High stem cell dose will not compensate for T cell depletion in allogeneic non-myeloablative stem cell transplantation.

The best strategies for non-myeloablative stem cell transplants (NST) are not known. We hypothesized that a high stem cell dose and post-transplant donor lymphocyte infusions (DLI) in a T cell-depleted NST setting may result in stable engraftment without severe GvHD. We used conditioning with 200 mg/kg cyclophosphamide, and ATG, a high peripheral stem cell dose of >10 x 10(6) CD34(+) cells/kg, T cell-depleted to <1 x 10(5) CD3(+) cells/kg followed by incremental DLI. Ten patients, 53 (42-61) years of age with hematological malignancy (CML in 3, MDS in 2, myeloma in 3 and CLL in 2) were included. All patients achieved initial engraftment, at a median 13.5 (10-20) days. Three patients achieved complete chimerism, four achieved a complete hematologic remission. In seven patients the graft ultimately failed. Acute GvHD grade II was seen in three patients after DLI. At a median follow-up of 28 months (range 15-35), eight patients are alive, none died of treatment-related complications. NST with T cell depletion to prevent GVHD results in a high graft failure rate. High stem cell dose (> or =10 x 10(6) CD34(+)cells/kg) and post-transplant DLI will not compensate for the lack of T cells to ensure stable engraftment.