Gene therapy for infectious diseases

Advancements in gene therapy for human diseases: Trend of current clinical trials

In an era of rapid scientific advancement, gene therapy has emerged as a groundbreaking approach with the potential to revolutionize the treatment of a myriad of diseases and medical conditions. The trend of current clinical trials suggests that there is growing interest and investment in exploring gene therapy as a viable treatment option. In 2023, a significant milestone was achieved with the approval of seven gene therapies by the Food and Drug Administration (FDA). Projections indicate that between 10 and 20 gene therapies could receive annual FDA approval by 2025. In this review, we conducted a comprehensive analysis of registered clinical trials on Clinicaltrials.gov to determine the progression status of gene therapies. Upon extraction of the data, we conducted a comprehensive analysis of the 2809 included studies. This involved a systematic approach, commencing with an overview, followed by a detailed examination of gene therapy strategies employed in various malignant and non-malignant disorders. Additionally, the study will cover the types of vectors utilized in current trials. Lastly, a meticulous review of 105 phase III-IV clinical trials was conducted to identify potential therapies demonstrating promise. We trust that the comprehensive overview provided will serve as a solid foundation for forthcoming research and study designs, ultimately contributing to the progression of gene therapy and its practical application within healthcare settings. Also, we anticipate that such inquiries will bolster the formulation of practical policies and guidelines for pharmaceutical companies engaged in gene therapy research and development.

Second-Generation Polyamidoamine Dendrimer Conjugated with Oligopeptides Can Enhance Plasmid DNA Delivery In Vitro

Poly(amidoamine) (PAMAM) dendrimers have attracted considerable attention in the field of gene therapy due to their flexibility in introducing different functional moieties and reduced toxicity at low generations. However, their transfection efficiency remains a limitation. Therefore, an essential approach for improving their transfection efficiency as gene carriers involves modifying the structure of PAMAM by conjugating functional groups around their surface. In this study, we successfully conjugated an RRHRH oligopeptide to the surface of PAMAM generation 2 (PAMAM G2) to create RRHRH-PAMAM G2. This construction aims to condense plasmid DNA (pDNA) and facilitate its penetration into cell membranes, leading to its promising potential for gene therapy. RRHRH-PAMAM G2/pDNA complexes were smaller than 100 nm and positively charged. Nano-polyplexes can enter the cell and show a high transfection efficiency after 24 h of transfection. The RRHRH-PAMAM G2 was non-toxic to HeLa, NIH3T3, A549, and MDA-MB-231 cell lines. These results strongly suggest that RRHRH-PAMAM G2 holds promise as a gene carrier for gene therapy owing to its biocompatibility and ability to deliver genes to the cell.

Nanotherapeutics with immunoregulatory functions for the treatment of bacterial infection

The advent of drug-resistant pathogens results in the occurrence of stubborn bacterial infections that cannot be treated with traditional antibiotics. Antibacterial immunotherapy by reviving or activating the body's immune system to eliminate pathogenic bacteria has confirmed promising therapeutic strategies in controlling bacterial infections. Subsequent studies found that antimicrobial immunotherapy has its own benefits and limitations, such as avoiding recurrence of infection and autoimmunity-induced side effects. Current studies indicate that the various antibacterial therapeutic strategies inducing immune regulation can achieve superior therapeutic efficacy compared with monotherapy alone. Therefore, summarizing the recent advances in nanomedicine with immunomodulatory functions for combating bacterial infections is necessary. Herein, we briefly introduce the crisis caused by drug-resistant bacteria and the opportunity for antibacterial immunotherapy. Then, immune-involved multimodal antibacterial therapy for the treatment of infectious diseases was systematically summarized. Finally, the prospects and challenges of immune-involved combinational therapy are discussed.

Unravelling the role of individual components in pBAE/polynucleotide polyplexes in the synthesis of tailored carriers for specific applications: on the road to rational formulations

Oligopeptide end-modified poly(β-amino ester)s (OM-pBAEs) offer a means for the effective implementation of gene therapeutics in the near future. A fine-tuning of OM-pBAEs to meet application requirements is achieved by the proportional balance of oligopeptides used and provide gene carriers with high transfection efficacy, low toxicity, precise targeting, biocompatibility, and biodegradability. Understanding the influence and conformation of each building block at molecular and biological levels is therefore pivotal for further development and improvement of these gene carriers. Herein, we unmask the role of individual OM-pBAE components and their conformation in OM-pBAE/polynucleotide nanoparticles using a combination of fluorescence resonance energy transfer, enhanced darkfield spectral microscopy, atomic force microscopy, and microscale thermophoresis. We found that modifying the pBAE backbone with three end-terminal amino acids produces unique mechanical and physical properties for each combination. Higher adhesion properties are seen with arginine and lysine-based hybrid nanoparticles, while histidine provides an advantage in terms of construct stability. Our results shed light on the high potential of OM-pBAEs as gene delivery vehicles and provide insights into the influence of the nature of surface charges and the chemical nature of the pBAE modifications on their paths towards endocytosis, endosomal escape, and transfection.

Immunological evaluation of a novel multi-antigenic DNA vaccine encoding SAG1, SAG3, MIC4, GRA5, GRA7, AMA1and BAG1 against Toxoplasma gondii in BALB/c mice

Many recent studies have been conducted to find new DNA vaccines based on Toxoplasma gondii antigens. DNA vaccines encoding complex of different antigens showed better immune responses compared to single antigen vaccine. In this study, we constructed a DNA vaccine encoding SAG1, SAG3, MIC4, GRA5, GRA7, AMA1 and BAG1 against T. gondii, and evaluated the immune response it induced in BALB/c mice. For this purposes, thirty BALB/c mice were randomly divided into three groups containing tenmice each. There were two negative control groups (PBSand pVAX1 vector) and one vaccination group (pVAX1-MAF, Multantigenic Fragment). On days 0, 14 and 28, the mice were immunized intramuscularly, and 5 weeks later they were challenged with T. gondii RH strain. The immune responses were evaluated using lymphocyte proliferation assay, T-cell subsets detection, and measurement of antibody and cytokine levels. The results showed that mice immunized with pVAX1-MAF developed high levels of IL-2, IL-12, IgG and IFN- γ as well as CD3+CD4+ T cells. In addition, the survival time of mice immunized by pVAX1-MAF was longer than that control mice. In conclusion, our results show that the multiple DNA vaccine encodingSAG1, SAG3, mic4, GRA5, GRA7, AMA and BAG1effectively enhanced humoral and cellular immune responses, and prolonged the survival time. Together this would suggest that further investigation may result in a promising candidate vaccine to treat toxoplasmosis.

