A rational approach to guide cost-effective de novo donor-specific antibody surveillance with tacrolimus immunosuppression.

De novo donor-specific antibody (dnDSA) after renal transplantation has been shown to correlate with antibody-mediated rejection and allograft loss. However, the lack of proven interventions and the time and cost associated with annual screening for dnDSA are difficult to justify for all recipients. We studied a well-characterized consecutive cohort (n = 949) with over 15 years of prospective dnDSA surveillance to identify risk factors that would help institute a resource-responsible surveillance strategy. Younger recipient age and HLA-DR/DQ molecular mismatch were independent predictors of dnDSA development. Combining both risk factors into recipient age molecular mismatch categories, we found that 52% of recipients could be categorized as low-risk for dnDSA development (median subclinical dnDSA-free survival at 5 and 10 years, 98% and 97%, respectively). After adjustment, multivariate correlates of dnDSA development included tacrolimus versus cyclosporin maintenance immunosuppression (hazard ratio [HR], 0.37; 95% CI, 0.2-0.6; P < .0001) and recipient age molecular mismatch category: intermediate versus low (HR, 2.48; 95% CI, 1.5-4.2; P = .0007), high versus intermediate (HR, 2.56; 95% CI, 1.6-4.2; P = .0002), and high versus low (HR, 6.36; 95% CI, 3.7-10.8; P < .00001). When combined, recipient age and HLA-DR/DQ molecular mismatch provide a novel data-driven approach to reduce testing by >50% while selecting those most likely to benefit from dnDSA surveillance.

Daratumumab for antibody-mediated rejection: Is it time to target the real culprit?

We report the case of a sensitized woman who underwent successful transplantation after a desensitization protocol, with an optically normal 8-day biopsy. At 3 months, she developed active antibody-mediated rejection (AMR) due to preformed donor-specific antibodies. It was decided to treat the patient with daratumumab, an anti-CD38 monoclonal antibody. The mean fluorescence intensity of donor-specific antibodies decreased, pathologic signs of AMR regressed, and kidney function returned to normal. A molecular assessment of biopsies was retrospectively performed. By doing so, regression of the molecular signature of AMR was evidenced between the second and third biopsies. Interestingly, the first biopsy revealed a gene expression profile of AMR, which helped retrospectively classify this biopsy as AMR, illustrating the relevance of molecular phenotyping of biopsy in high-risk situations such as desensitization.

Antibody-mediated rejection with and without donor-specific anti-human leucocyte antigen antibodies: performance of the peripheral blood 8-gene expression assay.

BACKGROUND: Recently a peripheral blood 8-gene expression assay was developed for non-invasive detection of antibody-mediated rejection (ABMR) after kidney transplantation. Its value has not yet been evaluated in detail in clinical scenarios with different baseline disease probability [human leucocyte antigen donor-specific antibodies (HLA-DSA)-positive versus HLA-DSA-negative cases at the time of stable graft function versus graft dysfunction]. METHODS: Here we investigated the diagnostic accuracy of the 8-gene expression assay for histology of ABMR (ABMRh) with or without HLA-DSA in a cross-sectional cohort study of 387 blood samples with a concomitant graft biopsy. RESULTS: In patients with HLA-DSA (n = 64), the 8-gene expression assay discriminated DSA-positive ABMRh (DSAposABMRh) cases (n = 16) with good diagnostic performance {area under the receiver operating characteristic curve [AUROC] 83.1% [95% confidence interval (CI) 70.8-95.3]}. Also, in HLA-DSA-negative samples (n = 323), a clinically relevant diagnostic performance for DSAnegABMRh cases was found (n = 30) with an AUROC of 75.8% (95% CI 67.4-84.4). The 8-gene assay did not discriminate DSAposABMRh cases from DSAnegABMRh cases. There was a net benefit for clinical decision-making when adding the 8-gene expression assay to a clinical model consisting of estimated glomerular filtration rate, proteinuria, HLA-DSA and age. CONCLUSION: The 8-gene expression assay shows great potential for implementation in the clinical follow-up of high-risk HLA-DSA-positive patients and clinical relevance in HLA-DSA-negative cases.

Successful Treatment of Antibody-Mediated Rejection by De Novo Donor Specific Antibody After Primary Renal Transplantation in a Recipient From a Cadaveric Donor: A Case Report.

