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The risk of a hemolytic reaction during the transfusion of ABO non‐identical PC is determined by the presence of natural anti‐A IgM antibodies, the titer of which may increase after infections. The aim of the study was to evaluate the titer of anti‐A isohemagglutinins in platelet concentrate (PC) obtained by apheresis from group O donors who experienced SARS‐CoV‐2 infection, and to compare the titer before and after infection. A retrospective single‐center analysis of 21 PC donors with a previous COVID‐19 history was performed. The results showed neither a statistically important increase in the anti‐A IgM antibody titers nor a significant correlation between the anti‐A IgM antibody level and anti‐SARS‐CoV‐2S1 antibody titer in the donors with an asymptomatic or mild COVID‐19. Further population‐based studies on anti‐A titers are necessary for a comprehensive assessment of this phenomenon.

ABO incompatibility is not a barrier to allogeneic stem cell transplant but may result in acute hemolytic reactions. As stem cell product manipulation is cumbersome, we are reporting the effectiveness and safety of donor-type red cell infusion as a method of reducing acute hemolytic reaction while using marrow as stem cell source. In major ABO-mismatched bone marrow transplants, manipulation of marrow product requires expertise and expensive equipment, which may not be readily available to transplant centers in low- and middle-income regions. The aim behind our study is to report a safe and effective strategy to reduce isohemagglutinin titers and prevent donor marrow infusion reactions in major ABO-mismatched transplants. We retrospectively analyzed 303 consecutive allogeneic bone marrow transplants (BMTs) for beta thalassemia major, between August 2015 and March 2020, with either major (n = 41) or bidirectional (n = 14) mismatches. When isohemagglutinin titers were 1:32 or higher, donor-type packed red blood cell was divided into 4 aliquots, irradiated and administered over 4 days at incremental volumes. Patients were observed for hemolytic reaction, and if no reaction, bone marrow was infused without manipulation. Out of 55 patients, 20 received donor-type blood infusion. Twelve patients showed evidence of mild hemolysis. None developed severe hemolytic or anaphylactic reaction. Titers were rechecked in 14 patients and all had reduction in titers, except for one. Our experience demonstrated that donor-type PRBC infusion is safe and effective in preventing acute hemolysis in major ABO-mismatched stem cell transplants even with bone marrow as graft source.

BackgroundPure red cell aplasia (PRCA) is one of the important complications in major ABO-incompatible allogeneic hematopoietic stem cell transplantation (HSCT). The established pathogenic factor of PRCA is the persistence of high anti-donor isohemagglutinins. As previously verified, the conditioning regimen and donor type were the factors associated with the development of PRCA in the small-sized studies. Currently, the prevalence, risk factors, and prognosis of PRCA are still worth studying to provide evidence.MethodsWe conducted a prospective nested case-control study to determine the prevalence, donor-related factors, and the outcomes of PRCA following major ABO-incompatible transplantation. A total of 469 patients who underwent ABO-incompatible grafts were observed.ResultsNone of the patients were diagnosed with PRCA with minor or bidirectional ABO-incompatible HSCT. Thirteen of the187 patients (7%; 95% confidence interval [CI], 3.9%–11.9%) developed PRCA following major ABO-incompatible HSCT. Eleven of the 13 patients with PRCA recovered entirely. Donor type was an independent factor associated with post-HSCT PRCA (odds ratio [OR]=0.030; 95% CI, 0.003–0.321; P=0.004). The cumulative incidence rates of post-HSCT PRCA in the context of major ABO-incompatible HSCT were 0.8%, 13.1%, and 27.2% for the haploidentical donor (HID), unrelated donor, and matched related donor, respectively. No significant influence of PRCA on transplantation outcomes was observed.In conclusion, post-HSCT PRCA is a rare and less threatening complication in major ABO-incompatible HSCT. The majority of patients with PRCA could recover. Additionally, HIDs for recipients may have a low risk of post-HSCT PRCA. This trial was registered at www.chictr.org.cn (#ChiCTR2000041412).

Background Isohemagglutinins against ABO antigens absent on both recipient and donor red blood cells (RBCs) increase or decrease after ABO-incompatible hematopoietic stem cell transplantation (HSCT). However, few reports have described the changes in the isohemagglutinin titers and the characteristics in patients with recurrent hematologic conditions after ABO-incompatible HSCT. Case report A 59-year-old female with acute erythroid leukemia received a peripheral blood stem cell transplant from her HLA-haploidentical daughter. The patient was typed as group O with anti- A (4+) and B (4+) isohemagglutinins, while the donor was typed as group B. The bone marrow cells achieved complete donor cell chimerism on Day 13 after HSCT. On Day 120, the patient showed 97% B RBC type with persistent anti-A (3+) and without anti-B antibodies. On Day 375, her leukemia relapsed, and recipient type O RBCs and anti-B antibodies sequentially reemerged. However, clinicolaboratory hemolysis and erythroid aplasia were not detected in the patient. Results The post-HSCT sera agglutinated the allo B RBCs, but not the donor B RBCs, while the pre-HSCT sera agglutinated both RBCs. The burst-forming/colony-forming units of erythroid formation from the donor peripheral blood stem cells were impaired by only the pre-HSCT sera and not by the post-HSCT sera. Conclusion To our knowledge, this is the first report investigating the characteristic changes of isohemagglutinins between the pre- and post-HSCT sera in a patient with recurrent acute myeloid leukemia. The present study suggests that the plasma cells producing anti-donor B RBCs in the patient have been selectively eliminated or induced into an anergic state by the post-HSCT immunologic reconstruction.

Patient: Female, 61 Final Diagnosis: Acute intravascular hemolysis Symptoms: Cherry colored urine • chills Medication: — Clinical Procedure: — Specialty: Pathology Objective: Rare disease Background: Platelet transfusion is a common clinical practice required for therapeutic purposes in the setting of symptomatic thrombocytopenia, and, in some cases, prophylactically for asymptomatic thrombocytopenia. Crossmatch compatibility is not routinely done for platelet transfusions, and transfusion of ABO non-identical platelets has been adapted as an acceptable clinical practice. Acute intravascular hemolysis due to ABO non-identical platelets is a rare but clinically significant entity. Our case report reinforces the importance of a vigilant clinical approach in case of ABO non-identical platelet transfusions. Case Report: We report the case of 61-year-old woman with blood group A, with chemotherapy-induced asymptomatic thrombocytopenia, who developed acute intravascular hemolysis following transfusion of group O single-donor platelets (SDPs). The patient was transfused 1 unit of single-donor platelets for bleeding prophylaxis, as her platelet count dropped to less than 10×109/L due to chemotherapy that she was receiving for acute myeloid leukemia (AML). Immediately after transfusion, the patient noticed cherry-colored urine; and within 12 h of transfusion, her hemoglobin dropped by more than 2.5 g/dL. A post-transfusion immunohematology work-up showed positive DAT and high titers of anti-A1 isohemagglutinins in the platelet donor, supporting the diagnosis of acute intravascular hemolysis due to ABO non-identical platelets. Conclusions: The possibility of acute intravascular hemolysis should be kept in mind in cases of transfusion of group O single donor platelets to non-group O recipients. ABO non-identical platelets, even with low isohemagglutinin titers, can cause significant adverse effects, particularly in newborns, children, and immunosuppressed and transfusion-dependent patients; therefore, a cautious clinical approach is recommended.

