AL-03. Donor chimerism in the peripheral blood at the day +14 after allo-HSCT predicts graft failure

Summary

Assessment of the molecular chimerism at the day +28 after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is used to predict all types of graft dysfunction including graft failure and rejection. It might be beneficial to establish prediction markers for a graft failure effective earlier than at the day +28. Our objective was to assess the significance of donor chimerism on the day +14 after allo-HSCT for predicting engraftment in patients with acute leukemia.

Materials and methods

Archival DNA samples isolated from the blood cells of 64 patients who received allo-HSCT at the National Medical Research Center for Hematology between 01.01.2020 and 27.06.2023 were used to monitor molecular chimerism. Patients of the study group were selected according to the availability of archival material for a retrospective study of chimerism, first transplantation from a haploidentical (≥2 mismatches according to the HLA system) or an unrelated partially compatible donor, diagnosis of acute leukemia, remission at the time of transplantation, and low-intensity conditioning regimen (RIC). The median age of patients was 49 years (26-63), 13 (59%) women and 9 (41%) men. The absence of engraftment by the day +28 was noted if the absolute number of neutrophils was less than 0.5×10^9/l; hemoglobin less than 70 g/l; platelets less than 20×10^9/l; donor hematopoiesis 0-5%; no relapse of the disease. Selection criteria for the control group were the same, except for the donor type: related and unrelated fully HLA compatible. The control group included 22 patients; the median age of patients was 39 years (19-59), 24 (54%) women and 18 (46%) men. Chimerism was monitored by STR-PCR using a multiplex CorDIS Plus kit (19 polymorphic STR markers and the X/Y locus of human amelogenin), followed by the separation of PCR products by capillary electrophoresis. Chimerism was calculated based on the percentage of unique donor and recipient markers in the informative STR loci using GeneMapper v. 4-0 software.

Results

In the group of patients with allo-HSCT from a partially HLA compatible donor, the level of donor chimerism in peripheral blood (PB) samples on day +14 was significantly lower in patients who had graft failure on day +28. For patients with engraftment, the median of donor chimerism was 87% (27-100%), without engraftment 54% (0-90%), (p<0.0089). ROC analysis was performed to test the dependence of the probabilities of errors in the classification of the target indicator (failure on day +28) from the level of donor chimerism on the day +14. We found that donor chimerism of 25% or lower in the PB on the day +14 is a good predictor of graft failure (AUC=0.79, p=0.0034). In accordance with the selected threshold level, all patients were divided into 2 groups (donor chimerism at < 25%, and >25%). In the <25% group, graft failure was detected in 100% of cases (3 out of 3), while in the group showing chimerism at >25%, the graft failure was detected in only 15% of cases (6 out of 39). In the control group with fully HLA compatible donor, the selected threshold of 25% was not significant for the prediction of graft failure.

Conclusion

Less than 25% of donor chimerism observed in PB on day +14 after allo-HSCT predicts graft failure on day +28 in patients with haploidentical or partially HLA compatible unrelated donor. Meanwhile, this index has no predictive value in the cohort of patients with a fully compatible donor.

Keywords

Graft failure, peripheral blood, donor chimerism, allo-HSCT, STR-PCR.