Regenerative cell transplantation approaches are highly promising potential therapeutics for spinal cord injury. Transplantation of neural stem and progenitor cells has advanced to clinical trials for SCI. However, there are major unanswered questions about the therapeutic mechanisms and biological features of these cells that must be addressed in order to reach robust and reproducible clinical improvements. I will discuss major findings from my lab regarding how biological sex, cellular composition, and other factors influence the interactions between host and grafted cells after SCI.