Background Hemolysis at the time of graft infusion is one of the immediate complications in major ABO-incompatible allogeneic hematopoietic stem cell transplants (HSCTs). We conducted a retrospective analysis to evaluate the efficacy of donor-type fresh frozen plasma (FFP) in reducing isohemagglutinin titer and preventing hemolysis, as well as its effect on delayed red cell engraftment. Materials and methods This is a single-center study on a series of 380 allogeneic HSCT between 2005 and 2015; of which 99 were either major (n = 74) or bidirectional (n = 25) ABO mismatched. Pre-transplant infusion of FFP, post-transplant complications and transfusion requirements were determined by retrospective review of individual medical records. Laboratory results were also reviewed for evidence of hemolysis and pure red cell aplasia (PRCA). Results Clinical manifestation of hemolysis attributable to ABO mismatch was present in one recipient of major ABO-incompatible peripheral blood stem cell (PBSC) with a titer of 64. Another recipient of major ABO-incompatible PBSC with a titer of 64 showed biochemical evidence of hemolysis. Both patients recovered with supportive treatment. Hemolysis did not occur in any patients with titer of 32 or less at the time of stem cell infusion. We were unable to demonstrate the influence of any variables on the incidence of PRCA. Conclusion Our experience demonstrated that donor-type FFP is safe and effective in preventing acute hemolysis in major ABO-mismatched HSCT. We have also established the titer of 64 as the threshold that may cause hemolysis and therefore efforts should be made to reduce titer to below this level.

BACKGROUND: Blood groups and anti-A isohemagglutinin may be involved in susceptibility to SARS-CoV-2 infection. MATERIALS AND METHODS: We retrospectively studied 268 COVID-19 convalescent plasma donors and 162 COVID-19 inpatients (total 430 subjects, confirmed by RT-PCR) and 2,212 healthy volunteer first-time blood donors as a control group. These were further divided into two groups: those with anti-A (blood types O and B) and those without it (types A and AB). Titres of nucleoproteins, and neutralizing SARS-CoV-2 antibody were measured in the convalescent plasma donors and inpatients. Multivariate logistic regression and non-parametric tests were applied. RESULTS: Persons having types O or B showed less infection prevalence than those of types A or AB (OR = 0·62, 95% CI 0·50-0·78; P

Background: Civilian and military guidelines recommend early balanced transfusion to patients with life-threatening bleeding. Low titer group O whole blood was introduced as the primary blood product for resuscitation of massive hemorrhage at Haukeland University Hospital, Bergen, Norway, in December 2017. In this report, we describe the whole blood program and present results from the first years of routine use. Study design and methods: Patients who received whole blood from December 2017 to April 2020 were included in our quality registry for massive transfusions. Post-transfusion blood samples were collected to analyze isohemagglutinin (anti-A/-B) and hemolysis markers. Administration of other blood products, transfusion reactions, and patient survival (days 1 and 30) were recorded. User experiences were surveyed for both clinical and laboratory staff. Results: Two hundred and five patients (64% male and 36% female) received 836 units in 226 transfusion episodes. Patients received a mean of 3.7 units (range 1–35) in each transfusion episode. The main indications for transfusion were trauma (26%), gastrointestinal (22%), cardiothoracic/vascular (18%), surgical (18%), obstetric (11%), and medical (5%) bleeding. There was no difference in survival between patients with blood type O when compared with non-group O. Haptoglobin level was lower in the transfusion episodes for non-O group patients, however no clinical hemolysis was reported. No patients had conclusive transfusion-associated adverse events. Both clinical and laboratory staff preferred whole blood to component therapy for massive transfusion. Discussion: The experience from Haukeland University Hospital indicates that whole blood is feasible, safe, and effective for in-hospital treatment of bleeding. publishedVersion

Up to 40% of donor-recipient pairs in SCT have some degree of ABO incompatibility, which may cause severe complications. The aim of this study was to describe available options and survey current practices by means of a questionnaire circulated within the EBMT Pediatric Diseases Working Party investigators. Major ABO incompatibility (donor's RBCs have antigens missing on the recipient's cell surface, towards which the recipient has circulating isohemagglutinins) requires most frequently an intervention in case of bone marrow grafts, as immediate or delayed hemolysis, delayed erythropoiesis and pure red cell aplasia may occur. RBC depletion from the graft (82%), recipient plasma-exchange (14%) were the most common practices, according to the survey. Graft manipulation is rarely needed in mobilized peripheral blood grafts. In case of minor incompatible grafts (donor has isohemagglutinins directed against recipient RBC antigens), isohemagglutinin depletion from the graft by plasma reduction/centrifugation may be considered, but acute tolerability of minor incompatible grafts is rarely an issue. According to the survey, minor ABO incompatibility was either managed by means of plasma removal from the graft, especially when isohemagglutinin titer was above a certain threshold, or led to no intervention at all (41%). Advantages and disadvantages of each method are discussed.

Pure red cell aplasia (PRCA) after ABO-incompatible allogeneic hematopoietic stem cell transplantation (HSCT) is caused by persisting host-derived isohemagglutinins directed against donor red blood cell (RBC) antigens. ABO antigen-specific immunoadsorption (ABO-IA) with Glycosorb®, commonly used for desensitization therapy in ABO-incompatible living donor renal transplantation, specifically eliminates circulating isohemagglutinins and might represent a novel treatment option for post-HSCT PRCA. In this prospective observational (n = 3) and retrospective (n = 3) analysis of six adult HSCT-recipients with PRCA, ABO-IA was initiated at 159 (range: 104-186) days following HSCT. The median treatment frequency was 4.5 (range: 3.9-5.5) sessions/week. ABO-IA-treatment led to a continuous decrease in isohemagglutinin titers. Reticulocytes increased to ≥30 G/L after 17.5 (range: 4-37) immunoadsorption sessions over 28.5 (range: 6-49) days and continued to rise after that. By the end of the 3-month follow-up period after discontinuation of ABO-IA, all patients showed a sustained remission of PRCA and were independent of erythropoietin-stimulating agents and transfusions. No case of infection or graft-versus-host disease was observed. After a median follow-up of 22.03 (range: 6.08-149.00) months after ABO-IA-treatment, all patients were alive and showed a stable RBC engraftment of the donor blood group. Our data provide the first evidence for ABO-IA as an effective treatment for post-HSCT PRCA.

