Stable antibody expression at therapeutic levels using the 2A peptide

Drug-cured experimental Trypanosoma cruzi infections confer long-lasting and cross-strain protection

BACKGROUND

The long term and complex nature of Chagas disease in humans has restricted studies on vaccine feasibility. Animal models also have limitations due to technical difficulties in monitoring the extremely low parasite burden that is characteristic of chronic stage infections. Advances in imaging technology offer alternative approaches that circumvent these problems. Here, we describe the use of highly sensitive whole body in vivo imaging to assess the efficacy of recombinant viral vector vaccines and benznidazole-cured infections to protect mice from challenge with Trypanosoma cruzi.

METHODOLOGY/PRINCIPAL FINDINGS

Mice were infected with T. cruzi strains modified to express a red-shifted luciferase reporter. Using bioluminescence imaging, we assessed the degree of immunity to re-infection conferred after benznidazole-cure. Those infected for 14 days or more, prior to the onset of benznidazole treatment, were highly protected from challenge with both homologous and heterologous strains. There was a >99% reduction in parasite burden, with parasites frequently undetectable after homologous challenge. This level of protection was considerably greater than that achieved with recombinant vaccines. It was also independent of the route of infection or size of the challenge inoculum, and was long-lasting, with no significant diminution in immunity after almost a year. When the primary infection was benznidazole-treated after 4 days (before completion of the first cycle of intracellular infection), the degree of protection was much reduced, an outcome associated with a minimal T. cruzi-specific IFN-γ+ T cell response.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that a protective Chagas disease vaccine must have the ability to eliminate parasites before they reach organs/tissues, such as the GI tract, where once established, they become largely refractory to the induced immune response.

Production of an antibody Fab fragment using 2A peptide in insect cells

Antibody Fab fragments consist of heavy chain (Hc) and light chain (Lc) polypeptides assembled with a disulphide bond. The production of a recombinant Fab fragment requires the simultaneous expression of two genes encoding both an Hc and an Lc in the same host cell. In the present study, we investigated the production of Fab fragments in lepidopteran insect cells using a bicistronic plasmid vector carrying the Hc and Lc genes linked with a 2A self-cleaving peptide sequence from the porcine teschovirus-1. We also examined the arrangement of a GSG spacer sequence and a furin cleavage site sequence with the 2A sequence. Western blot analysis and enzyme-linked immunosorbent assay (ELISA) of culture supernatants showed that Trichoplusia ni BTI-TN-5B1-4 (High Five) cells transfected with a plasmid in which the Hc and Lc genes were joined by the 2A sequence successfully secreted Fab fragments with antigen-binding activity after self-cleavage of the 2A peptide. The GSG linker enhanced 2A cleavage efficiency, and the furin recognition site was useful for removal of 2A residues from the Hc. Transfection with a single plasmid that contained sequences for GSG, the furin cleavage site, GSG, and the 2A peptide between the Hc and Lc genes exhibited a higher productivity than co-transfection with a set of plasmids separately carrying the Hc or Lc gene. These results demonstrate that bicistronic expression with the appropriate combination of a furin recognition site, GSG linkers, and a 2A peptide may be an effective way to efficiently produce recombinant antibody molecules in insect cells.

The Development and Characterization of an scFv-Fc Fusion-Based Gene Therapy to Reduce the Psychostimulant Effects of Methamphetamine Abuse

Methamphetamine (METH) continues to be among the most addictive and abused drugs in the United States. Unfortunately, there are currently no Food and Drug Administration-approved pharmacological treatments for METH-use disorder. We have previously explored the use of adeno-associated viral (AAV)-mediated gene transfer of an anti-METH monoclonal antibody. Here, we advance our approach by generating a novel anti-METH single-chain variable fragment (scFv)-Fc fusion construct (termed 7F9-Fc) packaged into AAV serotype 8 vector (called AAV-scFv-Fc) and tested in vivo and ex vivo. A range of doses [1 × 10¹⁰, 1 × 10¹¹, and 1 × 10¹² vector copies (vcs)/mouse] were administered to mice, eliciting a dose-dependent expression of 7F9-Fc in serum with peak circulating concentrations of 48, 1785, and 3831 µg/ml, respectively. Expressed 7F9-Fc exhibited high-affinity METH binding, IC₅₀ = 17 nM. Between days 21 and 35 after vector administration, at both 1 × 10¹¹ vc/mouse and 1 × 10¹² vc/mouse doses, the AAV-7F9-Fc gene therapy significantly decreased the potency of METH in locomotor assays. On day 116 post-AAV administration, mice expressing 7F9-Fc sequestered over 2.5 times more METH in the serum than vehicle-treated mice, and METH concentrations in the brain were reduced by 1.2 times the value for vehicle mice. These data suggest that an AAV-delivered anti-METH Fc fusion antibody could be used to persistently reduce concentrations of METH in the central nervous system. SIGNIFICANCE STATEMENT: In this manuscript, we describe the testing of a novel antimethamphetamine (METH) single-chain variable fragment-Fc fusion protein delivered in mice using gene therapy. The results suggest that the gene therapy delivery system can lead to the production of significant antibody concentrations that mitigate METH's psychostimulant effects in mice over an extended time period.

Bicistronic expression and differential localization of proteins in insect cells and Drosophila suzukii using picornaviral 2A peptides

Polycistronic expression systems in insects can be used for applications such as recombinant protein production in cells, enhanced transgenesis methods, and the development of novel pest-control strategies based on the sterile insect technique (SIT). Here we tested the performance of four picornaviral 2A self-cleaving peptides (TaV-2A, DrosCV-2A, FMDV 2A1/31 and FMDV 2A1/32) for the co-expression and differential subcellular targeting of two fluorescent marker proteins in cell lines (Anastrepha suspensa AsE01 and Drosophila melanogaster S2 cells). We found that all four 2A peptides showed comparable activity in cell lines, leading to the production of independent upstream and downstream proteins that were directed to the nucleus or membrane by a C-terminal nuclear localization signal (NLS) on the upstream protein and a poly-lysine/CAAX membrane anchor on the downstream protein. TaV-2A and DrosCV-2A were inserted into piggyBac constructs to create transgenic D. suzukii strains, confirming efficient ribosomal skipping in vivo. Interestingly, we found that the EGFP-CAAX protein was distributed homogeneously in the membrane whereas the DsRed-CAAX protein formed clumps and aggregates that induced extensive membrane blebbing. Accordingly, only flies expressing the DsRed-NLS and EGFP-CAAX proteins could be bred to homozygosity whereas expression of EGFP-NLS and DsRed-CAAX was lethal in the homozygous state. Our results therefore demonstrate that the 2A constructs and two novel targeting motifs are functional in D. suzukii, and that the combination of EGFP-NLS and DsRed-CAAX shows dosage-dependent lethality. These molecular elements could be further used to improve expression systems in insects and generate novel pest control strains.

