Functional analysis of the broadly neutralizing human anti-HIV-1 antibody 2F5 produced in transgenic BY-2 suspension cultures.

We report the production of an important human therapeutic antibody in plant cell suspension cultures and the functional analysis of that antibody, including a comparison with the same antibody produced in CHO cells. We established transgenic tobacco BY2 suspension cell cultures expressing the human monoclonal antibody 2F5, which shows broadly neutralizing activity against HIV-1. The antibody was directed to the endoplasmic reticulum of the plant cells and was isolated by cell disruption, followed by protein A chromatography. The plant-derived antibody was shown to be largely intact by SDS-PAGE and immunoblot. Antigen binding activity was investigated by electrophoretic mobility shift assay and quantitatively determined by ELISA and Biacore biosensor technology. Ligand binding properties were analyzed using the ectodomain of human Fc gammaRI for kinetic analysis. The plant-derived antibody showed similar kinetic properties and 89% of the binding capacity of its CHO-derived counterpart, but was only 33% as efficient in HIV-1 neutralization assays. Our results show that plant suspension cultures can be used to produce human antibodies efficiently and that the analysis methods used in this study, including biosensor technology, provide useful functional data about antibody performance. This highlights important issues raised by the use of plant systems to produce human biologics.

Recombinant soluble human Fcgamma receptor I with picomolar affinity for immunoglobulin G.

The ectodomain of human FcgammaRI (rsCD64) was expressed in HEK 293T cells and purified by immobilized-metal affinity chromatography. Binding activity to human IgG was verified by ELISA and the isotype-specificity determined by a surface plasmon resonance inhibition assay was found to be the same as for native CD64. The active concentration of the rsCD64 preparation was derived using a solution competition assay and was used for the subsequent kinetic analysis. Binding curves were well described by a simple monovalent interaction model confirming the known stoichiometry of the interaction. Mass-transport limitation was prevented by using sufficiently low surface capacities. For binding to the recombinant mouse/human chimeric antibody cPIPP (IgG1/kappa) a high association rate of k(ass)=1.7 x 10(6) (M s)(-1) and a low dissociation rate of k(diss)=1.8 x 10(-4) s(-1) were observed. The derived dissociation equilibrium constant of K(D)=110 pM was significantly lower than that reported for binding to native FcgammaRI.

The recombinant anti-EGF receptor immunotoxin 425(scFv)-ETA' suppresses growth of a highly metastatic pancreatic carcinoma cell line.

Pancreatic carcinoma still has the highest mortality rate in comparison to any other malignancy. Major reasons are late detection of disease, highly aggressive tumor growth and the early formation of metastases. Thus, novel effective therapies are urgently needed to improve the outcome of the patients. Overexpression of the epidermal growth factor receptor (EGFR) and its ligands has been implicated in the oncogenesis of pancreatic carcinoma and associated with an unfavorable prognosis. Consequently, the EGFR represents a specific target antigen suitable for immunotherapy. We generated a recombinant immunotoxin by fusing the anti-EGFR single chain fragment 425(scFv) to a truncated mutant of Pseudomonas Exotoxin A (ETA'). Using the expression vector pBM1.1, functional 425(scFv)-ETA' was periplasmically expressed under osmotic stress conditions in the presence of compatible solutes. The 72 kDa His10-tagged fusion protein was purified by a combination of metal-ion affinity and molecular size chromatography. Binding activity and specificity of the immunotoxin to the EGFR-positive pancreatic carcinoma cell line L3.6pl was confirmed by flow cytometry and ELISA. Finally, 425(scFv)-ETA' showed significant toxicity toward this cell line reaching 50% inhibition of cell proliferation at a concentration (IC50) of 7.5 ng/ml. This is the first report documenting the specific cytotoxicity of a recombinant immunotoxin towards metastatic pancreatic carcinoma cells, suggesting that EGFR-specific antibody toxins may become valuable therapeutic reagents for the treatment of pancreatic carcinoma.