Candidate diseases for prenatal gene therapy

Intrauterine Fetal Gene Therapy: Is That the Future and Is That Future Now?

Researchers are looking into techniques to intervene sooner and earlier in the disease process thanks to advances in disease genetics, etiologies, and prenatal diagnosis. We conducted a literature search in PubMed-indexed journals to provide an overview of the evolution of gene therapy, rationale for prenatal gene therapy, uses and risks of gene therapy, and ethical issues following the usage of gene therapy. Recent animal research has revealed that transmitting genetic material to a growing fetus through viral and non-viral vectors is conceivable besides proving how gene-editing technology is achieved by various mechanisms that utilize zinc finger nucleases, TAL effector nucleases, and clustered short palindromic repeats-Cas9 complex. This review offers an overview of the current knowledge in the field of prenatal gene therapy, as well as potential future research avenues. In addition, it weighs the risks of prenatal gene therapy, such as oncogenesis, genetic mutation transfer from mother to child, and fetal disruption, against the expected benefits, such as preventing the development of severe early-onset illness symptoms, targeting previously inaccessible organs, and establishing tolerance to the therapeutic transgenic protein, all of which lead to permanent somatic gene correction.

This review discusses the scientific, ethical, legal, and sociological implications of these groundbreaking genetic disease prevention techniques, as well as the parameters that must be satisfied for a future clinical application to be considered.

Intrauterine Hypoxia and Epigenetic Programming in Lung Development and Disease

Clinically, intrauterine hypoxia is the foremost cause of perinatal morbidity and developmental plasticity in the fetus and newborn infant. Under hypoxia, deviations occur in the lung cell epigenome. Epigenetic mechanisms (e.g., DNA methylation, histone modification, and miRNA expression) control phenotypic programming and are associated with physiological responses and the risk of developmental disorders, such as bronchopulmonary dysplasia. This developmental disorder is the most frequent chronic pulmonary complication in preterm labor. The pathogenesis of this disease involves many factors, including aberrant oxygen conditions and mechanical ventilation-mediated lung injury, infection/inflammation, and epigenetic/genetic risk factors. This review is focused on various aspects related to intrauterine hypoxia and epigenetic programming in lung development and disease, summarizes our current knowledge of hypoxia-induced epigenetic programming and discusses potential therapeutic interventions for lung disease.

Therapeutic expression of human clotting factors IX and X following adeno-associated viral vector-mediated intrauterine gene transfer in early-gestation fetal macaques

Adeno-associated viral vectors (AAVs) achieve stable therapeutic expression without long-term toxicity in adults with hemophilia. To avert irreversible complications in congenital disorders producing early pathogenesis, safety and efficacy of AAV-intrauterine gene transfer (IUGT) requires assessment. We therefore performed IUGT of AAV5 or -8 with liver-specific promoter-1 encoding either human coagulation factors IX (hFIX) or X (hFX) into Macaca fascicularis fetuses at ∼0.4 gestation. The initial cohort received 1 × 10¹² vector genomes (vgs) of AAV5-hFIX (n = 5; 0.45 × 10¹³ vg/kg birth weight), resulting in ∼3.0% hFIX at birth and 0.6–6.8% over 19–51 mo. The next cohort received 0.2–1 × 10¹³ vg boluses. AAV5-hFX animals (n = 3; 3.57 × 10¹³ vg/kg) expressed <1% at birth and 9.4–27.9% up to 42 mo. AAV8-hFIX recipients (n = 3; 2.56 × 10¹³ vg/kg) established 4.2–41.3% expression perinatally and 9.8–25.3% over 46 mo. Expression with AAV8-hFX (n = 6, 3.12 × 10¹³ vg/kg) increased from <1% perinatally to 9.8–13.4% >35 mo. Low expressers (<1%, n = 3) were postnatally challenged with 2 × 10¹¹ vg/kg AAV5 resulting in 2.4–13.2% expression and demonstrating acquired tolerance. Linear amplification–mediated-PCR analysis demonstrated random integration of 57–88% of AAV sequences retrieved from hepatocytes with no events occurring in or near oncogenesis-associated genes. Thus, early-IUGT in macaques produces sustained curative expression related significantly to integrated AAV in the absence of clinical toxicity, supporting its therapeutic potential for early-onset monogenic disorders.—Chan, J. K. Y., Gil-Farina I., Johana, N., Rosales, C., Tan, Y. W., Ceiler, J., Mcintosh, J., Ogden, B., Waddington, S. N., Schmidt, M., Biswas, A., Choolani, M., Nathwani, A. C., Mattar, C. N. Z. Therapeutic expression of human clotting factors IX and X following adeno-associated viral vector–mediated intrauterine gene transfer in early-gestation fetal macaques.

