Revisiting the Universal Donor: Does Exposure to O Blood Products Affect Patient Outcomes

Why ABO non-identical RBCs may cause harm: In addition to the two exploratory studies published by our group (Z. Sohl, personal communication, April 30th, 2020), other investigators have also suggested that ABO non-identical transfusions could be harmful. A retrospective study by Heal et al., evaluated the effects of a policy change to provide only ABO identical RBCs and platelets for patients undergoing stem cell transplantation and patients receiving treatment for hematological malignancies. A historical control group was used for comparison. The ABO identical policy resulted in less bleeding (5% vs. 15-20%) and improved survival.

Other retrospective studies have also shown ABO non-identical platelet transfusions to be associated with an increased risk of platelet refractoriness and that refractory patients had circulating immune complexes for several days. Post transfusion platelet count increments were also higher when ABO identical platelets were transfused. In a retrospective study of 153 patients undergoing primary coronary artery bypass graft or coronary valve replacement surgery, the transfusion of at least one ABO non-identical platelet pool was associated with an increased hospital stay, more days with fever, and more RBC transfusions. Other outcomes (mortality in hospital, length of stay in the intensive care unit, antibiotic days, and a total number of platelet transfusions) were not statistically different. A subgroup analysis (n=139) of patients who received at least two platelet pools showed a non-significant trend towards increased morbidity and mortality (8.6% vs. 1.9%; p=0.10) in recipients of ABO-matched platelets. A retrospective study by Lapierre et al. analyzed data from 186 consecutive children with neuroblastoma or brain tumors who were treated with high-dose chemotherapy followed by hematopoietic stem cell transplantation. The primary endpoint was hepatic veno-occlusive disease. In their multivariate analysis, two factors significantly increased the risk of this outcome: transfusion of platelet concentrates containing ABO-incompatible plasma and use of melphalan in the conditioning regimen. They concluded that transfusion of platelet concentrates containing ABO-incompatible plasma increases the risk of hepatic veno-occlusive disease and hypothesized that passive antibody binding to A and/or B antigens expressed on the surface of hepatic endothelial cells could be involved in the pathophysiology.

It is important to emphasize that a publication bias probably exists in this literature with primarily positive studies being reported, and most of the studies are observational (lower quality evidence). Many of the platelet studies also included both minor incompatibilities (plasma in the platelet product has ABO antibodies that react with the recipient's RBCs) and major incompatibilities (recipient's plasma has ABO antibodies that react with ABO antigens on the transfused platelets); however, this literature combined with our preliminary exploratory analyses (Z. Sohl, personal communication, April 30th, 2020) raises the hypothesis that ABO non-identical transfusions (whether minor or major) could impact patient outcomes and should be further explored.

Possible biological mechanism: The concept of transfusion-related immune modulation (TRIM) was defined over 30 years ago. More recent evidence suggests that biological mechanisms leading to TRIM can be the heterogeneous involving donor, product, and/or patient factors that contribute to patient morbidities and mortality. A conceptual framework for two possible mechanisms that could lead to harm post-transfusion are a proinflammatory pathway and an immunosuppression pathway. For both pathways, inflammation is one of the prime targets that contribute to the adverse events seen in recipients. In this study, the investigators will use biomarkers of inflammation to determine if the differences are seen between patients who receive ABO identical RBC or platelet transfusions compared to those receiving ABO non-identical blood products.

The investigators hypothesize that passive anti-A and anti-B (from group O donors) can bind to recipients' endothelial cells or soluble antigen causing circulating immune complexes that can signal cytokine generation and release causing a "cytokine storm". The severity of the storm may be tempered or enhanced by the secretor status of the recipient and possibly the donor, the titre of the passive antibody transfused, and Group A or AB recipients' subgroup status (A1/A2). Antibody incompatibility could also lead to small amounts of hemolysis, which could trigger an inflammatory response. The biomarkers frequently used to detect inflammation include interleukin-6 (IL-6); tumor necrosis factor-alpha (TNF-α); interleukin-8 (IL-8) and interleukin-1 beta (IL-1β); CD40 Ligand and, C-reactive protein (CRP). Markers of hemolysis in patients post-transfusion include bilirubin, haptoglobin, and lactate dehydrogenase. The investigators will also measure circulating immune complexes as these have been linked to inflammation and a serological profile of the donor/product and the patient will also be performed. A complete list of biomarkers is included below.