IL-6 Trans-signaling Controls Liver Regeneration After Partial Hepatectomy

Interleukin-6 (IL-6) is critically involved in liver regeneration after partial hepatectomy (PHX). Previous reports suggest that IL-6 trans-signaling through the soluble IL-6/IL-6R complex is involved in this process. However, the long-term contribution of IL-6 trans-signaling for liver regeneration after PHX is unknown. PHX-induced generation of the soluble IL-6R by ADAM (a disintegrin and metallo) proteases enables IL-6 trans-signaling, in which IL-6 forms an agonistic complex with the soluble IL-6 receptor (sIL-6R) to activate all cells expressing the signal-transducing receptor chain glycoprotein 130 (gp130). In contrast, without activation of ADAM proteases, IL-6 in complex with membrane-bound IL-6R and gp130 activates classic signaling. Here, we describe the generation of IL-6 trans-signaling mice, which exhibit boosted IL-6 trans-signaling and abrogated classic signaling by genetic conversion of all membrane-bound IL-6R into sIL-6R proteins phenocopying hyperactivation of ADAM-mediated shedding of IL-6R as single substrate. Importantly, although IL-6R deficient mice were strongly affected by PHX, survival and regeneration of IL-6 trans-signaling mice was indistinguishable from control mice, demonstrating that IL-6 trans-signaling fully compensates for disabled classic signaling in liver regeneration after PHX. Moreover, we monitored the long-term consequences of global IL-6 signaling inhibition versus IL-6 trans-signaling selective blockade after PHX by IL-6 monoclonal antibodies and soluble glycoprotein 130 as fragment crystallizable fusion, respectively. Both global IL-6 blockade and selective inhibition of IL-6 trans-signaling results in a strong decrease of overall survival after PHX, accompanied by decreased signal transducer and activator of transcription 3 phosphorylation and proliferation of hepatocytes. Mechanistically, IL-6 trans-signaling induces hepatocyte growth factor production by hepatic stellate cells. Conclusion: IL-6 trans-signaling, but not classic signaling, controls liver regeneration following PHX.

Effects of different 2A peptides on transgene expression mediated by tricistronic vectors in transfected CHO cells

Multicistronic vectors can increase transgene expression and decrease the imbalance of gene expression in the Chinese hamster ovary (CHO) cell expression system. Small, self-cleaving 2A peptides have a high cleavage efficiency and are essential for constructing high-expression multicistronic vectors. In this study, we investigated the effects of two different 2A peptides on transgene expression in CHO cells via their mediating action on tricistronic vectors. The enhanced green fluorescent protein (eGFP) and red fluorescent protein (RFP) genes were linked by the porcine teschovirus-1 (P2A) and Thosea asigna virus (T2A) peptides in a multicistronic vector. We transfected CHO cells with these vectors and screened for the presence of blasticidin-resistant colonies. Flow cytometry and real-time quantitative PCR (qPCR) were used to detect the expression levels of eGFP and RFP and the copy numbers of stably transfected cells. The results showed that P2A could enhance eGFP and RFP expression by 1.48- and 1.47-fold, respectively, compared to T2A. The expression levels of the genes were not proportional to their copy numbers. In conclusion, we found that P2A can effectively drive transgene expression in CHO cells and a potent 2A peptide can be used for recombinant protein production in the CHO cell system.

Biosimilar Gene Therapy: Investigational Assessment of Secukinumab Gene Therapy

Objective

Tumor necrosis factor-alpha (TNF-α), checkpoint inhibitors, and interleukin-17 (IL-17) are critical targets in inflammation and autoimmune diseases. Monoclonal antibodies (mAbs) have a successful portfolio in the treatment of chronic diseases. With the current progress in stem cells and gene therapy technologies, there is the promise of replacing costly mAbs production in bioreactors with a more direct and cost-effective production method inside the patient’s cells. In this paper we examine the results of an investigational assessment of secukinumab gene therapy.

Materials and Methods

In this experimental study, the DNA sequence of the heavy and light chains of secukinumab antibodies were cloned in a lentiviral vector. Human chorionic villous mesenchymal stem cells (CMSCs) were isolated and characterized. After lentiviral packaging and titration, part of the recombinant viruses was used for transduction of the CMSCs and the other part were applied for systemic gene therapy. The engineered stem cells and recombinant viruses were applied for ex vivo and in vivo gene therapy, respectively, in different groups of rat models. In vitro and in vivo secukinumab expression was confirmed with quantitative real-time polymerase chain reaction (qRT-PCR), western blot, and ELISA by considering the approved secukinumab as the standard reference.

Results

Cell differentiation assays and flow cytometry of standard biomarkers confirmed the multipotency of the CMSCs. Western blot and qRT-PCR confirmed in vitro gene expression of secukinumab at both the mRNA and protein level. ELISA testing of serum from treated rat models confirmed mAb overexpression for both in vivo and ex vivo gene therapies.

Conclusion

In this study, a lentiviral-mediated ex vivo and in vivo gene therapy was developed to provide a moderate dose of secukinumab in rat models. Biosimilar gene therapy is an attractive approach for the treatment of autoimmune disorders, cancers and other chronic diseases.

Optimization of a 2A self-cleaving peptide-based multigene expression system for efficient expression of upstream and downstream genes in silkworm

The multigene expression system is highly attractive to co-express multiple genes or multi-subunit complex-based genes for their functional studies, and in gene therapy and visual tracking of expressed proteins. However, the current multiple gene co-expression strategies usually suffer from severe inefficiency and unbalanced expression of multiple genes. Here, we report on an improved 2A self-cleaving peptide (2A)-based multigene expression system (2A-MGES), by introducing an optimized Kozak region (Ck) and altering the gene arrangement, both of which contributed to the efficient expression of two fluorescent protein genes in silkworm. By co-expressing DsRed and EGFP genes in insect cells and silkworms, the potent Ck was first found to improve the translation efficiency of downstream genes, and the expression of the flanking genes of 2A were improved by altering the gene arrangement in 2A-MGES. Moreover, we showed that combining Ck and an optimized gene arrangement in 2A-MGES could synergistically improve the expression of genes in the cell. Further, these two flanking genes, regulated by modified 2A-MGES, were further co-expressed in the middle silk gland and secreted into the cocoon, and both achieved efficient expression in the transgenic silkworms and their cocoons. These results suggested that the modified Ck-2A-MGES will be a potent tool for multiple gene expression, for studies of their functions, and their applications in insect species.

High-throughput reformatting of phage-displayed antibody fragments to IgGs by one-step emulsion PCR

Single-chain variable fragment (scFv) is the most common format for phage display antibody library. The isolated scFvs need to be reformatted to full-length IgGs for further characterization. High throughput reformatting of scFv to IgG without disrupting VH-VL pairing is of great demanding for exhaustive screening of all antibodies in IgG format. Herein, we developed a strategy based on the overlap extension PCR in emulsion to reformat scFv to IgG while maintain the accuracy and complexity of variable region pairing. Using CD40 as an example target, we reformatted phage display derived CD40 binding scFv library to IgG mammalian display library and isolated high affinity CD40 binding IgGs. This robust and reliable antibody reformatting approach could be integrated into any phage display based antibody drug discovery.

Immunization with Components of the Viral Fusion Apparatus Elicits Antibodies That Neutralize Epstein-Barr Virus in B Cells and Epithelial Cells

Epstein-Barr virus (EBV) causes infectious mononucleosis and is associated with epithelial-cell cancers and B cell lymphomas. An effective EBV vaccine is not available. We found that antibodies to the EBV glycoprotein gH/gL complex were the principal components in human plasma that neutralized infection of epithelial cells and that antibodies to gH/gL and gp42 contributed to B cell neutralization. Immunization of mice and nonhuman primates with nanoparticle vaccines that displayed components of the viral-fusion machinery EBV gH/gL or gH/gL/gp42 elicited antibodies that potently neutralized both epithelial-cell and B cell infection. Immune serum from nonhuman primates inhibited EBV-glycoprotein-mediated fusion of epithelial cells and B cells and targeted an epitope critical for virus-cell fusion. Therefore, unlike the leading EBV gp350 vaccine candidate, which only protects B cells from infection, these EBV nanoparticle vaccines elicit antibodies that inhibit the virus-fusion apparatus and provide cell-type-independent protection from virus infection.