Peptide-Based Nanoparticles for αvβ3 Integrin-Targeted DNA Delivery to Cancer and Uterine Leiomyoma Cells

Uterine leiomyoma is the most common benign tumor of the reproductive system. Current therapeutic options do not simultaneously meet the requirements of long-term efficiency and fertility preservation. Suicide gene delivery can be proposed as a novel approach to uterine leiomyoma therapy. Non-viral vehicles are an attractive approach to DNA delivery for gene therapy of both malignant and benign tumors. Peptide-based vectors are among the most promising candidates for the development of artificial viruses, being able to efficiently cross barriers of DNA transport to cells. Here we described nanoparticles composed of cysteine-crosslinked polymer and histidine-arginine-rich peptide modified with iRGD moiety and characterized them as vehicles for plasmid DNA delivery to pancreatic cancer PANC-1 cells and the uterine leiomyoma cell model. Several variants of nanoparticles were formulated with different targeting ligand content. The physicochemical properties that were studied included DNA binding and protection, interaction with polyanions and reducing agents, size, structure and zeta-potential of the peptide-based nanoparticles. Cytotoxicity, cell uptake and gene transfection efficiency were assessed in PANC-1 cells with GFP and LacZ-encoding plasmids. The specificity of gene transfection via αvβ3 integrin binding was proved in competitive transfection. The therapeutic potential was evaluated in a uterine leiomyoma cell model using the suicide gene therapy approach. The optimal formulation was found to be at the polyplex with the highest iRGD moiety content being able to transfect cells more efficiently than control PEI. Suicide gene therapy using the best formulation resulted in a significant decrease of uterine leiomyoma cells after ganciclovir treatment. It can be concluded that the application of iRGD-modified peptide-based nanoparticles has a high potential for cellular delivery of DNA therapeutics in favor of uterine leiomyoma gene therapy.

Application of bioengineered elastin-like polypeptide-based system for targeted gene delivery in tumor cells

Successful gene delivery depends on the entry of negatively charged DNAs and oligonucleotides across the various barriers of the tumor cells and localization into the nucleus for its transcription and protein translation. Here, we have reported a thermal responsive self-assemble and highly biocompatible, targeted ELP-based gene delivery system. These systems consist of cell-penetrating peptides, Tat and single or multiple repeats of IL-4 receptor targeting peptide AP-1 along the backbone of ELP. Cell-penetrating peptides were introduced for nuclear localization of genes of interest, AP-1 for targeting IL-4R highly expressed tumor cells and ELP for stable condensation favoring protection of nucleic acids. The designed multidomain fusion ELPs referred to as Tat-ELP, Tat-A₁E₂₈ and Tat-A₄V₄₈ were employed to generate formulation with pEGFP-N1. Profound formulation of stable complexes occurred at different molar ratios owing to electrostatic interactions of positively charged amino acids in polymers with negatively charged nucleic acids. Among the complexes, Tat-A₄V₄₈ containing four copies of AP-1 showed maximum complexation with pEGFP-N1 in lower molar ratio. The polymer-pEGFP complexes were further analyzed for its transfection efficiency in different cancer cell lines. Both the targeted polymers, Tat-A₄V₄₈ and Tat-A₁E₂₈ upon transfection displayed significant EGFP-expression with low toxicity in different cancer cells. Therefore, both Tat-A₄V₄₈ and Tat-A₁E₂₈ can be considered as novel transfection system for successful gene delivery with therapeutic applications.

Gene therapy: Comprehensive overview and therapeutic applications

Gene therapy is the product of man's quest to eliminate diseases. Gene therapy has three facets namely, gene silencing using siRNA, shRNA and miRNA, gene replacement where the desired gene in the form of plasmids and viral vectors, are directly administered and finally gene editing based therapy where mutations are modified using specific nucleases such as zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and clustered regulatory interspaced short tandem repeats (CRISPR)/CRISPR-associated protein (Cas)-associated nucleases. Transfer of gene is either through transformation where under specific conditions the gene is directly taken up by the bacterial cells, transduction where a bacteriophage is used to transfer the genetic material and lastly transfection that involves forceful delivery of gene using either viral or non-viral vectors. The non-viral transfection methods are subdivided into physical, chemical and biological. The physical methods include electroporation, biolistic, microinjection, laser, elevated temperature, ultrasound and hydrodynamic gene transfer. The chemical methods utilize calcium- phosphate, DAE-dextran, liposomes and nanoparticles for transfection. The biological methods are increasingly using viruses for gene transfer, these viruses could either integrate within the genome of the host cell conferring a stable gene expression, whereas few other non-integrating viruses are episomal and their expression is diluted proportional to the cell division. So far, gene therapy has been wielded in a plethora of diseases. However, coherent and innocuous delivery of genes is among the major hurdles in the use of this promising therapy. Hence this review aims to highlight the current options available for gene transfer along with the advantages and limitations of every method.

Dicationic amphiphiles bearing an amino acid head group with a long-chain hydrophobic tail for in vitro gene delivery applications

C14-P, C14-M, and C14-S lipids formed lipoplexes using pDNA. The lipoplex cellular uptake into the cells resulted in the release of nucleic acids. C14-P lipid showed superior eGFP transfection in non-cancer cell line and more apoptosis cell death in cancer cell line.

Could gene therapy cure HIV?

The Human Immunodeficiency Virus (HIV)/Acquired Immune Deficiency Syndrome (AIDS) continues to be a major global public health issue, having claimed almost 33 million lives so far. According to the recent report of the World Health Organization (WHO) in 2019, about 38 million people are living with AIDS. Hence, finding a solution to overcome this life-threatening virus can save millions of lives. Scientists and medical doctors have prescribed HIV patients with specific drugs for many years. Methods such antiretroviral therapy (ART) or latency-reversing agents (LRAs) have been used for a while to treat HIV patients, however they have some side effects and drawbacks causing their application to be not quite successful. Instead, the application of gene therapy which refers to the utilization of the therapeutic delivery of nucleic acids into a patient's cells as a drug to treat disease has shown promising results to control HIV infection. Therefore, in this review, we will summarize recent advances in gene therapy approach against HIV.

