China’s landscape in regenerative medicine

Skin derived precursors induced Schwann cells mediated tissue engineering-aided neuroregeneration across sciatic nerve defect

A central question in neural tissue engineering is how the tissue-engineered nerve (TEN) translates detailed transcriptional signals associated with peripheral nerve regeneration into meaningful biological processes. Here, we report a skin-derived precursor-induced Schwann cell (SKP-SC)-mediated chitosan/silk fibroin-fabricated tissue-engineered nerve graft (SKP-SCs-TEN) that can promote sciatic nerve regeneration and functional restoration nearly to the levels achieved by autologous nerve grafts according to behavioral, histological, and electrophysiological evidence. For achieving better effect of neuroregeneration, this is the first time to jointly apply a dynamic perfusion bioreactor and the ascorbic acid to stimulate the SKP-SCs secretion of extracellular matrix (ECM). To overcome the limitation of traditional tissue-engineered nerve grafts, jointly utilizing SKP-SCs and their ECM components were motivated by the thought of prolongating the effect of support cells and their bioactive cues that promote peripheral nerve regeneration. To further explore the regulatory model of gene expression and the related molecular mechanisms involved in tissue engineering-aided peripheral nerve regeneration, we performed a cDNA microarray analysis of gene expression profiling, a comprehensive bioinformatics analysis and a validation study on the grafted segments and dorsal root ganglia tissues. A wealth of transcriptomic and bioinformatics data has revealed complex molecular networks and orchestrated functional regulation that may be responsible for the effects of SKP-SCs-TEN on promoting peripheral nerve regeneration. Our work provides new insights into transcriptomic features and patterns of molecular regulation in nerve functional recovery aided by SKP-SCs-TEN that sheds light on the broader possibilities for novel repair strategies of peripheral nerve injury.

Strengthening regulations, recent advances and remaining barriers in stem cell clinical translation in China: 2015-2021 in review

A new regulatory regime is being implemented under strict scrutiny for translation of stem cell medical practices since 2015 in China. The new mode of governance is strengthening to curb the marketing of unproven stem cell therapeutic products. This article begins with a brief historical overview of stem cell research and development and then focuses on the policies and country-level guidelines in the past years for stem cell translational research. This study reveals several key observations on the major progress made and the challenges associated with clinical translation of stem cells in China. Given that stem cells or stem cell-based therapeutic products are already considered as biological 'drugs', this study would be conducive to a better understanding of China's approach to stem cell translational research, marketisation and industrialization in progress.

Combined use of chitosan-PGLA nerve grafts and bone marrow mononuclear cells to repair a 50-mm-long median nerve defect combined with an 80-mm-long ulnar nerve defect in the human upper arm

BACKGROUND

Severe peripheral nerve injury, especially the long-distance peripheral nerve defect caused severe functional disability to patients. And there is always a lack of effective and less side effects of repair methods for clinics. A case study was performed to observe the regenerative outcomes of the surgical repair of long-distance peripheral nerve defects in the upper arm with chitosan-poly(glycolide-co-lactide) (PGLA) nerve grafts combined with bone marrow mononuclear cells (BMMCs).

METHODS

The right upper arm of a 29-year-old woman was injured, leaving a 50-mm-long median nerve defect, an 80-mm-long ulnar nerve defect, and muscle and blood vessel disruptions. The nerve defects were repaired by implanting BMMC-containing chitosan-PGA nerve grafts on the 40th day after injury. A series of functional assessments were carried out from 2 weeks to 66 months after surgical repair. Sensory function was assessed by the pinprick test, two-point discrimination test and Semmes-Weinstein monofilament test. Motor function was evaluated by the range of motion of the wrist joint and muscle power. Autonomic function was monitored by laser-Doppler perfusion imaging (LDPI). Tissue morphology was observed through ultrasonic investigations.

RESULTS

No adverse events, such as infection, allergy, or rejection, caused by the treatment were detected during the follow-up period. Sensory and pinprick nociception in the affected thumb, index, and middle fingers were restored gradually from the 6th month after surgery. The monofilament tactile sensation was 0.4 g in the terminal finger pulp of the thumb and index finger, 2.0 g in the middle finger, and greater than 300 g in the ring finger and little finger at the 66th month. Motor function recovery was detected at the 5th month after surgery, when the muscle strength of the affected forearm flexors began to recover. At the 66th month after surgery, the patient's forearm flexor strength was grade 4, with 80° of palmar flexion, 85° of dorsal extension, 8° of radial deviation, 40° of ulnar deviation, 40° of anterior rotation, and 85° of posterior rotation of the affected wrist. The patient could perform holding, picking up, and some other daily activities with the affected hand. The patient's sweating function of the affected hand was close to the level of the healthy hand. LDPI showed that the skin blood flow perfusion was significantly increased, with perfusion similar to on the normal side in some areas. Neuromusculoskeletal ultrasonography showed the presence of nerve structures.