Rapid production of a chimeric antibody-antigen fusion protein based on 2A-peptide cleavage and green fluorescent protein expression in CHO cells

To enable large-scale antibody production, the creation of a stable, high producer cell line is essential. This process often takes longer than 6 months using standard limited dilution techniques and is very labor intensive. The use of a tri-cistronic vector expressing green fluorescent protein (GFP) and both antibody chains, separated by a GT2A peptide sequence, allows expression of all proteins under a single promotor in equimolar ratios. By combining the advantages of 2A peptide cleavage and single cell sorting, a chimeric antibody-antigen fusion protein that contained the variable domains of mouse IgG with a porcine IgA constant domain fused to the FedF antigen could be produced in CHO-K1 cells. After transfection, a strong correlation was found between antibody production and GFP expression (r = 0.69) using image analysis of formed monolayer patches. This enables the rapid selection of GFP-positive clones using automated image analysis for the selection of high producer clones. This vector design allowed the rapid selection of high producer clones within a time-frame of 4 weeks after transfection. The highest producing clone had a specific antibody productivity of 2.32 pg/cell/day. Concentrations of 34 mg/L were obtained using shake-flask batch culture. The produced recombinant antibody showed stable expression, binding and minimal degradation. In the future, this antibody will be assessed for its effectiveness as an oral vaccine antigen.

Zinc finger nuclease-mediated targeting of multiple transgenes to an endogenous soybean genomic locus via non-homologous end joining

Emerging genome editing technologies hold great promise for the improvement of agricultural crops. Several related genome editing methods currently in development utilize engineered, sequence-specific endonucleases to generate DNA double strand breaks (DSBs) at user-specified genomic loci. These DSBs subsequently result in small insertions/deletions (indels), base substitutions or incorporation of exogenous donor sequences at the target site, depending on the application. Targeted mutagenesis in soybean (Glycine max) via non-homologous end joining (NHEJ)-mediated repair of such DSBs has been previously demonstrated with multiple nucleases, as has homology-directed repair (HDR)-mediated integration of a single transgene into target endogenous soybean loci using CRISPR/Cas9. Here we report targeted integration of multiple transgenes into a single soybean locus using a zinc finger nuclease (ZFN). First, we demonstrate targeted integration of biolistically delivered DNA via either HDR or NHEJ to the FATTY ACID DESATURASE 2-1a (FAD2-1a) locus of embryogenic cells in tissue culture. We then describe ZFN- and NHEJ-mediated, targeted integration of two different multigene donors to the FAD2-1a locus of immature embryos. The largest donor delivered was 16.2 kb, carried four transgenes, and was successfully transmitted to T1 progeny of mature targeted plants obtained via somatic embryogenesis. The insertions in most plants with a targeted, 7.1 kb, NHEJ-integrated donor were perfect or near-perfect, demonstrating that NHEJ is a viable alternative to HDR for gene targeting in soybean. Taken together, these results show that ZFNs can be used to generate fertile transgenic soybean plants with NHEJ-mediated targeted insertions of multigene donors at an endogenous genomic locus.

Regulation of the neuropathy-associated Pmp22 gene by a distal super-enhancer

Peripheral nerve myelination is adversely affected in the most common form of the hereditary peripheral neuropathy called Charcot-Marie-Tooth Disease. This form, classified as CMT1A, is caused by a 1.4 Mb duplication on chromosome 17, which includes the abundantly expressed Schwann cell myelin gene, Peripheral Myelin Protein 22 (PMP22). This is one of the most common copy number variants causing neurological disease. Overexpression of Pmp22 in rodent models recapitulates several aspects of neuropathy, and reduction of Pmp22 in such models results in amelioration of the neuropathy phenotype. Recently we identified a potential super-enhancer approximately 90-130 kb upstream of the Pmp22 transcription start sites. This super-enhancer encompasses a cluster of individual enhancers that have the acetylated histone H3K27 active enhancer mark, and coincides with smaller duplications identified in patients with milder CMT1A-like symptoms, where the PMP22 coding region itself was not part of the duplication. In this study, we have utilized genome editing to create a deletion of this super-enhancer to determine its role in Pmp22 regulation. Our data show a significant decrease in Pmp22 transcript expression using allele-specific internal controls. Moreover, the P2 promoter of the Pmp22 gene, which is used in other cell types, is affected, but we find that the Schwann cell-specific P1 promoter is disproportionately more sensitive to loss of the super-enhancer. These data show for the first time the requirement of these upstream enhancers for full Pmp22 expression.

mRNA as novel technology for passive immunotherapy

While active immunization elicits a lasting immune response by the body, passive immunotherapy transiently equips the body with exogenously generated immunological effectors in the form of either target-specific antibodies or lymphocytes functionalized with target-specific receptors. In either case, administration or expression of recombinant proteins plays a fundamental role. mRNA prepared by in vitro transcription (IVT) is increasingly appreciated as a drug substance for delivery of recombinant proteins. With its biological role as transient carrier of genetic information translated into protein in the cytoplasm, therapeutic application of mRNA combines several advantages. For example, compared to transfected DNA, mRNA harbors inherent safety features. It is not associated with the risk of inducing genomic changes and potential adverse effects are only temporary due to its transient nature. Compared to the administration of recombinant proteins produced in bioreactors, mRNA allows supplying proteins that are difficult to manufacture and offers extended pharmacokinetics for short-lived proteins. Based on great progress in understanding and manipulating mRNA properties, efficacy data in various models have now demonstrated that IVT mRNA constitutes a potent and flexible platform technology. Starting with an introduction into passive immunotherapy, this review summarizes the current status of IVT mRNA technology and its application to such immunological interventions.

A novel approach for rapid high-throughput selection of recombinant functional rat monoclonal antibodies

Background

Most monoclonal antibodies against mouse antigens have been derived from rat spleen-mouse myeloma fusions, which are valuable tools for purposes ranging from general laboratory reagents to therapeutic drugs, and yet selecting and expressing them remains a time-consuming and inefficient process. Here, we report a novel approach for the rapid high-throughput selection and expression of recombinant functional rat monoclonal antibodies with different isotypes.

Results

We have developed a robust system for generating rat monoclonal antibodies through several processes involving simultaneously immunizing rats with three different antigens expressing in a mixed cell pools, preparing hybridoma cell pools, in vitro screening and subsequent cloning of the rearranged light and heavy chains into a single expression plasmid using a highly efficient assembly method, which can decrease the time and effort required by multiple immunizations and fusions, traditional clonal selection and expression methods. Using this system, we successfully selected several rat monoclonal antibodies with different IgG isotypes specifically targeting the mouse PD-1, LAG-3 or AFP protein from a single fusion. We applied these recombinant anti-PD-1 monoclonal antibodies (32D6) in immunotherapy for therapeutic purposes that produced the expected results.

Conclusions

This method can be used to facilitate an increased throughput of the entire process from multiplex immunization to acquisition of functional rat monoclonal antibodies and facilitate their expression and feasibility using a single plasmid.

