According to Dr Michael Watts, an expert in haematology and stem cells at University College London, there are just 10,000 primitive cells in the average adult's bloodstream. Of those, only 500 might have the potential to replace embryonic stem cells. Stem cell research requires millions of these cells.
Bone marrow donors are routinely treated with a drug known as G-CSF which "mobilises" stem cells from the bone marrow into the blood. After G-CSF treatment the donor's blood is passed through a centrifuge and back into their body, akin to a kidney dialysis machine, harvesting two or three hundred million primitive cells in the process.
Various properties of these primitive cells have been used to try and isolate the 5% or so with the highest stem cell potential, but no single technology has proved completely successful for human stem cells. This is where the optical stretcher could come to the rescue, picking those cells one by one according to the strength of their cytoskeletons. Watts explains that such an advance could have far-reaching consequences for medical treatments. "We could add significantly to our knowledge of stem cell biology toward developing cellular therapies," he says.
The optical stretcher can already test 3,600 cells per minute. This is not yet fast enough for industrial separation of millions of high grade stem cells, but it promises a realistic alternative to embryo use if it can be scaled up. Meanwhile, it is already being used to isolate low-grade stem cells which can develop into skin. In collaboration with medical professionals in Leipzig, elderly patients are being treated for persistent non-healing wounds. Low-grade stem cells isolated from the patient's own blood are applied to the wound to kick-start the healing process.