Methods. Forty-eight samples from bone marrow samples and peripheral blood from 34 non-myeloma patients were analyzed at different times after transplantation. Sixty-two samples from 22 myeloma patients were analyzed at different times after allogeneic stem cell transplantation, and results were compared with immuno,fixation and, in some cases, with PCR data using patient-specific primers.

Results. The median chimerism for T cells at day +100 was greater than 99.9% and remained stable on day +180 and 1 year after transplantation. In contrast, the median donor plasma cell chimerism at day +100 was 95.5%, at day +180 98.6%, at day +360 99.8%, and 2 or more years after transplantation greater than 99.9%. Sensitivity of real-time PCR using human short insertion/deletion polymorphisms (SIDP) was 10(-4) and in case of Y-PCR 10(-5). Sequential monitoring of donor plasma cell chimerism showed that increasing and stable chimerism were associated with ongoing remission in 15 out of 16 samples (93%), and decreases in chimerism predicted relapse in 5 out of 6 patients.

Conclusion. We conclude that plasma cell chimerism after allogeneic stem cell transplantation is delayed in comparison to T-cell chimerism. Sequential quantitative measurement of plasma cells after allogeneic stem cell transplantation with highly sensitive real-time PCR allows monitoring of residual host-tumor cells in patients with multiple myeloma and allows guiding adoptive immunotherapy strategies to enhance remission status and to prevent clinical relapse. (c) 2006 International Society for Experimental Hematology. Published by Elsevier Inc.