Everyone seems to be excited about stem cells. Their excellent promise as a treatment for a range of diseases and injuries mean almost guaranteed coverage for research. While some types of stem cells are already being used in treatment – for treating diseases of the blood and leukaemia, for example, multiple sclerosis and problems in the bone, skin and eye – there’s still a lot of hype and exaggeration, with some even selling empty promises to seriously ill or injured patients.
There are many different types of stem cells in the body and they have varying abilities. When most people think of stem cells, it’s often of embryonic stem cells, which have been controversial for ethical reasons, or their closely related cousins, induced pluripotent stem (iPS) cells, adult cells that have been reprogrammed to acquire stem cell-like properties. As the word “pluripotent” suggests, these stem cells have the capacity to transform into any cell type in the body, with the exception of egg and sperm cells.
There are other types of stem cells, however, that are considered to be “multipotent” – not quite as diverse in their abilities as pluripotent stem cells, but still able to turn into different cell types when stimulated in just the right way. These are mesenchymal stem cells, or MSCs, which have the capacity to differentiate into the cell types that give our bodies strength and structure: bones, cartilage, fat, muscle and tendons.
Therapies using MSCs are being touted as a great new hope for the treatment of serious chronic diseases such as colitis, diabetes, arthritis, cirrhosis, kidney disease, heart disease, chronic obstructive pulmonary disorder – the list goes on and on. In fact, there are currently over 700 MSC-based clinical trials, either ongoing or completed on the clinicaltrials.gov register.
It’s clear why there is so much interest in these cells. But can they really fulfil their promise – and do they have the capacity to harm as well as help us?
Regeneration and healing
There are two major promises that have been made when it comes to the use of MSCs in human medicine: their “regeneration potential”, that’s their potential to rebuild damaged tissues, such as bone, spinal cord and heart tissue; and their “healing properties”, which can reverse damage to diseased organs – for example, in arthritis and following organ transplantation.
The regenerative potential of MSCs has been studied since the late 1960s. In one of the earliest experiments with these cells, Alexander Friedenstein and colleagues showed that transplanting bone marrow to a different site of the body led to bone formation, which indicated that at least some cells in the bone marrow are able to change into bone cells – even in locations where bone would not be expected to grow.
Since then, researchers have worked out different signals that tell MSCs to change into specialised cell types. For example, the growth factor TGF-β can induce MSCs to turn into cartilage cells, which would be very helpful in repairing cartilage in arthritis sufferers.