QSPR modelling for investigation of different properties of aminoglycoside-derived polymers using 2D descriptors

The quantitative structure-property relationship (QSPR) method is commonly used to predict different physicochemical characteristics of interest of chemical compounds with an objective to accelerate the process of design and development of novel chemical compounds in the biotechnology and healthcare industries. In the present report, we have employed a QSPR approach to predict the different properties of the aminoglycoside-derived polymers (i.e. polymer DNA binding and aminoglycoside-derived polymers mediated transgene expression). The final QSPR models were obtained using the partial least squares (PLS) regression approach using only specific categories of two-dimensional descriptors and subsequently evaluated considering different internationally accepted validation metrics. The proposed models are robust and non-random, demonstrating excellent predictive ability using test set compounds. We have also developed different kinds of consensus models using several validated individual models to improve the prediction quality for external set compounds. The present findings provide new insight for exploring the design of an aminoglycoside-derived polymer library based on different identified physicochemical properties as well as predict their property before their synthesis.

Self-immolative Linkers in Prodrugs and Antibody Drug Conjugates in Cancer Treatment

BACKGROUND

The design of anti-cancer therapies with high anti-tumour efficacy and reduced toxicity continues to be challenging. Anti-cancer prodrug and antibody-drug-conjugate (ADC) strategies that can specifically and efficiently deliver cytotoxic compounds to cancer cells have been used to overcome some of the challenges. Key to the success of many of these strategies is a self-immolative linker, which after activation can release the drug payload. Various types of triggerable self-immolative linkers are used in prodrugs and ADCs to improve their efficacy and safety.

OBJECTIVE

Numerous patents have reported the significance of self-immolative linkers in prodrugs and ADCs in cancer treatment. Based on the recent patent literature, we summarise methods for designing the site-specific activation of non-toxic prodrugs and ADCs in order to improve selectivity for killing cancer cells.

METHODS

In this review, an integrated view of the potential use of prodrugs and ADCs in cancer treatment are provided. This review presents recent patents and related publications over the past ten years to 2020.

RESULTS

The recent patent literature has been summarised for a wide variety of self-immolative PABC linkers, which are cleaved by factors including responding to the difference between the extracellular and intracellular environments (pH, ROS, glutathione), by over-expressed enzymes (cathepsin, plasmin, β-glucuronidase) or bioorthogonal activation. The mechanism for self-immolation involves the linker undergoing a 1,4- or 1,6-elimination (via electron cascade) or intramolecular cyclisation to release cytotoxic drug at the targeted site.

CONCLUSION

This review provides the commonly used strategies from recent patent literature in the development of prodrugs based on targeted cancer therapy and antibody-drug conjugates, which show promising results in therapeutic applications.

Cyclodextrins based delivery systems for macro biomolecules

Macro biomolecules are of vital importance in regulating the biofunctions in organisms, in which proteins (including peptides when mentioned below) and nucleic acids (NAs) are the most important. Therefore, these proteins and NAs can be applied as "drugs" to regulate the biofunctions from abnormal to normal. Either for proteins and NAs, the most challenging thing is to avoid the biodegradation or physicochemical degradation before they reach the targeted location, and then functions as complete functional structures. Hence, appropriate delivery systems are very important which can protect them from these degradations. Cyclodextrins (CDs) based delivery systems achieved mega successes due to their outstanding pharmaceutical properties and there have been several reviews on CDs based small molecule drug delivery systems recently. But for biomolecules, which are getting more and more important for modern therapies, however, there are very few reviews to systematically summarize and analyze the CDs-based macro biomolecules delivery systems, especially for proteins. In this review, there were some of the notable examples were summarized for the macro biomolecules (proteins and NAs) delivery based on CDs. For proteins, this review included insulin, lysozyme, bovine serum albumin (BSA), green fluorescent protein (GFP) and IgG's, etc. deliveries in slow release, stimulating responsive release or targeting release manners. For NAs, this review summarized cationic CD-polymers and CD-cluster monomers as NAs carriers, notably, including the multicomponents targeting CD-based carriers and the virus-like RNA assembly method siRNA carriers.

Copolymer micelles function as pH-responsive nanocarriers to enhance the cytotoxicity of a HER2 aptamer in HER2-positive breast cancer cells

Efficient delivery of nucleic acids into target cells is crucial for nucleic acid-based therapies. Various nucleic acid delivery systems have been developed, each with its own advantages and limitations. We previously developed a nanoparticle-based delivery system for small chemical drugs using pH-responsive PEG₈-PDPA₁₀₀-PEG₈ polymer micelles as carriers. In this study, we extend the application of these pH-responsive micelle-like nanoparticles (MNPs) to deliver oligonucleotides. We demonstrate that the MNPs efficiently encapsulate and deliver oligonucleotides of different lengths (20-100 nt) into cells. The cargo oligonucleotides are rapidly released at pH 5.0. We prepared MNPs carrying a Texas red-fluorescently labeled anti-human epidermal growth factor receptor 2 (HER2) aptamer (HApt). Compared to free HApt, the HApt-MNPs resulted in significantly better cellular uptake, reduced cell viability, and increased apoptosis in SKBR3 breast cancer cells, which overexpress HER2. Moreover, HApt-MNPs were significantly less cytotoxic to MCF7 breast cancer cells, which express low levels of HER2. After cellular uptake, HApt-MNPs mainly accumulated in lysosomes; inhibition of lysosomal activity using bafilomycin A1 and LysoTracker Red staining confirmed that lysosomal activity and low pH were required for HApt-MNP accumulation and release. Furthermore, HER2 protein expression declined significantly following treatment with HApt-MNPs in SKBR3 cells, indicating that HApt-induced translocation of HER2 to lysosomes exerted a potent cytotoxic effect by altering signaling downstream of HER2. In conclusion, this pH-responsive and lysosome-targeting nanoparticle system can efficiently deliver oligonucleotides to specific target cells and has significant potential for nucleic acid-based cancer therapies.

