Quality assessment of recombinant proteins produced in plants

Assessing and Improving Protein Sample Quality

One essential prerequisite of any experiment involving a purified protein, such as interaction studies or structural and biophysical characterization, is to work with a "good-quality" sample in order to ensure reproducibility and reliability of the data. Here, we define a "good-quality" sample as a protein preparation that fulfills three criteria: (1) the preparation contains a protein that is pure and soluble and exhibits structural and functional integrity, (2) the protein must be structurally homogeneous, and (3) the preparation must be reproducible. To ensure effective quality control (QC) of all these parameters, we suggest to follow a simple workflow involving the use of gel electrophoresis, light scattering, and spectroscopic experiments. We describe the techniques used in every step of this workflow and provide easy-to-use standard protocols for each step.

Quality control of purified proteins to improve data quality and reproducibility: results from a large-scale survey

As the scientific community strives to make published results more transparent and reliable, it has become obvious that poor data reproducibility can often be attributed to insufficient quality control of experimental reagents. In this context, proteins and peptides reagents require much stricter quality controls than those routinely performed on them in a significant proportion of research laboratories. Members of the ARBRE-MOBIEU and the P4EU networks have combined their expertise to generate guidelines for the evaluation of purified proteins used in life sciences and medical trials. These networks, representing more than 150 laboratories specialized in protein production and/or protein molecular biophysics, have implemented such guidelines in their respective laboratories. Over a one-year period, the network members evaluated the contribution these guidelines made toward obtaining more productive, robust and reproducible research by correlating the applied quality controls to given samples with the reliability and reproducibility of the scientific data obtained using these samples in follow-up experiments. The results indicate that QC guideline implementation facilitates the optimization of the protein purification process and improves the reliability of downstream experiments. It seems, therefore, that investing in protein QC might be advantageous to all the stakeholders in life sciences (researchers, editors, and funding agencies alike), because this practice improves data veracity and minimizes loss of valuable time and resources. In the light of these conclusions, the network members suggest that the implementation of these simple QC guidelines should become minimal reporting practice in the publication of data derived from the use of protein and peptide reagents.

PDZ Sample Quality Assessment by Biochemical and Biophysical Characterizations

PDZ domains are small globular domains involved in protein-protein interactions. They participate in a wide range of critical cellular processes. These domains, very abundant in the human proteome, are widely studied by high-throughput interactomics approaches and by biophysical and structural methods. However, the quality of the results is strongly related to the optimal folding and solubility of the domains. We provide here a detailed description of protocols for a strict quality assessment of the PDZ constructs. We describe appropriate experimental approaches that have been selected to overcome the small size of such domains to check the purity, identity, homogeneity, stability, and folding of samples.

From gene to harvest: insights into upstream process development for the GMP production of a monoclonal antibody in transgenic tobacco plants

The EU Sixth Framework Programme Integrated Project 'Pharma-Planta' developed an approved manufacturing process for recombinant plant-made pharmaceutical proteins (PMPs) using the human HIV-neutralizing monoclonal antibody 2G12 as a case study. In contrast to the well-established Chinese hamster ovary platform, which has been used for the production of therapeutic antibodies for nearly 30 years, only draft regulations were initially available covering the production of recombinant proteins in transgenic tobacco plants. Whereas recombinant proteins produced in animal cells are secreted into the culture medium during fermentation in bioreactors, intact plants grown under nonsterile conditions in a glasshouse environment provide various 'plant-specific' regulatory and technical challenges for the development of a process suitable for the acquisition of a manufacturing licence for clinical phase I trials. During upstream process development, several generic steps were addressed (e.g. plant transformation and screening, seed bank generation, genetic stability, host plant uniformity) as well as product-specific aspects (e.g. product quantity). This report summarizes the efforts undertaken to analyse and define the procedures for the GMP/GACP-compliant upstream production of 2G12 in transgenic tobacco plants from gene to harvest, including the design of expression constructs, plant transformation, the generation of production lines, master and working seed banks and the detailed investigation of cultivation and harvesting parameters and their impact on biomass, product yield and intra/interbatch variability. The resulting procedures were successfully translated into a prototypic manufacturing process that has been approved by the German competent authority.

