The invention relates to a protein material which is effective to preserve progenitor cells, such as hematopoietic progenitor cells. The protein has an amino acid sequence comprising AQSLSFSFTKFD (SEQ ID NO:1) and a molecular weight of about 12 20 kD, or has an amino acid sequence comprising VVAVEFD (SEQ ID NO:3) and a molecular weight of about 15 20 kD. Heterodimers of the protein are described, and multimers thereof. Methods of using the protein of the invention for preserving progenitor cells in vitro, ex vivo, and in vivo are also described. The invention, therefore, include methods such as myeloablation therapies for cancer treatment wherein myeloid reconstitution is facilitated by means of the specified protein. Other therapeutic utilities are also enabled through the invention, for example, expanding progenitor cell populations ex vivo to increase chances of engraftation, improving conditions for transporting and storing progenitor cells, and facilitated gene therapy to treat and cure a broad range of life-threatening hematologic diseases.