The vast majority of the people who received Bluebird bio’s newly approved sickle cell disease medicine in a clinical trial remained free of the frequent pain crises typical of their condition, some for as long as five years, new study results show.

The therapy, now branded as Lyfgenia but previously known as lovo-cel, was one of two genetic medicines cleared by the Food and Drug Administration on Friday for sickle cell. The data, which will be presented Monday at the American Society of Hematology’s annual conference, offers a snapshot of what patients considering the new medicine might be able to expect from treatment.

To create Lyfgenia, Bluebird uses a benign virus to insert an engineered gene into patients’ own stem cells, giving those cells a blueprint to create a functional form of hemoglobin once returned. An important oxygen-carrying protein, hemoglobin is damaged in people with sickle cell.

Bluebird studied Lyfgenia in two clinical trials, tracking the treatment’s effectiveness and side effects for as long as five years. Among 34 evaluable patients, the drug eliminated vaso-occlusive episodes — the excruciating pain episodes that are a hallmark of sickle cell — between six and 18 months after infusion in 88% of patients, and severe crises in 94%. The study participants had experienced a median of three severe crises per year in the two years leading up to the trial.

Researchers also tracked anti-sickling hemoglobin levels in patients who received the treatment, with median levels hovering close to normal as of last study visits.

“We couldn’t really ask for too much better,” Julie Kanter, a professor at the University of Alabama and lead author of the study, said in a Saturday press briefing held by ASH.

Side effects to treatment were generally related to the conditioning regimen used to prepare patients for Lyfgenia. In order to ready bone marrow to receive the new, modified stem cells, patients are given busulfan, a chemotherapy that can cause mouth sores and low blood cell counts.

A few participants also reported chronic pain or exacerbation of existing pain. Though some treated people might still experience pain, they may be hospitalized for fewer days, and the therapy prevents the disease from progressing further by going “right at the root cause of the disease,” said Rich Colvin, Bluebird’s chief medical officer.

Previous damage caused to bones and organs before Lyfgenia won’t be undone by treatment, however.

Bluebird has been on a long road developing Lyfgenia. The company had to put two clinical studies on hold on hold in 2021 after two trial participants developed, respectively, leukemia and signs suggestive of a cancer-like bone marrow disease. In all, two patients enrolled in the trial died of leukemia, Bluebird said. Both were treated with drug products made via a manufacturing process the company has since changed.

Bluebird’s long development and trial delays have put it in a hard spot financially, forcing it last year to warn investors of its solvency. The company has since stabilized matters somewhat, including via layoffs, but has cash only to fund operations into the second quarter of next year.

Sickle cell disease is a genetic condition where blood cells contort into hard sickle shapes, causing them to build up and clog blood flow. These blockages cause pain crises that, over time, lead to organ damage and other complications. Approximately 100,000 people in the U.S. have the disease, many of whom are Black.

A handful of treatments exist to manage sickle cell symptoms, but only a bone marrow transplant can potentially cure the disease. However, few people have a matched donor and, even then, a transplant carries the risk of rejection by the patient’s body.

“Our main thing is to take care of people who have problems,” Colvin said. “Our first priority with people-centered development is to make sure that we do whatever we can to reduce the risk to our patients, keep them safe, make sure and monitor the therapies closely.”