Synergistic promotion of transient transgene expression in CHO cells by PDI/XBP-1s co-transfection and mild hypothermia.

Transient gene expression system is an important tool for rapid production of recombinant proteins in Chinese hamster ovary (CHO) cells. However, their low productivity is the main hurdle to overcome. An effective approach through which to obtain high protein yield involves targeting transcriptional, post-transcriptional events (PTEs), and culture conditions. Here, we investigated the effects of protein disulfide isomerase (PDI) and spliced X-box binding protein 1 (XBP-1s) co-overexpression combined with mild hypothermia on the transient yields of recombinant proteins in CHO cells. The results showed that the gene of interest (GOI) and the PDI/XBP-1s helper vector at a co-transfection ratio of 10:1 could obviously increase transient expression level of recombinant protein in CHO cells. However, PDI/XBP-1s overexpression had no significance effect on the mRNA levels of the recombinant protein, suggesting that it targeted PTEs. Moreover, the increased production was due to the enhancing of cell specific productivity, not related to cell growth, viability, and cell cycle. In addition, combined PDI/XBP-1s co-overexpression and mild hypothermia could further improve Adalimumab expression, compared to the control/37 °C and PDI/XBP-1s/37 °C, the Adalimumab volume yield of PDI/XBP-1s/33 °C increased by 203% and 142%, respectively. Mild hypothermia resulted in 3.52- and 2.33-fold increase in the relative mRNA levels of PDI and XBP-1s, respectively. In conclusion, the combination of PDI/XBP-1s overexpression and culture temperature optimization can achieve higher transient expression of recombinant protein, which provides a synergetic strategy to improve transient production of recombinant protein in CHO cells.

Juvenile Idiopathic Arthritis With Associated Inflammatory Bowel Disease and CARD8 Mutation.

Juvenile idiopathic arthritis is a common chronic childhood disease, with a prevalence of ∼1 per 1000 children. Arthritis can also be a manifestation of other inflammatory conditions, such as inflammatory bowel disease (IBD). Studies suggest a genetic influence in IBD, including mutations in CARD8. CARD8 is a negative regulator of the NLRP3 inflammasome, and mutations in this gene are hypothesized to induce gastrointestinal inflammation. However, few studies have evaluated this association and most have included a limited number of patients. We present a case of a pediatric patient with IBD-associated arthritis and a CARD8 mutation. Our patient is a 7-year-old female who was initially evaluated by rheumatology for right leg pain and an intermittent rash. She had clinically active arthritis on exam and was started on methotrexate with only slight improvement. Additional workup revealed sacroiliitis by imaging, elevated inflammatory markers, no anemia, and a variant of unknown significance in CARD8. Adalimumab was recommended but before medication initiation, our patient's symptoms progressed to worsening joint pain, fatigue, fevers, nausea, vomiting, diarrhea, and hematochezia. Infectious testing was negative. Fecal calprotectin was >8000 µg/g. A colonoscopy revealed IBD most consistent with Crohn's disease. Adalimumab was ultimately added, and she has responded well to combination therapy. This case report highlights the association between CARD8 mutations and IBD, especially in the setting of IBD-associated arthritis.

Analysis of thermostability for seven Phe to Ala and six Pro to Gly mutants in the Fab constant region of adalimumab.

To identify amino acids that play important roles in the structural stability of Fab, seven phenylalanine residues in the Fab constant region of the therapeutic antibody adalimumab were subjected to alanine mutagenesis. Six Fab mutants, H:F130A, H:F154A, H:F174A, L:F118A, L:F139A and L:F209A, showed decreased thermostability compared with wild-type Fab. In contrast, the Tm for the L:F116A mutant was 1.7°C higher than that of wild-type Fab, indicating that the F116 residue was unfavorable for Fab thermostability. Six proline mutants, H:P131G, H:P155G, H:P175G, L:P119G, L:P120G and L:P141G, were also prepared to investigate the effect of proline residues adjacent to mutated phenylalanine residues. The thermostability of the H:P155G and L:P141G mutants in particular was significantly reduced, with decreases in Tm of 5.0 and 3.0°C, respectively, compared with wild-type Fab. The H:P155 and L:P141 residues have a cis conformation, whereas the other mutated proline residues have a trans conformation. H:P155 and L:P141 had stacking interactions with the H:F154 and L:Y140, respectively, at the interface between the variable and constant regions. It is suggested that the interactions of the aromatic ring with a cis-form proline at the interface between the variable and constant regions is important for stability of Fab.

