Plant-produced idiotype vaccines for the treatment of non-Hodgkin's lymphoma: safety and immunogenicity in a phase I clinical study

Construction and characterization of a novel fusion protein MG7-scFv/SEB against gastric cancer

Antibody-targeted superantigen has been developed into a new strategy to treat many malignant tumors. In this study, for specific targeting to gastric cancer cell, superantigen SEB (Staphylococcal Enterotoxin B) was genetically fused to the single-chain variable fragment of gastric carcinoma-associated antibody MG7(MG7-scFv) that recognizes the MG7 antigen frequently expressed in gastric cancer cell. The recombinant MG7-scFv/SEB fusion proteins are expressed in E. coli as inclusion bodies, and the purified MG7-scFv/SEB retains high binding affinity with gastric cancer cell SGC-7901 (positive MG7 antigen expression). When incubated with effector cell-peripheral blood mononuclear cells (PBMCs), MG7-scFv/SEB could effectively inhibit the proliferation and induce apoptosis of SGC-7901. After being treated with MG7-scFv/SEB, PBMCs remarkably increased the production of Th1 cytokines (IFN-gamma, IL-2), and slightly increased the production of Th2 cytokines (IL-4, IL-10) in vitro. It was observed that gastric-tumor-bearing rats administrated with MG7-scFv/SEB showed more inflammatory cell infiltration, more significant tumor inhibition, and longer survival time than those of rats treated with SEB or NS (Normal Saline). The data indicated that MG7-scFv/SEB fusion protein could specifically target gastric cancer cell, enhance the activity of T cells and induce tumor cell apoptosis to exert the antitumor effect on gastric cancer.

Tumor immunogenicity and responsiveness to cancer vaccine therapy: the state of the art

Despite enormous effort, promising pre-clinical data in animal studies and over 900 clinical trials in the United States, no cancer vaccine has ever been approved for clinical use. Over the past decade a great deal of progress has been in both laboratory and clinical studies defining the interactions between developing tumors and the immune system. The results of these studies provide a rationale that may help explain the failure of recent therapeutic cancer vaccines in terms of vaccine principles, in selecting which tumors are the most appropriate to target and instruct the design and implementation of state-of-the-art cancer vaccines.

Tobacco, a highly efficient green bioreactor for production of therapeutic proteins

Molecular farming of pharmaceuticals in plants has the potential to provide almost unlimited amounts of recombinant proteins for use in disease diagnosis, prevention or treatment. Tobacco has been and will continue to be a major crop for molecular farming and offers several practical advantages over other crops. It produces significant leaf biomass, has high soluble protein content and is a non-food crop, minimizing the risk of food-chain contamination. This, combined with its flexibility and highly-efficient genetic transformation/regeneration, has made tobacco particularly well suited for plant-based production of biopharmaceutical products. The goal of this review is to provide an update on the use of tobacco for molecular farming of biopharmaceuticals as well the technologies developed to enhance protein production/purification/efficacy. We show that tobacco is a robust biological reactor with a multitude of applications and may hold the key to success in plant molecular farming.

Monoclonal antibody produced in plants efficiently treats West Nile virus infection in mice

Over the past decade, West Nile virus (WNV) has spread to all 48 of the lower United States as well as to parts of Canada, Mexico, the Caribbean, and South America, with outbreaks of neuroinvasive disease occurring annually. At present, no therapeutic or vaccine is available for human use. Epidemics of WNV and other emerging infectious disease threats demand cost-efficient and scalable production technologies that can rapidly transfer effective therapeutics into the clinical setting. We have previously reported that Hu-E16, a humanized anti-WNV mAb, binds to a highly conserved epitope on the envelope protein, blocks viral fusion, and shows promising postexposure therapeutic activity. Herein, we generated a plant-derived Hu-E16 mAb that can be rapidly scaled up for commercial production. Plant Hu-E16 was expressed at high levels within 8 days of infiltration in Nicotiana benthamiana plants and retained high-affinity binding and potent neutralizing activity in vitro against WNV. A single dose of plant Hu-E16 protected mice against WNV-induced mortality even 4 days after infection at rates that were indistinguishable from mammalian-cell-produced Hu-E16. This study demonstrates the efficacy of a plant-produced mAb against a potentially lethal infection several days after exposure in an animal challenge model and provides a proof of principle for the development of plant-derived mAbs as therapy against emerging infectious diseases.

