Scientists have found sources of skeletal stem cells (SSCs) in humans for the first time.
Stem cells that give rise to bone, cartilage and stroma (the spongy interior of bone) have long been sought in humans. Now an international team led by researchers at Stanford University School of Medicine in Stanford, California, has shown such cells exist in human adult and fetal bone marrow.
The researchers also show that certain other cells – from liposuctioned fat – could be induced to become skeletal stem cells, potentially providing a cheap and abundant source for future stem cell therapies. Their study was published in the journal Cell.
'For many years there's been this debate about a true human skeletal stem cell. This study unequivocally demonstrates that it's there and that it is self-renewing,' Professor Richard Oreffo at the University of Southampton who was not involved in the work, told The Scientist. 'There's still a lot to do, but this is a tremendous step forward for the field.'
They had difficulty in finding the markers associated with mice SSCs in human tissue, but by examining gene expression in the actively growing areas of fetal femurs they identified four key proteins. These turned out to be markers for SSCs in the human fetal bone.
In order to confirm that these cells were indeed skeletal stem cells, the team transplanted them into mouse kidney models, where some produced human 'ossicles', which contained bone, cartilage or stroma.
The human SSCs did not produce fat or adipose cells – an important point, as these are usually produced by a different type of stem cell, mesenchymal stem cells.
'This is a really valuable paper and a next step in the process of unraveling the stem and progenitor populations that are present in bone marrow,' Dr George Muschler, an orthopedic surgeon at the Cleveland Clinic who was not involved in the study, told The Scientist.
Dr John Adams at the David Geffen School of Medicine at the University of California, Los Angeles agreed the study was a 'major step forward' but he cautioned in Science: 'Whether they can isolate them [SSCs] in large enough quantities to be clinically useful, that's going to take a while to find out.'
Dr Longaker hopes the discovery will have clinical impact. 'I would hope that, within the next decade or so, this cell source will be a game-changer in the field of arthroscopic and regenerative medicine,' he said.
'The United States has a rapidly ageing population that undergoes almost two million joint replacements each year. If we can use this stem cell for relatively noninvasive therapies, it could be a dream come true.'