Rapid Transient Production of a Monoclonal Antibody Neutralizing the Porcine Epidemic Diarrhea Virus (PEDV) in Nicotiana benthamiana and Lactuca sativa

Functional Characterization of Pembrolizumab Produced in Nicotiana benthamiana Using a Rapid Transient Expression System

The striking innovation and clinical success of immune checkpoint inhibitors (ICIs) have undoubtedly contributed to a breakthrough in cancer immunotherapy. Generally, ICIs produced in mammalian cells requires high investment, production costs, and involves time consuming procedures. Recently, the plants are considered as an emerging protein production platform due to its cost-effectiveness and rapidity for the production of recombinant biopharmaceuticals. This study explored the potential of plant-based system to produce an anti-human PD-1 monoclonal antibody (mAb), Pembrolizumab, in Nicotiana benthamiana. The transient expression of this mAb in wild-type N. benthamiana accumulated up to 344.12 ± 98.23 μg/g fresh leaf weight after 4 days of agroinfiltration. The physicochemical and functional characteristics of plant-produced Pembrolizumab were compared to mammalian cell-produced commercial Pembrolizumab (Keytruda®). Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and western blot analysis results demonstrated that the plant-produced Pembrolizumab has the expected molecular weight and is comparable with the Keytruda®. Structural characterization also confirmed that both antibodies have no protein aggregation and similar secondary and tertiary structures. Furthermore, the plant-produced Pembrolizumab displayed no differences in its binding efficacy to PD-1 protein and inhibitory activity between programmed cell death 1 (PD-1) and programmed cell death ligand 1 (PD-L1) interaction with the Keytruda®. In vitro efficacy for T cell activation demonstrated that the plant-produced Pembrolizumab could induce IL-2 and IFN-γ production. Hence, this proof-of-concept study showed that the plant-production platform can be utilized for the rapid production of functional mAbs for immunotherapy.

Expression and Purification of a PEDV-Neutralizing Antibody and Its Functional Verification

Porcine epidemic diarrhea virus (PEDV) is a highly infectious and pathogenic virus causing high morbidity and mortality, especially in newborn piglets. There remain problems with contemporary PEDV vaccines, in part because of the rapid variation of PEDV, poor conferred immunity, and numerous side effects. The ability to produce PEDV-neutralizing antibodies suggests that we may be able to increase the success rate of PEDV prevention in piglets using these antibodies. In this study, we produced an anti-PEDV S protein monoclonal antibody (anti-PEDV mAb-2) that neutralized PEDV-CV777 (a G1 strain), PEDV-SDSX16 and PEDV-Aj1102 (two G2 strains). In vivo challenge experiments demonstrated that anti-PEDV mAb-2 inhibited the PEDV infection in piglets. We also produced three HEK293 cell lines that expressed anti-PEDV mAb-2. Overall, our study showed that anti-PEDV mAb-2 produced from hybridoma supernatants effectively inhibited PEDV infection in piglets, and the recombinant HEK293 cell lines expressed anti-PEDV mAb-2 genes.

RAP Tag and PMab-2 Antibody: A Tagging System for Detecting and Purifying Proteins in Plant Cells

An affinity tag system requires both high affinity and specificity. The RAP tag epitope DMVNPGLEDRIE, derived from rat podoplanin (PDPN), is specifically recognized by PMab-2 monoclonal antibodies in rats. Here, we demonstrated that high levels of PMab-2 can be produced in Nicotiana benthamiana and plant-derived PMab-2 possesses similar activity to CHO-derived PMab-2, and the RAP tag presents a useful tagging system for detecting and purifying proteins from plant cells. The heavy chain of PMab-2 fused with KDEL, an endoplasmic reticulum retention sequence, and the light chain of the antibody were introduced into N. benthamiana by agroinfiltration. The expression of PMab-2 peaked 4 days after agroinfiltration, and approximately 0.3 mg/g fresh weight of the antibody was accumulated. After purification, the plant-derived PMab-2 successfully recognized rat PDPN expressed in CHO-K1 cells and exhibited almost the same binding activity as CHO-derived PMab-2. The RAP-tagged proteins expressed in plant cells were specifically recognized by PMab-2. These results indicate that PMab-2 can accumulate at high levels in N. benthamiana and is easily purified and that the RAP tagging system presents a useful tool for detecting and purifying proteins of interest in plant cells.

Emergence of Novel Coronavirus 2019-nCoV: Need for Rapid Vaccine and Biologics Development

Novel Coronavirus (2019-nCoV) is an emerging pathogen that was first identified in Wuhan, China in late December 2019. This virus is responsible for the ongoing outbreak that causes severe respiratory illness and pneumonia-like infection in humans. Due to the increasing number of cases in China and outside China, the WHO declared coronavirus as a global health emergency. Nearly 35,000 cases were reported and at least 24 other countries or territories have reported coronavirus cases as early on as February. Inter-human transmission was reported in a few countries, including the United States. Neither an effective anti-viral nor a vaccine is currently available to treat this infection. As the virus is a newly emerging pathogen, many questions remain unanswered regarding the virus's reservoirs, pathogenesis, transmissibility, and much more is unknown. The collaborative efforts of researchers are needed to fill the knowledge gaps about this new virus, to develop the proper diagnostic tools, and effective treatment to combat this infection. Recent advancements in plant biotechnology proved that plants have the ability to produce vaccines or biopharmaceuticals rapidly in a short time. In this review, the outbreak of 2019-nCoV in China, the need for rapid vaccine development, and the potential of a plant system for biopharmaceutical development are discussed.

