Comparison of chromosome studies on PHA-stimulated blood and unstimulated bone marrow cells in recipients of lymphocyte depleted grafts using counterflow centrifugation.

We performed chromosome studies on 121 paired samples of phytohaemagglutinin-stimulated blood and unstimulated bone marrow cells from 57 recipients of lymphocyte depleted grafts using counterflow centrifugation. The paired samples were drawn simultaneously 6-108 months after transplantation. The incidence of mixed chimaerism was higher in blood than in bone marrow cells, both in patients who relapsed and in patients in continuous complete remission. The higher number of mixed lymphoid chimaeras is caused by autologous T lymphocytes which have survived the conditioning regimen and/or by donor lymphocytes which persisted after disappearance of the marrow graft. The type of blood and bone marrow chimaerism had no significant impact on the incidence of chronic GVHD but the overall incidence of chronic GVHD was too low to allow an accurate assessment. Cytogenetic analysis is a useful method for assessing chimaerism after bone marrow transplantation. Apart from its limited sensitivity for the demonstration of a minor cell population, discrepancies between chromosome studies of blood cells (lymphoid chimaerism) and bone marrow cells (myeloid/erythroid chimaerism) have to be taken into consideration.