Synthesis of intracellular reduction-sensitive amphiphilic polyethyleneimine and poly(ε-caprolactone) graft copolymer for on-demand release of doxorubicin and p53 plasmid DNA

This study aims to present a new intelligent polymeric nano-system used for combining chemotherapy with non-viral gene therapy against human cancers. An amphiphilic copolymer synthesized through the conjugation of low molecular weight polyethyleneimine (LMw-PEI) and poly(ε-caprolactone) (PCL) via a bio-cleavable disulfide linkage was successfully employed for the simultaneous delivery of drug and gene molecules into target cells. Compared to the conventional PCL copolymerization pathway, this paper represents a straightforward and efficient reaction pathway including the activation of PCL-diol hydroxyl end groups, cystamine attachment and LMw-PEI conjugation which are successfully performed at mild conditions as confirmed by FTIR and (1)H NMR. Thermal, morphological characteristics as well as biocompatibility of the copolymer were investigated. The copolymer showed great tendency to form positively charged nanoparticles (∼163.1nm, +35.3mV) with hydrophobic core and hydrophilic shell compartments implicating its potential for encapsulation of anti-cancer drug and plasmid DNA, respectively. The gel retardation assay confirmed that the nanoparticles could successfully inhibit the migration of pDNA at ∼5 nanoparticle/pDNAw/w. The in vitro cytotoxicity tests and LDH assay revealed that the cationic amphiphilic copolymer was essentially non-toxic in different carcinoma cell lines in contrast to branched PEI 25K. Moreover, the presence of redox sensitive disulfide linkages provided smart nanoparticles with on-demand release behavior in response to reducing agents such as cytoplasmic glutathione (GSH). Importantly, confocal microscopy images revealed that in contrast to free Dox, the nanoparticles were capable of faster internalizing into the cells and accumulating in the perinuclear region or even in the nucleus. Finally, the co-delivery of Dox and p53-pDNA using the copolymer displayed greater cytotoxic effect compared with the Dox-loaded nanoparticle counterpart as revealed by cell viability and Caspase 3 expression assay. These results suggest the copolymer as a promising candidate for the development of smart delivery systems.

STATEMENT OF SIGNIFICANCE

We employed cystamine dihydrochloride as a disulfide linkage for the conjugation of PCL diol and low molecular weight PEI segments through a straightforward and efficient reaction pathway at mild conditions. The new copolymer was essentially non-toxic in different carcinoma cell lines and showed great tendency to form positively charged nanoparticles. Therefore, it can be utilized as a promising platform for simultaneous drug and gene delivery to aggressive cancers. The results of drug and gene co-delivery experiments confirmed the pivotal role of disulfide linkage on the controlled release of both drug and gene molecules in response to glutathione concentration gradient between extracellular and intracellular microenvironments. In addition, the co-delivery of doxorubicin and p53 plasmid DNA using the new copolymer displayed greater cytotoxic effect compared with single agent (i.e. Dox) loaded counterpart, which indicated the significance of rapid dissociation of therapeutic agents from the carrier for synergistic cytotoxic effects on cancer cells.

A recombinant plasmid of composite cysteine proteinase inhibitor/glyceraldehyde-3-phosphate dehydrogenase gene of periodic Brugia malayi functions on DNA immunity in the host

OBJECTIVES

Both cysteine proteinase inhibitors (CPIs) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) play important roles in the pathogenesis of parasites and their relationship with the hosts. We constructed a new eukaryotic recombinant expression plasmid pcDNA3.1(+)-BmCPI/BmGAPDH of periodic Brugia malayi for investigation of the DNA vaccine-elicited immune responses.

MATERIALS AND METHODS

We cloned a gene encoding the CPIs and GAPDH from periodic B. malayi into vector pcDNA3.1. The composited plasmid or the control was injected into the tibialis anterior muscle of the hind leg in BALB/c mice, respectively. The target genes were detected by reverse transcription-polymerase chain reaction in muscle tissues. The stimulation index (SI) of T-lymphocyte proliferation and the levels of interferon-gamma (INF-g) and interleukin-4 ( IL-4) in serum were detected by thiazolyl blue tetrazolium blue and enzyme-linked immunosorbent assays.

RESULTS

The pcDNA3.1(+)-BmCPI/BmGAPDH was amplified from muscle tissues of the mice after immunisation. The SI of the immunised group was significantly higher than that of the two control groups (P < 0.05). The levels of INF-g and IL-4 of pcDNA3.1(+)-BmCPI/BmGAPDH group were both higher than those of the two control groups (P < 0.05). The level of INF-g of pcDNA3.1(+)-BmCPI/BmGAPDH group was significantly higher than that of pcDNA3.1(+)-BmCPI/CpG group (P < 0.05).

CONCLUSIONS

We conclude that the recombinant plasmid pcDNA3.1(+)-BmCPI/BmGAPDH could elicit specific humoural and cellular immune responses in mice.

Cell Penetrating Peptide Conjugated Chitosan for Enhanced Delivery of Nucleic Acid

Gene therapy is an emerging therapeutic strategy for the cure or treatment of a spectrum of genetic disorders. Nevertheless, advances in gene therapy are immensely reliant upon design of an efficient gene carrier that can deliver genetic cargoes into the desired cell populations. Among various nonviral gene delivery systems, chitosan-based carriers have gained increasing attention because of their high cationic charge density, excellent biocompatibility, nearly nonexistent cytotoxicity, negligible immune response, and ideal ability to undergo chemical conjugation. However, a major shortcoming of chitosan-based carriers is their poor cellular uptake, leading to inadequate transfection efficiency. The intrinsic feature of cell penetrating peptides (CPPs) for transporting diverse cargoes into multiple cell and tissue types in a safe manner suggests that they can be conjugated to chitosan for improving its transfection efficiency. In this review, we briefly discuss CPPs and their classification, and also the major mechanisms contributing to the cellular uptake of CPPs and cargo conjugates. We also discuss immense improvements for the delivery of nucleic acids using CPP-conjugated chitosan-based carriers with special emphasis on plasmid DNA and small interfering RNA.