A Broad and Potent H1-Specific Human Monoclonal Antibody Produced in Plants Prevents Influenza Virus Infection and Transmission in Guinea Pigs

Although seasonal influenza vaccines block most predominant influenza types and subtypes, humans still remain vulnerable to waves of seasonal and new potential pandemic influenza viruses for which no immunity may exist because of viral antigenic drift and/or shift. Previously, we described a human monoclonal antibody (hMAb), KPF1, which was produced in human embryonic kidney 293T cells (KPF1-HEK) with broad and potent neutralizing activity against H1N1 influenza A viruses (IAV) in vitro, and prophylactic and therapeutic activities in vivo. In this study, we produced hMAb KPF1 in tobacco plants (KPF1-Antx) and demonstrated how the plant-produced KPF1-Antx hMAb possesses similar biological activity compared with the mammalian-produced KPF1-HEK hMAb. KPF1-Antx hMAb showed broad binding to recombinant HA proteins and H1N1 IAV, including A/California/04/2009 (pH1N1) in vitro, which was comparable to that observed with KPF1-HEK hMAb. Importantly, prophylactic administration of KPF1-Antx hMAb to guinea pigs prevented pH1N1 infection and transmission in both prophylactic and therapeutic experiments, substantiating its clinical potential to prevent and treat H1N1 infections. Collectively, this study demonstrated, for the first time, a plant-produced influenza hMAb with in vitro and in vivo activity against influenza virus. Because of the many advantages of plant-produced hMAbs, such as rapid batch production, low cost, and the absence of mammalian cell products, they represent an alternative strategy for the production of immunotherapeutics for the treatment of influenza viral infections, including emerging seasonal and/or pandemic strains.

Recombinant Human Dentin Matrix Protein 1 (hDMP1) Expressed in Nicotiana benthamiana Potentially Induces Osteogenic Differentiation

Inductive molecules are critical components for successful bone tissue engineering. Dentin matrix protein-1 (DMP1), a non-collagenous protein in the bone matrix, has been shown to play roles in osteogenic differentiation and phosphate homeostasis. This study aimed to produce recombinant human dentin matrix protein-1 (hDMP1) in Nicotiana benthamiana and investigated the ability of this plant-produced DMP1 to induce osteogenesis in human periodontal ligament stem cells (hPDLSCs). The hDMP1 gene was cloned into the geminiviral vector for transient expression in N. benthamiana. We found that hDMP1 was transiently expressed in N. benthamiana leaves and could be purified by ammonium sulphate precipitation followed by nickel affinity chromatography. The effects of hDMP1 on the induction of cell proliferation and osteogenic differentiation were investigated. The results indicated that plant-produced hDMP1 could induce the cell proliferation of hPDLSCs and increase the expression levels of osteogenic genes, including osterix (OSX), type I collagen (COL1), bone morphogenetic protein-2 (BMP2), and Wnt3a. Moreover, the plant-produced hDMP1 promoted calcium deposition in hPDLSCs as determined by alizarin red S staining. In conclusion, our results indicated that plant-produced hDMP1 could induce osteogenic differentiation in hPDLSCs and could potentially be used as a bone inducer in bone tissue engineering.

Structural and In Vitro Functional Analyses of Novel Plant-Produced Anti-Human PD1 Antibody

Immunotherapy has emerged as a promising and effective treatment for cancer. The frequently used immunotherapy agents are immune checkpoint inhibitors, such as antibodies specific to PD1, PD-L1, or CTLA-4. However, these drugs are highly expensive, and most people in the world cannot access the treatment. The development of recombinant protein production platforms that are cost-effective, scalable, and safe is needed. Plant platforms are attractive because of their low production cost, speed, scalability, lack of human and animal pathogens, and post-translational modifications that enable them to produce effective monoclonal antibodies. In this study, an anti-PD1 IgG4 monoclonal antibody (mAb) was transiently produced in Nicotiana benthamiana leaves. The plant-produced anti-PD1 mAb was compared to the commercial nivolumab produced in CHO cells. Our results showed that both antibodies have similar protein structures, and the N-glycans on the plant-produced antibody lacks plant-specific structures. The PD1 binding affinity of the plant-produced and commercial nivolumab, determined by two different techniques, that is, enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR), are also comparable. Plant-produced nivolumab binds to human PD1 protein with high affinity and specificity, blocks the PD-1/PD-L1 interaction, and enhances T cell function, comparable to commercial nivolumab. These results confirmed that plant-produced anti-PD1 antibody has the potential to be effective agent for cancer immunotherapy.