Membrane penetrating peptides greatly enhance baculovirus transduction efficiency into mammalian cells

Baculovirus Display of Peptides and Proteins for Medical Applications

Baculoviridae is a large family of arthropod-infective viruses. Recombinant baculoviruses have many applications, the best known is as a system for large scale protein production in combination with insect cell cultures. More recently recombinant baculoviruses have been utilized for the display of proteins of interest with applications in medicine. In the present review we analyze the different strategies for the display of proteins and peptides on the surface of recombinant baculoviruses and provide some examples of the different proteins displayed. We analyze briefly the commercially available systems for recombinant baculovirus production and display and discuss the future of this emerging and powerful technology.

Baculoviruses in Gene Therapy and Personalized Medicine

This review will outline the role of baculoviruses in gene therapy and future potential in personalized medicine. Baculoviruses are a safe, non-toxic, non-integrative vector with a large cloning capacity. Baculoviruses are also a highly adaptable, low-cost vector with a broad tissue and host tropism due to their ability to infect both quiescent and proliferating cells. Moreover, they only replicate in insect cells, not mammalian cells, improving their biosafety. The beneficial properties of baculoviruses make it an attractive option for gene delivery. The use of baculoviruses in gene therapy has advanced significantly, contributing to vaccine production, anti-cancer therapies and regenerative medicine. Currently, baculoviruses are primarily used for recombinant protein production and vaccines.  This review will also discuss methods to optimize baculoviruses protein production and mammalian cell entry, limitations and potential for gene therapy and personalized medicine. Limitations such as transient gene expression, complement activation and virus fragility are discussed in details as they can be overcome through further genetic modifications and other methods. This review concludes that baculoviruses are an excllent candidate for gene therapy, personalized medicine and other biotherapeutic applications.

The Utilization of Cell-Penetrating Peptides in the Intracellular Delivery of Viral Nanoparticles

Viral particles (VPs) have evolved so as to efficiently enter target cells and to deliver their genetic material. The current state of knowledge allows us to use VPs in the field of biomedicine as nanoparticles that are safe, easy to manipulate, inherently biocompatible, biodegradable, and capable of transporting various cargoes into specific cells. Despite the fact that these virus-based nanoparticles constitute the most common vectors used in clinical practice, the need remains for further improvement in this area. The aim of this review is to discuss the potential for enhancing the efficiency and versatility of VPs via their functionalization with cell-penetrating peptides (CPPs), short peptides that are able to translocate across cellular membranes and to transport various substances with them. The review provides and describes various examples of and means of exploitation of CPPs in order to enhance the delivery of VPs into permissive cells and/or to allow them to enter a broad range of cell types. Moreover, it is possible that CPPs are capable of changing the immunogenic properties of VPs, which could lead to an improvement in their clinical application. The review also discusses strategies aimed at the modification of VPs by CPPs so as to create a useful cargo delivery tool.

Selected application of peptide molecules as pharmaceutical agents and in cosmeceuticals

Introduction: Peptide molecules are being vastly investigated as an emerging class of therapeutic molecules in recent years. Currently, 60 peptides have been approved by the US Food and Drug Administration (FDA), and more would enter the market in near future. Peptides have already opened their ways into cosmeceutical and food industries as well.Areas covered: Antibodies, vaccines, and antimicrobial agents are the major classes of therapeutic peptides. Additionally, peptides may be employed in drug development to support cell penetration or targeting. The interest in antimicrobial peptides is surging due to the increasing risk of antibiotic-resistant pathogens. Peptide vaccines with their significant advantages compared with traditional vaccines, are expected to find their place in coming years, especially for cancer, microbial and allergen-specific immunotherapy. The usage of peptides in cosmeceuticals is also growing rapidly.Expert opinion: Peptide synthesis has become accessible, and advances in peptide engineering, sequencing technologies, and structural bioinformatics have resulted in the rational designing of novel peptides. All these advancements would lead to the more prominent roles of peptides in the mentioned areas. In this review, we discuss applications of peptides in different fields including pharmaceuticals, cosmeceuticals, besides the critical factors in designing efficient peptide molecules.

