Safety and Tolerability Study of ST-503 for Refractory Pain Due to Peripheral Neuropathy (Small Fiber Predominant, SFN)

Inclusion Criteria

• Diagnostic characterization of Small Fiber Neuropathy (SFN) according to the Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities and Networks (ACTTION) criteria.
• Medical record documentation that pain is refractory to 2 of 3 categories of first line medical therapy for at ≥ 6 months prior to screening.
• Serum sample negative for pre-existing anti-AAV9 antibodies determined by assay detection limit

Exclusion Criteria

• Drug- and alcohol-related:

• Persons using opioid analgesics for under 3 months or persons who are not on a stable dose of opioids; if on a stable dose, the dose may decrease over the course of the study but should not be increased.
• History of known alcohol abuse, opioid analgesic abuse, or illicit drug abuse within 2 years of Screening.
• Positive urine test for drugs of abuse (including opiates, benzodiazepines, amphetamines, cocaine, barbiturates, and phencyclidine) without prescription and investigator approval, at Screening and Day -1.
• Use of cannabinoids is not permitted.
• Persons with Fabry's disease, with erythromelalgia, with peripheral neuropathies due to alcohol or drug toxicity, or with diagnosed channelopathies
• Procedure-related:

• Contraindications to LP, general anesthesia or sedation
• Any medical disorders that, in the opinion of the Investigator, could interfere with LP including but not limited to evidence for a pressure gradient between supratentorial and infratentorial compartments, Arnold-Chiari malformation, bleeding diathesis, clinically significant coagulopathy, thrombocytopenia, increased intracranial pressure, or spine disease or past surgical procedures involving the spine
• Infectious disease-related:

• Active viral infection or bacterial
• A severe infection (e.g., pneumonia, septicemia, central nervous system infections [e.g., meningitis, encephalitis]) within 12 weeks prior to Screening
• Hepatic disease- and hepatotoxic medication-related:

• Presence of clinically relevant liver disease
• Hepatic dysfunction as indicated by one or more of the following: i. Albumin ≤ 3.5 g/dL ii. Total bilirubin > 1.5 x ULN and direct bilirubin ≥0.5 mg/dL iii. Alkaline phosphatase (ALP) > 2 x ULN iv. Alanine transaminase (ALT) or aspartate transaminase (AST) > 1.5 x ULN
• Hepatotoxic medications should be avoided during the study period including acetaminophen exceeding 4 gm/day unless essential to patient's treatment, approved by investigator, and hepatic dysfunction is not identified
• Hepatotoxic supplement use during the study period
• Cancer-related:

a. History of cancer, including B-cell cancers, within 5 years of Screening

i. Exceptions to this exclusion are fully excised non-melanoma skin cancers, non-metastatic prostate cancer, and fully treated ductal carcinoma in situ of the breast, provided subject has been stable for at least 6 months

b. Previous autologous or allogeneic bone marrow transplant, peripheral stem cell transplant or solid organ transplantation

• Previously received gene or cellular therapy