Donor Chimerism Is a Key Predictor of Graft Failure and the Response of Adoptive Immunotherapy Following Allogeneic Hematopoietic Stem Cell Transplantation.

Objective: In order to evaluate the usefulness of chimerism quantitative monitoring for the early diagnosis of graft failure in different allogeneic Hematopoietic Stem Cell Transplantation (allo-HSCT) settings, as well as to predict the response to treatment with adoptive immunotherapy. Methods 235 patients who received allo-HSCT were evaluated. Serial and quantitative analysis of donor chimerism (DC)both prior to and following allo-HSCT or/and adoptive immunotherapy(AIT) were performed by STR-PCR. Samples obtained on days +7, +14, +21, + 28, +60, +90, +180, +270, +360 of transplantation or AIT and once a year thereafter, included bone marrow (BM) and peripheral blood (PB).Furthermore, chimerism was analyzed in T lymphocytes, CD3+ isolated by immunomagnetic means for 28 patients. 12 patients who experienced graft rejection or delayed engraftment received adoptive immunotherapy including immunosuppression withdrawal and/or donor lymphocyte infusions (DLI). Results Ten of 235 patients appeared graft failure(3 patients with initial en graft ment failure, 7 patients with graft rejection) and 2 patients presented delayed engraftment (4 ablative sibling BMT, 4 RIC-HSCT, 2 URD-PBSCT, 1 URD-CBT, 1 haploidentical-HSCT). Median age was 31.5 years(range:8–55). Donor chimerism remained low level(DC< 40%) during all the process of transplantation for three patients of graft failure(GF). One of them died for pancytopenia and other 2 patients restored autologous hematopoiesis. In addition, after initial engraftment(full donor chimerism or stable mixed chimerism were achieved at the beginning in these patients), graft rejection(GR) was diagnosed in 7 patients. Relapse was excluded by means of bone marrow smear, cytogenetics, molecular biology and minimal residual disease(MRD). Unfractionated chimerism of whole blood or bone marrow declined progressively at the median time of 3 months post transplantation. In 3/7 patients studied, T cells showed persistent MC with high %R(>60% in 2/7 and >82% in 1/7)).All these 10 patients with GF or GR received G-CSF. Meanwhile 8 of 10 patients accepted mobilized PBSC or donor lymphocyte infusion. A response to immunotherapy was achieved in 3 patients. One of them presented III° GVHD and chimerism converted to stable full donor chimerism(FDC) shortly after immunotherapy. DC of 2 patients who response to AIT converted to stable mixed chimerism(MC). While in the 5 patients without response, the level of DC decreased persistently. Furthermore, two patients received unrelated-PBSCT presented delay engraftment. Unfractionated chimerism inferior to 85% and converted to FDC following withdrawal of mycophenolate mofetil (MMF) and Cyclosporin A. Conclusion The results demonstrate that the decreasing value of DC (especially T cell chimerism) can identify the patients who have high risk of graft failure and can be used to guide adoptive immunotherapy intervention at early stage (including G-CSF and AIT).Sometimes, unfractionated chimerism or T cell chimerism is the only parameter to predict graft failure for the patient without specific tumor markers. As well as the sequential and quantitative monitoring of DC has been shown to be a valuable tool to early evaluate the efficacy of AIT. Furthermore, AIT is an effective treatment to prevent GR and to maintain full donor chimerism. Response of early AIT is superior to that of delay intervention therapy.