A new technique that converts A,
B and AB blood to type-O could soon come to Canada.
Hopes are high that this innovation — currently
in clinical trial in Denmark — will bring us a
more flexible and safer transfusion supply.
University of Copenhagen cellular
biologist Dr Henrik Clausen and his colleagues have
perfected a method of separating the A and B antigens
from red blood cells (RBCs) using two different enzymes.
Their findings, published online April 1 in Nature
Biotechnology, could eventually help keep Canada's
blood reservoirs full, according to Dr Dana Devine,
vice-president of medical, scientific and research affairs
at Canadian Blood Services.
"One of the drivers into this area
of scientific research is that the inventory of blood
collected is not balanced with the way blood is actually
used in hospitals," says Dr Devine. "We always have
leftovers of AB and B blood types because, in emergency
situations, doctors will always err on the side of caution
and pump a patient full of O-negative blood. O-neg is
used disproportionately to its distribution in the general
population."
MATCHMAKER
With an affordable conversion technology, the size of
Canada's reserve of O-negative blood would rise dramatically.
"This is a technology that's of interest to organizations
like Canadian Blood Services, simply because it gives
us an additional flexibility to manage our inventory,"
says Dr Devine.
And, she says, it would largely
eliminate blood mismatches in transfusions — a
potentially deadly mistake.
"If you look at statistics from
around the world, from those countries that collect
what we call 'hemo-vigilance' data, mismatched transfusions
are the number one cause of transfusion-associated mortality,"
she says.
According to the Public Health
Agency of Canada, up to 3% of all transfusions result
in an adverse event, a small number of which are fatal.
In the most serious cases, up to 80% are due to mismatched
blood groups.
STRANGE
BREW
The concept of stripping the A and B sugar molecules
from the surface of red blood cells is not new. In the
1980s, New York researchers showed that the B antigen
could be removed with a green coffee bean enzyme. However,
the process was deemed too costly and inefficient for
practical use, particularly because the conversion process
had to be carried out under highly acidic conditions
that damaged the RBCs. Additionally, no enzyme was known
that could remove the A antigen.
Unlike their coffee-bean predecessor,
the two enzymes discovered by Dr Clausen are more powerful,
work in neutral pH and at room temperature. The researchers
identified the two from among 2,500 potential bacterial
candidates: Bacteroides fragilis to remove the
B antigen, and Elizabethkingia meningosepticum,
which targets the A antigen.
Using an automated process developed
by Massachusetts-based biotech company ZymeQuest, all
the A and B sugar molecules on the RBC surface are removed
within an hour and can then be easily washed away. So
far, animal trials have shown no adverse reactions.
However, the technology does not
remove the rhesus factor antigen from the RBCs of people
with Rh-positive blood, who comprise 85% of the population.
Even when stripped of A or B antigens, Rh-positive blood
would trigger a potentially fatal acute hemolytic reaction
if transfused into someone with Rh-negative blood.
BALANCED
SUPPLY
Though the new technique is no panacea, every drop counts
when it comes to transfusion blood. Even a modest increase
in the available supply could be a major help. "It's
easy to see why [the ZymeQuest method] would be very
attractive to blood banks and hospitals, because it
can help them rebalance the available blood supply,"
says Dr Devine.
"I think it would make a much smoother
use of the donated blood in Canada," she adds. "I've
been in discussions with ZymeQuest for the last year,
monitoring their progress. We've actually been talking
about the possibility of using this technology in Canada,
once the clinical trials have been completed. From a
research perspective, we need to understand what it
would mean logistically to our blood bank system to
use this technology, if it comes to market."
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