CONCLUSIONS

These results suggest that chitosan-PGLA nerve grafts combined with BMMCs could effectively repair long-distance nerve defects and achieve good clinical results.

Comprehensive strategy of conduit guidance combined with VEGF producing Schwann cells accelerates peripheral nerve repair

Peripheral nerve regeneration requires stepwise and well-organized establishment of microenvironment. Since local delivery of VEGF-A in peripheral nerve repair is expected to promote angiogenesis in the microenvironment and Schwann cells (SCs) play critical role in nerve repair, combination of VEGF and Schwann cells may lead to efficient peripheral nerve regeneration. VEGF-A overexpressing Schwann cells were established and loaded into the inner wall of hydroxyethyl cellulose/soy protein isolate/polyaniline sponge (HSPS) conduits. When HSPS is mechanically distorted, it still has high durability of strain strength, thus, can accommodate unexpected strain of nerve tissues in motion. A 10 mm nerve defect rat model was used to test the repair performance of the HSPS-SC (VEGF) conduits, meanwhile the HSPS, HSPS-SC, HSPS-VEGF conduits and autografts were worked as controls. The immunofluorescent co-staining of GFP/VEGF-A, Ki67 and MBP showed that the VEGF-A overexpressing Schwann cells could promote the proliferation, migration and differentiation of Schwann cells as the VEGF-A was secreted from the VEGF-A overexpressing Schwann cells. The nerve repair performance of the multifunctional and flexible conduits was examined though rat behavioristics, electrophysiology, nerve innervation to gastrocnemius muscle (GM), toluidine blue (TB) staining, transmission electron microscopy (TEM) and NF200/S100 double staining in the regenerated nerve. The results displayed that the effects on the repair of peripheral nerves in HSPS-SC (VEGF) group was the best among the conduits groups and closed to autografts. HSPS-SC (VEGF) group exhibited notably increased CD31⁺ endothelial cells and activation of VEGFR2/ERK signaling pathway in the regenerated nerve tissues, which probably contributed to the improved nerve regeneration. Altogether, the comprehensive strategy including VEGF overexpressing Schwann cells-mediated and HSPS conduit-guided peripheral nerve repair provides a new avenue for nerve tissue engineering.

Tissue Engineering and Regenerative Medicine: Achievements, Future, and Sustainability in Asia

Exploring innovative solutions to improve the healthcare of the aging and diseased population continues to be a global challenge. Among a number of strategies toward this goal, tissue engineering and regenerative medicine (TERM) has gradually evolved into a promising approach to meet future needs of patients. TERM has recently received increasing attention in Asia, as evidenced by the markedly increased number of researchers, publications, clinical trials, and translational products. This review aims to give a brief overview of TERM development in Asia over the last decade by highlighting some of the important advances in this field and featuring major achievements of representative research groups. The development of novel biomaterials and enabling technologies, identification of new cell sources, and applications of TERM in various tissues are briefly introduced. Finally, the achievement of TERM in Asia, including important publications, representative discoveries, clinical trials, and examples of commercial products will be introduced. Discussion on current limitations and future directions in this hot topic will also be provided.

Research trends of stem cells in ischemic stroke from 1999 to 2018: A bibliometric analysis

OBJECTIVE

Many studies have evaluated the safety and efficacy of stem cells as therapeutic agents for ischemic stroke. We aimed to quantitatively assess the research trends of stem cell therapy for ischemic stroke.

PATIENTS AND METHODS

We searched the Web of Science Core Collection to identify relevant publications between 1999 and 2018. We used HistCite to summarize the critical information, including yearly records, authors, countries/regions, and institutions. VOSviewer was applied to map the collaborations between studies. Based on the title and abstract of each publication, MeSH terms were obtained using Medical Text Indexer to demonstrate evolutions of topic hotspots.

RESULTS

From 1999-2018, there were a total of 3,741 publications exploring the prospect of stem cells in ischemic stroke. Annual publication outputs grew from six records to 366 records. Stroke was the most high-profile journal because of its ranking first on the top productive and co-cited journal lists. The United States of America and China were the two most contributive countries of stem-cell research of ischemic stroke. Researchers were supposed to follow studies from productive institutions because of their consistent and systematic investigations in this field. Neural stem cells and mesenchymal stem cells were the most recognized cells for clinical translation.