Prevention of bubonic and pneumonic plague using plant-derived vaccines

Yersinia pestis, the causative agent of bubonic and pneumonic plague, is an extremely virulent bacterium but there are currently no approved vaccines for protection against this organism. Plants represent an economical and safer alternative to fermentation-based expression systems for the production of therapeutic proteins. The recombinant plague vaccine candidates produced in plants are based on the two most immunogenic antigens of Y. pestis: the fraction-1 capsular antigen (F1) and the low calcium response virulent antigen (V) either in combination or as a fusion protein (F1-V). These antigens have been expressed in plants using all three known possible strategies: nuclear transformation, chloroplast transformation and plant-virus-based expression vectors. These plant-derived plague vaccine candidates were successfully tested in animal models using parenteral, oral, or prime/boost immunization regimens. This review focuses on the recent research accomplishments towards the development of safe and effective pneumonic and bubonic plague vaccines using plants as bioreactors.

Genetically modified plants for non-food or non-feed purposes: straightforward screening for their appearance in food and feed

Genetically modified (GM) plants aimed at producing food/feed are part of regular agriculture in many areas of the World. Commodity plants have also found application as bioreactors, designated non-food/non-feed GM (NFGM) plants, thereby making raw material for further refinement to industrial, diagnostic or pharmaceutical preparations. Many among them may pose health challenge to consumers or livestock animals, if occurring in food/feed. NFGM plants are typically released into the environment, but are grown under special oversight and any among several containment practices, none of which provide full protection against accidental dispersal. Adventitious admixture with food or feed can occur either through distributional mismanagement or as a consequence of gene flow to plant relatives. To facilitate NFGM surveillance we propose a new mandatory tagging of essentially all such plants, prior to cultivation or marketing in the European Union. The suggested tag--Plant-Made Industrial or Pharmaceutical Products Tag (PMIP-T)--is envisaged to occur as a transgenic silent DNA identifier in host plants and designed to enable technically simple identification and characterisation of any NFGM. Implementation of PMIP-T would permit inexpensive, reliable and high-throughput screening for NFGM specifically. The paper outlines key NFGM prospects and challenges as well as the PMIP-T concept.

Plant-made vaccine antigens and biopharmaceuticals

Plant cells are ideal bioreactors for the production and oral delivery of vaccines and biopharmaceuticals, eliminating the need for expensive fermentation, purification, cold storage, transportation and sterile delivery. Plant-made vaccines have been developed for two decades but none has advanced beyond Phase I. However, two plant-made biopharmaceuticals are now advancing through Phase II and Phase III human clinical trials. In this review, we evaluate the advantages and disadvantages of different plant expression systems (stable nuclear and chloroplast or transient viral) and their current limitations or challenges. We provide suggestions for advancing this valuable concept for clinical applications and conclude that greater research emphasis is needed on large-scale production, purification, functional characterization, oral delivery and preclinical evaluation.

Plant-made vaccine antigens and biopharmaceuticals

Plant cells are ideal bioreactors for the production and oral delivery of vaccines and biopharmaceuticals, eliminating the need for expensive fermentation, purification, cold storage, transportation and sterile delivery. Plant-made vaccines have been developed for two decades but none has advanced beyond Phase I. However, two plant-made biopharmaceuticals are now advancing through Phase II and Phase III human clinical trials. In this review, we evaluate the advantages and disadvantages of different plant expression systems (stable nuclear and chloroplast or transient viral) and their current limitations or challenges. We provide suggestions for advancing this valuable concept for clinical applications and conclude that greater research emphasis is needed on large-scale production, purification, functional characterization, oral delivery and preclinical evaluation.

Lymphoma immunotherapy: vaccines, adoptive cell transfer and immunotransplant

Therapy for non-Hodgkin lymphoma has benefited greatly from basic science and clinical research such that chemotherapy and monoclonal antibody therapy have changed some lymphoma subtypes from uniformly lethal to curable, but the majority of lymphoma patients remain incurable. Novel therapies with less toxicity and more specific targeting of tumor cells are needed and immunotherapy is among the most promising of these. Recently completed randomized trials of idiotype vaccines and earlier-phase trials of other vaccine types have shown the ability to induce antitumor T cells and some clinical responses. More recently, trials of adoptive transfer of antitumor T cells have demonstrated techniques to increase the persistence and antitumor effect of these cells. Herein, we discuss lymphoma immunotherapy clinical trial results and what lessons can be taken to improve their effect, including the combination of vaccination and adoptive transfer in an approach we have dubbed 'immunotransplant'.

The production of biopharmaceuticals in plant systems

Biopharmaceuticals present the fastest growing segment in the pharmaceutical industry, with an ever widening scope of applications. Whole plants as well as contained plant cell culture systems are being explored for their potential as cheap, safe, and scalable production hosts. The first plant-derived biopharmaceuticals have now reached the clinic. Many biopharmaceuticals are glycoproteins; as the Golgi N-glycosylation machinery of plants differs from the mammalian machinery, the N-glycoforms introduced on plant-produced proteins need to be taken into consideration. Potent systems have been developed to change the plant N-glycoforms to a desired or even superior form compared to the native mammalian N-glycoforms. This review describes the current status of biopharmaceutical production in plants for industrial applications. The recent advances and tools which have been utilized to generate glycoengineered plants are also summarized and compared with the relevant mammalian systems whenever applicable.

