RP-A501 (AAV9.LAMP2B)

RP-A501 is an investigational gene therapy developed by Rocket Pharmaceuticals. It consists of a recombinant adeno-associated virus serotype 9 (AAV9) capsid containing a full-length human LAMP2B transgene and is given as a single intravenous infusion. It is not approved in the United States or authorized in the European Union, and no regulatory submission was found. In the United States it holds orphan drug designation (February 1, 2019), Fast Track designation (February 2019), regenerative medicine advanced therapy designation (announced February 7, 2023), and rare pediatric disease designation; in the European Union it holds PRIME designation (announced May 31, 2023) and orphan designation (August 16, 2023). The FDA placed the phase 1 trial on clinical hold in May 2021, with the lifting of that hold announced on August 16, 2021, and placed the phase 2 trial on clinical hold on May 23, 2025, lifting it in August 2025. As of October 2026, the company expects to complete dosing in the pivotal cohort by mid-2027, to report topline results in mid-2028, and to file a biologics license application in late 2028, and its presentation marks launch in mid-2029. Nine of the 12 participants of the pivotal cohort remained to be enrolled and treated, and the company describes the mid-2028 target as provisional. The application is intended to support accelerated approval, with success defined as at least 7 of 12 participants meeting both co-primary criteria at 12 months. The company states that meeting this criterion “would not, by itself, establish that RP-A501 will receive regulatory approval”, and its Form 10-K states that the FDA may require confirmatory clinical trials as a condition of accelerated approval.

The evidence comes from two open-label trials in males that have no control arm. In phase 1, 5 participants received 6.7 × 10¹³ GC/kg and 2 received 1.1 × 10¹⁴ GC/kg, efficacy is reported for 6 of the 7, and median follow-up is 5.7 years (range 4.3 to 7.1 years). At about 12 months, all 6 had myocardial LAMP2 protein expression of Grade 1 or higher and a decrease in left ventricular mass index of 10% or more (11% to 32%). At the most recent visit, the decrease was 10% or more in 4 of 6, cardiac troponin I had decreased by 31% to 99% and NT-proBNP by 31% to 90%, and 1 participant had Grade 0 LAMP2 staining at 30 and 36 months. In phase 2, 9 participants have been dosed and efficacy data cover 4, at 18 to 36 months: left ventricular mass index decreased by 10% or more in 3 and increased by 9% in 1, and no LAMP2 protein expression result has been reported. These are biopsy, imaging, and laboratory measures, and registry authors report that left ventricular hypertrophy in males “stabilizes before HF outcome”. The phase 1 publication covers 24 to 54 months; later phase 1 data and every phase 2 result are reported by the company alone. All efficacy data come from participants dosed at 6.7 × 10¹³ GC/kg or higher under immunomodulation regimens that differ from that of the pivotal cohort, which receives 3.8 × 10¹³ GC/kg. Three participants have received that dose, with about 3 months of safety follow-up and no efficacy result. The planned external comparator is a company-sponsored natural history study without reported results, and no document found states the method of comparison.

No randomized or concurrently controlled comparison of RP-A501 was found. Mixed-effects models of the International Danon Disease Registry give an increase in left ventricular mass in untreated males of 28.424 g per year of age in 20 participants without a heart failure outcome and 34.183 g per year in 13 with one. The company's October 2026 comparison cites unpublished data from the same registry: 39.86 ± 4.01 g per year in 22 untreated males, and an increase in BNP of 42.17 ± 18.46 pg/mL per year in 20, whereas an earlier registry abstract of 112 participants reported that BNP did not change over time. In the registry, a heart failure outcome occurred in 21 of 52 males (40.4%); in phase 1, 2 of 7 participants underwent heart transplantation, 5 months and 4.8 years after infusion. After heart transplantation, estimated 5-year graft survival was 87.1% (95% CI 63.6% to 95.9%) among 38 recipients, and in a European registry 5 of 8 male recipients of a transplant or assist device (62%) died within one year of the procedure. No direct or indirect comparison of RP-A501 with heart transplantation or with another gene therapy was found. No registered interventional trial of another product for Danon disease was found; an AAV2i8 vector carrying the LAMP2B transgene holds European orphan designation (May 22, 2025), and PPL-002, a gene-modified hematopoietic stem and progenitor cell therapy with preclinical data, holds FDA orphan drug designation. Approved single-dose intravenous AAV gene therapies for other diseases have labeled doses of 1.1 × 10¹⁴ vg/kg for Zolgensma and 3.0 × 10¹³ vg/kg for Fayuvi (both AAV9), 1.33 × 10¹⁴ vg/kg for Elevidys at 10 to 70 kg, and 2 × 10¹³ gc/kg for Hemgenix. The Zolgensma and Elevidys labels carry boxed warnings for serious liver injury and acute liver failure.

