Microglia replacement using engineered HSCs for treatment of leukodystrophies

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

Summary: Globoid cell leukodystrophy (GLD, Krabbe) is a fatal pediatric neurodegenerative disease caused by mutation of the lysosomal enzyme galactosylceramidase (GALC). The greatest hurdle to curing GLD is treatment of central nervous system (CNS) pathology. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is standard of care, thought to mitigate disease progression by replacing dysfunctional macrophages with competent donor surrogates that provide functional GALC to the brain via a mechanism called cross-correction. However, the brain engraftment of HSC-derived macrophages is inefficient, reducing therapeutic benefit. In addition, allo- HSCT must be administered pre-symptomatically in early infancy, most patients will not have a related HLA- matched donor, and transplants with alternative donors or HLA-mismatched grafts have significant toxicities such as graft-versus-host disease, infections, and death. Autologous HSCs can be genetically modified and transplanted either as part of an HSCT or via direct intracranial delivery. For both approaches, though, low microglia replacement remains the limiting factor to maximum therapeutic benefit. Our central hypothesis is that enhanced engraftment of autologous, genetically modified, GALC-sufficient macrophages throughout the CNS after HSC injection, will safely and effectively address GLD pathology and disease progression. To test this, we combine the expertise of two labs: the Bennett Lab, experts in microglial biology and engraftment; and the Kiem Lab, experts in HSC gene therapy and transplantation in the preclinical nonhuman primate (NHP) large animal model. This MPI approach will foster a unique environment in which we can both investigate the therapeutic potential of this approach in an appropriate mouse model of GLD, as well as demonstrate the translational potential of microglia replacement for the first time in the preclinical NHP model. In Aim 1 we will validate an approach to efficiently engineer murine HSCs with a CSF1R inhibitor resistant (IR) variant for donor cell drug selection, simultaneously with conditional GALC overexpression. We will further demonstrate the efficient engraftment of these cells into the Krabbe disease twitcher mouse model, and study its effects on brain cells, tissue, symptoms, and survival. In Aim 2 the Kiem Lab will work concurrently to establish the preclinical viability of this approach by demonstrating the species cross-reactivity of our editing approach to the nonhuman primate. We will then show the safe and efficient replacement of microglia by introducing IR- HSCs to the CNS of NHPs that have been conditioned with CSF1R inhibition. Completion of these aims will act synergistically to both validate this therapeutic approach in a disease model while also demonstrating translatability and safety in the preclinical NHP model, allowing rapid progression of this modality into the clinic.