Neutralization of NET-associated human ARG1 enhances cancer immunotherapy

Myeloid cells can restrain antitumor immunity by metabolic pathways, such as the degradation of L-arginine, whose concentrations are regulated by the arginase 1 (ARG1) enzyme. Results from preclinical studies indicate the important role of arginine metabolism in pancreatic ductal adenocarcinoma (PDAC) progression, suggesting a potential for clinical application; however, divergent evolution in ARG1 expression and function in rodents and humans has restricted clinical translation. To overcome this dichotomy, here, we show that neutrophil extracel-lular traps (NETs), released by spontaneously activated neutrophils isolated from patients with PDAC, create a microdomain where cathepsin S (CTSS) cleaves human (h)ARG1 into different molecular forms endowed with enhanced enzymatic activity at physiological pH. NET-associated hARG1 suppresses T lymphocytes whose pro-liferation is restored by either adding a hARG1-specific monoclonal antibody (mAb) or preventing CTSS-medi-ated cleavage, whereas small-molecule inhibitors are not effective. We show that ARG1 blockade, combined with immune checkpoint inhibitors, can restore CD8+ T cell function in ex vivo PDAC tumors. Furthermore, anti-hARG1 mAbs increase the frequency of adoptively transferred tumor-specific CD8+ T cells in tumor and enhance the effectiveness of immune checkpoint therapy in humanized mice. Thus, this study shows that ex-tracellular ARG1, released by activated myeloid cells, localizes in NETs, where it interacts with CTSS that in turn cleaves ARG1, producing major molecular forms endowed with different enzymatic activity at physiological pH. Once exocytosed, ARG1 activity can be targeted by mAbs, which bear potential for clinical application for the treatment of PDAC and require further exploration.

Automated summary

Preclinical studies have shown that myeloid cells can suppress antitumor immunity by degrading L-arginine, but differences in ARG1 expression and function in rodents and humans have hindered clinical translation. This study discovered that neutrophil extracellular traps (NETs) released by activated neutrophils in patients with PDAC create a microdomain where cathepsin S (CTSS) cleaves human ARG1 (hARG1) into different forms with enhanced enzymatic activity. These NET-associated hARG1 molecules suppress T lymphocytes, but their proliferation can be restored by blocking CTSS cleavage or using hARG1-specific monoclonal antibodies, suggesting potential therapeutic strategies for PDAC.