Allogeneic hematolymphoid microchimerism and prevention of autoimmune disease in the rat. A relationship between allo- and autoimmunity

Allogeneic stem cell transplantation for autoimmune diseases: nonmyeloablative conditioning regimens

Hematopoietic stem cell transplantation (HSCT) for autoimmune diseases have been, because of safety reasons, overwhelmingly autologous. Results are, in general, encouraging with improvement in quality of life, a remission of up to several years, and perhaps in some diseases improved survival. This indicates that further study of autologous HSCT especially under phase III design is warranted. However, the ultimate goal of HSCT is cure of otherwise incurable autoimmune diseases. For this reason, allogeneic HSCT in carefully selected high-risk patients with autoimmune diseases using strategies to minimize both regimen-related toxicity and graft-versus-host disease (GVHD) is ongoing at Northwestern University and will be reviewed briefly.

Induction of tolerance in autoimmune diseases by hematopoietic stem cell transplantation: getting closer to a cure?

Hematopoietic stem cells (HSCs) are the earliest cells of the immune system, giving rise to B and T lymphocytes, monocytes, tissue macrophages, and dendritic cells. In animal models, adoptive transfer of HSCs, depending on circumstances, may cause, prevent, or cure autoimmune diseases. Clinical trials have reported early remission of otherwise refractory autoimmune disorders after either autologous or allogeneic hematopoietic stem cell transplantation (HSCT). By percentage of transplantations performed, autoimmune diseases are the most rapidly expanding indication for stem cell transplantation. Although numerous editorials or commentaries have been previously published, no prior review has focused on the immunology of transplantation tolerance or development of phase 3 autoimmune HSCT trials. Results from current trials suggest that mobilization of HSCs, conditioning regimen, eligibility and exclusion criteria, toxicity, outcome, source of stem cells, and posttransplantation follow-up need to be disease specific. HSCT-induced remission of an autoimmune disease allows for a prospective analysis of events involved in immune tolerance not available in cross-sectional studies.

Will mixed chimerism cure autoimmune diseases after a nonmyeloablative stem cell transplant?

BACKGROUND

Mixed chimerism after allogeneic bone marrow transplantation has been shown to cure a number of genetic disorders in both the clinical and experimental settings. Although encouraging results have been reported from animal experiments, the role of mixed chimerism in eliminating autoimmune disorders is not clear.

METHODS

A 50-year-old man with extensive psoriasis received an allogeneic transplant from his brother after nonmyeloablative conditioning with fludarabine, melphalan, and Campath-1H for relapsed non-Hodgkin's lymphoma. The chimerism status and the immunological recovery after the transplant were serially monitored.

RESULTS

Twenty-one months after the transplant, the patient continues to be in complete remission from psoriasis and lymphoma with stable mixed chimerism (30% to 40% donor cells), despite significant recovery of T-cell subsets and antigen-specific response.

CONCLUSIONS

If mixed chimerism can be achieved safely with novel low-intensity conditioning regimens and results in sustained remission of autoimmune diseases, allogeneic transplantation may become a realistic therapy in the management of some patients with autoimmune disease.

Bone marrow transplantation for sickle cell disease: where do we go from here?

Bone marrow transplantation has curative potential for patients who have sickle cell disease. However, concerns about short-term and long-term toxicity, lack of suitable stem cell donors, and limited access to this treatment currently make it an infrequently utilized treatment for sickle cell disease. The current results of bone marrow transplantation for sickle cell disease and barriers to wider application are reviewed. Strategies that might lead to broader availability and reduced toxicity of bone marrow transplantation are discussed.

Resistance to HgCl2-Induced Autoimmunity in Haplotype-Heterozygous Mice Is an Intrinsic Property of B Cells

Exposure to low doses of mercury chloride induces autoantibodies to the nucleolar protein fibrillarin in H-2s, but not in H-2b, mice. Surprisingly, F1 crosses between resistant and sensitive haplotypes are resistant. Previously, we have shown that the resistance in these F1 mice was due to coexpression of the resistant class II allele. Using adoptive transfer techniques we have examined several mechanisms by which the resistant haplotype could be down-regulating the antifibrillarin response in F1 (s/b) mice. Similar to other autoimmune models, mercury-induced autoimmunity requires cognate MHC-restricted T cell help. The absence of autoantibody production in F1 mice was not due to a difference in thymic education or to the absence of antifibrillarin-specific T cell help. These results suggest that the resistance is due to an intrinsic property of the haplotype-heterozygous B cells.

Prevention of Transplant Rejection: Can Tolerance be Achieved with Immunosuppressive Treatment?

Successful solid organ transplantation is generally attributed to the increasingly precise ability of drugs to control rejection. However, it was recently shown that a few donor haematolymphoid cells can survive for decades in recipients of successful organ allografts, a phenomenon called microchimaerism. The association for decades of haematolymphoid chimaerism with allograft tolerance in experimental transplantation suggests that immunosuppressive drugs merely create a milieu that enables an allograft and its complement of passenger leucocytes to prime the recipient for graft acceptance.Exploitation of this concept requires a fundamental shift in the classical view of passenger leucocytes only as initiators of rejection. Microchimaerism has taught us that solid organ transplantation involves the transfer of two donor organ systems to the recipient: the allograft parenchyma and the donor haematolymphoid system in the form of donor stem cells contained within the passenger leucocyte compartment. Each has the potential to integrate with the corresponding recipient system and carry out normal physiological functions, such as immunological self definition. Resistance to initial integration by mature T cells requires some form of immunosuppression, but maintenance of donor immune system function will depend on renewable supply of cells, which can be provided by engrafted progenitors. Successful clinical application will depend on the development of low morbidity methods to enhance engraftment of donor haemopoietic stem cells.