The fact that Pmel levels equally increase upon transplantation of the D4M cells into either NSG or B6 mice suggests that non-immune cells may be mediating most of this increase. Indeed, the stromal compartment of adjacent fibroblasts has
been implicated as one prominent modulator of tumor cell behavior in vivo (Bhowmick et al., 2004; Eck et al., 2009; Marsh et al., 2013; Smalley et al., 2005).