Physicians at Children’s National Hospital in Washington, D.C., last week collected the stem cells of a young boy with sickle cell disease in preparation for what will be the first commercial infusion of a newly approved gene therapy from biotechnology company Bluebird bio.

The treatment, called Lyfgenia and cleared by the Food and Drug Administration in December, is made from a patient’s own stem cells, which are loaded with a gene encoding for an oxygen-carrying protein that’s defective in people with the blood disease.

Manufacturing is carried out in a central laboratory, from where the re-engineered cells are shipped back to treating hospitals to be infused into patients. From cell collection to product shipment, the entire process takes between 70 and 105 days, Bluebird estimates.

Last week’s cell collection, which was reported in detail by The New York Times, is an important milestone for sickle cell treatment.

The genetic disease is often described as the first to be categorized at the molecular level, after researchers identified changes in the protein hemoglobin that caused red blood cells to sickle and clump together in blood vessels. These blockages can cause debilitating pain and, over time, wreak damage on organs and joints.

Despite scientists’ understanding of sickle cell’s cause, treatments have been few and far between in the decades since discovery of defective hemoglobin as the disease’s root. A repurposed cancer drug called hydroxyurea is commonly used, but doesn’t work for everyone, while newer drugs have only modest effects. Stem cell transplants can be curative, though matched donors can be hard to find and the process comes with substantial risks.

Lyfgenia is one of two genetic therapies that offer hopes of something close to a cure. The other, called Casgevy and also approved last December, was the first therapy built around the gene editing technology CRISPR to be cleared by regulators.

Both therapies are among the most expensive drugs on the market. Bluebird set Lyfgenia’s price at $3.1 million, while Vertex Pharmaceuticals, which developed Casgevy with CRISPR Therapeutics, is charging $2.2 million for its treatment.

The high cost has raised concerns about patient access as well as impact on the budget of Medicaid, which covers many of the 20,000 or so people in the U.S. estimated to have sickle cell. For the first patient set to receive Lyfgenia, at least, treatment is being covered by his insurer, according to the Times.

Both companies are exploring “outcomes-based” contracts that link payment to treatment success, while the federal government is working to coordinate Medicaid coverage across state lines.

Other hurdles stand in the way. Manufacturing of both Lyfgenia and Casgevy is cumbersome and the treatment process lengthy. Patients must have undergone cell collection, possibly several times, and then receive “preconditioning” chemotherapy that’s designed to help the engineered stem cells properly engraft after they’re infused. This treatment carries the risk of infertility, which could give some patients pause.

Administration isn’t easy for hospitals, either, which need to set up comprehensive care teams and other services. Children’s National is one of more than 60 centers certified to administer Lyfgenia, Bluebird said.