MCPyV genome integrationwith MCC generally results in unaltered expression of the native sTantigen.90,105 Tumor regression in vivo was achieved withshort hairpin RNA-mediated elimination of MCPyV sT/LT antigen in MCCcell lines.105,106 These studies demonstrate thatMCC tumor cell growth in vitro and in xenograft models requires theexpression of MCPyV LT and sT antigens. This evidence concerns the gene LTA and neoplasm.