In phase 1, thrombotic microangiopathy occurred in 1 of 2 participants given 1.1 × 10¹⁴ GC/kg, as a grade 4 event managed with eculizumab and hemodialysis, and that dose was discontinued. In phase 2 at 6.7 × 10¹³ GC/kg it is listed in 2 of 4 participants (50.0%) in cohorts 1 and 2 and in 1 of 2 (50.0%) in cohort 3. Both participants of cohort 3, whose regimen contained the C3 inhibitor pegcetacoplan, had capillary leak syndrome with multi-organ damage, and 1 died on May 25, 2025, after bacteremia and sepsis; the investigation concluded that the events were likely the result of the combination of the C3 inhibitor and RP-A501. In phase 1, 3 of 7 participants had a grade 3 glucocorticoid-related exacerbation of skeletal myopathy. The modified protocol uses 3.8 × 10¹³ GC/kg with three doses of rituximab, sirolimus, and corticosteroids, without a prophylactic C3 inhibitor; in its first 3 participants, the company reports no thrombotic microangiopathy or capillary leak through 3 months and 1 Grade 3 increase in gamma-glutamyltransferase related to RP-A501 that resolved. Participants are hospitalized for infusion and monitoring, these 3 were discharged 1 to 2 weeks after infusion, immunosuppressive therapy is discontinued 2 to 3 months after infusion, and trial follow-up lasts 5 years. For class context, a random-effects meta-analysis of AAV gene therapy reported thrombotic microangiopathy in 4.7% and treatment-related death in 4.7%. The Zolgensma label states that thrombotic microangiopathy generally occurred within the first two weeks after infusion and calls for platelet counts at least weekly for the first month; the Elevidys label calls for weekly liver function monitoring for the first 3 months and proximity to a healthcare facility for at least 2 months. The rituximab, sirolimus, and eculizumab labels warn of fatal infections.

No approved therapy treats the cause of Danon disease; the 2023 international consensus statement states that there are “no available therapies to specifically treat Danon disease”. Heart transplantation was performed in 30 of 116 registry participants (25.9%), including 17 of 52 males (32.7%). Among the 38 recipients cited above, the median age at transplantation was 20.2 years, 2 died, and 2 underwent retransplantation. For a formulary decision, the following remain unknown: the price, for which no announcement, economic model, or health technology assessment was found (prices reported for two approved systemic AAV9 products, Zolgensma and Fayuvi, are $2.125 million and $3.95 million); the labeled population, given trial eligibility limited to males aged 8 years or older with an ejection fraction of 50% or more and an anti-AAV9 neutralizing antibody titer no higher than 1:40; the pivotal result, with 3 of 12 participants dosed; durability beyond a maximum follow-up of 7.1 years, given that a 2026 commentary describes the inability to re-dose after neutralizing antibody formation; the effect on extracardiac disease, which the consensus statement expects to be largely unaffected; the effect on survival or transplant-free survival, with event-free survival a secondary outcome followed to 60 months; outcomes in females and in children younger than 8 years, for whom no clinical data were found; and the number of eligible people, given prevalence estimates from 240 to 11,807 in one 2026 analysis, a company model of 10,000 to 11,000 people in the United States (about 4,000 male), more than 900 identified United States patients, and no source reporting how many meet the trial criteria.