Background With more hospitals using low-titer group O whole blood in trauma resuscitation, having an efficient screening method for low-titer donors is critical. Our blood center uses an automated screen for high-titer isohemagglutinins in our platelet donations while collecting detailed donor demographic information. Using this data, we can identify key demographics often associated with titer status, thereby helping develop a donor-triaging method for titering. Study Design and Methods Titer results were read with an automated microplate system as either high or low, based on agglutination, with a cutoff equivalent to 1:256 (both anti-A and anti-B). Donor demographic data analyzed included date of donation, blood group, age, gender, and ethnicity. Results 57,508 donations were collected from 2073 unique donors between 2014 and 2018. We found the following demographics to be correlated with titer status: gender, ABO blood group, age, and ethnicity. Variability in titer status was identified in 215 individuals. This represented around 10 % of the total unique donors and was split equally amongst gender. We also found that donors between the ages of 41–60 ha d the highest likelihood of having variability in titer status, peaking at 13 %, and this proportion declined past age 60. Conclusion Titer status is associated with the following donor demographics: gender, ABO type, age, and ethnicity. We also discovered that variability in titer status is correlated with age. In blood centers that do not have automated and routine titer screening procedure, these findings could be used as a method to efficiently identify low-titer donors a-priori.

Background ABO compatibility restriction on solid organ transplantation limits organ availability. In an effort to increase organ availability, pediatric ABO-incompatible heart transplants (ABOiHT) are now performed with similar outcomes to ABO-compatible transplants. Transfusion support can be challenging and currently there are no standard guidelines for blood product support, ABO isohemagglutinin (IH) titer cutoffs for transplant eligibility, or therapeutic intervention for these patients. The study aim was to survey current blood bank and antibody reduction practices for pediatric ABOiHT in the United States and Canada. Study design and methods A Web-based survey was sent to 50 US and Canadian pediatric blood bank directors. Participants were queried regarding pre-, intra-, and postoperative blood product support; ABO IH titer testing; and antibody reduction practices in ABOiHT recipients. Results We analyzed 21 responses from US and Canadian centers that perform pediatric ABOiHT. There is wide variation in the type of blood products transfused and the modification of these products among respondents in the pre-, intra-, and postoperative settings. The frequency of testing ABO IH titers, implementing therapeutic intervention, and the type of therapeutic intervention also vary greatly among the institutions. Conclusion Transfusion support of children with ABOiHT varies widely among blood banks in the United States and Canada. The choice of blood products and modifications utilized, titer thresholds for organ selection and medical decision points, and antibody reduction strategies are not standardized from center to center. As pediatric ABOiHTs become more common, a better understanding of optimal transfusion support and therapeutic intervention is needed.

Background Since 1996, ABO-incompatible heart transplantation has been undertaken by performing whole-body plasma exchange to remove isohemagglutinins using the cardiopulmonary bypass (CPB) circuit at the time of transplantation. This requires large volumes of donated blood and blood products, causes hemodynamic instability during the exchange transfusion, and limits practical use to small children. We sought to determine the efficacy of anti-A/B immunoadsorption within the CPB circuit on removal of isohemagglutinins in an ex vivo setting before its use clinically. Methods An anti-A/B immunoadsorption column was placed into a CPB circuit mimicking a typical ABO-incompatible transplant patient, which had been primed with type O whole human blood. Samples were taken for determination of isohemagglutinin titers following each plasma volume pass through the anti-A/B immunoadsorption column. Results There was a linear decrease of at least 1 dilution seen in both anti-A and anti-B IgG and IgM antibodies with each plasma volume pass through the column. This predictable removal allowed the formulation of selection criteria for ABO-incompatible heart transplantation given the reciprocal of titer and patient weight. This degree of predictability allowed us to use it successfully in the clinical setting, reducing antibodies to an undetectable level during ABO-incompatible heart transplantation. Conclusions The incorporation of an anti-A/B immunoadsorption column into the extracorporeal circuit reduces allogeneic blood product requirement for ABO-incompatible heart transplantation, while providing efficacious removal of anti-A and anti-B isohemagglutinins. This can be undertaken within the time period of CPB before graft reperfusion and expands the potential recipient pool to larger patients with higher isohemagglutinin titers.

Background Platelets (PLTs) collected and stored in PLT additive solution Intersol (PAS-C) are presumed to reduce recipient exposure to donor plasma components; however, the effects of PAS-C on PLT supernatant composition are poorly defined. Therefore, we compared the total protein concentration, isohemagglutinin titers, and HLA antibodies in supernatants of PAS-C PLTs to plasma PLTs. Study design and methods Apheresis PLTs from group O blood donors were collected into either 100% donor plasma (n = 50) or a mixture of 65% PAS-C/35% donor plasma (n = 50). Within 12 hours of collection, samples of the PLT supernatant were frozen and stored. PLT supernatants were assayed for total protein concentration and anti-A and anti-B titers and screened for HLA antibodies. Samples positive for HLA antibodies were further tested using single-antigen bead assays to determine antibody strength and specificity. Results Supernatants of PAS-C PLTs had significantly lower total protein concentration and anti-A and anti-B titers compared to plasma PLTs. There was no significant difference in the number of HLA antibody screen-positive PAS-C (3/50) compared to plasma PLT supernatants (2/50); however, the HLA antibody screen-positive supernatants of PAS-C PLTs had fewer HLA specificities (2) compared to those of the plasma PLTs (18). Conclusion Decreased plasma proteins likely underlie lower rates of allergic and febrile, nonhemolytic transfusion reactions from the infusion of PAS-C PLTs. Decreased anti-A and anti-B titers may prevent hemolysis from minor ABO mismatch. Lower HLA antibody specificities may mitigate transfusion-related acute lung injury.

Background AABB standards require a policy for assessing transfusing ABO-incompatible plasma. After a fatal hemolytic event with incompatible plasma, our institution instituted platelet donor population titer method for ABO antibodies on the PK7300, with high-titer being defined as having isohemagglutinin titers greater than 256. We recently switched titering platforms to the Neo Iris and we seek to determine the equivalent isohemagglutinin high-titer cutoff on the Neo Iris as compared to the PK7300. Methods We measured the titers on 299 apheresis platelet donors and compared its performance characteristics at various cutoffs to the PK7300 reference standard. Discrepant results were manually diluted and retested on the Neo Galileo. Furthermore, since the Neo Iris is able to determine isotype and antigen specific titers, we also characterized these features in our donor population. Results IgM titer of 128 on the Neo Iris has better accuracy compared to the titer of 64 (94 % vs 93.6 %). Eleven of sixteen discordant results were in agreement with Neo Iris. Blood group O had the highest IgG antibody titers for both anti-A and anti-B (p = 8.4E-17 and 4.3E-09, respectively). Additionally, group O donors exhibited lower anti-A2 than anti-A1 IgG titers. Discussion The Neo Iris titer cut-off of 128 had the best overall accuracy and correlation with a 256 cut-off on our laboratory developed test on the PK7300 platform. Additionally, we found that group O donors had the highest titer antibodies, with typically higher IgG titers than IgM, and generally multiple dilution levels greater than other blood types.

