We have previously demonstrated that ARG1- and PD-L1-specific T cells can directly target immunosuppressive cells (18,) (20,) (23), and we therefore hypothesized that a boost in the ARG1- and PD-L1-specific T-cell responses should lead to a reduction in the number of immunosuppressive cells in MPN which in turn could increase the tumor specific T-cell responses in treated patients. Here, ARG1 is linked to myeloproliferative disorder.