Development and Challenges of Nanovectors in Gene Therapy

In recent years, hundreds of genes have been linked to a variety of human diseases, and the field of gene therapy has emerged as a way to treat this wide range of diseases. The main goal of gene therapy is to find a gene delivery vehicle that can successfully target diseased cells and deliver therapeutic genes directly to their cellular compartment. The two main types of gene delivery vectors currently being investigated in clinical trials are recombinant viral vectors and synthetic nonviral vectors. Recombinant viral vectors take advantage of the evolutionarily optimized viral mechanisms to deliver genes, but they can be hard to specifically target in vivo and are also associated with serious side effects. Synthetic nonviral vectors are made out of highly biocompatible lipids or polymers, but they are much less efficient at delivering their genetic payload due to the lack of any active delivery mechanism. This mini review will introduce the current state of gene delivery in clinical trials, and discuss the specific challenges associated with each of these vectors. It will also highlight some specific gaps in knowledge that are limiting the advancement of this field and touch on the current areas of research being explored to overcome them.

Immunity to bovine herpesvirus 1: II. Adaptive immunity and vaccinology

Bovine herpesvirus 1 (BHV-1) infection is widespread and causes a variety of diseases. Although similar in many respects to the human immune response to human herpesvirus 1, the differences in the bovine virus proteins, immune system components and strategies, physiology, and lifestyle mean the bovine immune response to BHV-1 is unique. The innate immune system initially responds to infection, and primes a balanced adaptive immune response. Cell-mediated immunity, including cytotoxic T lymphocyte killing of infected cells, is critical to recovery from infection. Humoral immunity, including neutralizing antibody and antibody-dependent cell-mediated cytotoxicity, is important to prevention or control of (re-)infection. BHV-1 immune evasion strategies include suppression of major histocompatibility complex presentation of viral antigen, helper T-cell killing, and latency. Immune suppression caused by the virus potentiates secondary infections and contributes to the costly bovine respiratory disease complex. Vaccination against BHV-1 is widely practiced. The many vaccines reported include replicating and non-replicating, conventional and genetically engineered, as well as marker and non-marker preparations. Current development focuses on delivery of major BHV-1 glycoproteins to elicit a balanced, protective immune response, while excluding serologic markers and virulence or other undesirable factors. In North America, vaccines are used to prevent or reduce clinical signs, whereas in some European Union countries marker vaccines have been employed in the eradication of BHV-1 disease.

Gene therapy and DNA delivery systems

Gene therapy is a promising new technique for treating many serious incurable diseases, such as cancer and genetic disorders. The main problem limiting the application of this strategy in vivo is the difficulty of transporting large, fragile and negatively charged molecules like DNA into the nucleus of the cell without degradation. The key to success of gene therapy is to create safe and efficient gene delivery vehicles. Ideally, the vehicle must be able to remain in the bloodstream for a long time and avoid uptake by the mononuclear phagocyte system, in order to ensure its arrival at the desired targets. Moreover, this carrier must also be able to transport the DNA efficiently into the cell cytoplasm, avoiding lysosomal degradation. Viral vehicles are the most commonly used carriers for delivering DNA and have long been used for their high efficiency. However, these vehicles can trigger dangerous immunological responses. Scientists need to find safer and cheaper alternatives. Consequently, the non-viral carriers are being prepared and developed until techniques for encapsulating DNA can be found. This review highlights gene therapy as a new promising technique used to treat many incurable diseases and the different strategies used to transfer DNA, taking into account that introducing DNA into the cell nucleus without degradation is essential for the success of this therapeutic technique.

Evaluation of the adjuvant effect of pidotimod on the immune protection induced by UV-attenuated Toxoplasma gondii in mouse models

The current anti-Toxoplasma gondii drugs have many shortcomings and effective vaccines against T. gondii may contribute to the control of this pathogen. Pidotimod is a synthetic substance capable of stimulating both cellular and humoral immunity. To investigate the possible adjuvant effect of pidotimod on the immune response to T. gondii in Kunming mice induced by ultraviolet-attenuated T. gondii (UV-T.g), in this study, mice were immunized intraperitoneal (i.p.) with UV-T.g or UV-T.g co-administered with pidotimod (UV-T.g + PT). After infection or challenge by i.p. injection of 10(2) RH tachyzoites, the animal survival rate, parasite burden in peritoneal lavage fluids, liver histopathology, the level of serum anti-toxoplasma IgG antibody, and the mRNA expressions of IL-2, IFN-γ, and TNF-α from spleen analyzed using real-time PCR, were compared among different groups. The results showed that, compared with infected controls, infected mice treated with pidotimod had significantly increased survival rate and extended survival time, decreased parasite burden, improved liver histopathology, increased level of anti-toxoplasma IgG antibody, and increased mRNA expressions of Th1-type cytokine (IL-2, IFN-γ, and TNF-α) (P < 0.01), while mice vaccinated with UV-T.g and then challenged had even significantly increased survival rate and extended survival time, decreased parasite burden, improved liver histopathology, and increased mRNA expressions of Th1-type cytokines (IL-2, IFN-γ, and TNF-α) (P < 0.01); furthermore, vaccinated mice co-administered with pidotimod had even more lower parasite burden, milder liver histopathology, and higher levels of Th1-type cytokine and anti-toxoplasma IgG antibody (P < 0.01). Our data demonstrated that pidotimod in vivo could promote strong and specific humoral and cellular immune response to T. gondii challenge infection when co-administered with UV-attenuated T. gondii. It suggests that pidotimod may have the potential to be used as an effective vaccine adjuvant.