A 19-year-old Japanese male recipient, who received a living related kidney transplantation from his father at 5 years old, was hospitalized for second renal transplantation from a cadaveric donor. The recipient had had an antibody-mediated rejection (AMR) to the first transplanted kidney. HLA typing of A, B, and DRB showed 2 of 6 mismatches. Lymphocyte cytotoxicity test (LCT) and flow cytometry crossmatches (FCXM) were negative on T cells. Tacrolimus, mycophenolate mofetil, methylprednisolone, and basiliximab induction were used as the standard immunosuppressive therapy. After second renal transplantation, his serum creatinine level favorably decreased until postoperative day (POD) 7, but his serum creatinine level raised from POD 8. We performed steroid pulse and intravenous immunoglobulin (IVIG). The episode biopsy showed AMR although FCXM and LCT were still negative on T cell. To determine the cause of AMR, we examined LABScreen single antigen test (One Lambda, Canoga Park, Calif., United States), and there was a donor-specific antibody (DSA) that is DQB8 in pre- and post-second renal transplantation. The DSA was suspected de novo DSA for the first transplanted kidney. AMR was successfully treated with plasma exchange, IVIG, and rituximab.

Antibody-Mediated Rejection Due to Donor-Specific HLA-DQB1 and DQA1 Antibodies After Kidney Transplantation: A Case Report.

BACKGROUND: Donor-specific HLA antibody (DSA) is associated with the risk of allograft loss due to antibody-mediated rejection (ABMR). The majority of de novo DSA after kidney transplantation is directed toward donor HLA-DQ antigens. A HLA-DQ antigen is a heterodimer consisting of an alpha and beta chain. Traditionally, HLA-DQA1 typing has not been part of the pretransplant evaluation. Therefore, DQ alpha proteins are not usually taken into account in the interpretation of HLA-DQ antibody reactions. METHODS: We hereby present a case of a kidney transplant recipient with 0% pretransplant panel reactive antibody. She received kidney allograft from her husband. Two years after transplantation, she experienced abdominal swelling, and enlargement of transplanted kidney was identified. A biopsy of the allograft kidney demonstrated chronic active ABMR. DSAs were investigated using immunoglobulin G (IgG) and C1q single antigen bead (SAB) assay. HLAMatchmaker analysis was performed to identify eplets that explain the antibody reactivity patterns. RESULTS: The IgG SAB analysis of a patient's serum at the time of rejection showed positive reactions with all DQ2-carrying beads with mean fluorescence intensity (MFI) > 10000. However, the C1q assay demonstrated strong reaction to only HLA-DQA1∗05:01-DQB1∗02:01-carrying bead with MFI = 22462, whereas weak or no reactions against other HLA-DQ2-carrying beads were found. High-resolution HLA typing revealed that HLA-DQA1∗05:01 and DQB1∗02:01 were mismatched donor antigens. HLAMatchmaker analysis showed that the antibodies were reactive toward 40GR3 eplet on DQA1 and 45GE3 eplet on DQB1. CONCLUSIONS: This case highlights the clinical significance of antibodies specific to both DQ alpha and DQ beta chains after kidney transplantation.

Peripheral blood transcriptome analysis and development of classification model for diagnosing antibody-mediated rejection vs accommodation in ABO-incompatible kidney transplant.

The major obstacle to successful ABO blood group-incompatible kidney transplantation (ABOi KT) is antibody-mediated rejection (AMR). This study aimed to investigate transcriptional profiles through RNA sequencing and develop a minimally invasive diagnostic tool for discrimination between accommodation and early acute AMR in ABOi KT. Twenty-eight ABOi KT patients were selected: 18 with accommodation and 10 with acute AMR at the 10th day posttransplant protocol biopsy. Complete transcriptomes of their peripheral blood were analyzed by RNA sequencing. Candidate genes were selected by bioinformatics analysis, validated with quantitative polymerase chain reaction, and used to develop a classification model to diagnose accommodation. A total of 1385 genes were differentially expressed in accommodation compared with in AMR with P-adjusted < .05. Functional annotation and gene set enrichment analysis identified several immune-related and immunometabolic pathways. A 5-gene classification model including COX7A2L, CD69, CD14, CFD, and FOXJ3 was developed by logistic regression analysis. The model was further validated with an independent cohort and discriminated between accommodation and AMR with 92.7% sensitivity, 85.7% specificity, and 91.7% accuracy. Our study suggests that a classification model based on peripheral blood transcriptomics may allow minimally invasive diagnosis of acute AMR vs accommodation and subsequent patient-tailored immunosuppression in ABOi KT.

