Historically, the study of plant viruses has contributed greatly to the elucidation of eukaryotic biology. Recently, concurrent with the development of viruses into expression vectors, the biotechnology industry has developed an increasing number of disease therapies utilizing recombinant proteins. Plant virus vectors are viewed as a viable option for recombinant protein production. Employing pathogens in the process of creating added value to agriculture is, in effect, making an ally from an enemy. This review discusses the development and use of viruses as expression vectors, with special emphasis on (+) strand RNA virus systems. Further, the use of virus expression vectors in large-scale agricultural settings to produce recombinant proteins is described, and the technical challenges that need to be addressed by agriculturists and molecular virologists to fully realize the potential of this latest evolution of plant science are outlined.

SummaryPlants have been proposed as an attractive alternative for pharmaceutical protein production to current mammalian or microbial cell-based systems. Eukaryotic protein processing coupled with reduced production costs and low risk for mammalian pathogen contamination and other impurities have led many to predict that agricultural systems may offer the next wave for pharmaceutical product production. However, for this to become a reality, the quality of products produced at a relevant scale must equal or exceed the predetermined release criteria of identity, purity, potency and safety as required by pharmaceutical regulatory agencies. In this article, the ability of transient plant virus expression systems to produce a wide range of products at high purity and activity is reviewed. The production of different recombinant proteins is described along with comparisons with established standards, including high purity, specific activity and promising preclinical outcomes. Adaptation of transient plant virus systems to large-scale manufacturing formats required development of virus particle and Agrobacterium inoculation methods. One transient plant system case study illustrates the properties of greenhouse and field-produced recombinant aprotinin compared with an US Food and Drug Administration-approved pharmaceutical product and found them to be highly comparable in all properties evaluated. A second transient plant system case study demonstrates a fully functional monoclonal antibody conforming to release specifications. In conclusion, the production capacity of large quantities of recombinant protein offered by transient plant expression systems, coupled with robust downstream purification approaches, offers a promising solution to recombinant protein production that compares favourably to cell-based systems in scale, cost and quality.

Plant-made vaccines have been the subject of intense interest because they can be produced economically in large scale without the use of animal-derived components. Plant-made therapeutic vaccines against challenging chronic diseases, such as cancer, have received little research attention, and no previous human clinical trials have been conducted in this vaccine category. We document the feasibility of using a plant viral expression system to produce personalized (patient-specific) recombinant idiotype vaccines against follicular B cell lymphoma and the results of administering these vaccines to lymphoma patients in a phase I safety and immunogenicity clinical trial. The system allowed rapid production and recovery of idiotypic single-chain antibodies (scFv) derived from each patient's tumor and immunization of patients with their own individual therapeutic antigen. Both low and high doses of vaccines, administered alone or co-administered with the adjuvant GM-CSF, were well tolerated with no serious adverse events. A majority (>70%) of the patients developed cellular or humoral immune responses, and 47% of the patients developed antigenspecific responses. Because 15 of 16 vaccines were glycosylated in plants, this study also shows that variation in patterns of antigen glycosylation do not impair the immunogenicity or affect the safety of the vaccines. Collectively, these findings support the conclusion that plant-produced idiotype vaccines are feasible to produce, safe to administer, and a viable option for idiotypespecific immune therapy in follicular lymphoma patients.phase I clinical trial ͉ plant-made pharmaceutical ͉ single-chain antibodies I n recent years, non-Hodgkin's lymphoma (NHL) has become the most common hematologic malignancy in the United States with an estimated 54,000 new cases each year. Approximately 30% of these cases are follicular B cell lymphoma (1), with a median survival of 8-10 years from diagnosis (2). Most patients subjected to standard treatments, such as chemotherapy, radiation, or antibodies (2-9), still relapse (10-12). Newer approaches have focused on active immunotherapy through vaccination. For B cell lymphoma, the cell-surface Ig (Ig), or idiotype, is the unique tumorspecific antigen. In contrast to passive therapy, an idiotype-induced immune response is (i) highly tumor specific, thus sparing normal cells; (ii) potentially more durable; and (iii) protective against tumor cell variants that might ''escape'' under selective pressure, because the response is polyclonal (13-15).There exists a 20-year history of idiotype vaccination for follicular lymphoma in animal models and clinical trials. The original vaccine manufacturing process, still used today in the majority of clinical research, used a patient's lymphoma B cells to derive a mouse/ human heteromyeloma cell line for production of the tumor's monoclonal idiotype (16). Once purified, the idiotype antibody was chemically coupled to a highly immunogenic carrier protein, keyhole limpet haemocyanin (KLH), and administered w...

