Regenerative medicine in China: main progress in different fields

Regenerative medicine (RM) is an emerging interdisciplinary field of research and China has developed the research quickly and impressed the world with numerous research findings in stem cells, tissue engineering, active molecules and gene therapy. Important directions are induced differentiation of induced pluripotent stem and embryo stem cells as well as somatic stem cell differentiation potential and their application in trauma, burns, diseases of aging and nerve regeneration. The products ActivSkin and bone repair scaffolds have been approved and are applied in the clinic, and similar products are being studied. About 10 engineered growth-factor drugs for repair and regeneration have been approved and are used in the clinic. Gene therapy, therapeutic cloning and xenotransplantation are some of the strategies being studied. However, China needs to develop standards, regulations and management practices suitable for the healthy development of RM. Aspects that should be strengthened include sound administrative systems, laws, and technical specifications and guidelines; conservation of stem cell resources; emphasis on training and retention of talented stem cell researchers; and reasonable allocation of resources, diversification of investment and breakthroughs in key areas. Finally, broad and deep international cooperation is necessary. Electronic supplementary material The online version of this article (doi:10.1186/s40779-016-0096-z) contains supplementary material, which is available to authorized users.


Background
Since 2002, major foreign media has paid much attention to the progress of Regenerative Medicine (RM) in China included the Wall Street Journal, New Scientist and Times, and Journal of Applied Behavioral Analysis [1] (www.iias.nl/iiasn/29/IIASNL29_49.pdf ). In 2009, many articles were published in Nature and the subjournal Nature Reviews Molecular Cell Biology [2,3], Cell and subjournal Cell Stem Cell [4], New England Journal of Medicine [5], and Regenerative Medicine and Science [6][7][8]. Many media has noted the significant progress in China and interpreted China's policies on stem cells, tissue engineering and related areas. It noted that the Chinese government has invested a large amount of funding in RM represented by stem cell study, tissue engineering and clinical translational studies and the country has made great progress. Some reports indicated that the Chinese government will enhance investment in RM and has been active in recruiting well-trained researchers in the 21st century and that China is leading the area in some aspects. However, China still faces challenges in innovation, translational application, regulation, governance and management.

Stem cells Overview
Chinese researchers started to pay much attention to stem cells during the 1980s. In China, it is prohibited to conduct reproductive cloning, utilize a human embryo beyond day 14, fuse human and non-human gametes and implant research embryos into a human or animal uterus. The government has greatly invested in stem cell research concentrated in several key labs in Beijing and Institute of Zoology, the Chinese Academy of Sciences, cooperation with Yunnan provincial government established the Key Laboratory of Animal Reproductive Biology focused on rhesus monkey embryonic stem cell self-renewal mechanism with primate animal disease models, research stem cell pharmacology, and promoting Chinese clinical stem cell therapy. Other famous universities and institutes have established stem cell institutes or centers with or without international cooperation (Table 1). Thus, China is close to the global advanced-research level of embryo stem cells and other stem cells [9].

Basic stem cell studies
Before 2007, basic stem cell studies in China concentrated on bone-marrow and embryo stem cells [10].
Since then, China was gradually moving toward the top position in basic stem cell research [11]. Liu et al. [12] reported the first iPS cell line from rhesus monkey in Cell Stem Cell. In 2009, Zou et al. [13] first isolated reproductive stem cells and cultured reproductive stem cell strains capable of long-term self-renewal. Li et al. [14] first cultivated a mouse by using iPS cells. This was the first proof of the totipotency of iPS cells. This finding was elected by Times as one of the Global Top 10 Biomedicine Advances. The journal believed that "this study is a symbol of a major step forward of stem cell research". In early 2010, Esteban et al. [15] increased the iPS induction efficiency by 10-fold by adding vitamin C. The Proceedings of the National Academy of Science USA published the finding the new function of the stem cell factor receptor C-KIT and application in translational medicine [16]. Chinese researchers published their success in creating cell lines from androgenetic haploid embryonic stem cells, a breakthrough in embryo stem cell research [17]. In 2013, Hou et al. [18] used a small molecular compound to induce the reprogramming of somatic cells into multipotent stem cells. In 2013, Cell published a special "Spotlight on China" edition that highlighted the rapid development of immunology study in China and in particular, positively commented on the immunology aspects of applying stem cells for clinical treatment [19] (http://www.cell.com/spotlightonchina).