Second Tunisian case of Anti -Tja mediated recurrent abortions.

The diagnosis and the treatment of rare phenotypes remain a problematic situation in many countries especially in Tunisia. Individuals with rare phenotype may develop clinically significant red cell antibodies directed against the high incidence Antigens they lack. A 35 years old patient was referred to our laboratory to explain a high incidence (twelve) of recurrent miscarriage during the first and second terms of pregnancy. This patient was grouped as O Rhesus: 1, -2, -3, 4, 5 K:-1. In her plasma we identified a pan-reactive anti-PP1PK antibody (anti-Tja) recognized to be responsible of spontaneous recurrent abortions. The red cell phenotype was P1 and Tja negative. More investigations concluded to the absence of auto and other allo-antibodies association. Therapeutic plasmapheresis from early stages was suggested for the future pregnancy to remove anti-public antibodies in order to maintain normal placenta functions. The Anti-Tja antibody, naturally occurring in patients with rare p phenotype, has the ability to induce recurrent spontaneous miscarriages and to cause immediate hemolytic transfusion reactions. Despite the absence of compatible donors in her family, this patient is not in an impasse situation because two donors with the same phenotype were identified when investigating a first case in 2013.

CD68/CD31 immunohistochemistry double stain demonstrates increased accuracy in diagnosing pathologic antibody-mediated rejection in cardiac transplant patients.

Pathologic antibody-mediated rejection (pAMR) occurs in 10% of cardiac transplant patients and is associated with increased mortality. The endomyocardial biopsy remains the primary diagnostic tool to detect and define pAMR. However, certain challenges arise for the pathologist. Accurate identification of >10% of intravascular macrophages along with endothelial swelling, which remains a critical component of diagnosing pAMR, is one such challenge. We used double labeling with an endothelial and histiocytic marker to improve diagnostic accuracy. Twenty-two cardiac transplant endomyocardial biopsies were screened using a CD68/CD31 immunohistochemical (IHC) double stain. To determine whether pAMR diagnosis would change using the double stain, intravascular macrophage staining was compared to using CD68 alone. Twenty-two cardiac pAMR cases from patients were included. Fifty-nine percent of cases previously called >10% intravascular macrophage positive by CD68 alone were called <10% positive using the CD68/CD31 double stain. Not using the double stain was associated with a significant overcall. In C4d-negative cases, using the CD68/CD31 double stain downgraded the diagnosis of pAMR2 to pAMR1 in 32% of cases. It was concluded that more than one third of patients were overdiagnosed with pAMR using CD68 by IHC alone. We demonstrate the value of using a CD68/CD31 double stain to increase accuracy.

Nonvascularized human skin chronic allograft rejection.

A 65-year-old man had extensive burns of the lower legs in 1991, at the age of 40 years. He was treated by nonvascularized and de-epithelialized, allogeneic split-thickness skin allograft and cyclosporine monotherapy for 2 months. Ulcers developed between 10 and 25 years after transplantation and a surgical debridement on the lower extremities was required. Analyses of the removed tissue allografts showed chronic antibody-mediated and cellular rejection with extensive and dense fibrosis, and diffuse capillary C4d deposits. An anti-DRB1*08:01, donor-specific antibody was present. A unique clinical condition with late immunopathological features of human skin chronic allograft rejection is reported.

The quest to decipher HLA immunogenicity: Telling friend from foe.

Molecular mismatch load analysis was recently introduced as a means for performing risk stratification following organ transplantation. However, although good correlation was demonstrated between molecular mismatch load and generation of de novo donor-specific HLA antibody (DSA), quite a few exceptions exist, and the underlying factors that define HLA immunogenicity remain unclear. Herein, we present a new paradigm to interrogate differences between molecular mismatches that lead to the generation of de novo DSA and those that do not (the 2MM1DSA cohort). Specifically, patients transplanted across 2 HLA-DQ mismatches, who formed de novo DSA only to one mismatch (foe) but not the other (friend), provide a unique environment in which patient-specific factors that affect the immune response other than immunogenicity, such as infection and immunosuppression, can be controlled for. It further permits focusing on mismatches uniquely exhibited by the de novo DSA allele, rather than mismatches shared by both DSA and non-DSA alleles. This concept paper illustrates several examples, highlights the need for center-specific or population-specific cutoff values for posttransplant risk stratification, and mostly argues that if there is no direct correlation between molecular mismatch load and immunogenicity, then molecular mismatch load must not be adopted as an approach for equitable organ allocation.