Pharmacogenetic analysis of canonical versus noncanonical pathway of NF-kB in Crohn's disease patients under anti-tumor necrosis factor-α treatment.

OBJECTIVES: This study explores the potential of gene polymorphisms in the canonical and noncanonical NF-kB signaling pathway as a prediction biomarker of anti-tumor necrosis factor (TNF)α response in Crohn's patients. MATERIALS AND METHODS: A total of 109 Greek patients with Crohn's disease (CD) were recruited, and the genotype of TLR2 rs3804099, LTA rs909253, TLR4 rs5030728, and MAP3K14/NIK rs7222094 single nucleotide polymorphisms was investigated for association with response to anti-TNFα therapy. Patient's response to therapy was based on the Crohn's Disease Activity Index, depicting the maximum response within 24 months after initiation of treatment. RESULTS: Seventy-three patients (66.7%) were classified as responders while 36 as nonresponders (33.3%). Comparing allelic frequencies between responders and nonresponders, the presence of TLR2 rs3804099 T allele was associated with nonresponse (P = 0.003), even after stratification by anti-TNFα drugs (infliximab: P = 0.032, adalimumab: P = 0.026). No other association was identified for the rest of the polymorphisms under study. Haplotype analysis further enhanced the association of rs3804099 T allele with loss of response, even though the results were NS (P = 0.073). CONCLUSION: Our results suggest that polymorphisms in the canonical NF-kB pathway genes could potentially act as a predictive biomarker of anti-TNFα response in CD.

Effect of an intermolecular disulfide bond introduced into the first loop of CH1 domain of Adalimumab Fab on thermal stability and antigen-binding activity.

The introduction of intermolecular disulfide bonds by amino acid mutations is an effective method for stabilizing dimeric proteins. X-ray crystal structure of Fab of a therapeutic antibody, adalimumab, revealed the first loop of the CH1 domain to be partially unsolved at position 135-141. To find new sites for the introduction of intermolecular disulfide bonds in adalimumab Fab, Fab mutants targeting the unsolved region were predicted using molecular simulation software. Four Fab mutants, H:K137C-L:I117C, H:K137C-L:F209C, H:S138C-L:F116C and H:S140C-L:S114C, were expressed in the methylotrophic yeast Pichia pastoris. SDS-PAGE analysis of these mutants indicated that H:K137C-L:F209C, H:S138C-L:F116C and H:S140C-L:S114C mutants mostly formed intermolecular disulfide bonds, whereas some H:K137C-L:I117C mutants formed intermolecular disulfide bonds and some did not. Differential scanning calorimetry measurements showed increased thermal stability in all Fab mutants with engineered disulfide bonds. The bio-layer interferometry measurements, for binding of the antigen tumor necrotic factor α, indicated that Fab mutants had less antigen-binding activity than wild-type Fab. In particular, the KD value of H:K137C-L:F209C was ~17 times higher than that of wild-type Fab. Thus, we successfully introduced intermolecular disulfide bonds between the first loop region of the CH1 and CL domains and observed that it increases the thermostability of Fab and affects the antigen-binding activity.

A Stable CHO K1 Cell Line for Producing Recombinant Monoclonal Antibody Against TNF-α.

Monoclonal antibodies (mAbs) are one of the most significant molecules in protein therapeutics. They are employed in the field of immunology, oncology and organ transplant. They have been also been employed for alleviating several bacterial and viral infections. Moreover, they have revolutionized the area of targeted therapy and improved the quality of treatments, as compared to other cytotoxic drugs and therapies. mAbs bind to specific molecules on the antigen and exhibit specificity towards that molecule, i.e. epitope. Thus, mAbs have immense opportunity to be explored for personalized therapy. The introduction of targeted mAb-based therapeutics has promoted many important scientific achievements in rheumatology. This has warranted additional investigations for developing newer mAb producing clones, to supplement the limited industrial production of certain mAb therapeutics. In this investigation, an integrative approach comprising optimized expression, selection and expansion was adopted to develop a mammalian cell line expressing mAb against TNF-α.The resulting stable clone is anticipated to serve as an economic alternative to the industrial clones, especially for research purposes. The clone was constructed for development of biosimilar of the highly valued therapeutic antibody, Humira.

Construction of a full-length antibody phage display vector.