Baculovirus as a Tool for Gene Delivery and Gene Therapy

Based on its ability to express high levels of protein, baculovirus has been widely used for recombinant protein production in insect cells for more than thirty years with continued technical improvements. In addition, baculovirus has been successfully applied for foreign gene delivery into mammalian cells without any viral replication. However, several CpG motifs are present throughout baculoviral DNA and induce an antiviral response in mammalian cells, resulting in the production of pro-inflammatory cytokines and type I interferon through a Toll-like receptor (TLR)-dependent or -independent signaling pathway, and ultimately limiting the efficiency of transgene expression. On the other hand, by taking advantage of this strong adjuvant activity, recombinant baculoviruses encoding neutralization epitopes can elicit protective immunity in mice. Moreover, immunodeficient cells, such as hepatitis C virus (HCV)- or human immunodeficiency virus (HIV)-infected cells, are more susceptible to baculovirus infection than normal cells and are selectively eliminated by the apoptosis-inducible recombinant baculovirus. Here, we summarize the application of baculovirus as a gene expression vector and the mechanism of the host innate immune response induced by baculovirus in mammalian cells. We also discuss the future prospects of baculovirus vectors.

Zinc-Finger Nucleases Induced by HIV-1 Tat Excise HIV-1 from the Host Genome in Infected and Latently Infected Cells

Highly active anti-retroviral therapy (HAART) cannot clear infected cells harboring HIV-1 proviral DNA from HIV-1-infected patients. We previously demonstrated that zinc-finger nucleases (ZFNs) can specifically and efficiently excise HIV-1 proviral DNA from latently infected human T cells by targeting long terminal repeats (LTRs), a novel and alternative antiretroviral strategy for eradicating HIV-1 infection. To prevent unwanted off-target effects from constantly expressed ZFNs, in this study, we engineered the expression of ZFNs under the control of HIV-1 LTR, by which ZFN expression can be activated by the HIV-1 (Trans-Activator of Transcription) Tat protein. Our results show that functional expression of ZFNs induced by Tat excise the integrated proviral DNA of HIV-NL4-3-eGFP in approximately 30% of the population of HIV-1-infected cells. The results from HIV-1-infected human primary T cells and latently infected T cells treated with the inducible ZFNs further validated that proviral DNA can be excised. Taken together, positively regulated expression of ZFNs in the presence of HIV-1 Tat may provide a safer and novel implementation of genome-editing technology for eradicating HIV-1 proviral DNA from infected host cells.

Gene transduction in mammalian cells using Bombyx mori nucleopolyhedrovirus assisted by glycoprotein 64 of Autographa californica multiple nucleopolyhedrovirus

Autographa californica multiple nucleopolyhedrovirus (AcMNPV), an alphabaculovirus, has been widely utilized for protein expression in not only insect cells but also mammalian cells. AcMNPV is closely related to Bombyx mori nucleopolyhedrovirus (BmNPV), and nucleotide sequences of AcMNPV genes have high similarity with those of BmNPV. However, the transduction of BmNPV into mammalian cells has not been reported. In this study, we constructed a recombinant BmNPV (BmNPVΔbgp/AcGP64/EGFP) whose surface 64 kDa glycoprotein (BmGP64) was substituted with that from AcMNPV (AcGP64). BmNPVΔbgp/AcGP64/EGFP also carried an EGFP gene under the control of the CMV promoter. BmNPVΔbgp/AcGP64/EGFP successfully transduced HEK293T cells. In comparison, a control construct (BmNPVΔbgp/BmGP64/EGFP) which possessed BmGP64 instead of AcGP64 did not express EGFP in HEK293T cells. The transduction efficiency of BmNPVΔbgp/AcGP64/EGFP was lower than that of an AcMNPV based-BacMam GFP transduction control. This result indicates that AcGP64 facilitates BmNPV transduction into HEK293T cells. BmNPV can be prepared easily on a large scale because BmNPV can infect silkworm larvae without any special equipment, even though specific diet is needed for silkworm rearing. BmNPV gene transduction into mammalian cells can potentially be applied easily for gene delivery into mammalian cells.

Topoisomerase II Inhibitors Can Enhance Baculovirus-Mediated Gene Expression in Mammalian Cells through the DNA Damage Response

BacMam is an insect-derived recombinant baculovirus that can deliver genes into mammalian cells. BacMam vectors carrying target genes are able to enter a variety of cell lines by endocytosis, but the level of expression of the transgene depends on the cell line and the state of the transduced cells. In this study, we demonstrated that the DNA damage response (DDR) could act as an alternative pathway to boost the transgene(s) expression by BacMam and be comparable to the inhibitors of histone deacetylase. Topoisomerase II (Top II) inhibitor-induced DDR can enhance the CMV-IE/enhancer mediated gene expression up to 12-fold in BacMam-transduced U-2OS cells. The combination of a Top II inhibitor, VM-26, can also augment the killing efficiency of a p53-expressing BacMam vector in U-2OS osteosarcoma cells. These results open a new avenue to facilitate the application of BacMam for gene delivery and therapy.

