,20] and significantly determines the tumour growth [17,18,54,63,64,65]. This evidence concerns the gene ARG1 and neoplasm.