Antibody phage display technology plays an important role in the development of monoclonal antibodies, humanization, and affinity evolution of antibodies. Thus far, antibody phage display mainly focuses on the display of antibody variable region or antigen-binding fragments. In this study, we constructed a new phage display system that can display full-length IgG antibodies on M13 phage. The phage display vector contains open reading frames (ORFs) encoding full-length the heavy and light chains of the antibody. NcoI/XhoI restriction enzyme sites were used to clone the variable region of the heavy chain into the heavy chain ORF, and SalI/NotI sites were used to clone the light chain variable region. SnaBI and SbfI restriction enzyme sites were designed between the cloning sites of heavy and light chains, respectively, to increase the cloning efficiency. The full-length antibodies of nivolumab against programmed death factor 1, trastuzumab against human epidermal growth factor 2, diL2K against the cluster of differentiation 3 epsilon, and adalimumab against tumor necrosis factor- alpha were displayed on phage with the vector. Phage-displayed antibodies showed their original antigen-binding activity. An amber codon shifted the vector to express IgG in non-suppressed Escherichia coli. The heavy and light chains of the E. coli-expressed antibodies could be detected through western blotting, and the antigen-binding activity was confirmed using an enzyme-linked immunosorbent assay. Biopanning was carried out with a model phage display antibody library, and the results showed that the novel phage system could be used for antibody library construction and highly efficient antibody screening. The reported system is the first full-length antibody phage display system.

Glycosylation decreases aggregation and immunogenicity of adalimumab Fab secreted from Pichia pastoris.

Glycoengineering of therapeutic proteins has been applied to improve the clinical efficacy of several therapeutics. Here, we examined the effect of glycosylation on the properties of the Fab of the therapeutic antibody, adalimumab. An N-glycosylation site was introduced at position 178 of the H chain constant region of adalimumab Fab through site-directed mutagenesis (H:L178N Fab), and the H:L178N Fab was produced in Pichia pastoris. Expressed mutant Fab contained long and short glycan chains (L-glyco Fab and S-glyco Fab, respectively). Under the condition of aggregation of Fab upon pH shift-induced stress, both of L-glyco Fab and S-glyco Fab were less prone to aggregation, with L-glyco Fab suppressing aggregation more effectively than the S-glyco Fab. Moreover, the comparison of the antigenicity of glycosylated and wild-type Fabs in mice revealed that glycosylation resulted in the suppression of antigenicity. Analysis of the pharmacokinetic behaviour of the Fab, L-glyco Fab and S-glyco Fab indicated that the half-lives of glycosylated Fabs in the rats were shorter than that of wild-type Fab, with L-glyco Fab having a shorter half-life than S-glyco Fab. Thus, we demonstrated that the glycan chain influences Fab aggregation and immunogenicity, and glycosylation reduces the elimination half-life in vivo.

Characterization of the internal translation initiation region in monoclonal antibodies expressed in Escherichia coli.

Monoclonal antibodies (mAbs) represent an important platform for the development of biotherapeutic products. Most mAbs are produced in mammalian cells, but several mAbs are made in Escherichia coli, including therapeutic fragments. The NISTmAb is a well-characterized reference material made widely available to facilitate the development of both originator biologics and biosimilars. Here, when expressing NISTmAb from codon-optimized constructs in E. coli (eNISTmAb), a truncated variant of its heavy chain was observed. N-terminal protein sequencing and mutagenesis analyses indicated that the truncation resulted from an internal translation initiation from a GTG codon (encoding Val) within eNISTmAb. Using computational and biochemical approaches, we demonstrate that this translation initiates from a weak Shine-Dalgarno sequence and is facilitated by a putative ribosomal protein S1-binding site. We also observed similar internal initiation in the mAb adalimumab (the amino acid sequence of the drug Humira) when expressed in E. coli Of note, these internal initiation regions were likely an unintended result of the codon optimization for E. coli expression, and the amino acid pattern from which it is derived was identified as a Pro-Ser-X-X-X-Val motif. We discuss the implications of our findings for E. coli protein expression and codon optimization and outline possible strategies for reducing the likelihood of internal translation initiation and truncated product formation.

Study of the mechanism for increased protein expression via transcription potency reduction of the selection marker.

