Summary:Two patients with Philadelphia-positive chronic myelogenous leukemia underwent allogeneic bone marrow transplantation from a related HLA mismatched donor (patient 1) or from an unrelated HLA-identical donor (patient 2). Following bone marrow transplantation partial engraftment (patient 1) or graft failure (patient 2) occurred followed by autologous Philadelphia negative hematopoietic recovery either spontaneously (patient 1) or after infusion of autologous bone marrow rescue (patient 2). Neither Philadelphia chromosome, nor bcr-abl rearrangement was detectable by PCR analysis up to 7 years (patient 1) and 9 years (patient 2) post-transplantation. These two observations indicate that sustained engraftment of allogeneic bone marrow stem cells following a myeloablative regimen is not necessary to cure chronic myelogenous leukemia. It is hypothesized that the proliferative advantage of Philadelphia-negative progenitors and the anti-leukemic effect of lymphocytes in the graft have resulted in prolonged remission of the patients.

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