The Role of Nonhuman Primate Animal Models in the Clinical Development of Pluripotent Stem Cell Therapies

Non-human primate pluripotent stem cells for the preclinical testing of regenerative therapies

Non-human primates play a key role in the preclinical validation of pluripotent stem cell-based cell replacement therapies. Pluripotent stem cells used as advanced therapy medical products boost the possibility to regenerate tissues and organs affected by degenerative diseases. Therefore, the methods to derive human induced pluripotent stem cell and embryonic stem cell lines following clinical standards have quickly developed in the last 15 years. For the preclinical validation of cell replacement therapies in non-human primates, it is necessary to generate non-human primate pluripotent stem cell with a homologous quality to their human counterparts. However, pluripotent stem cell technologies have developed at a slower pace in non-human primates in comparison with human cell systems. In recent years, however, relevant progress has also been made with non-human primate pluripotent stem cells. This review provides a systematic overview of the progress and remaining challenges for the generation of non-human primate induced pluripotent stem cells/embryonic stem cells for the preclinical testing and validation of cell replacement therapies. We focus on the critical domains of (1) reprogramming and embryonic stem cell line derivation, (2) cell line maintenance and characterization and, (3) application of non-human primate pluripotent stem cells in the context of selected preclinical studies to treat cardiovascular and neurodegenerative disorders performed in non-human primates.

Preclinical models and technologies to advance nanovaccine development

The remarkable success of targeted immunotherapies is revolutionizing cancer treatment. However, tumor heterogeneity and low immunogenicity, in addition to several tumor-associated immunosuppression mechanisms are among the major factors that have precluded the success of cancer vaccines as targeted cancer immunotherapies. The exciting outcomes obtained in patients upon the injection of tumor-specific antigens and adjuvants intratumorally, reinvigorated interest in the use of nanotechnology to foster the delivery of vaccines to address cancer unmet needs. Thus, bridging nano-based vaccine platform development and predicted clinical outcomes the selection of the proper preclinical model will be fundamental. Preclinical models have revealed promising outcomes for cancer vaccines. However, only few cases were associated with clinical responses. This review addresses the major challenges related to the translation of cancer nano-based vaccines to the clinic, discussing the requirements for ex vivo and in vivo models of cancer to ensure the translation of preclinical success to patients.

Generation of macrophages with altered viral sensitivity from genome-edited rhesus macaque iPSCs to model human disease

Because of their close biological similarity to humans, non-human primate (NHP) models are very useful for the development of induced pluripotent stem cell (iPSC)-based cell and regenerative organ transplantation therapies. However, knowledge on the establishment, differentiation, and genetic modification of NHP-iPSCs, especially rhesus macaque iPSCs, is limited. We succeeded in establishing iPSCs from the peripheral blood of rhesus macaques (Rh-iPSCs) by combining the Yamanaka reprograming factors and two inhibitors (GSK-3 inhibitor [CHIR 99021] and MEK1/2 inhibitor [PD0325901]) and differentiated the cells into functional macrophages through hematopoietic progenitor cells. To confirm feasibility of the Rh-iPSC-derived macrophages as a platform for bioassays to model diseases, we knocked out TRIM5 gene in Rh-iPSCs by CRISPR-Cas9, which is a species-specific HIV resistance factor. TRIM5 knockout (KO) iPSCs had the same differentiation potential to macrophages as did Rh-iPSCs, but the differentiated macrophages showed a gain of sensitivity to HIV infection in vitro. Our reprogramming, gene editing, and differentiation protocols used to obtain Rh-iPSC-derived macrophages can be applied to other gene mutations, expanding the number of NHP gene therapy models.

Strategies and Challenges to Improve Cellular Programming-Based Approaches for Heart Regeneration Therapy

Limited adult cardiac cell proliferation after cardiovascular disease, such as heart failure, hampers regeneration, resulting in a major loss of cardiomyocytes (CMs) at the site of injury. Recent studies in cellular reprogramming approaches have provided the opportunity to improve upon previous techniques used to regenerate damaged heart. Using these approaches, new CMs can be regenerated from differentiation of iPSCs (similar to embryonic stem cells), the direct reprogramming of fibroblasts [induced cardiomyocytes (iCMs)], or induced cardiac progenitors. Although these CMs have been shown to functionally repair infarcted heart, advancements in technology are still in the early stages of development in research laboratories. In this review, reprogramming-based approaches for generating CMs are briefly introduced and reviewed, and the challenges (including low efficiency, functional maturity, and safety issues) that hinder further translation of these approaches into a clinical setting are discussed. The creative and combined optimal methods to address these challenges are also summarized, with optimism that further investigation into tissue engineering, cardiac development signaling, and epigenetic mechanisms will help to establish methods that improve cell-reprogramming approaches for heart regeneration.

