CD81 and cancer: While CD81 function has primarily been studied in immune cells (Vences-Catalán et al., 2015; Maecker and Levy, 1997; Quast et al., 2011; van Zelm et al., 2010), this newly identified function of CD81 in cancer metastasis is tumor cell intrinsic and can be independent of adaptive immunity, as shown in both immunocompetent and immunocompromised mice.