BBT-059, a long-acting IL-11 analog, mitigates hematopoietic acute radiation syndrome (HARS) when administered as late as 48h following acute radiation exposure, a time when most other H-ARS medical countermeasures (MCMs) are not effective. The offeror proposes to complete IND-enabling safety toxicology studies of BBT-059, manufacture a GMP lot of BBT-059, and write and submit an Investigational New Drug (IND) application to the Food and Drug Administration (FDA) to begin testing BBT-059 in humans.