Discrimination of Stem Cell Status after Subjecting Cynomolgus Monkey Pluripotent Stem Cells to Naïve Conversion

An expedition in the jungle of pluripotent stem cells of non-human primates

For nearly three decades, more than 80 embryonic stem cell lines and more than 100 induced pluripotent stem cell lines have been derived from New World monkeys, Old World monkeys, and great apes. In this comprehensive review, we examine these cell lines originating from marmoset, cynomolgus macaque, rhesus macaque, pig-tailed macaque, Japanese macaque, African green monkey, baboon, chimpanzee, bonobo, gorilla, and orangutan. We outline the methodologies implemented for their establishment, the culture protocols for their long-term maintenance, and their basic molecular characterization. Further, we spotlight any cell lines that express fluorescent reporters. Additionally, we compare these cell lines with human pluripotent stem cell lines, and we discuss cell lines reprogrammed into a pluripotent naive state, detailing the processes used to attain this. Last, we present the findings from the application of these cell lines in two emerging fields: intra- and interspecies embryonic chimeras and blastoids.

Current state of stem cell research in non-human primates: an overview

The remarkable similarity between non-human primates (NHPs) and humans establishes them as essential models for understanding human biology and diseases, as well as for developing novel therapeutic strategies, thereby providing more comprehensive reference data for clinical treatment. Pluripotent stem cells such as embryonic stem cells and induced pluripotent stem cells provide unprecedented opportunities for cell therapies against intractable diseases and injuries. As continue to harness the potential of these biotechnological therapies, NHPs are increasingly being employed in preclinical trials, serving as a pivotal tool to evaluate the safety and efficacy of these interventions. Here, we review the recent advancements in the fundamental research of stem cells and the progress made in studies involving NHPs.

Attempts for deriving extended pluripotent stem cells from common marmoset embryonic stem cells

Extended pluripotent stem cells (EPSCs) derived from mice and humans showed an enhanced potential for chimeric formation. By exploiting transcriptomic approaches, we assessed the differences in gene expression profile between extended EPSCs derived from mice and humans, and those newly derived from the common marmoset (marmoset; Callithrix jacchus). Although the marmoset EPSC-like cells displayed a unique colony morphology distinct from murine and human EPSCs, they displayed a pluripotent state akin to embryonic stem cells (ESCs), as confirmed by gene expression and immunocytochemical analyses of pluripotency markers and three-germ-layer differentiation assay. Importantly, the marmoset EPSC-like cells showed interspecies chimeric contribution to mouse embryos, such as E6.5 blastocysts in vitro and E6.5 epiblasts in vivo in mouse development. Also, we discovered that the perturbation of gene expression of the marmoset EPSC-like cells from the original ESCs resembled that of human EPSCs. Taken together, our multiple analyses evaluated the efficacy of the method for the derivation of marmoset EPSCs.

Assisted Reproductive Techniques and Genetic Manipulation in the Common Marmoset

Genetic modification of nonhuman primate (NHP) zygotes is a useful method for the development of NHP models of human diseases. This review summarizes the recent advances in the development of assisted reproductive and genetic manipulation techniques in NHP, providing the basis for the generation of genetically modified NHP disease models. In this study, we review assisted reproductive techniques, including ovarian stimulation, in vitro maturation of oocytes, in vitro fertilization, embryo culture, embryo transfer, and intracytoplasmic sperm injection protocols in marmosets. Furthermore, we review genetic manipulation techniques, including transgenic strategies, target gene knock-out and knock-in using gene editing protocols, and newly developed gene-editing approaches that may potentially impact the production of genetically manipulated NHP models. We further discuss the progress of assisted reproductive and genetic manipulation techniques in NHP; future prospects on genetically modified NHP models for biomedical research are also highlighted.

Establishment of novel common marmoset embryonic stem cell lines under various conditions

Pluripotent stem cells (PSCs), embryonic stem cells (ESCs), and induced PSCs (iPSCs) are excellent tools for studying embryonic development in organisms and classified into naïve and primed states. ESC-derived germline chimera individuals can be produced by injecting naïve ESCs/iPSCs into preimplantation embryos, and conversion of primed human ESCs/iPSCs into a naïve state provides insights into epiblast cell features. Non-human ESCs/iPSCs are alternatives to human naïve ESCs/iPSCs, which elicit ethical issues. In this study, we used the common marmoset (Callithrix jacchus) as an animal model. Since 1996, 16 marmoset ESC lines have been established. Because most of these ESC lines are female and were derived >10 years ago, new ESCs, particularly male marmoset ESC lines, are needed. Here, we successfully established 17 novel marmoset ESC lines, including six male ESC lines from in vitro-fertilized (IVF) embryos and 12 ESC lines under feeder-free conditions. This report is the first to establish ESC lines using feeder-free conditions and IVF preimplantation blastocysts in marmosets, and these novel ESC lines could potentially facilitate future non-human primate ESC studies.

In Vitro and In Vivo Interspecies Chimera Assay Using Early Pig Embryos

Chimeric pigs harboring organs derived from human stem cells are promising for patient-specific regenerative therapies. Induced pluripotent stem cells (iPSCs) can contribute to all cell types of the fetus, including germline after injection into embryos. However, ethical concerns prohibit testing human iPSCs in chimera assays. Here, we evaluated porcine embryos as hosts for an interspecies chimera assay using iPSCs from either cynomolgus monkeys (cyiPSCs) or mouse (miPSCs). To establish an in vitro culture system compatible for cyiPSCs and porcine embryos, we determined blastocyst development in eight different stem cell media. The highest developmental rates of blastocysts were achieved in Knockout Dulbecco's modified Eagle's medium with 20% knockout serum replacement. We found that cyiPSCs injected into porcine embryos survived in vitro and were mostly located in the trophectoderm (TE). Instead, when miPSCs were injected into porcine embryos, the cells rapidly proliferated. The behavior of chimeras developed in vitro was recapitulated in vivo; cyiPSCs were observed in the TE, but not in the porcine epiblast. However, when miPSCs were injected into in vivo derived porcine embryos, mouse cells were found in both, the epiblast and TE. These results demonstrate that porcine embryos could be useful for evaluating the interspecies chimera-forming ability of iPSCs from different species.

