The use of cell-delivered gene therapy for the treatment of HIV/AIDS

An Update on the HIV DNA Vaccine Strategy

In 2020, the global prevalence of human immunodeficiency virus (HIV) infection was estimated to be 38 million, and a total of 690,000 people died from acquired immunodeficiency syndrome (AIDS)–related complications. Notably, around 12.6 million people living with HIIV/AIDS did not have access to life-saving treatment. The advent of the highly active antiretroviral therapy (HAART) in the mid-1990s remarkably enhanced the life expectancy of people living with HIV/AIDS as a result of improved immune functions. However, HAART has several drawbacks, especially when it is not used properly, including a high risk for the development of drug resistance, as well as undesirable side effects such as lipodystrophy and endocrine dysfunctions, which result in HAART intolerability. HAART is also not curative. Furthermore, new HIV infections continue to occur globally at a high rate, with an estimated 1.7 million new infections occurring in 2018 alone. Therefore, there is still an urgent need for an affordable, effective, and readily available preventive vaccine against HIV/AIDS. Despite this urgent need, however, progress toward an effective HIV vaccine has been modest over the last four decades. Reasons for this slow progress are mainly associated with the unique aspects of HIV itself and its ability to rapidly mutate, targeting immune cells and escape host immune responses. Several approaches to an HIV vaccine have been undertaken. However, this review will mainly discuss progress made, including the pre-clinical and clinical trials involving vector-based HIV DNA vaccines and the use of integrating lentiviral vectors in HIV vaccine development. We concluded by recommending particularly the use of integrase-defective lentiviral vectors, owing to their safety profiles, as one of the promising vectors in HIV DNA vaccine strategies both for prophylactic and therapeutic HIV vaccines.

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.

Analysis and dissociation of anti-HIV effects of shRNA to CCR5 and the fusion inhibitor C46

BACKGROUND

The gene therapeutic Cal-1 comprises the anti-HIV agents: (i) sh5, a short hairpin RNA to CCR5 that down-regulates CCR5 expression and (ii) maC46 (C46), a peptide that inhibits viral fusion with the cell membrane. These constructs were assessed for inhibition of viral replication and selective cell expansion in a number of settings.

METHODS

HIV replication, selective outgrowth and cell surface viral binding were analysed with a single cycle infection assay of six pseudotyped HIV strains and a static and longitudinal passaging of MOLT4/CCR5 cells with HIV. Pronase digestion of surface virus and fluorescence microscopy assessed interactions between HIV virions and transduced cells.

RESULTS

Cal-1 reduced CCR5 expression in peripheral blood mononuclear cells to CCR5Δ32 heterozygote levels. Even low level transduction resulted in significant preferential expansion in MOLT4/CCR5 gene-containing cells over a 3-week HIV challenge regardless of viral suppression [12.5% to 47.0% (C46), 46.7% (sh5), 62.2% (Dual), respectively]. The sh5 and Dual constructs at > 95% transduction also significantly suppressed virus to day 12 in the passage assay and all constructs, at varying percentage transduction inhibited virus in static culture. No escape mutations were present through 9 weeks of challenge. The Dual construct significantly suppressed infection by a panel of CCR5-using viruses, with its efficacy being independently determined from the single constructs. Dual and sh5 inhibited virion internalisation, as determined via pronase digestion of surface bound virus, by 70% compared to 13% for C46.

CONCLUSIONS

The use of two anti-HIV genes allows optimal preferential survival and inhibition of HIV replication, with the impact on viral load being dependent on the percentage of gene marked cells.

Gene Therapy Approaches to Functional Cure and Protection of Hematopoietic Potential in HIV Infection

Although current antiretroviral drug therapy can suppress the replication of human immunodeficiency virus (HIV), a lifelong prescription is necessary to avoid viral rebound. The problem of persistent and ineradicable viral reservoirs in HIV-infected people continues to be a global threat. In addition, some HIV-infected patients do not experience sufficient T-cell immune restoration despite being aviremic during treatment. This is likely due to altered hematopoietic potential. To achieve the global eradication of HIV disease, a cure is needed. To this end, tremendous efforts have been made in the field of anti-HIV gene therapy. This review will discuss the concepts of HIV cure and relative viral attenuation and provide an overview of various gene therapy approaches aimed at a complete or functional HIV cure and protection of hematopoietic functions.

