Generation and assembly of secretory antibodies in plants

Production of secretory immunoglobulin A by a single mammalian cell

Secretory IgA (sIgA) plays a critical role in providing protection against infection at the mucosal surfaces. Normally, sIgA is the product of two different cell types with heavy, light, and J chains produced by the plasma cells, whereas secretory component (SC), a cleavage product of the polymeric immunoglobulin receptor (pIgR), is added during the transit of dimeric IgA through the epithelial cell layer. In the current study, by introducing a gene for the processed form of SC into a cell line that produces dimeric IgA, we have succeeded in creating a single cell that is able to produce and secrete covalently joined sIgA. To our knowledge, this is the first time it has been possible to efficiently produce large quantities of sIgA of defined specificity in mammalian cells. The sIgA made using this approach has great potential as an immunotherapeutic.

Antibody engineering

The development of recombinant techniques for the rapid cloning, expression, and characterization of cDNAs encoding antibody (Ab) subunits has revolutionized the field of antibody engineering. By fusion to heterologous protein domains, chain shuffling, and inclusion of self-assembly motifs, novel molecules such as bispecific Abs can now be generated which possess the subset of functional properties designed to fit the intended application. Rapid technological developments in phage display of peptides and proteins have led to a plethora of applications directed towards immunology and antibody engineering. Many of the problems associated with the therapeutic use of Abs are being addressed by the application of these new techniques.

Kawasaki disease: update on diagnosis, treatment, and a still controversial etiology

Diagnosis of Kawasaki syndrome still relies solely on clinical criteria because the etiology is unknown. However, the function and structure of different bacterial superantigens as potential pathogens are discussed. In this regard, the recent determination of the crystal structure of the toxic shock syndrome toxin-1 superantigen complexed with major histocompatibility complex class II suggests potential implications for the controversial findings concerning a role of those superantigens in Kawasaki disease. Although a specific therapy is not available, coronary complications can be significantly reduced with the help of intravenous immunoglobulin therapy combined with oral aspirin.

Caries prevention: current strategies, new directions

Despite major advances in caries prevention, a large subset of the U.S. population still needs additional control measures. In numerous other countries, needs are escalating as caries rates continue to rise. Building on current strategies and new insights into the specific mechanisms of caries initiation, researchers are creatively using a variety of new technologies, especially in molecular biology, to fashion a new generation of preventive measures.

Antibody production and engineering in plants

Plants have always been important in the pharmaceutical industry, and plant biotechnology now offers new applications. The use of heterologous expression systems for production of recombinant proteins including antibodies is no longer novel. Attention has now turned towards the end-user, and specifically to engineering the antibody to precise requirements. In expanding the choice of production systems, plants offer unique alternatives for antibody users not only in the bulk production of antibody molecules but also in the ability to assemble full-length and complex, multimeric antibodies. Although the initial investment of time and effort is substantial compared to that of other expression systems, antibody production on an agricultural scale can be envisioned, and the economy of this approach opens many new areas for potential antibody applications in addition to their traditional research and pharmaceutical uses.

Bacterial and plant-produced scFv proteins have similar antigen-binding properties

A gene encoding a single-chain variable (scFv) antibody fragment was expressed as a cytoplasmic and endoplasmic reticulum-targeted protein in transgenic tobacco plants. In both cases, the scFv accumulated up to 0.01% of total soluble protein (TSP). The same scFv fragment was also produced in the periplasm of Escherichia coli. Measurement of the affinity by ELISA indicates that the affinity of the bacterially made scFv is about 80-fold lower than that of the parental Fab fragment. The results suggest that the affinity of the plant-produced scFv fragments is reduced to a similar extent, implying that all the plant-produced scFv fragments are antigen binding.

The joining (J) chain is present in invertebrates that do not express immunoglobulins

Joining (J) chain is a component of polymeric, but not monomeric, immunoglobulin (Ig) molecules and may play a role in their polymerization and transport across epithelial cells. To date, study of the J chain has been confined to vertebrates that produce Ig and in which the J chain displays a considerable degree of structural homology. The role of the J chain in Ig polymerization has been questioned and, since the J chain can be expressed in lymphoid cells that do not produce Ig, it is possible that the J chain may have other functions. To explore this possibility, we have surveyed J-chain gene, mRNA, and protein expression by using reverse transcriptase-coupled PCR, Northern blot analysis, and immunoblot analysis in invertebrate species that do not produce Ig. We report that the J-chain gene is expressed in invertebrates (Mollusca, Annelida, Arthropoda, Echinodermata, and Holothuroidea), as well as in representative vertebrates (Mammalia, Teleostei, Amphibia). Furthermore, J-chain cDNA from the earthworm has a high degree of homology (68-76%) to human, mouse, and bovine J chains. Immunohistochemical studies reveal that the J chain is localized in the mucous cells of body surfaces, intestinal epithelial cells, and macrophage-like cells of the earthworm and slug. This study suggests that the J chain is a primitive polypeptide that arose before the evolution of Ig molecules and remains highly conserved in extent invertebrates and vertebrates.

