Lentiviral Hematopoietic Stem Cell Gene Therapy in Inherited Immune and Lysosomal Enzyme Deficiencies

Abstract

Rare diseases affect millions of people worldwide. Many of those are inherited disorders resulting in chronic disability and requiring cost-intensive care. Hematopoietic stem cell gene therapy has been developed over more than 20 years. At the state of the art, gene therapy is within reach for diseases in which (i) the genetic defect is identified, (ii) the diagnosis is made sufficiently early for a meaningful therapeutic intervention, (iii) a specific animal model is available for efficacy and safety evaluation. Appropriate therapeutic transgenes should also comply with certain biological criteria. Third-generation lentiviral vectors have been made self-inactivating (SIN) by deletion of enhancer regions from the LTR sequences thus reducing the risk of influencing nearby genes, resulting in favorable safety profiles. At the present time, lentiviral hematopoietic stem cell gene therapy has entered the stage of initial clinical implementation for immune deficiencies and lysosomal storage disorders. We discuss initial clinical trials using these vectors for selected metabolic storage disorders, which include adrenoleukodystrophy, metachromatic leukodystrophy, Hurler (MPS I), Pompe (GSD II), and Fabry diseases. This brief review summarizes the development and current clinical implementation of these approaches.