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.

Utilization of Human Induced Pluripotent Stem Cells for Cardiac Repair

The paracrine effect, mediated by chemical signals that induce a physiological response on neighboring cells in the same tissue, is an important regenerative mechanism for stem cell-based therapy. Exosomes are cell-secreted nanovesicles (50–120 nm) of endosomal origin, and have been demonstrated to be a major contributor to the observed stem cell-mediated paracrine effect in the cardiac repair process. Following cardiac injury, exosomes deriving from exogenous stem cells have been shown to regulate cell apoptosis, proliferation, angiogenesis, and fibrosis in the infarcted heart. Exosomes also play a crucial role in the intercellular communication between donor and recipient cells. Human induced pluripotent stem cells (hiPSCs) are promising cell sources for autologous cell therapy in regenerative medicine. Here, we review recent advances in the field of progenitor-cell derived, exosome-based cardiac repair, with special emphasis on exosomes derived from hiPSCs.

Enhanced wound healing promotion by immune response-free monkey autologous iPSCs and exosomes vs. their allogeneic counterparts

Background

Comparing non-inbred autologous and allogeneic induced pluripotent stem cells (iPSCs) and their secreted subcellular products among non-human primates is critical for choosing optimal iPSC products for human clinical trials.

Methods

iPSCs were induced from skin fibroblastic cells of adult male rhesus macaques belonging to four unrelated consanguineous families. Teratoma generativity, host immune response, and skin wound healing promotion were evaluated subsequently.

Findings

All autologous, but no allogeneic, iPSCs formed teratomas, whereas all allogeneic, but no autologous, iPSCs caused lymphocyte infiltration. Macrophages were not detectable in any wound. iPSCs expressed significantly more MAMU A and E of the major histocompatibility complex (MHC) class I but not more other MHC genetic alleles than parental fibroblastic cells. All topically disseminated autologous and allogeneic iPSCs, and their exosomes accelerated skin wound healing, as demonstrated by wound closure, epithelial coverage, collagen deposition, and angiogenesis. Allogeneic iPSCs and their exosomes were less effective and viable than their autologous counterparts. Some iPSCs differentiated into new endothelial cells and all iPSCs lost their pluripotency in 14 days. Exosomes increased cell viability of injured epidermal, endothelial, and fibroblastic cells in vitro. Although exosomes contained some mRNAs of pluripotent factors, they did not impart pluripotency to host cells.

Interpretation

Although all of the autologous and allogeneic iPSCs and exosomes accelerated wound healing, allogeneic iPSC exosomes were the preferred choice for “off-the shelf” iPSC products, owing to their mass-production, with no concern of teratoma formation.

Fund

National Natural Science Foundation of China and National Key R&D Program of China.

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Autologous but not allogeneic rhesus macaque iPSCs generate teratomas.

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Non-inbred allogeneic but not autologous iPSCs attract lymphocytes.

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Both autologous and allogeneic iPSCs and their exosomes promote wound healing.

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Both autologous iPSCs and exosomes promote better wound healing than their allogeneic counterparts.

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iPSCs lost their pluripotency in vivo. Exosomes did not impart pluripotency to host cells.

Efficient differentiation of cardiomyocytes and generation of calcium-sensor reporter lines from nonhuman primate iPSCs

Nonhuman primate (NHP) models are more predictive than rodent models for developing induced pluripotent stem cell (iPSC)-based cell therapy, but robust and reproducible NHP iPSC-cardiomyocyte differentiation protocols are lacking for cardiomyopathies research. We developed a method to differentiate integration-free rhesus macaque iPSCs (RhiPSCs) into cardiomyocytes with >85% purity in 10 days, using fully chemically defined conditions. To enable visualization of intracellular calcium flux in beating cardiomyocytes, we used CRISPR/Cas9 to stably knock-in genetically encoded calcium indicators at the rhesus AAVS1 safe harbor locus. Rhesus cardiomyocytes derived by our stepwise differentiation method express signature cardiac markers and show normal electrochemical coupling. They are responsive to cardiorelevant drugs and can be successfully engrafted in a mouse myocardial infarction model. Our approach provides a powerful tool for generation of NHP iPSC-derived cardiomyocytes amenable to utilization in basic research and preclinical studies, including in vivo tissue regeneration models and drug screening.

