In addition, the recent discovery that tumorigenic cells, particularly melanoma cells expressing ABCB5+, can also express immune co-stimulatory and/or co-inhibitory molecules (e.g., PD-1/PD-L1; CTLA4) [14,20] has allowed an entirely new and effective therapeutic approach for metastatic melanoma patients and, more recently, even for other human solid tumors as well, based on the administration of immune checkpoint antibodies [26,27,28,29,30,31,32,33,34,35] that can trigger a strong, clinically effective T cell mediated anti-tumor response. The gene discussed is ABCB5; the disease is melanoma.