Development of transgenic rice seed accumulating a major Japanese cedar pollen allergen (Cry j 1) structurally disrupted for oral immunotherapy

Soybean seed protein storage vacuoles for expression of recombinant molecules

Soybean is one of the most important protein sources for human consumption and livestock feed. Soy production also allows the biosynthesis of edible oils, biodiesel, and biofertilizers. With the advent of modern agricultural biotechnology, soybean plants have also converted into bioreactors of therapeutic proteins and industrial enzymes. Soybean's characteristics, such as protein storage vacuoles (PSVs) and other unique organelles, allow the plant to be exploited as an accumulator of heterologous proteins under high stability and scalability conditions, and that maintains its basic functions. This review reports the main aspects of heterologous protein accumulation in soybean PSVs.

Functional rice with tandemly repeated Cbl-b ubiquitin ligase inhibitory pentapeptide prevents denervation-induced muscle atrophy in vivo

Ubiquitin ligase Casitas B-lineage lymphoma-b (Cbl-b) play a critical role in nonloading-mediated skeletal muscle atrophy: Cbl-b ubiquitinates insulin receptor substrate-1 (IRS-1), leading to its degradation and a resulting loss in muscle mass. We reported that intramuscular injection of a pentapeptide, DGpYMP, which acts as a mimic of the phosphorylation site in IRS-1, significantly inhibited denervation-induced skeletal muscle loss. In order to explore the possibility of the prevention of muscle atrophy by diet therapy, we examined the effects of oral administration of transgenic rice containing Cblin (Cbl-b inhibitor) peptide (DGYMP) on denervation-induced muscle mass loss in frogs. We generated transgenic rice seeds in which 15 repeats of Cblin peptides with a WQ spacer were inserted into the rice storage protein glutelin. A diet of the transgenic rice seeds had significant inhibitory effects on denervation-induced atrophy of the leg skeletal muscles in frogs, compared with those receiving a diet of wild-type rice.

Seeds as Economical Production Platform for Recombinant Proteins

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The cost-effective production of high-quality and biologically active recombinant molecules especially proteins is extremely desirable. Seed-based recombinant protein production platforms are considered as superior choice owing to lack of human/animal pathogenic organisms, lack of cold chain requirements for transportation and long-term storage, easy scalability and development of edible biopharmaceuticals in plants with objective to be used in purified or partially processed form is desirable. This review article summarizes the exceptional features of seed-based biopharming and highlights the needs of exploiting it for commercial purposes. Plant seeds offer a perfect production platform for high-value molecules of industrial as well as therapeutic nature owing to lower water contents, high protein storage capacity, weak protease activity and long-term storage ability at ambient temperature. Exploiting extraordinarily high protein accumulation potential, vaccine antigens, antibodies and other therapeutic proteins can be stored without effecting their stability and functionality up to years in seeds. Moreover, ability of direct oral consumption and post-harvest stabilizing effect of seeds offer unique feature of oral delivery of pharmaceutical proteins and vaccine antigens for immunization and disease treatment through mucosal as well as oral route.

Development of Rice-Seed-Based Oral Allergy Vaccines Containing Hypoallergenic Japanese Cedar Pollen Allergen Derivatives for Immunotherapy

Allergen-specific immunotherapy is the only available curative treatment for IgE-mediated allergen diseases. A safe hypoallergenic allergen derivative with high efficiency is required as a tolerogen to induce immune tolerance to the causitive allergens. In this study, to generate a rice-based oral allergy vaccine for Japanese cedar (JC) pollinosis, the tertiary structures of major JC pollen allergens, Cry j 1 and Cry j 2, were more completely destructed by shuffling than the previous ones without losing immunogenicity and then were specifically expressed in the endosperm of transgenic rice seed. They accumulated at high levels and were deposited in endoplasmic reticulum (ER) and ER-derived protein bodies. The low allergenicity of these deconstructed Cry j 1 and Cry j 2 allergens was evaluated by examining their binding activities to the specific IgE antibody and by the basophil degranulation test.

Next generation immunotherapy for tree pollen allergies

Tree pollen induced allergies are one of the major medical and public health burdens in the industrialized world. Allergen-Specific Immunotherapy (AIT) through subcutaneous injection or sublingual delivery is the only approved therapy with curative potential to pollen induced allergies. AIT often is associated with severe side effects and requires long-term treatment. Safer, more effective and convenient allergen specific immunotherapies remain an unmet need. In this review article, we discuss the current progress in applying protein and peptide-based approaches and DNA vaccines to the clinical challenges posed by tree pollen allergies through the lens of preclinical animal models and clinical trials, with an emphasis on the birch and Japanese red cedar pollen induced allergies.

