Early fetal gene delivery utilizes both central and peripheral mechanisms of tolerance induction

Thymus transplantation as immunotherapy for the enhancement and/or correction of T cell function

The thymus is where T cells, among the most important immune cells involved in biological defense and homeostasis, are produced and developed. The thymus plays an important role in the defense against infection and cancer as well as the prevention of autoimmune diseases. However, the thymus gland atrophies with age, which might have pathological functions, and in some circumstances, there is a congenital defect in the thymus. These can be the cause of many diseases related to the dysregulation of T cell functions. Thus, the enhancement and/or normalization of thymic function may lead to protection against and treatment of a wide variety of diseases. Therefore, thymus transplantation is considered a strong candidate for permanent treatment. The status and issues related to thymus transplantation for possible immunotherapy are discussed although it is still at an early stage of development.

Investigating Optimal Autologous Cellular Platforms for Prenatal or Perinatal Factor VIII Delivery to Treat Hemophilia A

Patients with the severe form of hemophilia A (HA) present with a severe phenotype, and can suffer from life-threatening, spontaneous hemorrhaging. While prophylactic FVIII infusions have revolutionized the clinical management of HA, this treatment is short-lived, expensive, and it is not available to many A patients worldwide. In the present study, we evaluated a panel of readily available cell types for their suitability as cellular vehicles to deliver long-lasting FVIII replacement following transduction with a retroviral vector encoding a B domain-deleted human F8 transgene. Given the immune hurdles that currently plague factor replacement therapy, we focused our investigation on cell types that we deemed to be most relevant to either prenatal or very early postnatal treatment and that could, ideally, be autologously derived. Our findings identify several promising candidates for use as cell-based FVIII delivery vehicles and lay the groundwork for future mechanistic studies to delineate bottlenecks to efficient production and secretion of FVIII following genetic-modification.

Delivery technologies for in utero gene therapy

Advances in prenatal imaging, molecular diagnostic tools, and genetic screening have unlocked the possibility to treat congenital diseases in utero prior to the onset of clinical symptoms. While fetal surgery and in utero stem cell transplantation can be harnessed to treat specific structural birth defects and congenital hematological disorders, respectively, in utero gene therapy allows for phenotype correction of a wide range of genetic disorders within the womb. However, key challenges to realizing the broad potential of in utero gene therapy are biocompatibility and efficiency of intracellular delivery of transgenes. In this review, we outline the unique considerations to delivery of in utero gene therapy components and highlight advances in viral and non-viral delivery platforms that meet these challenges. We also discuss specialized delivery technologies for in utero gene editing and provide future directions to engineer novel delivery modalities for clinical translation of this promising therapeutic approach.

Gene and Stem Cell Therapies for Fetal Care: A Review

Importance

Gene and stem cell therapies have become viable therapeutic options for many postnatal disorders. For select conditions, prenatal application would provide improved outcomes. The fetal state allows for several theoretical advantages over postnatal therapy, including immune immaturity and cellular niche accessibility.

Observations

Advances in prenatal diagnostic accuracy and surgical precision, as well as improvements in stem cell and gene therapy methods, have made prenatal gene and stem cell therapy realistic. Studies in mouse models and early human trials demonstrate the feasibility of these approaches. Additional efforts are under way to streamline fetal applications of stem cell and gene therapy while carefully considering best ethical practice and following established regulatory pathways.

Conclusions and Relevance

Fetal stem cell and gene therapy bring important therapeutic opportunities for select disorders that present in the fetal and neonatal periods. While this field is in its infancy, these therapies are starting to be available clinically, and clinicians should be aware of their benefits and challenges.

Mechanistic Insights into Factor VIII Immune Tolerance Induction via Prenatal Cell Therapy in Hemophilia A

Purpose of Review

Prenatal stem cell and gene therapy approaches are amongst the few therapies that can promise the birth of a healthy infant with specific known genetic diseases. This review describes fetal immune cell signaling and its potential influence on donor cell engraftment, and summarizes mechanisms of central T cell tolerance to peripherally-acquired antigen in the context of prenatal therapies for Hemophilia A.

