A novel strategy for proteome-wide ligand screening using cross-linked phage matrices.

To find a suitable ligand from a complex antigen system is still a mission to be accomplished. Here we have explored a novel "library against proteome" panning strategy for ligand screening and antigen purification from a complex system using phage-displayed antibody technology. Human plasma proteome was targeted for phage library panning. During the process, the panning was carried out in solution, using a biotin/streptavidin beads separation system, for three rounds. Nine monoclonal phages, bound tightly to a number of unknown plasma proteins, were selected from the last round, six of which were directly employed as cross-linked matrices to purify their corresponding antigens from the plasma. The proteins isolated by G5 and E1 matrices were identified as amyloid protein and apolipoprotein A-I precursor, respectively. The results demonstrated that it was feasible to simultaneously obtain a number of ligand phages for various antigens, including low abundant proteins in a non-comparative proteome-wide system.

Induction of anti-tumor immunity by lyophilized myeloma cells secreting GM-CSF.

We have previously demonstrated that a low dose of live myeloma FO cells induced a cellular immunity against tumor without additional modulating factors. In the present study, lyophilized myeloma FO cells were used to induce anti-tumor immunity. In a myeloma vaccination model, immunization with lyophilized myeloma FO cells alone induced a slight response. However, the immunity was dramatically enhanced by myeloma FO cells transfected with a recombinant adenovirus, Adv-1/GM-CSF. The immunocytochemical staining of Adv-1/GM-CSF transfected myeloma FO cells confirmed that more than 90% of cells were positive with GM-CSF expression. Results of sandwich ELISA showed the amount of secreted GM-CSF was 240 ng/24 h per 10(6) cells. Immunization with lyophilized myeloma FO cells secreting GM-CSF prevented the tumor growth in 60% of BALB/c mice. Antibodies against myeloma FO cells were found in the sera of immunized mice. Tumor-specific T-cell response was also evaluated using cytotoxic T lymphocyte assay. In conclusion, lyophilized myeloma FO cells secreting GM-CSF can be used as a potent vaccine to induce strong and protective anti-tumor immunity.

Preparation and characterization of scFv for affinity purification of reteplase.

The work was to explore the feasibility of protein affinity purification using ligand isolated from phage library. Reteplase was used as the model protein and a humanized semi-synthetic single chain fragment variable phage library as the source of ligand. After four rounds of biopanning, reteplase-specific phage clones were greatly enriched. The scFv gene from the best phage clone was inserted to pET-29a and expressed in E. coli Rosseta. After purification by nickel-affinity and refolding, this scFv protein was proven to recognize reteplase specifically and sensitively in ELISA and dot-blotting. Its binding constant to reteplase was 1.84x10(-8) M, measured by surface plasmon resonance. After immobilized on Sepharose 4B, the scFv was used for the affinity purification of reteplase from milk. It was found that reteplase was highly purified from the starting material. In conclusion, it has been demonstrated that humanized scFv prepared with this approach could be used as a practical affinity ligand for efficient and cost-effective purification of reteplase, as well as other therapeutic proteins.

Expression, purification, and characterization of a novel recombinant fusion protein, rhTPO/SCF, in Escherichia coli.

Thrombopoietin (TPO) is the principal regulatory cytokine of megakaryopoiesis and thrombopoiesis and promotes all aspects of megakaryocyte development. Stem cell factor (SCF) is mainly a pleiotropic cytokine acting on hematopoiesis by promoting the survival and proliferation of hematopoietic stem cells and has a potent synergistic effect on megakaryopoiesis in the presence of TPO. Here, we report the construction, expression, and purification of a novel recombinant human thrombopoietin/stem cell factor (rhTPO/SCF) fusion protein, which consists of a truncated human thrombopoietin (1-157 a.a.) plus a truncated human stem cell factor (1-145 a.a.), linked by a peptide (GGGGSPGGSGGGGSGG). The TPO/SCF gene was cloned into the Escherichia coli expression vector pET28a and expressed in BL21(DE3) strain. The rhTPO/SCF constituted up to 6% of the total bacterial protein. Co-expression with E. coli chaperones, Trigger Factor (TF) and GroES/GroEL, and lowering cultivation temperature cooperatively improved the solubility of expressed rhTPO/SCF, resulting in about fourfold increase in the yield soluble rhTPO/SCF. The rhTPO/SCF was purified to homogeneity using anion exchange followed by metal affinity chromatography. Western blot analysis confirmed the identity of the purified protein. rhTPO/SCF stimulated a dose-dependent cell proliferation in both TF1 and Mo7e cell lines.