Most human tissues do not regenerate spontaneously, which is why “cell therapy and tissue engineering ” are promising alternative treatments. The principle is simple: patients' or donors' cells are collected and introduced into the injured tissues or organs directly or in a porous 3D material, with or without modification of their properties. Their use in new therapeutic areas will depend on advances in biology, materials science and engineering.
There is an extraordinarily wide range of opportunities for clinical applications of regenerative medicine. Among possible medium-term therapeutic applications are, cardiac insufficiency, preparation of small diameter arteries, treatment of atherosclerosis, cartilage defects, bone repair, burns, diabetes, liver or bladder regeneration, and neurodegenerative disorders. This concept of regenerative medicine is an emerging multidisciplinary field involving surgery, medicine, biology, chemistry, mechanics and engineering which can be defined as “the way to improve health and quality of life by restoring, maintaining, or enhancing tissue and organ functions”.
Since the 1960s and the therapeutic use of hematopoietic stem cells of bone marrow origin, there has been increasing interest in the study of undifferentiated progenitors that have the ability to proliferate and differentiate in different tissues. Although initially it may seem best to choose an autologous cell, these cells are generally not easily available, they are frequently in a pathological state and expansion cannot be extended to all tissues and organs. This explains the growing interest in stem cells that are produced during the development of the embryo, then of the foetus and finally in adult tissues and organs. Different stem cells (SC) with different potential can be isolated and characterised (totipotent, mesenchymal of different origins, especially those present in tissues...). It is undeniable that cells like bone marrow, adipose tissue or Wharton Jelly stem cells, which have limited potential, are of potential interest for applications because they are easily separated and prepared and no ethical problems are involved in their use.
Adult or embryonic stem cells are incontestably major subjects of research and for the development of therapeutic applications but are a sensitive subject which can sometimes trigger highly emotional reactions. Embryonic stem cells can apparently self-renew without limit in culture, but the mechanisms underlying this capacity are still not completely understood. However, they should lead to new knowledge and current research on the mechanisms behind intercellular communications, differentiation, and proliferation are based on the idea that, by mastering their regeneration potential, new clinical applications will become possible.
Despite the acknowledged promise of embryonic stem cells, in many cases adult stem cells provide a more interesting approach to clinical applications. In other respects, some lineages of adult stem cells are capable of greater plasticity than is assumed based on their tissue origin. Nowadays, mesenchymal stem cells, which were originally described in bone marrow, represent an enormous potential value for regenerative medicine. During the last 10 years, these multipotent cells have generated considerable interest, and mesenchymal stem cells in particular have been shown to escape allogenic immune response and be capable of immunomodulatory activity. These properties may be of great interest in regenerative medicine in the future, but today it is probably better to consider mesenchymal stem cells as a mixed population of progenitors rather than as homogeneous stem cells.
Recently, cells isolated from amniotic fluid also appeared to be of potential interest in regenerative medicine. These cells express some markers also expressed by embryonic stem cells and appear to be similar to stem cells isolated from Wharton Jelly.
The full potential of these stem cells is not yet known and it is possible that all the types of cell needed for regenerative medicine could be obtained from umbilical cord, placenta and amniotic fluid.
The regeneration of tissue is and will remain a challenge for the future development of cell therapy and tissue engineering. Many problems remain to be solved and scientific and technical knowledge is lacking that could lead to the development of innovative strategies to facilitate cell differentiation, increase the yield of cells and ensure a standardised product, overcome the risks of teratogenic effects and/or immune reactions, enable grafting via direct cell or biotissue transplantation and avoid legal issues involved in national regulations. It can be also noted that recently (since 2005–2006) tissue engineering had been replaced by cell therapy. The focus has switched from organ growth to cell therapy where cells are implanted to restore damaged or diseased tissues (in vivo engineering).
This book does not claim to be a handbook which covers all aspects of regenerative medicine or cell therapy. For those purposes, a much larger volume would be needed.
In this volume, the first part (11 chapters), is devoted to basic knowledge of stem cells. The second part (20 chapters) is dedicated to potential clinical applications (hematology, cardiac, vascular, osteoarticular, liver, skin, etc.) without having been able to envisage all the applications that will doubtless be developed in the coming decade. We hope that this book will provide a stimulus for basic researchers and clinicians involved in regenerative medicine or cell therapy.
The editor would like to thank all the authors for their outstanding contributions which enabled the publication of this volume.