Treatment designed to work across different genetic mutations

At a glance:

• A new gene therapy is designed to treat the life-threatening disorder no matter which specific genetic mutation a patient has.
• The therapy is ready to test in clinical trials.
• Work offers proof of concept that gene therapies can treat disease by targeting a shared problem that various individual mutations lead to.

Efforts to develop a gene therapy for Diamond-Blackfan anemia (DBA) — a rare, life-threatening disorder in which bone marrow cannot make mature, functioning red blood cells — have been hampered by the fact that at least 30 different genetic mutations can cause the disorder.

A team led by researchers at Harvard Medical School has now cleared that obstacle by developing a universal gene therapy for DBA, one designed to correct the bone marrow defect no matter the patient’s specific mutation.

The experimental therapy is ready to test in clinical trials, the team reports Nov. 11 in Cell Stem Cell.

“This is one of first examples where we can develop a gene therapy that can target dozens of mutations with a single vector,” said senior author Vijay Sankaran, the HMS Jan Ellen Paradise, MD Professor of Pediatrics at Boston Children’s.

The work provides proof of concept that gene therapies can treat rare or complex blood diseases not by correcting individual mutations but by targeting a problem that all the mutations lead to, the team said.

All roads lead to GATA1

Children with DBA, which was first described in 1938 at Boston Children’s, have few treatment options. A handful with well-matched donors can be cured with bone marrow transplants, but most rely on steroids, which have side effects, or regular blood transfusions.

Most of the gene mutations known to lead to DBA were discovered at Boston Children’s over the past 15 years by Sankaran and Hanna Gazda. These mutations mostly affect ribosomes: structures within cells that play a key role in building the body’s proteins.

But in 2012, as an intern in pediatrics, Sankaran found that a few patients instead had mutations in a gene called GATA1, a key regulatory factor that controls the earliest steps of red blood cell production.

Sankaran subsequently found that the ribosomal mutations reduce the number of functional ribosomes in cells, which prevents GATA1 protein from being produced.

When Sankaran added GATA1 protein back to blood stem cells taken from patients with DBA, the cells were better able to differentiate into red cells.

These findings suggested that raising GATA1 levels could treat DBA in patients with mutations in the GATA1 gene itself and in patients with the ribosome-related mutations.

Developing a gene delivery system

Supported by the Therapeutic and Medical Device Accelerator at Boston Children’s, Sankaran’s team then set about developing a vector — an engineered, non-infectious lentivirus — that could deliver the GATA1 gene into patients.

But there was another big challenge: When the team delivered GATA1 into blood stem cells in a lab dish, they immediately differentiated into mature red cells and didn’t engraft in bone marrow.

“We only wanted the gene to be expressed after the stem cells differentiate,” Sankaran said. “That problem was not trivial.”

In the new work — led by Richard Voit, then in the Sankaran Lab and now at UT Southwestern — the researchers devised a way to control GATA1 expression so the gene could be inserted in blood stem cells that travel to the bone marrow but would turn on only in progenitors of red blood cells.

Lab experiments showed increased production of mature red blood cells, while the stem cells themselves retained their stem cell activity.

The researchers also found that the gene therapy vector inserts GATA1 only at the intended location in the genome, allaying concerns about unintentional insertion near any cancer-causing genes.

“As far as we can tell, this approach is very safe,” Sankaran said.

The team is now filing an Investigational New Drug application with the FDA in hopes of starting a clinical trial.

Broader implications

In lab tests, the therapy stimulated markedly greater red blood cell production than other treatment methods explored to date. However, only a clinical trial will demonstrate whether this remains true in patients.

The team hopes that if the gene therapy proves safe and effective, it will help alleviate racial and ethnic health disparities associated with lack of bone marrow transplant donor matches for people with DBA.

Sankaran is also excited about the implications for other gene therapies.

The work demonstrates for the first time how “the reach of any hematopoietic gene therapy could be broadened if you target the downstream mechanism rather than each of the individual components,” he said. “This could open up avenues for a whole other set of blood diseases.”