The main obstacle to organ and cell transplantation is rejection, in which the recipient’s immune system attacks the graft as "foreign." In 1954 Dr. Murray performed the first successful kidney transplant between identical twins, proving that genetic identity minimizes rejection. He later combined low-dose irradiation with azathioprine so that unrelated people could also receive organs. Dr. Thomas developed a therapy for leukemia in which chemotherapy and total-body irradiation wipe out the patient’s marrow, followed by infusion of donor bone-marrow stem cells. The new marrow regenerates healthy blood cells and can cure otherwise fatal blood cancers. He also led studies that controlled graft-versus-host disease (GVHD), making the procedure safer. Today, more than 100,000 solid-organ transplants—kidneys, livers, hearts, and more—are performed each year. Hematopoietic stem cell transplantation has become standard for leukemia and immune deficiencies, with steadily improving survival. These technologies intersect with regenerative medicine and gene therapy, shaping the future of healthcare. Murray and Thomas opened an entirely new therapeutic field: transplantation medicine.

Organ transplantation is an interdisciplinary field that merges surgery, immunology, and logistics. Joseph Murray’s 1954 identical-twin kidney transplant proved surgical feasibility while eliminating allorejection. He later established pharmacologic immunosuppression with azathioprine and corticosteroids, enabling HLA-mismatched grafts. Parallel advances in HLA typing and cross-match assays almost eliminated hyperacute rejection. Murray’s work laid the foundation for kidney, heart, liver, and composite-tissue programs worldwide. E. Donnall Thomas devised a protocol in which total-body irradiation and high-dose cyclophosphamide ablate the patient’s marrow, followed by donor hematopoietic stem-cell infusion, curing acute leukemia and aplastic anemia. He analyzed GVHD mechanisms and introduced prophylaxis with methotrexate and cyclosporine. Later studies revealed the graft-versus-leukemia effect, emphasizing the delicate balance between immune attack and tolerance. Today, haploidentical transplantation, cord-blood transplantation, and CAR-T therapies all build on these concepts. Ethical frameworks for organ allocation and donor registries also trace back to their pioneering work. Thus, the 1990 Nobel Prize honors decades of multidisciplinary progress that turned once-fatal diseases into treatable conditions.

Murray developed a renal-transplant protocol combining low-dose total-body irradiation with azathioprine, achieving long-term graft survival despite partial HLA mismatching. His case series implicated CD4+ T cells as key mediators of acute rejection, catalyzing the development of calcineurin inhibitors. Thomas performed the first human allogeneic bone-marrow transplant in 1963, initially hampered by severe GVHD and infections. He standardized myeloablative TBI plus cyclophosphamide conditioning and restricted donors to HLA-identical siblings, markedly reducing treatment-related mortality. A 1977 NEJM paper showed that early BMT after remission induction improved disease-free survival in AML and highlighted the clinical graft-versus-leukemia effect. Thomas further demonstrated that serum clean-up and metronidazole-based gut decontamination lowered GVHD incidence, influencing modern barrier-unit design. These data formed the nucleus of the CIBMTR registry, underpinning contemporary real-world evidence analyses. Immunologically, mixed chimerism and regulatory T-cell induction emerged as next-generation tolerance strategies. Today, non-myeloablative conditioning, post-transplant cyclophosphamide, and CRISPR editing of donor HSCs extend Murray and Thomas’s concepts. Their achievements established "transplantation sciences," integrating solid-organ and hematopoietic stem-cell transplantation. The work remains a benchmark for rapid bench-to-bedside translation, as reflected by thousands of annual citations and continual guideline revisions.