Early establishment of chimerism in the B and T lymphoid lineages after transplantation of allogeneic mobilized blood cells in leukemic patients

Background. The use of allogeneic recombinant human granulocyte colony-stimulating factor (rhG-CSF)-mobilized blood cells was recently evaluated in patients with malignancies. Methods. Ten patients with leukemia were transplanted with allogeneic blood cells from HLA-identical sex-mismatched siblings; blood cells were mobilized with recombinant rhG-CSF. Up to 6 months after transplantation, blood and bone marrow samples were obtained from the recipient and analyzed for the presence of donor cells, using fluorescence in situ hybridization with specific probes hybridizing to sex chromosomes. Results. Analysis of blood and bone marrow smears demonstrated a complete chimera, as early as day 15 after transplantation. Furthermore, marrow and blood CD4(+,) CD8(+), CD19(+), and CD34(+) cells were sorted using direct immunofluorescence and flow cytometry: fluorescence in situ hybridization analysis on sorted cells demonstrated that most progenitors and most cells in the T- and B-cell lineages were of donor origin as early as day 15 after transplantation. Conclusions. Together with recently reported results, this study demonstrates that allogeneic rhG-CSF-mobilized blood cells contain primitive hematopoietic progenitors that can repopulate all lymphoid and myeloid lineages. Establishment of chimerism seems to be quick and stable, including the T- and B-cell lineages. Although establishment of chimerism in mitogen-responsive T cells is readily assayable with conventional cytogenetics, our study provides additional insight on the reconstitution of the B lineage and T-cell subsets after allogeneic transplantation in patients with leukemia.