The Application of Sequential and Quantitative Analysis of Donor Chimerism in Adoptive Immunotherapy Following Allogeneic Stem Cell Transplantation.

Objective In order to investigate the value of sequential and quantitative analysis of chimerism to predict relapse or graft rejection after allogeneic stem cell transplantation, to determine the optional time point of adoptive immunotherapy and to estimate the efficacy of adoptive immunotherapy.

Methods 70 patients who received HLA compatible allo-HSCT were evaluated. Peripheral blood and bone marrow were collected before and after transplantation in different period. Serial and quantitative analysis of donor chimerism (DC) both prior to and following adoptive immunotherapy were performed by multiplex PCR amplification of STR markers (STR-PCR) and capillary electrophoresis with fluorescence detection.

Results 13 of 70 patients relapsed at median time of 6months post transplant (4/13 patients developed hematologic relapse and 9/13 patients appeared cytogenetic or molecular relapse respectively). 2 of 70 patients experienced graft rejection. Before the time of relapse or graft rejection, STR-PCR indicated the decreasing DC in all 15 patients, at levels ranging from 24.8%~86.2%. The declining value of donor chimerism (DC< 90%) was detected in four patients 26 days before relapse or graft rejection diagnosed clinically. Adoptive immunotherapy was used to treat 15 patients(9 CML, 5 AML, 1 MDS). A response to immunotherapy was achieved in 6 patients(6 CML) following withdrawal of CsA and in a further 4 patients(2 CML, 1 M₂, 1 MDS) after additional donor lymphocyte infusion(DLI). In these patients, the value of DC increased with convertion to a predominant donor profile (>90%) or converted to stable full donor chimerism(FDC)(6 patients) or stable mixed chimerism(MC)(4 patients) shortly after immunotherapy. All these 10 patients who responsed to immunotherapy developed acute or chronic GVHD. While in the patients without response, the level of DC decreased persistently or declined after transient increasing. Three patients without response received second DLI but remain failed to therapy.

Conclution The results demonstrate that the decreasing value of DC can identify the patients who have high risk of relapse or graft failure and can be used to guide adoptive immunotherapy implementation at early stage. The sequential and quantitative monitoring of DC has been shown to be a valuable tool to determine the optional time point of immunotherapy and to early evaluate the efficacy of treatment. Furthermore, it can present a rational basis for treatment intensification in patients who did not respond to first-line DLI treatment