Stable transfection of mammalian cells using various expression cassettes for exogenous gene expression has been well established. The impact of critical factors in these cassettes, such as promoter and enhancer elements, on recombinant protein production in mammalian cells has been studied extensively to optimize the expression efficiency. However, few studies on the correlation between the strength of selection marker and the expression of gene of interest (GOI) have been reported. Here we investigated the correlation between the strength of a widely used selection marker, glutamine synthetase (GS) gene, and gene of interest in which the expression of GOI is driven by mouse cytomegalovirus (mCMV) major immediate early (MIE) promoter whereas the expression of GS is controlled by SV40E (Simian vacuolating virus 40E) promoter. We used a green fluorescent protein and the adalimumab antibody (heavy and light chain) as two distinct examples for the gene of interest. We then decreased the expression of GS gene by engineering a specific region of its SV40E promoter in these expression cassettes. By comparing the expression of GS and GOI at transcription and translation level before and after the SV40E promoter was weakened, we found that lower GS expression due to weaker SV40E transcription correlated well with the higher expression of recombinant proteins, mainly by increasing the copy number of GS and GOI integration into host cell genome.

The transient production of anti-TNF-α antibody Adalimumab and a comparison of its characterization to the biosimilar Cinorra.

Recombinant antibodies have emerged over the last few decades as the fastest growing class of therapeutic proteins for autoimmune diseases. Post-translation modifications of antibodies produced by human cell lines are highly consistent with those existing in natural human proteins and this is a major advantage of utilizing these cell lines. Cinorra is a biosimilar form of the antibody Adalimumab, which is an antagonist of TNF-α used for the treatment of autoimmune diseases. Adalimumab and Cinorra were produced by stable expression from CHO cells. The aim of this study was to select HEK cells as a host for producing Adalimumab to reveal whether the antibody produced by this human-derived cell line has similar characterization to Cinorra. Adalimumab was transiently produced in HEK-293T cells, characterized and analyzed for its properties. Circular dichroism spectroscopy confirmed a strong structural similarity of the expressed antibody with Cinorra. Likewise its binding activity and kinetic affinity to TNF-α (EC50 = 416.5 ng/ml, KD = 3.89 E-10 M,) were highly similar to that of Cinorra (EC50 = 421.2 ng/ml and KD = 3.34 E-10 M,). Additionally there was near identical neutralization of TNF-α-mediated cellular cytotoxicity (IC50 of the expressed = 4.93 nM; IC50 of Cinorra = 4.5 nM). Results indicate that Adalimumab produced by HEK-293T cells possesses a similarly efficient function and biological activity to Cinorra. Consequently, human-derived host cells with human post-translational modifications might potentially provide a basis for the development of Adalimumab with pharmaceutical properties for research and therapeutic use.

Introduction of a glycosylation site in the constant region decreases the aggregation of adalimumab Fab.

The production of therapeutic monoclonal antibodies is costly; therefore, antigen-binding fragments (Fabs) can be used instead. However, their tendency toward aggregation can reduce the half-life in the plasma and the therapeutic effectiveness. To examine the effect of glycosylation on the properties of the Fab of a therapeutic antibody, an N-glycosylation site was introduced at position 178 of the H-chain constant region of adalimumab Fab through site-directed mutagenesis of L178 N (H:L178 N Fab), and then H:L178 N Fab was expressed in Pichia pastoris. SDS-PAGE analysis with treatment of N-glycosidase F or periodic acid-Schiff reagent showed that H:L178 N Fab contained a relatively low glycan level. Moreover, the H:L178 N mutation did not decrease the binding activity and thermal stability of Fab, and H:L178 N Fab was more resistant to protease digestion than wild-type Fab. The aggregation of Fab induced by pH-shift stress was measured by monitoring the optical density at 350 nm. Although the wild-type Fab showed a large increase in optical density with an increase of protein concentration, no such increase of turbidity during aggregation was found in H:L178 N Fab. These results demonstrated that glycosylation at position 178 of the H-chain constant region of adalimumab Fab can prevent protein aggregation, and therefore serve as a potentially effective platform for drug development.

A new CHO (Chinese hamster ovary)-derived cell line expressing anti-TNFα monoclonal antibody with biosimilar potential.

