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Background Daratumumab (DARA), a human IgG1 K monoclonal antibody targeting CD38, is used to treat refractory multiple myeloma patients. CD38 is expressed on many cell types (RBCs, granulocytes, lymphocytes, etc.), and thus, DARA can interfere with serological tests. Information regarding how DARA affects anti‐granulocyte antibody (AGA) testing and optimal neutralization of DARA will help laboratories perform accurate testing. Methods Screening of AGA was performed by the granulocyte agglutination test (GAT) and the flow cytometric granulocyte immunofluorescence test (Flow‐GIFT). Samples were tested from patients on DARA ( n = 7), non‐transfused blood donors (healthy controls, n = 7) and AGA reactive samples (positive controls, n = 5). Two neutralization experiments, CD38 removal with DTT and DARA epitope blockage with mouse anti‐CD38, were evaluated. Results Positive reactivity of human IgG binding was observed in 5/7 DARA cases when tested by Flow‐GIFT; however, all 7 cases had negative GAT agglutination results. Further studies by Flow‐GIFT revealed DARA concentrations >0·63 μg/ml bound to granulocytes. DARA binding was negated by DTT though a reduced Flow‐GIFT sensitivity was observed in positive control samples due to increased background detection of human IgG. Mouse anti‐CD38 neutralized the detection of human IgG observed in DARA‐treated patient serum without effecting controls. Conclusion We established that DARA can interfere with AGA testing, leading to false positive Flow‐GIFT results without causing GAT agglutination. DTT treatment increased background binding of secondary antibodies causing a decrease in Flow‐GIFT sensitivity. In comparison, blockage of the DARA binding epitope using mouse anti‐CD38 antibody was effective in neutralizing DARA interference while maintaining Flow‐GIFT sensitivity.

Background: Immune checkpoint inhibitors (ICIs) frequently cause thyroid dysfunction but their underlying mechanism remains unclear. We have previously demonstrated increased circulating natural killer (NK) cells and human leukocyte antigen (HLA)-DR surface expression on inflammatory intermediate CD14 + CD16 + monocytes in programmed cell death protein-1 (PD-1) inhibitor-treated patients. This study characterizes intrathyroidal and circulating immune cells and class II HLA in ICI-induced thyroiditis. Methods: This is a single-center prospective cohort study of 10 patients with ICI-induced thyroiditis by flow cytometry of thyroid fine needle aspirates ( n = 9) and peripheral blood ( n = 7) as compared with healthy thyroid samples ( n = 5) and healthy volunteer blood samples ( n = 44); HLA class II was tested in n = 9. Results: ICI-induced thyroiditis samples demonstrated overall increased T lymphocytes (61.3% vs. 20.1%, p = 0.00006), CD4 − CD8 − T lymphocytes (1.9% vs. 0.7%, p = 0.006), and, as a percent of T lymphocytes, increased CD8 + T lymphocytes (38.6% vs. 25.7%; p = 0.0259) as compared with healthy thyroid samples. PD-1 inhibitor-induced thyroiditis had increased CD4 + PD1 + T lymphocytes (40.4% vs. 0.8%; p = 0.021) and CD8 + PD1 + T lymphocytes (28.8% vs. 1.5%; p = 0.038) in the thyroid compared with the blood. Circulating NK cells, certain T lymphocytes (CD4 + CD8 + , CD4 − CD8 − T, gamma – delta), and intermediate monocytes were increased in ICI-induced thyroiditis. Six patients typed as HLA-DR4-DR53 and three as HLA-DR15. Conclusions: ICI-induced thyroiditis is a T lymphocyte-mediated process with intra-thyroidal predominance of CD8 + and CD4 − CD8 − T lymphocytes. The HLA haplotypes may be involved but need further evaluation. These findings expand the limited understanding of ICI-induced thyroiditis, which could be further translated to guide immunomodulatory therapies for advanced thyroid cancer.