Background. Due to its high sensitivity, the flow cytometry crossmatch (FCXM) has been described as valuable tool for identifying an optimal donor. We here focused on the impact of ABO incompatibility on FCXM results. Methods. We analyzed 29 ABO incompatible and 89 ABO compatible donor-recipient pairs (73 and 175 data sets, respectively) prior to living donor kidney transplantation. In all patients, lymphocytotoxic crossmatches for B and T cells were negative. Results. Recipients with blood group O (A to O and B to O) displayed significantly (P < 0.05) higher T-FCXM results than those with blood group A and B (A to B, B to A and AB to A), respectively. Donor-specific T-FCXM responses (Δ MFI values) were significantly higher (P < 0.05) in ABO incompatible vs. compatible pairs (ABO incompatible recipients with blood group O: 32 ± 6; with blood group A: 19 ± 7; with blood group B: 7 ± 4; recipients with ABO compatibility: 3 ± 2, respectively, data represent mean ± SEM). Consistent with the T-FCXM results donor-specific isohemagglutinins (IgG titers) were significantly higher in recipients with blood group O vs. A, both prior to rituximab treatment and plasmapheresis/immune adsorption (P = 0.004) and immediately prior to transplantation, i.e., after rituximab and antibody-depleting therapies (P = 0.04). Conclusions. ABO incompatibility was associated with higher T-FCXM responses, especially in recipients with blood group O. This finding has major impact on the interpretation of flow crossmatch results. Current cut-off values need to be reassessed in the ABO incompatible setting. This article is protected by copyright. All rights reserved.

Background Isohemagglutinins (anti-A and anti-B) mediate hemolytic transfusion reactions, antibody-mediated rejection of solid-organ transplants, and delayed engraftment after stem cell transplant. However, quantification of isohemagglutinins is often labor intensive and operator dependent, limiting availability and interfacility comparisons. We evaluated an automated, solid-phase and agglutination-based antibody titer platform versus manual gel testing. Study design and methods Plasma samples were obtained from 54 randomly selected patients. Titers were determined by our laboratory's standard assay (manual dilution followed by manual gel testing) and were compared to results obtained on a fully automated blood bank analyzer (Galileo NEO, Immucor). The analyzer determined immunoglobulin G (IgG) antibodies using solid-phase and immunoglobulin M (IgM) antibodies by direct hemagglutination. Results Isohemagglutinin titers obtained by manual gel versus the automated assay generally (>80%) agreed within one doubling dilution, and always (100%) agreed within two dilutions. Among O samples, the gel titer and the highest titer obtained with the automated assay (either IgG or IgM) were similar in paired, nonparametric analysis (p = 0.06 for anti-A; p = 0.13 for anti-B). Gel titers from group A and group B patients were slightly higher than the highest titer obtained using the automated assay (p = 0.04 for group A; p = 0.009 for group B), although these differences were within the accepted error of measurement. Conclusion Manual and automated methodologies yielded similar isohemagglutinin titers. Separate quantification of IgM and IgG isohemagglutinins via automated titration may yield additional insight into hemolysis, graft survival after ABO-incompatible transplantation, and red blood cell engraftment after ABO-incompatible stem cell transplant.

Purpose UNOS has liberalized the criteria for ABO incompatible (ABOi) heart transplant (HT) for patients less than two years of age. However, to date, the impact of high isohemagglutinin titers on graft survival has not been studied. Methods Pediatric recipients (age ;1:16). Results Of 1687 HT performed in patients less than 2 years of age, 209 (13%) received ABOi transplants. (Figure 1) Majority of recipients listed for ABOi transplants had blood group O (67.5%). 18/209 (8.6%) recipients had high titers pre-transplant. Compared to ABOc recipients, ABOi recipients had similar distribution of age, gender, ethnicity, and were on similar cardiac support (inotropes, ventilator, ECMO, VAD) (p >; 0.05 for all). The wait-list times were also similar between both groups (64.2±50.8 vs 63.5±45.4 days, p >; 0.05). In patients less than 2 years, compared to ABOc transplants, ABOi transplants had similar 1-year (12.8 vs. 11%; P=0.39) and overall graft failure (21.1 vs. 19.9%; P=0.68). Compared to those with low-titers, patients transplanted with high isohemagglutinin titers, had similar 1-year (5.6% vs 12.6%; P=0.70) and overall graft failure (16.7% vs 18.2%; P=0.99) (Figure 1). Conclusion Overall, utilization of ABOi transplantation is low in the relevant age group with most common recipients being blood group O. The use of ABOi transplant does not involve patient selection bias and has not affected the wait time. ABOi transplant recipients have graft survival similar to ABOc recipients. Most importantly, strength of anti-A or B titers do not impact graft survival in ABOi recipients.

Purpose ABO-incompatible (ABO-I) heart transplantation (HT) is used in children Methods Two MP (Prismaflex) and two CP (Spectra Optia, Terumo BCT) circuits were incorporated into four separate CBP circuits primed with high titer type O donor whole blood. Assays were performed to determine baseline isohemagglutinin titers and then at 30 minute increments until completion of the run (two plasma volume exchanges) at two hours. Results There was a decrease in anti-A and anti-B IgM and IgG titers with both MP and CP. Mean anti-A and anti-B titer reduction was 4.625 titers (93.7% change) and 4.375 titers (93.8% change) using MP and CP, respectively. At 2 hours of apheresis, CP reduced 62.5% of all ITs to ≤ 1:4, while MP reduced 50% of ITs to ≤1:4. Both demonstrated similar hemolytic and thrombotic profiles. Conclusion In this in vitro plasmapheresis model of IT reduction, both MP and CP incorporated into the CPB circuit can be used quickly and effectively to reduce circulating IT. While CP may have some greater efficiency, further study is necessary to verify this in vivo.

