Does Partial Donor Chimerism (PDC) Increase the Risk of Relapse in Pediatric Patients with Leukemia Undergoing Reduced Intensity Conditioning (RIC) Hematopoietic Stem Cell Transplant (HSCT)

Relapse risks are higher with RIC regimens in comparison with standard conditioning. We report a retrospective single-center study of patients transplanted at Lurie Children's Hospital of Chicago between 2000 and 2015. Medical records were reviewed of patients enrolled in an IRB approved RIC trial. 46 consecutive patients were identified, 4 patients were excluded due incomplete data. The 42 patients (males n=21, females n=21) with a median12 (range 1-27) years of age who underwent allogeneic HSCT (matched related n= 15, matched unrelated n= 27) after RIC regimen: fludarabine 30 mg/m2 daily for 5 days, busulfan (two single daily doses to achieve an AUC of 4000μmol/min) and rabbit anti-thymocyte globulin 2 mg/kg/day for 5 days or extracorporeal photopheresis. All patients received peripheral blood hematopoietic progenitor cells. Patients diagnosis: acute myeloid leukemia (n= 14), acute lymphoblastic leukemia (n=21), chronic myeloid leukemia (n=6) and juvenile myelo-monocytic leukemia (n=1). All were in complete remission at the time of transplant. Chimerism analysis was performed weekly. Here we evaluated days +30, +60 and +100. Chimerism testing was performed by VNTR (n=37), STR (n=5) PCR depending on the method utilized by the lab at the time of HSCT. Assessment of risk of relapse was estimated by Kaplan-Meier method using GraphPAD (Prism 5.0) comparing full donor chimerism (FDC) (>95% donor) vs. partial donor chimerism (PDC) (<95% donor) using wilcoxon signed rank test p value (<0.05 was considered significant) along with hazard ratio and 95% CI of ratio. Regardless of achieving full or partial donor chimerism at days +30, +60 and +100, there was no difference in relapse rate or overall survival (See table 1).Table 1Assessment of Risk of Relapse by Comparing FDC to PDCDay +30 (n= 42)Day +60 (n= 35)Day +100 (n= 31)FDC (n= 26)PDC (n= 16)FDC (n= 24)PDC (n= 11)FDC (n= 25)PDC (n= 6)Relapse (n=24)1410135122Wilcoxon p value0.790.130.27Hazard ratio(95% CI of ratio)1.02 (0.300-3.48)2.83 (0.71-11.21)0.58 (0.91-3.74) Open table in a new tab