Recent Advances in Lentiviral Vaccines for HIV-1 Infection

The development of an effective HIV vaccine to prevent and/or cure HIV remains a global health priority. Given their central role in the initiation of adaptive immune responses, dendritic cell (DC)-based vaccines are being increasingly explored as immunotherapeutic strategies to enhance HIV-specific T cells in infected individuals and, thus, promote immune responses that may help facilitate a functional cure. HIV-1-based lentiviral (LV) vectors have inherent advantages as DC vaccine vectors due to their ability to transduce non-dividing cells and integrate into the target cell genomic DNA, allowing for expression of encoded antigens over the lifespan of the cell. Moreover, LV vectors may express additional immunostimulatory and immunoregulatory proteins that enhance DC function and direct antigen-specific T cells responses. Recent basic and clinical research efforts have broadened our understanding of LV vectors as DC-based vaccines. In this review, we provide an overview of the pre-clinical and clinical LV vector vaccine studies for treating HIV to date. We also discuss advances in LV vector designs that have enhanced DC transduction efficiency, target cell specificity, and immunogenicity, and address potential safety concerns regarding LV vector-based vaccines.

Recent advances on anti-HIV vaginal delivery systems development

A review of the recent outcomes regarding technologies to prevent vaginal transmission of HIV, mainly by using antiretroviral (ARV) drugs formulated as microbicides. An introduction about the HIV transmission mechanisms by the vaginal route is included, together with the recent challenges faced for development of successful microbicide products. The outcomes of clinical evaluations are mentioned, and the different formulation strategies studied to-date, with the requirements, advantages, disadvantages and limitations of each dosage-form type, are presented. Finally, the recent attempts to apply various types of nanotechnologies in order to develop advanced microbicide-products and overcome existing limitations, are discussed.

Vaginal gene therapy

In the last years, vaginal gene therapy has gained increasing attention mainly for the treatment and control of sexually transmitted infections. DNA delivery has been also suggested to improve reproductive outcomes for women with deficiencies in the female reproductive tract. Although no product has reached clinical phase, preclinical investigations reveal the potential of the vaginal tract as an effective administration route for gene delivery. This review focuses on the main advantages and challenges of vaginal gene therapy, and on the most used nucleic acid delivery systems, including viral and non-viral vectors. Additionally, the advances in the application of vaginal gene therapy for the treatment and/or prevention of infectious diseases such as the human immunodeficiency virus (HIV), the human papillomavirus (HPV) or the herpes simplex virus (HSV) are presented.

A quantitative comparison of anti-HIV gene therapy delivered to hematopoietic stem cells versus CD4+ T cells

Gene therapy represents an alternative and promising anti-HIV modality to highly active antiretroviral therapy. It involves the introduction of a protective gene into a cell, thereby conferring protection against HIV. While clinical trials to date have delivered gene therapy to CD4+T cells or to CD34+ hematopoietic stem cells (HSC), the relative benefits of each of these two cellular targets have not been conclusively determined. In the present analysis, we investigated the relative merits of delivering a dual construct (CCR5 entry inhibitor + C46 fusion inhibitor) to either CD4+T cells or to CD34+ HSC. Using mathematical modelling, we determined the impact of each scenario in terms of total CD4+T cell counts over a 10 year period, and also in terms of inhibition of CCR5 and CXCR4 tropic virus. Our modelling determined that therapy delivery to CD34+ HSC generally resulted in better outcomes than delivery to CD4+T cells. An early one-off therapy delivery to CD34+ HSC, assuming that 20% of CD34+ HSC in the bone marrow were gene-modified (G+), resulted in total CD4+T cell counts ≥ 180 cells/ µL in peripheral blood after 10 years. If the uninfected G+ CD4+T cells (in addition to exhibiting lower likelihood of becoming productively infected) also exhibited reduced levels of bystander apoptosis (92.5% reduction) over non gene-modified (G-) CD4+T cells, then total CD4+T cell counts of ≥ 350 cells/ µL were observed after 10 years, even if initially only 10% of CD34+ HSC in the bone marrow received the protective gene. Taken together our results indicate that: 1.) therapy delivery to CD34+ HSC will result in better outcomes than delivery to CD4+T cells, and 2.) a greater impact of gene therapy will be observed if G+ CD4+T cells exhibit reduced levels of bystander apoptosis over G- CD4+T cells.