Context.— As pharmacogenetic testing is incorporated into routine care, it is essential for laboratories to provide accurate and consistent results. Certified laboratories must successfully complete proficiency testing. Objectives.— To understand and examine trends in participation and performance of laboratories participating in the College of American Pathologists pharmacogenetic proficiency testing surveys. Design.— Results from College of American Pathologists pharmacogenetic proficiency testing challenges from 2012 through 2017 were reviewed for concordance with expected genotype and phenotype for each sample (intended responses). Results.— Laboratories correctly reported results for 96.7% to 100% of samples with no variants. Excluding CYP2D6, laboratories correctly detected and reported variant alleles for each gene (93.7%–99.2% correct). CYP2D6 showed lower concordance, with 83.1% of laboratories reporting the intended genotype across all samples; however, in many cases, the laboratories that did not report a variant allele did not test for that allele. Among laboratories reporting the intended genotype, most successfully reported the intended phenotype (85.9%–99.0%). Conclusions.— Although laboratories are generally performing well, there is room for additional improvement, particularly for challenging genes, such as CYP2D6. Efforts in the field of pharmacogenomics to recommend alleles that should be included in clinical tests, identify reference materials, and standardize translation from genotype to phenotype may address some of the remaining variability in results.

BACKGROUND Determination of blood donor hemoglobin (Hb) levels is a pre‐requisite to ensure donor safety and blood product quality. We aimed to identify Hb measurement practices across blood donation services and to what extent differences associate with low‐Hb deferral rates. METHODS An online survey was performed among Biomedical Excellence for Safer Transfusion (BEST) Collaborative members, extended with published data. Multivariable negative‐binomial regression models were built to estimate adjusted associations of minimum donation intervals, Hb cut‐offs (high, ≥13.5 g/dL in men or ≥ 12.5 g/dL in women, vs. lower values), iron monitoring (yes/no), providing or prescribing iron supplementation (yes/no), post‐versus pre‐donation Hb measurement and geographical location (Asian vs. rest), with low‐Hb deferral rates. RESULTS Data were included from 38 blood services. Low‐Hb deferral rates varied from 0.11% to 8.81% among men and 0.84% to 31.85% among women. Services with longer minimum donation intervals had significantly lower deferral rates among both women (rate ratio, RR 0.53, 95%CI 0.33‐0.84) and men (RR 0.53, 95%CI 0.31‐0.90). In women, iron supplementation was associated with lower Hb deferral rates (RR 0.47, 95%CI 0.23‐0.94). Finally, being located in Asia was associated with higher low‐Hb deferral rates; RR 9.10 (95%CI 3.89‐21.27) for women and 6.76 (95%CI 2.45‐18.68) for men. CONCLUSION Differences in Hb measurement and eligibility criteria, particularly longer donation intervals and iron supplementation in women, are associated with variations in low‐Hb deferral rates. These insights could help improve both blood donation service efficiency and donor care.

BACKGROUNDSingle antigen bead (SAB) assays are used to identify human leukocyte antigen (HLA) antibodies in patients with platelet refractoriness due to HLA Class I alloimmunization. Some laboratories use serum pretreatment regimens to eliminate interference from immunoglobulin M antibodies and complement. These modifications may contribute to interlaboratory variability, which is a recognized problem with the SAB assay.STUDY DESIGN AND METHODSFive patientsʼ sera were overnight shipped to 12 laboratories in the United States and internationally. Recipients used their labʼs SAB procedure to identify HLA Class I antibodies. The resultant mean fluorescence intensity (MFI) data were compared by instrumentation, bead lot, and pretreatment regimens. Laboratory‐specific cutoffs for positive antibodies were applied to the results.RESULTSInterlaboratory variability for MFI values appears to be associated with different pretreatment regimens. The coefficient of variation (CV) of MFI from samples pretreated with ethylenediaminetetraacetic acid, dithiothreitol, or heat inactivation (EDHI) were similar, ranging from 14% to 56% (mean, 22%). For samples with no pretreatment, the CVs were significantly higher than EDHI‐treated samples, ranging from 25% to 74% (mean, 39%; 95% confidence interval, 12.10‐21.90; p < 0.0001). An intralaboratory comparison of pretreatment regimens confirmed these findings. Some positive antibody specificities present in EDHI‐treated samples were negative in corresponding samples with no pretreatment when laboratory‐specific cutoffs for positive antibodies were applied.CONCLUSIONOur results show that greater interlaboratory precision can be achieved when samples are pretreated with EDHI as opposed to no pretreatment, likely because these pretreatments eliminate interference from inhibitors. Inhibitors may mask antibodies, leading to missed (or uncalled) specificities when no pretreatment is used.

