A Study of AAV2-hAQP1 Gene Therapy in Participants With Radiation-Induced Late Xerostomia

Inclusion Criteria: * Completed beam radiation therapy for head and neck cancer at least 3 years prior to the first screening visit * No history of recurrent head and neck cancer, parotid gland cancer, or a second primary cancer, except for treated basal cell or squamous cell carcinoma of the skin or in situ cervical carcinoma * An unstimulated whole saliva flow rate (mL/min) \>0 (i.e., at least one drop of saliva in the collection tube) * A stimulated whole saliva flow rate (mL/min) within a specified range after mechanical stimulation by chewing * Average screening XQ Total Score at or above a specified threshold * No evidence of head and neck cancer, defined as a negative otolaryngology exam and a negative computed tomography (CT) scan of the head, neck, and chest with contrast. If a participant has had a magnetic resonance imaging (MRI) study, CT scan, positron emission tomography (PET), or fluorodeoxyglucose-positron emission tomography (FDG-PET) scan of the head, neck, and chest within 6 months of signing the informed consent form (and at least 3 years after the completion of radiotherapy), then that scan may be used for eligibility determination and a CT scan at screening will not be required. If the CT of the neck captures images from the forehead down to the neck, no CT of the head is required. * Either received treatment with one or more prescription sialagogues and elected to discontinue therapy or, in consultation with their physician, elected not to initiate such treatment * Participants taking a prescription sialagogue (specifically, pilocarpine or cevimeline) must stop that medication at least 2 weeks prior to Screening and be willing to refrain from taking such medications for the duration of the study * Participants who require medication for an underlying medical condition that is known to affect salivary output must be on stable doses of such medications for at least one month prior to the first screening visit Exclusion Criteria: * History of recurrent head and neck cancer, parotid gland cancer, or a second primary cancer, except for treated basal cell or squamous cell carcinoma of the skin or in situ cervical carcinoma * History of systemic autoimmune disease affecting the salivary glands (e.g., Sjogren's disease) * Currently using systemic immunosuppressive medication(s) (e.g., corticosteroids or biologics) or treated with one within 4 weeks of the first screening visit. Note: Topical, inhaled, or intranasal corticosteroids are permitted. * Active viral infection with Epstein-Barr virus (EBV), defined as a positive anti-VCA IgM. In the event a potential participant has a positive anti-VCA IgM, they may be rescreened 2-4 months later at which time a positive Epstein-Barr Virus Nuclear Antigen (EBNA) will be considered as evidence of resolved EBV infection. * Evidence of active Hepatitis C virus (HCV) infection * Evidence of human immunodeficiency virus (HIV) infection * Diagnosis of myasthenia gravis * Personal or family history of acute or chronic angle-closure glaucoma (ACG), or at increased risk of developing ACG, or had prophylactic treatment to reduce the risk of developing ACG * Known allergy or hypersensitivity to glycopyrrolate * Current smokers or history of smoking within the preceding 3 years (includes vaping with tobacco additives) * Current alcohol misuse or a history of the same within the preceding 3 years, as defined by local guidance. In North America, an average intake for men of more than 14 drinks per week, and for women more than 7 drinks per week, consistent with the US National Institute of Alcohol Abuse and Alcoholism. In the UK, an average intake of more than 14 units per week for both men and women, consistent with the UK Chief Medical Officers' Low Risk Drinking Guidelines. * Poorly controlled diabetes (hemoglobin A1c \>7%)