The roles and regulation of TBX3 in development and disease

TBX3, a member of the ancient and evolutionary conserved T-box transcription factor family, is a critical developmental regulator of several structures including the heart, mammary glands, limbs and lungs. Indeed, mutations in the human TBX3 lead to ulnar mammary syndrome which is characterized by several clinical malformations including hypoplasia of the mammary and apocrine glands, defects of the upper limb, areola, dental structures, heart and genitalia. In contrast, TBX3 has no known function in adult tissues but is frequently overexpressed in a wide range of epithelial and mesenchymal derived cancers. This overexpression greatly impacts several hallmarks of cancer including bypass of senescence, apoptosis and anoikis, promotion of proliferation, tumour formation, angiogenesis, invasion and metastatic capabilities as well as cancer stem cell expansion. The debilitating consequences of having too little or too much TBX3 suggest that its expression levels need to be tightly regulated. While we have a reasonable understanding of the mutations that result in low levels of functional TBX3 during development, very little is known about the factors responsible for the overexpression of TBX3 in cancer. Furthermore, given the plethora of oncogenic processes that TBX3 impacts, it must be regulating several target genes but to date only a few have been identified and characterised. Interestingly, while there is compelling evidence to support oncogenic roles for TBX3, a few studies have indicated that it may also have tumour suppressor functions in certain contexts. Together, the diverse functional elasticity of TBX3 in development and cancer is thought to involve, in part, the protein partners that it interacts with and this area of research has recently received some attention. This review provides an insight into the significance of TBX3 in development and cancer and identifies research gaps that need to be explored to shed more light on this transcription factor.

Induction of the germ cell fate from pluripotent stem cells in cynomolgus monkeys†

In vitro reconstitution of germ-cell development from pluripotent stem cells (PSCs) has created key opportunities to explore the fundamental mechanisms underlying germ-cell development, particularly in mice and humans. Importantly, such investigations have clarified critical species differences in the mechanisms regulating mouse and human germ-cell development, highlighting the necessity of establishing an in vitro germ-cell development system in other mammals, such as non-human primates. Here, we show that multiple lines of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) in cynomolgus monkeys (Macaca fascicularis; cy) can be maintained stably in an undifferentiated state under a defined condition with an inhibitor for WNT signaling, and such PSCs are induced efficiently into primordial germ cell-like cells (PGCLCs) bearing a transcriptome similar to early cyPGCs. Interestingly, the induction kinetics of cyPGCLCs from cyPSCs is faster than that of human (h) PGCLCs from hPSCs, and while the transcriptome dynamics during cyPGCLC induction is relatively similar to that during hPGCLC induction, it is substantially divergent from that during mouse (m) PGCLC induction. Our findings delineate common as well as species-specific traits for PGC specification, creating a foundation for parallel investigations into the mechanism for germ-cell development in mice, monkeys, and humans.

The Cynomolgus Macaque MHC Polymorphism in Experimental Medicine

Among the non-human primates used in experimental medicine, cynomolgus macaques (Macaca fascicularis hereafter referred to as Mafa) are increasingly selected for the ease with which they are maintained and bred in captivity. Macaques belong to Old World monkeys and are phylogenetically much closer to humans than rodents, which are still the most frequently used animal model. Our understanding of the Mafa genome has progressed rapidly in recent years and has greatly benefited from the latest technical advances in molecular genetics. Cynomolgus macaques are widespread in Southeast Asia and numerous studies have shown a distinct genetic differentiation of continental and island populations. The major histocompatibility complex of cynomolgus macaque (Mafa MHC) is organized in the same way as that of human, but it differs from the latter by its high degree of classical class I gene duplication. Human polymorphic MHC regions play a pivotal role in allograft transplantation and have been associated with more than 100 diseases and/or phenotypes. The Mafa MHC polymorphism similarly plays a crucial role in experimental allografts of organs and stem cells. Experimental results show that the Mafa MHC class I and II regions influence the ability to mount an immune response against infectious pathogens and vaccines. MHC also affects cynomolgus macaque reproduction and impacts on numerous biological parameters. This review describes the Mafa MHC polymorphism and the methods currently used to characterize it. We discuss some of the major areas of experimental medicine where an effect induced by MHC polymorphism has been demonstrated.

Xenogeneic chimera-Generated by blastocyst complementation-As a potential unlimited source of recipient-tailored organs

Blastocyst complementation refers to the injection of cells into a blastocyst. The technology allows for the creation of chimeric animals, which have the potential to be used as an unlimited source of organ donors. Pluripotent stem cells could be generated from a patient in need of a transplantation and injected into a large animal blastocyst (potentially of a pig), leading to the creation of organ(s) allowing immunosuppression-free transplantation. Various chimera combinations have already been generated, but one of the most recent steps leads to the creation of human-pig chimeras, which could be studied at an embryo stage. Although still far from clinical reality, the potential application is almost unlimited. The present review illustrates the historical steps of intra- and interspecific blastocyst complementation in rodents and large animals, specifically looking at its potential for generation of organ grafts. We also speculate on how it could change transplant indications, on its economic impact, and on the linked ethical concerns.