Tracie Profaizer

Immunogenicity of decellularized cryopreserved allografts in pediatric cardiac surgery: comparison with standard cryopreserved allografts.

BACKGROUND Recognition of the immunogenicity of standard cryopreserved allografts has led to the development of new decellularized allografts (CryoValve SG; CryoLife, Inc, Kennesaw, Ga). This preliminary study examined the HLA antibody response to these decellularized allografts and compared it with the response to standard allograft material. METHODS We prospectively measured the frequency of panel-reactive HLA class I (HLA-A, HLA-B, and HLA-C) and class II (HLA-DR/DQ) alloantibodies in 14 children (age 8.5 +/- 7.9 years) receiving decellularized, cryopreserved allografts, including 6 undergoing allograft patch insertion and 8 with a valved pulmonary allograft. We compared them with 20 historical control subjects (age 1.7 +/- 2.4 years) undergoing implantation of standard cryopreserved allografts, 8 with valves and 12 with allograft patch. All patients had panel-reactive antibody levels measured before and at 1, 3, and 12 months after the operation. HLA class I and class II panel-reactive antibody levels were determined with a sensitive flow cytometry technique. RESULTS We found panel-reactive antibody levels in decellularized allografts to be elevated slightly from preoperative levels for both class I and class II antibodies at 1, 3, and 12 months (P >.05). The panel-reactive antibody level for both class I and class II antibodies were significantly lower for decellularized allografts as compared to standard allografts. Functionally, the allografts were similar with decellularized valved grafts showing a peak echo-determined systolic gradient of 13 +/- 15 mm Hg at 8 +/- 2.6 months postoperatively as compared to a gradient of 24 +/- 18 mm Hg measured 12 +/- 6 months postoperatively in standard allografts (P =.11). CONCLUSIONS Decellularized grafts elicited significantly lower levels of class I and class II HLA antibody formation at 1, 3, and 12 months after implantation than did standard cryopreserved allografts. Early hemodynamic function of decellularized grafts was similar to that of standard cryopreserved allograft valves. Further experience is necessary to determine whether the reduced immunogenicity of decellularized allografts will truly allow tissue ingrowth and improved long-term durability in patients.

Prospective Randomized Trial of Azathioprine in Cryopreserved Valved Allografts in Children

BACKGROUND The purpose of this study was to prospectively assess the effects of azathioprine on the humoral immune response to HLA alloantigens and allograft function in children receiving cryopreserved valved allografts. METHODS We randomized 13 children to receive azathioprine or not to receive azathioprine (controls) after receiving a cryopreserved valved allograft. Azathioprine patients received intraoperatively 4 mg/kg of azathioprine and 2.0 +/- 0.5 mg/kg once daily for 3 months after operation. Panel reactive antibodies against HLA class I and class II alloantigens were measured before, 1 month, and 3 months after operation. RESULTS Panel reactive antibodies were not significantly different between the azathioprine and control groups before (0.0% +/- 0% versus 1.6% +/- 1%), 1 month (59% +/- 17% versus 71% +/- 12%), or 3 months (84% +/- 15% versus 96% +/- 1.3%) after operation. There were no differences in degree of allograft valve stenosis between azathioprine (31.5 +/- 26 mm Hg, 13.4 +/- 7 months postoperatively) and control groups (25.4 +/- 11 mm Hg, 17.2 +/- 10 months postoperatively) or allograft valve insufficiency. CONCLUSIONS Azathioprine does not significantly decrease the immune response to HLA alloantigens or affect the function of cryopreserved valved allografts used in children to repair congenital heart defects.

Repeat donor HLA-DR mismatches in renal transplantation: is the increased failure rate caused by noncytotoxic HLA-DR alloantibodies?

INTRODUCTION Data from the UCLA/UNOS and Collaborative Transplant Studies Registries indicate that mismatched HLA-DR alloantigens expressed on a former donor renal allograft should not be repeated because of significantly poorer long-term survival. METHODS Retransplant candidates waiting for another renal allograft were screened for HLA class II alloantibodies (aAb) using direct complement-dependent cytotoxicity and several sensitive aAb binding assays. RESULTS When screened by complement-dependent cytotoxicity, 46% of the patients were aAb negative. In contrast, using aAb binding assays, 90% of the patients had HLA-DR aAb specific for previous HLA-DR allograft mismatches. Most important, no directly cytotoxic HLA-DR antibody was detected in 9 of 27 patients. CONCLUSION Our studies suggest that crossing the same HLA-DR mismatch in a subsequent transplant may result in poorer survival due to underlying donor-specific HLA-DR aAb. If confirmed in a retrospective study of retransplant patients, B cell donor cross-matches using antiglobulin complement-dependent cytotoxicity or flow cytometry would appear essential if this barrier were to be crossed.