Electronic supplementary material

The online version of this article (10.1186/s12865-018-0274-8) contains supplementary material, which is available to authorized users.

Adeno-associated virus gene delivery of broadly neutralizing antibodies as prevention and therapy against HIV-1

Vectored gene delivery of HIV-1 broadly neutralizing antibodies (bNAbs) using recombinant adeno-associated virus (rAAV) is a promising alternative to conventional vaccines for preventing new HIV-1 infections and for therapeutically suppressing established HIV-1 infections. Passive infusion of single bNAbs has already shown promise in initial clinical trials to temporarily decrease HIV-1 load in viremic patients, and to delay viral rebound from latent reservoirs in suppressed patients during analytical treatment interruptions of antiretroviral therapy. Long-term, continuous, systemic expression of such bNAbs could be achieved with a single injection of rAAV encoding antibody genes into muscle tissue, which would bypass the challenges of eliciting such bNAbs through traditional vaccination in naïve patients, and of life-long repeated passive transfers of such biologics for therapy. rAAV delivery of single bNAbs has already demonstrated protection from repeated HIV-1 vaginal challenge in humanized mouse models, and phase I clinical trials of this approach are underway. Selection of which individual, or combination of, bNAbs to deliver to counter pre-existing resistance and the rise of escape mutations in the virus remains a challenge, and such choices may differ depending on use of this technology for prevention versus therapy.

Construction strategies for developing expression vectors for recombinant monoclonal antibody production in CHO cells

Recent years have seen the use of recombinant proteins in the treatment of different diseases. Among them, monoclonal antibodies (mAbs) are currently the fastest growing class of bio-therapeutic recombinant proteins. Chinese hamster ovary (CHO) cells are the most commonly used host cells for production of these recombinant mAbs. Expression vectors determine the expression level and quality of recombinant mAbs. Currently, few construction strategies for recombinant mAbs expression vectors in CHO cells have been developed, including monocistronic vector, multiple-promoter expression vector, and tricistronic vector mediated by internal ribosome entry site (IRES) or Furin-2A element. Among them, Furin-2A-mediated vector is an effective approach due to advantages of high "self-cleavage" efficiency, and equal expression of light and heavy chains from a single open reading frame. Here, we have reviewed the progress in development of different strategies for constructing recombinant mAb expression vectors in CHO cells and its potential advantages and disadvantages.

"Therapeutic applications of the 'NPGP' family of viral 2As"

Oligopeptide "2A" and "2A-like" sequences ("2As"; 18-25aa) are found in a range of RNA virus genomes controlling protein biogenesis through "recoding" of the host-cell translational apparatus. Insertion of multiple 2As within a single open reading frame (ORF) produces multiple proteins; hence, 2As have been used in a very wide range of biotechnological and biomedical applications. During translation, these 2A peptide sequences mediate a eukaryote-specific, self-"cleaving" event, termed "ribosome skipping" with very high efficiency. A particular advantage of using 2As is the ability to simultaneously translate a number of proteins at an equal level in all eukaryotic systems although, naturally, final steady-state levels depend upon other factors-notably protein stability. By contrast, the use of internal ribosome entry site elements for co-expression results in an unbalanced expression due to the relative inefficiency of internal initiation. For example, a 1:1 ratio is of particular importance for the biosynthesis of the heavy-chain and light-chain components of antibodies: highly valuable as therapeutic proteins. Furthermore, each component of these "artificial polyprotein" systems can be independently targeted to different sub-cellular sites. The potential of this system was vividly demonstrated by concatenating multiple gene sequences, linked via 2A sequences, into a single, long, ORF-a polycistronic construct. Here, ORFs comprising the biosynthetic pathways for violacein (five gene sequences) and β-carotene (four gene sequences) were concatenated into a single cistron such that all components were co-expressed in the yeast Pichia pastoris. In this review, we provide useful information on 2As to serve as a guide for future utilities of this co-expression technology in basic research, biotechnology, and clinical applications.

Neutralizing Anti-Hemagglutinin Monoclonal Antibodies Induced by Gene-Based Transfer Have Prophylactic and Therapeutic Effects on Influenza Virus Infection

Hemagglutinin (HA) of influenza virus is a major target for vaccines. HA initiates the internalization of the virus into the host cell by binding to host sialic acid receptors; therefore, inhibition of HA can significantly prevent influenza virus infection. However, the high diversity of HA permits the influenza virus to escape from host immunity. Moreover, the vaccine efficacy is poor in some high-risk populations (e.g., elderly or immunocompromised patients). Passive immunization with anti-HA monoclonal antibodies (mAbs) is an attractive therapy; however, this method has high production costs and requires repeated inoculations. To address these issues, several methods for long-term expression of mAb against influenza virus have been developed. Here, we provide an overview of methods using plasmid and viral adeno-associated virus (AAV) vectors that have been modified for higher expression of neutralizing antibodies in the host. We also examine two methods of injection, electro-transfer and hydrodynamic injection. Our results show that antibody gene transfer is effective against influenza virus infection even in immunocompromised mice, and antibody expression was detected in the serum and upper respiratory tract. We also demonstrate this method to be effective following influenza virus infection. Finally, we discuss the perspective of passive immunization with antibody gene transfer for future clinical trials.

Immunomimetic Designer Cells Protect Mice from MRSA Infection

Many community- and hospital-acquired bacterial infections are caused by antibiotic-resistant pathogens. Methicillin-resistant Staphylococcus aureus (MRSA) predisposes humans to invasive infections that are difficult to eradicate. We designed a closed-loop gene network programming mammalian cells to autonomously detect and eliminate bacterial infections. The genetic circuit contains human Toll-like receptors as the bacterial sensor and a synthetic promoter driving reversible and adjustable expression of lysostaphin, a bacteriolytic enzyme highly lethal to S. aureus. Immunomimetic designer cells harboring this genetic circuit exhibited fast and robust sense-and-destroy kinetics against live staphylococci. When tested in a foreign-body infection model in mice, microencapsulated cell implants prevented planktonic MRSA infection and reduced MRSA biofilm formation by 91%. Notably, this system achieved a 100% cure rate of acute MRSA infections, whereas conventional vancomycin treatment failed. These results suggest that immunomimetic designer cells could offer a therapeutic approach for early detection, prevention, and cure of pathogenic infections in the post-antibiotic era.

Video Abstract

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A closed-loop gene network with bacterial sense-and-destroy actuation

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Direct diagnosis of implant-associated infections through blood biomarkers

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Early prevention of MRSA infection, as well as biofilm formation, in vivo

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Curing acute MRSA infections as an alternative to antibiotic therapy

Synthetic cytokine receptors transmit biological signals using artificial ligands

Cytokine-induced signal transduction is executed by natural biological switches, which among many others control immune-related processes. Here, we show that synthetic cytokine receptors (SyCyRs) can induce cytokine signaling using non-physiological ligands. High-affinity GFP- and mCherry-nanobodies were fused to transmembrane and intracellular domains of the IL-6/IL-11 and IL-23 cytokine receptors gp130 and IL-12Rβ1/IL-23R, respectively. Homo- and heterodimeric GFP:mCherry fusion proteins as synthetic cytokine-like ligands were able to induce canonical signaling in vitro and in vivo. Using SyCyR ligands, we show that IL-23 receptor homodimerization results in its activation and IL-23-like signal transduction. Moreover, trimeric receptor assembly induces trans-phosphorylation among cytokine receptors with associated Janus kinases. The SyCyR technology allows biochemical analyses of transmembrane receptor signaling in vitro and in vivo, cell-specific activation through SyCyR ligands using transgenic animals and possible therapeutic regimes involving non-physiological targets during immunotherapy.

