Adeno-Associated Virus Vector-Mediated Liver Gene Therapy for Crigler-Najjar Syndrome

Project Information

CureCN

Grant agreement ID: 755225

DOI

10.3030/755225

Project closed

EC signature date 5 December 2017

Start date 1 January 2018

End date 31 December 2023

Funded under

• SOCIETAL CHALLENGES - Health, demographic change and well-being

Total cost

€ 6 249 103,75

EU contribution

€ 6 249 103,75

Coordinated by

ASSOCIATION GENETHON
France

Periodic Reporting for period 4 - CureCN (Adeno-Associated Virus Vector-Mediated Liver Gene Therapy for Crigler-Najjar Syndrome)

Reporting period: 2022-07-01 to 2023-12-31

Summary of the context and overall objectives of the project

The CureCN project, that ended on December 31st, 2023, aimed at the development of a curative gene therapy against the ultra-rare Crigler-Najjar syndrome (CN). CN is a life-threatening liver disease which affects one in a million individuals at birth caused by the deficiency of a liver-specific enzyme (uridine diphosphate Glucuronosyltransferase 1A1) that leads to the accumulation of toxic unconjugated bilirubin in all body tissues. Untreated, CN causes irreversible neurological damage in the brain and leads to death. The only curative treatment currently available is liver transplantation that implies high risks of complications.
Phototherapy – a treatment with blue light – reduces bilirubin levels, but it is very burdensome as it requires up to 14-hour therapy per day, loses efficacy over time and does not eliminate the risk of life-threatening spikes of bilirubin. CN patients depend upon a liver transplant in the long term as it represents the only curative treatment available. On the other hand, transplanted patients live under continue immunosuppression and are exposed to the risk of developing tumors, in particular melanoma. The lack of a curative treatment for CN results in a shortened life expectancy of the affected patients. The overall goal of the CureCN consortium was to prove the safety and efficacy of an adeno-associated virus (AAV) gene therapy in a clinical trial and make it available to patients.
The project’s main objectives were to:
-Develop a curative AAV gene therapy and validate a technology transposable to many other inherited liver-related disorders
-Prove the safety and efficacy of the vector-mediated gene transfer with AAV in a clinical trial
-Provide a treatment suitable for young CN patients as well as for older patients with a pre-existing immunity to AAV
-Identify a clinically ready method to eradicate pre-existing immunity to AAV
-Accelerate the orphan drug development towards marketing authorization
-Establish the first global CN patient registry to provide better information for patients, families, healthcare providers and the general public about CN syndrome and existing treatments.
At the end of the CureCN project, the clinical trial is in its pivotal phase, and first pediatric patients were dosed.A world CN registry of patients was created, data were collected all along the project from a pool of more than 200 patients and is still actively used by physicians all over the world, with the help of CN patients associations to make this registry known to patients. Some major pre-clinical work was also performed to determine the safety and efficacy of gene transfer in neonate and juvenile animals, to support the clinical study in pediatric patients. CureCN also aimed at addressing fundamental limiting issues associated pre-existing immunity to AAV. To this aim, some work was performed during the CureCN program to develop novel technologies for the modulation of antibody responses directed against AAV vectors through removal of pre-existing antibodies to AAV from the bloodstream.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the 4th and last period of the project, the CureCN partners have taken significant additional steps toward the realization of the objectives.These steps consisted in pursuing the manufacturing of GMP lots of AAV8-hUGT1A1 vector used to treat the participants of the clinical trial. Safety results from patients of the first two cohorts were very positive. With the second dose of the escalation phase of the clinical study, positive results in terms of efficacy were also obtained: patients had a reduction in total bilirubin levels in blood and were able to stop phototherapy 16 weeks after treatment. The DSMB validated the decision to move forward with the pivotal phase of the study. It was also accepted to amend the clinical protocol in order to allow sirolimus treatment in pediatric patients. Cohort 3 has started: 5 patients were dosed. A world registry of CN patients was created and consists in a GCP-compliant, web-based platform in which the privacy of patients is secured, and the intellectual property of the contributing centers is protected. Data were collected all along the project from a pool of more than 200 patients; a first analysis revealed the lethality of the disease when availability of the treatment is limited. In addition, a questionnaire on the Quality of life was proposed to CN patients. The analysis of this questionnaire demonstrated a negative impact of CN syndrome and phototherapy on the quality of life of CN patients.
Preclinical work went on, to carefully determine the safety and efficacy of gene transfer in neonate and juvenile animals. In order to determine the optimal age of the recipient and the optimal dose of vector to achieve stable gene transfer in neonatal and juvenile Ugt1-/- mice and rats, a set of genes that could be used as proliferation markers and help discriminate between growing and adult livers was identified.The expression profile of these genes has been comparatively evaluated in mice and humans at different ages for validation. Integration studies did not reveal genotoxicity. CureCN also aimed at addressing fundamental limiting issues associated to the AAV vector technology. Development of persisting, high-titer anti-AAV neutralizing antibodies (Nabs) after vector infusion prevents vector re-administration. The absence of a method to control the formation of anti-AAV Nab precludes enrolment of very young children in the trial. In this population vector genome dilution occurs due to liver proliferation and therapeutic efficacy is not expected in the long term.
To this aim, preclinical work was performed to assess the safety and efficacy of the combination of immunosuppression with the investigational drug was continued in preclinical models of CN syndrome. The results showed that a single injection of ImmTOR nanoparticles (also called SVP[Rapa]) at the time of vector administration blocked the induction of neutralizing antibodies (Nabs) and allowed re-administration of the vector.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

One of the main limitations of all gene therapies based on AAV vectors aimed at treating paediatric indications is the persistence of the transgene expression. Vector re-administration is currently not feasible, due to the formation of Nabs for the AAV vectors. Promising results in CureCN projects were obtained to overcome this limitation by implementing new disruptive technologies, with the potential to revolutionize the entire field of AAV gene therapy by changing the treatment modality from “once in life” to “on demand based on therapeutic need”.
Pre-existing immunity to AAV is a major limitation to a wider application of AAV gene transfer in humans, as it prevents up to 60% of patients from receiving AAV vector administration.During the CureCN program, a new approach was envisaged and, if successful, can be broadly implemented in other gene therapy trials to treat eligible patients, regardless of their serology status.
After 5 years, the clinical trial has made progress toward a curative treatment for all CN patients, including very young children, will change dramatically the way the disease is managed. An effective treatment will prevent irreversible brain damage caused by bilirubin spikes during trauma / illness occurring during childhood and adolescence in CN patients treated with phototherapy. Thanks to the CureCN European program, we are getting closer to make available such treatment to CN patients.

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