Pol III Promoters to Express Small RNAs: Delineation of Transcription Initiation

Pol III promoters such as U6 are commonly used to express small RNAs, including small interfering RNA, short hairpin RNA, and guide RNA, for the clustered regularly interspaced short palindromic repeats genome-editing system. However, whether the small RNAs were precisely expressed as desired has not been studied. Here, using deep sequencing to analyze small RNAs, we show that, for mouse U6 promoter, sequences immediately upstream of the putative initiation site, which is often modified to accommodate the restriction enzyme sites that enable easy cloning of small RNAs, are critical for precise transcription initiation. When the promoter is kept unmodified, transcription starts precisely from the first available A or G within the range of positions −1 to +2. In addition, we show that transcription from another commonly used pol III promoter, H1, starts at multiple sites, which results in variability at the 5′ end of the transcripts. Thus, inaccuracy of 5′ end of small RNA transcripts might be a common problem when using these promoters to express small RNAs based on currently believed concepts. Our study provides general guidelines for minimizing the variability of initiation, thereby enabling more accurate expression of small RNAs.

Preclinical safety and efficacy of an anti-HIV-1 lentiviral vector containing a short hairpin RNA to CCR5 and the C46 fusion inhibitor

Gene transfer has therapeutic potential for treating HIV-1 infection by generating cells that are resistant to the virus. We have engineered a novel self-inactivating lentiviral vector, LVsh5/C46, using two viral-entry inhibitors to block early steps of HIV-1 cycle. The LVsh5/C46 vector encodes a short hairpin RNA (shRNA) for downregulation of CCR5, in combination with the HIV-1 fusion inhibitor, C46. We demonstrate here the effective delivery of LVsh5/C46 to human T cell lines, peripheral blood mononuclear cells, primary CD4(+) T lymphocytes, and CD34(+) hematopoietic stem/progenitor cells (HSPC). CCR5-targeted shRNA (sh5) and C46 peptide were stably expressed in the target cells and were able to effectively protect gene-modified cells against infection with CCR5- and CXCR4-tropic strains of HIV-1. LVsh5/C46 treatment was nontoxic as assessed by cell growth and viability, was noninflammatory, and had no adverse effect on HSPC differentiation. LVsh5/C46 could be produced at a scale sufficient for clinical development and resulted in active viral particles with very low mutagenic potential and the absence of replication-competent lentivirus. Based on these in vitro results, plus additional in vivo safety and efficacy data, LVsh5/C46 is now being tested in a phase 1/2 clinical trial for the treatment of HIV-1 disease.

Targeted genome engineering in human induced pluripotent stem cells by penetrating TALENs

Background

Zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs) have been successfully used to knock out endogenous genes in stem cell research. However, the deficiencies of current gene-based delivery systems may hamper the clinical application of these nucleases. A new delivery method that can improve the utility of these nucleases is needed.

Results

In this study, we utilized a cell-penetrating peptide-based system for ZFN and TALEN delivery. Functional TAT-ZFN and TAT-TALEN proteins were generated by fusing the cell-penetrating TAT peptide to ZFN and TALEN, respectively. However, TAT-ZFN was difficult to purify in quantities sufficient for analysis in cell culture. Purified TAT-TALEN was able to penetrate cells and disrupt the gene encoding endogenous human chemokine (C-C motif) receptor 5 (CCR5, a co-receptor for HIV-1 entry into cells). Hypothermic treatment greatly enhanced the TAT-TALEN-mediated gene disruption efficiency. A 5% modification rate was observed in human induced pluripotent stem cells (hiPSCs) treated with TAT-TALEN as measured by the Surveyor assay.

Conclusions

TAT-TALEN protein-mediated gene disruption was applicable in hiPSCs and represents a promising technique for gene knockout in stem cells. This new technique may advance the clinical application of TALEN technology.

Electronic supplementary material

The online version of this article (doi:10.1186/2045-9769-2-5) contains supplementary material, which is available to authorized users.

A review of nanotechnological approaches for the prophylaxis of HIV/AIDS

Successful treatment and control of HIV/AIDS is one of the biggest challenges of 21st century. More than 33 million individuals are infected with HIV worldwide and more than 2 million new cases of HIV infection have been reported. The situation demands development of effective prevention strategies to control the pandemic of AIDS. Due to lack of availability of an effective HIV vaccine, antiretroviral drugs and nucleic acid therapeutics like siRNA have been explored for HIV prophylaxis. Clinical trials shave shown that antiretroviral drugs, tenofovir and emtricitabine can offer some degree of HIV prevention. However, complete prevention of HIV infection has not been achieved yet. Nanotechnology has brought a paradigm shift in the diagnosis, treatment and prevention of many diseases. The current review discusses potential of various nanocarriers such as dendrimers, polymeric nanoparticles, liposomes, lipid nanocarriers, drug nanocrystals, inorganic nanocarriers and nanofibers in improving efficacy of various modalities available for HIV prophylaxis.

