Bone marrow transplantation: a new strategy for intractable diseases.

Bone marrow transplantation is becoming a powerful strategy for the treatment of hematologic disorders (leukemia, aplastic anemia, etc.), congenital immunodeficiencies, metabolic disorders and also autoimmune diseases. Using various animal models for autoimmune diseases, we have previously found that allogeneic (not autologous) bone marrow transplantation can be used to treat autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, immune thrombocytic purpura, insulin-dependent diabetes mellitus, chronic glomerulonephritis and certain types of non-insulin-dependent diabetes mellitus. In contrast, we have found that the transplantation of T-cell-depleted bone marrow cells or partially purified hemopoietic stem cells from autoimmune-prone mice to normal mice leads to the induction of autoimmune diseases in the recipients. These findings have recently been confirmed even in humans; autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis and Crohn's disease were resolved after allogeneic bone marrow transplantation. However, there have recently been reports on the rapid recurrence or persistence of autoimmune diseases after autologous bone marrow transplantation. Conversely, the adoptive transfer of autoimmune diseases such as myasthenia gravis, insulin-dependent diabetes mellitus and Graves' disease by allogeneic bone marrow transplantation from donors to recipients has been reported. Owing to these findings, we have proposed that autoimmune diseases are "stem cell disorders." We have thus succeeded in treating autoimmune diseases in various autoimmune-prone mice, except MRL/lpr mice, by conventional bone marrow transplantation. The MRL/lpr mouse itself is radiosensitive (<8.5 Gy), while the abnormal hemopoietic stem cells of the MRL/lpr mouse are radioresistant (>8.5 Gy); conventional bone marrow transplantation (8.5 Gy plus bone marrow transplantation) has a transient effect on autoimmune diseases, which recur three months after the bone marrow transplantation. However, bone marrow transplantation plus bone grafts (to recruit donor stromal cells) completely prevents the recurrence of autoimmune diseases in MRL/lpr mice. Donor-derived stromal cells (including mesenchymal stem cells) thus seem to play a crucial role in successful allogeneic bone marrow transplantation, since there is a major histocompatibility complex restriction between hemopoietic stem cells and stromal cells. We have, however, found that the combination of bone marrow transplantation plus bone grafts has no effect on the treatment of autoimmune diseases in MRL/lpr mice, since MRL/lpr mice become more radiosensitive after the onset of lupus nephritis due to the development of uremic enterocolitis. To reduce the cytotoxic effect of radiation on the intestine, we carried out fractionated irradiation and devised a new strategy. We injected allogeneic whole bone marrow cells (including a small number [<3%] of T cells, hemopoietic stem cells and stromal cells) from donors directly into the intra-bone marrow of recipients so that donor-derived hemopoietic cells including stromal cells could effectively accumulate in the bone marrow. All the MRL/lpr mice survived more than one year (>60 weeks after birth) without the recurrence of autoimmune diseases, and immunological functions were completely restored even when the radiation dose was reduced to 5 Gy x 2. These findings suggest that intra-bone marrow injection-bone marrow transplantation can be used to treat intractable autoimmune diseases under reduced radiation doses without using any immunosuppressants.Intra-bone marrow injection-bone marrow transplantation seems to be the best strategy for allogeneic bone marrow transplantation: 1) no graft-versus-host disease develops even if T cells are not depleted from the bone marrow; 2) no graft failure occurs even if the dose of radiation as the conditioning for bone marrow transplantation is reduced to 5 Gy x 2; 3) hemopoietic recovery is rapid; and 4) T-cell functions are completely restored even in donor-recipient combinations across the major histocompatibility complex barriers. Using cynomolgus monkeys, we have recently established a new method (the "perfusion method") for collecting bone marrow cells from the long bones (femur, humerus, etc.) without peripheral blood contamination. This method has various advantages: 1) no graft-versus-host disease develops even in cynomolgus monkeys, since the percentage of T cells in the bone marrow cells collected is less than 3%; 2) a large number of bone marrow cells can be collected quickly and safely; and 3) the bone marrow cells collected contain stromal cells including mesenchymal stem cells. We therefore believe that this method (intra-bone marrow injection-bone marrow transplantation in conjunction with the perfusion method) will become a powerful new strategy for not only allogeneic bone marrow transplantation but also organ transplantation in conjunction with bone marrow transplantation. Furthermore, this method could become a valuable strategy in regeneration therapy for injured organs and tissues (myocardial infarction, cerebral infarction, Alzheimer's disease, etc.), since it can efficiently reconstitute the recipient with both donor-derived hemopoietic stem cells and mesenchymal stem cells.