Nuclear Transfer

ADVANCING CUTTING-EDGE TECHNOLOGY

NUCLEAR TRANSFER

Applications In Research

SCNT and iPSC techniques are used in regenerative medicine institutes for research and in clinical investigations aimed at creating patient pluripotent cell lines for personalized medicine [4, 36]. Nuclear transfer techniques are widely used in embryo research in model organisms, such as mouse and primate embryos, to study early developmental events such as meiosis progression, causes of chromosome segregation errors or for studies on mtDNA replacement therapy (MRT) [30]. In USA such research is also permitted on human gametes and human embryos, under the strict FDA regulation that no genetically altered embryo is allowed to progress to fetus stages or used for clinical purposes. Several research studies have applied GV transfer and Spindle transfer in model organisms [17, 18, 37-44] and in human gametes [13, 19, 25-30, 32-34, 45-47]( see Applications in research under Human Egg Reconstitution (H.E.R IVF)).

APPLICATIONS IN CLINICAL INVESTIGATION
& FDA REGULATIONS

There are several applications of genetic editing that do not involve nuclear transfer and are approved for clinical procedures. In 2014, the Riken Center for Developmental Biology in Japan created the first patient-derived iPSC monolayer of retinal pigmented epithelium (RPE) that was transplanted back to the patient’s eye suffering from age-related macular degeneration. The replaced epithelium arrests vision deterioration in patients and, importantly, no safety concerns have been reported up to date [48, 49].

More recently, in August 2017, the FDA approved the first gene therapy in USA: a treatment called tisagenlecleucel provided by Novartis, where the patients’ own white blood cells are genetically reprogrammed to fight childhood B-cell acute lymphoblastic leukemia [50, 51]. The gene editing involves adding a transgene for the chimeric antigen receptor CAR, which directs the T cells to target leukemia cells [51]. About 600 children and young adults get this devastating disease every year and can potentially benefit from such new treatment, which was shown to cause remission in 83% of 63 young patients with the disease. Tisagenlecleucel can also cause a set of serious safety concerns, requiring medical staff training and readiness to counteract the reactions.

Gene therapy is also offered in Europe for a genetic disease which is fatal in early life: severe combined immunodeficiency (SCID) due to adenosine deaminase (ADA) defect, thought to occur in about 15 babies per year in Europe. The gene therapy treatment is called Strimvelis and was approved by the European Commission in 2016. It entails purifying hematopoietic stem cells from the newborn, and adding the gene to these cells via lentiviral vector encoding ADA, so that they can produce normally functioning adenosine deaminase protein, and then reintroducing the genetically altered cells back to the newborns [52].

Gene Therapy

In 2015, the UK Parliament approved human PNT for the prevention of inheritance of Mitochondrial Disease (Mito Disease), but as of today the technique has not been applied to patients in UK yet. In 2016, Dr John Zhang, founder of Darwin Life, conducted ST for mtDNA replacement and created the first baby boy alleviated from this genetic disease (in Mexico) [26]. This groundbreaking achievement is the first demonstration of the nuclear transfer technique successfully applied in reproductive medicine.

For women who are carriers of high mutation levels of mitochondrial DNA (mtDNA), conceiving healthy children requires their eggs to undergo mitochondrial replacement therapy (MRT) where the unhealthy mtDNA is replaced with healthy mtDNA from a donor. 0.5% of the population carries pathogenic mitochondrial DNA [53], which leads to diseases in at least 1 in 6500 of the population [25, 54]. Mitochondrial Disease (Mito Disease) is attributed to the systemic failure of the cells’ mitochondria. The mitochondria are the primary source of synthesizing ATP, the energy that fuels cell functions. Damage to the mitochondria prevents cells from generating the energy required to sustain life, and subsequent organ and biological system failure occurs.