ABO-incompatible liver transplants (ABO-ILT) have re-emerged as an alternate option for select patients awaiting transplant. However, treatment protocols for children undergoing deceased donor ABO-ILT are not standardized. We implemented a novel immunosuppression (IS) protocol for children undergoing deceased donor ABO-ILT based on pre-transplant isohemagglutinin (IH) titers. Children with high pre-transplant IH titers (≥1:32) underwent an enhanced IS protocol including plasmapheresis, rituximab, IVIG, and mycophenolate, while children with IH titers ≤ 1:16 received steroids and tacrolimus. We retrospectively assessed our outcomes of ABO-ILT with ABO-compatible recipients of similar age and diagnosis over a 2-year period. Ten children with median age of 8.9 months underwent ABO-ILT, 4/10 patients underwent enhanced IS due to high IH titers. Rates of complications (rejection, infections, biliary and vascular) at both 1 year and up to 3 years post-transplant were comparable between the groups. Patients with ABO-ILT had good graft function with 100% survival at a median follow up of 3.3 years. In conclusion, immunosuppression tailored to pre-transplant IH titers in pediatric deceased donor ABO-ILT is feasible and can achieve outcomes similar to ABO-CLT at 1 and 3 years post-transplantation.

ABO-incompatible (ABOi) cardiac transplantation is now used widely in infants with isohemagglutinin titers1:4, but there is increasing evidence that ABOi transplantation can also be used in children with significantly higher titers. We reviewed our high-titer ABOi transplants and report our results here.Patients who underwent ABOi cardiac transplantation from 2000 to 2013 with pre-existing isohemagglutinin titers of ≥1:16 were identified from departmental databases. Outcomes were reviewed using medical and laboratory records.Thirty patients underwent ABOi cardiac transplantation between 2000 and 2013. Twelve (40%) had pre-transplant isohemagglutinin titers of ≥1:16 and were included for further study. Median age was 14.9 (range 9.8 to 107.3) months and median weight was 9.6 (range 7.6 to 25) kg. Five (42%) were male. Pre-transplant diagnosis was cardiomyopathy in 8 of 12 (67%) and congenital heart disease in 4 of 12 (33%). Highest pre-transplant isohemagglutinin titer was 1:256 in 2 patients. Four patients (33%) had early antibody-mediated rejection (AMR), all within 15 days post-transplant. Management included use of rituximab, bortezomib, immunoadsorption and eculizumab. Three patients died but no deaths were associated with high isohemagglutinin titers.ABOi cardiac transplantation in patients with isohemagglutinin titers ≥1:16 is possible. AMR may occur early and immunoadsorption has proven effective at decreasing antibody titers.

OBJECTIVE: Brazilian legislation has recently suggested the use of the qualitative hemolysin test instead of isohemagglutinin titers as prophylaxis for acute hemolysis related to plasma-incompatible platelet transfusions. The efficacy of this test in preventing hemolytic reactions has never been evaluated while isohemagglutinin titers have been extensively studied. The main objective of this study was to evaluate the correlation between the results of these two tests. The impact of each type of prophylaxis on the platelet inventory management and the ability of the qualitative hemolysin test to prevent red cell sensitization after the transfusion of incompatible units were also studied. METHODS: A total of 246 donor blood samples were evaluated using both isohemagglutinin titers and the qualitative hemolysin test, and the results were statistically compared. Subsequently, 600 platelet units were tested using the hemolysin assay and the percentage of units unsuitable for transfusion was compared to historical data using isohemagglutinin titers (cut-off: 100). Moreover, ten patients who received units with minor ABO incompatibilities that were negative for hemolysis according to the qualitative hemolysin test were evaluated regarding the development of hemolysis and red cell sensitization (anti-A or anti-B). RESULTS: Isohemagglutinin titration and the results of qualitative hemolysin test did not correlate. The routine implementation of the qualitative hemolysin test significantly increased the percentage of platelet units found unsuitable for transfusions (15-65%; p-value

BACKGROUND Recent publications have raised concerns that liquid immune globulins (IGs) may be associated with either a higher or a lower frequency of hemolytic events compared to lyophilized IGs, among other reasons due to the differences of their isohemagglutinin content. The aim of this study was to evaluate the relationship of hemolytic events to product presentation (liquid versus lyophilized) and to examine the relationship between total IG doses administered and the individual isohemagglutinin titers of IG lots infused. STUDY DESIGN AND METHODS The reporting rate as well as the proportional reporting rate (PRR) of hemolytic events for liquid (Gammagard liquid [GGL]) and lyophilized IG (Gammagard S/D [GGSD]) received spontaneously from the United States was calculated. For all hemolytic events received spontaneously from global sources, total IG doses (g/kg body weight) and the loading dose of isohemagglutinins (total IG dose infused × isohemagglutinin titers of infused lots) were determined. RESULTS With 0.27 and 0.33 cases per 1 million grams distributed, the reporting rates for GGL and GGSD are comparable, further confirmed by a PRR of 1.0 (95% confidence interval, 0.4-2.7). Hemolytic events for GGL and GGSD were observed with low loading doses of isohemagglutinins, and lots with high isohemagglutinin titers did not contribute to the development of hemolytic events in a higher proportion than lots with low titers CONCLUSIONS Hemolysis associated with GGL or GGSD can occur even with low loading doses of isohemagglutinins. Data presented do not indicate that high isohemagglutinin titers of IG products play a major role in the development of these events.

BACKGROUND: ABO-incompatible (ABOi) infant heart transplantation results in B-cell tolerance to graft A/B antigens, confirming human susceptibility to acquired immunologic or "neonatal" tolerance as described originally in murine models. Starting with this clinical observation, we sought to model neonatal ABOi organ transplantation to allow mechanistic studies of tolerance. METHODS: Plasma anti-A/B antibodies were measured over time in piglets to establish developmental antibody kinetics. Blood group O piglets received kidney allografts from group A (AO-incompatible) or group O (AO-compatible) donors under cyclosporine immunosuppression. Anti-A antibodies were measured serially after transplantation; A/H antigen expression and allograft rejection were assessed in graft biopsies. RESULTS: Anti-A antibodies developed in naive piglets in a kinetic pattern analogous to human infants; anti-B remained low. After transplantation, anti-A antibodies developed similarly in AO-incompatible and AO-compatible groups and were not suppressed by cyclosporine. A/H antigen expression was persistent in all graft biopsies; however, A/H antigens were not detected in vascular endothelium. Cellular and antibody-mediated rejection was absent or minimal in early and late biopsies in both groups, with one exception. CONCLUSIONS: Naturally delayed isohemagglutinin production in piglets is analogous to the developmental kinetics in human infants. However, in contrast to deficient anti-A antibody production as seen long-term after "A-into-O" infant heart transplant recipients, normal anti-A antibody production after "A-into-O" piglet kidney transplantation indicates that tolerance did not develop despite graft A antigen persistence. These findings suggest that the impact on the host immune system of exposure to nonself ABH antigens during early life in human heart versus porcine kidney grafts may depend on expression in vascular endothelium.

