AIM:A strategy for viral vaccine design is the use ofconserved peptides to overcome the problem of sequencediversity.At present it is still unclear whether conservedpeptide is safe as a candidate vaccine.We reported it herefor the first time not only to highlight the biohazard issueand safety importance for viral peptide vaccine,but also toexplore the effect of a fully conserved peptide on HBVreplication within the carboxyl terminus of HBx.METHODS:We synthesized the fully conserved peptide (CP)with nine residues,FVLGGCRHK.HBV-producing 2.2.15 cellswere treated with or without 3.5 μM CP for 36 hours.Quantitative detection of viral DNA was performed by real-time PCR.HBV antigens were determined by enzyme-linkedimmunoadsorbent assay (ELISA).Quantitative analyses ofp53 and Bax proteins were based on immunofiuorescence.Flow cytometry was performed to detect cell cycle andapoptosis.RESULTS:Both extracellular and intracellular copies of HBVDNA per ml were significantly increased after incubationwith 3.5 μM of CP.HBsAg and HBeAg in the cultured mediumof CP-treatment cells were as abundant as untreated controlcells.CP influenced negatively the extracellular viral geneproducts,and 3.5 μM CP could significantly inhibit intracellularHBsAg expression.In response to CP,intracellular HBeAgdisplayed an opposite pattern to that of HBsAg,and 3.5μMCP could efficiently increase the level of intracellular HBeAg.Flow cytometric analyses exhibited no significant changeson cell cycle,apoptosis,p53 and Bax proteins in 2.2.15 cellswith or without CP.CONCLUSION:Together with the results generated fromthe synthetic peptide,we address that the conserved region,a domain of HBx,may be responsible for modulating HBVreplication.As conserved peptides from infectious microbesare used as immunogens to elicit immune responses,theirlatent biological hazard for human beings should beevaluated. AIM: A strategy for viral vaccine design is the use ofconserved peptides to overcome the problem of sequencediversity. At present it is still unclear whether conserved peptide is safe as a candidate vaccine. We reported it here for the first time not only to highlight the biohazard issue and safety importance for viral peptide vaccine, but also toexplore the effect of a fully conserved peptide on HBVreplication within the carboxyl terminus of HBx. METHODS: We synthesized the fully conserved peptide (CP) with nine residues, FVLGGCRHK.HBV- producing 2.2.15 cellswere treated with or without 3.5 μM CP for 36 hours. Quantitative detection of viral DNA was performed by real-time PCR. HBV antigens were determined by enzyme-linked immunosorbent assay (ELISA). Quantitative analyzes of p53 and Bax proteins were based on immunofiuorescence. Flow cytometry was performed to detect cell cycle andapoptosis.RESULTS: Both extracellular and intracellular copies of HBVDNA per ml were significantly increased after incuba tion with 3.5 μM of CP. HBsAg and HBeAg in the cultured medium of CP-treatment cells were as abundant as untreated control cells. CP-dependent negatively the extracellular viral gene products, and 3.5 μM CP could inhibit intracellular HBsAg expression. In response to CP, intracellular HBeAgdisplayed an opposite pattern to that of HBsAg, and 3.5 μM CP could efficiently increase the level of intracellular HBeAg.Flow cytometric analysis exhibits no significant changeson cell cycle, apoptosis, p53 and Bax proteins in 2.2.15 cells with or without CP. generated from the synthetic peptide, we address that the conserved region, a domain of HBx, may be responsible for modulating HBVreplication. As conserved peptides from infectious microbesare used as immunogens to elicit immune responses, theirlatent biological hazards for human beings should be evaluated.