ARG1 and neoplasm: As the expression of the cornerstone immunoregulatory proteins PD-L1 and ARG1 is increased in MPN, we speculate that vaccination against both of these will enhance the anti-tumor immune response in patients, and we have consequently launched a phase I/II clinical vaccination trial with PD-L1- and ARG1-derived epitopes in patients with MPN (NCT04051307).