The impact of donor-recipient ABO incompatibility on long-term BMT outcomes remains controversial. A common strategy is to deplete the donor marrow of red cells, although this variably reduces the number of CD34+ cells. This 10-year retrospective study assessed the impact of recipient plasma exchange in major ABO-incompatible allogeneic BMT on outcomes and survival. Target Ab titres were ≤ 1:4 for anti-A and ≤ 1:8 for anti-B. Patients with higher titres underwent plasma exchange before marrow infusion. Of 133 patients who underwent allogeneic BMT, 34 had a major ABO-incompatible donor. The median number of exchanges was 2 (range 1-4). There were no acute haemolytic transfusion reactions. Engraftment times, transfusion requirements and acute and chronic GVHD were no different from those of patients with an ABO-identical donor. Treatment-related mortality at 100 days was 21% in the group with a major ABO-incompatible donor and 17% in the group with an identical donor (P=0.8). Plasma exchange of the recipient is a safe method of managing donor-recipient major ABO incompatibility before BMT without the risk of haematopoietic progenitor cell loss associated with red cell depletion of the graft.

ABO-mismatched bone marrow transplants have resulted in delayed red cell production in patients who have persistently elevated anti-ABO isohemagglutinin titers. We present a patient with chronic myelogenous leukemia who received an HLA-matched, ABO-incompatible bone marrow transplant from his sister. Post-transplant, he developed pure red cell aplasia with exuberant production of donor red cell precursors by in vitro BFU-E assay. Restriction fragment length polymorphism (RFLP) analysis of bone marrow, peripheral blood and BFU-E colonies demonstrated only donor type DNA post-transplant. However, the patient had persistently elevated isohemagglutinin titer and Ph1 chromosome-positive metaphases on chromosome analysis, indicating the presence of persistent host lymphocytes. With onset of acute graft vs. host disease (GVHD), the isohemagglutinin titer dropped, Ph1 chromosome-positive metaphases disappeared, and full hematopoietic recovery ensued. Longitudinal analysis of RFLP's, isohemagglutinin titers and chromosomes may be helpful in understanding the immunological interplay following allogeneic bone marrow transplantation.

Introduction Adult ABO-incompatible liver transplantation is associated with a high risk of graft failure due to antibody-mediated humoral rejection (AMR). We evaluated the effects of a protocol using preoperative removal of isohemagglutinin, rituximab prophylaxis, and intrahepatic arterial infusion (HAI) therapy for ABO-incompatible adult living donor liver transplantation (LDLT). Patients and Methods Between March 2005 and September 2007, we performed 94 adult LDLTs, including 3 ABO-incompatible cases. All ABO-incompatible LDLT patients underwent administration of 375 mg/m2 rituximab on preoperative days 15 and 8 without splenectomy, as well as preoperative removal of isohemagglutinin using plasma exchange, and HAI therapy for postoperative 21 days. Results Postoperative anti-donor blood-type antibody titer and B-cell level were effectively suppressed by early rituximab prophylaxis in all patients. HAI therapy was effective to prevent AMR and even resolved mild AMR. However, all patients suffered bacterial infections, and 1 died of septicemia with good graft function. Another subject died of late-onset AMR that occurred after discontinuation of HAI therapy. Conclusion An ABO-incompatible LDLT protocol using plasma exchange, rituximab prophylaxis, and intra-HAI therapy effectively suppressed anti-A/B antibody and prevented AMR. But this protocol should be further improved to reduce infectious complications and late onset of AMR.

Donor organ shortage in pediatric heart transplantation (HTx) is causing mortality rates of 30-50% on the waiting list. Due to immaturity of the immune system of newborns and infants, ABO-incompatible HTx may be an option to increase donor availability. We present our experience with ABO-incompatible HTx.Three infants were transplanted ABO-incompatible since 12/2004: (1) hypoplastic left heart complex, (2) restrictive hypertrophic cardiomyopathy, (3) dilative cardiomyopathy. Age at HTx was 7, 5, and 3.5 months. All recipients had blood type O, donors were A, A, and B. Informed consent was given by parents, the ethics committee, and Eurotransplant.Preoperative isohemagglutinin titers were low (Patient 1: 1:4 for anti-A1, A2, B, Patient 2: 1:4, 1:1, 1:4 for anti-A1, A2, B, respectively, and Patient 3: 0 for all, but quick spin 1+ for all). Intraoperatively, plasma was separated from red blood cells and discarded up to six times until antibodies were eliminated. Immunosuppressive induction with ATG was started for 5 days. Basic immunosuppression consisted of tacrolimus, mycophenolate mofetil, and prednisone. Extubation was performed on days 15, 2, and 1, respectively. After a follow-up of 17, 16, and 12 months all patients are well, ventricular function is excellent without any acute rejection periods; Patient 1 is still on dialysis. Isohemagglutinin titers against donor blood type have disappeared in follow-up.ABO-incompatible cardiac transplantation shows good short-term results in young infants and seems to be a safe procedure to lower the mortality on the waiting list.

ABO-incompatible kidney and liver transplants can be performed successfully by depleting anti-A or anti-B isoagglutinins pretransplant and by suppressing their development posttransplant. With these protocols, humoral rejection can be avoided. Recovery of isohemagglutinin antibody levels without humoral rejection suggests accommodation, the ability of an organ allograft to survive in the presence of anti-graft antibodies and complement, may be the protective mechanism preventing late antibody-mediated rejection. This may be related to the ability of endothelial cells, the target of antibody-mediated rejection, to upregulate protective genes, including those encoding heme oxygenase-1 (HO-1) that then block the proinflammatory response of the endothelial cells and thereby rejection. Induced expression of HO-1 in the endothelial cells of the graft before transplantation may prevent apoptosis of those cells after transplantation, and prevent the generation of endothelial cell-based inflammation that leads to rejection. Experimental and clinical studies in ABO-incompatible models will be required to examine this hypothesis, and determine whether carbon monoxide (CO) might be able to modulate antibody-mediated rejection after ABO-incompatible transplantation.

