Mucopolysaccharidoses type I gene therapy

Abstract

Mucopolysaccharidoses type I (MPS I) is an inherited metabolic disease characterized by a malfunction of the α-l-iduronidase (IDUA) enzyme leading to the storage of glycosaminoglycans in the lysosomes. This disease has longtime been studied as a therapeutic target for those studying gene therapy and many studies have been done using various vectors to deliver the IDUA gene for corrective treatment. Many vectors have difficulties with efficacy and insertional mutagenesis concerns including adeno-associated viral (AAV) vectors. Studies of AAV vectors treating MPS I have seemed promising, but recent deaths in gene therapy clinical trials for other inherited diseases using AAV vectors have left questions about their safety. Additionally, the recent modifications to adenoviral vectors leading them to target the vascular endothelium minimizing the risk of hepatotoxicity could lead to them being a viable option for MPS I gene therapy when coupled with gene editing technologies like CRISPR/Cas9.

Keywords: CRISPR; adenovirus; gene editing; gene therapy; mucopolysaccharidosis type I.

FIGURE 1

Ex vivo vs in vivo gene therapy. Ex vivo gene therapies follow a method in which one harvests cells from the patient and then makes the necessary correction with a system to deliver the gene therapy in a petri dish. Following correction, the cells are cultured in a sterile setting before ultimately being returned to the patient. Ex vivo gene therapy methods for mucopolysaccharidoses type (MPS I) have been attempted to improve upon hematopoietic stem cell transplantation (HSCT) and lessen the possibility of graft failure without worrying about dose‐dependent reactions in vivo. In contrast, in vivo gene therapies are less invasive than ex vivo methods and typically involve a patient receiving a single dose with the gene therapy via injection. The gene therapy is then delivered by a vector to the target cell. The target cells then produce the corrective protein and secrete them to allow for cross correction to other unmodified cells. In MPS I, an in vivo strategy is highly desirable due to the minimally invasive process for patients and potential long‐term effects

FIGURE 2

A gene editing approach to gene therapy. In the strategy pictured, based on Stephens et al's 2019 method to treat hemophilia B, two vectors are delivered to the patient via intravenous injection for a gene editing therapy strategy. The donor vector includes the corrective cDNA along with the gRNA for CRISPR purposes. The editor vector includes Cas9. Placing the Cas9 and gRNA on separate vectors ensures that only cells that receive both vectors are edited. Once injected, the vectors would make their way to the liver where the viral capsid would interact with hepatocytes to release the encapsulated DNA into the cell. Once both vectors have provided DNA to the cell, the CRISPR/Cas9 system takes over to integrate the corrective gene into the albumin locus. These cells are then permanently edited to produce and secrete the corrective protein and secrete it for cross correction to surrounding cells

FIGURE 3

A proposed improved method to utilize the CRISPR/Cas9 system for the treatment of mucopolysaccharidoses type (MPS I). The current method of gene editing therapy focuses on targeting the liver for cellular sourcing., However, this method could lead to concerns with hepatotoxicity due to the targeting of the liver. A method targeting the vascular endothelium rather than the liver would bypass hepatotoxicity concerns while also leading to secretion of the corrective protein directly into the blood stream for cross correction. By utilizing an adenovirus (Ad) vector modified with a myeloid binding peptide (MBP), we can achieve this and potentially establish long‐term, stable correction of MPS I