Modified Stem Cell Transplant Procedure Shows Favorable Results in Adults Living with Severe Sickle Cell Disease

Less Toxic Approach to Haploidentical Bone Marrow Transplantation in Adults Living with Severe Sickle Cell Disease Offers Promise 

LBA-4: Reduced Intensity Haploidentical Bone Marrow Transplantation in Adults with Severe Sickle Cell Disease: BMT CTN

(SAN DIEGO, Dec. 12, 2023) – Stem cell transplantation is a potentially curative treatment for sickle cell disease (SCD), but it is not feasible for most people, often due to a lack of suitable donors or the inability to tolerate the intensive chemotherapy required as part of the treatment. In a new study, presented during the 65th American Society of Hematology (ASH) Annual Meeting and Exposition, adults living with severe SCD saw good outcomes from a modified transplantation procedure that broadens the potential donor pool and includes a gentler conditioning regimen, suggesting a less toxic approach could allow a much broader array of people to benefit from the treatment. 

“This is a pragmatic approach for adults with SCD, and the results are fantastic,” said Adetola A. Kassim, MBBS, MS, professor of medicine at Vanderbilt University Medical Center, the study’s lead author. “It actually beat our expectations. This study has clearly shown that you can take selected adult patients with significant comorbidities to transplant, and hopefully change the trajectory of their disease.” 

The trial is the largest multi-center study to date to test the modified approach in adults with SCD. 

SCD is an inherited blood disorder in which red blood cells become misshapen, diminishing their ability to carry oxygen. It causes episodes of severe pain, called vaso-occlusive crises, as well as damage to tissues and organs that accrue over time and can lead to early death. A stem cell transplant can cure the disease by removing the stem cells that produce misshapen blood cells and replacing them with stem cells from a donor that will make healthy blood cells. 
The standard transplantation procedure for SCD requires that the donor be a sibling with a high degree of genetic similarity and that the recipient be healthy enough to tolerate a high-intensity chemotherapy regimen as part of the procedure. In the modified procedure used for the study, called related, reduced intensity haploidentical bone marrow transplantation, the donor only needs to be “half-matched” genetically to the recipient, broadening the pool of potential donors to include not only siblings but parents, children, cousins, aunts, and uncles.

While fewer than one-quarter of people with SCD have a matched sibling who could potentially serve as a donor, about 90% have a relative who could serve as a half-matched donor. In addition, because it uses a lower intensity conditioning regimen, the modified approach is more easily tolerated by people with health problems such as organ damage, a complication of SCD that becomes more common with age. 

As a result of these modifications, a much broader group of people living with SCD could be eligible for reduced intensity haploidentical bone marrow transplantation than for conventional matched-donor transplantation, including older individuals, those with more comorbidities, and those without a matched sibling donor. 

For the study, researchers enrolled 54 individuals living with SCD with a history of stroke or reduced heart functioning, pain episodes, or frequent blood transfusions. Forty-two participants ultimately underwent the modified stem cell transplantation procedure. At two years, the overall rate of survival following the transplant was 95% and the estimated rate of event-free survival (defined as survival without graft failure or a second infusion of stem cells) was 88%. 
At 100 days following the transplant, 4.8% of patients experienced a primary graft failure and 4.8% experienced adverse events of grade three or higher. Infections were common; 78.6% of patients experienced at least one hospital admission following their transplant, most due to infections. Two participants died within the first year after the transplant, one from organ failure and one from fluid buildup in the lungs associated with COVID-19 infection. 

Most participants experienced significant improvements in markers of healthy blood functioning, a reduction in pain episodes and fatigue, and improved heart and lung functioning. Overall, researchers said that the results suggest the modified procedure can achieve results that are comparable to conventional stem cell transplantation and is tolerable even for people with health conditions that would make them ineligible for a conventional transplant. 
In future studies, the researchers plan to focus on opportunities to reduce rates of infection, enhance supportive care, and preserve fertility among people undergoing the procedure. They also plan to continue to follow trial participants to track long-term outcomes. 

“Some of these patients are really thriving and now getting back into the community,” said Dr. Kassim. “Our hope is that long-term follow-up will be able to quantify the added value of curing patients of SCD.” Dr. Kassim added that most patients were off immunosuppression therapy at both the one and two-year post-transplant timepoints with no significant chronic graft-versus-host disease, providing evidence that the study’s cyclophosphamide-based post-transplant regimen helped to reduce the risk of this serious complication.

Researchers noted that for many people, the feasibility of this treatment will depend not only on the availability of family donors, but on costs and insurance coverage, the ability to take time off work and even temporarily relocate to undergo the procedure, and the availability of family and caregiver support. 

This study was funded by the National Heart, Lung and Blood Institute and the National Cancer Institute.

Adetola Kassim, MBBS, MS, of Vanderbilt University, will discuss this study in the Late-Breaking Abstracts Session on Tuesday, Dec. 12, 2023, at 9:00 a.m. Pacific time in Hall A (San Diego Convention Center).

The American Society of Hematology (ASH) (hematology.org) is the world’s largest professional society of hematologists dedicated to furthering the understanding, diagnosis, treatment, and prevention of disorders affecting the blood. For more than 60 years, the Society has led the development of hematology as a discipline by promoting research, patient care, education, training, and advocacy in hematology.

ASH’s flagship journal, Blood (bloodjournal.org) is the most cited peer-reviewed publication in the field, and Blood Advances (bloodadvances.org) is an open-access, online journal that publishes more peer-reviewed hematology research than any other academic journal worldwide. Two new journals will be joining the Blood Journals portfolio in 2024, Blood Neoplasia (bloodneoplasia.org) and Blood Vessels, Thrombosis & Hemostasis (bloodvth.org).

Contact:  
Melissa McGue, ASH, [email protected]
Kira Sampson, ASH, [email protected] 
Brianne Cannon, FleishmanHillard, [email protected]