16th IHIW: international histocompatibility working group in hematopoietic cell transplantation

Leveraging Hematopoietic Cell Transplant Data and Biorepository Resources at the Center for International Blood and Marrow Transplant Research to Improve Patient Outcomes

Hematopoietic cell transplantation (HCT) has undergone many advances over the decades. Trends in HCT utilization have been impacted by research based on the data and samples collected by the Center for International Blood and Marrow Transplant Research (CIBMTR). Here, we provide a summary report of the CIBMTR Biorepository resource and describe the biospecimen inventory along with collection and request procedures. The diversity captured in this inventory reflects transplant activity, and these samples can be leveraged for secondary analyses to generate more data and insights to advance the field. We describe how our resources have already impacted HCT practice and elaborate on possibilities for further collaboration and utilization to maximize capabilities and research opportunities. Hematopoietic cell transplant data and biorepository resources at the CIBMTR have been and continue to be leveraged to improve patient outcomes.

Investigation of HLA susceptibility alleles and genotypes with hematological disease among Chinese Han population

Several genes involved in the pathogenesis have been identified, with the human leukocyte antigen (HLA) system playing an essential role. However, the relationship between HLA and a cluster of hematological diseases has received little attention in China. Blood samples (n = 123913) from 43568 patients and 80345 individuals without known pathology were genotyped for HLA class I and II using sequencing-based typing. We discovered that HLA-A*11:01, B*40:01, C*01:02, DQB1*03:01, and DRB1*09:01 were prevalent in China. Furthermore, three high-frequency alleles (DQB1*03:01, DQB1*06:02, and DRB1*15:01) were found to be hazardous in malignant hematologic diseases when compared to controls. In addition, for benign hematologic disorders, 7 high-frequency risk alleles (A*01:01, B*46:01, C*01:02, DQB1*03:03, DQB1*05:02, DRB1*09:01, and DRB1*14:54) and 8 high-frequency susceptible genotypes (A*11:01-A*11:01, B*46:01-B*58:01, B*46:01-B*46:01, C*01:02-C*03:04, DQB1*03:01-DQB1*05:02, DQB1*03:03-DQB1*06:01, DRB1*09:01-DRB1*15:01, and DRB1*14:54-DRB1*15:01) were observed. To summarize, our findings indicate the association between HLA alleles/genotypes and a variety of hematological disorders, which is critical for disease surveillance.

Circulating cancer-specific CD8 T cell frequency is associated with response to PD-1 blockade in Merkel cell carcinoma

Understanding cancer immunobiology has been hampered by difficulty identifying cancer-specific T cells. Merkel cell polyomavirus (MCPyV) causes most Merkel cell carcinomas (MCCs). All patients with virus-driven MCC express MCPyV oncoproteins, facilitating identification of virus (cancer)-specific T cells. We studied MCPyV-specific T cells from 27 patients with MCC using MCPyV peptide-HLA-I multimers, 26-color flow cytometry, single-cell transcriptomics, and T cell receptor (TCR) sequencing. In a prospective clinical trial, higher circulating MCPyV-specific CD8 T cell frequency before anti-PD-1 treatment was strongly associated with 2-year recurrence-free survival (75% if detectable, 0% if undetectable, p = 0.0018; ClinicalTrial.gov: NCT02488759). Intratumorally, such T cells were typically present, but their frequency did not significantly associate with response. Circulating MCPyV-specific CD8 T cells had increased stem/memory and decreased exhaustion signatures relative to their intratumoral counterparts. These results suggest that cancer-specific CD8 T cells in the blood may play a role in anti-PD-1 responses. Thus, strategies that augment their number or mobilize them into tumors could improve outcomes.

Sequence Variations Within HLA-G and HLA-F Genomic Segments at the Human Leukocyte Antigen Telomeric End Associated With Acute Graft-Versus-Host Disease in Unrelated Bone Marrow Transplantation

Acute graft-versus-host disease (aGVHD) is defined as a syndrome of an immunological response of graft to the host that occurs early after allogeneic hematopoietic stem cell transplantation (HCT). This disease is frequently observed even in HCT matched for human leukocyte antigen (HLA) alleles at multiple gene loci. Although the HLA region represents complex and diverse genomic characteristics, detailed association analysis is required for the identification of uncharacterized variants that are strongly associated with aGVHD. We genotyped three loci, OR2H2, HLA-F-AS1, and HLA-G, that are located in the 460 kb of HLA telomeric region and statistically analyzed the genotypes including HLA-DPB1 with clinical and transplantation outcomes using 338 unrelated bone marrow transplantation (UR-BMT) patient–donor pairs who were matched for HLA-A, HLA-B, HLA-C, HLA-DRB1, and HLA-DQB1 (HLA-10/10). Multivariate analyses demonstrated that HLA-F-AS1 and HLA-DPB1 mismatches were associated with grade II–IV aGVHD (hazard ratio (HR), 1.76; 95% CI, 1.07–2.88; p = 0.026; and HR, 1.59; CI, 1.02–2.49; p = 0.042, respectively). There was no confounding between HLA-F-AS1 and HLA-DPB1 (p = 0.512), suggesting that the HLA-F-AS1 mismatch has a strong effect on aGVHD independently of HLA-DPB1. Moreover, a stratified analysis suggested possible associations of HLA-F-AS1, HLA-DPB1, and/or HLA-G mismatches with grade II–IV aGVHD and the more severe grade III–IV aGVHD. These findings provide new insights into understanding the molecular mechanism of aGVHD caused by HLA-matched UR-BMT.

