The Complex Ethics of First In Human Stem Cell Clinical Trials

Hyaluronan-based hydrogel integrating exosomes for traumatic brain injury repair by promoting angiogenesis and neurogenesis

With wide clinical demands, therapies for traumatic brain injury (TBI) are far from satisfactory. Combining the merits of stem cells but avoiding the risk of immunologic rejection, bone marrow mesenchymal stem cell-derived exosomes (BME) attract increasing interests and have been proved effective for TBI repair by intravenous or in situ injection. However, difficulties in sustained delivery or aggregation in lesion sites remain obstacle to using BME for TBI. Inspired by that hydrogels are promising to bridge the destroyed neural gap and provide neural niches, we raised a novel strategy of incorporating BME into hyaluronan-collagen hydrogel (DHC-BME) to achieve both mimicking of brain matrix and steady release of exosomes, and thus realizing TBI repair. External characterizations proved that the BME and DHC synergistically promoted neural stem cells (NSCs) differentiation into neurons and oligodendrocytes while inhibited astrocytes differentiation. DHC-BME induced angiogenesis and neurogenesis, from endogenous NSC recruitment to neuronal differentiation and vascularization to synergistically promote axonal regeneration, remyelination, synapse formation and even brain structural remodeling, and lastly, neurological functional recovery of TBI.

Mesenchymal stem cells maintain the microenvironment of central nervous system by regulating the polarization of macrophages/microglia after traumatic brain injury

Mesenchymal stem cells (MSCs), which are regarded as promising candidates for cell replacement therapies, are able to regulate immune responses after traumatic brain injury (TBI). Secondary immune response following the mechanical injury is the essential factor leading to the necrosis and apoptosis of neural cells during and after the cerebral edema has subsided and there is lack of efficient agent that can mitigate such neuroinflammation in the clinical application. By means of three molecular pathways (prostaglandin E2 (PGE2), tumor-necrosis-factor-inducible gene 6 protein (TSG-6), and progesterone receptor (PR) and glucocorticoid receptors (GR)), MSCs induce the activation of macrophages/microglia and drive them polarize into the M2 phenotypes, which inhibits the release of pro-inflammatory cytokines and promotes tissue repair and nerve regeneration. The regulation of MSCs and the polarization of macrophages/microglia are dynamically changing based on the inflammatory environment. Under the stimulation of platelet lysate (PL), MSCs also promote the release of pro-inflammatory cytokines. Meanwhile, the statue of macrophages/microglia exerts significant effects on the survival, proliferation, differentiation and activation of MSCs by changing the niche of cells. They form positive feedback loops in maintaining the homeostasis after TBI to relieving the secondary injury and promoting tissue repair. MSC therapies have obtained great achievements in several central nervous system disease clinical trials, which will accelerate the application of MSCs in TBI treatment.

THERAPY OF ENDOCRINE DISEASE: Islet transplantation for type 1 diabetes: so close and yet so far away

Over the past decades, tremendous efforts have been made to establish pancreatic islet transplantation as a standard therapy for type 1 diabetes. Recent advances in islet transplantation have resulted in steady improvements in the 5-year insulin independence rates for diabetic patients. Here we review the key challenges encountered in the islet transplantation field which include islet source limitation, sub-optimal engraftment of islets, lack of oxygen and blood supply for transplanted islets, and immune rejection of islets. Additionally, we discuss possible solutions for these challenges.