Protective immunity induced by a DNA vaccine-encoding Toxoplasma gondii microneme protein 11 against acute toxoplasmosis in BALB/c mice

Toxoplasma gondii is one of the most prevalent intracellular parasites and is threatening the health of both humans and animals, therefore causing incalculable economic losses worldwide. Vaccination is thought to be an efficient way of controlling toxoplasmosis. T. gondii microneme protein 11 (MIC11) is a soluble microneme protein which is presumably considered facilitating the early stage of cell invasion. To evaluate the protective efficacy of T. gondii MIC11, in the present study, a new DNA vaccine-encoding the α-chain of T. gondii MIC11 was constructed using the pcDNA3.1 vector. Expression of MIC11 from this vector was confirmed by indirect immunofluorescence assay following transfection into baby hamster kidney (BHK) cells. Intramuscular immunization of BALB/c mice with pcDNA/MIC11 was carried out to evaluate the immune responses by serum antibodies titers, lymphoproliferation assay, and cytokines assay. The protective efficacy was evaluated by survival rate in mice after challenging with highly virulent strain of T. gondii. The results demonstrated that this vaccination elicited significant humoral responses and T. gondii lysate antigen (TLA)-stimulated lymphoproliferation (p < 0.05). Compared to controls, the pcDNA/MIC11 immunized mice had high production of IFN-γ, IL-12, and IL-2 (p < 0.05), but not IL-4 (p > 0.05), indicating that a predominant Th1 type response was developed. The vaccination also increased the survival rate of immunized mice when they were challenged with a lethal dose of tachyzoites of T. gondii RH strain. These data suggest that T. gondii MIC11 is a reasonable vaccine candidate deserving further studies, and pcDNA/MIC11 is a potential strategy for the control of toxoplasmosis.

Targeted gene delivery by new folate-polycationic amphiphilic cyclodextrin-DNA nanocomplexes in vitro and in vivo

AIM

Development and evaluation of a new targeted gene delivery system by first preforming self-assembled nanocomplexes from a polycationic amphiphilic cyclodextrin (paCD) and pDNA and then decorating the surface of the nanoparticles with folic acid (FA).

EXPERIMENTAL SECTION

The cyclodextrin derivative (T2) is a tetradecacationic structure incorporating 14 primary amino groups and 7 thioureido groups at the primary face of a cyclomaltoheptaose (β-CD) core and 14 hexanoyl chains at the secondary face.

RESULTS AND CONCLUSIONS

T2 complexed and protected pDNA (luciferase-encoding plasmid DNA, pCMVLuc) and efficiently mediated transfection in vitro and in vivo with no associated toxicity. The combination of folic acid with CDplexes afforded ternary nanocomplexes (Fol-CDplexes) that enhanced significantly the transfection activity of pCMVLuc in human cervix adenocarcinoma HeLa cells, especially when formulated with 1 μg FA/μg DNA. The observed transfection enhancement was associated to specific folate receptor (FR)-mediated internalization of Fol-CDplexes, as corroborated by employing a receptor-deficient cell line (HepG2) and an excess of free folic acid. The in vivo studies, including luciferase reporter gene expression and biodistribution, indicated that 24h after intravenous administration of the T2-pDNA nanocomplexes, transfection takes part mainly in the liver and partially in the lung. Interestingly, the corresponding Fol-CDplexes lead to an increase in the transfection activity in the lung and the liver compared to non-targeted CDplexes. Folate-CDplexes developed in this study have improved transfection efficiency and although various methods have been used for the preparation of ligand-DNA-complexes, covalent binding is usually needed and insoluble aggregates are formed unless the concentration of the components is minimized. However, the complexes developed by first time in this work were prepared by simple mixing. The synthetic nature of this formulation provides the potential of flexibility in terms of composition and the capability of inexpensive and large-scale production of the complexes. These nanovectors may be an adequate alternative to viral vectors for gene therapy in the future.

Design of multifunctional non-viral gene vectors to overcome physiological barriers: dilemmas and strategies

Gene-based therapeutics hold great promise for medical advancement and have been used to treat various human diseases with mixed success. However, their therapeutic application in vivo is limited due largely to several physiological barriers. The design of non-viral gene vectors with the ability to overcome delivery obstacles is currently under extensive investigation. These efforts have placed an emphasis on the development of multifunctional vectors able to execute multiple tasks to simultaneously overcome both extracellular and intracellular obstacles. However, the assembly of these different functionalities into a single system to create multifunctional gene vectors faces many conflicts that largely limit the safe and efficient application of lipoplexes and polyplexes in a systemic delivery. In the review, we have described the dilemmas inherent in the design of a viable, non-viral gene vector equipped with multiple functionalities. The strategies directed towards individual delivery barriers are first summarized, followed by a focus on the design of so-called smart multifunctional vectors with the capability to overcome the delivery difficulties of gene medicines, including the so-called the "polycation dilemma", the "PEG dilemma" and the "package and release dilemma".

Controlled-release system of single-stranded DNA triggered by the photothermal effect of gold nanorods and its in vivo application

Gold nanorods have strong absorption bands in the near-infrared region, in which light penetrates deeply into tissues. The absorbed light energy is converted into heat by gold nanorods, the so-called 'photothermal effect'. Hence, gold nanorods are expected to act not only as on-demand thermal converters for photothermal therapy but also as controllers of a drug-release system responding to irradiation by near-infrared light. To achieve a controlled-release system that can be triggered by light irradiation, double-stranded DNA (dsDNA) was modified on gold nanorods. When the dsDNA-modified gold nanorods were irradiated by near-infrared light, the single-stranded DNA (ssDNA) was released from gold nanorods due to the photothermal effect. The amount of released ssDNA was dependent upon the power and exposure time of light irradiation. Release of ssDNA was also observed in tumors grown on mice after light irradiation. Such a controlled-release system of oligonucleotide triggered by the photothermal effect could expand the applications of gold nanorods that have unique optical characteristics in medicinal fields.

Protective immunity induced by Toxoplasma gondii rhoptry protein 16 against toxoplasmosis in mice

Toxoplasma gondii can infect a large variety of domestic and wild animals and human beings, sometimes causing severe pathology. Rhoptries are involved in T. gondii invasion and host cell interaction and have been implicated as important virulence factors. In this study, we constructed a DNA vaccine expressing rhoptry protein 16 (ROP16) of T. gondii and evaluated the immune responses it induced in Kunming mice. The gene sequence encoding ROP16 was inserted into the eukaryotic expression vector pVAX I. We immunized Kunming mice intramuscularly. After immunization, we evaluated the immune response using a lymphoproliferative assay, cytokine and antibody measurements, and the survival times of mice challenged lethally. The results showed that mice immunized with pVAX-ROP16 developed a high level of specific antibody responses against T. gondii ROP16 expressed in Escherichia coli, a strong lymphoproliferative response, and significant levels of gamma interferon (IFN-γ), interleukin-2 (IL-2), IL-4, and IL-10 production compared with results for other mice immunized with either empty plasmid or phosphate-buffered saline, respectively. The results showed that pVAX-ROP16 induces significant humoral and cellular Th1 immune responses. After lethal challenge, the mice immunized with pVAX-ROP16 showed a significantly (P < 0.05) prolonged survival time (21.6 ± 9.9 days) compared with control mice, which died within 7 days of challenge. Our data demonstrate, for the first time, that ROP16 triggers a strong humoral and cellular response against T. gondii and that ROP16 is a promising vaccine candidate against toxoplasmosis, worth further development.

