Skysona (elivaldogene autotemcel)

The only gene therapy approved for cerebral ALD. Since August 2025 it is meant for boys who lack an HLA-matched stem cell donor; a donor stem cell transplant is the standard of care, and no trial has compared the 2 head to head.

Cerebral ALD is caused by changes in the ABCD1 gene, which leave the body without working ALD protein (ALDP). Without it, very long chain fatty acids (VLCFAs) build up and can set off inflammation that destroys the brain's white matter. To make Skysona, doctors collect the boy's blood-forming stem cells, and a lab adds working copies of ABCD1 using a lentiviral vector called Lenti-D. After chemotherapy clears the bone marrow, the modified cells are infused back, settle in the marrow and produce blood cells, including monocytes that make working ALDP. The label says this is believed to help break down VLCFAs and slow or possibly prevent further inflammation and loss of myelin, the insulating coating on nerve fibers. Because the vector inserts itself into the cells' DNA, including into a cancer-related gene called MECOM, the same step that makes the therapy work appears to have caused the blood cancers seen in some patients^[1].

Skysona carries a boxed warning for blood cancer. Life-threatening myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) have occurred, diagnosed from 14 months to 10 years after treatment, and the label says the cancers appear to be caused by Skysona^[1]. The label updated in August 2025 reports blood cancers in 10 of 67 trial patients (15%), up from 3 of 67 (4%) at approval. Of those 10, 9 received a donor stem cell transplant, 1 had MDS come back after transplant, and 1 death related to cancer treatment had occurred. Some boys developed cancer before the therapy had time to help their CALD^[5]. Other warnings cover serious and sometimes fatal infections (severe in 21% of patients), low blood counts that can last more than a year, slow platelet recovery with a higher bleeding risk, possible failure of the new cells to take hold (engraft), and allergic reactions to the DMSO preservative. The studies had no placebo group, and many side effects come from the chemotherapy. From the start of chemotherapy through 24 months, the most common were painful mouth and gut sores called mucositis (92%), nausea (84%), vomiting (76%), fever with low white cells (73%), hair loss (72%), decreased appetite (64%), abdominal pain (45%), constipation (42%), fever (36%), headache (28%), diarrhea (28%) and rash (21%). Serious side effects occurred in 54% of patients. Treated patients can test falsely positive on PCR tests for HIV^[1].

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Approved for boys 4 to 17 years old with early, active CALD, meaning no or mild symptoms (neurologic function score of 1 or less), gadolinium enhancement on brain MRI and Loes scores of 0.5 to 9, who do not have an available HLA-matched donor for a stem cell transplant. It does not treat or prevent adrenal insufficiency. The only study patient with a full deletion of the ABCD1 gene lost the benefit, possibly because of an immune response, and it has not been studied in CALD caused by head trauma or in children under 4. Because of the cancer risk and uncertain long-term durability, the label urges careful thought about timing, especially for boys with isolated pyramidal tract disease, whose symptoms usually do not start until adulthood. A negative HIV test is required before cells are collected.

Source: Genetix CARES patient support

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The FDA based approval on 2 single-arm studies with no placebo group, ALD-102 (NCT01896102, 32 boys) and ALD-104 (NCT03852498, 35 boys), in boys with early, active CALD, meaning Loes MRI scores of 0.5 to 9, gadolinium enhancement on MRI and a neurologic function score of 1 or less. Results were compared with untreated boys from a natural history study. In the label's analysis of boys who had or developed symptoms, an estimated 72% of 11 treated boys were alive without a major functional disability 24 months after symptoms began, against 43% of 7 untreated boys. Major functional disabilities include loss of communication, cortical blindness, tube feeding, total incontinence, wheelchair dependence and complete loss of voluntary movement. There were too few data to compare how well Skysona works against a donor stem cell transplant, although survival in the first 9 months was better than after a transplant from a mismatched donor, and no treated boy developed significant graft versus host disease^[1]. In ALD-102, none of the 29 boys who completed 24 months had a major functional disability, and at a median follow-up of 6 years, 26 of 32 (81%) were free of such disabilities^[7]. Patients are followed in the long-term study LTF-304 (NCT02698579)^[14].

The therapy was developed by bluebird bio under the name Lenti-D, or eli-cel^[12]. It received orphan drug designation on April 19, 2012, rare pediatric disease designation on August 9, 2017 and breakthrough therapy designation on May 21, 2018. An FDA advisory committee met on June 9, 2022, and the FDA granted accelerated approval on September 16, 2022 with a rare pediatric disease priority review voucher^[6][2]. The label was updated with more blood cancer information on April 5, 2024^[3]. After announcing an investigation into additional blood cancer reports in November 2024, the FDA required label changes, approved on August 7, 2025, that strengthened the boxed warning and limited use to boys without an available HLA-matched donor^[5][4]. To keep the approval, the company must follow ALD-102 and ALD-104 patients for at least 10 years and study at least 24 newly treated boys with more advanced early disease for at least 5 years^[2]. After a sale to new private owners announced in June 2025, bluebird bio renamed itself Genetix Biotherapeutics on September 18, 2025^[9].