Allocation to highly sensitized patients based on acceptable mismatches results in low rejection rates comparable to nonsensitized patients.

Whereas regular allocation avoids unacceptable mismatches on the donor organ, allocation to highly sensitized patients within the Eurotransplant Acceptable Mismatch (AM) program is based on the patient's HLA phenotype plus acceptable antigens. These are HLA antigens to which the patient never made antibodies, as determined by extensive laboratory testing. AM patients have superior long-term graft survival compared with highly sensitized patients in regular allocation. Here, we questioned whether the AM program also results in lower rejection rates. From the PROCARE cohort, consisting of all Dutch kidney transplants in 1995-2005, we selected deceased donor single transplants with a minimum of 1 HLA mismatch and determined the cumulative 6-month rejection incidence for patients in AM or regular allocation. Additionally, we determined the effect of minimal matching criteria of 1 HLA-B plus 1 HLA-DR, or 2 HLA-DR antigens on rejection incidence. AM patients showed significantly lower rejection rates than highly immunized patients in regular allocation, comparable to nonsensitized patients, independent of other risk factors for rejection. In contrast to highly sensitized patients in regular allocation, minimal matching criteria did not affect rejection rates in AM patients. Allocation based on acceptable antigens leads to relatively low-risk transplants for highly sensitized patients with rejection rates similar to those of nonimmunized individuals.

Back signaling of HLA class I molecules and T/NK cell receptor ligands in epithelial cells reflects the rejection-specific microenvironment in renal allograft biopsies.

The role of endothelial cells in the pathophysiology of antibody-mediated rejection after renal transplantation has been widely investigated. We expand this scenario to the impact of epithelial cells on the microenvironment during rejection. Primary proximal tubular epithelial cells were stimulated via HLA class I, CD155 and CD166 based on their potential signal-transducing capacity to mediate back signaling after encounter with either T/NK cells or donor-specific antibodies. Upon crosslinking of these ligands with mAbs, PTEC secreted IL-6, CXCL1,8,10, CCL2, and sICAM-1. These proteins were also released by PTEC as consequence of a direct interaction with T/NK cells. Downmodulation of the receptor CD226 on effector cells confirmed the involvement of this receptor/ligand pair in back signaling. In vivo, CD155 and CD166 expression was detectable in proximal and distal tubuli of renal transplant biopsies, respectively. The composition of the protein microenvironment in these biopsies showed a substantial overlap with the PTEC response. Cluster and principal component analyses of the microenvironment separated unsuspicious from rejection biopsies and, furthermore, ABMR, TCMR, and borderline rejection. In conclusion, our results provide evidence that epithelial cells may contribute to the rejection process and pave the way to a better understanding of the pathomechanisms of kidney allograft rejection.

Specificity, strength, and evolution of pretransplant donor-specific HLA antibodies determine outcome after kidney transplantation.

In this cohort study (N = 924), we investigated the evolution and clinical significance of pretransplant donor-specific HLA antibodies (preDSA), detected in the single-antigen beads assay but complement-dependent cytotoxicity crossmatch-negative. Donor specificity of the preDSA (N = 107) was determined by high-resolution genotyping of donor-recipient pairs. We found that in 52% of the patients with preDSA, preDSA spontaneously resolved within the first 3 months posttransplant. PreDSA that persisted posttransplant had higher pretransplant median fluorescence intensity values and more specificity against DQ. Patients with both resolved and persistent DSA had a high incidence of histological picture of antibody-mediated rejection (ABMRh ; 54% and 59% respectively). Patients with preDSA that persisted posttransplant had worse 10-year graft survival compared to resolved DSA and preDSA-negative patients. Compared to cases without preDSA, Cox modeling revealed an increased risk of graft failure only in the patients with persistent DSA, in the presence (hazard ratio [HR] = 8.3) but also in the absence (HR = 4.3) of ABMRh . In contrast, no increased risk of graft failure was seen in patients with resolved DSA. We conclude that persistence of preDSA posttransplant has a negative impact on graft survival, beyond ABMRh . Even in the absence of antibody-targeting therapy, low median fluorescence intensity DSA and non-DQ preDSA often disappear early posttransplantation and are not deleterious for graft outcome.

Sex differences in preformed panel-reactive antibody levels and outcomes in patients undergoing heart transplantation.