Cochlear Gene Therapy for Sensorineural Hearing Loss: Current Status and Major Remaining Hurdles for Translational Success

Sensorineural hearing loss (SNHL) affects millions of people. Genetic mutations play a large and direct role in both congenital and late-onset cases of SNHL (e.g., age-dependent hearing loss, ADHL). Although hearing aids can help moderate to severe hearing loss the only effective treatment for deaf patients is the cochlear implant (CI). Gene- and cell-based therapies potentially may preserve or restore hearing with more natural sound perception, since their theoretical frequency resolution power is much higher than that of cochlear implants. These biologically-based interventions also carry the potential to re-establish hearing without the need for implanting any prosthetic device; the convenience and lower financial burden afforded by such biologically-based interventions could potentially benefit far more SNHL patients. Recently major progress has been achieved in preclinical studies of cochlear gene therapy. This review critically evaluates recent advances in the preclinical trials of gene therapies for SNHL and the major remaining challenges for the development and eventual clinical translation of this novel therapy. The cochlea bears many similarities to the eye for translational studies of gene therapies. Experience gained in ocular gene therapy trials, many of which have advanced to clinical phase III, may provide valuable guidance in improving the chance of success for cochlear gene therapy in human trials. A discussion on potential implications of translational knowledge gleaned from large numbers of advanced clinical trials of ocular gene therapy is therefore included.

High-efficiency transduction of spinal cord motor neurons by intrauterine delivery of integration-deficient lentiviral vectors

Integration-deficient lentiviral vectors (IDLVs) are promising gene delivery tools that retain the high transduction efficiency of standard lentiviral vectors, yet fail to integrate as proviruses and are instead converted into episomal circles. These episomes are metabolically stable and support long-term expression of transgenes in non-dividing cells, exhibiting a decreased risk of insertional mutagenesis. We have embarked on an extensive study to compare the transduction efficiency of IDLVs pseudotyped with different envelopes (vesicular stomatitis, Rabies, Mokola and Ross River viral envelopes) and self-complementary adeno-associated viral vectors, serotype-9 (scAAV-9) in spinal cord tissues after intraspinal injection of mouse embryos (E16). Our results indicate that IDLVs can transduce motor neurons (MNs) at extremely high efficiency regardless of the envelope pseudotype while scAAV9 mediates gene delivery to ~ 40% of spinal cord motor neurons, with other non-neuronal cells also transduced. Long-term expression studies revealed stable gene expression at 7 months post-injection. Taken together, the results of this study indicate that IDLVs may be efficient tools for in utero cord transduction in therapeutic strategies such as for treatment of inherited early childhood neurodegenerative diseases.

In utero therapy for congenital disorders using amniotic fluid stem cells

Congenital diseases are responsible for over a third of all pediatric hospital admissions. Advances in prenatal screening and molecular diagnosis have allowed the detection of many life-threatening genetic diseases early in gestation. In utero transplantation (IUT) with stem cells could cure affected fetuses but so far in humans, successful IUT using allogeneic hematopoietic stem cells (HSCs), has been limited to fetuses with severe immunologic defects and more recently IUT with allogeneic mesenchymal stem cell transplantation, has improved phenotype in osteogenesis imperfecta. The options of preemptive treatment of congenital diseases in utero by stem cell or gene therapy changes the perspective of congenital diseases since it may avoid the need for postnatal treatment and reduce future costs. Amniotic fluid stem (AFS) cells have been isolated and characterized in human, mice, rodents, rabbit, and sheep and are a potential source of cells for therapeutic applications in disorders for treatment prenatally or postnatally. Gene transfer to the cells with long-term transgenic protein expression is feasible. Recently, pre-clinical autologous transplantation of transduced cells has been achieved in fetal sheep using minimally invasive ultrasound guided injection techniques. Clinically relevant levels of transgenic protein were expressed in the blood of transplanted lambs for at least 6 months. The cells have also demonstrated the potential of repair in a range of pre-clinical disease models such as neurological disorders, tracheal repair, bladder injury, and diaphragmatic hernia repair in neonates or adults. These results have been encouraging, and bring personalized tissue engineering for prenatal treatment of genetic disorders closer to the clinic.

Gene therapy for the neurological manifestations in lysosomal storage disorders

Over the past several years, considerable progress has been made in the development of gene therapy as a therapeutic strategy for a variety of inherited metabolic diseases, including neuropathic lysosomal storage disorders (LSDs). The premise of gene therapy for this group of diseases is borne of findings that genetic modification of a subset of cells can provide a more global benefit by virtue of the ability of the secreted lysosomal enzymes to effect cross-correction of adjacent and distal cells. Preclinical studies in small and large animal models of these disorders support the application of either a direct in vivo approach using recombinant adeno-associated viral vectors or an ex vivo strategy using lentiviral vector-modified hematopoietic stem cells to correct the neurological component of these diseases. Early clinical studies utilizing both approaches have begun or are in late-stage planning for a small number of neuropathic LSDs. Although initial indications from these studies are encouraging, it is evident that second-generation vectors that exhibit a greater safety profile and transduction activity may be required before this optimism can be fully realized. Here, I review recent progress and the remaining challenges to treat the neurological aspects of various LSDs using this therapeutic paradigm.