Cytokine-induced signaling acts as an ON/OFF switch dependent on the presence of ligands. Here the authors construct synthetic cytokine receptors responsive to synthetic ligands able to activate canonical signaling pathways.

Sustained secretion of anti-tumor necrosis factor α monoclonal antibody from ex vivo genetically engineered dermal tissue demonstrates therapeutic activity in mouse model of rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a symmetric inflammatory polyarthritis associated with high concentrations of pro-inflammatory, cytokines including tumor necrosis factor (TNF)-α. Adalimumab is a monoclonal antibody (mAb) that binds TNF-α, and is widely used to treat RA. Despite its proven clinical efficacy, adalimumab and other therapeutic mAbs have disadvantages, including the requirement for repeated bolus injections and the appearance of treatment limiting anti-drug antibodies. To address these issues, we have developed an innovative ex vivo gene therapy approach, termed transduced autologous restorative gene therapy (TARGT), to produce and secrete adalimumab for the treatment of RA.

METHODS

Helper-dependent (HD) adenovirus vector containing adalimumab light and heavy chain coding sequences was used to transduce microdermal tissues and cells of human and mouse origin ex vivo, rendering sustained secretion of active adalimumab. The genetically engineered tissues were subsequently implanted in a mouse model of RA.

RESULTS

Transduced human microdermal tissues implanted in SCID mice demonstrated 49 days of secretion of active adalimumab in the blood, at levels of tens of microgram per milliliter. In addition, transduced autologous dermal cells were implanted in the RA mouse model and demonstrated statistically significant amelioration in RA symptoms compared to naïve cell implantation and were similar to recombinant adalimumab bolus injections.

CONCLUSIONS

The results of the present study report microdermal tissues engineered to secrete active adalimumab as a proof of concept for sustained secretion of antibody from the novel ex vivo gene therapy TARGT platform. This technology may now be applied to a range of antibodies for the therapy of other diseases.

Efficient development of a stable cell pool for antibody production using a single plasmid

Therapeutic antibodies are the fastest growing group of biopharmaceuticals. Evaluation of drug candidates requires a sufficient amount of antibodies. Production of antibodies with stable cell pools is an efficient strategy to produce grams of proteins for drug candidate selection. Many methods have been described for developing stable cell pools for antibody expression. However, most of the reported methods are laborious due to the low frequency of high producers. In this study, we determined optimal vectors and screening parameters to develop a strategy for efficient construction of stable antibody expressing cell pools. The cell pool constructed using the optimized strategy consistently yielded a higher expression titer, up to 10-fold improvement. Further, this method resulted in a higher ratio of the cell pools with the main product peak above 95% as assessed by size-exclusion chromatography. High producers could be obtained by means of screening five 96-well plates. This strategy will greatly reduce clone-screening size during Clinical Lead Selection. This study provides a platform with efficient design of plasmids and screening strategies for significant cost and labour savings in high expression of two-subunit proteins such as antibodies.

Gene Transfer of ZMapp Antibodies Mediated by Recombinant Adeno-Associated Virus Protects Against Ebola Infections

Vectored delivery of the ZMapp antibody cocktail (c2G4, c4G7, and c13C6) by using recombinant adeno-associated viruses (rAAVs) could be useful for preventive immunization against Ebola virus infections because rAAVs can generate long-term antibody expression. Three rAAVs (serotype 9) encoding chimeric ZMapp antibodies were produced by triple-plasmid transfection up to 10 L-scale in WAVE bioreactors using HEK293 cells grown in suspension/serum-free conditions. Efficacy of AAV-c2G4 via intravenous (i.v.), intramuscular (i.m.), and intranasal (i.n.) routes of administration was evaluated in mice with two different doses of 2.7 × 10¹⁰ and 13.0 × 10¹⁰ vector genomes (vg). The best protective efficacies after Ebola challenge were obtained with the i.v. and i.m. routes. Serum concentrations of ZMapp antibodies positively correlated with survivability. Efficacy of the rAAV-ZMapp cocktail was then evaluated at a higher dose of 30.0 × 10¹⁰ vg. It conferred a more robust protection (90% i.v. and 60% i.m.) than rAAV-c4G7 (30%) and rAAV-c13C6 (70%), both administered separately at the same dose. Delivery of rAAV-c2G4 alone achieved up to 100% protection (100% i.v. and 90% i.m.) at the same dose. In conclusion, the preventive treatment was effective in mice. However, no advantage was observed for using the rAAV-ZMapp cocktail in comparison to the utilization of the single rAAV-c2G4.

Prolonged in vivo expression and anti-tumor response of DNA-based anti-HER2 antibodies

Antibody gene transfer presents an appealing alternative to conventional antibody protein therapy. This pre-clinical study evaluates the impact of various parameters on the pharmacokinetics and efficacy of in vivo expressed DNA-based anti-HER2 monoclonal antibodies (mAbs), newly engineered and delivered via intramuscular electrotransfer in mice. Plasma concentrations of trastuzumab and 4D5, its murine IgG1 equivalent, peaked on average between 1–15 µg/ml, depending on the administration and configuration of the encoding plasmid DNA (pDNA). A dual expression cassette system outperformed a single 2A-based cassette, and the CAG promoter was superior to a muscle-specific ΔUSE-based promoter. A ‘gene therapy-compatible’ Gene Transport Unit (gtGTU, FIT Biotech), a plasmid backbone that co-encodes viral elements, failed to improve in vivo reporter and mAb expression compared to a conventional plasmid. In BALB/c mice, trastuzumab detection was lost within two weeks after pDNA administration due to anti-drug antibodies. This host immune response was addressed by expressing trastuzumab in immune-compromised mice, or by gene transfer of murine 4D5 in BALB/c mice. Both approaches maintained single-digit µg/ml mAb concentrations for at least six to nine months, and allowed to boost mAb expression over time by pDNA re-dosing. In a breast cancer mouse model, prophylactic and therapeutic DNA-based trastuzumab or 4D5 led to complete tumor regressions, thereby rivalling with the administration of milligrams of mAb protein. In conclusion, our study demonstrates proof of concept for antibody gene transfer in cancer, provides critical insights in the engineering and application of DNA-based antibodies, and serves to advance this modality in oncology and beyond.

Multigene delivery in mammalian cells: Recent advances and applications

Systems for multigene delivery in mammalian cells, particularly in the context of genome engineering, have gained a lot of attention in biomolecular research and medicine. Initially these methods were based on RNA polymerase II promoters and were used for the production of protein complexes and for applications in cell biology such as reprogramming of somatic cells to stem cells. Emerging technologies such as CRISPR/Cas9-based genome engineering, which enable any alteration at the genomic level of an organism, require additional elements including U6-driven expression cassettes for RNA expression and homology constructs for designed genome modifications. For these applications, systems with high DNA capacity, flexibility and transfer rates are needed. In this article, we briefly give an update on some of recent strategies that facilitate multigene assembly and delivery into mammalian cells. Also, we review applications in various fields of biology that rely on multigene delivery systems.

