Increased expression of the immune checkpoint receptors Programmed cell death receptor 1 (PD-1), Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4), Lymphocyte-activation gene 3 (LAG-3), and Inducible T-cell COStimulator (ICOS) on both CD4+ and CD8+ T cells have been observed in cutaneous T-cell lymphoma [19]. Here, ICOS is linked to primary cutaneous T-cell non-Hodgkin lymphoma.