Host sex and transplanted human induced pluripotent stem cell phenotype interact to influence sensorimotor recovery in a mouse model of cortical contusion injury

Traumatic brain injury (TBI) is a substantial cause of disability and death worldwide. Primary head trauma triggers chronic secondary injury mechanisms in the brain that are a focus of therapeutic efforts to treat TBI. Currently, there is no successful clinical strategy to repair brain injury. Cell transplantation therapies have demonstrated promise in attenuating secondary injury mechanisms of neuronal death and dysfunction in animal models of brain injury. In this study, we used a unilateral cortical contusion injury (CCI) model of sensorimotor brain injury to examine the effects of human induced pluripotent stem cell (hiPSC) transplantation on pathology in male and female adult mice. We determined transplanted hiPSC-derived neural stem cells (NSCs) and neuroblasts but not astrocytes best tolerate the injured host environment. Surviving NSC and neuroblast cells were clustered at the site of injection within the deep layers of the cortex and underlying corpus callosum. Cell grafts extended neuritic processes that crossed the midline into the contralateral corpus callosum or continued laterally within the external capsule to enter the ipsilateral entorhinal cortex. To determine the effect of transplantation on neuropathology, we performed sensorimotor behavior testing and stereological estimation of host neurons, astrocytes, and microglia within the contused cortex. These measures did not reveal a consistent effect of transplantation on recovery post-injury. Rather the positive and negative effects of cell transplantation were dependent on the host sex, highlighting the importance of developing patient-specific approaches to treat TBI. Our study underscores the complex interactions of sex, neuroimmune responses and cell therapy in a common experimental model of TBI.