CRISPR cure for sickle cell
nearly 100% effective after three years
Newly released data shows nearly universal efficacy with no
drop in effectiveness.
By B. David Zarley
June
25, 2022
When CRISPR Therapeutics
and Vertex used gene editing to try to cure heritable blood disorders in 2019,
it marked the first CRISPR trial outside
of China.
A year later, the trial
— using the CRISPR gene editor to treat sickle cell disease and beta
thalassemia — showed promising results, Freethink reported in
2020.
Now, three years after
the trial began, the researchers have presented new data showing that the
treatment continues to be effective.
“These data provide
further evidence that this treatment has the potential to be transformational
for patients with sickle cell disease and beta thalassemia,” trial abstract author
Stephan A. Grupp of the Children’s Hospital of Philadelphia said in a statement.
New
data shows that the CRIPR sickle cell and beta thalassemia treatment continues
to be effective even three years out.
The diseases: Severe
sickle cell disease (SCD) and transfusion-dependent beta thalassemia (TDT) are
both caused by genetic mutations impacting hemoglobin, the molecule red blood
cells use to carry oxygen throughout the body.
In SCD, atypical
hemoglobin causes the red blood cells to twist out of shape, contorting into
crescents — or sickles — that cannot deliver oxygen as well. The disease can
cause tiredness and shortness of breath, and periodic sickle cell crises cause
intense pain.
In TDT, patients do not
produce enough hemoglobin at all, sometimes requiring repeated blood
transfusions, which have their own risks and side effects.
Both can be treated by a
stem cell transplant from a suitable donor, which not only requires finding a good
match but may also require suppressing the patient’s immune system.
The therapy: The
CRISPR treatment, originally dubbed CTX001 and now called exa-cel, is a
one-time treatment that genetically alters the patient’s own cells to produce
the kind of hemoglobin found at birth, which isn’t distorted, allowing red
blood cells to work properly.
The new data, presented
at the European Hematology Association Congress but yet to be published in a
peer-reviewed journal, reported results from 75 patients.
Of the TDT patients, 42
out of 44 were blood transfusion-free up to 37.2 months after their exa-cel
infusion, according to CRISPR Therapeutics and
Vertex. They are essentially cured of
the disease.
The
CRISPR therapy is a one-time treatment that genetically alters the patient’s
own cells.
The remaining two
patients needed much less transfusion volume, and all of the TDT patients had
elevated levels of fetal hemoglobin and total hemoglobin in their blood.
All of the SCD patients
were free from sickle cell attacks, up to 32.3 months later.
Two of the TDT patients
suffered adverse effects possibly related to exa-cel, including delayed growth
of white blood cells and a low blood platelet count, both of which resolved on
their own.
Importantly, the team
found no evidence of exa-cel’s effectiveness waning over time, even three years
after infusion.
“Although we must
continue to investigate the durability of these results, I am excited about the
current data,” Grupp said.