Scaleable manufacture of HIV-1 entry inhibitor griffithsin and validation of its safety and efficacy as a topical microbicide component

To prevent sexually transmitted HIV, the most desirable active ingredients of microbicides are antiretrovirals (ARVs) that directly target viral entry and avert infection at mucosal surfaces. However, most promising ARV entry inhibitors are biologicals, which are costly to manufacture and deliver to resource-poor areas where effective microbicides are urgently needed. Here, we report a manufacturing breakthrough for griffithsin (GRFT), one of the most potent HIV entry inhibitors. This red algal protein was produced in multigram quantities after extraction from Nicotiana benthamiana plants transduced with a tobacco mosaic virus vector expressing GRFT. Plant-produced GRFT (GRFT-P) was shown as active against HIV at picomolar concentrations, directly virucidal via binding to HIV envelope glycoproteins, and capable of blocking cell-to-cell HIV transmission. GRFT-P has broad-spectrum activity against HIV clades A, B, and C, with utility as a microbicide component for HIV prevention in established epidemics in sub-Saharan Africa, South Asia, China, and the industrialized West. Cognizant of the imperative that microbicides not induce epithelial damage or inflammatory responses, we also show that GRFT-P is nonirritating and noninflammatory in human cervical explants and in vivo in the rabbit vaginal irritation model. Moreover, GRFT-P is potently active in preventing infection of cervical explants by HIV-1 and has no mitogenic activity on cultured human lymphocytes.

Anti-idiotype antibody response after vaccination correlates with better overall survival in follicular lymphoma

Previous studies demonstrated that vaccination-induced tumor-specific immune response is associated with superior clinical outcome in patients with follicular lymphoma. Here, we investigated whether this positive correlation extends to overall survival (OS). We analyzed 91 untreated patients who received CVP chemotherapy (cyclophosphamide, vincristine, and prednisone) followed by idiotype vaccination. Idiotype proteins were produced either by the hybridoma method or by expression of recombinant idiotype-encoding sequences in mammalian or plant-based expression systems. We found that achieving a complete response/complete response unconfirmed (CR/CRu) to CVP and making an anti-idiotype antibody are 2 independent factors that each correlated with longer OS at 10 years (89% vs 68% with or without a CR/CRu, P = .024; 90% vs 69% with or without tumor-specific antibody production; P = .027). In the subset of patients who received hybridoma-generated vaccines, we found that anti-idiotype production was even more highly associated with superior OS (P < .002); this was the case even in patients with a partial response (PR) to CVP (P < .001).

Future of idiotypic vaccination for B-cell lymphoma

During the last three decades, idiotypic vaccination has cleared all the hurdles between preclinical studies and randomized clinical trials, assuming the forerunner role among human therapeutic cancer vaccines. However, over the last few months, the very same Phase III clinical trials that were supposed to consecrate idiotype vaccines as the first such products to reach the market have, one after another, begun failing to achieve their main end points. While their negative outcome had been predicted long ago, it must be underlined that most clinical studies on idiotypic vaccination have shown a substantial correlation between induction of an idiotype-specific immune response and improvement of clinical outcome. Failures of late-stage clinical trials were due to severe pitfalls in their study design and not necessarily to idiotypic vaccination itself. Therefore, it is desirable that dedicated scientists and clinicians persevere until confirming ultimately the clinical benefit of a broadly and readily available idiotype vaccine.

Display of peptides on the surface of tobacco mosaic virus particles

In this review, we focus on the potential that tobacco mosaic virus (TMV) has as a carrier for immunogenic epitopes, and the factors that must be considered in order to bring products based on this platform to the market. Large Scale Biology Corporation developed facile and scaleable methods for manufacture of candidate peptide display vaccines based on TMV. We describe how rational design of peptide vaccines can improve the manufacturability of particular TMV products. We also discuss downstream processing and purification of the vaccine products, with particular attention to the metrics that a product must attain in order to meet criteria for regulatory approval as injectable biologics.

Plant-produced vaccines: promise and reality

Plant-produced vaccines are a much-hyped development of the past two decades, whose time to embrace reality may have finally come. Vaccines have been developed against viral, bacterial, parasite and allergenic antigens, for humans and for animals; a wide variety of plants have been used for stable transgenic expression as well as for transient expression via Agrobacterium tumefaciens and plant viral vectors. A great many products have shown significant immunogenicity; several have shown efficacy in target animals or in animal models. The realised potential of plant-produced vaccines is discussed, together with future prospects for production and registration.