Stem cell transplantation for severe autoimmune diseases: progress and problems.

Since Morton and Siegel's epochal experiments 30 years ago animal models have been successfully utilized both for transfer and resolution of autoimmune diseases (AID). More recently human lymphocyte xenografts have reproduced clinical AID in SCID mice. Allogeneic stem cell transplantation demonstrated therapeutic potential in fully developed autoimmune disease. Mixed allogeneic chimerism induced by a sublethal approach has also been shown to prevent and even reverse autoimmune insulitis in nonobese diabetic (NOD) mice. More unexpectedly it was found that experimental adjuvant arthritis (AA) and experimental allergic encephalomyelitis (EAE) could be cured by means of total body irradiation (TBI) followed by autologous hemolymphopoietic stem cell (HSC) transplantation. It was postulated that the newly developing T cells might be tolerant to self antigens. The transfer of AID from affected donors to recipients of allogeneic HSC transplants has been reported for many organ-specific AID, including diabetes (IDDM), thyroiditis, myasthenia gravis and thrombocytopenic purpura (AITP); rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) were not transferred. Conversely patients with the combination of AID and a severe blood disease (leukemia, aplasia) were cured of both diseases following allogeneic BMT, with the notable exception of a relapse in a patient with RA despite full donor engraftment. Allogeneic transplants are certainly more promising as far as concerns a resolution of AID, because they may also exert a graft-versus-autoimmunity effect by gradually eradicating the recipient's lymphopoiesis, but transplant related mortality (TRM) is considered still too high to employ this procedure consistently. New non-myeloablative conditioning regimens, designed to allow the donor's immune system to take over, are already utilized for malignant and non-malignant hematologic diseases, and may become an attractive option for severe, refractory AID. For the time being, however, autologous procedures are still safer, and are being utilized in many projects worldwide. The EBMT/EULAR Registry has collected over 70 patient reports. The more numerous and favorable results have been obtained up to now in multiple scleosis and in systemic lupus erythematosus; the worst in refractory autoimmune thrombocytopenic purpura. No definite conclusions as to the efficacy of autologous HSC transplantation, from marrow or from blood, with or without T-cell depletion, may be drawn at this time, but the feeling is that real cures will be very difficult to obtain by this approach, and that corticosteroid-free remissions and a general lowering of the autoimmune potential will be more realistic goals. Accurate comparisons with already existing aggressive immunosuppressive protocols will become necessary, if possible by means of prospective randomized clinical studies.