Dear Editor,rnGenetic code expansion based on orthogonal tRNA-ami-noacyl tRNA synthetase is an emerging technology to site-specifically incorporate unnatural amino acids(UAAs)into viral proteins to produce UAA-controlled replication-de-fective virus.Briefly,aminoacyl tRNA synthase is used to transfer specific UAAs to corresponding tRNA to form aminoacyl tRNA,which then inserts the UAAs into the synthetic peptide chain by specifically recognizing the nonsense codon,such as the amber stop codon(Wang et al.,2001).Previously,it has been applied to prokaryotic cells,eukaryotic cells and some kinds of viruses,such as hepatitis D virus,adenovirus and human immunodeficiency virus type 1(HIV-1)(Lin et al.,2013;Wang et al.,2014;Zhang et al.,2016).Subsequently,the technology has been successfully utilized to construct a replication-incompetent influenza vaccine candidate(Si et al.,2016).From what has been mentioned above,genetic code expansion strategy has great prospects to be extensively applied to important human pa-thogens when combined with reverse genetic approaches.