Compensatory rebalancing of rice prolamins by production of recombinant prolamin/bioactive peptide fusion proteins within ER-derived protein bodies

Bioactive peptide was produced by fusion to rice prolamins in transgenic rice seeds. Their accumulation levels were affected by their deposition sites and by compensatory rebalancing between prolamins within PB-Is. Peptide immunotherapy using analogue peptide ligands (APLs) is one of promising treatments against autoimmune diseases. Use of seed storage protein as a fusion carrier is reasonable strategy for production of such small size bioactive peptides. In this study, to examine the efficacy of various rice prolamins deposited in ER-derived protein bodies (PB-Is), the APL12 from the Glucose-6-phosphate isomerase (GPI325-339) was expressed by fusion to four types of representative prolamins under the control of the individual native promoters. When the 14 and 16 kDa Cys-rich prolamins, which were localized in middle layer of PB-Is, were used for production of the APL12, they highly accumulated in transgenic rice seeds (~ 200 µg/grain). By contrast, fusion to the 10 and 13 kDa prolamins, which were localized in the core and outermost layer of PB-Is, resulted in lower levels of accumulation (~ 40 µg/grain). These results suggest that accumulation levels were highly affected by their deposition sites. Next, when different prolamin/APL12 fusion proteins were co-expressed to increase accumulation levels, they could not be increased so much as their expected additive levels. High accumulation of one type prolamin/APL12 led to reduction of other type(s) prolamin/APL12 to maintain the limited amounts of prolamins that can be deposited in PB-Is. Moreover, suppression of endogenous seed proteins by RNA interference also did not significantly enhance the accumulation levels of prolamin/APL12. These findings suggest that there may be compensatory rebalancing mechanism that controls the accumulation levels of prolamins deposited within PB-Is.

Cellular Localization of Wheat High Molecular Weight Glutenin Subunits in Transgenic Rice Grain

Rice (Oryza sativa L.) is a primary global food cereal. However, when compared to wheat, rice has poor food processing qualities. Dough that is made from rice flour has low viscoelasticity because rice seed lacks storage proteins that are comparable to gluten protein from wheat. Thus, current research efforts aim to improve rice flour processing qualities through the transgenic expression of viscoelastic proteins in rice seeds. In this study, we characterized the transgenic expression of wheat glutenin subunits in rice seeds. The two genes 1Dx5_KK and 1Dy10_JK, which both encode wheat high-molecular-weight glutenin subunits that confer high dough elasticity, were cloned from Korean wheat cultivars KeumKang and JoKyung, respectively. These genes were inserted into binary vectors under the control of the rice endosperm-specific Glu-B1 promoter and were expressed in the high-amylose Korean rice cultivar Koami (Oryza sativa L.). Individual expression of both glutenin subunits was confirmed by SDS-PAGE and immunoblot analyses performed using T₃ generation of transgenic rice seeds. The subcellular localization of 1Dx5_KK and 1Dy10_JK in the rice seed endosperm was confirmed by immunofluorescence analysis, indicating that the wheat glutenin subunits accumulate in protein body-II and novel protein body types in the rice seed. These results contribute to our understanding of engineered seed storage proteins in rice.

An overview on the strategies to exploit rice endosperm as production platform for biopharmaceuticals

Cereal seed has been utilized as production platform for high-value biopharmaceutical proteins. Especially, protein bodies (PBs) in seeds are not only natural specialized storage organs of seed storage proteins (SSPs), but also suitable intracellular deposition compartment for recombinant proteins. When various recombinant proteins were produced as secretory proteins by attaching N terminal ER signal peptide and C terminal KDEL endoplasmic reticulum (ER) retention signal or as fusion proteins with SSPs, high amounts of recombinant proteins can be predominantly accumulated in the PBs. Recombinant proteins bioencapsulated in PBs exhibit high resistance to digestive enzymes in gastrointestinal tract than other intracellular compartments and are highly stable at ambient temperature, thus allowing oral administration of PBs containing recombinant proteins as oral drugs or functional nutrients in cost-effective minimum processed formulation. In this review, we would like to address key factors determining accumulation levels of recombinant proteins in PBs. Understanding of bottle neck parts and improvement of specific deposition to PBs result in much higher levels of production of high quality recombinant proteins.

Deposition mode of transforming growth factor-β expressed in transgenic rice seed

Mouse TGF-β highly accumulated by expressing as a secretory homodimeric protein in transgenic rice endosperm. It was tightly deposited in ER-derived PBs by interaction with cysteine-rich prolamins. TGF-β is one of the key players involved in the induction and maintenance of mucosal immune tolerance to dietary proteins through the induction of regulatory T cells. In order to utilize rice-based TGF-β as a tool to promote oral immune tolerance induction, high production of TGF-β is essentially required. When the codon-optimized mTGF-β was expressed as a secretory protein by ligating an N-terminal signal peptide and C-terminal KDEL ER retention signal under the control of the endosperm-specific rice storage protein glutelin GluB-1 promoter, accumulation level was low in stable transgenic rice seeds. Then, to increase the accumulation level of mTGF-β, it was expressed as fusion proteins by inserting into the C terminus of acidic subunit of glutelin GluA and the variable region of 26 kDa globulin. When fused with the glutelin, it could accumulate well as visible bands by CBB staining gel, but not for the 26 kDa globulin. Unexpectedly, expression of homodimeric mTGF-β linked by a 6×Gly1×Ser linker as secretory protein resulted in higher level of accumulation. This expression level was further enhanced by reduction of some endogenous prolamins by RNA interference. The monomeric and dimeric mTGF-βs were deposited in ER-derived PBs containing prolamins. When highly produced in rice seed, it is notable that most of ER-derived PBs were distorted and granulated. Step-wise extraction of storage proteins from rice seeds suggested that the mTGF-β strongly interacted with cysteine-rich prolamins via disulfide bonds. This result was also supported by the finding that reducing agent was absolutely required for mTGF-β extraction.