Therapeutic applications
The practice of stem cell clinical trials or treatment in China dates back to bone-marrow transplantation in the 1960s, really the transplantation of stem cells in bone marrow. China declared the legality of stem cell treatment as a medical technique following the United Kingdom and the United States.
For therapeutic applications, Zhu and colleagues treated a woman who had chopsticks inserted into her brain from the eyes, which resulted in frontal cerebral-cortex injury. The authors cultivated the brain tissue attached to the chopsticks and were interested in stem cell-motivated selfrepair [20]. In 2009, Sheng et al. [21] regenerated sweat glands by using bone-marrow mesenchymal stem cells (MSCs). This technology has been applied in more than 30 cases with follow-up for more than four years. In 2013, umbilical-cord MSC transplantation was performed in patients with post-traumatic brain syndrome. A total of 40 patients with post-traumatic brain syndrome were randomized to receive stem cell or control treatment. Umbilical-cord MSC transplantation improved the neurological function of the patients. However, these results need to be confirmed by prospective, randomized, multi-center, large clinical studies [22]. At the website of the State Food and Drug Administration (SFDA) (http://www.sda.gov.cn/ WS01/CL0001/) (date of search: 2013-08-01), a few stem cell-related products have been approved for clinical trials ( Table 2). Before 2005, China had no stem cell therapies and activity factor clinical trials registered at ClinicalTrials.gov (http://www.clinicaltrials.gov/, Fig. 1) (Additional files 1 and 2). After then, Chinese scholars have been paying increasing attention to this issue and the projects registered have been increasing annually, reaching 138 in 2012. In 2013, at the time of our search (August 20, 2013), the number of projects registered reached 28.

Comparison with research-advanced countries on stem cells
The United States maintains a leading position in stem cell research, for a significant difference between the United States and China (Fig. 2). The United States has implemented strict management since 1998. The CAS, MST and MH in China started to make laws and policies associated with stem cells in 2003. However, China has improved a variety of policies so far and hopes for real enforcement. In countries such as the United Kingdom and Sweden, collecting human embryonic stem cells for application is relatively free but is more stringent in other countries. In all countries, human cloning and destruction of human embryos are prohibited.
In the field of stem cell drug development and clinical trials, before December 31, 2009, the US Food and Drug Administration (FDA) approved 2,980 projects on stem cell therapy. In 2009, it allowed Geron, a biotech company in California, to perform the world's first clinical trial on human embryonic stem cells, which was a milestone in the history of medicine (http:// www.biotech.org.cn/information/85021). Subsequently, another clinical trial of human embryonic stem cells, performed by Advanced Cell Technology, was approved by the US FDA. In 2010, the United Kingdom approved its first stem cell trial in humans. In recent years, 3 stem cell therapeutic agents have been approved in South Korea. A stem cell product, Prochymal (manufactured by Osiris), was approved by Health Canada in May 2012. This product was the first non-prescribed MSC agent approved by a developed country for treating acute graftversus-host disease worldwide. In addition, the Australian Therapeutic Goods Administration approved the production and supply of an autologous mesenchymal precursor cell product, Mesoblast. About 3,500 clinical trials involving somatic stem cells are registered by the US National Institutes of Health. More than 2,000 clinical trials of stem cell therapy are ongoing. Most of these clinical trials are phase I to II. These clinical trials were performed mainly in the United States and Europe. In China, stem cell therapy is restricted, and the hospitals need to file with the regulatory authorities to perform studies. In 2012, the project "Mesenchymal stem cells in myocardial infarction injection", involving one of the three stem cell drugs improved for clinical trials in China 6 years ago, completed its phase I clinical trials. Before this, the SFDA approved two stem cell drugs for clinical trials: "primitive bone-marrow MSCs" and "autologous bone-marrow MSC injection".
For stem cell drugs, China has lagged behind other countries in strong stem cell research capability. Because of lack of detailed rules in laws, the stem cell market is in chaos driven by financial interests. The chaos in the area of stem cell therapy in China was reported in the New England Journal of Medicine [5] and Nature [23,24] in 2009 and 2010. The articles indicated concern about the safety of stem cell therapy in China. The MH has implemented regulations on the clinical application of cutting-edge therapies such as stem-cell injections. In December 2011, the MH report of quality control in the implementation of stem cell clinical study and application indicated that stem cell clinical study and application activities not approved by the MH or SFDA should be discontinued (Table 2). A total of 35 stem cell clinical trials have been performed in mainland China, 3 in Hong Kong and 22 in Taipei. As compared with the leading countries in the area of stem cell research, in China, the number of stem cell clinical trials is significantly smaller. The application of stem cells has mainly focused on hematopoietic stem cells and MSCs because of the type of stem cells used in clinical trials of hematological diseases, vascular diseases and diabetes mellitus.
Therefore, the gap between China and the United States as well as other leading countries in stem cell research is mainly characterized by innovation, regulation, and quality control. The review procedure and laws on stem cell clinical trials have not been established and the long-term mechanism needs to be improved.    (Tables 3 and 4).