Cell-penetrating peptides transport therapeutics into cells

Nearly 30years ago, certain small, relatively nontoxic peptides were discovered to be capable of traversing the cell membrane. These cell-penetrating peptides, as they are now called, have been shown to not only be capable of crossing the cell membrane themselves but can also carry many different therapeutic agents into cells, including small molecules, plasmid DNA, siRNA, therapeutic proteins, viruses, imaging agents, and other various nanoparticles. Many cell-penetrating peptides have been derived from natural proteins, but several other cell-penetrating peptides have been developed that are either chimeric or completely synthetic. How cell-penetrating peptides are internalized into cells has been a topic of debate, with some peptides seemingly entering cells through an endocytic mechanism and others by directly penetrating the cell membrane. Although the entry mechanism is still not entirely understood, it seems to be dependent on the peptide type, the peptide concentration, the cargo the peptide transports, and the cell type tested. With new intracellular disease targets being discovered, cell-penetrating peptides offer an exciting approach for delivering drugs to these intracellular targets. There are hundreds of cell-penetrating peptides being studied for drug delivery, and ongoing studies are demonstrating their success both in vitro and in vivo.

Ubiquitin-modified hepatitis B virus core antigen effectively facilitates antigen presentation and enhances cytotoxic T lymphocyte activity via the cytoplasmic transduction peptide in vitro

Cluster of differentiation (CD)8+ cytotoxic T lymphocytes (CTLs) have a key role in the elimination of hepatitis B virus (HBV)-infected cells. Ubiquitin (Ub) functions as a marker for protein degradation, which may promote the generation of peptides appropriate for major histocompatibility complex class I presentation, while the HBV core antigen (HBcAg) possesses marked immunogenic properties. However, it remains to be elucidated whether Ub-modified HBcAg is able to effectively elicit significant CD8+ CTL activity. In order to address this issue, a prokaryotic vector was constructed to express the Ub-HBcAg-cytoplasmic transduction peptide (CTP). The fusion protein was successfully expressed and subsequently pulsed into bone-marrow-derived dendritic cells (DCs). It was confirmed that with assistance from the cell‑penetrating properties of CTP, the fusion protein was able to directly penetrate into the cytoplasm of DCs. The results revealed that the Ub-HBcAg-CTP fusion protein not only increased the expression of surface molecules in DCs and cytokine secretion from proliferating T cells, but also induced T cells to differentiate into specific CTLs and enhanced their antiviral ability. In conclusion, the Ub-HBcAg-CTP fusion protein promoted DC maturation, enhanced the presentation of targeting antigens and efficiently induced HBcAg‑specific CTL immune responses in vitro.

Targeted genome correction by a single adenoviral vector simultaneously carrying an inducible zinc finger nuclease and a donor template

Zinc finger nuclease (ZFN) technology, which can be used to induce targeted genome correction in the presence of a DNA donor template, is becoming an attractive strategy for treating monogenic diseases. This strategy requires efficient delivery of ZFN and donor template into cells, ideally, in a single viral vector to achieve efficient genome editing and to avoid unwanted mutagenesis. In this study, we successfully produced a single adenoviral (Ad) vector with high titer that carried a ZFN expression cassette and a donor template simultaneously. We then demonstrated that this single Ad system could mediate efficient site-specific genome correction in vitro and ex vivo. The gene correction efficiency of the single Ad was significantly higher than that of the double Ad system. This novel vector will be a promising ZFN and donor delivery system for treatment of monogenic diseases.

Bioengineered baculoviruses as new class of therapeutics using micro and nanotechnologies: principles, prospects and challenges

Designing a safe and efficient gene delivery system is required for success of gene therapy trials. Although a wide variety of viral, non-viral and polymeric nanoparticle based careers have been widely studied, the current gene delivery vehicles are limited by their suboptimal, non-specific therapeutic efficacy and acute immunological reactions, leading to unwanted side effects. Recently, there has been a growing interest in insect-cell-originated baculoviruses as gene delivery vehicles for diverse biomedical applications. Specifically, the emergence of diverse types of surface functionalized and bioengineered baculoviruses is posed to edge over currently available gene delivery vehicles. This is primarily because baculoviruses are comparatively non-pathogenic and non-toxic as they cannot replicate in mammalian cells and do not invoke any cytopathic effect. Moreover, emerging advanced studies in this direction have demonstrated that hybridizing the baculovirus surface with different kinds of bioactive therapeutic molecules, cell-specific targeting moieties, protective polymeric grafts and nanomaterials can significantly improve the preclinical efficacy of baculoviruses. This review presents a comprehensive overview of the recent advancements in the field of bioengineering and biotherapeutics to engineer baculovirus hybrids for tailored gene therapy, and articulates in detail the potential and challenges of these strategies for clinical realization. In addition, the article illustrates the rapid evolvement of microfluidic devices as a high throughput platform for optimizing baculovirus production and treatment conditions.