Abstract Abstract 467 Background: While donor-recipient disparity at HLA loci is associated with greater risk for severe acute graft vs. host disease (GVHD) and inferior survival after unrelated donor allogeneic hematopoietic cell transplantation (HCT), the impact of amino acid substitution (AAS) at peptide binding pockets of the HLA molecule is incompletely understood. Methods: Adult and pediatric patients who received myeloablative or reduced intensity/non-myeloablative first unrelated bone marrow or peripheral blood stem cell transplantation for AML, ALL, CML or MDS between 1988 and 2009 were included. Donors and patients were fully high resolution matched for HLA-A, B, C, and DRB1 (8/8) or had single mismatch (7/8) at one HLA class I locus. Among 7/8 donor-recipient pairs, cases were categorized based on the presence or absence of the AAS of interest at positions 9, 77, 99, 116, or 156 of the class I molecule. In multivariable analysis accounting for patient, disease, and transplantation variables, we studied the independent impact of AAS at these residues on risk for grade III-IV acute GVHD, chronic GVHD, treatment-related mortality, primary malignancy relapse, and overall survival. We compared 7/8 donor-recipient pairs with AAS of interest to 7/8 pairs without these AAS in the primary analyses. Additionally, we performed this analysis restricted to each HLA class I locus. Results: Donor-recipient pairs were 8/8 matched (n=5282), 7/8 with AAS of interest (n=1713), or 7/8 without AAS of interest (n=318). In multivariable analysis, AAS at position 116 was associated with increased risk for grade III-IV acute GVHD (HR 1.21, 1.04–1.42, p=0.0165). No other significant association was detected between AAS studied and clinical outcomes. In multivariable analysis restricted to each class I HLA locus, we detected the following: Among 7/8 matched pairs with mismatch at HLA-C, AAS at position 116 was associated with increased risk for severe acute GVHD (HR 1.42, 1.13–1.79, p=0.0031) and inferior OS (HR 1.2, 1.01–1.41, p=0.0343). AAS at position 99 was associated with increased TRM (HR 1.37, 1.11–1.69, p=0.0037). Of 7/8 pairs with mismatch at HLA-B, AAS at position 9 was associated with increased chronic GVHD (HR 2.19, 1.31–3.66, p=0.0029). Specific amino acid substitution pairs with frequency > 30 were tested for association with HCT outcomes. None met the significance level of 0.00125, pre-specified for multiple comparisons. Conclusions: These results support the concept that AAS at key peptide-binding residues in the HLA class I molecule are associated with increased risk for severe acute GVHD and lower survival. Disclosures: No relevant conflicts of interest to declare.

Abstract Previously in our lab, a missense mutation in the MASTL (FLJ14813) gene on human chromosome 10 was linked to an autosomal dominantly inherited thrombocytopenia in a single pedigree. The mutation results in an amino acid change from glutamic acid at position 167 to aspartic acid and correlates with the inheritance of the disorder in all the affected individuals. The patients present with mild thrombocytopenia with an average platelet count of 60,000 platelets per microliter of blood. Northern blot analysis indicates that MASTL mRNA is restricted in its expression to hematopoietic and cancer cell lines. Functional studies presented here demonstrate a direct relationship between the transient knockdown of the Microtubule Associated Serine/Threonine Like (MASTL) kinase expression and the reduction of circulating thrombocytes in zebrafish (Danio rerio) while erythrocytes development normally. This transient knockdown of MASTL in zebrafish correlates with a decrease in the expression of the thrombopoietin receptor, c-mpl, and the CD41 platelet adhesion GpIIb protein but has no effect on essential housekeeping zebrafish gene, EF1α. The transient expression of a fluorescent protein fused to MASTL and E167D MASTL kinase demonstrates that MASTL localizes to the nucleus of cells as determined by confocal microscopy and TO-PRO-3 counterstain.

