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Chimerism and tolerance in transplantation
1Transplantation Institute, University of Pittsburgh Medical Center, 3459 Fifth Avenue, Pittsburgh, PA 15213, USA. mangantl@msx.upmc.edu
Summary
Donor leukocyte chimerism is key to successful organ and bone marrow transplants. This involves reciprocal immune system responses leading to tolerance, improving transplant outcomes.
Area of Science:
- Immunology
- Transplantation Biology
Background:
- Early studies linked donor-specific allotolerance in animals to leukocyte chimerism.
- Bone marrow transplantation in humans initially extended these findings.
- Organ transplantation was historically thought to occur without chimerism.
Observation:
- Clinical organ transplantation succeeded without apparent leukocyte chimerism.
- Discovery of microchimerism in long-term organ recipients challenged previous assumptions.
- This suggested organ engraftment relies on chimerism-dependent partial tolerance.
Findings:
- Alloengraftment in both bone marrow and organ transplants results from reciprocal immune reactions.
- Coexisting donor and recipient immune systems lead to clonal exhaustion and deletion.
- Mechanisms of nonresponsiveness, including clonal exhaustion-deletion and immune ignorance, were elucidated.
Implications:
- Understanding these mechanisms demystifies transplantation science.
- Insights improve immunosuppression timing and dosage for human transplant recipients.
- This paradigm unifies understanding of bone marrow and organ transplantation success.