Advances in detection of covalently closed circular DNA of hepatitis B virus

HBV belongs to the hepatotropic DNA virus family and replicates through reverse transcription. One of the most critical steps in the viral life cycle is that HBV rcDNA (relaxed circular DNA) is transferred to the nucleus where it is converted into cccDNA (covalently closed circular DNA). cccDNA serves as a transcription template for mRNAs and pgRNA, which are ready for the production of new virions. Currently, most antiviral agents can not eliminate HBV cccDNA effectively, which is the key reason for persistent virus infection, reactivation of virus after termination of antiviral therapy and drug resistance. In addition, HBV cccDNA has become an effective index for identifying the states of HBV infection and evaluating efficacy of antiviral therapy. Here, we review research progresses in detection and clinical significance of HBV cccDNA. Key words: Hepatitis B virus; Covalently closed circular DNA; Relaxed circular DNA