Characterization of polyion complex micelles designed to address the challenges of oligonucleotide delivery

PURPOSE

To optimize oligonucleotide (ODN)-based polyion complex micelles (PICMs) by studying the effects of polymer composition and length on their properties.

METHODS

Atom transfer radical polymerization was used to synthesize copolymers with increasing hydrophilic nonionic and cationic block lengths. PICMs were prepared by mixing the copolymers and ODN at various nitrogen-to-phosphate (N/P) ratios and characterized by gel electrophoresis and dynamic light scattering. The stability of the complexes towards dissociation was tested using a competitive assay with heparin. Finally, protection of the incorporated ODN against DNAse I degradation was evaluated.

RESULTS

A library of copolymers composed of poly(ethylene glycol) (PEG) and poly(aminoethyl methacrylate) (PAEMA) and/or poly((dimethylamino)ethylmethacrylate) (PDMAEMA) was synthesized. All polymers efficiently interacted with the ODN at N/P ratios approaching 1.5. Narrowly distributed but easily dissociable PICMs were obtained using PEG 5000 and short DMAEMA chains. Shortening the PEG block to 2000, increasing the number of cationic units and using AEMA produced more stable complexes but at the cost of colloidal properties. All polymers were able to protect the ODN from nuclease degradation.

CONCLUSIONS

PEG 3000-based PICMs possess good colloidal properties, intermediate stability towards dissociation and adjustable buffering capacity, making them potentially useful for the delivery of nucleic acid drugs.

Comparison of cholera toxin A2/B and murine interleukin-12 as adjuvants of Toxoplasma multi-antigenic SAG1-ROP2 DNA vaccine

Toxoplasmosis can lead to severe pathology in both humans and animals. However, an effective vaccine for humans has not been successfully developed. In this study, we used multi-antigenic SAG1-ROP2 as a DNA vaccine and cholera toxin A2/B subunit and murine interleukin-12 to compare their effectiveness as genetic adjuvants. Bagg albino/c (BAL/c) mice were immunized intramuscularly with pcDNA3.1-SAG1-ROP2 alone (control group), or pcDNA3.1-SAG1-ROP2 with co-administration of pCTA2/B or pIL-12, respectively. After immunization, the effectiveness of these two adjuvants were compared using lymphocyte proliferation assay, cytokine and antibody measurements. The group co-administered pIL-12 elicited stronger humoral and Th1-type cellular immune responses than those immunized with pcDNA3.1-SAG1-ROP2 alone, while in the group co-administered pCTA2/B there was no obvious enhancement of immunity. When challenged with Toxoplasma gondii RH strain, mice immunized with pIL-12 co-administration had significantly higher survival rates, whereas there was no notable augmentation of immunity in pCTA2/B group. Therefore, since pIL-12 significantly enhanced the antigenicity of multi-antigenic DNA vaccine, this suggests that IL-12 is a better and more effective adjuvant than CTA2/B in this situation.

Evaluation of the immune response induced by multiantigenic DNA vaccine encoding SAG1 and ROP2 of Toxoplasma gondii and the adjuvant properties of murine interleukin-12 plasmid in BALB/c mice

The heavy incidence and severe or lethal damages of toxoplasmosis clearly indicate the need for the development of a more effective vaccine. In the present study, we constructed a multiantigenic DNA vaccine, eukaryotic plasmid pcDNA3.1-SAG1-ROP2, expressing surface protein SAG1 and rhoptry protein ROP2 of Toxoplasma gondii, and examined the expression ability of the DNA vaccine in HeLa cells by Western blot. Afterwards, we investigated the efficacy of pcDNA3.1-SAG1-ROP2 with or without co-administration of a plasmid encoding murine interleukin-12 (pIL-12) as a genetic adjuvant to protect Bagg albino/c mice against toxoplasmosis. After T. gondii RH strain challenge, mice immunized with pcDNA3.1-SAG1-ROP2 displayed significant high survival rates. Moreover, the protection was markedly enhanced by pIL-12 co-administration. The results of lymphocyte proliferation assay, cytokine, and antibody determinations show that mice immunized with pcDNA3.1-SAG1-ROP2 elicited stronger humoral and Th1-type cellular immune responses than those immunized with single-gene plasmids, empty plasmid, or phosphate-buffered saline. Furthermore, co-immunization with IL-12 genes resulted in a dramatic enhancement of these responses. Our study indicates that the introduction of multiantigenic DNA vaccine is more powerful and efficient than single-gene vaccine, and the co-delivery of pIL-12 further enhanced the potency of multiantigenic DNA vaccine.

Current status of gene therapy strategies to treat HIV/AIDS

Progress in developing effective gene transfer approaches to treat HIV-1 infection has been steady. Many different transgenes have been reported to inhibit HIV-1 in vitro. However, effective translation of such results to clinical practice, or even to animal models of AIDS, has been challenging. Among the reasons for this failure are uncertainty as to the most effective cell population(s) to target, the diffuseness of these target cells in the body, and ineffective or insufficiently durable gene delivery. Better understanding of the HIV-1 replicative cycle, host factors involved in HIV-1 infection, vector biology and application, transgene technology, animal models, and clinical study design have all contributed vastly to planning current and future strategies for application of gene therapeutic approaches to the treatment of AIDS. This review focuses on the newest developments in these areas and provides a strong basis for renewed optimism that gene therapy will have an important role to play in treating people infected with HIV-1.