BACKGROUND: Sex differences in panel-reactive antibody (PRA) levels in heart transplant recipients and their association with transplant-related outcomes are mostly unknown. METHODS: In 20 181 (24.7% women) first-time heart transplant recipients included from July 2004 to March 2015 in the prospective Organ Procurement and Transplantation Network (OPTN), we studied sex differences in most recent (mr) and peak (p)PRA and outcomes (graft failure, rejection, cardiac allograft vasculopathy [CAV], retransplantation, and mortality). Median follow-up (all-cause mortality) was 6 years. Analyses are based on OPTN data (March 6, 2017). RESULTS: MrPRA levels were associated with all-cause mortality (hazard ratio, 95% confidence interval: class I 1.03, 1.01-1.04, P < 0.001) and acute rejection (class II 1.08, 1.03-1.14, P = 0.0044). PPRA levels were associated with all-cause mortality (class I 1.02, 1.00-1.04, P = 0.015) and CAV (class II 1.03, 1.01-1.06, P = 0.020). Sex interactions were seen for the association of pPRA and graft failure with a higher risk in women, and for pPRA and CAV with a higher risk in men. CONCLUSIONS: PRA were associated with different transplant-related outcomes in both sexes. However, women with elevated pPRA were shown to be at higher risk for graft failure, whereas higher levels of pPRA were more hazardous for men in developing CAV.

Safety and efficacy of eculizumab for the prevention of antibody-mediated rejection after deceased-donor kidney transplantation in patients with preformed donor-specific antibodies.

The presence of preformed donor-specific antibodies in transplant recipients increases the risk of acute antibody-mediated rejection (AMR). Results of an open-label single-arm trial to evaluate the safety and efficacy of eculizumab in preventing acute AMR in recipients of deceased-donor kidney transplants with preformed donor-specific antibodies are reported. Participants received eculizumab as follows: 1200 mg immediately before reperfusion; 900 mg on posttransplant days 1, 7, 14, 21, and 28; and 1200 mg at weeks 5, 7, and 9. All patients received thymoglobulin induction therapy and standard maintenance immunosuppression including steroids. The primary end point was treatment failure rate, a composite of biopsy-proved grade II/III AMR (Banff 2007 criteria), graft loss, death, or loss to follow-up, within 9 weeks posttransplant. Eighty patients received transplants (48 women); the median age was 52 years (range 24-70 years). Observed treatment failure rate (8.8%) was significantly lower than expected for standard care (40%; P < .001). By 9 weeks, 3 of 80 patients had experienced AMR, and 4 of 80 had experienced graft loss. At 36 months, graft and patient survival rates were 83.4% and 91.5%, respectively. Eculizumab was well tolerated and no new safety concerns were identified. Eculizumab has the potential to provide prophylaxis against injury caused by acute AMR in such patients (EudraCT 2010-019631-35).

Red blood cell alloantibodies are associated with increased alloimmunization against human leukocyte antigens.

BACKGROUND: Alloantibodies recognizing human leukocyte antigens (HLA) can cause immune-mediated refractoriness to platelet transfusion. An association between HLA alloimmunization and red blood cell (RBC) alloimmunization has been suggested but remains uncertain. STUDY DESIGN AND METHODS: We tested for HLA alloantibodies in 660 patients with and without RBC alloantibodies. Calculated panel reactive antibody (cPRA) values were determined for HLA alloimmunized patients. Current and historical diagnoses and blood product exposure were catalogued. Variables associated with high-level HLA alloimmunization (cPRA ≥ 90%) were evaluated. RESULTS: The cohort included 366 women and 294 men with median age of 66 years (interquartile range [IQR], 53-76). The number of patients with and without RBC alloantibodies was 447 and 213, respectively. Among patients with and without RBC alloantibodies, 20.6% and 8.5% had a cPRA ≥ 90%, respectively (p < 0.0001). In univariate analyses of men and nulliparous women and previously pregnant women, the median number of RBC alloantibodies was significantly higher in patients with a cPRA ≥ 90% (p < 0.0001). The number of RBC alloantibodies remained an independent predictor of a cPRA ≥ 90% in multivariate analysis (odds ratio [OR] 1.50, 95% confidence interval [CI] 1.22-1.85). Other independent predictors of a cPRA ≥ 90% were parity (OR 1.26, 95% CI 1.08-1.47), age (OR 0.98, 95% CI 0.97-1.00), history of renal disease (OR 1.88, 95% CI 1.02-3.48), and number of non-leukoreduced products transfused (OR 1.02, 95% CI 1.00-1.04). CONCLUSIONS: RBC alloimmunization was significantly associated with HLA alloimmunization with a cPRA ≥ 90%. RBC alloimmunization status combined with specific components of the clinical history may estimate the risk of high-level HLA alloimmunization.

