Antisense oligonucleotide acts a complementary nucleotide to the messenger RNA of the major immediate-early region proteins of human cytomegalovirus, it disrupts the replication of the virus through an antisense mechanism[1].Fomivirsen is 21-mer phosphorothioate ASO with CpG motif near its 5′ end, with the sequence 5′-GCG TTT GCT CTT CTT CTT GCG-3′, resulting in mRNA degradation by RNase H-mediated mechanism[2].Fomivirsen inhibits CMV replication in human retinal pigment epithelial (RPE) cells and in human fibroblast cells (MRC-5 cells) in a dose-dependent manner. The mean IC 50 are 0.03 μM for RPE cells and 0.2 μM for MRC5 cells[1].