PROJECT SUMMARY/ABSTRACT Stem cell technologies offer new promise for some of the most devastating medical conditions that currently lack treatments. To harness the full therapeutic potential of stem cells, however, it will be necessary to understand how to direct their differentiation to appropriate cell phenotypes, understand how they may change with in vitro manipulation, and how the external milieu may influence their fidelity after transplantation into injured or diseased host networks. These gaps in knowledge are the cornerstones of my long-term training plan. My research goal is to become an independent scientist pursuing translationally relevant research. To do so, I will build upon my technical in vitro skills from undergraduate research, and now use a model of pre-clinical spinal cord injury as a testbed for my hypotheses regarding the therapeutic potential of transplanted engineered cells. More than half of all spinal cord injuries occur at the cervical level resulting in major respiratory deficits and complications. These deficits are largely due to the disruption of descending bulbospinal respiratory pathways and damage to spinal respiratory motor circuits. While current therapies are aimed at enhancing the plasticity of spared networks, they fail to treat the underlying cause of deficits: neural loss. One promising strategy for neural repair is the use of cellular transplants, yet very little is known about their phenotype, development, and connectivity to host networks after transplantation. Importantly, even less is known about how these cells change with each manipulation in vitro (e.g., addition of growth factors, how cryopreservation may change the phenotypic potential, etc.). Neural precursor cells (NPCs) have been used for decades to repair the injured central nervous system. However, these donor cell populations are highly heterogeneous, have not been well characterized and preparation of these cells for transplantation may further alter their heterogeneity. A primary goal of the present study is to address this issue and enhance their therapeutic potential by enriching for specific subsets of spinal interneurons known to contribute to beneficial plasticity and repair. The current proposal will test the therapeutic potential of refined populations of donor NPCs, enriched with pre-motor V0 spinal interneurons, to promote anatomical (Aim 1) and functional (Aim 2) improvement post-SCI.