6 December 2018 - - US-based clinical-stage biotechnology company Magenta Therapeutics (NASDAQ: MGTA) presented initial Phase 2 clinical data and preclinical research on its MGTA-456 program at the 60th annual meeting of the American Society of Hematology, the company said.

MGTA-456 is a cell therapy providing a high dose of hematopoietic stem cells that are well-matched to the patient, administered through a transplant procedure.

The ongoing Phase 2 study in inherited metabolic disorders aims to enroll 12 patients with cerebral adrenoleukodystrophy, metachromatic leukodystrophy or globoid cell leukodystrophy, and previously also enrolled patients with Hurler's syndrome.

The primary endpoint of the study is engraftment after transplantation and the secondary endpoint is transplant-related safety and tolerability.

Early data from this Phase 2 study were highlighted in a poster presentation by John Wagner, M.D., director, Blood and Marrow Transplantation Division, University of Minnesota.

In a separate oral presentation, Kevin Goncalves, Ph.D., Magenta Therapeutics, highlighted data showing that MGTA-456 significantly improves engraftment and the number of human microglia in the brains of transplanted mice; Tony Boitano, Ph.D., Magenta Therapeutics, presented a third data set showing that MGTA-456 contains large doses of the cells responsible for engraftment, which are also correlated with rapid neutrophil recovery in patients following transplant.

Five patients treated and evaluable: two with cALD, three with Hurler's syndrome.

Five of five patients treated with MGTA-456 met the primary endpoint of successful engraftment by day 42 following the transplant procedure.

In recent historical cohorts of patients undergoing regular cord blood transplantation with identical pre-transplant conditioning, up to 32% did not engraft at comparable time points.

The patients treated with MGTA-456 had minimal neutropenia, lasting for a median of 1 day.

In the historical cohort, neutropenia lasted for a median of 8 days.

The two patients with cALD showed resolution/reduction of gadolinium enhancement on MRI, an indicator of brain inflammation, by day 28 post-transplant. Resolution of gadolinium enhancement is correlated with long-term disease benefit in patients with cALD.

Patients with Hurler's syndrome showed an increase in blood leukocyte Idua enzyme, the enzyme that is deficient in untreated patients with Hurler's syndrome, suggesting that transplant with MGTA-456 is beginning to affect the disease in these patients.

Patients with Hurler's syndrome showed a marked decline in urine total glycosaminoglycan levels, which is correlated with improved long-term disease outcomes.

Two treatment-related adverse events were observed: one grade 1 vomiting and one grade 3 nausea, both of which were transient.

MGTA-456, A First-in-Class Cell Therapy Produced from a Single Cord Blood Unit, Enables A Reduced Intensity Conditioning Regimen and Enhances Speed and Level of Human Microglia Engraftment in the Brains of NSG Mice.

NSG mice were transplanted with MGTA-456 or unexpanded cord blood after being conditioned with total body irradiation or either high- or low-dose busulfan, and engraftment of microglial cells in the brain was measured.

In sublethally-irradiated animals, MGTA-456 led to an 11-fold increase in hematopoietic engraftment and a 24-fold increase in microglial engraftment in the brain (p