Whole thorax irradiation of non-human primates induces persistent nuclear damage and gene expression changes in peripheral blood cells

We investigated the cytogenetic and gene expression responses of peripheral blood cells of non-human primates (NHP, Macaca mulatta) that were whole-thorax irradiated with a single dose of 10 Gy. In this model, partial irradiation of NHPs in the thoracic region (Whole Thorax Lung Irradiation, WTLI) allows the study of late radiation-induced lung injury, while avoiding acute radiation syndromes related to hematopoietic and gastrointestinal injury. A transient drop in circulating lymphocytes and platelets was seen by 9 days, followed by elevations in respiratory rate, circulating neutrophils, lymphocytes, and monocytes at 60-100 days, corresponding to computed tomography (CT) and histologic evidence of pneumonitis, and elective euthanasia of four animals. To evaluate long-term DNA damage in NHP peripheral blood lymphocytes after 10 Gy WTLI, we used the cytokinesis-block micronucleus (CBMN) assay to measure chromosomal aberrations as post-mitotic micronuclei in blood samples collected up to 8 months after irradiation. Regression analysis showed significant induction of micronuclei in NHP blood cells that persisted with a gradual decline over the 8-month study period, suggesting long-term DNA damage in blood lymphocytes after WTLI. We also report transcriptomic changes in blood up to 30 days after WTLI. We isolated total RNA from peripheral blood at 3 days before and then at 2, 5 and 30 days after irradiation. We identified 1187 transcripts that were significantly changed across the 30-day time course. From changes in gene expression, we identified biological processes related to immune responses, which persisted across the 30-day study. Response to oxygen-containing compounds and bacteria were implicated by gene-expression changes at the earliest day 2 and latest, day 30 time-points. Gene expression changes suggest a persistent altered state of the immune system, specifically response to infection, for at least a month after WTLI.

Cardiac Regeneration with Human Pluripotent Stem Cell-Derived Cardiomyocytes

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), which are collectively called pluripotent stem cells (PSCs), have emerged as a promising source for regenerative medicine. Particularly, human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have shown robust potential for regenerating injured heart. Over the past two decades, protocols to differentiate hPSCs into CMs at high efficiency have been developed, opening the door for clinical application. Studies further demonstrated therapeutic effects of hPSC-CMs in small and large animal models and the underlying mechanisms of cardiac repair. However, gaps remain in explanations of the therapeutic effects of engrafted hPSC-CMs. In addition, bioengineering technologies improved survival and therapeutic effects of hPSC-CMs in vivo. While most of the original concerns associated with the use of hPSCs have been addressed, several issues remain to be resolved such as immaturity of transplanted cells, lack of electrical integration leading to arrhythmogenic risk, and tumorigenicity. Cell therapy with hPSC-CMs has shown great potential for biological therapy of injured heart; however, more studies are needed to ensure the therapeutic effects, underlying mechanisms, and safety, before this technology can be applied clinically.

Rhesus Macaque iPSC Generation and Maintenance

The rhesus macaque (Macaca mulatta) is physiologically and phylogenetically similar to humans, and therefore represents an invaluable model for the pre-clinical assessment of the safety and feasibility of iPSC-derived cell therapies. The use of an excisable polycistronic lentiviral STEMCCA vector to reprogram rhesus fibroblasts or bone marrow stromal cells (BMSCs) into RhiPSCs is described. After reprogramming, the pluripotency transgenes can be removed by transient expression of Cre, leaving a residual genetic tag that may be useful for identification of RhiPSC-derived tissues in vivo. Finally, the steps to maintain pluripotency during passaging of RhiPSCs, required for successful utilization of RhiPSCs, is described. © 2017 by John Wiley & Sons, Inc.