Stem cell therapies and their challenges

Stem cell therapy aims to repair tissue that cannot heal itself, either by transplanting stem cells (or cells made from them), or by stirring the body's own stem cells into action. Most such therapies are still experimental and costly. The one well-established therapy is bone marrow transplantation, used for blood cancers and blood disorders.

Some areas of research:

• Nerves and eyes: ALS (motor neurone disease), using bone marrow and iPS cells, is in trials; in spinal cord injury, researchers try to regrow nerve fibres; and retinal cells made from ESCs have improved vision in some patients.
• Skin and heart: keratinocyte stem cells taken from plucked hair follicles can grow new skin with little risk of rejection, healing burns faster than conventional grafts. Therapies to restore heart muscle and blood vessels are being studied.
• Autoimmune diseases: cells derived from blood stem cells are being tested for type 1 diabetes. In multiple sclerosis, where the immune system damages the myelin sheath around nerves, bone marrow and neural stem cells may help rebuild it. Cartilage cells (chondrocytes) are being tried for rheumatoid arthritis.
• Industry uses heart and nerve cells made from stem cells as disease models and for screening drugs.

Challenges:

• Immune rejection: transplanted cells from another person may be attacked. Drugs that suppress the immune system leave the patient open to infection. Using iPS cells made from the patient's own cells may avoid this.
• Tumours: ESCs divide indefinitely, and if any remain unspecialised after transplant, they might form tumours.
• Safety: risks such as contamination and infection must be ruled out.

So stem cells offer great promise, but each step must be taken carefully.