TNFRSF4 and Merkel cell skin cancer: WT, T271I or N342Y GL8 Env Fc-SUs bound to feline CD134 expressing MCC cells (Fig. 6A, row 1) but not to control MCC cells (Fig. 6A, row 4), consistent with the usage of feline CD134 as a receptor on MCC cells (Fig. 3B).