EFFECTS OF CHIMERISM ON GRAFT-VERSUS-HOST DISEASE, DISEASE RECURRENCE, AND SURVIVAL AFTER HLA-IDENTICAL MARROW TRANSPLANTATION IN IRAN

Background: The coexistence of recipientʹs and donorʹs hematopoietic systems after allogeneic marrow transplantation is called mixed chimerism. Objective: The objective of this study was to evaluate the effects of MC on graft-versus-host disease (GVHD), disease recurrence, and survival after HLA identical marrow transplantation in a transplant center in Iran. Methods: The association of MC with acute GVHD, disease recurrence, survival, and relapsefree survival was investigated in 91 patients who underwent either bone (n = 12) or peripheral blood (n = 79) HLA-identical marrow transplantation. Chimerism was assessed using multiplex amplification of short tandem repeats (STR). Patients had thalassemia (n = 19), acute myelogenous leukemia (AML) (n = 29), acute lymphocytic leukemia (ALL) (n = 20), chronic myelogenous leukemia (CML) (n = 18), and other diseases (n = 5). The median age was 21 (range: 3 – 50) years. There were 38 (42%) female and 53 (58%) male participants. Conditioning was made through busulfan plus cyclophosphamide in 34 patients; busulfan plus fludarabin in 51 patients; and busulfan plus fludarabin plus antithymocyte globulin in 6 patients. The median follow-up was 13 months. Results: On day +30, complete chimerism (CC) was observed in 72 (79%) patients, MC in 15 (17%), and no chimerism in 4 patients. The incidence of acute GVHD was significantly (P = 0.01) lower in mixed chimeras than in complete chimeras. There was no significant difference in acute GVHD grade (I, II vs. III, IV) between the two groups. The incidence of relapse was 18%. There was no difference in relapse rate between MC and CC groups. Overall survival was 89%. There was no significant difference in the overall survival between MC and CC group (96% vs. 85%, respectively). Relapse-free survival was 80% that was not significantly different between the two groups. Conclusion: Despite some previous reports, we found no significant difference in the survival and relapse rates between MC and CC groups.