CD4 and melanoma: Even though at different levels, Mela1 and SLM8 spheroid cells also showed upregulated expression of IL-16, a pleiotropic cytokine that is a natural ligand of CD4 and is a chemo-attractant for CD4+ T cells, particularly T regulatory cells [47], and SNAI2 (Slug), a master regulator of neural crest cell specification and migration and is implicated in melanoma progression [48], [49] (Fig. 6A).