Concentrated protein body product derived from rice endosperm as an oral tolerogen for allergen-specific immunotherapy--a new mucosal vaccine formulation against Japanese cedar pollen allergy

The endoplasmic reticulum-derived type-I protein body (PB-I) from rice endosperm cells is an ideal candidate formulation for the oral delivery of bioencapsulated peptides as tolerogens for allergen-specific immunotherapy. In the present study, PBs containing the deconstructed Japanese cedar pollen allergens Cryptomeria japonica 1 (Cry j 1) and Cry j 2 were concentrated by treatment with thermostable α-amylase at 90°C to remove the starch from milled rice powder, which resulted in a 12.5-fold reduction of dry weight compared to the starting material. The modified Cry j 1 and Cry j 2 antigens in this concentrated PB product were more resistant to enzymatic digestion than those in the milled seed powder despite the absence of intact cell wall and starch, and remained stable for at least 10 months at room temperature without detectable loss or degradation. The high resistance of these allergens could be attributed to changes in protein physicochemical properties induced by the high temperature concentration process, as suggested by the decreased solubility of the antigens and seed proteins in PBs in step-wise-extraction experiments. Confocal microscopy showed that the morphology of antigen-containing PB-Is was preserved in the concentrated PB product. The concentrated PB product induced specific immune tolerance against Cry j 1 and Cry j 2 in mice when orally administered, supporting its potential use as a novel oral tolerogen formulation.

Novel transgenic rice-based vaccines

Oral vaccination can induce both systemic and mucosal antigen-specific immune responses. To control rampant mucosal infectious diseases, the development of new effective oral vaccines is needed. Plant-based vaccines are new candidates for oral vaccines, and have some advantages over the traditional vaccines in cost, safety, and scalability. Rice seeds are attractive for vaccine production because of their stability and resistance to digestion in the stomach. The efficacy of some rice-based vaccines for infectious, autoimmune, and other diseases has been already demonstrated in animal models. We reported the efficacy in mice, safety, and stability of a rice-based cholera toxin B subunit vaccine called MucoRice-CTB. To advance MucoRice-CTB for use in humans, we also examined its efficacy and safety in primates. The potential of transgenic rice production as a new mucosal vaccine delivery system is reviewed from the perspective of future development of effective oral vaccines.

Transgenic rice endosperm as a bioreactor for molecular pharming

Plants provide a promising expression platform for producing recombinant proteins with several advantages in terms of high expression level, lower production cost, scalability, and safety and environment-friendly. Molecular pharming has been recognized as an emerging industry with strategic importance that could play an important role in economic development and healthcare in China. Here, this review represents the significant advances using transgenic rice endosperm as bioreactor to produce various therapeutic recombinant proteins in transgenic rice endosperm and large-scale production of OsrHSA, and discusses the challenges to develop molecular pharming as an emerging industry with strategic importance in China.

The trafficking pathway of a wheat storage protein in transgenic rice endosperm

BACKGROUND AND AIMS

The trafficking of proteins in the endoplasmic reticulum (ER) of plant cells is a topic of considerable interest since this organelle serves as an entry point for proteins destined for other organelles, as well as for the ER itself. In the current work, transgenic rice was used to study the pattern and pathway of deposition of the wheat high molecular weight (HMW) glutenin sub-unit (GS) 1Dx5 within the rice endosperm using specific antibodies to determine whether it is deposited in the same or different protein bodies from the rice storage proteins, and whether it is located in the same or separate phases within these.

METHODS

The protein distribution and the expression pattern of HMW sub-unit 1Dx5 in transgenic rice endosperm at different stages of development were determined using light and electron microscopy after labelling with antibodies.

KEY RESULTS

The use of HMW-GS-specific antibodies showed that sub-unit 1Dx5 was expressed mainly in the sub-aleurone cells of the endosperm and that it was deposited in both types of protein body present in the rice endosperm: derived from the ER and containing prolamins, and derived from the vacuole and containing glutelins. In addition, new types of protein bodies were also formed within the endosperm cells.

CONCLUSIONS

The results suggest that the HMW 1Dx5 protein could be trafficked by either the ER or vacuolar pathway, possibly depending on the stage of development, and that its accumulation in the rice endosperm could compromise the structural integrity of protein bodies and their segregation into two distinct populations in the mature endosperm.

Engineering complex metabolic pathways in plants

Metabolic engineering can be used to modulate endogenous metabolic pathways in plants or introduce new metabolic capabilities in order to increase the production of a desirable compound or reduce the accumulation of an undesirable one. In practice, there are several major challenges that need to be overcome, such as gaining enough knowledge about the endogenous pathways to understand the best intervention points, identifying and sourcing the most suitable metabolic genes, expressing those genes in such a way as to produce a functional enzyme in a heterologous background, and, finally, achieving the accumulation of target compounds without harming the host plant. This article discusses the strategies that have been developed to engineer complex metabolic pathways in plants, focusing on recent technological developments that allow the most significant bottlenecks to be overcome.