CONCLUSION

With the growth of publications concerning the role of stem cells in ischemic stroke treatment, bibliometrics helps researchers to get insights of academic collaborations, research trends, and hot topics in the study field.

Tissue-engineered nerve grafts using a scaffold-independent and injectable drug delivery system: a novel design with translational advantages

OBJECTIVE

Currently commercially available nerve conduits have demonstrated suboptimal clinical efficacy in repairing peripheral nerve defects. Although tissue-engineered nerve grafts (TENGs) with sustained release of neurotrophic factors (NTFs) are experimentally proved to be more effective than these blank conduits, there remains a lack of clinical translation. NTFs are typically immobilized onto scaffold materials of the conduit via adsorption, specific binding or other incorporation techniques. These scaffold-based delivery strategies increase complexity and cost of conduit fabrication and lack flexibility in choosing different drugs. Therefore, to facilitate clinical translation and commercialization, we construct a TENG using a scaffold-independent drug delivery system (DDS).

APPROACH

This study adopted a scaffold-independent DDS based on methoxy-poly (ethylene glycol)-b-poly(γ-ethyl-L-glutamate) (mPEG-PELG) thermosensitive hydrogels that undergo sol-to-gel transition at body temperature. In addition, TENG, a chitosan scaffold filled with nerve growth factor (NGF)-loaded mPEG-PELG that gel in the lumen upon injection during surgery and function as a drug-releasing conduit-filler, was designed. Subsequently, the efficacy of DDS and therapeutic effects of TENG were assessed.

MAIN RESULTS

The results demonstrated that NGF-loaded mPEG-PELG controllably and sustainably released bioactive NGF for 28 d. When bridging a 10 mm rat sciatic nerve gap, the morphological, electrophysiological, and functional analyses revealed that NGF-releasing TENG (Scaffold  +  NGF/mPEG-PELG) achieved superior regenerative outcomes compared to plain scaffolds and those combined with systemic delivery of NGF (daily intramuscular injection (IM)), and its effects were relatively similar to autografts.

SIGNIFICANCE

This study has proposed a TENG using thermosensitive hydrogels as an injectable implant to controllably release NGF, which has promising therapeutic potential and translatability. Such TENGs obviate the need for conduit modification, complex preloading or binding mediators, therefore they allow the ease of drug switching in clinical practice and greatly simplify the manufacturing process due to the independent preparation of drug delivery system.

Prevascularization promotes endogenous cell-mediated angiogenesis by upregulating the expression of fibrinogen and connective tissue growth factor in tissue-engineered bone grafts

BACKGROUND

Vascularization is one of the most important processes in tissue-engineered bone graft (TEBG)-mediated regeneration of large segmental bone defects. We previously showed that prevascularization of TEBGs promoted capillary vessel formation within the defected site and accelerated new bone formation. However, the precise mechanisms and contribution of endogenous cells were not explored.

METHODS

We established a large defect (5 mm) model in the femur of EGFP⁺ transgenic rats and implanted a β-tricalcium phosphate (β-TCP) scaffold seeded with exogenous EGFP^- cells; the femoral vascular bundle was inserted into the scaffold before implantation in the prevascularized TEBG group. Histopathology and scanning electron microscopy were performed and connective tissue growth factor (CTGF) and fibrin expression, exogenous cell survival, endogenous cell migration and behavior, and collagen type I and III deposition were assessed at 1 and 4 weeks post implantation.

RESULTS

We found that the fibrinogen content can be increased at the early stage of vascular bundle transplantation, forming a fibrin reticulate structure and tubular connections between pores of β-TCP material, which provides a support for cell attachment and migration. Meanwhile, CTGF expression is increased, and more endogenous cells can be recruited and promote collagen synthesis and angiogenesis. By 4 weeks post implantation, the tubular connections transformed into von Willebrand factor-positive capillary-like structures with deposition of type III collagen, and accelerated angiogenesis of endogenous cells.

CONCLUSIONS

These findings demonstrate that prevascularization promotes the recruitment of endogenous cells and collagen deposition by upregulating fibrinogen and CTGF, directly resulting in new blood vessel formation. In addition, this molecular mechanism can be used to establish fast-acting angiogenesis materials in future clinical applications.

