Development of blastocyst complementation technology without contributions to gametes and the brain

Efficiency of embryo complementation and pluripotency maintenance following multiple passaging of in vitro-derived bovine embryos

Context Current methods to obtain bovine embryos of high genetic merit include approaches that require skilled techniques for low-efficiency cloning strategies. Aims The overall goal herein was to identify the efficacy of alternative methods for producing multiple embryos through blastomere complementation while determining maintenance of cell pluripotency. Methods Bovine oocytes were fertilised in vitro to produce 4-cell embryos from which blastomeres were isolated and cultured as 2-cell aggregates using a well-of-the-well system. Aggregates were returned to incubation up to 7days (Passage 1). A second passage of complement embryos was achieved by splitting 4-cell Passage 1 embryos. Passaged embryos reaching the blastocyst stage were characterised for cell number and cell lineage specification in replicate with non-reconstructed zona-intact embryos. Key results Passage 1 and 2 embryo complements yielded 29% and 25% blastocyst development, respectively. Passage 1 embryos formed blastocysts, but with a reduction in expression of SOX2 and decreased size compared to non-reconstructed zona-intact embryos. Passage 2 embryos had a complete lack of SOX2 expression and a reduction in transcript abundance of SOX2 and SOX17, suggesting loss of pluripotency markers that primarily affected inner cell mass (ICM) and hypoblast formation. Conclusions In vitro fertilised bovine embryos can be reconstructed with multiple passaging to generate genetically identical embryos. Increased passaging drives trophectoderm cell lineage specification while compromising ICM formation. Implications These results may provide an alternative strategy for producing genetically identical bovine embryos through blastomere complementation with applications towards the development of trophoblast and placental models of early development.

Mesendodermal cells fail to contribute to heart formation following blastocyst injection

Blastocyst complementation offers an opportunity for generating transplantable whole organs from donor sources. Pluripotent stem cells (PSCs) have traditionally served as the primary donor cells due to their ability to differentiate into any type of body cell. However, the use of PSCs raises ethical concerns, particularly regarding their uncontrollable differentiation potential to undesired cell lineages such as brain and germline cells. To address this issue, various strategies have been explored, including the use of genetically modified PSCs with restricted lineage potential or lineage-specified progenitor cells as donors. In this study, we tested whether nascent mesendodermal cells (MECs), which appear during early gastrulation, can be used as donor cells. To do this, we induced Bry-GFP+ MECs from mouse embryonic stem cells (ESCs) and introduced them into the blastocyst. While donor ESCs gave rise to various regions of embryos, including the heart, Bry-GFP+ MECs failed to contribute to the host embryos. This finding suggests that MECs, despite being specified from PSCs within a few days, lack the capacity to assimilate into the developing embryo.

Generation of allogeneic and xenogeneic functional muscle stem cells for intramuscular transplantation

Satellite cells, the stem cells of skeletal muscle tissue, hold a remarkable regeneration capacity and therapeutic potential in regenerative medicine. However, low satellite cell yield from autologous or donor-derived muscles hinders the adoption of satellite cell transplantation for the treatment of muscle diseases, including Duchenne muscular dystrophy (DMD). To address this limitation, here we investigated whether satellite cells can be derived in allogeneic or xenogeneic animal hosts. First, injection of CRISPR/Cas9-corrected Dmdmdx mouse induced pluripotent stem cells (iPSCs) into mouse blastocysts carrying an ablation system of host satellite cells gave rise to intraspecies chimeras exclusively carrying iPSC-derived satellite cells. Furthermore, injection of genetically corrected DMD iPSCs into rat blastocysts resulted in the formation of interspecies rat-mouse chimeras harboring mouse satellite cells. Notably, iPSC-derived satellite cells or derivative myoblasts produced in intraspecies or interspecies chimeras restored dystrophin expression in DMD mice following intramuscular transplantation and contributed to the satellite cell pool. Collectively, this study demonstrates the feasibility of producing therapeutically competent stem cells across divergent animal species, raising the possibility of generating human muscle stem cells in large animals for regenerative medicine purposes.

Chimeric Livers: Interspecies Blastocyst Complementation and Xenotransplantation for End-Stage Liver Disease

Orthotopic liver transplantation (OLT) currently serves as the sole definitive treatment for thousands of patients suffering from end-stage liver disease; and the existing supply of donor livers for OLT is drastically outpaced by the increasing demand. To alleviate this significant gap in treatment, several experimental approaches have been devised with the aim of either offering interim support to patients waiting on the transplant list or bioengineering complete livers for OLT by infusing them with fresh hepatic cells. Recently, interspecies blastocyst complementation has emerged as a promising method for generating complete organs in utero over a short timeframe. When coupled with gene editing technology, it has brought about a potentially revolutionary transformation in regenerative medicine. Blastocyst complementation harbors notable potential for generating complete human livers in large animals, which could be used for xenotransplantation in humans, addressing the scarcity of livers for OLT. Nevertheless, substantial experimental and ethical challenges still need to be overcome to produce human livers in larger domestic animals like pigs. This review compiles the current understanding of interspecies blastocyst complementation and outlines future possibilities for liver xenotransplantation in humans.