Introduction of effective treatments such as (double filtration) plasmapheresis, splenectomy, intravenous immunoglobulin and potent immunosuppressive agents including anti-CD20 monoclonal antibody, has greatly improved graft outcome in ABO-incompatible transplantation. The measurement of anti-blood group A/B antibody titers is considered to be important, because it would provide useful information on prognosis and indication of transplantation, selection of treatments and prediction of acute rejection. Isohemagglutinin assay in serial-doubling dilutions of serum sample by tube test has been basically used in most institutions. However, detailed assay procedure seemed to vary between institutions. Furthermore, the determination by visual observation might cause a problem of inter-examiner variability. The Japanese ABO-Incompatible Transplantation Committee has conducted a series of nationwide surveys to assess the current status of inter-institutional variation in measurement of anti-A/B antibody titer. In the first survey, serum samples from 6 healthy volunteers with blood groups A (n = 2), B (n = 2) and O (n = 2) were sent to 29 institutions where ABO-incompatible kidney or liver transplantation has been performed. Anti-A/B antibody titer was measured by its own protocol. Inter-institutional difference of measured values reached to 32-fold and 256-fold in IgM and IgG, respectively. As this variability was too wide for detailed analysis, the provisional standard protocol for the assay was determined according to the result of questionnaire survey. Next, 38 and 40 institutions participated in the second (in 2004) and the third survey (in 2005), respectively. Anti-A/B antibody titers of serum samples were measured by the standard procedure. Analysis of survey revealed that intra-institutional variation was reduced to below 8-fold (mostly 2- to 4-fold), although several institutions still needed some guidance. Standardization of the assay procedure and quality control survey would be necessary to improve the accuracy of measurement. Significance of measurement of anti-A/B antibody titer in ABO-incompatible transplantation should be discussed after the result of multi-center study is obtained.

Background: The measurement of anti-blood groups A and B antibody (Ab) titers is considered to be important in ABO-incompatible transplantation. However, no standard method for quantitative determination has yet been established in Japan. Inter-examiner variability was likely because Ab titer was determined mainly by visual observation. In order to assess inter-institutional variation in the measurement of anti-A/B Ab titer, a series of surveys was conducted by the Japanese ABO-incompatible Transplantation Committee. Methods and Results: In 2003, the first national survey was conducted. Serum samples from six healthy volunteers with blood groups A (n=2), B (n=2) and O (n=2) were sent to 29 institutions and anti-A/B Ab titer was measured by their customary methods. Isohemagglutinin assay in serial-doubling dilutions of serum using a test tube was widely used in all institutions. Inter-institutional difference between maximum and minimum value reached as much as 32-fold in immunoglobulin M (IgM) and 256-fold in IgG. As detailed protocol for assay seemed to be different between institutions, we attempted to standardize the protocol based on the result of a questionnaire survey. In 2004, a second survey was conducted in the same manner as the previous one, except participation involved 38 institutions and the measurement was performed in a uniform way using a provisional standard protocol. Analysis of the survey revealed that intra-institutional variation was reduced to below eightfold, except that several institutions showed a large difference from the mean titer and required some guidance. Conclusions: A periodical quality control survey is considered necessary to improve the accuracy of measurement. Anti-A/B Ab titer would provide useful information towards the prediction of rejection and the indication of treatments such as (double filtration) plasmapheresis, splenectomy, anti-CD20 monoclonal antibody and intravenous immunoglobulin. Standardization of the assay for anti-A/B Ab titer is essential for the fulfillment of a precise multicenter study, which will elucidate the significance of the measurement of anti-A/B Ab titer.

We report a case of pure red cell aplasia (PRCA) subsequent to an allogeneic bone marrow transplantation with a major ABO mismatch, which was resistant to the standard treatment options such as plasma exchange, erythropoietin and changes in the immunosuppressive treatment. Accordingly, two cycles of Rituximab therapy were administered without success. The patient had a chronic graft-vs.-host disease of the liver, which meant that an additional donor leukocyte infusion could not be introduced. Instead, purified CD34(+) cells were administered after fludarabine and antithymocyte globulin therapy. As a result, the PRCA was resolved and the antidonor isohemagglutinin titer became undetectable.

A serological follow‐up study was carried out on 27 children (1–12 years old) with visceral and/or ocular toxocariasis, after treatment with thiabendazole. A total of 159 serum samples were collected in a period ranging from 22–116 months. Enzyme‐linked immunosorbent assays (IgG, IgA, and IgE ELISA) were standardized, using excretory–secretory antigens obtained from the second‐stage larvae of a Toxocara canis culture. The sensitivity found for the IgG, IgA, and IgE ELISA, as determined in visceral toxocariasis patients, was 100%, 47.8%, and 78.3%, respectively. Approximately 84% of the patients presented single or multiple parasitosis, as diagnosed by stool examination, yet such variables did not appear to affect the anti‐Toxocara immune response. Titers of specific IgE antibody showed a significant decrease during the first year after treatment, followed by a decrease in the IgA titers in the second year, and in the IgG titers from the fourth year onwards. Sera from all patients presented high avidity IgG antibodies, indicating that they were in the chronic phase of the disease. Moreover, 1 year after treatment, the level of leukocytes, eosinophils, and anti‐A isohemagglutinin in patients decreased significantly. The present data suggest that IgE antibodies plus eosinophil counts are helpful parameters for patient follow‐up after chemotherapy. J. Clin. Lab. Anal. 20:164–172, 2006. © 2006 Wiley‐Liss, Inc.

ABO-incompatible liver transplants (LTX) have been associated with a high risk of antibody-mediated rejection, poor patient and graft survival, and a high risk of vascular thrombosis and ischemic bile duct complications. We used pretransplantation and posttransplantation double-volume total plasma exchange (TPE), splenectomy, and quadruple immunosuppression (cyclophosphamide or mycophenolate mofetil, prednisone, cyclosporine or tacrolimus, and OKT3 induction) in 14 patients receiving ABO-incompatible LTX between June 1992 and February 2001: A(1) to O (seven), B to O (two), B to A (two), A to B (one), AB to A (one), and AB to O (one). Actuarial 1- and 5-year patient and graft survival rates are 71.4% and 61.2 % and 71.4% and 61.2%, respectively, with a mean follow-up of 62.9 +/- 39.4 months. Ten acute cellular rejections occurred, and the mean time to the first episode was 62 +/- 33 days. All were steroid sensitive. No antibody-mediated rejection or vascular thromboses occurred. Pretransplantation pre-TPE immunoglobulin (Ig) G mean isohemagglutinin titers were 262 +/- 326, compared with pretransplantation post-TPE titers of 65 +/- 103 (P =.04). Eight of nine patients with measurable titers before and after TPE achieved a reduction in titers. The mean number of posttransplantation TPE was 5.5 +/- 4.1 (range, 0 to 12), and the last TPE was on postoperative day 9.4 +/- 5.3. IgG isohemagglutinin titers 2 weeks posttransplantation had increased to 153 +/- 309 (P =.03 compared with pretransplantation pre-TPE IgG). ABO-incompatible liver transplantations can be performed with acceptable patient and graft survival rates with a low risk of antibody-mediated rejection with a combination of TPE, splenectomy, and quadruple immunosuppression. Recovery of isohemagglutinin antibody levels without humoral rejection suggests that accommodation may be the protective mechanism preventing late antibody-mediated rejection.

