Safety and Proof-of-Concept (POC) Study With AMT-130 in Adults With Early Manifest Huntington's Disease

Prior treatment

• Receipt of an experimental agent within 60 days or five half-lives prior to Screening or anytime over the duration of this study.
• Participation in an investigational trial or investigational paradigm (such as exercise/physical activity, cognitive therapy, brain stimulation) within 60 days prior to Screening or anytime over the duration of this study.
• Any history of gene therapy, RNA or DNA targeted HD specific investigational agents, such as antisense oligonucleotides (ASOs), cell transplantation or any other experimental brain surgery.
• Hospitalization for any major medical or surgical procedure involving general anesthesia within 12 weeks of Screening or planned during the study
• Known or suspected intolerance or hypersensitivity to the investigational product(s), closely-related compounds, or any of the stated ingredients

Other illness

• Brain and spinal pathology that may interfere with the surgical delivery of AMT-130 or represents a significant neurologic comorbid disorder
• Malignancy within 5 years of Screening, except for basal or squamous cell carcinoma of the skin or carcinoma in situ of the cervix that has been successfully treated
• Any known allergy to gadoteridol (ProHance)
• Known allergy, sensitivity, or other contraindication to medications in the immunosuppression regimen in this protocol.
• Any participant with an active infection (e.g., coronavirus disease 2019 \[COVID-19\]) at Screening or at the time of treatment that requires medical intervention. Participants may rescreen, or if screened eligible and an open surgical slot is available, may receive treatment after recovery.

Lab values

• Current or recurrent disease, (including pre-existing cardiovascular or pulmonary conditions) infection, or other significant concurrent medical condition or medications that could confound clinical and laboratory evaluations or could affect a participant's safety or their ability to undergo the neurosurgical procedure or comply with the procedures and study visit schedule
• Screening laboratory values (as measured by the central laboratory): a. Alanine aminotransferase (ALT) \>2 × upper limit of normal (ULN) b. Aspartate aminotransferase (AST) \>2 × ULN c. Total bilirubin \>2 × ULN d. Alkaline phosphatase (ALP) \>2 × ULN e. Creatinine \>1.5 × ULN f. Platelet count \<100,000/mm3g.Prothrombin time (PT) \>1.2 × ULN h. Partial thromboplastin time (PTT) \>1.2 × ULN

Other

• Evidence of suicide risk
• Presence of an implanted deep brain stimulation device, ventriculoperitoneal or other CSF shunt, or other implanted catheter
• Any contraindication to 3.0 Tesla MRI as per local guidelines
• Any contraindication to lumbar puncture as per local guidelines
• Cohort 4 ONLY: Inability to establish a safe trajectory to administer AMT-130 to the target structures, as assessed by neuroimaging.

• Able and willing to provide written informed consent prior to the study and study-related procedure
• Participants 25 to 65 years of age of both sexes
• Cohorts 1, 2, \& 4: Early manifest HD as defined by a UHDRS total functional capacity (TFC) score of 9 to 13 and EITHER a diagnostic confidence level (DCL) of 4 OR a DCL of 3 if the subject either meets the definition of multidimensional manifest HD (UHDRS question 80) or has cognitive symptoms
• Cohort 3: Early manifest HD as defined by a UHDRS TFC score of ≥ 11 and EITHER a DCL of 4 or a DCL of 3 with either a positive "Yes" response to UHDRS Question 80 (multidimensional manifest diagnosis on motor, cognitive, behavioral, functional) or DSM5 criteria for cognitive disorder (Movement Disorder Society Task Force criteria).
• HTT gene expansion testing with the presence of ≥40 CAG repeats
• Striatal MRI volume requirements per hemisphere:
• Cohorts 1, 2, \& 3: Putamen ≥2.5 cm\^3 (per side); Caudate ≥2.0 cm\^3 (per side)
• Cohort 4: Putamen \<2.5 cm\^3 (on either side); Caudate \<2.0 cm\^3 (on either side)
• All HD concomitant medications (addressing motor, behavioral, and cognitive symptoms) must be stable for 3 months prior to Screening with no change in clinical symptoms requiring change in medication prior to anticipated administration procedure
• Able and willing to comply with all procedures and the study visit schedule as outlined in the protocol
• All female participants of childbearing potential (FOCP) must have a negative serum pregnancy test at Screening, (and Visit 1A, as appropriate), a negative pregnancy urine dipstick at Baseline, and not be breastfeeding. All FOCPs and sexually mature males must be compliant with a highly effective birth control method.