Efficient recovery of recombinant proteins from cereal endosperm is affected by interaction with endogenous storage proteins

Cereal seeds are versatile platforms for the production of recombinant proteins because they provide a stable environment for protein accumulation. Endogenous seed storage proteins, however, include several prolamin-type polypeptides that aggregate and crosslink via intermolecular disulfide bridges, which could potentially interact with multimeric recombinant proteins such as antibodies, which assemble in the same manner. We investigated this possibility by sequentially extracting a human antibody expressed in maize endosperm, followed by precipitation in vitro with zein. We provide evidence that a significant proportion of the antibody pool interacts with zein and therefore cannot be extracted using non-reducing buffers. Immunolocalization experiments demonstrated that antibodies targeted for secretion were instead retained within zein bodies because of such covalent interactions. Our findings suggest that the production of soluble recombinant antibodies in maize could be enhanced by eliminating or minimizing interactions with endogenous storage proteins.

The use of rice seeds to produce human pharmaceuticals for oral therapy

Rice (Oryza sativa L.) is the major staple food consumed by half of the world's population. Rice seeds have gained recent attention as bioreactors for the production of human pharmaceuticals such as therapeutic proteins or peptides. Rice seed production platforms have many advantages over animal cell or microbe systems in terms of cost-effectiveness, scalability, safety, product stability and productivity. Rice seed-based human pharmaceuticals are expected to become innovative therapies as edible drugs. Therapeutic proteins can be sequestered within natural cellular compartments in rice seeds and protected from harsh gastrointestinal environments. This review presents the state-of-the-art on the construction of gene cassettes for accumulation of pharmaceutical proteins or peptides in rice seeds, the generation of transgenic rice plants, and challenges involved in the use of rice seeds to produce human pharmaceuticals.

Transgenic rice seeds accumulating recombinant hypoallergenic birch pollen allergen Bet v 1 generate giant protein bodies

A versatile hypoallergenic allergen derivative against multiple allergens is an ideal tolerogen for allergen-specific immunotherapy. Such a tolerogen should exhibit high efficacy, without side effects, when administered at high doses and should be applicable to several allergens. Tree pollen chimera 7 (TPC7), a hypoallergenic Bet v 1 tolerogen against birch pollen allergy, was previously selected by DNA shuffling of 14 types of Fagales tree pollen allergens. In this study, transgenic rice seed accumulating TPC7 was generated as an oral vaccine against birch pollen allergy by expressing this protein as a secretory protein using the N-terminal signal peptide and the C-terminal KDEL tag under the control of an endosperm-specific glutelin promoter. The highest level of TPC7 accumulation was approximately 207 µg grain(-1). Recombinant TPC7 is a glycoprotein with high mannose-type N-glycan, but without β1,2-xylose or α1,3-fucose, suggesting that TPC7 is retained in the endoplasmic reticulum (ER). TPC7 is deposited as a novel, giant spherical ER-derived protein body, >20 µm in diameter, which is referred to as the TPC7 body. Removal of the KDEL retention signal or mutation of a cysteine residue resulted in an alteration of TPC7 body morphology, and deletion of the signal peptide prevented the accumulation of TPC7 in rice seeds. Therefore, the novel TPC7 bodies may have formed aggregates within the ER lumen, primarily due to the intrinsic physicochemical properties of the protein.

Production of a chimeric allergen derived from the major allergen group 1 of house dust mite species in Nicotiana benthamiana

Plants are widely accepted as a general platform for the large-scale production of recombinant proteins, which has been demonstrated by the successful expression of various exogenous proteins. Using plants as a bioreactor for mass production of target proteins for vaccines is thought to show the most potential. This study explores whether a chimeric allergen R8, derived from the major allergen group 1 of house dust mites species (Dermatophagoides farinae and Dermatophagoides pteronyssinus), is expressed in tobacco. The highly efficient and useful Tobacco mosaic virus RNA-based overexpression (TRBO) vector was used to investigate expression of the R8 molecule in tobacco by agroinfection. Presence of R8 was detected using SDS-PAGE and Western blotting. Purified allergens were characterized using IgE-binding activity assay and allergen-specific immunotherapy (ASIT) in murine asthmatic models. The recombinant R8 was successfully expressed in tobacco leaves. The pro-peptide was observed in the herbaceous leaf extracts. This protein exhibits properties similar to the parental allergen ProDer f 1 expressed in Escherichia coli or tobacco with respect to IgE immunoreactivity. R8 also rectifies imbalance of TH1/TH2 cells. An herbaceous plant expression system model allows mass production of R8, which might be used in the future for diagnosis of asthma or production of a candidate vaccine for allergen-specific immunotherapy of asthma.

