Search

Aim: To construct prokaryotic expression vector of HAb18G, and express high level of this fusion protein in E. coli and to identify its function and immunogenicity., Methods: The HAb18G full length cDNA from pBluescript/HAb18G was obtained by PCR and cloned into prokaryotic expression vector pRSET-C and then transformed into E. coli BL21(DE3) to induce its expression. Expressed products were analyzed by SDS-PAGE and laser thin layer scan. The purified HAb18G protein was identified by gelatin enzymogram and ELISA., Results: Endonuclease digestion and DNA sequencing proved that HAb18G cDNA was cloned correctly into the expression vector. Result of SDS-PAGE showed that the relative molecular mass of the expressed product HAb18G fusion protein was 34,600, which was in accordance with predicted relative molecular mass value. Laser thin layer scan showed that the expressed product accounted for 33% of the total bacteria protein. Result of enzymogram was negative whereas the result of ELISA was positive., Conclusion: It was testified that the protein HAb18G has immunogenicity but no bioactivity. The high level prokaryotic expression of HAb18G lay the foundation for manufacturing the HAb18G protein in great quantities and proceeding to its relative research.

Aim: To express secretively chimeric Fab antibody HAb18 (cFab) against human hepatocellular carcinoma in Pichia pastoris., Methods: Genes encoding CL chain and Fd fragment of cFab antibody HAb18 were subcloned into vectors pPIC9K and pPICZalphaA, respectively. After confirmed by DNA sequence analysis, the recombinant plasmids pPIC9K/CL and pPICZalphaA/Fd were transformed into the genome of Pichia pastoris GS115. Mut(+) multiple insert transformants were screened by G418 and Zeocin and then induced with 5 mL/L methanol to express cFab., Results: 4 days after methanol induction, 26 mg/L of the cFab fragment was detected in the culture supernatant. Western blot proved that the expressed protein could specifically bind with HAb18GEF antigen., Conclusion: The successful expression of cFab/HAb18 in Pichia pastoris lays the foundation for large-scale production and further application of the antibody.

Aim: To compare characteristics of polyclonal anti-sera against extracellular domain of hepatoma-associated antigen HAb18G/CD147(HAb18GEF) generated by different immunization schemes., Methods: BALB/c mice were immunized with GST-HAb18GEF fusion protein expressed in E.coli (routine immunization method), recombinant eukaryotic expression plasmid pcDNA3/HAb18G (intramuscular injection) and pcDNA3/HAb18G plasmid followed by human hepatoma cells booster (DNA-cell booster), respectively. The titers and Ig subclasses of polyclonal anti-sera against denatured and natural HAb18GEF were detected by indirect ELISA and cell ELISA, respectively. The specific binding of polyclonal anti-sera prepared by different immunization schemes to denatured HAb18GEF was analyzed by Western blot. The specific binding of polyclonal anti-sera produced by DNA-cell booster immunization to natural HAb18G antigen on hepatoma cells was detected by immunofluorescence staining., Results: GST-HAb18GEF immunization could induce polycolonal antibody IgG1 with higher titer mainly against denatured or linear epitopes on HAb18GEF. Antibody induced by pcDNA3/HAb18G intramuscular immunization was IgG2a with lower titer against natural epitopes on HAb18GEF. DNA-cell booster immunization could induce generation of polycolonal antibody IgG2a and IgG1 of moderate titers against the native epitopes on HAb18G., Conclusion: The polycolonal sera with different titers against different epitopes on HAb18GEF can be induced by different immunization schemes.

Aim: To prepare humanized Fab antibody by guided selection and chain shuffling technique., Methods: Human Fd and C(L) repertoire genes were amplified by RT-PCR from PBMCs of patients with hepatocellular carcinoma. Human-murine chimeric C(L) genes were paired with the human Fd repertoire genes to construct phage antibody library. After four rounds of panning against HAb18GE, chimeric antibodies containing humanized Fd gene and binding to HAb18GE were obtained. Then the selected Fd genes were paired with the human C(L) repertoire genes to construct a humanized Fab antibody gene library. After four rounds of panning, completely humanized Fab antibodies were obtained., Results: After six rounds of panning, 7 chimeric Fab genes were obtained from the Fab gene library with 2 x 10 (7) pfu. Using the selected seven Fd genes, the humanized Fab gene library of 0.8 x 10 (7) pfu was constructed. After four rounds of panning, 2 humanized Fab genes with the strongest reactivity to HAb18G were obtained. DNA sequencing showed that Fds of the two humanized Fabs had the same DNA sequence, which belonged to IgG2, just the same as the parent antibody. And the C(L) belonged to kappa type, and V kappa 3 family., Conclusion: By guided-selection and chain shuffling technique, the humanized Fab antibody against HAb18G is obtained, which lays the foundation for further research.

Aim: To clone Fab gene of mAb HAb18 against human hepatocellular carcinoma and express it in E.coli., Methods: The cDNAs of kappa chain and Fd of mAb HAb18 were amplified by RT-PCR and cloned into prokaryotic expression vector pComb3 which was transfected into competent E.coli to express Fab by IPTG induction. The specificity of the expressed Fab was tested by ELISA and immunofluorescence staining., Results: The Fab gene of mAb HAb18 was successfully amplified and expressed in E.coli. The results of competitive ELISA and immunofluorescence staining showed that the expressed Fab had specific antigen-binding activity., Conclusion: HAb18 Fab was prepared successfully, which lays the foundation for its further application to diagnosis and therapy of human hepatocellular carcinoma.

Aim: To construct a anti-dodecane-tertraacetic acid-yttrium(DOTA-Y) immune Fab phage antibody library., Methods: BALB/c were immunized with BSA-Y-DOTA which was prepared by DOTA-conjugated BSA and chelated with Y. After determination of anti-serum, total RNA was extracted from splenic lymphocytes of immuned mice. The heavy chain Fd and light chain Kappa genes repertoires of immunoglobulin were amplified respectively by RT-PCR, and then the amplified products were cloned into the reconstructive phage vector pComb3M to construct anti-DOTA-Y Fab antibody. And then, the recombination rate, diversity and display of Fab antibody library were identified by restriction endonuclease digestion, DNA sequencing and ELISA., Results: BSA-Y-DOTA was prepared successfully, and a higher titer of immune sera was achieved. The amplified gene fragments of Fd and Kappa chain by RT-PCR were correct and the length was with about 650 bp, and were inserted exactly. The sink size of Fab phage display library reached 8 x 10(7), the re-combination rate was about 90%, and it possesed great diversity. In addition, ELISA detection showed that there was Fab expression on the phage library., Conclusion: An immune Fab phage antibody library of DOTA-Y has been constructed successfully, which lays a solid foundation for screening specific anti-DOTA-Y antibody.