Isolation and characterization of recombinant antibody fragments against CDC2a from Arabidopsis thaliana

Isolation of Adhirons Specific for Plant Protoplast Membrane Biomarkers Is Simplified by Phagemid Design

Phage display is an effective method to retrieve binders specific for a target epitope from a large clone library. Nevertheless, the panning process allows for the accumulation of some contaminant clones into the selected phage pool and, consequently, each clone requires individual screening to verify its actual specificity. This step is time-consuming, independently on the chosen method, and relies on the availability of reliable reagents. Since phages display a single binder responsible for the antigen recognition but their coat is formed by several repeats of the same proteins, the targeting of coat epitopes is often exploited to amplify the signal. Commercial anti-M13 antibodies are commonly labeled with peroxidase or FITC but customized antibodies might be necessary for specific applications. Here, we report a protocol describing the selection of anti-protoplast Adhirons that relies on the availability of nanobodies fused to a fluorescent protein to use during flow cytometry screening. Specifically, when preparing our Adhiron synthetic library, we designed a new phagemid that allows the expression of the clones fused to three tags. These can interact with a large variety of commercial and home-made reagents, selected according to the needs of the downstream characterization process. In the described case, we combined the ALFA-tagged Adhirons with an anti-ALFAtag nanobody fused with the fluorescent protein mRuby3.

Expression of Single Chain Variable Fragment (scFv) Molecules in Plants: A Comprehensive Update

Single chain variable fragments (scFvs) are generated by joining together the variable heavy and light chain of a monoclonal antibody (mAb) via a peptide linker. They offer some advantages over the parental mAb such as low molecular weight, heterologous production, multimeric form, and multivalency. The scFvs were produced against more than 50 antigens till date using 10 different plant species as the expression system. There were considerable improvements in the expression and purification strategies of scFv in the last 24 years. With the growing demand of scFv in therapeutic and diagnostic fields, its biosynthesis needs to be increased. The easiness in development, maintenance, and multiplication of transgenic plants make them an attractive expression platform for scFv production. The review intends to provide comprehensive information about the use of plant expression system to produce scFv. The developments, advantages, pitfalls, and possible prospects of improvement for the exploitation of plants in the industrial level are discussed.

An optimized yeast display strategy for efficient scFv antibody selection using ribosomal skipping system and thermo resistant yeast

OBJECTIVES

Establish a method to restrict unexpected fragments including stop codons in scFv library and generate a thermo resistant strain for screening of thermal stable scFv sequences.

RESULTS

Here, we have constructed a T2A-Leu2 system for selection of yeast surface display libraries that blocks amplification of "stop codon" plasmids within the library, thereby increasing the quality of the library and efficiency of the selection screen. Also, we generated a temperature-resistant yeast strain, TR1, and validated its combined use with T2A-Leu2 for efficient screening. Thus, we developed a general approach for a fast and efficient screening of scFv libraries using a ribosomal skipping system and thermo-resistant yeast.

CONCLUSIONS

The method highlights the utility of the T2A-Leu2-based ribosomal skipping strategy for increasing the quality of the input library for selection, along with an optimized selection protocol based on thermo-resistant yeast cells.

The next generation of antimicrobial peptides (AMPs) as molecular therapeutic tools for the treatment of diseases with social and economic impacts

Anti-infective drugs have had a key role in the contemporary world, contributing to dramatically decrease mortality rates caused by infectious diseases worldwide. Antimicrobial peptides (AMPs) are multifunctional effectors of the innate immune system of mucosal surfaces and present antimicrobial activity against a range of pathogenic viruses, bacteria, and fungi. However, the discovery and development of new antibacterial drugs is a crucial step to overcome the great challenge posed by the emergence of antibiotic resistance. In this review, we outline recent advances in the development of novel AMPs with improved antimicrobial activities that were achieved through characteristic structural design. In addition, we describe recent progress made to overcome some of the major limitations that have hindered peptide biosynthesis.

Rapid transient expression of human granulocyte-macrophage colony-stimulating factor in two industrial cultivars of tobacco (Nicotiana tabacum L.) by agroinfiltration

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Successful expression of human cytokine GM-CSF in two industrial tobacco cultivars is achieved.

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Rapid cloning in two binary destination vectors is accomplished by using Gateway approach.

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Agrobacterial infiltration procedure is optimized and shown to require the surface tension lowering agent Silwet L-77.

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Accumulation of recombinant protein was confirmed by using high affinity monoclonal hemagglutinin tag antibodies.

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Production of hGM-CSF has been achieved without plant codon usage optimization.

We report the production of hGM-CSF cytokine in leaves of industrial tobacco cultivars DH-17 and DH-27 by using Agrobacterium-mediated transient expression. We prove the concept that very high biomass industrial tobacco plants are suitable platforms for rapid, low cost production of foreign proteins. Successful transient expression of the GM-CSF was achieved in less than three months, opening the possibility for future applications of this approach in rapid response production of various proteins of non-plant origin in industrial tobacco.