ER stress response induced by the production of human IL-7 in rice endosperm cells

Rice seed has been used as a production platform for high value recombinant proteins. When mature human interleukin 7 (hIL-7) was expressed as a secretory protein in rice endosperm by ligating the N terminal glutelin signal peptide and the C terminal KDEL endoplasmic reticulum (ER) retention signal to the hIL-7 cytokine to improve production yield, this protein accumulated at levels visible by Coomassie Brilliant Blue staining. However, the production of this protein led not only to a severe reduction of endogenous seed storage proteins but also to a deterioration in grain quality. The appearance of aberrant grain phenotypes (such as floury and shrunken) was attributed to ER stress induced by the retention of highly aggregated unfolded hIL-7 in the ER lumen, and the expression levels of chaperones such as BiPs and PDIs were enhanced in parallel with the increase in hIL-7 levels. The activation of this ER stress response was shown to be mainly mediated by the OsIRE1-OsbZIP50 signal cascade, based on the appearance of unconventional splicing of OsbZIP50 mRNA and the induction of OsBiP4&5. Interestingly, the ER stress response could be induced by lower concentrations of hIL-7 versus other types of cytokines such as IL-1b, IL-4, IL-10, and IL-18. Furthermore, several ubiquitin 26S proteasome-related genes implicated in ER-associated degradation were upregulated by hIL-7 production. These results suggest that severe detrimental effects on grain properties were caused by proteo-toxicity induced by unfolded hIL-7 aggregates in the ER, resulting in the triggering of ER stress.

Oral immunotherapy with transgenic rice seed containing destructed Japanese cedar pollen allergens, Cry j 1 and Cry j 2, against Japanese cedar pollinosis

Transgenic rice accumulating the modified major Japanese cedar pollen allergens, Cryptomeria japonica 1 (Cry j 1) and Cryptomeria japonica 2 (Cry j 2), which were deconstructed by fragmentation and shuffling, respectively, in the edible part of the seed was generated by transformation of a good-tasting rice variety, 'Koshihikari'. These modified cedar pollen antigens were deposited in ER-derived protein bodies (PB-I), which are suitable for delivery to the mucosal immune system in gut-associated lymphoid tissue when orally administered because antigens bioencapsulated in PB-I are resistant against hydrolysis by intestinal enzymes and harsh environments. Mice fed transgenic seeds daily for three weeks and then challenged with crude cedar pollen allergen showed marked suppression of allergen-specific CD4(+) T-cell proliferation, IgE and IgG levels compared with mice fed nontransgenic rice seeds. As clinical symptoms of pollinosis, sneezing frequency and infiltration of inflammatory cells such as eosinophils and neutrophils were also significantly reduced in the nasal tissue. These results imply that oral administration of transgenic rice seeds containing the structurally disrupted Cry j 1 and Cry j 2 antigens, serving as universal antigens, is a promising approach for specific immunoprophylaxis against Japanese cedar pollinosis.

Molecular strategies to engineer transgenic rice seed compartments for large-scale production of plant-made pharmaceuticals

The use of plants as bioreactors for the large-scale production of recombinant proteins has emerged as an exciting area of research. The current shortages in protein therapeutics due to the capacity and economic bottlenecks faced with modern protein production platforms (microbial, yeast, mammalian) has driven considerable attention towards molecular pharming. Utilizing plants for the large-scale production of recombinant proteins is estimated to be 2-10% the cost of microbial platforms, and up to 1,000-fold more cost effective than mammalian platforms (Twyman et al. Trends Biotechnol 21:570-578, 2003; Sharma and Sharma, Biotechnol Adv 27:811-832, 2009). In order to achieve an economically feasible plant production host, protein expression and accumulation must be optimized. The seed, and more specifically the rice seed has emerged as an ideal candidate in molecular pharming due to its low protease activity, low water content, stable protein storage environment, relatively high biomass, and the molecular tools available for manipulation (Lau and Sun, Biotechnol Adv 27:1015-1022, 2009).

Recombinant protein yield in rice seed is enhanced by specific suppression of endogenous seed proteins at the same deposit site

Human IL-10 (hIL-10) is a therapeutic treatment candidate for inflammatory allergy and autoimmune diseases. Rice seed-produced IL-10 can be effectively delivered directly to gut-associated lymphoreticular tissue (GALT) via bio-encapsulation. Previously, the codon-optimized hIL-10 gene was expressed in transgenic rice with the signal peptide and endoplasmic reticulum (ER) retention signal (KDEL) at its 5' and 3' ends, respectively, under the control of the endosperm-specific glutelin GluB-1 promoter. The resulting purified hIL-10 was biologically active. In this study, the yield of hIL-10 in transgenic rice seed was improved. This protein accumulated at the intended deposition sites, which had been made vacant through the selective reduction, via RNA interference, of the endogenous seed storage proteins prolamins or glutelins. Upon suppression of prolamins that were sequestered into ER-derived protein bodies (PB-I), hIL-10 accumulation increased approximately 3-fold as compared to rice seed with no such suppression and reached 219 μg/grain. In contrast, reducing the majority of the glutelins stored in protein-storage vacuoles (PB-II) did not significantly affect the accumulation of hIL-10. Considering that hIL-10 is synthesized in the ER lumen and subsequently buds off in ER-derived granules called IL-10 granules in a manner similar to PB-Is, these results indicate that increases in the available deposition space for the desired recombinant proteins may be crucial for improvements in yield. Furthermore, efficient dimeric intermolecular formation of hIL-10 by inhibiting interaction with Cys-rich prolamins also contributed to the enhanced formation of IL-10 bodies. Higher yield of hIL-10 produced in rice seeds is expected to have broad application in the future.

