Haemopoietic reconstitution by donor-derived myelodysplastic progenitor cells after haemopoietic stem cell transplantation

A 50-year-old woman who was retrospectively diagnosed with an early asympto matic myelodysplastic syndrome (MDS) served as a haemopoietic stem cell don or for her HLA-identical sister who had chemotherapy-refractory non-Hodgkin 's lymphoma. The MDS of the donor was classified as refractory anaemia (RA) and cytogenetically characterized by deletion of the long arm of chromosom e 20 [del(20q)]. Donor cell engraftment in marrow and peripheral blood was analysed over a period of 5 months after transplant using conventional cyto genetics, fluorescence in situ hybridization, and variable number of tandem repeats. Neutrophil counts >0.5 x 10(9)/l and platelet counts >20 x 10(9)/ l were reached promptly on days 12 and 24, respectively Throughout the peri od of observation the percentage of cells with the del(20q) abnormality in the recipient's mac-row and peripheral blood was comparable to the proporti on of these cells in the donor. These data indicate that the abnormal clone was capable of homing to the marrow, proliferating, differentiating, and t herefore contributing to haemopoiesis in a relatively efficient manner. Thi s implies that MDS progenitor cells may not have homing and growth deficien cies, a finding that has particular relevance for autologous transplantatio n in MDS patients where tumour cells potentially contaminate the graft.