Chimerism studies using in situ hybridization for the Y chromosome after T cell-depleted bone marrow transplantation

In situ hybridization for the Y chromosome (Y-ISH) was used to monitor engraftment in 10 patients with hematological malignancies who had received T cell-depleted marrow transplants from sex-mismatched donors, seven of whom were only partially HLA-matched. In the three patients who engrafted, as the peripheral counts rose, the percentage of host peripheral blood and marrow mononuclear cells decreased steadily, although host cells (less than 1%) could still be detected as late as day 252. The percentage of host granulocytes fell rapidly to less than 0.2%. Seven patients did not achieve full engraftment by day 28. Those with a low percentage of host cells (less than 1%) improved with observation or treatment with steroids, while those with a high or increasing percentage of host cells did not improve even after treatment with GM-CSF or with repeat marrow infusion without reconditioning. In one patient with graft failure, the residual host cells were predominantly CD8+ CD57+ and CD3+ CD56+, phenotypes consistent with non-MHC-restricted cytotoxic T cells. Lack of full engraftment in recipients of T cell-depleted marrow is not always associated with autologous reconstitution and does not always require retransplantation. Y-ISH may be useful for monitoring patients at high risk for graft failure in order to detect adverse trends in mixed chimerism that will alter therapy early after transplantation.