The correlation of the PLT increment with other clinical outcomes and the effect of leukoreduction on HLA-matched PLT transfusion could not be determined. Prospective studies utilizing current technology and examining clinical outcomes are necessary to demonstrate the effectiveness of HLA-matched PLT transfusion.

Cross-matched PLTs are useful in increasing PLT counts in alloimmunized, transfusion-refractory HT patients, but data about their impact on hemorrhage and mortality are lacking.

Extended molecular characterization of HLA genes in the IHWG reference B-lymphoblastoid cell lines (B-LCLs) was one of the major goals for the 17th International HLA and Immunogenetics Workshop (IHIW). Although reference B-LCLs have been examined extensively in previous workshops complete high-resolution typing was not completed for all the classical class I and class II HLA genes. To address this, we conducted a single-blind study where select panels of B-LCL genomic DNA samples were distributed to multiple laboratories for HLA genotyping by next-generation sequencing methods. Identical cell panels comprised of 24 and 346 samples were distributed and typed by at least four laboratories in order to derive accurate consensus HLA genotypes. Overall concordance rates calculated at both 2- and 4-field allele-level resolutions ranged from 90.4% to 100%. Concordance for the class I genes ranged from 91.7 to 100%, whereas concordance for class II genes was variable; the lowest observed at HLA-DRB3 (84.2%). At the maximum allele-resolution 78 B-LCLs were defined as homozygous for all 11 loci. We identified 11 novel exon polymorphisms in the entire cell panel. A comparison of the B-LCLs NGS HLA genotypes with the HLA genotypes catalogued in the IPD-IMGT/HLA Database Cell Repository, revealed an overall allele match at 68.4%. Typing discrepancies between the two datasets were mostly due to the lower-resolution historical typing methods resulting in incomplete HLA genotypes for some samples listed in the IPD-IMGT/HLA Database Cell Repository. Our approach of multiple-laboratory NGS HLA typing of the B-LCLs has provided accurate genotyping data. The data generated by the tremendous collaborative efforts of the 17th IHIW participants is useful for updating the current cell and sequence databases and will be a valuable resource for future studies.

IntroductionDonor‐recipient HLA compatibility is an important determinant of transplant outcomes. Allele‐group to allele‐level imputations help assign HLA genotypes when allele‐level genotypes are not available during donor selection.MethodsWe evaluated the performance of HaploStats, an allele‐level multi‐locus HLA genotype imputation tool from the National Marrow Donor Program, in a cross‐sectional study including hematopoietic stem cell donors (HSCD) from Quebec, Canada. A total of 144 self‐identified Caucasian HSCD genotyped at the allele‐group and allele‐level for HLA‐A, ‐B, ‐C, ‐DRB1, and ‐DQB1 loci were studied. We compared allele‐level genotypes imputed by HaploStats to those obtained by the reference standard, sequenced‐based typing (SBT).ResultsImputation performance, determined by allele‐level genotype recall (fraction of matching imputed and sequenced genotypes) was 97%, 96%, 95%, 84%, and 81% for HLA‐A, ‐B, ‐C, ‐DRB1, and ‐DQB1 loci, respectively. Our sample deviated from Hardy‐Weinberg equilibrium only at the HLA‐DRB1 locus. Residual ambiguity, determined by typing resolution scores (TRS), was greatest for HLA class II loci (average TRS 0.65 and 0.80 for DRB1 and DQB1, respectively). In contrast, average TRS of 0.88, 0.84, and 0.92 was observed for HLA‐A, ‐B, and ‐C, respectively.ConclusionsHLA allele imputation from ambiguous genotypes demonstrate satisfactory prediction accuracy for HLA class I but modest prediction accuracy for HLA class II loci in self‐identified Caucasian HSCD from Quebec. While consideration of high‐resolution allele and haplotype frequencies in the Quebec population may improve the performance of available allele‐level multi‐locus genotype imputation tools in Quebec, this study suggests that genotyping at the first two field level should be conducted whenever possible.

Background: Cell death, as determined by complement-dependent cytotoxicity or antibody binding, as assessed by flow cytometry, are the two main methods histocompatibility laboratories use to identify HLA antibodies. Conventional cytotoxicity assays, even anti-human globulin (AHG) enhanced, are relatively insensitive, subjective and require complement fixation. In contrast, antibody binding assays (e.g.: flow cytometry crossmatch, FCXM) are sensitive, objective, and complement independent. When sera from potential transplant recipients test positive by both methods, most centers would not proceed to transplant unless patients undergo desensitization. However, when the CDC crossmatch is negative but the FCXM positive, how or whether to proceed is controversial. Frequently, both assays are performed.Methods: In this study, we developed a comprehensive procedure that determines cell death, and antibody binding in a single assay: the cytotoxic flow crossmatch (cFCXM). The assay was validated in parallel studies with two other conventional methodologies, namely AHG and FCXM.Results: Using a combination of eight cells and 15 sera, we have determined an optimal method for the simultaneous detection of HLA antibody binding and cytotoxicity using a single platform. Additionally, we have identified three distinct patterns of HLA antibody reactivity: (1) AHG