Transgenic Plants Created for Oral Immunization Against Diarrheal Diseases

We have created transgenic plants that express subunit antigens of infectious bacteria and viruses. These proteins have been isolated and characterized to demonstrate that they retain immunogenic properties. When raw potatoes containing the recombinant immunogens were fed to mice, the animals were orally immunized. Research completed to date has demonstrated the feasibility of using a genetically-engineered food as an inexpensive oral vaccine production and delivery system for diarrheal disease. The system could be a convenient means to deliver vaccines to travelers. It also has great potential as an appropriate technology for producing vaccines "in country" in the developing world. This review focuses on work from our group on recombinant subunit vaccines in potato tubers against enterotoxigenic Escherichia coli and Norwalk virus.

Antibody production in plants

Production of heterologous proteins in plants has become increasingly efficient due to recent advances in plant biotechnology. Heterologous proteins that have specifically attracted a great deal of attention are plant-produced monoclonal antibodies. A variety of applications for these so-called plantibodies have been explored since they were first expressed in tobacco seven years ago. Both full length antibodies and antibody fragments produced in transgenic plants offer many intriguing possibilities to plant molecular biologists and plant breeders. However, questions such as how cellular targeting influences the expression and accumulation of these proteins in plants still need to be answered before the technology can be used commercially, on a large-scale.

Recombinant proteins for medical use: the attractions and challenges

Recombinant proteins that have survived the challenges of process development and clinical trials are becoming blockbuster medical products. Growth factors, enzymes and antibodies are being improved by mutational approaches, fused with other proteins, and even chemically modified in vitro. Drug development and testing approaches have advanced, and proteins produced in transgenic animals are new becoming available. Future protein products might include cancer vaccines and therapies for a variety of genetic diseases, but alternative treatments involving gene therapy or small synthetic compounds will provide competition.

Immunotherapeutic potential of antibodies produced in plants

Plants are capable of synthesizing and assembling virtually every kind of antibody molecule, ranging from the smallest antigen-binding domains and fragments, to full-length, and even multimeric, antibodies. A number of plant hosts can be used, and because this is a versatile expression system that can be scaled-up to agricultural proportions, a cheap and plentiful supply of antibodies could be made available. Immunotherapy is one of the many potential uses for bulk quantities of antibody. In particular, passive immunotherapy of mucosal surfaces may be possible, because functional secretory antibodies can be engineered in plants.

Altered hepatic transport of immunoglobulin A in mice lacking the J chain

We have created J chain knockout mice to define the physiologic role of the J chain in immunoglobulin synthesis and transport. The J chain is covalently associated with pentameric immunoglobulin (Ig) M and dimeric IgA and is also expressed in most IgG-secreting cells. J chain-deficient mice have normal serum IgM and IgG levels but markedly elevated serum IgA. Although polymeric IgA was present in the mutant mice, a larger proportion of their serum IgA was monomeric than was found in wild-type mouse serum. Bile and fecal IgA levels were decreased in J chain-deficient mice compared with wild-type mice, suggesting inefficient transport of J chain-deficient IgA by hepatic polymeric immunoglobulin receptors (pIgR). The pIgR-mediated transport of serum-derived IgA from wild-type and mutant mice was assessed in Madin-Darby canine kidney (MDCK) cells transfected with the pIgR. These studies revealed selective transport by pIgR-expressing MDCK cells of wild-type IgA but not J chain-deficient IgA. We conclude that although the J chain is not required for IgA dimerization, it does affect the efficiency of polymerization or have a role in maintaining IgA dimer stability. Furthermore, the J chain is essential for efficient hepatic pIgR transport of IgA.

High-level production and long-term storage of engineered antibodies in transgenic tobacco seeds

We have used transgenic tobacco seeds to produce large amounts of a functionally active engineered antibody. A gene infusion encoding an antigen-binding single chain Fv protein (scFv) that recognizes the hapten oxazolone was constructed and used as a model. After characterization in a bacterial expression system ,the scFv gene was cloned into a plant expression cassette conferring seed specific expression, and transferred using Agrobacterium-mediated transformation, into Nicotiana tabacum. The expressed scFv could be detected in the developing as well as ripe seeds of regenerated transgenic plants, and the functionally active scFv is stabaly deposited and accumulates up to 0.67% of the total soluble seed protein. After storage of ripe transgenic tobacco seeds for one year at room temperature there was no loss of scFv protein or its antigen-binding activity.