Genome-Edited Cell Lines for High-Throughput Screening

Measurement of gene expression for high-throughput screening is an increasingly used technique that has been developed for not only gene dosage disorders resulting from disease-associated copy number variations, but also for induction/repression of genes modulating the severity of a disease phenotype. Traditional methods have employed transient or stable transfection of reporter constructs in which a single reporter is driven by selected regulatory elements from the candidate gene. However, individual regulatory elements are inherently unable to capture the integrated regulation of multiple enhancers at the endogenous locus, and random reporter insertion can result in neighborhood effects that impact the physiological responsiveness of the reporter. Therefore, we outline a general method of employing genome editing to insert reporters into the 3' UTR of a candidate gene, which has been used successfully in our studies of the Pmp22 gene associated with Charcot-Marie-Tooth disease. The method employs genome editing to insert two nonhomologous reporters that maximize the efficiency of identification of biologically active molecules through concordant responses in small molecule screening. We include a number of aspects of the design and construction of these reporter assays that will be applicable to creation of similar assays in a variety of cell types.

Exchanging the order of carotenogenic genes linked by porcine teschovirus-1 2A peptide enable to optimize carotenoid metabolic pathway in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae serves as a promising host for the production of a wide range of chemical compounds and fuels. Currently, simultaneous expression of several genes could be achieved via the use of 2A viral peptides, yet detailed characterizations to assess the discrepancy of different orders of genes linked by 2A peptides are rarely sufficient. In this study, we investigated the effects of the order of genes linked by porcine teschovirus-1 2A (P2A) peptide on the metabolic pathway in S. cerevisiae. A heterologous carotenoid biosynthetic system involving nine kinds of polycistronic expression of codon-optimized carotenogenic genes GGPPS, CARB and CARRP from Blakeslea trispora was introduced into S. cerevisiae. The order of genes in the polycistronic segment was exchanged; β-carotene production by engineered yeasts was significantly different. The highest β-carotene yield was achieved in transformants carrying the plasmid, with CARB as the first gene in the polycistronic construct regardless of the location of GGPPS, CARRP. In addition, we found that β-carotene production was coupled with the growth in engineered strain with the highest β-carotene content during the shake flask fermentation and fed-batch fermentation. A novel microbial heterologous carotenoid production system was established by optimizing the order of genes linked by P2A peptide sequences in a polycistronic expression construct. The observation of the importance of the order in a polycistronic construct may be used to increase yields in other P2A peptide-containing expression systems.

The yeast Saccharomyces cerevisiae serves as a promising host for the production of a wide range of chemical compounds and fuels.

An Effective Way of Producing Fully Assembled Antibody in Transgenic Tobacco Plants by Linking Heavy and Light Chains via a Self-Cleaving 2A Peptide

Therapeutic monoclonal antibodies (mAbs) have evolved into an important class of effective medicine in treatment of various diseases. Since the antibody molecule consists of two identical heavy chains (HC) and two light chains (LC), each chain encoded by two different genes, their expressions at similar levels are critical for efficient assembly of functional recombinant mAbs. Although the plant-based expression system has been tested to produce fully assembled recombinant mAbs, coordinately expressing HC and LC at similar levels in a transgenic plant remains a challenge. A sequence coding for a foot-and-mouth disease virus (FMDV) 2A peptide has been successfully used to link two or more genes, which enable the translated polyprotein to be "self-cleaved" into individual protein in various genetically modified organisms. In the present study, we exploited the usage of F2A in Ebola virus monoclonal antibody (EBOV mAb) production. We found that transgenic tobacco plants carrying a transcription unit containing HC and LC linked by 2A not only produced similar levels of HC and LC but also rendered a higher yield of fully assembled EBOV mAb compared to those expressing HC and LC in two independent transcription units. Purified EBOV mAb bound to an Ebola epitope peptide with apparent K_d -values of 90.13-149.2 nM, indicating its proper assembly and high affinity binding to Ebola epitope peptide. To our knowledge, this is the first report showing mAb production by overexpressing a single transcription unit consisting of HC, LC and 2A in stable transformed tobacco plants.

Production of Functional Anti-Ebola Antibodies in Pichia pastoris

The 2013-2016 Ebola outbreak highlighted the limited treatment options and lack of rapid response strategies for emerging pathogen outbreaks. Here, we propose an efficient development cycle using glycoengineered Pichia pastoris to produce monoclonal antibody cocktails against pathogens. To enable rapid genetic engineering of P. pastoris, we introduced a genomic landing pad for reliable recombinase-mediated DNA integration. We then created strains expressing each of the three monoclonal antibodies that comprise the ZMapp cocktail, and demonstrated that the secreted antibodies bind to the Ebola virus glycoprotein by immunofluorescence assay. We anticipate that this approach could accelerate the production of therapeutics against future pathogen outbreaks.

Gene therapy for colorectal cancer using adenovirus-mediated full-length antibody, cetuximab

Cetuximab is a chimeric monoclonal antibody, approved to treat patients with metastatic colorectal cancer (mCRC), head and neck squamous cell carcinoma (HNSCC), non-small-cell lung cancer (NSCLC) for years. It functions by blocking the epidermal growth factor receptor (EGFR) from receiving signals or interacting with other proteins. Although the demand for cetuximab for the treatment of cancer patients in clinics is increasing, the complicated techniques involved and its high cost limit its wide applications. Here, a new, cheaper form of cetuximab was generated for cancer gene therapy. This was achieved by cloning the full-length cetuximab antibody into two serotypes of adenoviral vectors, termed as AdC68-CTB and Hu5-CTB. In vivo studies showed that a single dose of AdC68-CTB or Hu5-CTB induced sustained cetuximab expression and dramatically suppressed tumor growth in NCI-H508– or DiFi-inoculated nude mice. In conclusion, gene therapy using adenovirus expressing full-length cetuximab could be a novel alternative method for the effective treatment of colorectal cancer.

AAV8-antiVEGFfab Ocular Gene Transfer for Neovascular Age-Related Macular Degeneration

Sustained suppression of VEGF is needed in many patients with neovascular age-related macular degeneration (NVAMD), and gene transfer of a VEGF-neutralizing protein is a promising approach to achieve it. Initial clinical trials testing this approach have shown encouraging signals, but evidence of robust transgene expression and consistent antiangiogenic and antipermeability activity has been lacking. In this study, we demonstrate expression of an anti-human VEGF antibody fragment (antiVEGFfab) after subretinal injection of AAV8-antiVEGFfab. In transgenic mice expressing human VEGF in retina (rho/VEGF mice), a model of type 3 choroidal neovascularization (NV), eyes injected with ≥1 × 10⁷ gene copies (GC) of AAV8-antiVEGFfab had significantly less mean area of NV than null vector-injected eyes. A dose-dependent response was observed with modest reduction of NV with ≤3 × 10⁷, >50% reduction with ≥1 × 10⁸ GC and almost complete elimination of NV with 3 × 10⁹ or 1 × 10¹⁰ GC. In Tet/opsin/VEGF mice, in which doxycycline-induced high expression of VEGF leads to severe vascular leakage and exudative retinal detachment (RD), reduction of total RD by 70%-80% occurred with 3 × 10⁹ or 1 × 10¹⁰ GC of AAV8-antiVEGFfab, an effect that was sustained for at least a month. These data strongly support initiating clinical trials testing subretinal injection of AAV8-antiVEGFfab in patients with NVAMD.

