All patients remain off oral cysteamine up to 36 months post gene therapy

Sustained engraftment and durable reduction in leukocyte cystine levels across all patients

Received positive regulatory feedback from US and UK agencies

CAMBRIDGE, MA, USA I May 18, 2023 IAVROBIO, Inc. (Nasdaq: AVRO), a leading clinical-stage gene therapy company working to free people from a lifetime of genetic disease, today announced follow-up data demonstrating a durable treatment effect across key measures out to 36 months from a collaborator-sponsored Phase 1/2 clinical trial1 evaluating an investigational gene therapy for the treatment of cystinosis. These data are being presented at the 26th Annual Meeting of the American Society of Gene and Cell Therapy (ASGCT) in Los Angeles, California, on May 18, 2023.

Cystinosis is a rare, progressive disease with a high treatment burden and unmet need. The fully enrolled Phase 1/2 clinical trial is monitoring long-term safety and efficacy in six adult patients affected by the most severe and common form of cystinosis who previously had been treated with the standard of care (SOC), cysteamine. The patients’ own hematopoietic stem cells (HSCs) were genetically modified to express a functional version of cystinosin, the protein that is deficient in people living with cystinosis. Preliminary data suggest that post-gene therapy, functional cystinosin is produced throughout the body as evidenced by clinical measures in multiple tissues, including the eyes, skin and gastrointestinal mucosa, as well as by neurocognitive tests suggestive of activity in the central nervous system. No adverse events (AEs) related to the drug product or serious adverse events have been reported to date.

“These data show that genetically modifying a patient’s own HSCs has the potential to restore functional cystinosin and systemically reduce the accumulation of cystine, laying the foundation for a registration-enabling clinical trial,” said AVROBIO Chief Medical Officer Essra Ridha, M.D., MRCP, FFPM. “We are excited about moving this investigational gene therapy closer to patients.”

In addition to the data presented, the Company also announced positive and productive meetings with the U.K. Medicines and Healthcare products Regulatory Agency (MHRA) and U.S. Food and Drug Administration (FDA) designed to align on regulatory paths and obtain feedback on this program.

Data show investigational HSC gene therapy durably and systemically impacts neurocognitive measures and reduces cystine levels in the blood, and crystal accumulation in the skin and gastrointestinal mucosa

Follow-up data suggest that after receiving HSC gene therapy, patients can produce functional cystinosin protein throughout the body. As a result, leukocyte cystine levels in the blood have decreased below baseline in all six patients, and stabilized up to 36 months out from treatment. Skin and gastrointestinal mucosa biopsies reveal a decline in tissue cystine crystals below baseline in the first four patients, who have been observed for at least 12 months, with two patients observed up to 24 months.

Patients with cystinosis typically do not see an improvement in visual spatial or visual motor function over time in standardized tests evaluating the ability of the brain to interpret and translate visual information into an exact motor response. The first four patients treated with gene therapy have shown an improvement or stabilization of scores on the Beery – Buktenica Developmental Test of visual motor integration, up to 36 months out, suggesting a potential impact on the neuropathology of the disease.

These data represent an extension of trends that have previously been measured, confirming the durability of the treatment effect up to 36 months.

Safety and tolerability profile remains strong

Preliminary data from this trial suggest that this HSC gene therapy is well tolerated, with no AEs related to the drug product to date. All AEs were related to myeloablative conditioning, stem cell mobilization, the underlying disease, co-morbid or pre-existing conditions. The majority of AEs were mild or moderate and resolved without clinical sequelae.

An oral presentation by Dr. Cherqui on these data, “Phase 1/2 Clinical Trial of Autologous Hematopoietic Stem and Progenitor Cell Gene Therapy for Cystinosis,” will occur today at 3:45 PM PT in the session Metabolic, Storage, Endocrine, Liver and Gastrointestinal Disease II of the ASGCT Annual Meeting. Further details on the Phase 1/2 trial (NCT03897361) are available on

About cystinosis

Cystinosis is a rare, progressive disease marked by the accumulation of cystine in cellular organelles known as lysosomes. This buildup causes progressive organ damage and debilitating corneal damage, swallowing dysfunction, chronic kidney disease leading to end-stage renal disease and muscle wasting leading to a shortened lifespan. Currently, more than 90% of treated cystinosis patients require a renal transplant in the second or third decade of life. The current standard of care for cystinosis is cysteamine, a treatment regimen that can require dozens of pills per day, does not prevent overall disease progression and carries side effects, such as breath and body odor and gastrointestinal complications, which may be difficult to tolerate.


Our vision is to bring personalized gene therapy to the world. We target the root cause of genetic disease by introducing a functional copy of the affected gene into patients’ own hematopoietic stem cells (HSCs), with the goal of durably expressing the therapeutic protein throughout the body, including the central nervous system. Our first-in-class pipeline includes clinical programs for Gaucher disease, cystinosis and Hunter syndrome, as well as a preclinical program for Pompe disease. Our proprietary plato® gene therapy platform is scalable for planned global commercialization. We are headquartered in Cambridge, Mass. For additional information, visit, and follow us on Twitter and LinkedIn.

1The collaborator-sponsored Phase 1/2 clinical trial for cystinosis is funded in part by grants to UCSD from the California Institute for Regenerative Medicine (CIRM), Cystinosis Research Foundation (CRF) and National Institutes of Health (NIH).