ABSTRACT The purpose of the proposed grant application is to further develop a therapeutic regimen focused on radiological/nuclear medical countermeasures. Very few medical products have been shown to counter the acute and long-term injuries that can result from a nuclear or radiological accident or attack. Medical products and regimens that mitigate and/or treat radiation injury post-exposure (i.e., administration of first dose to start at least 24 hours after radiation exposure), with emphasis on broad activity (i.e. multi-syndrome and/or multi-tissue), ease of administration in a mass casualty and emergency scenario; safety; and long shelf-life are still to be developed and are thus of high priority. Therapeutic administration of recombinant proteins to lethally irradiated wild-type mice resulted in mitigation of lethal total body irradiation. These findings suggest that pharmacologic augmentation of the activity such proteins might offer a rational approach to the mitigation of tissue injury and lethality caused by ionizing radiation.