HLA alleles and drug hypersensitivity reactions

The human leucocyte antigen (HLA) system is well known for its association with certain diseases such as ankylosing spondylitis, celiac disease and many others. More recently, severe and even fatal drug hypersensitivity reactions linked to particular HLA alleles have been discovered. The significance of these discoveries has led the European Medicines Agency (EMA) and its member state agencies to recommend HLA gene testing before initiation of drug treatment. To date, the following drugs have been identified as causing significant drug hypersensitivity reactions in patients who have the following HLA alleles: abacavir and HLA‐B*57:01, carbamazepine and HLA‐B*15:02/A*31:01 and finally allopurinol and HLA‐B*58:01. This review will outline and discuss these three drugs and their associated HLA alleles as well as examine the pathogenesis of the drug hypersensitivity reactions.

HLA genotyping in the clinical laboratory: comparison of next‐generation sequencing methods

Implementation of human leukocyte antigen (HLA) genotyping by next‐generation sequencing (NGS) in the clinical lab brings new challenges to the laboratories performing this testing. With the advent of commercially available HLA‐NGS typing kits, labs must make numerous decisions concerning capital equipment and address labor considerations. Therefore, careful and unbiased evaluation of available methods is imperative. In this report, we compared our in‐house developed HLA NGS typing with two commercially available kits from Illumina and Omixon using 10 International Histocompatibility Working Group (IHWG) and 36 clinical samples. Although all three methods employ long range polymerase chain reaction (PCR) and have been developed on the Illumina MiSeq platform, the methodologies for library preparation show significant variations. There was 100% typing concordance between all three methods at the first field when a HLA type could be assigned. Overall, HLA typing by NGS using in‐house or commercially available methods is now feasible in clinical laboratories. However, technical variables such as hands‐on time and indexing strategies are sufficiently different among these approaches to impact the workflow of the clinical laboratory.

Celiac disease and HLA typing using real-time PCR with melting curve analysis

Celiac disease (CD) is an autoimmune disease characterized by chronic diarrhea, inflammatory lesions of small bowel and nutritional malabsorption. CD is strongly associated with the presence of HLA-DQB*02, DQB*03:02 and DQA*05. The absence of any one of these three human leukocyte antigen (HLA) alleles rules out the diagnosis of CD in suspected patients. Here, we describe a novel method to detect the presence of these specific HLA alleles using real-time polymerase chain reaction (PCR) with melting curve analysis. Compared with current HLA typing assays, the real-time PCR method is faster, requires fewer handling steps and provides 100% sensitivity and specificity for typing of HLA-DQB*02, DQB*03:02 and DQA*05 alleles.

Report on the effects of fragment size, indexing, and read length on HLA sequencing on the Illumina MiSeq

Single-molecule sequencing should allow for unambiguous, accurate, and high-throughput HLA typing. In this proof of principle study, we investigated the effects of fragment size for library preparation, indexing strategy, and read length on HLA typing. Whole gene amplicons of HLA-A, B, C, DRB1, and DQB1 were obtained by long-range PCR. For library preparation, two fragment sizes were evaluated: 100-300bp and 300-600bp. For sample multiplexing, two indexing strategies were compared: indexing-by-amplicon, where each individual amplicon is barcoded, and indexing-by-patient, where each patients five loci are equimolarly pooled after PCR and indexed with the same barcode. Sequencing was performed on an Illumina MiSeq instrument using paired-end 150bp and 250bp read lengths. Our results revealed that the 300-600bp fragments in the 2×250 MiSeq group gave the most accurate sequencing results. There was no difference in HLA typing results between the two indexing strategies, suggesting that indexing-by-patient, which is much simpler, is a viable option. In conclusion, enzymatic fragmentation of pooled whole gene amplicons is a suitable strategy for HLA typing by next-generation sequencing on the Illumina MiSeq.

HLA genotyping using the Illumina HLA TruSight next-generation sequencing kits: A comparison

Illumina first introduced their TruSight human leucocyte antigen (HLA) next‐generation sequencing (NGS) typing kit in 2015 and subsequently followed up with a new version in 2016. Here we report on our experience comparing the two versions of the Illumina HLA NGS kits.

Human Leukocyte Antigen Typing by Next-Generation Sequencing

Human leukocyte antigen (HLA) allele ambiguities are the result of limitations of current HLA typing methodologies. Ambiguities maybe due to polymorphisms in unsequenced regions of HLA genes or cis/trans variants that cannot be distinguished by Sanger sequencing. Next generation sequencing (NGS) can resolve these two sources of ambiguity because the entire gene can be sequenced. Commercially available HLA NGS genotyping kits enable laboratories to deliver high-quality and unambiguous HLA typing results at an affordable cost. Third generation sequencing technologies are poised to further improve sequencing quality, shorten turn-around and library preparation times, as well as provide full-gene phasing.