Preclinical Testing of the Safety and Tolerability of Lentiviral Vector–Mediated Above-Normal Alpha-L-Iduronidase Expression in Murine and Human Hematopoietic Cells Using Toxicology and Biodistribution Good Laboratory Practice Studies

Abstract

In order to support the clinical application of hematopoietic stem cell (HSC) gene therapy for mucopolysaccharidosis I (MPS I), biosafety studies were conducted to assess the toxicity and tumorigenic potential, as well as the biodistribution of HSCs and progenitor cells (HSPCs) transduced with lentiviral vectors (LV) encoding the cDNA of the alpha-iduronidase (IDUA) gene, which is mutated in MPS I patients. To this goal, toxicology and biodistribution studies were conducted, employing Good Laboratory Practice principles. Vector integration site (IS) studies were applied in order to predict adverse consequences of vector gene transfer and to obtain HSC-related information. Overall, the results obtained in these studies provided robust evidence to support the safety and tolerability of high-efficiency LV-mediated gene transfer and above-normal IDUA enzyme expression in both murine and human HSPCs and their in vivo progeny. Taken together, these investigations provide essential safety data to support clinical testing of HSC gene therapy in MPS I patients. These studies also underline criticisms associated with the use of currently available models, and highlight the value of surrogate markers of tumorigenicity that may be further explored in the future. Notably, biological evidence supporting the efficacy of gene therapy on MPS I disease and its feasibility on patients' HSCs were also generated, employing clinical-grade LVs. Finally, the clonal contribution of LV-transduced HSPCs to hematopoiesis along serial transplantation was quantified in a minimum of 200-300 clones, with the different level of repopulating cells in primary recipients being reflected in the secondary.

Lentiviral Hematopoietic Stem Cell Gene Therapy in Inherited Immune and Lysoso- mal Enzyme Deficiencies

“…Using a codon optimized IDUA gene driven by a cellular promoter in a lentiviral vector to transduce hematopoietic stem cells, we demonstrated long-term expression in the hematopoietic system resulting in full correction of the Hurler phenotype (unpublished) without any severe adverse effects. Similar results and a further safety analysis were obtained in a parallel study [43,44], completing the preclinical analysis enabling an initial clinical trial in selected patients.…”

Hematopoietic Stem Cell Gene Therapy for Storage Disease: Current and New Indications

“…Other investigators confirmed these initial findings in models of other LSDs characterized by severe CNS involvement, such as GM1 gangliosidosis, MPS IH, MPS IIIA, globoid cell leukodystrophy, and others. [44][45][46][47][48][49] These results highlighted the concept that therapeutic HSC transplantation actually corrects a nervous system damage-response pathway defective in LSD. Vector-mediated overexpression of the therapeutic enzyme in macrophages/microglia may serve to enhance the corrective potential of this pathway and to dampen its destructive capacity.…”

Genome Editing for Mucopolysaccharidoses

“…Proof of the therapeutic potential of this strategy for MPS has been accomplished with lentiviral vectors. Specifically, for MPSI, preclinical studies in mouse models demonstrated improved efficacy, compared to transplantation using unmodified cells expressing endogenous levels of the enzyme [73,74]. This strategy is currently being tested in patients with severe MPSI (NCT03488394) and preliminary data from lentiviral delivery in HSPCs in humans, suggesting that this approach is effective in the CNS [75].…”