Graft-versus-host reaction spares normal stem cells in chronic myelogenous leukemia

Chronic myelogenous leukemia is a clonal proliferative disorder of pluripotent hematopoietic stem cells. Cure may be achieved by myeloablative conditioning treatment and marrow transplantation. In addition, allogeneic marrow can exert a graft-versus-leukemia effect. The graft-versus-leukemia effect may be directed against leukemia-specific antigens or against antigens on all hematopoietic cells, or it can be part of a graft-versus-host reaction. We report an informative post-transplant course of a patient with yet another leukemia-specific effect. This patient was transplanted with marrow from his HLA-identical sister in an advanced phase of CML and developed acute and chronic GVHD. After a severe pneumonia a high proportion of his metaphases in the bone marrow were male and Philadelphia chromosome negative. Later all metaphases were again female and leukemic cells could not be detected by reverse transcriptase polymerase chain reaction analysis (RT-PCR) for BCR/ABL. This course indicates that normal hematopoietic stem cells may survive intensive chemotherapy, bone marrow transplantation and GVHD. They may be recruited from a dormant state into proliferation during severe infections. In contrast, CML may be eliminated by the graft-versus-host reaction that recognizes recruited cells and spares dormant cells.