Evaluating the efficiency of CHEF and CMV promoter with IRES and Furin/2A linker sequences for monoclonal antibody expression in CHO cells

In recent years, monoclonal antibodies (mAbs) have been developed as powerful therapeutic and diagnostic agents and Chinese hamster ovary (CHO) cells have emerged as the dominant host for the recombinant expression of these proteins. A critical step in recombinant expression is the utilization of strong promoters, such as the Chinese Hamster Elongation Factor-1α (CHEF-1) promoter. To compare the strengths of CHEF with cytomegalovirus (CMV) promoter for mAb expression in CHO cells, four bicistronic vectors bearing either internal ribosome entry site (IRES) or Furin/2A (F2A) sequences were designed. The efficiency of these promoters was evaluated by measuring level of expressed antibody in stable cell pools. Our results indicated that CHEF promoter-based expression of mAbs was 2.5 fold higher than CMV-based expression in F2A-mediated vectors. However, this difference was less significant in IRES-mediated mAb expressing cells. Studying the stability of the F2A expression system in the course of 18 weeks, we observed that the cells having CHEF promoter maintained their antibody expression at higher level than those transfected with CMV promoter. Further analyses showed that both IRES-mediated vectors, expressed mAbs with correct size, whereas in antibodies expressed via F2A system heterogeneity of light chains were detected due to incomplete furin cleavage. Our findings indicated that the CHEF promoter is a viable alternative to CMV promoter-based expression in F2A-mediated vectors by providing both higher expression and level of stability.

Polycistronic gene expression in Aspergillus niger

Background

Genome mining approaches predict dozens of biosynthetic gene clusters in each of the filamentous fungal genomes sequenced so far. However, the majority of these gene clusters still remain cryptic because they are not expressed in their natural host. Simultaneous expression of all genes belonging to a biosynthetic pathway in a heterologous host is one approach to activate biosynthetic gene clusters and to screen the metabolites produced for bioactivities. Polycistronic expression of all pathway genes under control of a single and tunable promoter would be the method of choice, as this does not only simplify cloning procedures, but also offers control on timing and strength of expression. However, polycistronic gene expression is a feature not commonly found in eukaryotic host systems, such as Aspergillus niger.

Results

In this study, we tested the suitability of the viral P2A peptide for co-expression of three genes in A. niger. Two genes descend from Fusarium oxysporum and are essential to produce the secondary metabolite enniatin (esyn1, ekivR). The third gene (luc) encodes the reporter luciferase which was included to study position effects. Expression of the polycistronic gene cassette was put under control of the Tet-On system to ensure tunable gene expression in A. niger. In total, three polycistronic expression cassettes which differed in the position of luc were constructed and targeted to the pyrG locus in A. niger. This allowed direct comparison of the luciferase activity based on the position of the luciferase gene. Doxycycline-mediated induction of the Tet-On expression cassettes resulted in the production of one long polycistronic mRNA as proven by Northern analyses, and ensured comparable production of enniatin in all three strains. Notably, gene position within the polycistronic expression cassette matters, as, luciferase activity was lowest at position one and had a comparable activity at positions two and three.

Conclusions

The P2A peptide can be used to express at least three genes polycistronically in A. niger. This approach can now be applied to heterologously express entire secondary metabolite gene clusters polycistronically or to co-express any genes of interest in equimolar amounts.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0780-z) contains supplementary material, which is available to authorized users.

In Vivo Production of Monoclonal Antibodies by Gene Transfer via Electroporation Protects against Lethal Influenza and Ebola Infections

Monoclonal antibodies (mAbs) have wide clinical utility, but global access is limited by high costs and impracticalities associated with repeated passive administration. Here, we describe an optimized electroporation-based DNA gene transfer platform technology that can be utilized for production of functional mAbs in vivo, with the potential to reduce costs and administration burdens. We demonstrate that multiple mAbs can be simultaneously expressed at protective concentrations for a protracted period of time using DNA doses and electroporation conditions that are feasible clinically. The expressed mAbs could also protect mice against lethal influenza or Ebola virus challenges. Our findings suggest that this DNA gene transfer platform technology could be a game-changing advance that expands access to effective mAb therapeutics globally.

Selective antibody activation through protease-activated pro-antibodies that mask binding sites with inhibitory domains

Systemic injection of therapeutic antibodies may cause serious adverse effects due to on-target toxicity to the antigens expressed in normal tissues. To improve the targeting selectivity to the region of disease sites, we developed protease-activated pro-antibodies by masking the binding sites of antibodies with inhibitory domains that can be removed by proteases that are highly expressed at the disease sites. The latency-associated peptide (LAP), C2b or CBa of complement factor 2/B were linked, through a substrate peptide of matrix metalloproteinase-2 (MMP-2), to an anti-epidermal growth factor receptor (EGFR) antibody and an anti-tumor necrosis factor-α (TNF-α) antibody. Results showed that all the inhibitory domains could be removed by MMP-2 to restore the binding activities of the antibodies. LAP substantially reduced (53.8%) the binding activity of the anti-EGFR antibody on EGFR-expressing cells, whereas C2b and CBa were ineffective (21% and 9.3% reduction, respectively). Similarly, LAP also blocked 53.9% of the binding activity of the anti-TNF-α antibody. Finally, molecular dynamic simulation showed that the masking efficiency of LAP, C2b and CBa was 33.7%, 10.3% and −5.4%, respectively, over the binding sites of the antibodies. This strategy may aid in designing new protease-activated pro-antibodies that attain high therapeutic potency yet reduced systemic on-target toxicity.

Targeted insertion of an anti-CD2 monoclonal antibody transgene into the GGTA1 locus in pigs using FokI-dCas9

Xenotransplantation from pigs has been advocated as a solution to the perennial shortage of donated human organs and tissues. CRISPR/Cas9 has facilitated the silencing of genes in donor pigs that contribute to xenograft rejection. However, the generation of modified pigs using second-generation nucleases with much lower off-target mutation rates than Cas9, such as FokI-dCas9, has not been reported. Furthermore, there have been no reports on the use of CRISPR to knock protective transgenes into detrimental porcine genes. In this study, we used FokI-dCas9 with two guide RNAs to integrate a 7.1 kilobase pair transgene into exon 9 of the GGTA1 gene in porcine fetal fibroblasts. The modified cells lacked expression of the αGal xenoantigen, and secreted an anti-CD2 monoclonal antibody encoded by the transgene. PCR and sequencing revealed precise integration of the transgene into one allele of GGTA1, and a small deletion in the second allele. The cells were used for somatic cell nuclear transfer to generate healthy male knock-in piglets, which did not express αGal and which contained anti-CD2 in their serum. We have therefore developed a versatile high-fidelity system for knocking transgenes into the pig genome for xenotransplantation purposes.

Antibody gene transfer with adeno-associated viral vectors as a method for HIV prevention

Broadly neutralizing antibodies (bNAbs) against human immunodeficiency virus (HIV) show great promise in HIV prevention as they are capable of potently neutralizing a considerable breadth of genetically diverse strains. Passive transfer of monoclonal bNAb proteins can confer protection in animal models of HIV infection at modest concentrations, inspiring efforts to develop an HIV vaccine capable of eliciting bNAb responses. However, these antibodies demonstrate high degrees of somatic mutation and other unique characteristics that may hinder the ability of conventional approaches to consistently and effectively produce bNAb analogs. As an alternative strategy, we and others have proposed vector-mediated gene transfer to generate long-term, systemic production of bNAbs in the absence of immunization. Herein, we review the use of adeno-associated virus (AAV) vectors for delivery of HIV bNAbs and antibody-like proteins and summarize both the advantages and disadvantages of this strategy as a method for HIV prevention.

