This study was designed to test the feasibility and safety of long-term expression of high levels of secreted human interleukin-1 receptor antagonist (hIL-1ra) protein in mice by retroviral transduction of hematopoietic stem cells. The retroviral vector, CRIP-MFG-hIL-1ra (MFG-IRAP), carrying the hIL-1ra gene was used to infect mouse bone marrow (BM) which was subsequently injected into lethally irradiated mice. All of the mice survived and greater than 98% of the white blood cells (WBC) of these mice were of donor type from 2-13 months after transplantation. All of the mice had hIL-1ra protein in their sera (40-1200 ng of hIL-1ra/ml) at all assay periods for at least 15 months after transplantation. Bone marrow from seven of seven primary recipients produced at least one secondary recipient with sustained, high serum levels of hIL-1ra, indicating that hematopoietic stem cells had been successfully transduced. Although the hIL-1ra was biologically active when assayed in vitro, the mice appeared to be well and their WBC counts and hematocrit (HCT) were not significantly different from those of lethally-irradiated mice given BM cells infected with the same vector carrying the lacZ gene. There was also no evidence of alterations of white cell subpopulations. These results demonstrate that systemic production of biologically active hIL-1ra can be obtained by retrovirus-mediated gene transfer to hematopoietic stem cells and that this level of expression and secretion into the serum is compatible with normal BM engraftment, hematopoietic recovery and survival of the lethally irradiated recipient mice. These hIL-1ra-expressing mice represent a model to examine the functions of IL-1 and hIL-1ra and to determine the ability of hIL-1ra to reduce susceptibility to chronic diseases such as rheumatoid arthritis as well as effects of aging such as bone degeneration. The data further suggest that transduction and transplantation of hematopoietic stem cells is a potential method for delivery of hIL-1ra and other secreted therapeutic gene products for systemic diseases.