Mito Disease is most commonly found in children causing widespread, systemic failure, developmental issues with the brain, heart, lungs and musculoskeletal system. These failures are often accompanied by repressed endocrine systems, respiratory issues, and, in many cases, result in early childhood death. A study by the Wellcome Trust Centre for Mitochondrial Research estimated that the average number of births among women at risk for transmitting pathogenic mitochondrial DNA mutations is around 778 births per year in the USA [55]. In order to prevent the onset of Mito Disease, the maternal egg cytoplasm has to be fully replaced with a healthy donor’s cytoplasm carrying healthy mtDNA, while keeping the mother’s genetic material [30].

Inheritable Mitochondrial Disease

In 2015, the UK Parliament approved human PNT for the prevention of inheritance of Mitochondrial Disease (Mito Disease), but as of today the technique has not been applied to patients in UK yet. In 2016, Dr John Zhang, founder of Darwin Life, conducted ST for mtDNA replacement and created the first baby boy alleviated from this genetic disease (in Mexico) [26]. This groundbreaking achievement is the first demonstration of the nuclear transfer technique successfully applied in reproductive medicine.

For women who are carriers of high mutation levels of mitochondrial DNA (mtDNA), conceiving healthy children requires their eggs to undergo mitochondrial replacement therapy (MRT) where the unhealthy mtDNA is replaced with healthy mtDNA from a donor. 0.5% of the population carries pathogenic mitochondrial DNA [53], which leads to diseases in at least 1 in 6500 of the population [25, 54]. Mitochondrial Disease (Mito Disease) is attributed to the systemic failure of the cells’ mitochondria. The mitochondria are the primary source of synthesizing ATP, the energy that fuels cell functions. Damage to the mitochondria prevents cells from generating the energy required to sustain life, and subsequent organ and biological system failure occurs.

Mito Disease is most commonly found in children causing widespread, systemic failure, developmental issues with the brain, heart, lungs and musculoskeletal system. These failures are often accompanied by repressed endocrine systems, respiratory issues, and, in many cases, result in early childhood death. A study by the Wellcome Trust Centre for Mitochondrial Research estimated that the average number of births among women at risk for transmitting pathogenic mitochondrial DNA mutations is around 778 births per year in the USA [55]. In order to prevent the onset of Mito Disease, the maternal egg cytoplasm has to be fully replaced with a healthy donor’s cytoplasm carrying healthy mtDNA, while keeping the mother’s genetic material [30].

Potential option for LGBT couples

MRT may create an additional opportunity for couples from the LGBT community around the world who prefer to have their own children over adoption or other options. Specifically, Spindle Transfer is directly applicable for the case of two female partners who wish to share biological children containing a combination of both their genetic composition. In this case, MRT would enable the combination of cytoplasmic environment from one partner and nuclear components from the other partner.

Potential option for women with infertility

Nuclear transfer has been previously applied to two women who suffered from infertility, unrelated to mtDNA disease or advanced aging. In 2003, the first pregnancy from human NT occurred after pronuclear transfer, for a 30-year old woman in China who had two failed IVF cycles due to persistent embryo arrest at the 2-cell stage [46]. In 2017, the pronuclear transfer technique was applied to a 34-year old woman in Ukraine who was also suffering from infertility and this resulted in a healthy birth.

Cytoplasm replacement for aging eggs

According to the latest statistics released by the Centers for Disease Control and Prevention (CDC), the birth rates for women 30 years of age or older continue to rise. By 2016 women aged 30 or older exhibited higher birth rate than women aged 25–29 for the first time since 1940. However, older women are known to exhibit reduced birth rates due to their lower quality of eggs [56] as well as dramatically higher rates of aneuploidy [57, 58]. The emerging trend of delaying having children combined with the fertility problems associated with advanced maternal age calls for the research and development of new IVF techniques to meet growing demands. The regulatory mechanisms responsible for assembly of the meiotic spindle in the cytoplasm of the oocyte can be replaced with younger components from a young oocyte with the aims of egg rejuvenation and rescue of meiosis errors [25]. For more educational information on total cytoplasm replacement for the prevention of Mito Disease, please see H.E.R IVF: Human Egg Reconstitution.