MHC antigen expression in human first trimester spinal cord with implications for clinical transplantation procedures

Introduction to Cartilage

Cartilage is a supporting connective tissue that, together with the bone, forms the framework supporting the body as a whole. There are many distinct types of cartilage, which exhibit numerous similarities as well as differences. Among them, articular cartilage is the best known and the most studied type. Articular cartilage is the thin layer of connective tissue that covers the articulating ends of bones in synovial (diarthrodial) joints. It provides a smooth surface for joint movement and acts as a load-bearing medium that protects the bone and distributes stress. The intense interest in articular cartilage is motivated by the critical role its degradation plays in arthritis and related joint diseases, which are the number one cause of disability in humans. This chapter discusses the physical, chemical and cellular properties of cartilage that give the tissue its extraordinary load-bearing characteristics.

Plasticity of fetal cartilaginous cells

Tissue-specific stem cells found in adult tissues can participate in the repair process following injury. However, adult tissues, such as articular cartilage and intervertebral disc, have low regeneration capacity, whereas fetal tissues, such as articular cartilage, show high regeneration ability. The presence of fetal stem cells in fetal cartilaginous tissues and their involvement in the regeneration of fetal cartilage is unknown. The aim of the study was to assess the chondrogenic differentiation and the plasticity of fetal cartilaginous cells. We compared the TGF-β3-induced chondrogenic differentiation of human fetal cells isolated from spine and cartilage tissues to that of human bone marrow stromal cells (BMSC). Stem cell surface markers and adipogenic and osteogenic plasticity of the two fetal cell types were also assessed. TGF-β3 stimulation of fetal cells cultured in high cell density led to the production of aggrecan, type I and II collagens, and variable levels of type X collagen. Although fetal cells showed the same pattern of surface stem cell markers as BMSCs, both type of fetal cells had lower adipogenic and osteogenic differentiation capacity than BMSCs. Fetal cells from femoral head showed higher adipogenic differentiation than fetal cells from spine. These results show that fetal cells are already differentiated cells and may be a good compromise between stem cells and adult tissue cells for a cell-based therapy.

Effect of inflammatory cytokines on major histocompatibility complex expression and differentiation of human neural stem/progenitor cells

To develop transplantation of neural stem/progenitor cells (NSPCs) as a successful treatment of neurodegenerative disorders, the possible induction of an inflammatory response following implantation needs to be taken into consideration. Inflammatory cytokines can upregulate major histocompatibility complex (MHC) expression on transplanted cells, thereby rendering them more susceptible to graft rejection. Furthermore, cytokines also have a profound effect on cell differentiation, migration, and proliferation, which can greatly affect the outcome of transplantation. Here we studied the effect of three inflammatory cytokines, interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6), from three different species (human, monkey, rat) on expression of MHC molecules and differentiation of two human NSPC lines derived from striatum and hippocampus. Human and monkey IFN-gamma strongly upregulate MHC expression in both NSPC lines in a dose-dependent manner, whereas rat IFN-gamma has an effect on MHC expression only in hippocampal cells. Furthermore, TNF-alpha, but not IL-6, upregulates MHC expression in both NSPC lines. Differentiation of NSPCs in the presence of cytokines showed that IFN-gamma increased the neuronal yield threefold in striatal NSPC cultures and increased the number of oligodendrocytes twofold in hippocampal NSPC cultures. Addition of TNF-alpha enhanced gliogenesis in both cell lines, whereas IL-6 stimulated neurogenesis. Human NSPC lines' response to cytokines is therefore species specific and also dependent on the NSPCs' region of origin. The successful translation of different cell lines from animal models to clinical trials could be substantially influenced by the species-specific regulation of MHC and differentiation as reported here. Disclosure of potential conflicts of interest is found at the end of this article.

Human neural stem cells and astrocytes, but not neurons, suppress an allogeneic lymphocyte response

Transplantation of human neural stem cells (NSCs) and their derivatives is a promising future treatment for neurodegenerative disease and traumatic nervous system lesions. An important issue is what kind of immunological reaction the cellular transplant and host interaction will result in. Previously, we reported that human NSCs, despite expressing MHC class I and class II molecules, do not trigger an allogeneic T cell response. Here, the immunocompetence of human NSCs, as well as differentiated neural cells, was further studied. Astrocytes expressed both MHC class I and class II molecules to a degree equivalent to that of the NSCs, whereas neurons expressed only MHC class I molecules. Neither the NSCs nor the differentiated cells triggered an allogeneic lymphocyte response. Instead, these potential donor NSCs and astrocytes, but not the neurons, exhibited a suppressive effect on an allogeneic immune response. The suppressive effect mediated by NSCs most likely involves cell-cell interaction. When the immunogenicity of human NSCs was tested in an acute spinal cord injury model in rodent, a xenogeneic rejection response was triggered. Thus, human NSCs and their derived astrocytes do not initiate, but instead suppress, an allogeneic response, while they cannot block a graft rejection in a xenogeneic setting.

Low immunogenicity of in vitro-expanded human neural cells despite high MHC expression

The ability to expand human neural precursor cells in vitro offers new possibilities for future cell therapies. However, concern over immunologically based rejection of in vitro-expanded human neural cells confounds their use as donor cells. Here, we demonstrate that the expression of human leukocyte antigen (HLA) class I and II molecules, but not the co-stimulatory proteins CD40, CD80 and CD86, substantially increase during expansion of neurospheres. Furthermore, peripheral lymphocytes were unresponsive when co-cultured with in vitro-expanded neural cells. Taken together, these results suggest a low immunogenicity of these cultured human neural cells despite HLA incompatibility and high HLA expression.

Cellular transplantation strategies for spinal cord injury and translational neurobiology

Basic science advances in spinal cord injury and regeneration research have led to a variety of novel experimental therapeutics designed to promote functionally effective axonal regrowth and sprouting. Among these interventions are cell-based approaches involving transplantation of neural and non-neural tissue elements that have potential for restoring damaged neural pathways or reconstructing intraspinal synaptic circuitries by either regeneration or neuronal/glial replacement. Notably, some of these strategies (e.g., grafts of peripheral nerve tissue, olfactory ensheathing glia, activated macrophages, marrow stromal cells, myelin-forming oligodendrocyte precursors or stem cells, and fetal spinal cord tissue) have already been translated to the clinical arena, whereas others have imminent likelihood of bench-to-bedside application. Although this progress has generated considerable enthusiasm about treating what once was thought to be a totally incurable condition, there are many issues to be considered relative to treatment safety and efficacy. The following review reflects on different experimental applications of intraspinal transplantation with consideration of the underlying pathological, pathophysiological, functional, and neuroplastic responses to spinal trauma that such treatments may target along with related issues of procedural and biological safety. The discussion then moves to an overview of ongoing and completed clinical trials to date. The pros and cons of these endeavors are considered, as well as what has been learned from them. Attention is primarily directed at preclinical animal modeling and the importance of patterning clinical trials, as much as possible, according to laboratory experiences.