Although in the syngenetic tumor models in C57BL/6 mice PD-1 has been shown to be expressed mainly on CD8+ T cells [24], it might be also present on different types of both innate and adaptive immune cells, such as NK cells, NKT cells, monocytes, macrophages, B cells as well as CD4+ T cells including Tregs [25]. The gene discussed is CD4; the disease is neoplasm.