Long-Term Restoration of Thymidine Phosphorylase Function and Nucleoside Homeostasis Using Hematopoietic Gene Therapy in a Murine Model of Mitochondrial Neurogastrointestinal Encephalomyopathy

Abstract

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a metabolic disorder caused by mutations in TYMP, encoding thymidine phosphorylase (TP). In MNGIE patients, TP dysfunction produces systemic thymidine and deoxyuridine accumulation, which ultimately impairs mitochondrial DNA replication and results in mitochondrial dysfunction. To date, only allogeneic hematopoietic stem cell transplantation has demonstrated long-term clinical efficacy, but high morbidity and mortality associated with this procedure necessitate the search for safer alternatives. In a previous study, we demonstrated that hematopoietic stem cell gene therapy using a lentiviral vector containing the coding sequence of TYMP restored the biochemical homeostasis in an animal model of MNGIE. In the present follow-up study, we show that ectopic expression of TP in the hematopoietic system restores normal nucleoside levels in plasma, as well as in tissues affected in MNGIE such as small intestine, skeletal muscle, brain, and liver. Mitochondrial dNTP pool imbalances observed in liver of the animal model were also corrected by the treatment. The biochemical effects were maintained at least 20 months even with low levels of chimerism. No alterations in the blood cell counts or other toxic effects were observed in association with the lentiviral transduction or TP overexpression. These results further support the notion that gene therapy is a feasible treatment option for MNGIE.

Preclinical Efficacy and Safety Evaluation of Hematopoietic Stem Cell Gene Therapy in a Mouse Model of MNGIE

“…Third-generation self-inactivating lentiviral (LV) vectors are currently used successfully in clinical trials for other metabolic disorders. 16 , 17 , 18 The present study supplements and confirms previous reports 19 , 20 by using (1) a highly efficient transduction method, (2) clinically applicable LV vectors to evaluate the therapeutic efficacy to reverse the biochemical phenotype and extends these reports by demonstrating (3) therapeutic efficacy of HSGCT in reversing pathological changes, particularly those of the brain, and assessing (4) potential adverse effects such as pheno- and genotoxicity.…”

Transplantation, gene therapy and intestinal pathology in MNGIE patients and mice

“…The HSCT procedure carries a high mortality rate [ 5 ]. Recently, HSCGT has been explored in Tymp −/- Upp1 −/− mice, providing higher enzymatic levels compared to HSCT and abating the risk of graft-versus-host disease [ 12 ]. Due to intrinsic limitations of the mouse model, i.e.…”

“…lack of an apparent clinical phenotype, only biochemical correction was shown after HSCGT. Moreover, the pathological changes in the intestine of Tymp −/- Upp1 −/− mice were never evaluated [ 12 ]. Here, we show that the transplanted gene modified cells engrafted well in recipient mice, leading to clearance of systemic nucleosides.…”

“…Restoration of gastrointestinal integrity by available treatments however has not yet been addressed. Also, whether small intestine pathology is recapitulated in the mouse model of MNGIE is not known [ 11 , 12 ]. In this study, we also evaluated the effects of treatment on small intestinal pathology of MNGIE patients and mice.…”

Mitochondrial neurogastrointestinal encephalomyopathy: approaches to diagnosis and treatment

“…The first approach employed a lentiviral vector which was targeted to the haematopoietic progenitor cells with the aim of restoring the activity of thymidine phosphorylase in the blood cells. Although metabolic correction of the biochemical abnormalities was achieved, the survival time of the treated mice was reduced, which was a consequence of the procedure requiring myelosuppression [109][110][111] . In the second approach, mice were treated with an adeno-associated virus vector containing the TYMP coding sequence which was targeted to the liver.…”