Engineering antibody-like inhibitors to prevent and treat HIV-1 infection

Purpose of review

Here we discuss recently developed HIV-1 entry inhibitors that can target multiple epitopes on the HIV-1 envelope glycoprotein (Env), with an emphasis on eCD4-Ig. Some of these inhibitors are more potent and broader than any single antibody characterized to date. We also discuss the use of recombinant adeno-associated virus (rAAV) vectors as a platform for long-term expression of these inhibitors.

Recent findings

Much of the exterior of HIV-1 Env can be targeted by broadly neutralizing antibodies (bNAbs). Recent studies combine the variable regions or Fabs from different bNAbs, often with the receptor-mimetic components, to create broad, potent, and hard-to-escape inhibitors. rAAV vectors can express these inhibitors for years in vivo, highlighting their ability to prevent or treat HIV-1 infection.

Summary

By targeting multiple epitopes on Env, bispecific and antibody-like inhibitors can be broader and more potent than bNAbs. These inhibitors can provide long-term protection from, and perhaps suppression of, HIV-1 if they are administered by a delivery platform, like rAAV vectors, but only after rAAV limitations are addressed.

Progress in HIV-1 antibody research using humanized mice

PURPOSE OF REVIEW

Recent discoveries of highly potent broadly HIV-1 neutralizing antibodies provide new opportunities to successfully prevent, treat, and potentially cure HIV-1 infection. To test their activity in vivo, humanized mice have been shown to be a powerful model and were used to investigate antibody-mediated prevention and therapy approaches. In this review, we will summarize recent findings in humanized mice that have informed on the potential use of broadly neutralizing antibodies targeting HIV-1 in humans.

RECENT FINDINGS

Humanized mouse models have been used to demonstrate the antiviral efficacy of HIV-1 neutralizing antibodies in vivo. It has been shown that a combination of antibodies can suppress viremia below the limit of detection and targets the HIV-1 reservoir. Moreover, passively administered antibodies and vector-mediated antibody production protect humanized mice from HIV-1 infection. Finally, immunization studies in knock-in/transgenic mice carrying human antibody gene segments have informed on potential vaccination strategies to induce broad and potent HIV-1 neutralizing antibodies.

SUMMARY

Humanized mouse models are of great value for HIV-1 research. They represent a highly versatile in vivo system to investigate novel approaches for HIV-1 prevention and therapy and expedite the critical translation from basic findings to clinical application.

Use of a gamma-2 herpesvirus as a vector to deliver antibodies to rhesus monkeys

The gamma-2 herpesvirus of rhesus monkeys, rhesus monkey rhadinovirus (RRV), persists principally in B cells of its host. We constructed recombinant strains of RRV expressing the rhesus monkey-derived anti-SIV monoclonal antibodies 4L6 and 5L7 and compared the RRV-mediated in vivo delivery of these antibodies in rhesus monkeys with previous studies that utilized intramuscular delivery with an adeno-associated virus (AAV) vector. Recombinant RRV-4L6 and RRV-5L7 were both shown to stably produce the antibodies in persistently infected B-cell lines in culture. Two RRV-negative rhesus monkeys were experimentally infected with recombinant RRV-4L6 and two with recombinant RRV-5L7. Following infection, the appearance of the delivered antibody was readily detected in all four animals. However, the levels of the delivered antibody were considerably lower than what has been typically observed following intramuscular AAV delivery. Furthermore, three of the four monkeys had an antibody response to the delivered antibody as had been observed previously with intramuscular AAV delivery of these same antibodies. We conclude that this recombinant herpesvirus has no inherent advantage over AAV for delivery of potentially therapeutic monoclonal antibodies in a rhesus monkey model.

State of play and clinical prospects of antibody gene transfer

Recombinant monoclonal antibodies (mAbs) are one of today's most successful therapeutic classes in inflammatory diseases and oncology. A wider accessibility and implementation, however, is hampered by the high product cost and prolonged need for frequent administration. The surge in more effective mAb combination therapies further adds to the costs and risk of toxicity. To address these issues, antibody gene transfer seeks to administer to patients the mAb-encoding nucleotide sequence, rather than the mAb protein. This allows the body to produce its own medicine in a cost- and labor-effective manner, for a prolonged period of time. Expressed mAbs can be secreted systemically or locally, depending on the production site. The current review outlines the state of play and clinical prospects of antibody gene transfer, thereby highlighting recent innovations, opportunities and remaining hurdles. Different expression platforms and a multitude of administration sites have been pursued. Viral vector-mediated mAb expression thereby made the most significant strides. Therapeutic proof of concept has been demonstrated in mice and non-human primates, and intramuscular vectored mAb therapy is under clinical evaluation. However, viral vectors face limitations, particularly in terms of immunogenicity. In recent years, naked DNA has gained ground as an alternative. Attained serum mAb titers in mice, however, remain far below those obtained with viral vectors, and robust pharmacokinetic data in larger animals is limited. The broad translatability of DNA-based antibody therapy remains uncertain, despite ongoing evaluation in patients. RNA presents another emerging platform for antibody gene transfer. Early reports in mice show that mRNA may be able to rival with viral vectors in terms of generated serum mAb titers, although expression appears more short-lived. Overall, substantial progress has been made in the clinical translation of antibody gene transfer. While challenges persist, clinical prospects are amplified by ongoing innovations and the versatility of antibody gene transfer. Clinical introduction can be expedited by selecting the platform approach currently best suited for the mAb or disease of interest. Innovations in expression platform, administration and antibody technology are expected to further improve overall safety and efficacy, and unlock the vast clinical potential of antibody gene transfer.

Coordinated protein co-expression in plants by harnessing the synergy between an intein and a viral 2A peptide

A novel approach is developed for coordinated expression of multiple proteins from a single transgene in plants. An Ssp DnaE mini-intein variant engineered for hyper-N-terminal autocleavage is covalently linked to the foot-and-mouth disease virus 2A (F2A) peptide with unique ribosome skipping property, via a peptide linker, to create an 'IntF2A' self-excising fusion protein domain. This IntF2A domain acts, in cis, to direct highly effective release of its flanking proteins of interest (POIs) from a 'polyprotein' precursor in plants. This is successfully demonstrated in stably transformed cultured tobacco cells as well as in different organs of transgenic tobacco plants. Highly efficient polyprotein processing mediated by the IntF2A domain was also demonstrated in lettuce and Nicotiana benthamiana based on transient expression. Protein constituents released from the polyprotein precursor displayed proper function and accumulated at similar levels inside the cells. Importantly, no C-terminal F2A extension remains on the released POIs. We demonstrated co-expression of as many as three proteins in plants without compromising expression levels when compared with those using single-protein vectors. Accurate differential cellular targeting of released POIs is also achieved. In addition, we succeeded in expressing a fully assembled and functional chimeric anti-His Tag antibody in N. benthamiana leaves. The IntF2A-based polyprotein transgene system overcomes key impediments of existing strategies for multiprotein co-expression in plants, which is particularly important for gene/trait stacking.