Tissue-engineering studies
In 2007, the SFDA approved the first tissue-engineering product, ActivSkin, developed by the Fourth Military Medical University, Xi'an, which made China the second country in the world with the technology of artificial skin after the United States. Moreover, the country continued to develop tissue-engineered de-cellular dermal matrix, skin containing adipose layers, skin containing pigmentation, skin containing capillary-like network, skin containing hair follicles and dermal equivalents. In 2010, the SFDA approved bone-repair scaffolds developed by Fuzhai Cui, in Tsinghua University. This material has been used in 30,000 patients and was promoted to other parts of the world. Other products include tissue-engineered tendons, cartilage/bone, and neural tubes, etc ( Table 4). The data could be collected on the website of the SFDA. Fundamental research or investigational use has been conducted for tissue-engineered oral mucosa, bladder, artificial liver and kidney, heart valve prostheses, cardiac patch, blood vessel, nerves, urethra, testes and thyroid glands. Thus, scientists in China have an interest in different fields and are involved in tissueengineered grafts to repair and regenerate tissues and organ. In 2012, Science reviewed the development of tissue engineering in China; work from Xiaosong Gu at Nantong University, Yilin Cao at Shanghai Jiaotong University and Fuzhai Cui at Tsinghua University were highlighted for their outstanding contribution in this area [8].

Comparison with other research-advanced countries
The concept of tissue engineering was formally proposed by the US National Science Foundation in 1987. Moreover, the United States subsidized research projects for tissue engineering as early as 1988. Institutions involved are research institutes (National Aeronautics and Space Administration, the US Department of Energy, NIH), universities (Massachusetts Institute of Technology, Harvard Medical School, Georgia Institute of Technology, and University of California at San Diego), and enterprises (Sandoz, Organogenesis, Advanced Tissue).
The US FDA granted marketing approval to about 10 products including tissue-engineered skin and cartilage. In China, tissue-engineered skin has been approved, which marked the beginning of the industry for tissueengineering products. The technical level of China in tissue engineering is basically geared to international standards, but the delay in tissue-engineered research and translational application in China stems mainly from regulations and product standards. With respect to tissue-engineering publications, China exceeded Germany, Table 3 Centers/key laboratories for stem cell biology and tissue engineering  Japan and the United Kingdom as early as in 2000 and the gap with these countries has widened since 2008.

Growth factors Overview
The supplement of exogenous bioactive factors is important for accelerating wound healing and tissue regeneration. These bioactive factors include basic or acidic fibroblast growth factor (bFGF or aFGF), epidermal growth factor, nerve growth factor and bone morphogenetic protein.
Some have been approved for clinical application as new drugs and approved with good clinical effects.

New growth factors
As early as in 1991, Chinese scientists published the first academic monograph that systematically addressed "growth factor and wound healing". Since 1998, they have published results of a series of multicenter, randomized clinical trial about growth factors accelerating wound healing in The Lancet and other international journals [25]. The results indicated that bFGF and other active molecules play a key role in regulating tissue and organ repair and regeneration. About 10 growth-factor products have been approved by the SFDA and used in the clinic (Table 5). Compared with China, the United States is more cautious about the clinical application of growth factors. Only recombinant human platelet-derived growth factor by Chiron was approved by the FDA in 1998 and is used for debridement healing and repair of advanced diabetic foot ulcers, severe burns, skin diseases, and bone and teeth defects. The recombinant human keratinocyte growth factor palifermin, by Amgen, was approved in 2004 and is used for treatment of severe oral mucositis caused by chemoradiotherapy. Therefore, the number is far less than that of growth factors approved in China.
Cell differentiation and dedifferentiation induced by growth factors are a "hot" topic in RM. In 2001, Chinese scientists published results of a series of in vivo and vitro studies dealing with epidermal cells dedifferentiating into epidermal stem cells in The Lancet and other international journals [26,27], which addressed dedifferentiation as a new approach to make stem cells from skin. Particularly, the authors found that growth factors have a significant dedifferentiation effect on cells in vivo settings. Although the innovative theory immediately caused controversy between Chinese and foreign scholars, this groundbreaking thinking has great significance for the later practice of using active factors to reprogram adult cells into adult stem cells. These results offer direct evidence that the potential of plasticity and transdifferentiation of some adult tissue stem cells could lead to differentiation into other series of cell types without developmental correlation [28].

