# Integrase-Deficient Lentiviral Vector as a Platform for Efficient CRISPR/Cas9-Mediated Gene Editing for Mucopolysaccharidosis IVA

## TL;DR

Researchers developed a gene therapy using a modified virus to treat a rare genetic disorder causing skeletal issues, showing promising results in mice.

## Contribution

A novel integrase-deficient lentiviral vector (IDLV) platform for CRISPR/Cas9-mediated gene editing in MPS IVA was developed and tested.

## Key findings

- The IDLV platform achieved supraphysiological GALNS activity and normalized keratan sulfate levels in vitro.
- In vivo, the IDLV treatment led to sustained plasma GALNS activity, reduced KS, and partial correction of heart and bone pathology in newborn MPS IVA mice.
- The approach showed no vector toxicity and minimal antibody responses in treated mice.

## Abstract

Mucopolysaccharidosis IVA (MPS IVA) is a lysosomal storage disorder causing systemic skeletal dysplasia due to a deficiency of N-acetyl-galactosamine-6-sulfate sulfatase (GALNS) enzyme activity, leading to the impaired degradation and accumulation of glycosaminoglycans (GAGs), keratan sulfate (KS) and chondroitin-6-sulfate. While treatments such as enzyme replacement therapy (ERT) and hematopoietic stem cell transplantation (HSCT) are available, they have significant limitations regarding efficacy in skeletal tissues and long-term safety, highlighting the need for more effective therapies. We evaluated a novel gene therapy approach using a dual Integrase-deficient lentiviral vector (IDLV) to deliver an expression cassette that includes human GALNS cDNA and Cas9 sgRNA, targeting the upstream region of the mouse Galns initial codon. This approach leverages the endogenous promoter to drive transgene expression. We assessed in vitro transduction, editing, and functional correction in NIH3T3 and MPS IVA mouse fibroblasts. In vivo efficacy was successfully evaluated via the facial vein injection in MPS IVA newborn mice. In vitro, this IDLV platform demonstrated supraphysiological GALNS activity in cell lysate, resulting in the normalization of KS levels. In vivo direct IDLV platform in newborn MPS IVA mice led to sustained plasma GALNS activity, reduced plasma KS, and favorable biodistribution. Partial correction of heart and bone pathology was observed, with no vector toxicity and minimal antibody responses. This dual IDLV-CRISPR/Cas9 approach effectively mediated targeted GALNS knock-in, yielding sustained enzyme activity, reduced KS storage, and partial pathological amelioration in MPS IVA mice. In conclusion, IDLVs represent an efficient, safe platform for delivering the CRISPR/Cas9 gene editing system for MPS IVA.