Sustained Complete Metabolic Remission After Allogeneic Hematopoietic Stem Cell Transplantation in Patients with Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE).
Authors: Halter Joerg , Schuepbach WM Michael , Casali Carlo , Elhasid Ronit , Fay Keith , Hammans Simon , Illa Isabel , Kappeler Liliane , Kraehenbuehl Stephan , Lehmann Thomas , Mandel Hanna , Marti Ramon , Mattle Heinrich , Orchard Kim H. , Savage David , Sue Carolyn , Valcárcel David , Gratwohl Alois , Hirano Michio 
Published: October 2019

Abstract
Abstract 1181
Poster Board I-203
MNGIE is an autosomal recessive disorder of nucleotide metabolism due to TYMP gene mutations that cause loss of activity of thymidine phosphorylase (TP). As a result, thymidine (Thd) and deoxyuridine (dUrd) plasma and tissue levels increase and cause nucleotide pool imbalances. This leads to instability of mitochondrial DNA with loss of mitochondrial respiratory chain functions. Clinical consequences manifest as a multisystemic disease with severe gastrointestinal dysmotility, most severe cachexia (BMI 10-17 kg/m2 in our patients), ptosis and/or ophthalmoparesis, peripheral neuropathy and leukencephalopathy. While TP is not expressed in all tissues, cellular and plasma Thd and dUrd levels appear to be in equilibrium among all body compartments. Mononuclear white blood cells and platelets are rich in TP activity and can transiently restore TP activity upon transfusions. Therefore allogeneic HSCT was tested as a permanent replacement therapy by several teams. A coorperative group under the auspices of the WBMT collected the global experiences. So far, 10 patients underwent an attempt for HSCT between 2005-2009. One patient stopped conditioning due to toxicity and did not proceed to transplantation. Nine patients had 12 allogeneic HSCT. They were 6 males and 3 females with a median age of 28y (range 10-41y) at transplantation. All were symptomatic at time of HSCT (5 on parenteral nutrition). A variety of different conditioning regimens and GvHD prevention strategies were used. Fludarabine was included in all conditioning regimens, combined with busulfan or cyclosphoshamide, melphalan, thiotepa or TBI. T cell depletion (TCD) with ATG, alemtuzumab or in vitro TCD was performed in 10 HSCT. GvHD prevention with sirolimus or calcineurin inhibitors was used in combination with mycophenolate mofetil or methotrexate. Graft source for first transplants was peripheral blood stem cells (PBSC) in 4, bone marrow (BM) in 3 and cord blood in 2. PBSC and BM donors were HLA-identical siblings in 2, phenotypic identical parent in 1 and unrelated donors in 4 (3 with 10/10 HLA-match, 1 with 9/10-match). Engraftment was problematic. Three primary graft failures and two late graft failures were observed. A second HSCT was performed in three patients, all engrafted but two died due to TRM. The two patients without a second HSCT died from their disease. Four patients developed acute GvHD grade I-IV.
To date, five patients are alive 8-48 months posttransplant, three after related PBSC-HSCT, one after unrelated BM-HSCT (10/10-HLA identical), one after two HSCTs with BM and PBSC respectively from the same unrelated 10/10-HLA identical donor. In all of these patients metabolism normalized as measured by normal Thd and dUrd levels. All surviving patients are off parenteral nutrition without further weight loss or increase in body weight. Gastrointestinal symptoms improved and in the two patients with the longest follow up a slight improvement of neurological symptoms can be observed now. Further time is needed to determine whether other disturbed organ functions will be reversible.

Conclusion:
Allogeneic HSCT can restore full metabolic function and halt and restore clinical signs and symptoms in this otherwise unrelenting progressive disease. Engraftment was identified as a key obstacle. Still, the optimal transplant regimen needs to be defined to improve patients' outcome. A common consensus transplant protocol and disease specific pre- and posttransplant evaluation protocol was developed with participation of all involved teams.

Disclosures:
Gratwohl: Amgen: Research Funding; Roche: Research Funding; Novartis: Research Funding; BMS: Research Funding; Pfizer: Research Funding. Hirano:Athena Diagnostics: Speakers Bureau; Pfizer: Research Funding.