Tumor necrosis factor alpha (TNFα) is a pro-inflammatory cytokine that mediates the homeostasis of immune responses; its exacerbated production is associated with the pathogenesis of autoimmune and chronic inflammatory diseases. Anti-TNFα drugs have revolutionized the treatment of inflammatory conditions such as rheumatoid arthritis and Crohn's disease. Currently, a worldwide race is on stage for the production of biosimilars moved by patent expiration of monoclonal antibodies (mAbs), such as anti-TNFα adalimumab. Our goal was to develop the first stage of an adalimumab biosimilar candidate with potential for national production, through the generation of a productive and stable cell line and assess its functionality. The robotic system ClonePix was used for screening and isolation of colonies from transfected CHO-S stable pools plated in semisolid medium. Selected clones were expanded based on growth and productivity. Purified mAbs from different clones were tested for binding and functional activity. The binding affinity of the denominated adabut clones to TNFα and FcRγ did not differ statistically when compared to reference adalimumab. One functional activity assay demonstrated the antibody neutralization capacity of the cytotoxicity induced by TNFα in L929 murine fibroblasts. A second assay confirmed adabut as an antagonist of the TNFα activity by the inhibition of the cell adhesion molecule expression in HUVEC cultures. The binding and functional activity analyses performed with selected adabut clones in comparison to reference adalimumab represent an important status of "non-inferiority," part of the process required for a biosimilar development. We generated and selected high-quality adabut clones which mAbs may be further developed as the first in-house made Brazilian biosimilar, demonstrating a success case for our incipient biotechnology industry, or also modified as biobetters, thus representing an innovative strategy for the patients' welfare.

Stable Expression of Adalimumab in Nicotiana tabacum.

Production of monoclonal antibodies and pharmaceutical proteins in transgenic plants has been the focus of many research efforts for close to 30 years. Use of plants as bioreactors reduces large-scale production costs and minimizes risk for human pathogens contamination. Stable nuclear transformation of the plant genome offers a clear advantage in agricultural protein production platforms, limited only by the number of hectares that can be cultivated. We report here, for the first time, successful and stable expression of adalimumab in transgenic Nicotiana tabacum plants. The plant-derived adalimumab proved fully active and was shown to rescue L929 cells from the in vitro lethal effect of rhTNFα just as effectively as commercially available CHO-derived adalimumab (Humira). These results indicate that agricultural biopharming is an efficient alternative to mammalian cell-based expression platforms for the large-scale production of recombinant antibodies.

Molecular mechanisms of action of anti-TNF-α agents - Comparison among therapeutic TNF-α antagonists.

Tumor necrosis factor (TNF)-α is a potent pro-inflammatory and pathological cytokines in inflammatory diseases such as rheumatoid arthritis and inflammatory bowel diseases. Anti-TNF-α therapy has been established as an efficacious therapeutic strategy in these diseases. In clinical settings, three monoclonal anti-TNF-α full IgG1 antibodies infliximab, adalimumab, and golimumab, PEGylated Fab' fragment of anti-TNF-α antibody certolizumab pegol, extracellular domain of TNF receptor 2/IgG1-Fc fusion protein etanercept, are almost equally effective for rheumatoid arthritis. Although monoclonal full IgG1 antibodies are able to induce clinical and endoscopic remission in inflammatory bowel diseases, certolizumab pegol without Fc portion has been shown to be less effective for inflammatory bowel diseases compared to full IgG1 antibodies. In addition, there are no evidences that etanercept leads clinical remission in inflammatory bowel diseases. Besides the common effect of anti-TNF-α agents on neutralization of soluble TNF-α, each anti-TNF-α agent has its own distinctive pharmacological properties which cause the difference in clinical efficacies. Here we focus on the distinctions of action of anti-TNF-α agents especially in following points; (1) blocking ability against ligands, transmembrane TNF-α and lymphotoxin, (2) effects toward transmembrane TNF-α-expressing cells, (3) effects toward Fcγ receptor-expressing cells, (4) degradation and distribution in inflamed tissue. Accumulating evidence will give us the idea how to modify anti-TNF-α agents to enhance the clinical efficacy in inflammatory diseases.

A novel engineered interchain disulfide bond in the constant region enhances the thermostability of adalimumab Fab.