Oral immunization with a live recombinant attenuated Salmonella typhimurium protects mice against Toxoplasma gondii

The natural site of infection for T. gondii is the mucosal surface of the intestine, so the protective immunity obtained after natural infection with T. gondii points to the importance of developing a vaccine that stimulates mucosal defences. In this study, an aroA- and aroD- attenuated strain of Salmonella typhimurium (BRD509) has been used to deliver the recombinant eukaryotic plasmid pSAG(1-2)/CTA2/B expressing a multi-antigenic gene encoding SAG1 and SAG2 of T. gondii linked to A2/B subunits of cholera toxin as a candidate oral T. gondii vaccine. Immunoblot analysis showed compound gene expression in HeLa cells in vitro and intragastric immunization of mice with the recombinant salmonella resulted in the induction of humoral and Th1 type cellular immune responses and afforded protection against RH strain T. gondii challenge. Anti-T. gondii IgG values increased markedly in the BRD509/pSAG(1-2)-CTA2/B immunized group; these values were significantly higher than those in the negative controls (P = 0.008). With CTA2/B genetic adjuvant, the T. gondii-specific response was predominantly Th1, indicating that the CTA(2)/B genetic adjuvant was able to overcome the strong Th2-bias of the antigen (IgG2a >> IgG1). Antigen-specific T cell proliferative responses and CTL activity were significantly enhanced when cholera toxin CTA2/B genetic adjuvant was used (P = 0.009; P = 0.006). Culture supernatants from antigen-stimulated splenocytes from mice in these groups were also examined by ELISA for Th1- and Th2-type cytokines; mean IFN-gamma levels produced after oral immunization with BRD509/pSAG(1-2)-CTA2/B were about nine-fold higher than after immunization with BRD509/pSAG(1-2) (P = 0.007). On the other hand, the levels of IL-4 were low for all groups and no increase was seen in the presence of CTA2/B genetic adjuvant. When the immunized mice were intraperitoneally challenged with 10(3) tachyzoites of the highly virulent RH strain, the survival time of the mice immunized with BRD509/pSAG(1-2)-CTA2/B was markedly longer than other groups (P = 0.003) and a 40% survival rate was achieved. This is the first report that demonstrates that an oral attenuated salmonella DNA vaccine can induce protective immunity against the acute phase of T. gondii infection.

Capsid-targeted viral inactivation can destroy dengue 2 virus from within in vitro

Capsid-targeted viral inactivation (CTVI) has emerged as a conceptually powerful antiviral strategy that exploits viral structural proteins to target a destructive enzyme specifically into progeny virions. We have recently demonstrated the principle of CTVI against dengue virus infection and observed a modest therapeutic effect in vitro (Arch Virol 2005, 150: 659-669). Here we tested a prophylactic model of CTVI, in which mammalian cells stably expressing the dengue 2 virus capsid protein fused to a nuclease were infected with dengue virus and determined the effects on progeny virion infectivity. CTVI efficiently destroyed dengue 2 virus from within and decreased the infectious titers by 10(3)- to 10(4)-fold, suggesting that CTVI has potential in the prophylactic application for dengue virus infection.

Design and development of polymers for gene delivery

The lack of safe and efficient gene-delivery methods is a limiting obstacle to human gene therapy. Synthetic gene-delivery agents, although safer than recombinant viruses, generally do not possess the required efficacy. In recent years, a variety of effective polymers have been designed specifically for gene delivery, and much has been learned about their structure-function relationships. With the growing understanding of polymer gene-delivery mechanisms and continued efforts of creative polymer chemists, it is likely that polymer-based gene-delivery systems will become an important tool for human gene therapy.

Molecular strategies to inhibit HIV-1 replication

The human immunodeficiency virus type 1 (HIV-1) is the primary cause of the acquired immunodeficiency syndrome (AIDS), which is a slow, progressive and degenerative disease of the human immune system. The pathogenesis of HIV-1 is complex and characterized by the interplay of both viral and host factors. An intense global research effort into understanding the individual steps of the viral replication cycle and the dynamics during an infection has inspired researchers in the development of a wide spectrum of antiviral strategies. Practically every stage in the viral life cycle and every viral gene product is a potential target. In addition, several strategies are targeting host proteins that play an essential role in the viral life cycle. This review summarizes the main genetic approaches taken in such antiviral strategies.

Inhibition of HIV-1 gene expression by retroviral vector-mediated small-guide RNAs that direct specific RNA cleavage by tRNase ZL

The tRNA 3'-processing endoribonuclease (tRNase Z or 3' tRNase; EC 3.1.26.11) is an essential enzyme that removes the 3' trailer from pre-tRNA. The long form (tRNase ZL) can cleave a target RNA in vitro at the site directed by an appropriate small-guide RNA (sgRNA). Here, we investigated whether this sgRNA/tRNase ZL strategy could be applied to gene therapy for AIDS. We tested the ability of four sgRNA-expression plasmids to inhibit HIV-1 gene expression in COS cells, using a transient-expression assay. The three sgRNAs guide inhibition of HIV-1 gene expression in cultured COS cells. Analysis of the HIV-1 mRNA levels suggested that sgRNA directed the tRNase ZL to mediate the degradation of target RNA. The observation that sgRNA was localized primarily in nuclei suggests that tRNase ZL cleaves the HIV-1 mRNA when complexed with sgRNA in this location. We also examined the ability of two retroviral vectors expressing sgRNA to suppress HIV-1 expression in HIV-1-infected Jurkat T cells. sgRNA-SL4 suppressed HIV-1 expression almost completely in infected cells for up to 18 days. These results suggest that the sgRNA/tRNase ZL approach is effective in downregulating HIV-1 gene expression.

Gene therapy. Therapeutic approaches and implications

The present article is an overview of gene therapy with an emphasis on different approaches and its implications in the clinic. Genetic interventions have been applied to the diagnosis of and therapy for an array of human diseases. The initial concept of gene therapy was focused on the treatment of genetic diseases. Subsequently, the field of gene therapy has been expanded, with a major focus on cancer. Although the results of early gene therapy-based clinical trials have been encouraging, there is a need for gene delivery vectors that feature reduced immunogenicity and improved targeting ability. The results of phases I/II clinical trials have suggested the important role of gene therapy as a versatile and powerful treatment tool, especially for human cancers. One reasonable expectation is that performing gene therapy at an earlier stage in the disease process or for minimal residual disease may be more advantageous.