Comparison of chimerism of red cells with that of granulocytes, T-lymphocytes, and bone marrow cells in recipients of bone marrow grafts depleted of lymphocytes using counterflow centrifugation.

We analyzed the origin of red cells (using red cell phenotyping), T lymphocytes (using both cytogenetic analysis and restriction fragment length polymorphism studies), and of granulocytes and bone marrow cells (using restriction fragment length polymorphism studies) in 10 consecutive patients. All received bone marrow grafts depleted of lymphocytes using counterflow centrifugation. Analyses were performed on identically timed samples from 6 months after transplantation onward. After correction for the higher sensitivity of red cell phenotyping, results of red cell phenotyping were concordant with restriction fragment length polymorphism studies of granulocytes and bone marrow cells in all cases studied. Outcome of cytogenetic analysis and restriction fragment length polymorphism studies of T lymphocytes were concordant in all 10 cases. Two patients had only mixed chimerism in T lymphocytes but not in red cells nor in granulocytes; in one of these two patients the absence of mixed chimerism was confirmed with restriction fragment length polymorphism studies of bone marrow cells; bone marrow cells of the second patient were not available for analysis with restriction fragment length polymorphisms, but cytogenetic analysis of his bone marrow cells showed only metaphases of donor type. These data show that red cell phenotyping represents the hematopoietic chimeric state of granulocytes and nucleated bone marrow cells. Cytogenetic analysis or restriction fragment length polymorphism studies of T lymphocytes increases the number of instances of mixed chimerism, but this reflects the higher incidence of mixed chimerism in the clonogenic T cell population. These cells are less sensitive to radiochemotherapy than the hematopoietic stem cells and have retained the capacity for (limited) selfrenewal.