Other: gene therapy, therapeutic cloning and xenotransplantation
Gene therapy has an important place in neuron, cardiovascular and islet-cell regeneration. Self-developed recombinant hepatic growth factor is the first gene therapy product for cardiovascular disease and is now in a phase II clinical trial. In addition, pcD2/hVEGF121 gene therapy for peripheral vascular diseases has been approved by the SFDA for a special clinical trial, so China is the second country conducting such research after the United States.
"Therapeutic cloning" has always been listed as a national basic research program. It is divided into upper, middle, and lower research parts according to national strategic planning. Drs. Guoxiang Chen (Transgenic Research Center in Shanghai), Huizhen Sheng and Yilin Cao (Shanghai Second Medical University) are responsible for the upper, middle and lower research parts, respectively. With cloning, cells may be induced to differentiate into specific tissue and organs in vitro, such as skin, cartilage, heart, liver, kidney and bladder, then these tissues and organs are implanted into patients.
Xenotransplantation is being accepted gradually in addition to tissue engineering and stem cell technology. The first batch of inbred Wuzhishan mini-pigs with GT knockout (homozygous with 2 copies of GGTA1 gene deletion) were established by Deng and colleagues at the institute of animal husbandry. Pigskin excipients with reduced immunogenicity treated by several different means have been approved by the SFDA. In addition, patents have been applied for α-galactosidase-treated porcine heart valve, pericardium and ligament. Functional cells and various humanized organs for human transplantation may be obtained if the same method is applied in large animals. The immunological rejection of xenotransplantation would be overcome and result in functional organs.

Conclusions
In 2012, a special edition of Science (sponsored supplement for Regenerative Medicine in China) gave a comprehensive snapshot of the development of RM in China, with particular emphasis on stem cells, tissue engineering and trauma. As the core scientific journal, Science echoed with positive comments for the achievements in China. For scientists in China, change and challenge in RM exists. Although its achievements are remarkable and impressed, China needs to strengthen the following aspects: (1) Sound administrative system, laws, technical specifications and guidelines. China has not yet established a truly effective management system for clinical application of somatic stem cells, and detailed regulatory rules are not clear. The standards for stem cell conservation, research, clinical trials, eligibility criteria for hospital and medical staff performing stem cell therapy, relevant instruments and devices remain to be determined. In 2009, the ministry of health put stem cell therapy into "third class medical technology", which Mainly due to it involved the major ethical issues, and the security and effectiveness still need to further confirm by the specification of clinical trials research. In March 2015, the National Health Development Planning Commission and the China Food and Drug Administration jointly issued the "stem cell clinical research management approach (trial)", which is first normative management documents about stem cell clinical research of China. Aim is restraint the action of stem cells in clinical research and to safeguard the rights and interests of the subjects, promote the healthy development of stem cell research [29]. The implementation should be in accordance with the guidelines for stem cell clinical translation released by the International Society of Stem Cell Research. Ethical norms and legal provisions should be strictly followed to constrain the application and clinical trials of stem cells. Emphasis should be paid on the protection of intellectual property, allowing healthy and orderly development of the study of RM.
(2) Emphasis on training and retention of talented stem cell researchers. China has become an important member in RM competition. However, some prominent problems should be solved. Compared with international advanced levels, in China, the scale and overall level of stem cell and RM research still has a long way to go. The government must strengthen and improve the ethics construction and education in scientific research units, enterprises, hospitals to, enhance the management and cognitive level of medical staffs engaged in stem cell research. There is not much originality, especially not many innovative ideas and research directions that can lead the trend. China lacks worldwide influential scientists in the area of tissue regeneration (including stem cell, tissue engineering) and coordination among multidisciplinary experts. (3) Reasonable allocation of resources and breakthroughs. China will use the limited funds to concentrate on RM research in inducing stem cell differentiation, synchronous repair and regeneration of multiple impaired tissues, construction of tissueengineered major organs and driving tissue-engineered products from bench to bedside. Substantial progresses and breakthroughs have been made in further establishing and improving the rules and laws involved in RM and construction of a RM translational base. (4) Broad and deep international cooperation. China should continue to emphasize in-depth and practical cooperation with foreign well-known universities, scientific centers and key laboratories. printer. This printer has successfully printed small proportions of cartilage tissue of human ears and liver. This biomaterial 3D printer is characterized by a great variety of printed biomaterials, low incidence of cell damage, high printing precision and convenient operation. The development of nano-intellectual materials for RM is important. The intellectual biomaterials may induce molecular modifications of degradable materials, resulting in the interactions between cell integrins, induction of cell proliferation and differentiation and synthesis and assembly of extracellular matrix, thereby initiating the body's regenerative system. For example, the new intellectual biomaterial can have the function of signal transduction and control the release of growth factors or drugs intelligently, thus inducing the regenerative repair of tissues and organs directly. Finally, RM in China in the next 10 years is expected to achieve substantial progress in systemic and effective regulation as well as a management system for RM research, application and synchronous repair by inducing stem cells and regenerating a variety of impaired tissues. The construction of major organs by tissue engineering and large-scale application of tissueengineered products will be completed. These achievements will bring hope to China improve healthcare and build a healthy society [30].