Disclosed are methods of obtaining an expanded population of mammalian ex vivo cells for treating a mammalian subject by (a) administering to a subject an effective amount of an agent that confers a growth disadvantage to at least a subset of endogenous cells at the site of engraftment; (b) administering to the subject an effective amount of a mitogenic stimulus for the ex vivo cells; and (c) administering the ex vivo cells to the subject, wherein the ex vivo cells engraft at the site and proliferate to a greater extent than the subset of endogenous cells, to repopulate at least a portion of the engraftment site with the ex vivo cells. The repopulated cells can be harvested or left at the engraftment site. Methods of treating brain injury in a subject by engrafting ex vivo cells at the site of injury are also described.