Embryonic Vs Adult Stem Cells

ES versus adult stem cells
The most frequently discussed types of stem cells include ES cells and adult tissue-specific stem cells. These differ in many aspects, each type offering some specific advantages but their usage also has some disadvantages. ES cells can divide easily beyond the Hayflick limit and they remain stable. These pluripotent cells can produce any cell in our body including gametes and as such they may be utilised in therapy of a broad spectrum of diseases. When they form aggregates ES cells will spontaneously differentiate and produce embryoid bodies containing structures (such as blood islands) typical for early developmental stages. Homologous recombination applied to ES cells has revolutionized the study of gene function. ES cells thus represent an irreplaceable tool in studies of mammalian development and molecular regulation of a cell fate choice. Moreover, ES cells have been used as in vitro models for drug screening and toxicity studies. Unfortunately the usage of ES cells has also serious disadvantages. First, isolation of these cells is associated with the death of the embryo and therefore this approach has many ethical drawbacks. Second, a direct systemic administration of primitive ES leads to formation of tumours (teratomas). Finally, in cell therapy, ES cells would be rejected because they are not histocompatible with the patient (they were derived from another organism).

Because of these drawbacks, many investigators focus on adult (tissue-specific) stem cells. If derived from the patient's own tissues they will be fully histocompatible and as such accepted by the host immune system. However, not all tissues are easily accessible for stem cell isolation and their long-term culture may be problematic. Because of their multipotency they represent an ideal source to treat the tissue from which they were harvested.

Mesenchymal stem cells
The mesenchyme is a primitive embryonic tissue which gives rise to definitive connective tissues, cartilages and bones. As a result stem cells isolated from adult connective tissues were called mesenchymal stem cells. These stem cells can be quite easily isolated: the source tissue is usually well accessible, the cells are well propagated in vitro but the resulting cells are quite heterogeneous. They show the capacity to generate cells of the bone, cartilage, adipose, and tendons lineage. They are also endowed with a remarkable plasticity and they were proved to generate lots of diverse cells: nervous, cardiac, liver, endothelial etc. Mesenchymal stem cells have been frequently obtained from the bone marrow (sometimes referred to as bone marrow stromal cells). Stem cells with similar properties have been derived from the dental pulp and other tissues. In medicine, mesenchymal stem cells may be used to accelerate healing of wounds and injured tissues. Mesenchymal stem cells can interact with epithelial cells; these interactions are crucial for tissue repair as well as for organ morphogenesis. Mesenchymal stem cells can also modulate the immune response since they are known for their immunosuppressive and anti-inflammatory activities. Moreover, they could be used to repair microenvironment of many tissues including bone marrow stroma and thus support the acceptance of haemopoietic cells. Their enormous plasticity makes these cells the most suitable candidate for stem cell therapy.

The PurStem project is focussed particularly on mesenchymal stem cells.