When the sFc-CD134 pre-treated pseudotypes were plated onto control MCC cells (Fig. 4E), cells that are CD134-negative and CXCR4-positive[49], we observed no evidence of enhanced infection by adding increasing concentrations of sFc-CD134 (values are expressed as percent infection of control MCC cells compared with MCC-CD134). Here, CXCR4 is linked to Merkel cell skin cancer.