Recent Findings

During early gestation, different subsets of antigen presenting cells take up peripherally-acquired, non-inherited antigens and induce the deletion of antigen-reactive T-cell precursors in the thymus, demonstrating the potential for using prenatal cell and gene therapies to induce central tolerance to FVIII in the context of prenatal diagnosis/therapy of Hemophilia A.

Summary

Prenatal cell and gene therapies are promising approaches to treat several genetic disorders including Hemophilia A and B. Understanding the mechanisms of how FVIII-specific tolerance is achieved during ontogeny could help develop novel therapies for HA and better approaches to overcome FVIII inhibitors.

Fetal Gene Therapy Using a Single Injection of Recombinant AAV9 Rescued SMA Phenotype in Mice

Symptoms of spinal muscular atrophy (SMA) disease typically begin in the late prenatal or the early postnatal period of life. The intrauterine (IU) correction of gene expression, fetal gene therapy, could offer effective gene therapy approach for early onset diseases. Hence, the overall goal of this study was to investigate the efficacy of human survival motor neuron (hSMN) gene expression after IU delivery in SMA mouse embryos. First, we found that IU-intracerebroventricular (i.c.v.) injection of adeno-associated virus serotype-9 (AAV9)-EGFP led to extensive expression of EGFP protein in different parts of the CNS with a great number of transduced neural stem cells. Then, to implement the fetal gene therapy, mouse fetuses received a single i.c.v. injection of a single-stranded (ss) or self-complementary (sc) AAV9-SMN vector that led to a lifespan of 93 (median of 63) or 171 (median 105) days for SMA mice. The muscle pathology and number of the motor neurons also improved in both study groups, with slightly better results coming from scAAV treatment. Consequently, fetal gene therapy may provide an alternative therapeutic approach for treating inherited diseases such as SMA that lead to prenatal death or lifelong irreversible damage.

In utero stem cell transplantation and gene therapy: rationale, history, and recent advances toward clinical application

Recent advances in high-throughput molecular testing have made it possible to diagnose most genetic disorders relatively early in gestation with minimal risk to the fetus. These advances should soon allow widespread prenatal screening for the majority of human genetic diseases, opening the door to the possibility of treatment/correction prior to birth. In addition to the obvious psychological and financial benefits of curing a disease in utero, and thereby enabling the birth of a healthy infant, there are multiple biological advantages unique to fetal development, which provide compelling rationale for performing potentially curative treatments, such as stem cell transplantation or gene therapy, prior to birth. Herein, we briefly review the fields of in utero transplantation (IUTx) and in utero gene therapy and discuss the biological hurdles that have thus far restricted success of IUTx to patients with immunodeficiencies. We then highlight several recent experimental breakthroughs in immunology, hematopoietic/marrow ontogeny, and in utero cell delivery, which have collectively provided means of overcoming these barriers, thus setting the stage for clinical application of these highly promising therapies in the near future.

Hemophilia A: an ideal disease to correct in utero

Hemophilia A (HA) is the most frequent inheritable defect of the coagulation proteins. The current standard of care for patients with HA is prophylactic factor infusion, which is comprised of regular (2-3 times per week) intravenous infusions of recombinant or plasma-derived FVIII to maintain hemostasis. While this treatment has greatly increased the quality of life and lengthened the life expectancy for many HA patients, its high cost, the need for lifelong infusions, and the fact that it is unavailable to roughly 75% of the world's HA patients make this type of treatment far from ideal. In addition, this lifesaving therapy suffers from a high risk of treatment failure due to immune response to the infused FVIII. There is thus a need for novel treatments, such as those using stem cells and/or gene therapy, which have the potential to mediate long-term correction or permanent cure following a single intervention. In the present review, we discuss the clinical feasibility and unique advantages that an in utero approach to treating HA could offer, placing special emphasis on a new sheep model of HA we have developed and on the use of mesenchymal stromal cells (MSC) as cellular vehicles for delivering the FVIII gene.

