Terminal Protein-specific scFv Production by Phage Display

BACKGROUND: One of the important factors in the prognosis of chronic hepatitis B patient is the degree of replication of hepatitis B virus (HBV). It has been known that HBV DNA polymerase plays the essential role in the replication of HBV. HBV DNA polymerase is composed of four domains, TP (Terminal protein), spacer, RT (Reverse transcriptase) and RNaseH. Among these domains, tyrosine, the 65th residue of TP is an important residue in protein-priming reaction that initiates reverse transcription. If monoclonal antibody that recognizes around tyrosine residue were selected, it could be applied to further study of HBV replication. METHODS: To produce TP-specific scFv (single-chain Fv) by phage display, mice were immunized using synthetic TP-peptide contains 57~80th amino acid residues of TP domain. After isolation of mRNA of heavy-variable region (VH) and light-chain variable region (VL) from the spleen of the immunized mouse, DNA of VH and VL were obtained by RT-PCR and joined by a DNA linker encoding peptide (Gly4Ser)3 as a scFv DNA fragments. ScFv DNA fragments were cloned into a phagemid vector. ScFv was expressed in E.coli TG1 as a fusion protein with E tag and phage gIII. To select the scFv that has specific affinity to TP-peptide from the phage-antibody library, we used two cycles of panning and colony lift assay. RESULTS: The TP-peptide-specific scFv was isolated by selection process using TP-peptide as an antigen. Selected scFv had 30 kDa of protein size and its nucleotide sequences were analyzed. Indirect- and competitive-ELISA revealed that the selected scFv specifically recognized both TP-peptide and the HBV DNA polymerase. CONCLUSION: The scFv that recognizes the TP domain of the HBV DNA polymerase was isolated by phage display.

Emergence of YMDD Motif Mutant Hepatitis B Virus during Short-erm Lamivudine Therapy / 대한간학회지

BACKGROUND/AIMS: The emergence of lamivudine-resistant mutant hepatitis B virus (HBV), with aminoacid substitution in the YMDD motif of DNA polymerase, has been reported in the long-term lamivudine use group. However there is no report about the emergence of mutant viruses during the short-term lamivudine therapy. The objective of this study was to investigate the emergence of YMDD mutant HBV during short-term lamivudine therapy. METHODS: We evaluated twenty-eight chronic hepatitis B patients who were HBeAg and HBV DNA positive and treated with lamivudine 100mg p.o. daily for 12 weeks. First, we investigated the emergence of YMDD mutants by nested polymerase chain reaction (PCR) method developed by Chayama et al in 19 patients who lost HBV DNA during lamivudine therapy but showed HBV DNA re-emergence 2 weeks after the end of therapy. Second, DNA subcloning and sequencing of HBV DNA polymerase including YMDD motif was undertaken in one patient's serial blood samples at 0, 8, 12 weeks to confirm the results of nested PCR. RESULTS: YMDD motif mutation was detected in 17(90%) out of 19 patients at the end of therapy and the type of mutations were YIDD only. At the end of therapy, mutant was predominant in 5 patients, both mutant and wild type were similar in proportion in 3 patients, and wild type was predominant in 9 patients. When we carried out nested PCR serially with samples of 0, 2, 4, 8, 12, 14 weeks after initiation of therapy in 5 patients who were mutant predominant at 12 weeks, YIDD mutant began to be detected from 2 weeks in 4 patients and from 4 weeks in one patient. However, rapid turnover from mutant to wild type happened after the end of therapy, so only wild type was detected in 3 patients and wild type became predominant in 2 patients at 2 weeks after the end of therapy. All the sequencing results of serial blood samples in one patient were consistent with nested PCR data. CONCLUSIONS: The presence of YMDD motif HBV polymerase mutant may be possible before administration of lamivudine in Korean chronic hepatitis B patients. Nested PCR assay would be an useful method to detect YMDD mutant.

Anti-HBc IgM and anti-delta screening by EIA method

The clinical value of an enzyme-linked immunosorbent assay (ELISA) for the detection of anti-HBc IgM was evaluated by testing 202 sera from acute viral hepatitis B (AVHB), hepatitis B (HB), chronic hepatitis (CAH), chronic liver disease (CLD), cirrhosis, primary hepatoma, HBsAg carrier, acute viral hepatitis A (AVHA), hepatitis A (HA), non-A, non-B (NANB) hepatitis and miscellaneous conditions other than hepatic disease, and 19 additional various hepatic disease cases were examined for anti-delta. In clinical situations the accurate diagnosis of HB is not always possible and the differential diagnosis seems to be very important especially in making decisions of treatment and estimation of prognosis. In overall cases the highest positive rate of anti-HBc IgM was found in AVHB as shown as 74.3% (26/35) comparing to other conditions in which the positive rate was extremely low (2.1%). The anti-HBc IgM appeared to be highly specific to AVHB (83.9%) as compared to the other. The positive rate of HBsAg was high in AVHB, CAH and HBsAg carrier (100.0%) followed by CLD, cirrhosis and HB (up to 70.8%). The ALT activities and ALPalb fractions were significantly high in AVHB (p less than 0.005). The correlation between the positivity of anti-HBc IgM and highly abnormal ALT appeared be high. AVHB was confined mostly to 10-20 age group and the male to female ratio was about 6 to 1. Subgroup of AVHB II with positive anti-HBc IgM appeared to have a greater chance being positive for HBsAg and ALPalb. The S/N ratio of anti-HBc IgM was as high as 20 which was unique to AVHB.

Properties of Hepatitis B Virus Associated DNA Polymerase

The nature of hepatitis B virus (HBV) particle associated DNA polymerase was studied in relation to various enzyme inhibitors including antiviral agents. HBV DNA polymerase required high concentration of MgCl2(> 30 mM) and neutral pH for its full activity. p-chloromercuribenzoate was a strong inhibitor (85% inhibition at 1 mM) but N-ethylmaleimide had much less inhibitory effect (20% inhibition at 10 mM). Phosphonoformic acid showed the greatest inhibitory effect on HBV-DNA polymerase (almost complete inhibition at 100 microM) among phosphocompounds tested. Adenine arabinoside triphosphate (ara-ATP) and cytosine arabinoside triphosphate (ara-CTP) were competitive inhibitors with respect to their respective deoxyribonucleoside triphosphate (dATP and dCTP). Ara-CPT was a stronger inhibitor of HBV-DNA polymerase compared to ara-ATP. Ki values for ara-ATP and ara-CTP were 15.0 microM and 11.7 microM , respectively. HBV-DNA polymerase is characteristic in its ionic requirements and susceptibilities to certain inhibitors.