WNT pathway signaling is associated with microvascular injury and predicts kidney transplant failure.

Microvascular injury is associated with accelerated kidney transplant dysfunction and allograft failure. Molecular pathology can identify new mechanisms of microvascular injury while improving on the diagnostic and prognostic capabilities of traditional histology. We conducted a case-control study of archived kidney biopsy specimens stored up to 10 years with microvascular injury (n = 50) compared with biopsy specimens without histologic injury (n = 45) from patients of similar age, race, and sex. We measured WNT gene expression with a multiplex quantification platform by using digital barcoding, given the importance of WNT reactivation to the response to wounding in the kidney microvasculature and other compartments. Of 210 genes from a commercial WNT panel, 71 were associated with microvascular injury and 79 were associated with allograft failure, with considerable overlap of genes between each set. Molecular pathology identified 46 biopsy specimens with molecular evidence of microvascular injury; 18 (39%) were either C4d negative, donor-specific antibody negative, or had no microvascular injury by histology. The majority of cases with molecular evidence of microvascular injury had poor long-term outcomes. We identified novel WNT pathway genes associated with microvascular injury and allograft failure in residual clinical biopsy specimens obtained up to 10 years earlier. Further mechanistic studies may identify the WNT pathway as a new diagnostic and therapeutic target.

Generating automated kidney transplant biopsy reports combining molecular measurements with ensembles of machine learning classifiers.

We previously reported a system for assessing rejection in kidney transplant biopsies using microarray-based gene expression data, the Molecular Microscope® Diagnostic System (MMDx). The present study was designed to optimize the accuracy and stability of MMDx diagnoses by replacing single machine learning classifiers with ensembles of diverse classifier methods. We also examined the use of automated report sign-outs and the agreement between multiple human interpreters of the molecular results. Ensembles generated diagnoses that were both more accurate than the best individual classifiers, and nearly as stable as the best, consistent with expectations from the machine learning literature. Human experts had ≈93% agreement (balanced accuracy) signing out the reports, and random forest-based automated sign-outs showed similar levels of agreement with the human experts (92% and 94% for predicting the expert MMDx sign-outs for T cell-mediated (TCMR) and antibody-mediated rejection (ABMR), respectively). In most cases disagreements, whether between experts or between experts and automated sign-outs, were in biopsies near diagnostic thresholds. Considerable disagreement with histology persisted. The balanced accuracies of MMDx sign-outs for histology diagnoses of TCMR and ABMR were 73% and 78%, respectively. Disagreement with histology is largely due to the known noise in histology assessments (ClinicalTrials.gov NCT01299168).

Fatal acute hemolytic transfusion reaction due to anti-B from a platelet apheresis unit stored in platelet additive solution.

BACKGROUND: Hemolytic transfusion reactions from out-of-group plasma in platelet (PLT) transfusions are uncommon, with most involving passive transfer of anti-A. Only rare reactions have ever been reported due to anti-B. STUDY DESIGN AND METHODS: An apheresis PLT product was donated by a blood group O male, processed using PLT additive solution, and pathogen reduced. Postreaction recipient testing included an antibody screen using gel technology, a direct antiglobulin test (DAT) using immunoglobulin G and C3, and an eluate against group O and B cells. Postreaction donor testing included measuring anti-B titers in saline, with and without anti-human globulin. RESULTS: A 60-year-old blood group B patient with relapsed acute myeloid leukemia developed confusion, fever, and hypotension within hours after a blood group O PLT transfusion. The posttransfusion reaction evaluation was remarkable for a positive DAT 3+ for C3; the eluate showed anti-B. Rapid extravascular hemolysis occurred, with a 50% decline in hemoglobin, a high lactate dehydrogenase, and a high bilirubin. She was resuscitated with fluids, blood products, pressors, and oxygen and died of asystole 60 hours later. The donor's anti-B titers were 128 by tube testing at immediate spin and 512 at the anti-human globulin phase. Notably, a group B patient at a different hospital received a split of the same apheresis unit, with no reaction. CONCLUSION: To our knowledge, this is the first fatality reported from passively transfused anti-B. The fact that one transfusion recipient died whereas another did not have any reported reaction highlights the potential importance of recipient variables in isohemagglutinin-mediated hemolysis.