Engineering HIV-1-resistant T-cells from short-hairpin RNA-expressing hematopoietic stem/progenitor cells in humanized BLT mice

Down-regulation of the HIV-1 coreceptor CCR5 holds significant potential for long-term protection against HIV-1 in patients. Using the humanized bone marrow/liver/thymus (hu-BLT) mouse model which allows investigation of human hematopoietic stem/progenitor cell (HSPC) transplant and immune system reconstitution as well as HIV-1 infection, we previously demonstrated stable inhibition of CCR5 expression in systemic lymphoid tissues via transplantation of HSPCs genetically modified by lentiviral vector transduction to express short hairpin RNA (shRNA). However, CCR5 down-regulation will not be effective against existing CXCR4-tropic HIV-1 and emergence of resistant viral strains. As such, combination approaches targeting additional steps in the virus lifecycle are required. We screened a panel of previously published shRNAs targeting highly conserved regions and identified a potent shRNA targeting the R-region of the HIV-1 long terminal repeat (LTR). Here, we report that human CD4⁺ T-cells derived from transplanted HSPC engineered to co-express shRNAs targeting CCR5 and HIV-1 LTR are resistant to CCR5- and CXCR4- tropic HIV-1-mediated depletion in vivo. Transduction with the combination vector suppressed CXCR4- and CCR5- tropic viral replication in cell lines and peripheral blood mononuclear cells in vitro. No obvious cytotoxicity or interferon response was observed. Transplantation of combination vector-transduced HSPC into hu-BLT mice resulted in efficient engraftment and subsequent stable gene marking and CCR5 down-regulation in human CD4⁺ T-cells within peripheral blood and systemic lymphoid tissues, including gut-associated lymphoid tissue, a major site of robust viral replication, for over twelve weeks. CXCR4- and CCR5- tropic HIV-1 infection was effectively inhibited in hu-BLT mouse spleen-derived human CD4⁺ T-cells ex vivo. Furthermore, levels of gene-marked CD4⁺ T-cells in peripheral blood increased despite systemic infection with either CXCR4- or CCR5- tropic HIV-1 in vivo. These results demonstrate that transplantation of HSPCs engineered with our combination shRNA vector may be a potential therapy against HIV disease.

Gene therapy: therapeutic applications and relevance to pathology

This review discusses gene therapy as a new treatment paradigm where genetic material is introduced into cells for therapeutic benefit. The genetic material is the 'drug'. It can have a transient or ongoing effect depending on whether or not the introduced genetic material becomes part of the host cell DNA. Different delivery and gene technologies are chosen by investigators to maximise gene delivery to, and expression within, the target cells appropriate for the disease indication. The presence and expression of the introduced genetic material is monitored by molecular means so that treatment efficacy can be assessed via changes in surrogate and/or actual markers of disease. Of interest to the pathologist will be the approaches being developed for the disease indications highlighted and the monitoring of treatment efficacy.

Phase I/II Clinical Trials Using Gene-Modified Adult Hematopoietic Stem Cells for HIV: Lessons Learnt

Gene therapy for individuals infected with HIV has the potential to provide a once-only treatment that will act to reduce viral load, preserve the immune system, and mitigate cumulative toxicities associated with highly active antiretroviral therapy (HAART). The authors have been involved in two clinical trials (phase I and phase II) using gene-modified adult hematopoietic stem cells (HSCs), and these are discussed as prototypic trials within the general field of HSC gene therapy trials for HIV. Taken as a group these trials have shown (i) the safety of both the procedure and the anti-HIV agents themselves and (ii) the feasibility of the approach. They point to the requirement for (i) the ability to transduce and infuse as many as possible gene-containing HSC and/or (ii) high engraftment and in vivo expansion of these cells, (iii) potentially increased efficacy of the anti-HIV agent(s) and (iv) automation of the cell processing procedure.

Ex vivo gene therapy for HIV-1 treatment

Until recently, progress in ex vivo gene therapy (GT) for human immunodeficiency virus-1 (HIV-1) treatment has been incremental. Long-term HIV-1 remission in a patient who received a heterologous stem cell transplant for acquired immunodeficiency syndrome-related lymphoma from a CCR5(-/-) donor, even after discontinuation of conventional therapy, has energized the field. We review the status of current approaches as well as future directions in the areas of therapeutic targets, combinatorial strategies, vector design, introduction of therapeutics into stem cells and enrichment/expansion of gene-modified cells. Finally, we discuss recent advances towards clinical application of HIV-1 GT.