The Fusion Protein of CTP-HBcAg18-27-Tapasin Mediates the Apoptosis of CD8(+)T Cells and CD8(+) T Cell Response in HLA-A2 Transgenic Mice

BACKGROUND

HBV-specific cytotoxic T lymphocyte (CTL) activity is believed to play a critical role in controlling HBV infection. The phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway manipulates cell fate decisions in many different cell types by regulating the activity of downstream effectors. We have previously testified that the fusion protein of CTP-HBcAg18-27--Tapasin could enter the cytoplasm of dendritic cells and efficiently induce robust specific CTL response in vitro.

OBJECTIVES

In the present study, we evaluated specific CTL response and the level of apoptosis of CD8+ T cells induced by CTP-HBcAg18-27-Tapasin in HLA-A2 transgenic mice (H-2Kb). Meanwhile, we preliminary investigated PI3K, phosphorylation level of Akt, and mammalian target of rapamycin (mTOR) as positive regulator of the magnitude and effector function of the hepatitis B virus-specific cytotoxic T lymphocytes in HLA-A2 transgenic mice.

MATERIALS AND METHODS

HLA-A2 transgenic mice were immunized by intramuscular injection in the hind legs three times at one-week intervals with PBS, CTP-HBcAg18-27-Tapasin (50 μg), CTP-HBcAg18-27 (50 μg), HBcAg18-27-Tapasin (50 μg), and HBcAg18-27 (50 μg). One week after the last immunization, mice were sacrificed and splenocytes were harvested in strile condition. The specific CTL response was analyzed by flow cytometry and enzyme linked immunosorbent assay (ELISA); the expression of (PI3K)/Akt signaling was detected by RT-PCR and western blot.

RESULTS

The results showed that CTP-HBcAg18-27-Tapasin significantly increased the percentages of IFN-γ(+) CD8α(+) T cells, the numbers of these polyfunctional triple-cytokine-producing (IFN-γ, TNF-α, and IL-2) CD8(+)T cells, the secretion of cytokine IFN-γ, IL-2, and TNF-α, while in comparison to control group, it significantly decreased the percentage of apoptotic CD8(+) T cells in HLA-A2 transgenic mice. Moreover, the expression of PI3K, P-Akt, and P-mTOR was significantly upregulated in CTP-HBcAg18-27-Tapasin group compared with control groups.

CONCLUSIONS

In conclusion, CTP-HBcAg18-27-Tapasin could reduce apoptosis of CD8(+) T cells, increase the percentages of IFN-γ(+) CD8α(+) T cells, and elicit cell-mediated immunity in HLA-A2 transgenic mice; these processes were associated with activation of the PI3K/Akt signaling pathway.

Noncovalently associated cell-penetrating peptides for gene delivery applications

The use of various cell-penetrating peptides (CPPs) to deliver genetic material for gene therapy applications has been a topic of interest for more than 20 years. The delivery of genetic material by using CPPs can be divided into two categories: covalently bound and electrostatically bound. Complexity of the synthesis procedure can be a significant barrier to translation when using a strategy requiring covalent binding of CPPs. In contrast, electrostatically complexing CPPs with genetic material or with a viral vector is relatively simple and has been demonstrated to improve gene delivery in both in vitro and in vivo studies. This review highlights gene therapy applications of complexes formed noncovalently between CPPs and genetic material or viruses.

The modification of Tapasin enhances cytotoxic T lymphocyte activity of intracellularly delivered CTL epitopes via cytoplasmic transduction peptide