Expression of hypoallergenic Der f 2 derivatives with altered intramolecular disulphide bonds induces the formation of novel ER-derived protein bodies in transgenic rice seeds

House dust mites (HDM) are the most common source of indoor allergens and are associated with allergic diseases worldwide. To benefit allergic patients, safer and non-invasive mucosal routes of oral administration are considered to be the best alternative to conventional allergen-specific immunotherapy. In this study, transgenic rice was developed expressing derivatives of the major HDM allergen Der f 2 with reduced Der f 2-specific IgE reactivity by disrupting intramolecular disulphide bonds in Der f 2. These derivatives were produced specifically as secretory proteins in the endosperm tissue of seeds under the control of the endosperm-specific glutelin GluB-1 promoter. Notably, modified Der f 2 derivatives aggregated in the endoplasmic reticulum (ER) lumen and were deposited in a unique protein body (PB)-like structure tentatively called the Der f 2 body. Der f 2 bodies were characterized by their intracellular localization and physico-chemical properties, and were distinct from ER-derived PBs (PB-Is) and protein storage vacuoles (PB-IIs). Unlike ER-derived organelles such as PB-Is, Der f 2 bodies were rapidly digested in simulated gastric fluid in a manner similar to that of PB-IIs. Oral administration in mice of transgenic rice seeds containing Der f 2 derivatives encapsulated in Der f 2 bodies suppressed Der f 2-specific IgE and IgG production compared with that in mice fed non-transgenic rice seeds, and the effect was dependent on the type of Der f 2 derivative expressed. These results suggest that engineered hypoallergenic Der f 2 derivatives expressed in the rice seed endosperm could serve as a basis for the development of viable strategies for the oral delivery of vaccines against HDM allergy.

The hypocholesterolemic activity of transgenic rice seed accumulating lactostatin, a bioactive peptide derived from bovine milk β-lactoglobulin

Lactostatin is a novel pentapeptide (IIAEK) derived from bovine milk β-lactoglobulin with greater hypocholesterolemic activity than β-sitosterol, the drug commonly used to treat hypercholesterolemia. We developed transgenic rice expressing lactostatin as a fusion protein with seed storage protein (SSP) glutelins under the control of three different endosperm-specific promoters. Lactostatin accumulated in transgenic rice seed at approximately 1.6 mg/g seeds (dry seeds) without any apparent influence on seed traits such as endogenous SSP expression levels or alterations in the intracellular structures of endosperm cells. Short-term (three day) oral administration of the glutelin fraction containing lactostatin (namely three times of 300 mg/kg body weight/day) extracted from transgenic rice seeds resulted in hypocholesterolemic activity in rats; namely, the serum low-density-lipoprotein (LDL) cholesterol level was significantly reduced accompanied by a significant increase in beneficial serum high-density-lipoprotein (HDL) cholesterol.

Functional genomics of rice pollen and seed development by genome-wide transcript profiling and Ds insertion mutagenesis

Rice pollen and seed development are directly related to grain yield. To further improve rice yield, it is important for us to functionally annotate the genes controlling pollen/seed development and to use them for rice breeding. Here we first carried out a genome-wide expression analysis with an emphasis on genes being involved in rice pollen and seed development. Based on the transcript profiling, we have identified and functionally classified 82 highly expressed pollen-specific, 12 developing seed-specific and 19 germinating seed-specific genes. We then presented the utilization of the maize transposon Dissociation (Ds) insertion lines for functional genomics of rice pollen and seed development and as alternative germplasm resources for rice breeding. We have established a two-element Activator/Dissociation (Ac/Ds) gene trap tagging system and generated around 20,000 Ds insertion lines. We have subjected these lines for screens to obtain high and low yield Ds insertion lines. Some interesting lines have been obtained with higher yield or male sterility. Flanking Sequence Tags (FSTs) analyses showed that these Ds-tagged genes encoded various proteins including transcription factors, transport proteins, unknown functional proteins and so on. They exhibited diversified expression patterns. Our results suggested that rice could be improved not only by introducing foreign genes but also by knocking out its endogenous genes. This finding might provide a new way for rice breeder to further improve rice varieties.

Antigen-specific immunotherapy against allergic rhinitis: the state of the art

Allergic rhinitis is the most prevalent type I allergy in industrialized countries. Pollen scattering from trees or grasses often induces seasonal allergic rhinitis, which is known as pollinosis or hay fever. The causative pollen differs across different areas and times of the year. Impaired performance due to pollinosis and/or medication used for treating pollinosis is considered to be an important reason for the loss of concentration and productivity in the workplace. Antigen-specific immunotherapy is an only available curative treatment against allergic rhinitis. Subcutaneous injection of allergens with or without adjuvant has been commonly used as an immunotherapy; however, recently, sublingual administration has come to be considered a safer and convenient alternative administration route of allergens. In this review, we focus on the safety and protocol of subcutaneous and sublingual immunotherapy against seasonal allergic rhinitis. We also describe an approach to selecting allergens for the vaccine so as to avoid secondary sensitization and adverse events. The biomarkers and therapeutic mechanisms for immunotherapy are not fully understood. We discuss the therapeutic biomarkers that are correlated with the improvement of clinical symptoms brought about by immunotherapy as well as the involvement of Tr1 and regulatory T cells in the therapeutic mechanisms. Finally, we focus on the current immunotherapeutic approach to treating Japanese cedar pollinosis, the most prevalent pollinosis in Japan, including sublingual immunotherapy with standardized extract, a transgenic rice-based edible vaccine, and an immunoregulatory liposome encapsulating recombinant fusion protein.

