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Sickle Cell: Good Outcomes for Haploidentical Transplants

SAN DIEGO — A small group of adult and pediatric patients with sickle cell disease (SCD) reached high 2-year survival after undergoing reduced-intensity haploidentical stem cell transplantation, a new phase 2 trial reports. It is much easier to find eligible haploidentical donors — half-matched or partially matched — than eligible hematopoietic donors.

Of 42 patients aged 15-45 who were fully treated, 95% survived to 2 years post transplant (overall survival, (95% CI, 81.5%-98.7%), and 88% reached the primary endpoint of event-free survival at 2 years (95% CI, 73.5%-94.8%), according to the findings, which were released at the annual meeting of the American Society of Hematology.

At an ASH news briefing, study lead author Adetola A. Kassim, MBBS, MS, of Vanderbilt University Medical Center, in Nashville, Tennessee, said the results support haploidentical stem cell transplants “as a suitable and tolerable curative therapy for adults with sickle cell disease and severe end-organ toxicity such as stroke or pulmonary hypertension, a population typically excluded from participating in gene therapy.”

Dr. Kassim added that the findings are especially promising since there are so many potential donors in stem-cell transplants: “Your siblings can be donors, your parents can be donors, your cousins can be donors. First-, second-, and third-degree relatives can be donors. So there’s really endless donors within the family.”

In an interview, Mayo Clinic SCD specialist Asmaa Ferdjallah, MD, MPH, of Mayo Clinic in Rochester, Minnesota, who was not involved with the study but is familiar with its findings, said stem cell transplant is the only option to cure SCD.

“This is advantageous because SCD is otherwise a chronic disease that is marked by chronic pain, risk of stroke, frequent interruptions of school/work due to sick days, and decreased life span,” she said. “Most patients, assuming they can tolerate the conditioning chemotherapy that is given before transplant, are eligible.”

Matched sibling donors are preferable, but they can be hard to find, she said. It hasn’t been clear whether half-matched donors are feasible options in SCD, she said. “This means that, if you are a patient with sickle cell disease, and you don’t have a suitable matched donor, haploidentical transplant is not a recommendation we can make outside of enrollment in a clinical trial.”

For the study, researchers enlisted 54 patients with SCD and prior stroke, recurrent acute chest syndrome or pain, chronic transfusion regimen, or tricuspid valve regurgitant jet velocity ≥2.7 m/sec. Participants had to have an HLA-haploidentical first-degree relative donor who would donate bone marrow.

“The median age was 22.8 years at enrollment; 47/54 (87%) of enrolled participants had hemoglobin SS disease, 40/54 (74.1%) had a Lansky/Karnofsky score of 90-100 at baseline, and 41/54 (75.9%) had an HLA match score of 4/8,” the researchers reported. “Recurrent vaso-occlusive pain episodes (38.9%), acute chest syndrome (16.8%), and overt stroke (16.7%) were the most common indications for transplant.”

“We knew going into this that we were going to get very high-risk patients,” Dr. Kassim said.

Forty-two patients went through with transplants. As for adverse events, 2 patients died, all within the first year, of organ failure and acute respiratory distress syndrome; 4.8% of participants had primary graft failure, and 2.4% had secondary graft failure before day 100. “The cumulative incidence of grades II-IV acute GVHD [graft-versus-host disease] at day 100 was 26.2% (95% CI, 14.0%-40.2%), and grades III-IV acute GVHD at day 100 was 4.8% (95% CI, 0.9%-14.4%).”

The outcomes are similar to those in transplants with matched sibling donors, Dr. Kassim said.

Dr. Ferdjallah said the new study is “robust” and impressive, although it’s small.

“As a clinician, these are the kind of outcomes I have been hoping for,” Dr. Ferdjallah said. “I have been very reluctant to suggest haploidentical transplant for my sickle cell disease patients. However, reviewing the results of this study with my motivated patients and families can help us both to use shared medical decision-making and come together with what is best for that specific patient.”

As for adverse events, she said they “confirm a fear of using haploidentical transplant, which is graft failure. Fortunately, out of 42 who proceeded to transplant, only 2 had primary graft failure and 1 had secondary graft failure. This is not overtly a large number. Of course, we would hope for more durable engraftment. The other side effects including GVHD and infection are all to be expected.”

As for cost, Dr. Kassim said the transplants run from $200,000 to $400,000 vs over $2 million for gene therapy, and Dr. Ferdjallah said insurance is likely to cover the treatment.

Moving ahead, Dr. Ferdjallah said she looks forward to getting study data about pediatric patients specifically. For now, “we should consider HLA-haploidentical seriously in patients with sickle cell disease and no available HLA-matched donors.”

Grants to the Blood and Marrow Transplant Clinical Trials Network from the National Heart, Lung, and Blood Institute and National Cancer Institute funded the study. Dr. Kassim had no disclosures. Some other authors disclosed various and multiple relationships with industry. Dr. Ferdjallah has no disclosures.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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