LONDON, England (CNN) -- Stem cells are considered a holy grail of medical research. They are thought to hold immense potential for treating a wide range of diseases and disabilities.
Claudia Castillo, 30, suffered from tuberculosis for years.
However, they have also been the source of much heated debate -- particularly the use of embryonic stem cells.
In the case of Claudia Castillo, a 30-year-old Colombian mother of two living in Barcelona, her own adult stem cells have been used to grow a new section of trachea -- an airway essential for breathing. It is a first and could revolutionize stem cell use.
What are stem cells?
Most adult cells in the body have a particular purpose that cannot be changed. For example, a liver cell has specific functions and cannot take on the roll of cells in other organs.
Stem cells are different. They retain the potential to turn into may types of different cells.
Why are they considered useful?
When a stem cell divides it has the potential to remain the same or become a cell with a more specialized function. Scientists believe this ability could be harnessed to turn them into a repair kit for the body.
They believe they could be used to grow healthy tissue -- as in Claudia Castillo's case -- to replace parts of the body damaged or affected by disease.
They also hope it could be used to treat conditions like Parkinson's and Alzheimer's, the after effects of strokes, arthritis, burns and spinal conditions.
What types of stem cells are used?
Scientists typically work with two kinds of stem cells: embryonic stem cells and adult stem cells, which have different functions and characteristics.
Till now, scientists have believed the most useful stem cells have come from embryos.
This is because embryonic cells are pluripotent -- they have the ability to become any type of cell.
They have also been comparatively easy to grow in lab conditions, proving much more useful to researchers who require a large number of cells for replacement therapies.
However, stem cells are also found in adult organs and it is these cells that will now become the focus of more research. They are rarer and have been much harder to grow in the lab. They have been considered much less pluripotent.
The advantage of using adult stem cells is that they can be taken from the patient and then reintroduced, meaning rejection by the immune system is not a problem.
Is stem cell use controversial?
Yes, very. Some campaigners are fiercely opposed to the use of embryonic stem cells.
They are typically taken from lab-created embryos aged just four or five days, however, opponents argue they are living human beings and should not be used for experiments and destroyed.
Opposition to their use has been particularly vociferous in the U.S., where President George W. Bush banned the use of government funds for embryonic stem cell research.
However, most groups are supportive of adult stem cell research. So, this breakthrough represents a giant step.
The race is on to replicate the success with Castillo. In the past, because adult stem cells were considered stuck in their ways, the focus had been on embryonic cells but now scientists and doctors will be wanting to see if adult cells can be used to treat a wider range of conditions.