Gene therapy for liver enzyme deficiencies: what have we learned from models for Crigler-Najjar and tyrosinemia?

Charge-altering releasable transporters (CARTs) for the delivery and release of mRNA in living animals

Functional delivery of mRNA to tissues in the body is key to implementing fundamentally new and potentially transformative strategies for vaccination, protein replacement therapy, and genome editing, collectively affecting approaches for the prevention, detection, and treatment of disease. Broadly applicable tools for the efficient delivery of mRNA into cultured cells would advance many areas of research, and effective and safe in vivo mRNA delivery could fundamentally transform clinical practice. Here we report the step-economical synthesis and evaluation of a tunable and effective class of synthetic biodegradable materials: charge-altering releasable transporters (CARTs) for mRNA delivery into cells. CARTs are structurally unique and operate through an unprecedented mechanism, serving initially as oligo(α-amino ester) cations that complex, protect, and deliver mRNA and then change physical properties through a degradative, charge-neutralizing intramolecular rearrangement, leading to intracellular release of functional mRNA and highly efficient protein translation. With demonstrated utility in both cultured cells and animals, this mRNA delivery technology should be broadly applicable to numerous research and therapeutic applications.

Recent developments in transposon-mediated gene therapy

INTRODUCTION

The continuous improvement of gene transfer technologies has broad implications for stem cell biology, gene discovery, and gene therapy. Although viral vectors are efficient gene delivery vehicles, their safety, immunogenicity and manufacturing challenges hamper clinical progress. In contrast, non-viral gene delivery systems are less immunogenic and easier to manufacture.

AREAS COVERED

In this review, we explore the emerging potential of transposons in gene and cell therapy. The safety, efficiency, and biology of novel hyperactive Sleeping Beauty (SB) and piggyBac (PB) transposon systems will be highlighted for ex vivo gene therapy in clinically relevant adult stem/progenitor cells, particularly hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), myoblasts, and induced pluripotent stem (iPS) cells. Moreover, efforts toward in vivo transposon-based gene therapy will be discussed.

EXPERT OPINION

The latest generation SB and PB transposons currently represent some of the most attractive systems for stable non-viral genetic modification of primary cells, particularly adult stem cells. This paves the way toward the use of transposons as a non-viral gene therapy approach to correct hereditary disorders including those that affect the hematopoietic system. The development of targeted integration into "safe harbor" genetic loci may further improve their safety profile.

Paediatric liver transplantation for metabolic disorders. Part 2: Metabolic disorders with liver lesions

Liver based metabolic disorders account for 10 to 15% of the indications for paediatric liver transplantation. In the last three decades, important progress has been made in the understanding of these diseases, and new therapies have emerged. Concomitantly, medical and surgical innovations have lead to improved results of paediatric liver transplantation, patient survival nowadays exceeding 80% 10 year after surgery with close to normal quality of life in most survivors. This review is a practical update on medical therapy, indications and results of liver transplantation, and potential future therapies, for the main liver based metabolic disorders in which paediatric liver transplantation may be considered. Part 1 focuses on metabolic based liver disorders without liver lesions, and part 2 on metabolic liver diseases with liver lesions.

Lentiviral vectors that express UGT1A1 in liver and contain miR-142 target sequences normalize hyperbilirubinemia in Gunn rats

BACKGROUND & AIMS

Crigler-Najjar type 1 (CN-I) is an inherited liver disease caused by an absence of bilirubin-uridine 5'-diphosphate-glucuronosyltransferase (UGT1A1) activity. It results in life-threatening levels of unconjugated bilirubin, and therapeutic options are limited. We used adult Gunn rats (an animal model of the disease) to evaluate the efficiency of lentiviral-based gene therapy to express UGT1A1 in liver.

METHODS

Gunn rats were given intraportal injections of VSVG-pseudotyped lentiviral vectors that encode UGT1A1 under the control of a liver-specific transthyretin promoter (mTTR.hUGT1A1); this vector does not contain target sequences for miR-142, a microRNA that is expressed specifically in hematopoietic cells. Rats were also injected with the vector mTTR.hUGT1A1.142T, which contains 4 copies of the miR-142 target sequences; its messenger RNA should be degraded in antigen-presenting cells. Bilirubinemia was monitored, and the presence of transduced hepatocytes was analyzed by quantitative polymerase chain reaction. Vector expression was tested in vitro in rat hematopoietic cells.

RESULTS

In Gunn rats, bilirubin levels normalized 2 weeks after administration of mTTR.hUGT1A1. However, hyperbilirubinemia resumed 8 weeks after vector administration, concomitant with the induction of an immune response. In contrast, in rats injected with mTTR-UGT1A1.142T, bilirubin levels normalized for up to 6 months and transduced cells were not eliminated.

CONCLUSIONS

Lentiviral vectors that express UGT1A1 reduce hyperbilirubinemia in immunocompetent Gunn rats for at least 6 months. The immune response against virally expressed UGT1A1 can be circumvented by inclusion of miR-142 target sequences, which reduce vector expression in antigen-presenting cells. This lentiviral-based gene therapy approach might be developed to treat patients with CN-I.