CD4 and primary cutaneous T-cell non-Hodgkin lymphoma: Indeed, reactive CD4+ T cells, CD8+ T cells and natural killer (NK) cells isolated from CTCL patients are able to kill autologous malignant T cells in vitro, and high numbers of CD8+ lymphocytes in skin lesions and/or blood are linked to a favorable prognosis [30, 32, 34–37].