Safer Lentiviral Gene Therapy for Cerebral Adrenoleukodystrophy Using an Endogenous ABCD1 Promoter

Overview

Cerebral adrenoleukodystrophy (ALD) is a devastating neurological disease caused by mutations in the ABCD1 gene, leading to accumulation of very long chain fatty acids and progressive brain demyelination. While a recently FDA-licensed lentiviral gene therapy has demonstrated clinical benefit, post-treatment data have raised safety concerns: a notable fraction of treated patients developed myelodysplasia requiring allogeneic transplantation, likely linked to the viral promoter used to drive ABCD1 expression. This offering presents a next-generation lentiviral vector system designed to improve both safety and therapeutic efficacy for cerebral ALD patients.

The solution centers on two key innovations: replacing the current vector's myeloproliferative sarcoma virus (MPSV) promoter with the endogenous human ABCD1 promoter to reduce insertional oncogenesis risk, and incorporating a human cell surface marker (such as tNGFR, tEGFR, or CD19) onto transduced hematopoietic stem cells to enable positive selection using Miltenyi magnetic bead technology. Together, these modifications aim to deliver a gene therapy that is both safer and more effective than current standards of care.

Technical specifications

Key features:

• Endogenous promoter system: A lentiviral vector utilizing the human ABCD1 promoter, cloned and characterized by the research team, to drive physiologically regulated expression of the therapeutic gene
• Surface-marker selection: Incorporation of human cell surface antigens (tNGFR, tEGFR, or CD19) on transduced CD34+ hematopoietic stem cells, enabling magnetic bead-based positive selection via Miltenyi technology
• Dual safety mechanism: The tEGFR and CD19 markers also enable negative selection in vivo using cetuximab (anti-EGFR antibody) or blinatumomab (CD19/CD3 bispecific antibody) for targeted elimination of transduced cells if needed
• Ex vivo stem cell expansion: Leverages prior clinical trial experience with hematopoietic stem cell expansion to improve engraftment and therapeutic outcomes
• Validated preclinical models: An NSG ALD (ABCD1-negative) mouse model with human cord blood transplantation at 450 cGy, assessed via flow cytometry for brain engraftment and C26 lysoPC assays for very long chain fatty acid reduction in plasma and brain

Technology readiness level

The vector constructs are currently in preclinical development. Initial experiments comparing the endogenous human ABCD1 promoter to the MPSV promoter in human endothelial cells have shown comparable expression levels, supporting feasibility. An NSG ALD mouse model has been established with active engraftment and biomarker assays, and transplantation experiments using human cord blood are underway. Future validation will involve direct head-to-head comparison of the novel vector constructs with selection markers in vitro and in vivo, building on the team's prior clinical experience with tNGFR-based selection. The program is positioned to advance toward clinical trial design pending further preclinical confirmation of safety and efficacy.