No beneficial effects on biomarker or clinical efficacy endpoints

This is a multicenter, open-label study to assess the safety and tolerability of iluzanebart (also referred to as VGL101) in subjects with documentation of a gene mutation in the CSF1R gene for the treatment of adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) and to evaluate the effects of iluzanebart on imaging and biomarkers of disease progression in subjects with ALSP. Participants will receive infusions of iluzanebart approximately every 4 weeks for 1 year. The study includes a 52-week, open-label Core Study, followed by a Long-Term Extension (LTE), which provides subjects who complete the original 52-week study (Core Study) with the option to continue treatment for up to an additional 2 years.

Key Inclusion Criteria:

• Participants who have documentation of a gene mutation in the CSF1R gene

• Participants fulfill both (Parts A and B) of the following criteria:

  1. The participant has more than 2 findings of clinical signs or symptoms in the following categories:

     1. Cognitive impairment or psychiatric problem
     2. Pyramidal signs on neurological examination
     3. Extrapyramidal signs, such as rigidity.
     4. Epilepsy

  2. MRI findings consistent with ALSP, specifically, bilateral cerebral white matter lesions with or without thinning of the corpus callosum, on the Screening MRI.

• The participant must have a study partner (i.e., caregiver, family member, friend, etc.) who, in the investigator's judgment, has frequent and sufficient contact with the subject so as to be able to provide accurate information about the participant's health and cognitive and functional abilities. The study partner must be willing to sign a study partner ICF.

Key Exclusion Criteria:

• The participant has any neurological disease that poses a risk to the participant or can produce cognitive, motor, or behavioral impairment similar to ALSP, including, but not limited to, brain tumor, hydrocephalus, Alzheimer's disease, frontotemporal dementia (FTD), ALS, stroke, Huntington disease, multiple sclerosis, Parkinson's disease, and Down syndrome.
• Participant with any condition or situation that, in the opinion of the investigator or sponsor medical personnel, may place the subject at significant risk, confound the study results, or interfere significantly with the participant's participation in the study.