Gene therapy: the promise of a permanent cure

Gene therapy offers the possibility of a permanent cure for any of the more than 10,000 human diseases caused by a defect in a single gene. Among these diseases, the hemophilias represent an ideal target, and studies in both animals and humans have provided evidence that a permanent cure for hemophilia is within reach.

In utero transplantation: Disparate ramifications

In utero stem cell transplantation, which promises treatment for a host of genetic disorders early in gestation before disease effect stems from Ray Owen’s seminal observation that self-tolerance, is acquired during gestation. To date, in utero transplantation (IUT) has proved useful in characterizing the hematopoietic stem cell. Recent observations support its use as an in vivo method to further understanding of self-tolerance. Preclinical development continues for its application as a treatment for childhood hematolymphoid diseases. In addition, IUT may offer therapeutic options in the treatment of diabetes among other diseases. Thus IUT serves as a technique or system important in both a basic and applied format. This review summarizes these findings.

Mesenchymal stem cells contribute to endogenous FVIII:c production

Besides the liver, it has been difficult to identify which organ(s) and/or cellular component(s) contribute significantly to the production of human FVIII:c (FVIII). Thus far, only endothelial cells have been shown to constitute a robust extrahepatic source of FVIII, possibly explaining both the diverse presence of FVIII mRNA in the body, and the observed increase in FVIII levels during liver failure. Here, we investigate whether human mesenchymal stem cells (MSC), ubiquitously present in different organs, could also contribute to FVIII production. MSC isolated from human lung, liver, brain, and bone marrow expressed FVIII message as determined by quantitative-RT-PCR. Using an antibody specific for FVIII, confocal microscopy, and umbilical cord-derived endothelial cells (HUVEC) as a negative control, we demonstrated that, in MSC, FVIII protein was not stored in granules; rather, it localized to the perinuclear region. Furthermore, functional FVIII was detected in MSC supernatants and cell lysates by aPTT and chromogenic assays. These results demonstrate that MSC can contribute at low levels to the functional FVIII pool, and advance the understanding of the physiology of FVIII production and secretion.

Pseudotyped AAV vector-mediated gene transfer in a human fetal trachea xenograft model: implications for in utero gene therapy for cystic fibrosis

Background

Lung disease including airway infection and inflammation currently causes the majority of morbidities and mortalities associated with cystic fibrosis (CF), making the airway epithelium and the submucosal glands (SMG) novel target cells for gene therapy in CF. These target cells are relatively inaccessible to postnatal gene transfer limiting the success of gene therapy. Our previous work in a human-fetal trachea xenograft model suggests the potential benefit for treating CF in utero. In this study, we aim to validate adeno-associated virus serotype 2 (AAV2) gene transfer in a human fetal trachea xenograft model and to compare transduction efficiencies of pseudotyping AAV2 vectors in fetal xenografts and postnatal xenograft controls.

Methodology/Principal Findings

Human fetal trachea or postnatal bronchus controls were xenografted onto immunocompromised SCID mice for a four-week engraftment period. After injection of AAV2/2, 2/1, 2/5, 2/7 or 2/8 with a LacZ reporter into both types of xenografts, we analyzed for transgene expression in the respiratory epithelium and SMGs. At 1 month, transduction by AAV2/2 and AAV2/8 in respiratory epithelium and SMG cells was significantly greater than that of AAV2/1, 2/5, and 2/7 in xenograft tracheas. Efficiency in SMG transduction was significantly greater in AAV2/8 than AAV2/2. At 3 months, AAV2/2 and AAV2/8 transgene expression was >99% of respiratory epithelium and SMG. At 1 month, transduction efficiency of AAV2/2 and AAV2/8 was significantly less in adult postnatal bronchial xenografts than in fetal tracheal xenografts.

Conclusions/Significance

Based on the effectiveness of AAV vectors in SMG transduction, our findings suggest the potential utility of pseudotyped AAV vectors for treatment of cystic fibrosis. The human fetal trachea xenograft model may serve as an effective tool for further development of fetal gene therapy strategies for the in utero treatment of cystic fibrosis.

