Clinical Impact of Recipient-Derived Isoagglutinin Levels in ABO-Incompatible Hematopoietic Stem Cell Transplantation

Quantifying HLA Mismatches at Epitope Level in Haplo-HSCT: Impact in the Outcome in Strategies Using PTCy

Haploidentical haematopoietic stem cell transplantation (haplo-HSCT) is one of the most effective therapies for treating malignant haematological disorders. However, HLA disparities are significant barriers to the success of this process since they increase the risk of graft versus host disease (GvHD). HLA disparities quantification could help to anticipate the probability and degree of GvHD, but the best tool for such quantification remains a challenge. The aim of this study was to quantify the degree of HLA epitope incompatibilities using PIRCHE (Predicted Indirectly Recognisable HLA Epitopes) algorithm for immunogenicity prediction and their potential relationship with GvHD degree and clinical outcome. We studied 145 patients who underwent a haplo-HSCT with post-transplant cyclophosphamide (PTCy) from a related donor between 2013 and 2020 at our centre evaluating molecular HLA mismatches by PIRCHE-algorithm. Patients with PIRCHE Score (PS) I + II > 38 in GvH direction, developed acute GvHD grade II-IV earlier than their counterparts (HR: 1.71, 95% CI: 1.02-2.87, p = 0.032). In addition, PS-B > 1 in GvH direction was an independent risk factor for chronic GvHD, (HR: 2.51, 95% CI 1.17-5.36, p = 0.017). A higher incidence of relapse was found for patients with PS-II > 28 HvG (HR: 9.16, 95% CI: 2.47-33.92, p < 0.001) which also favoured a worse GvHD/relapse-free survival in patients with PS-II > 27 in HvG direction (HR: 1.88, 95% CI: 1.11-3.18, p = 0.017). These findings indicate that the alloreactivity inferred by epitope HLA disparities is associated with post-transplant outcomes. Thus, analysing PS could benefit the selection of the most suitable donors allowing patient stratification based on HLA mismatches in the context of haplo-HSCT with PTCy.

Rituximab added to conditioning regimen significantly improves erythroid engraftment in major incompatible ABO-group hematopoietic stem cell transplantation

ABO-group major incompatibility hematopoietic stem cell transplantation (HSCT) increases the risk of delayed red cell engraftment and other immunological complications. In this study, we evaluated the efficacy of pre-transplant infusion of rituximab in patients with ABO-incompatibility in improving red blood cell engraftment after HSCT, measured by time to reach transfusion independence. We performed a retrospective, single-center study including 131 consecutive patients transplanted with major or bidirectional ABO-incompatible grafts between 1st January 2013 and 31st December 2019. Fifty-one patients received an infusion of rituximab during the conditioning regimen, while 80 patients did not receive any additional preventive treatment. Time to transfusion independence was significantly reduced for patients treated with rituximab (1 month, 95% CI, 0.5-2) compared with the control group (3.2 months, 95% CI 1.5-3.2, p = 0.02). By multivariable analysis, rituximab use was associated with a faster red blood cell (RBC) engraftment (RR 1.88, 95% CI 1.17-3.03, p = 0.009), while a pre-transplant anti-donor isohemagglutinins titer >1:128 was associated with delayed transfusion independence (RR 0.61, 95% CI 0.37-0.99, p = 0.05). Although limited by the retrospective nature of the study, the results of this analysis suggest that rituximab added to conditioning regimens is feasible, safe, and able to improve post-transplant red blood cell engraftment.

Immuno-Hematologic Complexity of ABO-Incompatible Allogeneic HSC Transplantation

ABO incompatibility is not considered a contraindication for hematopoietic stem cell transplantation (HSCT). Approximately 30% of transplants from related donors and up to 50% of transplants from unrelated donors are ABO incompatible. Immuno-hematologic investigations allow to estimate donor/recipient ABO mismatch and anti-A/B isohemagglutinin (IHA) titration in the pre-HSCT phase. Immediate hemolysis or delayed complications (passenger lymphocyte syndrome and pure red cell aplasia) can occur post HSCT. Some preventive measures take into consideration either decision-making algorithms based on the recipient's IHA titration or clinical protocols for the removal/reduction of IHAs through plasma exchange or immunoadsorption procedures. Product manipulation through red blood cell (RBC) and/or plasma depletion can also be taken into account. Currently, the best approach in the management of ABO-incompatible transplant is not defined in expert consensus documents or with solid evidence. In addition, the methods for IHA titration are not standardized. A transfusion strategy must consider both the donor's and recipient's blood group systems until the RBC engraftment catches on and ABO conversion (forward and reverse typing) is confirmed on two consecutive and independent samples. Therefore, ABO incompatibility in HSCT represents a demanding immuno-hematologic challenge and requires all necessary preventive measures, including the appropriate selection of ABO blood components for transfusion.

Donor-type red blood cell transfusion to deplete isoagglutinins prior to allogeneic stem cell transplantation from ABO major incompatible bone marrow donors

ABO incompatibility affects approximately 40% of allogeneic stem cell transplants in Caucasian patient populations. Because bone marrow (BM), the preferred graft from paediatric sibling donors and for non-malignant diseases, has a red blood cell (RBC) content similar to blood, anti-donor isoagglutinins must either be depleted from the recipient or RBCs removed from the graft. To achieve tolerability of unmanipulated BM grafts, we used controlled infusions of donor ABO-type RBC units to deplete isoagglutinins before the transplant. This retrospective study evaluates the outcomes of 52 ABO major incompatible BM transplants performed at our centre between 2007 and 2019. The use of donor-type RBC transfusions was well tolerated. They effectively reduced isoagglutinins levels, typically achieving target titres after one (60%) or two (29%) transfusions. The approach allowed for successful and uneventful infusions of unmanipulated BM which provided timely engraftment. The transplant outcomes were not inferior to those of a matched-pair control group of patients with ABO-identical donors.