Stem cell therapy is increasingly becoming a more common form of medicine – and animals are benefiting too.
Stem cell therapy for animals has seen breakthroughs
Stem cell therapy is increasingly becoming a more mainstream form of medicine. Usually applied to humans, the use of this regenerative treatment is now also being extended to animals – including cats and dogs. Regenerative medicine, particularly stem cell treatment has seen many advancements in recent years with some groundbreaking studies coming to light.
Taking the cells from bone marrow, umbilical cords, blood or fat, stem cells can grow to become any kind of cell and the treatment has seen many successes in animals. The regenerative therapy has been useful particularly for treatment of spinal cord and bone injuries as well as problems with tendons, ligaments and joints.
Breakthrough: embryonic stem cell lines obtained from pig
“Expanded Potential Stem Cells” (EPSCs) have been obtained from pig embryos for the first time. The cells offer groundbreaking potential for studying embryonic development and producing transnational research in genomics and regenerative medicine, biotechnology and agriculture.
The cells have been efficiently derived from pig preimplantation embryos and a new culture medium developed in Hong Kong and Cambridge enabled researchers from the FLI to establish permanent embryonic stem cell lines. The cells have been discovered in a collaboration between research groups from the Institute of Farm Animal Genetics at the Friedrich-Loeffler-Institut (FLI) in Mariensee, Germany, the Wellcome Trust Sanger Institute in Cambridge, UK and the University of Hong Kong, Li Ka Shing Faculty of Medicine, School of Biomedical Sciences.
Embryonic stem cells (ESC) are derived from the inner cells of very early embryos, the so-called blastocysts. Embryonic stem cells are all-rounders and can develop into various cell types of the body in the culture dish. This characteristic is called pluripotency. Previous attempts to establish pluripotent embryonic stem cell lines from farm animals such as pigs or cattle have resulted in cell lines that have not really fulfilled all properties of pluripotency and were therefore called “ES-like”.
Dr Monika Nowak-Imialek of the FLI said: “Our porcine EPSCs isolated from pig embryos are the first well-characterized cell lines worldwide. EPSC’s great potential to develop into any type of cell provides important implications for developmental biology, regenerative medicine, organ transplantation, disease modelling and screening for drugs”.
The stem cells can renew themselves meaning they can be kept in culture indefinitely, and also show the typical morphology and gene expression patterns of embryonic stem cells. Somatic cells have a limited lifespan, so these new stem cells are much better suited for long selection processes. It has been shown that these porcine stem cell lines can easily be modified with new genome editing techniques such as CRISPR/Cas, which is particularly interesting for the generation of porcine disease models.
The EPSC’s have a high capacity to develop not only into numerous cell types of the organism, but also into extraembryonic tissue, the trophoblasts, making them very unique and lending them their name. This capacity could prove valuable for the future promising organoid technology, where organ-like small cell aggregations are grown in 3D aggregates that can be used for research into early embryo development, various disease models and testing of new drugs in petri dishes. In addition, the authors were able to show that trophoblast stem cells can be generated from their porcine stem cells, offering a unique possibility to investigate functions or diseases of the placenta in vitro.
Reprogrammed stem cell-derived neurons survive long-term in pigs with spinal cord injuries
A major hurdle to using neural stem cells derived from genetically different donors to replace damaged or destroyed tissues, such as in a spinal cord injury, has been the persistent rejection of the introduced material (cells), necessitating the use of complex drugs and techniques to suppress the host’s immune response.
Earlier this year, an international team led by scientists at University of California San Diego School of Medicine successfully grafted induced pluripotent stem cell (iPSC)-derived neural precursor cells back into the spinal cords of genetically identical adult pigs with no immunosuppression efforts. The grafted cells survived long-term, displayed differentiated functionality and caused no tumours.
The researchers also demonstrated that the same cells showed similar long-term survival in adult pigs with different genetic backgrounds after only short course use of immunosuppressive treatment once injected into injured spinal cord.
Senior author of the paper Martin Marsala, MD, professor in the Department of Anesthesiology at UC San Diego School of Medicine said: “The promise of iPSCs is huge, but so too have been the challenges. In this study, we’ve demonstrated an alternate approach.