Antibody-based metabolic engineering in plants

Genetic engineering is a powerful tool for the manipulation of cellular metabolism and the development of plant varieties with enhanced biological and nutrional functions. Several strategies are available for the in vivo modulation of enzymatic activities, allowing metabolic flux to be directed towards desired biochemical products. Such strategies include the simultaneous expression and/or suppression of multiple genes encoding rate-limiting enzymes, ectopic expression of transcription factors, and the RNA-based inhibition of catabolic enzymes. As an alternative approach, recombinant antibodies expressed in plants have been used to inactivate or sequestrate specific host proteins or compounds, resulting in significant changes to metabolic pathways. The impact of this approach depends on prudent selection of the target antigen, careful antibody design, appropriate subcellular targeting and stable accumulation of the recombinant antibodies in planta. Here, we describe the current status of antibody-based metabolic engineering in plants, discuss procedures for the optimisation of this technology and consider the remaining challenges to its widespread use.

CD3 x CD28 cross-interacting bispecific antibodies improve tumor cell dependent T-cell activation

Bispecific antibodies (Bs-Abs) containing an anti-CD3 and an anti-TAA specificity can recruit T cells to the tumor for cancer immunotherapy. To be effective, efficient activation at the tumor site is a prerequisite. This can be achieved by triggering both the T-cell receptor and the co-stimulatory molecule CD28. We engineered two recombinant cross-interacting Bs-Abs (CriBs-Abs) by incorporating a peptide tag and its cognate single-chain variable fragment (scFv), respectively, into a pair of (tumor x CD3) and (tumor x CD28) binding Bs-Abs. A 30-fold lower concentration of the activating CriBs-Ab as compared to non interacting Bs-Ab was sufficient for strong T-cell activation in the presence of tumor cells. One thousand-fold higher concentrations of both CriBs-Abs were required for marginal T-cell activation (70-fold below maximal response) in the absence of tumor cells. An optimized stoichiometry (1 : 1000) of activating versus co-stimulating CriBs-Ab thus allowed low doses of activating CriBs-Ab to induce tumor-cell dependent T-cell activation when used in combination with high concentrations of the pre-targeted co-stimulating CriBs-Ab in vitro. This indicates a large window of operation in which only tumor cell dependent T-cell activation is induced and systemic tumor cell independent T-cell activation is avoided, while ensuring optimal activation with a low concentration of the activating CriBs-Ab, which has the highest potential to induce toxic effects in vivo.

Transient expression in tobacco leaves of an aglycosylated recombinant antibody against the epidermal growth factor receptor

When generating stably transformed transgenic plants, transient gene expression experiments are especially useful to rapidly confirm that the foreign molecule of interest is correctly assembled and retains its biological activity. TheraCIM(R) (CIMAB S.A., Havana) is a recombinant humanized antibody against the Epidermal Growth Factor receptor (EGF-R), now in clinical trials for cancer therapy in Cuba and other countries. An aglycosylated version (Asn 297 was mutated for Gln 297) of this antibody was transiently expressed in tobacco leaves after vacuum-mediated infiltration of recombinant Agrobacterium tumefaciens that carried a binary plasmid bearing the antibody heavy and light chain genes and plant regulation signals. Protein extracts from "agroinfiltrated" leaves were tested by ELISA and Western blot, showing that the fully assembled antibody was accumulated in plant tissues. The absence of plant specific glycans did not interfere in the assembling or in the activity of the plantibody, as demonstrated in this work. Indirect immunofluorescence demonstrated that the aglycosylated antibody expressed in plants recognizes the EGF-R expressed on the surface of A431 human tumor culture cells.

Production and glycosylation of plant-made pharmaceuticals: the antibodies as a challenge

Antibodies have long been recognized for their diagnostic and therapeutic potential. The rapidly increasing number of monoclonal antibodies approved for immunotherapy has paved the way to an even greater demand for these molecules. In order to satisfy this growing demand and to increase the production capacity, alternative systems based on antibody production in transgenic organisms are being actively explored. In this paper, we focus on transgenic plants as a promising system for the scale-up and processing of plant-made pharmaceuticals. In particular, we point out the advantages and limitations induced by glycosylation of plant-made antibodies for human therapy.

Generation and characterisation of functional recombinant antibody fragments against RNA replicase NIb from plum pox virus

A monoclonal antibody (mAb 2A) able to react against the RNA replicase NIb from plum pox virus (PPV) was obtained and used for generating a specific scFv fragment. The VH and VL coding sequences were cloned and expressed as a fusion scFv protein to alkaline phosphatase. This fusion protein was able to recognise viral NIb in both Western and tissue-print ELISA blots. The affinity and specificity of scFv2A for NIb was similar to that of the parental mAb and the region YLEAFY from PPV-NIb was identified by PEPSCAN assay as the putative epitope. Isolated VH domains from scFv2A were also expressed as fusion to alkaline phosphatase. However, their ability to react against NIb was greatly altered. scFv2A fragments were transiently expressed in the cytosol of Nicotiana benthamiana and although they accumulated to low levels, inhibition-ELISA results indicated that they retained antigen-binding activity.

Immunomodulation of phytohormones and functional proteins in plant cells

Recombinant antibodies expressed ectopically in plant cells recognize their corresponding antigens and can therefore bind specifically to phytohormones and proteins in vivo. The generation of antibody-antigen complexes interferes with the functions of the targets and affects the phenotype of transgenic plants. Recombinant antibodies can accumulate in different cell compartments and organs of transgenic plants at different stages of development. High levels of expression of specific, high-affinity antibodies are required for immunomodulation. Here, we discuss several models and examples of the antibody-mediated modulation of phytohormone and protein functions in terms of their potential for plant research.