Generation of germ cell-deficient pigs by NANOS3 knockout

NANOS3 is an evolutionarily conserved gene expressed in primordial germ cells that is important for germ cell development. Germ cell deletion by NANOS3 knockout has been reported in several mammalian species, but its function in pigs is unclear. In the present study, we investigated the germline effects of NANOS3 knockout in pigs using CRISPR/Cas9. Embryo transfer of CRISPR/Cas9-modified embryos produced ten offspring, of which one showed wild-type NANOS3 alleles, eight had two mutant NANOS3 alleles, and the other exhibited mosaicism (four mutant alleles). Histological analysis revealed no germ cells in the testes or ovaries of any of the nine mutant pigs. These results demonstrated that NANOS3 is crucial for porcine germ cell production.

In Vivo Generation of Organs by Blastocyst Complementation: Advances and Challenges

The ultimate goal of regenerative medicine is to replace damaged cells, tissues or whole organs, in order to restore their proper function. Stem cell related technologies promise to generate transplants from the patients' own cells. Novel approaches such as blastocyst complementation combined with genome editing open up new perspectives for organ replacement therapies. This review summarizes recent advances in the field and highlights the challenges that still remain to be addressed.

The road to generating transplantable organs: from blastocyst complementation to interspecies chimeras

Growing human organs in animals sounds like something from the realm of science fiction, but it may one day become a reality through a technique known as interspecies blastocyst complementation. This technique, which was originally developed to study gene function in development, involves injecting donor pluripotent stem cells into an organogenesis-disabled host embryo, allowing the donor cells to compensate for missing organs or tissues. Although interspecies blastocyst complementation has been achieved between closely related species, such as mice and rats, the situation becomes much more difficult for species that are far apart on the evolutionary tree. This is presumably because of layers of xenogeneic barriers that are a result of divergent evolution. In this Review, we discuss the current status of blastocyst complementation approaches and, in light of recent progress, elaborate on the keys to success for interspecies blastocyst complementation and organ generation.

ISSCR guidelines for the transfer of human pluripotent stem cells and their direct derivatives into animal hosts

The newly revised 2021 ISSCR Guidelines for Stem Cell Research and Clinical Translation includes scientific and ethical guidance for the transfer of human pluripotent stem cells and their direct derivatives into animal models. In this white paper, the ISSCR subcommittee that drafted these guidelines for research involving the use of nonhuman embryos and postnatal animals explains and summarizes their recommendations.

Generating liver using blastocyst complementation: Opportunities and challenges

Orthotopic liver transplantation (OLT) is the only definitive treatment option for many patients with end-stage liver disease. Current supply of donor livers for OLT is not keeping up with the growing demand. To overcome this problem, a number of experimental strategies have been developed either to provide a bridge to transplant for patients on the waiting list or to bioengineer whole livers for OLT by replenishing them with fresh supplies of hepatic cells. In recent years, blastocyst complementation has emerged as the most promising approach for generating whole organs and, in combination with gene editing technology, it has revolutionized regenerative medicine. This methodology was successful in producing xenogeneic organs in animal hosts. Blastocyst complementation has the potential to produce whole livers in large animals that could be xenotransplanted in humans, thereby reducing the shortage of livers for OLT. However, significant experimental and ethical barriers remain for the production of human livers in domestic animals, such as the pig. This review summarizes the current knowledge and provides future perspectives for liver xenotransplantation in humans.

Generation of donor organs in chimeric animals via blastocyst complementation

The lack of organs for transplantation is an important problem in medicine today. The growth of organs in chimeric animals may be the solution of this. The proposed technology is the interspecific blastocyst complementation method in combination with genomic editing for obtaining “free niches” and pluripotent stem cell production methods. The CRISPR/Cas9 method allows the so-called “free niches” to be obtained for blastocyst complementation. The technologies of producing induced pluripotent stem cells give us the opportunity to obtain human donor cells capable of populating a “free niche”. Taken together, these technologies allow interspecific blastocyst complementation between humans and other animals, which makes it possible in the future to grow human organs for transplantations inside chimeric animals. However, in practice, in order to achieve successful interspecific blastocyst complementation, it is necessary to solve a number of problems: to improve methods for producing “chimeric competent” cells, to overcome specific interspecific barriers, to select compatible cell developmental stages for injection and the corresponding developmental stage of the host embryo, to prevent apoptosis of donor cells and to achieve effective proliferation of the human donor cells in the host animal. Also, it is very important to analyze the ethical aspects related to developing technologies of chimeric organisms with the participation of human cells. Today, many researchers are trying to solve these problems and also to establish new approaches in the creation of interspecific chimeric organisms in order to grow human organs for transplantation. In the present review we described the historical stages of the development of the blastocyst complementation method, examined in detail the technologies that underlie modern blastocyst complementation, and analyzed current progress that gives us the possibility to grow human organs in chimeric animals. We also considered the barriers and issues preventing the successful implementation of interspecific blastocyst complementation in practice, and discussed the further development of this method

[George Lucas: prophet of transhumanism?]

Star Wars, a "general public" film saga, raises questions about human nature and transhumanism. It features different characters who are neither "real" humans nor robots; there are creatures that can be likened to advanced humans (cyborgs, chimeras or genetically-modified humans). Based on the "Star Wars" movie, we will approach some ways of modifying the human person both in his body and in his consciousness and we will wonder about the man of tomorrow by asking ourselves if George Lucas (director of the first film released) might have not been a visionary of the men of tomorrow.