Levels and Stability of Expression of Transgenes

It is well known that in a given cell, at a particular time, only a fraction of the entire genome is expressed. Expression of a gene, nuclear, or organellar starts with the onset of transcription and ends in the synthesis of the functional protein. The regulation of gene expression is a complex process that requires the coordinated activity of different proteins and nucleic acids that ultimately determine whether a gene is transcribed, and if transcribed, whether it results in the production of a protein that develops a phenotype. The same also holds true for transgenic crops, which lie at the very core of insert design.

There are multiple checkpoints at which the expression of a gene can be regulated and controlled. Much of the emphasis of studies related to gene expression has been on regulation of gene transcription, and a number of methods are used to effect the control of gene expression. Controlling transgene expression for a commercially valuable trait is necessary to capture its value. Many gene functions are either lethal or produce severe deformity (resulting in loss of value) if over-expressed. Thus, expression of a transgene at a particular site or in response to a particular elicitor is always desirable.

Role of genetic factors and environmental conditions in recombinant protein production for molecular farming

Plants are generally considered to represent a promising heterologous expression system for the production of valuable recombinant proteins. Minimal upstream plant production cost is a salient feature driving the development of plant expression systems used for the synthesis of recombinant proteins. For such a plant expression system to be fully effective, it is first essential to improve plant productivity by plant biomass after inserting genes of interest into a suitable plant. Plant productivity is related closely to its growth and development, both of which are affected directly by environmental factors. These environmental factors that affect the cultivation conditions mainly include temperature, light, salinity, drought, nutrition, insects and pests. In addition, genetic factors that affect gene expression at the transcriptional, translational, and post-translational levels are considered to be important factors related to gene expression in plants. Thus, these factors influence both the quality and quantity of recombinant protein produced in transgenic plants. Among the genetic factors, the post-translational process is of particular interest as it influences subcellular localization, protein glycosylation, assembly and folding of therapeutic proteins, consequently affecting both protein quantity and biological quality. In this review, we discuss the effects of cultivation condition and genetic factors on recombinant protein production in transgenic plants.

T-cell epitopes of aeroallergens

OBJECTIVE

To describe the current knowledge of the T-cell epitopes of common aeroallergens, how they were discovered, and implications for future therapy.

DATA SOURCES

PubMed search of English-language articles without date limits pertaining to T-cell epitopes of aeroallergens included on a standard skin test panel.

STUDY SELECTION

A total of 127 articles were screened based on the results of the PubMed search and cross-indexed as needed. The highest quality and most clinically relevant articles were included for discussion.

RESULTS

Of the 47 allergen extracts included on the standard skin test panel at our instittition, T-cell epitopes have been described for 13. Immunodominant epitopes have been used for peptide immunotherapy trials.

CONCLUSIONS

T-cell epitopes have been characterized for a minority of common aeroallergens. However, knowledge is rapidly expanding and can lay the groundwork for therapies that specifically target T cells.

Plant seeds as bioreactors for recombinant protein production

Plants are attractive expression systems for the economic production of recombinant proteins. Among the different plant-based systems, plant seed is the leading platform and holds several advantages such as high protein yields and stable storage of target proteins. Significant advances in using seeds as bioreactors have occurred in the past decade, which include the first commercialized plant-derived recombinant protein. Here we review the current progress on seeds as bioreactors, with focus on the different food crops as production platforms and comprehensive strategies in optimizing recombinant protein production in seeds.

Deposition of a recombinant peptide in ER-derived protein bodies by retention with cysteine-rich prolamins in transgenic rice seed

A 7Crp peptide composed of seven major human T cell epitopes derived from the Japanese cedar pollen allergens Cry j 1 and Cry j 2 is an ideal tolerogen for peptide immunotherapy against Japanese cedar pollinosis. To maximize the accumulation level of the 7Crp peptide in transgenic rice seed, we tested endosperm specific promoters and intracellular localizations suitable for stable accumulation. A 7Crp peptide carrying the KDEL ER retention signal directed by the 2.3-kb promoter of the glutelin GluB-1, which contains a signal peptide, accumulated at the highest level of about 60 microg/grain. Notably, the 7Crp peptide predominantly accumulated in ER-derived protein bodies irrespective of the presence of various sorting signals or expression as a fusion protein with glutelin. We attribute this abnormal pattern of accumulation to the formation of disulfide bonds between the 7Crp peptide and cysteine-rich (Cys-rich) prolamin storage proteins. Furthermore, the formation of these aggregates induced the chaperone proteins BiP and PDI as an ER stress response.

Plant-based strategies aimed at expressing HIV antigens and neutralizing antibodies at high levels. Nef as a case study

The first evidence that plants represent a valid, safe and cost-effective alternative to traditional expression systems for large-scale production of antigens and antibodies was described more than 10 years ago. Since then, considerable improvements have been made to increase the yield of plant-produced proteins. These include the use of signal sequences to target proteins to different cellular compartments, plastid transformation to achieve high transgene dosage, codon usage optimization to boost gene expression, and protein fusions to improve recombinant protein stability and accumulation. Thus, several HIV/SIV antigens and neutralizing anti-HIV antibodies have recently been successfully expressed in plants by stable nuclear or plastid transformation, and by transient expression systems based on plant virus vectors or Agrobacterium-mediated infection. The current article gives an overview of plant expressed HIV antigens and antibodies and provides an account of the use of different strategies aimed at increasing the expression of the accessory multifunctional HIV-1 Nef protein in transgenic plants.

