A curative gene therapy for Diamond-Blackfan anemia nears the clinic

When someone goes to the doctor with a common ailment, such as an infection, they will likely receive treatment and be functionally cured within days, forgetting the experience soon after. This experience contrasts with patients with a rare disease for which treatments are not straightforward, such as Diamond-Blackfan anemia (DBA). DBA is primarily a disease of poor red blood cell production. Due to mutations in genes responsible for the ribosome, the cell’s protein factory, the body cannot make enough red blood cells. This leads to oxygen deprivation across tissues and serious lifelong and potentially life-threatening consequences.

For patients with DBA, a quagmire of medical information and suboptimal choices can affect the rest of their lives. There are many potential treatments, all with complications, and the only curative therapy is allogeneic bone marrow transplantation, which is expensive, logistically challenging and carries its own dangerous complications. No one can be blamed for wondering: Where could a better, more accessible cure come from?

“I got started on DBA because there is a pressing need for newer treatments for patients,” said Senthil Bhoopalan, MBBS, PhD, St. Jude Department of Bone Marrow Transplantation and Cellular Therapy. “Fifty years ago, the standard of care was corticosteroids and blood transfusions across their lifetime, both with significant long-term side effects. The only curative therapy was bone marrow transplantation — which remains true today, but we are now one step closer to another curative option.”

Bhoopalan has spent the last five years trying to change the treatment reality for children with DBA. His efforts, using gene therapy to restore a gene that is broken in certain forms of the disease, were recently published in Molecular Therapy. 

“We demonstrated both the safety and efficacy of our vector in our model system,” Bhoopalan, the first and co-corresponding author, said. “The exciting thing now is that we are developing a clinical trial from these results.”

“Senthil has worked relentlessly to develop a cure for DBA by investigating the biology of the disease, developing new experimental technologies and building upon the late Brian Sorrentino’s groundbreaking work on curing X-linked severe combined immunodeficiency,” said senior and co-corresponding author Mitchell J. Weiss, MD, PhD, St. Jude Department of Hematology chair. “As an institution, we built the expertise and infrastructure to create and evaluate lentiviral gene therapy vectors and capitalized on Sorrentino’s experience to create another potentially curative therapy.” 

Boosting blood cells while lessening lentiviral vector liability

The most common dysfunctional gene in DBA is RPS19, which codes for a key component of the ribosome responsible for decoding genetic information during protein synthesis called the 40S subunit. Therefore, Bhoopalan created a gene therapy that puts a functional RPS19 gene into blood-forming (hematopoietic) stem cells. He engineered a lentiviral vector, which integrates into cellular DNA, to deliver the gene safely. Findings showed that adding RPS19 to the DNA of DBA-like, RPS19-mutated human blood-making stem cells rescued ribosome function, increased blood cell production and unexpectedly let corrected stem cells outcompete DBA stem cells.

“We confirmed some clinical studies indicating that DBA affects not only red blood cells but also blood stem cells,” Weiss said. “And that feature may be possible to leverage therapeutically, resulting in better curative therapies.” The group previously showed that RPS19 deficiency negatively affects stem cell function in a separate manuscript in JCI Insight.

Normally, patients undergo a physically taxing process during lentiviral vector gene therapy. Clinicians collect blood stem cells from the patient, then transduce those cells with the lentiviral vector in a lab. Meanwhile, the patient receives high-intensity chemotherapy to destroy their remaining disease-affected stem cells in a process called conditioning. Once conditioning is completed, patients receive the corrected cells that will populate the now-empty stem cell niche in the bone marrow. The researchers’ new results suggest that high-intensity chemotherapy may not be needed for DBA gene therapy.

“The rescued cells had a competitive survival advantage over the uncorrected stem cells,” Bhoopalan explained. “Our data suggests lentiviral vector-corrected stem cells will expand over time and take over the bone marrow. That means we may be able to use low-intensity conditioning, which will reduce treatment-related toxicity for these patients.”

Curing DBA safely

While the lentiviral vector approach promises lower toxicity, a major part of the study was dedicated to evaluating safety. Gene therapy has held the promise of curing genetic diseases for decades but also carries significant downsides if developed improperly. The study performed a thorough preclinical analysis to examine the RPS19-lentiviral vector for every known major toxicity in preparation for a future clinical trial, which is ultimately the only way to determine whether the treatment is safe and effective.

Additionally, they showed that the unique biology of RPS19 insulates against another potential issue: toxicity due to overexpression if too many lentiviral vectors enter the same cell, and some cells end up with multiple copies of the gene. “We are also lucky that the RPS19 protein level is tightly regulated by cells, so the cellular machinery is actively helping us maintain safety by degrading excess RPS19 protein,” Bhoopalan explained. “The cell won’t let us overexpress it. We don’t have to worry about it and can focus on getting the gene into as many stem cells as possible to cure the disease.” 

Cures come from committed St. Jude researchers

Now that safety and efficacy have been demonstrated in a model system, the group is preparing for a clinical trial, hoping to launch in 2026. The effort shows the true power of bench-to-bedside research at St. Jude and the research infrastructure for gene therapy that took many years to build.

“Senthil started this project from scratch, used the available tools at hand and has now brought his work to the verge of a clinical trial,” Weiss said. “He’s a physician-scientist who developed a new treatment approach with his own hands in the lab, and now he’s going to take this treatment all the way to patients. It’s very exciting.”

“We wanted to develop a new option for patients with DBA, and with my physician-scientist background, I could see the exciting potential of this gene therapy,” Bhoopalan concluded. “At St. Jude, we have the infrastructure, the resources and outstanding collaborators to bring an idea from the lab all the way to the kids who need it. We are starting with RPS19 and, one day, hope to target other DBA genes as well.”