[Paleopsych] Laser beams sort stem cells by springiness

[Steve Hovland]

18:22 12 April 2005
NewScientist.com news service
Shaoni Bhattacharya
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Web Links
Josef Kas, University of Leipzig 
<http://www.uni-leipzig.de/~pwm/kas/jkas/jkcv.html>
Institute of Physics, UK <http://www.iop.org/>
Optical trapping group, St Andrew's University 
<http://www.st-andrews.ac.uk/~atomtrap/index.htm>
Sex and cloning, New Scientist <http://www.newscientist.com/channel/sex>
 
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Measuring the "stretchiness" of cells using a new laser technique promises 
to pinpoint human stem cells in blood and distinguish cancerous cells from 
benign ones, say researchers.
Using an "optical stretcher", which pushes and pulls individual cells to 
measure their elasticity, Josef Kas and Jochen Guck from the University of 
Leipzig in Germany successfully separated adult stem cells from human 
blood.
They say they can also pick out cancerous cells from biopsies as small as 
just 50 cells - traditional methods need between 10,000 and 100,000 cells 
to give a diagnosis. Furthermore, the researchers say this is the first 
test able to identify metastatic cancer cells - those which are prone to 
spreading through the body to form secondary tumours - without actually 
locating any metastatic tumours.
"We have developed a very good way to recognise different cells based on 
something known since the 1950s - that very different cells have very 
different skeletons," says Kas.
He says the optical technique developed by the team is relatively simple 
and low cost, yet could offer a highly specific way of identifying stem 
cells, with the added benefit of a high throughput. "Sometimes the simple 
ideas are the ones people overlook," he told New Scientist, adding that its 
simplicity is the reason for its broad applications.
The new technique could lead to advances in medical treatments, says 
Michael Watts, a haematology and stem cell expert at University College 
London, UK. "We could significantly add to our knowledge of stem cell 
biology, [aiding the search for] cellular therapies," he says.
Kicking back
"This is really an amazing technique," says Kishan Dholakia, professor of 
physics at St Andrew's University, UK. He says it might allow diagnoses 
from very small samples from patients in the future - reducing the need for 
distressing or damaging tests.
Cells from most organisms have an internal scaffolding, called a 
cytoskeleton, which keeps their shape and helps them move. But this 
structure is less strong in cells which either have no reason to organise 
themselves, like primitive stem cells, or because they "de-differentiate", 
like cancer cells - which lose the special characteristics of the tissues 
in which they originated.
This means that stem cells and cancerous cells 
<http://www.newscientist.com/article.ns?id=mg17723863.100> are more springy 
than other cells. And metastatic cells are suppler still.
Using the optical technique, cells from a sample are pushed one by one into 
a gap between two opposing infrared lasers. As the light from each laser 
beam enters the cell, it changes momentum because the cell has a higher 
refractive index. This gives the cell a "kick back", explains Kas, and when 
the beam leaves the cell it gives it a "kick forward".
The kicks in opposite directions stretch the cell, and the amount by which 
the cell extends can be measured and used to identify it from a population 
of cells. Two beams are needed to keep the cell in a stable configuration.
The technique differs from previous "optical tweezers" methods - which use 
just one focused laser beam to hold a cell in place. However, this could 
damage or alter the cell, and at higher intensities it could just "fry 
everything", says Kas.
Oral cancers
The optical stretcher can already test 3600 cells per minute. And as well 
as being highly specific, it does not require the use of expensive chemical 
markers currently needed to identify stem cells, he says.
"The real excellence is they have got a good flow rate and throughput," 
says Dholakia. They have overcome the technical difficulty of channelling 
cells through the tiny space between two lasers, which he likens to trying 
to individually catch and squeeze many footballs bobbing in a river.
The new technique is currently being used to separate stem cells to treat 
elderly patients for persistent non-healing wounds and also at a heart 
clinic in Leipzig where doctors plan to inject a patient's own stem cells 
back into their heart muscle to aid recovery in the wake of a heart attack.
The device will also be trialled for screening cancers. Dentists in Leipzig 
will take swabs from patients to test for oral cancer, which is normally 
detected only when a tumour has developed, by which time the effects are 
devastating.
The work was presented by Kas at the Institute of Physics meeting in 
Warwick, UK, on Tuesday.