Abstract Background: Platelet transfusions are important for supporting patients with hematologic disorders. Refractoriness to platelet transfusions may lead to serious complications and pose a challenge to clinical management. A variety of laboratory strategies to optimize transfusion support in this population are being used; however, data on clinical correlation and success of these interventions is limited. We report the laboratory testing, transfusion yield, and clinical correlation in a cohort of patients receiving cross-matched platelet units. Methods: All consecutive adult patients refractory to platelet transfusions (failure to increment platelet count by 10 x 10(9) times two) with platelet crossmatch performed between June 2014 and April 2016 at our institution were included. Detailed clinical information, laboratory data of the crossmatch results, and Single Antigen Bead (SAB; Luminex) for each platelet unit cross-matched was retrospectively collected. Mean fluorescence intensity (MFI) of antibodies directed towards donor platelet HLA antigens identified through SAB were grouped into zones according to previously validated laboratory data: green zone (<4,000 MFI), yellow zone (4000-10000) and red zone (>10,000). Adequate transfusion yield was defined as an absolute increase of at least 10 x 10((9)/L platelets on a post-transfusion (i.e., within 1 hour) sample. Patients with major bleeding per International Society on Thrombosis and Haemostasis (ISTH) criteria, palpable splenomegaly, fever during transfusion, DIC, active sepsis, or antibodies directed against human platelet antigens were excluded from the final analysis. Importantly, the Hematologist and Pathologist were blinded to the other's data until collection was completed. Data analysis correlating adequate transfusion yield and laboratory parameters was performed. Results: 22 patients (72% female) met our study criteria. All patients had a hematologic malignancy with prolonged pancytopenia after chemotherapy, 4 (18%) had undergone allogeneic bone marrow transplantation. A total of 422 platelet cross-matches were performed, with 17 patients ultimately receiving 46 cross-matched units. The indication for transfusion was: prophylactic 35 (76%), bleeding 4 (9%) and peri-procedural 7 (15%). Ten (22%) transfusion events were excluded: splenomegaly 3, fever 4 and active severe bleeding 2. In one case a post transfusion platelet count was not performed. The overall success rate of transfusion was 64% (23/36). All transfusions leading to an adequate yield had a negative crossmatch. Of the 13 ineffective transfusions, 2 had a positive crossmatch. Based on single antigen MFI assignment, 26 (74%) donor units were classified as green zone, 8 (23%) yellow and 1 (3%) red. The success rates according to the single MFI zone assignment are presented in Table 1. These MFI-defined assignments were predictive of clinically successful transfusions. Conclusion: Selection of appropriate donor platelet units in refractory patients is a challenge that is managed in a variety of ways. While crossmatching is sometimes necessary, a strategy of antigen-avoidance can dramatically increase the identification of potentially effective platelet units for many patients. Understanding of how to navigate HLA antibody data is essential for identifying which HLA antigens should be avoided. Based on these data, in general, our practice is to avoid transfusing a platelet when there is a donor specific antibody of 8,000 MFI or greater. Furthermore, in our dataset there were two patients with both successful and unsuccessful transfusions after receiving crossmatch-negative units with green zone assignment. This finding highlights the limitations of laboratory testing and emphasizes the importance of post-transfusion platelet counts for continuously improving the platelet support of each immune-refractory patient. Disclosures No relevant conflicts of interest to declare.