Of the primary Th2 cytokines (i.e., IL-4, IL-5, IL-10, IL-13), we identified IL-10 as the dominant driver of CTCL-mediated immunosuppression, as we were able to rescue IFN-γ production in normal T cells with the addition of an IL-10-neutralizing antibody. Here, IL10 is linked to primary cutaneous T-cell non-Hodgkin lymphoma.