Production of recombinant allergens in plants

A large percentage of allergenic proteins are of plant origin. Hence, plant-based expression systems are considered ideal for the recombinant production of certain allergens. First attempts to establish production of plant-derived allergens in plants focused on transient expression in Nicotiana benthamiana infected with recombinant viral vectors. Accordingly, allergens from birch and mugwort pollen, as well as from apple have been expressed in plants. Production of house dust mite allergens has been achieved by Agrobacterium-mediated transformation of tobacco plants. Beside the use of plants as production systems, other approaches have focused on the development of edible vaccines expressing allergens or epitopes thereof, which bypasses the need of allergen purification. The potential of this approach has been convincingly demonstrated for transgenic rice seeds expressing seven dominant human T cell epitopes derived from Japanese cedar pollen allergens. Parallel to efforts in developing recombinant-based diagnostic and therapeutic reagents, different gene-silencing approaches have been used to decrease the expression of allergenic proteins in allergen sources. In this way hypoallergenic ryegrass, soybean, rice, apple, and tomato were developed.

Efficient induction of oral tolerance by fusing cholera toxin B subunit with allergen-specific T-cell epitopes accumulated in rice seed

Cholera toxin B (CTB) subunit is an efficient mucosal carrier molecule for induction of oral tolerance to antigens and allergens. Here, T-cell epitopes of Cry j 1 and Cry j 2, major allergens in Japanese cedar pollen, were expressed in rice seed as a fusion protein with either CTB or rice glutelin as a control. Feeding mice with rice seed containing CTB-fused T-cell epitopes suppressed allergen-specific IgE responses and pollen-induced clinical symptoms at 50-fold lower doses of T-cell epitopes than required when using control seed. Our findings present a novel potential strategy for immunotherapy of type-I allergy.

Development and evaluation of transgenic rice seeds accumulating a type II-collagen tolerogenic peptide

Type II collagen (CII) in joint cartilage is known to be a major auto-antigen in human rheumatoid arthritis. Several animal model- and clinical-studies on tolerance-based immunotherapy for the arthritis have been conducted by administrating synthetic immunodominant peptides through an oral route. In the present study, to produce a tolerogenic peptide with therapeutic potential in transgenic rice plants, a gene construct producing glutelin fusion protein with tandem four repeats of a CII(250-270) peptide (residues 250-270) (GluA-4XCII(250-270)) containing a human T-cell epitope was introduced with a selection marker, hygromycin phosphotransferase gene (hygromycin-resistance gene) (hph), by co-transformation. Several transgenic plants with high and stable expression of gluA-4XCII ( 250-270 ), but no hph, were selected based on both DNA and protein analyses. The GluA-4XCII(250-270) fusion proteins were detected as both precursor and processed forms mainly in a glutelin fraction of rice endosperm protein extracts and in protein-body rich fractions prepared by density gradient ultracentrifugation. The amount of accumulated CII(250-270) peptide was immunochemically estimated to be about 1 microg per seed. Feeding DBA/1 mice the transgenic rice seeds (25 microg of the peptide per mouse a day) for 2 weeks showed tendencies lowering and delaying serum specific-IgG2a response against subsequent and repeated intraperitoneal-injection of type II collagen. Taken these together, the CII-immunodominant peptide could effectively be produced and accumulated as a glutelin-fusion protein in the transgenic rice seeds, which might be useful as pharmaceutical materials and functional food for prevention and therapy for anti-CII autoimmune diseases like human rheumatoid arthritis.

The human immunodeficiency virus antigen Nef forms protein bodies in leaves of transgenic tobacco when fused to zeolin

Protein bodies (PB) are stable polymers naturally formed by certain seed storage proteins within the endoplasmic reticulum (ER). The human immunodeficiency virus negative factor (Nef) protein, a potential antigen for the development of an anti-viral vaccine, is highly unstable when introduced into the plant secretory pathway, probably because of folding defects in the ER environment. The aim of this study was to promote the formation of Nef-containing PB in tobacco (Nicotiana tabacum) leaves by fusing the Nef sequence to the N-terminal domains of the maize storage protein gamma-zein or to the chimeric protein zeolin (which efficiently forms PB and is composed of the vacuolar storage protein phaseolin fused to the N-terminal domains of gamma-zein). Protein blots and pulse-chase indicate that fusions between Nef and the same gamma-zein domains present in zeolin are degraded by ER quality control. Consistently, a mutated zeolin, in which wild-type phaseolin was substituted with a defective version known to be degraded by ER quality control, is unstable in plant cells. Fusion of Nef to the entire zeolin sequence instead allows the formation of PB detectable by electron microscopy and subcellular fractionation, leading to zeolin-Nef accumulation higher than 1% of total soluble protein, consistently reproduced in independent transgenic plants. It is concluded that zeolin, but not its gamma-zein portion, has a positive dominant effect over ER quality control degradation. These results provide insights into the requirements for PB formation and avoidance of quality-control degradation, and indicate a strategy for enhancing foreign protein accumulation in plants.