Effects of Granulocyte-Macrophage Colony-Stimulating (GM-CSF) Factor on Corneal Epithelial Cells in Corneal Wound Healing Model

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic cytokine that activates granulocyte and macrophage cell lineages. It is also known to have an important function in wound healing. This study investigated the effect of GM-CSF in wound healing of human corneal epithelial cells (HCECs). We used human GM-CSF derived from rice cells (rice cell-derived recombinant human GM-CSF; rhGM-CSF). An in vitro migration assay was performed to investigate the migration rate of HCECs treated with various concentrations of rhGM-CSF (0.1, 1.0, and 10.0 μg/ml). MTT assay and flow cytometric analysis were used to evaluate the proliferative effect of rhGM-CSF. The protein level of p38MAPK was analyzed by western blotting. For in vivo analysis, 100 golden Syrian hamsters were divided into four groups, and their corneas were de-epithelialized with alcohol and a blade. The experimental groups were treated with 10, 20, or 50 μg/ml rhGM-CSF four times daily, and the control group was treated with phosphate-buffered saline. The corneal wound-healing rate was evaluated by fluorescein staining at the initial wounding and 12, 24, 36, and 48 hours after epithelial debridement. rhGM-CSF accelerated corneal epithelial wound healing both in vitro and in vivo. MTT assay and flow cytometric analysis revealed that rhGM-CSF treatment had no effects on HCEC proliferation. Western blot analysis demonstrated that the expression level of phosphorylated p38MAPK increased with rhGM-CSF treatment. These findings indicate that rhGM-CSF enhances corneal wound healing by accelerating cell migration.

Quality assessment and optimization of purified protein samples: why and how?

Purified protein quality control is the final and critical check-point of any protein production process. Unfortunately, it is too often overlooked and performed hastily, resulting in irreproducible and misleading observations in downstream applications. In this review, we aim at proposing a simple-to-follow workflow based on an ensemble of widely available physico-chemical technologies, to assess sequentially the essential properties of any protein sample: purity and integrity, homogeneity and activity. Approaches are then suggested to optimize the homogeneity, time-stability and storage conditions of purified protein preparations, as well as methods to rapidly evaluate their reproducibility and lot-to-lot consistency.

Effect of rice cell-derived human granulocyte-macrophage colony-stimulating factor on 5-fluorouracil-induced mucositis in hamsters

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important regulator of the maturation and function of cells in the granulocyte and macrophage lineages, and also plays a significant role in wound healing. In a previous study, we expressed human GM-CSF in rice cells (rice cell-derived human GM-CSF; rhGM-CSF). The purpose of the present study was to evaluate its effect on wound healing in oral mucositis. Oral mucositis was induced in Syrian hamster cheek pouches by 5-fluorouracil treatment and mechanical scratching. Ulcerated areas were treated from days 3 to 14 with an application of 200 µL saline, or of the same volume of a solution containing 0.04, 0.2, or 1 µg/mL rhGM-CSF. Treatment of hamsters with rhGM-CSF reduced the ulcerated areas of the oral mucosa, compared with the control. Early in the healing process, the mucositis tissue layer of the rhGM-CSF-treated group showed significantly decreased myeloperoxidase activity and increased numbers of proliferating cell nuclear antigen (PCNA)-positive cells. Treatment with rhGM-CSF also affected expression of inflammatory cytokines in the ulcerative mucosal tissue. These results demonstrate the efficacy of plant-produced rhGM-CSF in wound healing and have significant implications for the development of rhGM-CSF as a therapeutic agent for ulcerative oral mucositis.

Unconventional microbial systems for the cost-efficient production of high-quality protein therapeutics

Both conventional and innovative biomedical approaches require cost-effective protein drugs with high therapeutic potency, improved bioavailability, biocompatibility, stability and pharmacokinetics. The growing longevity of the human population, the increasing incidence and prevalence of age-related diseases and the better comprehension of genetic-linked disorders prompt to develop natural and engineered drugs addressed to fulfill emerging therapeutic demands. Conventional microbial systems have been for long time exploited to produce biotherapeutics, competing with animal cells due to easier operation and lower process costs. However, both biological platforms exhibit important drawbacks (mainly associated to intracellular retention of the product, lack of post-translational modifications and conformational stresses), that cannot be overcome through further strain optimization merely due to physiological constraints. The metabolic diversity among microorganisms offers a spectrum of unconventional hosts, that, being able to bypass some of these weaknesses, are under progressive incorporation into production pipelines. In this review we describe the main biological traits and potentials of emerging bacterial, yeast, fungal and microalgae systems, by comparing selected leading species with well established conventional organisms with a long run in protein drug production.