Delayed donor red cell engraftment and pure red cell aplasia (PRCA) are well-recognized complications of major ABO-incompatible hematopoietic stem cell transplantation (SCT) performed by means of myeloablative conditioning. To evaluate these events following reduced-intensity nonmyeloablative SCT (NST), consecutive series of patients with major ABO incompatibility undergoing either NST (fludarabine/cyclophosphamide conditioning) or myeloablative SCT (cyclophosphamide/high-dose total body irradiation) were compared. Donor red blood cell (RBC) chimerism (initial detection of donor RBCs in peripheral blood) was markedly delayed following NST versus myeloablative SCT (median, 114 versus 40 days;P

Implementation of ABO-incompatible (ABOi) pediatric heart transplantation has contributed to significant reduction in the mortality of infants on the waiting list, without increasing the risk of rejection. This has been attributed to the immature and therefore not fully competent immune system in this population group, which results in lower production of isohemagglutinins compared to older children and adults. Serial evaluations of isohemagglutinin titers in infants revealed cases with absence of donor specific anti-blood group antibodies. However, it is currently unknown whether continuous exposure to donor antigens is necessary to prevent formation of donor specific isohemagglutinins (DSI) in recipients. We are reporting a case of an infant who underwent ABOi heart transplantation, with no evidence of DSI even 4 years after ABO-compatible retransplantation. Hence, temporary exposure to donor antigens in infants may contribute to permanent absence of donor specific anti-blood group antibodies, suggesting the possibility of induced permanent B cell tolerance.

Background The gel agglutination assay has been approved by the Food and Drug Administration as an alternative to the tube assay for the detection of red cell antibodies. It has also been approved recently by the Food and Drug Administration for ABO blood grouping and D typing. Study design and methods Tube and gel agglutination assays were compared for ABO grouping and D typing of 100 donor and 100 patient specimens. ABO grouping of 14 specimens of known ABO groups and D typing of 10 specimens with weak D were also compared. When antigen typing or isohemagglutinin results differed, gel testing was repeated by the use of modified incubation times, reagent or specimen volumes, and red cell concentrations. Results ABO grouping and D typing in all patient and donor specimens concurred. B isohemagglutinins were not detected in seven group A specimens. Six of seven discrepancies were resolved when gel tests were incubated at room temperature with increased serum or plasma volume. Weak D was detected in all 10 specimens tested by both assays. When weak A and/or B were tested with monoclonal antibody reagents, the correct phenotypes were identified in 9 specimens by gel assay and in 10 by tube assay. Using human antisera, 6 specimens were correctly phenotyped by gel assay and 7 by tube assay. Conclusion The gel assay performed as well as the tube assay in detection of A, B, and D, but the tube assay was slightly better at detecting B isohemagglutinins. The gel assay can be used in place of the tube assay for ABO blood grouping and D typing.

Platelet concentrates from ABO-identical donors are the com-ponents of choice for transfusions. Since platelet inventoriesare generallyinsufficientandbecausethereisusuallyahigherfrequency of group O donors, perfect matches are not alwayspossible and therefore ABO-incompatible platelet transfu-sions are an accepted practice when ABO-identical plateletsare unavailable.

Many causes for ABO discrepancy between red blood cell and serum testing have been cited in the literature. ABO discrepancy due to weak or absent reverse type is most often seen at the extremes of age. We report a case of ABO discrepancy in a 25-year-old woman who presented for wisdom teeth extraction. Initial serologic workup revealed total absence of isohemagglutinin anti-B in this group A, D+ individual. Further evaluation revealed decreased levels of all classes of immunoglobulins and a medical history significant for multiple episodes of infection. Based on the patient’s history and laboratory data, she was diagnosed with common variable immunodeficiency (CVID). CVID can cause ABO discrepancy in an adult patient because of an absent ABO reverse type. Immunohematology 1997;13:80–83.

ABO incompatibility is a barrier for solid organ transplantation, but not for hematopoietic stem cell transplantation. To investigate tolerance induction, we enrolled patients who had undergone minor ABO-incompatible (O into A group, n = 6) and ABO-identical (O into O group, n = 4) bone marrow transplantation (BMT). None of the six O into A patients were positive for recipient-specific (anti-blood group A) isohemagglutinins, whereas all four O into O patients were. Peripheral blood mononuclear cells (PBMCs) were engrafted into NOD/SCID/gamma(c)(null) (NOG) mice, followed by sensitization of blood group A red blood cells. Anti-blood group A antibodies (Abs) in the sera of the patients and the human PBMC-engrafted NOG mice were measured by enzyme-linked immunosorbent assays. Anti-blood group A Abs in the patients' sera were significantly correlated with anti-A isohemagglutinin titers (p < 0.01). In the human PBMC-engrafted NOG mice, anti-blood group A Abs were significantly lower in the O into A group than in the O into O group (p < 0.05), despite ex vivo restimulation of B cells. The results of this study suggest that long after receiving minor ABO-incompatible BMT, B cells derived from newly engrafted donor precursor cells were induced tolerance to recipient-specific antigens.

Background Intentional blood group (BG)-incompatible (ABOi) heart transplantation in childhood is emerging in many centers. Safety limits remain undetermined. In this multicenter study we have compiled experience on clinical and immunologic boundaries. Methods Data from six centers in Europe and North America on ABOi transplantation were collected in a standardized survey. Results Fifty-eight ABOi transplants were performed in 57 patients. Median age at transplant was 6.8 months (0.03 to 90 months); post-transplant follow-up was 37.7 months (0.46 to 117 months), accumulating 188 patient-years. Forty-seven percent of the patients received pretransplant mechanical circulatory support. Donors were either blood group A ( n = 25), B ( n = 18) or AB ( n = 15). The median peak antibody titer to the donor BG pretransplant was 1:8 (0 to 1:64) for anti-A and 1:4 (0 to 1:32) for anti-B. Titers against the donor BG were lower post- than pretransplant in B recipients ( p = 0.02), whereas third-party antibodies in BG O recipients developed normally post-transplant. Induction immunosuppression included anti-thymocyte globulin (61%), basiliximab (32%) or none (7%). All patients received calcineurin inhibitors, including 62% with mycophenolate mofetil, 10% with azathioprine, 2% with everolimus and 24% with steroids. There were 4 episodes of cellular rejection (Grade≥2R) and 7 antibody-mediated rejections. Five patients underwent antibody removal post-transplant. One patient developed severe graft vasculopathy. Freedom from death or retransplantation was 100%/96%/69% at 1/5/10 years. No graft loss was attributed to BG antibodies. Conclusions Successful ABOi heart transplantation can be performed at an older age and with higher isohemagglutinin titers than initially assumed and using similar immunosuppressive regimens as for ABO-compatible transplants. Rejection and graft vasculopathy are rare. Persistently low titers of antibodies to the donor BG post-transplant suggest elements of tolerance and/or accommodation.