Introduction BAY 81‐8973 is a full‐length recombinant factor VIII (FVIII) with the same primary amino acid sequence as sucrose‐formulated recombinant FVIII (rFVIII‐FS) but is produced with advanced manufacturing technologies. Aim To analyse the pharmacokinetics (PK) of BAY 81‐8973 after single and multiple dosing across different age and ethnic groups in the LEOPOLD clinical trial programme. Methods The LEOPOLD trials enrolled patients with severe haemophilia A aged 12–65 years (LEOPOLD I and II) or ≤12 years (LEOPOLD Kids) with ≥150 (LEOPOLD I and II) or ≥50 (LEOPOLD Kids) exposure days to any FVIII product and no history of FVIII inhibitors. PK were assessed using chromogenic and one‐stage assays (only chromogenic assay for LEOPOLD Kids) after a single 50‐IU kg−1 dose of BAY 81‐8973 and, in a subset of patients in LEOPOLD I, after repeated dosing. Pharmacokinetic analyses were also performed based on age (18 to 65, 12 to <18, 6 to <12 and <6 years) and ethnicity (Asian and non‐Asian). Results Pharmacokinetic assessments in the LEOPOLD I trial showed non‐inferiority of BAY 81‐8973 vs. rFVIII‐FS. The PK of BAY 81‐8973 were comparable after single and multiple dosing. Age‐based analysis in the three trials showed that plasma concentrations were slightly lower for children, but similar for adolescents compared with adults. Pharmacokinetic results were similar in the different ethnic groups. Conclusions Results of the LEOPOLD trials show that the BAY 81‐8973 pharmacokinetic profile is non‐inferior to rFVIII‐FS. Similar BAY 81‐8973 pharmacokinetic values were observed following single and repeated dosing and across ethnic groups.

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The cytoplasmic male sterility (CMS) trait of at least one line of Viea faba plants is always associated with the presence of high molecular weight double-stranded RNA in the leaf tissue extracts. Subcellular fractions of leaf tissue from CMS and fertile maintainer plants were initially analyzed in an attempt to locate, identify, and characterize the genetic material involved with the sterility trait. This CMS-associated high molecular weight RNA was found only in the cytosol of the "447" male sterile line ofV. faba plants and could not be isolated from the recurrent parent (maintainer), from lines that had been fertility-restored, or from lines that had reverted from the sterile condition. We have been able to move the CMS-associated RNA from donor to fertile host plants through a dodder bridge. These hosts not only contain the RNA but now exhibit a male sterile phenotype, as detected by visual examination of the flower, the pollen, morphological characteristics, and pollen staining ability.Male sterility is most useful for the production of commercial amounts of hybrid seed if the factors responsible for the trait are maternally inherited. Sources of such a cytoplasmic male sterility (CMS) have been found in many different species of plants (1). In the maize and sorghum cytoplasmic male sterile lines, it has been demonstrated that the genetic information responsible for the CMS trait resides in the mitochondria (2-4) apparently as episomal DNA (5). Research on these monocotyledonous plants has led to a transposon-like model for the mitochondrial CMS DNA (6). However, there has been very little research on the causes of CMS in the dicotyledonous plants. There have been suggestions that viruses or virus-like particles (VLPs) are responsible for the sterility in the broad bean plants (Vidafaba L.) and petunias (7-9).An electron microscopic study of "447" male sterile, maintainer, restored, and reverted V.faba lines has shown the presence of cytoplasmic spherical bodies (=70 nm in diameter) in only the male sterile plants (8). In a short report we have indicated that there are particles in the CMS plants that contain a family of double-stranded RNA (dsRNA) molecules (10); we now further characterize these nucleic acids and identify one of them as consistently being associated with the sterility trait.The dsRNA particle appears to have characteristics similar to a virus, leading us to help substantiate a mechanism of sterility which is quite different from that involving the episomal DNA in maize mitochondria. These results and the eventual transfer of the dsRNA agent and the CMS biological trait provide compelling biochemical evidence that cytoplasmic male sterility in the broad bean plant is caused by the presence of at least one dsRNA species. MATERIALS AND METHODSPlant Material. Seeds of V.faba L. were provided by D. A. Bond (Plant Breeding Institute, Cambridge, England) and P. Berthelem (Institut National de la Recherche Agronomique Station for Plant Improvement, LeRheu, France) or were purchased from...

We have cloned and functionally expressed a tyrosinase gene from Streptomyces antibioticus in Escherichia coli under the control of an inducible bacteriophage T7 promoter. Recombinant E. coli cells containing the induced tyrosinase gene produced melanin pigments on agar plates and in liquid culture when supplemented with copper and tyrosine. The expression of an additional open reading frame from the mel gene locus of S. antibioticus was required for high-level melanin production in E. coli. Our results also show that it is possible to screen other classes of precursor compounds for incorporation into melanin pigments with unique colors and other biochemical features. In addition, it may be possible to screen for enhanced melanin production in the absence of added precursors to identify overproducing mutants in the amino acid biosynthetic pathways of E. coli. The ability to screen for a melanin phenotype in recombinant E. coli provides new opportunities for production of novel melanins and for protein engineering of tyrosinases with altered catalytic properties.