Recent advances in fetal gene therapy

Over the first decade of this new millennium gene therapy has demonstrated clear clinical benefits in several diseases for which conventional medicine offers no treatment. Clinical trials of gene therapy for single gene disorders have recruited predominantly young patients since older subjects may have suffered irrevocablepathological changes or may not be available because the disease is lethal relatively early in life. The concept of fetal gene therapy is an extension of this principle in that diseases in which irreversible changes occur at or beforebirth can be prevented by gene supplementation or repair in the fetus or associated maternal tissues. This article ccnsiders the enthusiasm and skepticism held for fetal gene therapy and its potential for clinical application. It coversa spectrum of candidate diseases for fetal gene therapy including Pompe disease, Gaucher disease, thalassemia, congenital protein C deficiency and cystic fibrosis. It outlines successful and not-so-successful examples of fetal gene therapy in animal models. Finally the application and potential of fetal gene transfer as a fundamental research tool for developmental biology and generation of somatic transgenic animals is surveyed.

Organ targeted prenatal gene therapy--how far are we?

Prenatal gene therapy aims to deliver genes to cells and tissues early in prenatal life, allowing correction of a genetic defect, before long-term tissue damage has occurred. In contrast to postnatal gene therapy, prenatal application can target genes to a large population of dividing stem cells, and the smaller fetal size allows a higher vector-to-target cell ratio to be achieved. Early-gestation delivery may allow the development of immune tolerance to the transgenic protein which would facilitate postnatal repeat vector administration if needed. Targeting particular organs will depend on manipulating the vector to achieve selective tropism and on choosing the most appropriate gestational age and injection method for fetal delivery. Intra-amniotic injection reaches the skin, and other organs that are bathed in the fluid however since gene transfer to the lung and gut is usually poor more direct injection methods will be needed. Delivery to the liver and blood can be achieved by systemic delivery via the umbilical vein or peritoneal cavity. Gene transfer to the central nervous system in the fetus is difficult but newer vectors are available that transduce neuronal tissue even after systemic delivery.

Fetal muscle gene therapy/gene delivery in large animals

Gene delivery to the fetal muscles is a potential strategy for the early treatment of muscular dystrophies. In utero muscle gene therapy can also be used to treat other genetic disorders such as hemophilia, where the missing clotting proteins may be secreted from the treated muscle. In the past few years, studies in small animal models have raised the hopes that a phenotypic cure can be obtained after fetal application of gene therapy. Studies of efficacy and safety in large animals are, however, essential before clinical application can be considered in the human fetus. For this reason, the development of clinically applicable strategies for the delivery of gene therapy to the fetal muscles is of prime importance. In this chapter, we describe the protocols for in utero ultrasound-guided gene delivery to the ovine fetal muscle in early gestation. In particular, procedures to inject skeletal muscle groups such as the thigh and thoracic musculature and targeting the diaphragm in the fetus are described in detail.

Fetal gene therapy: opportunities and risks

Advances in human prenatal medicine and molecular genetics have allowed the diagnosis of many genetic diseases early in gestation. In-utero transplantation of allogeneic hematopoietic stem cells (HSC) has been successfully used as a therapy in different animal models and recently also in human fetuses. Unfortunately, clinical success of this novel treatment is limited by the lack of donor cell engraftment in non-immunocompromised hosts and is thus restricted to diseases where the fetus is affected by severe immunodeficiency. Gene therapy using genetically modified autologous HSC circumvents allogeneic HLA barriers and constitutes one of the most promising new approaches to correct genetic deficits in the fetus. Recent developments of strategies to overcome failure of efficient transduction of quiescent hematopoietic cells include the use of new vector constructs and transduction protocols. These improvements open new perspectives for gene therapy in general and for prenatal gene transfer in particular. The fetus may be especially susceptible for successful gene therapy due to the immunologic naiveté of the immature hematopoietic system during gestation, precluding an immune reaction towards the transgene. Ethical issues, in particular those regarding treatment safety, must be taken into account before clinical trials with fetal gene therapy in human pregnancies can be initiated.