Embodiments are directed to a method of treating acute radiation syndrome comprising administering to a subject following exposure to radiation a PIF peptide. Some embodiments describe a method of treating acute radiation syndrome following radiation exposure comprising transplanting bone marrow that has been exposed to a PIF peptide prior to transplantation into a subject. Other embodiments describe a method of increasing engraftment of a transplanted organ tissue or cell by pre exposing the organ tissue or cell to a PIF peptide.