“We took skin cells from an adult pig, an animal species with strong similarities to humans in spinal cord and central nervous system anatomy and function, reprogrammed them back to stem cells, then induced them to become neural precursor cells (NPCs), destined to become nerve cells. Because they are syngeneic – genetically identical with the cell-graft recipient pig – they are immunologically compatible. They grow and differentiate with no immunosuppression required”.
Co-author Samuel Pfaff, PhD, professor and Howard Hughes Medical Institute Investigator at Salk Institute for Biological Studies, said: “Using RNA sequencing and innovative bioinformatic methods to deconvolute the RNA’s species-of-origin, the research team demonstrated that pig iPSC-derived neural precursors safely acquire the genetic characteristics of mature CNS tissue even after transplantation into rat brains.”
NPCs were grafted into the spinal cords of syngeneic non-injured pigs with no immunosuppression – finding that the cells survived and differentiated into neurons and supporting glial cells at all observed time points. The grafted neurons were detected functioning seven months after transplantation.
Then researchers grafted NPCs into genetically dissimilar pigs with chronic spinal cord injuries, followed by a transient four-week regimen of immunosuppression drugs again finding long-term cell survival and maturation.
Marsala continued: “Our current experiments are focusing on generation and testing of clinical grade human iPSCs, which is the ultimate source of cells to be used in future clinical trials for treatment of spinal cord and central nervous system injuries in a syngeneic or allogeneic setting.
“Because long-term post-grafting periods between one and two years are required to achieve a full grafted cells-induced treatment effect, the elimination of immunosuppressive treatment will substantially increase our chances in achieving more robust functional improvement in spinal trauma patients receiving iPSC-derived NPCs.
“In our current clinical cell-replacement trials, immunosuppression is required to achieve the survival of allogeneic cell grafts. The elimination of immunosuppression requirement by using syngeneic cell grafts would represent a major step forward” said co-author Joseph Ciacci, MD, a neurosurgeon at UC San Diego Health and professor of surgery at UC San Diego School of Medicine.
Stem cells for blood vessel repair in animals
Other recent advancements include the advancement toward having a long-lasting “repair caulk” for blood vessels. A new method has been for generating endothelial cells, which make up the lining of blood vessels, from human induced pluripotent stem cells. When endothelial cells are surrounded by a supportive gel and implanted into mice with damaged blood vessels, they become part of the animals’ blood vessels, surviving for more than 10 months.
The research was carried out by stem cell researchers at Emory University School of Medicine and could form the basis of a treatment for peripheral artery disease, derived from a patient’s own cells.
Young-sup Yoon, MD, PhD, who led the team, said: “We tried several different gels before finding the best one. This is the part that is my dream come true: the endothelial cells are really contributing to endogenous vessels.
“When cells are implanted on their own, many of them die quickly, and the main therapeutic benefits are from growth factors they secrete. When these endothelial cells are delivered in a gel, they are protected. It takes several weeks for most of them to migrate to vessels and incorporate into them.
“Other groups had done this type of thing before, but the main point is that all of the culture components we used would be compatible with clinical applications”.
This research is particularly successful as previous attempts to achieve the same effect elsewhere had implanted cells lasting only a few days to weeks, using mostly adult stem cells, such as mesenchymal stem cells or endothelial progenitor cells. The scientists also designed a gel to mimic the supportive effects of the extracellular matrix. When encapsulated by the gel, cells could survive oxidative stress inflicted by hydrogen peroxide that killed unprotected cells. The gel is biodegradable, disappearing over the course of several weeks.
The scientists tested the effects of the encapsulated cells by injecting them into mice with hindlimb ischemia (restricted blood flow in the leg), a model of peripheral artery disease.
After 4 weeks, the density of blood vessels was highest in mice implanted with gel-encapsulated endothelial cells. The mice were “nude,” meaning genetically immunodeficient, facilitating acceptance of human cells.
The scientists found that implanted cells produce pro-angiogenic and vasculogenic growth factors. In addition, protection by the gel augmented and prolonged the cells’ ability to contribute directly to blood vessels. To visualise the implanted cells, they were labelled beforehand with a red dye, while functioning blood vessels were labelled by infusing a green dye into living animals. Implanted cells incorporated into vessels, with the highest degree of incorporation occurring at 10 months.