In chronic inflammation, macrophages and neutrophils, which are derived from bone marrow, play a pivotal role. Therefore, reconstitution of bone marrow with anti-inflammatory stem cells may modify inflammation. In this study, transplantation-based gene therapy was applied to glomerular inflammation for a long-lasting suppression of the glomerular damage seen in chronic nephritis. Bone marrow cells were harvested from male donor mice, which had received 5-fluorouracil 3 days previously, and transduced with an interleukin 1 (IL-1) receptor antagonist (IL-1Ra) or a mock gene using a retrovirus vector. After confirmation that transduced cells possessed the transgene at approximately 0.7 copies per cell and secreted recombinant IL-1Ra, these cells were infused into sublethally irradiated (6 Gy) female recipients once daily for 4 consecutive days. These female recipient mice had the male Y antigen in bone marrow, liver, and spleen, and 10% to 20% of their spleen cells possessed the transgene even 8 weeks after transplantation. Glomerulonephritis was then induced in these mice. Renal function and histology were retarded in the mice whose bone marrow was reconstituted with IL-1Ra-producing cells compared with mock transduced cells. In situ hybridization using a Y painting probe revealed that transplanted donor cells were recruited into the glomerulus upon induction of nephritis, suggesting therapeutic effects were channeled through the secretion of IL-1Ra from these cells. Furthermore, the survival rate after a second challenge with nephrotoxic antibody was significantly improved in the IL-1Ra chimera. These results suggest that reconstitution of bone marrow for continuous supply of anti-inflammatory cells may be a useful strategy for the treatment of chronic inflammation.