Previous studies have demonstrated that the therapeutic vaccine based on the enhancement of hepatitis B virus (HBV)-specific cytotoxic T lymphocyte (CTL) activity may lead to viral clearance in HBV-infected individuals. The endoplasmic reticulum (ER) chaperone Tapasin plays an important role in major histocompatibility complex (MHC) class I assembly and enhances specific MHC class I-restricted CTL activity by allowing more peptides to be translocated into the ER. Combining the specificity of hepatitis B core antigen (HBcAg) CTL epitope, the cell-penetrating property of cytoplasmic transduction peptide (CTP), and chaperone Tapasin may elicit robust specific HBV immune responses. In the present study, we confirmed the cytoplasmic localization preference of CTP-HBcAg(18-27)-Tapasin fusion protein in vitro and evaluated the effects on promoting bone marrow-derived dendritic cells (BMDCs) maturation and enhancing T cells response to generate specific CTLs. Our results showed that CTP-HBcAg(18-27)-Tapasin fusion protein could not only penetrate into the cytoplasm exactly and effectively to elevate Tapasin expression, but also increase the expression of surface molecules (CD80, CD83, CD86, and MHC-I) and secretion of cytokine (IL-12p70) of DCs. Moreover, DCs treated with the above fusion proteins increased significantly the cytokine secretion of proliferated T cells in vitro, the percentages of IFN-γ(+)CD8(+) T cells and specific CTL responses compared with control groups. In conclusion, the modification of Tapasin can enhance the presentation of targeting antigens via intracellular delivery to DCs and elicit specific CTL immune responses efficiently.

A gene delivery system for insect cells mediated by arginine-rich cell-penetrating peptides

Most bioactive macromolecules, such as protein, DNA and RNA, basically cannot permeate into cells freely from outside the plasma membrane. Cell-penetrating peptides (CPPs) are a group of short peptides that possess the ability to traverse the cell membrane and have been considered as candidates for mediating gene and drug delivery into living cells. In this study, we demonstrate that three arginine-rich CPPs (SR9, HR9 and PR9) are able to form stable complexes with plasmid DNA and deliver DNA into insect Sf9 cells in a noncovalent manner. The transferred plasmid DNA containing enhanced green fluorescent protein (EGFP) and red fluorescent protein (RFP) coding regions could be expressed in cells functionally assayed at both the protein and RNA levels. Furthermore, treatment of cells with CPPs and CPP/DNA complexes resulted in a viability of 84-93% indicating these CPPs are not cytotoxic. These results suggest that arginine-rich CPPs appear to be a promising tool for insect transgenesis.

Angiopoietin-1-expressing adipose stem cells genetically modified with baculovirus nanocomplex: investigation in rat heart with acute infarction

The objective of this study was to develop angiopoietin-1 (Ang1)-expressing genetically modified human adipose tissue derived stem cells (hASCs) for myocardial therapy. For this, an efficient gene delivery system using recombinant baculovirus complexed with cell penetrating transactivating transcriptional activator TAT peptide/deoxyribonucleic acid nanoparticles (Bac-NP), through ionic interactions, was used. It was hypothesized that the hybrid Bac- NP(Ang1) system can efficiently transduce hASCs and induces favorable therapeutic effects when transplanted in vivo. To evaluate this hypothesis, a rat model with acute myocardial infarction and intramyocardially transplanted Ang1-expressing hASCs (hASC-Ang1), genetically modified by Bac-NP(Ang1), was used. Ang1 is a crucial pro-angiogenic factor for vascular maturation and neovasculogenesis. The released hAng1 from hASC-Ang1 demonstrated profound mitotic and anti-apoptotic activities on endothelial cells and cardiomyocytes. The transplanted hASC-Ang1 group showed higher cell retention compared to hASC and control groups. A significant increase in capillary density and reduction in infarct sizes were noted in the infarcted hearts with hASC-Ang1 treatment compared to infarcted hearts treated with hASC or the untreated group. Furthermore, the hASC-Ang1 group showed significantly higher cardiac performance in echocardiography (ejection fraction 46.28% ± 6.3%, P < 0.001 versus control, n = 8) than the hASC group (36.35% ± 5.7%, P < 0.01, n = 8), 28 days post-infarction. The study identified Bac-NP complex as an advanced gene delivery vehicle for stem cells and demonstrated its potential to treat ischemic heart disease with high therapeutic index for combined stem cell-gene therapy strategy.

Baculovirus as a gene delivery vector: recent understandings of molecular alterations in transduced cells and latest applications

Baculovirus infects insects in nature and is non-pathogenic to humans, but can transduce a broad range of mammalian and avian cells. Thanks to the biosafety, large cloning capacity, low cytotoxicity and non-replication nature in the transduced cells as well as the ease of manipulation and production, baculovirus has gained explosive popularity as a gene delivery vector for a wide variety of applications. This article extensively reviews the recent understandings of the molecular mechanisms pertinent to baculovirus entry and cellular responses, and covers the latest advances in the vector improvements and applications, with special emphasis on antiviral therapy, cancer therapy, regenerative medicine and vaccine.