Genipin-Cross-Linked Chitosan Nerve Conduits Containing TNF-α Inhibitors for Peripheral Nerve Repair

Tissue engineered nerve grafts (TENGs) are considered a promising alternative to autologous nerve grafting, which is considered the "gold standard" clinical strategy for peripheral nerve repair. Here, we immobilized tumor necrosis factor-α (TNF-α) inhibitors onto a nerve conduit, which was introduced into a chitosan (CS) matrix scaffold utilizing genipin (GP) as the crosslinking agent, to fabricate CS-GP-TNF-α inhibitor nerve conduits. The in vitro release kinetics of TNF-α inhibitors from the CS-GP-TNF-α inhibitor nerve conduits were investigated using high-performance liquid chromatography. The in vivo continuous release profile of the TNF-α inhibitors released from the CS-GP-TNF-α inhibitor nerve conduits was measured using an enzyme-linked immunosorbent assay over 14 days. We found that the amount of TNF-α inhibitors released decreased with time after the bridging of the sciatic nerve defects in rats. Moreover, 4 and 12 weeks after surgery, histological analyses and functional evaluations were carried out to assess the influence of the TENG on regeneration. Immunochemistry performed 4 weeks after grafting to assess early regeneration outcomes revealed that the TENG strikingly promoted axonal outgrowth. Twelve weeks after grafting, the TENG accelerated myelin sheath formation, as well as functional restoration. In general, the regenerative outcomes following TENG more closely paralleled findings observed with autologous grafting than the use of the CS matrix scaffold. Collectively, our data indicate that the CS-GP-TNF-α inhibitor nerve conduits comprised an elaborate system for sustained release of TNF-α inhibitors in vitro, while studies in vivo demonstrated that the TENG could accelerate regenerating axonal outgrowth and functional restoration. The introduction of CS-GP-TNF-α-inhibitor nerve conduits into a scaffold may contribute to an efficient and adaptive immune microenvironment that can be used to facilitate peripheral nerve repair.

Various changes in cryopreserved acellular nerve allografts at -80°C

The experimental design evaluated histological, mechanical, and biological properties of allogeneic decellularized nerves after cryopreservation in a multi-angle, multi-directional manner to provide evidence for long-term preservation. Acellular nerve allografts from human and rats were cryopreserved in a cryoprotectant (10% fetal bovine serum, 10% dimethyl sulfoxide, and 5% sucrose in RPMI1640 medium) at −80°C for 1 year, followed by thawing at 40°C or 37°C for 8 minutes. The breaking force of acellular nerve allografts was measured using a tensile test. Cell survival was determined using L-929 cell suspensions. Acellular nerve allografts were transplanted into a rat model with loss of a 15-mm segment of the left sciatic nerve. Immunohistochemistry staining was used to measure neurofilament 200 expression. Hematoxylin-eosin staining was utilized to detect relative muscle area in gastrocnemius muscle. Electron microscopy was applied to observe changes in allograft ultrastructure. There was no obvious change in morphological appearance or ultrastructure, breaking force, or cytotoxicity of human acellular nerve allografts after cryopreservation at −80°C. Moreover, there was no remarkable change in neurofilament 200 expression, myelin sheath thickness, or muscle atrophy when fresh or cryopreserved rat acellular nerve allografts were applied to repair nerve injury in rats. These results suggest that cryopreservation can greatly extend the storage duration of acellular nerve tissue allografts without concomitant alteration of the physiochemical and biological properties of the engineered tissue to be used for transplantation.

Stem Cell Research and Clinical Translation: A Roadmap about Good Clinical Practice and Patient Care

The latest research achievements in the field of stem cells led in 2016 to the publication of “Guidelines for Stem Cell Research and Clinical Translation” by the International Society for Stem Cell Research (ISSCR). Updating the topics covered in previous publications, the new recommendations offer interesting ethical and scientific insights. Under the common principles of research integrity, protection of patient's welfare, respect for the research subjects, transparency and social justice, the centrality of good clinical practice, and informed consent in research and translational medicine is supported. The guidelines implement the abovementioned publications, requiring rigor in all areas of research, promoting the validity of the scientific activity results and emphasizing the need for an accurate and efficient public communication. This paper aims to analyze the aforementioned guidelines in order to provide a valid interpretive tool for experts. In particular, a research activity focused on the bioethical, scientific, and social implications of the new recommendations is carried out in order to provide food for thought. Finally, as an emerging issue of potential impact of current guidelines, an overview on implications of compensation for egg donation is offered.