Study Uses Gene Editing to Take Brakes Off Lab-based Red Blood Cell Production
October 22, 2015
Read coverage in Time, Genome
Web and Harvard
Turning off a single gene leads to a roughly three-to-five-fold gain in
the yield of laboratory methods for producing red blood cells from stem cells, according
to a multi-institutional team led by
researchers at Dana-Farber/Boston Children's Cancer and Blood Disorders Center.
These findings, published in Cell Stem
Cell, suggest a way to cost-effectively manufacture red blood cells from
stem cells; the patients who could potentially benefit include those who cannot
use blood currently available in blood banks.
Previous research has shown that it is possible to use various methods
to force different kinds of stem cells to produce transfusion-grade red blood
cells in a laboratory, but, at a cost between $8,000 and $15,000 per unit of
blood, the processes are expensive. This is the first study to combine stem
cells, powerful gene editing tools, and data from genome-wide association
The research team behind the Cell
Stem Cell study—led by senior author and Dana-Farber/Boston Children's
pediatric hematologist Vijay
Sankaran, MD, PhD—homed in on their target gene, called SH2B3, after GWAS data revealed naturally occurring variations in the
gene's sequence that reduce its activity result in increased red blood cell
"There's a variation in SH2B3
found in about 40 percent of people that leads to modestly higher red blood
cell counts," Sankaran said. "But if you look at people with really
high red blood cell levels, they often have rare SH2B3 mutations. That said to us that here is a target where you
can partially or completely eliminate its function as a way of increasing red
blood cells robustly.
"There are many patients with rare blood types or blood disorders
who need very specific kinds of blood and cannot accept most donated
blood," Sankaran continued. "Also, there are patients for whom there
is a possibility of using red blood cells as a way of delivering therapies."
Sankaran and his collaborators—including study co-first authors Felix
Giani, Claudia Fiorini, PhD, and Aoi Wakabayashi of Dana-Farber/Boston
Children's—wanted to see if were possible to use SH2B3 as a target to genetically increase the yield of
laboratory-based red blood cell production processes (as opposed to tweaking
cells in culture by adding cytokines and other factors). To do, so, they first
used RNA interference (RNAi, which silences gene expression) to turn down SH2B3 in donated adult, human,
blood-forming stem cells (hematopoietic stem and progenitor cells, or HSPCs)
and HSPCs from human umbilical cord blood.
The team's data confirmed that shutting off SH2B3 with RNAi skews an HSPC's profile of cell production to favor
red blood cells. Adult and cord blood stem cells treated with RNAi produced three-to-five
and five-to-seven times more red blood cells than controls, respectively. Using
multiple tests, the team found that the red blood cells produced by RNAi were
essentially indistinguishable from control cells.
Sankaran and his team recognized that their HSPC/RNAi approach would be very
difficult to scale up to a level that could impact the clinical need for red
blood cells. Thus, in a separate set of experiments, they used CRISPR gene
editing to permanently shut off SH2B3
in human embryonic stem cell (hESC) lines, which can be readily renewed in a
laboratory. They then treated the edited cells with a cocktail of factors known
to encourage blood cell production. Under these conditions, the edited hESCs
produced three times more red blood cells than controls. Again, the team could
find no significant differences between red blood cells from the edited stem
cells and controls.
Sankaran thinks that SH2B3's
enforces some kind of upper limit on how much red blood cell precursors respond
to calls for more red blood cell production.
"This is a nice approach because it removes the brakes that
normally keep cells restrained and limit how much red blood cell precursors
respond to different laboratory conditions," Sankaran explained.
He notes that in his vision, stem cells edited to keep SH2B3 turned off would be maintained in
culture as a kind of cellular starter and used to produce red blood cells for
treatment purposes; the edited stem cells themselves would never be used for
He also believes that with further development, the combination of
CRISPR and hESCs could increase the yields and reduce the costs of producing
red blood cell in the laboratory to the level where commercial-scale manufacture
could be feasible.
"This is allowing us to get close to the cost of normal
donor-derived blood units," he said. ""If we can get the costs down
to about $2,000 per unit, that's a reasonable cost."
This study was supported by the National Heart, Lung and Blood Institute
(grant number R01HL119099, P01HL032262), the National Institute of Diabetes and
Digestive and Kidney Diseases (grant numbers F30DK103359, R01DK097768,
P30DK049216, K08DK093705) and the National Institute of General Medical
Sciences (grant numbers K99HG008399, K99HG008171).