This is a single group Phase 1/Phase 2, 1-arm, open-label study with SAR444836, an adeno-associated virus (AAV) vector-mediated gene transfer of human phenylalanine hydroxylase (PAH), for the treatment of adult participants with phenylketonuria (PKU) on a chronic, stable diet. The purpose of the study is to evaluate the safety and efficacy of SAR444836 in reducing phenylalanine (Phe) levels and in the elimination of a Phe restricted diet.

Participants will receive a one-time intravenous (IV) administration of SAR444836.

The study is constituted of 2 separate parts: a dose escalation part, and a dose expansion part where subsequent participants will be administered a safe and effective dose level identified during the dose escalation part. In both study parts, clinical and laboratory assessments will be collected to: a) assess the incidence of adverse events, and b) evaluate the effect of SAR444836 on reductions in blood Phe levels and maintenance of these Phe levels after elimination of a Phe restricted diet.

The study duration will be for a minimum duration of 5 years following SAR444836 administration, for each participant and includes a 6-week screening phase, a 96-week treatment follow-up period after SAR444836 administration, followed by an additional 3 years of long-term safety (and efficacy) monitoring.

There will be a total of 47 study visits. Many study visits may occur as remote visits and be performed by a qualified in-home service provider.

Actual study duration for an individual participant may be longer than 5 years due to the administration of SAR444836 to participants in Stage 1A in a serial fashion, the duration of the screening period, and/or other factors such as delays in scheduling study visits.

Inclusion Criteria:

• Adult males, and females of non-childbearing potential, 18-65 years of age at the time of informed consent.
• Participants must have uncontrolled classical PKU due to PAH deficiency (despite Phe-restricted dietary management or Palynziq) in the judgement of the Investigator.
• Two historical plasma Phe values ≥ 600 μmol/L in the preceding 12 months while on Phe restricted diet therapy. Two plasma Phe values ≥ 600 μmol/L drawn at least 72 hours apart during the screening period while on Phe restricted diet therapy in the absence of an acute illness.
• Participant has the ability and willingness to maintain their present diet for the duration of the Post-treatment Follow-up Phase (through Week 96), unless otherwise directed as per protocol
• Body mass index (BMI) ≤ 35 kg/m2
• Willingness to use effective methods of contraception.
• Capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol.

Exclusion Criteria:

• Presence of neutralizing antibodies against the AAV SNY001 capsid

• Abnormal liver function laboratory testing evidenced by alanine aminotransferase (ALT)>1.5X upper limit normal (ULN), aspartate transaminase (AST)>1.5X ULN, alkaline phosphatase >1.5X ULN, Total and direct bilirubin >1.5X ULN (bilirubin levels above the laboratory's normal range are acceptable in individuals with a documented history or laboratory evidence of Gilbert's Disease)

• Any significant underlying liver disease or any of the following documented diagnoses, indicative of significant underlying liver disease:

  • Portal hypertension; or
  • Splenomegaly; or
  • Hepatic encephalopathy

• Serum albumin measurement below the lower limit of normal of the laboratory OR AST-to-Platelet Ratio Index > 1.0

• Serum creatinine >1.5X ULN

• Hemoglobin A1c >6.5% or fasting glucose >126 mg/dL

• Screening laboratory testing demonstrating any of the following:

  • HIV; or
  • active or prior hepatitis B virus (HBV) infection defined as positive test for hepatitis B surface antigen (HBsAg) or positive test for hepatitis B core antibody (total HBcAb) or detectable HBV DNA; or
  • active hepatitis C virus (HCV) infection defined as positive test for hepatitis C antibody followed by detectable HCV RNA or if a participant is presently receiving (or has received within 6 months prior to screening) anti-viral therapy for hepatitis C

• Clinically significant, active bacterial, viral, fungal, or parasitic infection (based on Investigator's judgement)

The above information is not intended to contain all considerations relevant to a potential participation in a clinical trial.

Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org