We constructed a system for expressing the Fab of the therapeutic human monoclonal antibody adalimumab at a yield of 20 mg/L in the methylotrophic yeast Pichia pastoris. To examine the contribution of interchain disulfide bonds to conformational stability, we prepared adalimumab Fab from which the interchain disulfide bond at the C-terminal region at both the CH1 and CL domains was deleted by substitution of Cys with Ala (FabΔSS). DSC measurements showed that the Tm values of FabΔSS were approximately 5 °C lower than those of wild-type Fab, suggesting that the interchain disulfide bond contributes to conformational thermostability. Using computer simulations, we designed a novel interchain disulfide bond outside the C-terminal region to increase the stability of FabΔSS. The resulting Fab (mutSS FabΔSS) had the mutations H:V177C and L:Q160C in FabΔSS, confirming the formation of the disulfide bond between CH1 and CL. The thermostability of mutSS FabΔSS was approximately 5 °C higher than that of FabΔSS. Therefore, the introduction of the designed interchain disulfide bond enhanced the thermostability of FabΔSS and mitigated the destabilization caused by partial reduction of the interchain disulfide bond at the C-terminal region, which occurs in site-specific modification such as PEGylation.

Label-free live cell imaging by Confocal Raman Microscopy identifies CHO host and producer cell lines.

As a possible viable and non-invasive method to identify high producing cells, Confocal Raman Microscopy was shown to be able to differentiate CHO host cell lines and derivative production clones. Cluster analysis of spectra and their derivatives was able to differentiate between different producer cell lines and a host, and also distinguished between an intracellular region of high lipid and protein content that in structure resembles the Endoplasmic Reticulum. This ability to identify the ER may be a major contributor to the identification of high producers. PCA enabled the discrimination even of host cell lines and their subclones with inherently higher production capacity. The method is thus a promising option that may contribute to early, non-invasive identification of high potential candidates during cell line development and possibly could also be used for proof of identity of established production clones.

Rheumatoid arthritis response to treatment across IgG1 allotype - anti-TNF incompatibility: a case-only study.

INTRODUCTION: We have hypothesized that incompatibility between the G1m genotype of the patient and the G1m1 and G1m17 allotypes carried by infliximab (INX) and adalimumab (ADM) could decrease the efficacy of these anti-tumor necrosis factor (anti-TNF) antibodies in the treatment of rheumatoid arthritis (RA). METHODS: The G1m genotypes were analyzed in three collections of patients with RA totaling 1037 subjects. The first, used for discovery, comprised 215 Spanish patients. The second and third were successively used for replication. They included 429 British and Greek patients and 393 Spanish and British patients, respectively. Two outcomes were considered: change in the Disease Activity Score in 28 joint (ΔDAS28) and the European League Against Rheumatism (EULAR) response criteria. RESULTS: An association between less response to INX and incompatibility of the G1m1,17 allotype was found in the discovery collection at 6 months of treatment (P = 0.03). This association was confirmed in the replications (P = 0.02 and 0.08, respectively) leading to a global association (P = 0.001) that involved a mean difference in ΔDAS28 of 0.4 units between compatible and incompatible patients (2.3 ± 1.5 in compatible patients vs. 1.9 ± 1.5 in incompatible patients) and an increase in responders and decrease in non-responders according to the EULAR criteria (P = 0.03). A similar association was suggested for patients treated with ADM in the discovery collection, but it was not supported by replication. CONCLUSIONS: Our results suggest that G1m1,17 allotypes are associated with response to INX and could aid improved therapeutic targeting in RA.

NMR-based structural validation of therapeutic antibody produced in Nicotiana benthamiana.

KEY MESSAGE: We successfully developed a method for metabolic isotope labeling of recombinant proteins produced in transgenic tobacco. This enabled assessment of structural integrity of plant-derived therapeutic antibodies by NMR analysis. A variety of expression vehicles have been developed for the production of promising biologics, including plants, fungi, bacteria, insects, and mammals. Glycoprotein biologics often experience altered folding and post-translational modifications that are typified by variant glycosylation patterns. These differences can dramatically affect their efficacy, as exemplified by therapeutic antibodies. However, it is generally difficult to validate the structural integrity of biologics produced using different expression vehicles. To address this issue, we have developed and applied a stable-isotope-assisted nuclear magnetic resonance (NMR) spectroscopy method for the conformational characterization of recombinant antibodies produced in plants. Nicotiana benthamiana used as a vehicle for the production of recombinant immunoglobulin G (IgG) was grown in a (15)N-enriched plant growth medium. The Fc fragment derived from the (15)N-labeled antibody thus prepared was subjected to heteronuclear two-dimensional (2D) NMR measurements. This approach enabled assessment of the structural integrity of the plant-derived therapeutic antibodies by comparing their NMR spectral properties with those of an authentic IgG-Fc derived from mammalian cells.