Immunogenetics of heteroclitic recognition of HLA-DQB1 55R eplet specificity by human alloantibody

Heteroclitic antibodies bind to a related antigen with higher affinity than to the immunizing antigen to which they were generated. This uncommon phenomenon is not well characterized for antibodies to HLA antigens. Here we analyzed allosera reactivity from two transplant recipients sensitized to mismatched donor alleles DQB1*06:01 and DQB1*06:02 respectively. Epitope analysis demonstrated the reactivity of both sera was restricted to DQB1*04, 05, and 06 alleles, with a specificity associated with the 55R eplet. Serum from one of these subjects (TE) was significantly more reactive with DQB1*04 alleles than the immunizing DQB1*06:01 or other alleles, a pattern not present in serum from the other patient. Antibody absorption/elution experiments using B cell lines expressing DQB1*06:01 or DQB1*04:02 alleles confirmed that the heteroclitic TE antibody eluted from cells carrying DQB1*06:01 was significantly more reactive with beads carrying the DQB1*04 alleles than with the DQB1*06 or other alleles. The significantly higher reactivity of the heteroclitic alloantibody with DQB1*04 specificity was explained structurally by variations of amino acid residues within 3.5 Å of 55R. These findings have important implications for the interpretation of DQ alloantibody cross-reactivity frequently observed in transplant recipients.

Human leucocyte antigen diversity: A biological gift to escape infections, no longer a barrier for haploidentical Hemopoietic Stem Cell Transplantation

Since the beginning of life, every multicellular organism appeared to have a complex innate immune system although the adaptive immune system, centred on lymphocytes bearing antigen receptors generated by somatic recombination, arose in jawed fish approximately 500 million years ago. The major histocompatibility complex MHC, named the Human leucocyte antigen (HLA) system in humans, represents a vital function structure in the organism by presenting pathogen-derived peptides to T cells as the main initial step of the adaptive immune response. The huge level of polymorphism observed in HLA genes definitely reflects selection, favouring heterozygosity at the individual or population level, in a pathogen-rich environment, although many are located in introns or in exons that do not code for the antigen-biding site of the HLA. Over the past three decades, the extent of allelic diversity at HLA loci has been well characterized using high-resolution HLA-DNA typing and the number of new HLA alleles, produced through next-generation sequencing methods, is even more rapidly increasing. The level of the HLA system polymorphism represents an obstacle to the search of potential compatible donors for patients affected by haematological disease proposed for a hematopoietic stem cell transplant (HSCT). Data reported in literature clearly show that antigenic and/or allelic mismatches between related or unrelated donors and patients influences the successful HSCT outcome. However, the recent development of the new transplant strategy based on the choice of haploidentical donors for HSCT is questioning the role of HLA compatibility, since the great HLA disparities present do not worsen the overall clinical outcome. Nowadays, NGS has contributed to define at allelic levels the HLA polymorphism and solve potential ambiguities. However, HLA functions and tissue typing probably need to be further investigated in the next future, to understand the reasons why in haploidentical transplants the presence of a whole mismatch haplotype between donors and recipients, both the survival rate and the incidence of acute GvHD or graft rejection are similar to those reported for unrelated HSCTs.

HLA genotyping by next-generation sequencing of complementary DNA

Background

Genotyping of the human leucocyte antigen (HLA) is indispensable for various medical treatments. However, unambiguous genotyping is technically challenging due to high polymorphism of the corresponding genomic region. Next-generation sequencing is changing the landscape of genotyping. In addition to high throughput of data, its additional advantage is that DNA templates are derived from single molecules, which is a strong merit for the phasing problem. Although most currently developed technologies use genomic DNA, use of cDNA could enable genotyping with reduced costs in data production and analysis. We thus developed an HLA genotyping system based on next-generation sequencing of cDNA.

Methods

Each HLA gene was divided into 3 or 4 target regions subjected to PCR amplification and subsequent sequencing with Ion Torrent PGM. The sequence data were then subjected to an automated analysis. The principle of the analysis was to construct candidate sequences generated from all possible combinations of variable bases and arrange them in decreasing order of the number of reads. Upon collecting candidate sequences from all target regions, 2 haplotypes were usually assigned. Cases not assigned 2 haplotypes were forwarded to 4 additional processes: selection of candidate sequences applying more stringent criteria, removal of artificial haplotypes, selection of candidate sequences with a relaxed threshold for sequence matching, and countermeasure for incomplete sequences in the HLA database.

Results

The genotyping system was evaluated using 30 samples; the overall accuracy was 97.0% at the field 3 level and 98.3% at the G group level. With one sample, genotyping of DPB1 was not completed due to short read size. We then developed a method for complete sequencing of individual molecules of the DPB1 gene, using the molecular barcode technology.

Conclusion

The performance of the automatic genotyping system was comparable to that of systems developed in previous studies. Thus, next-generation sequencing of cDNA is a viable option for HLA genotyping.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4300-7) contains supplementary material, which is available to authorized users.

[The impact of HLA haplotype and alleles mismatches of donor-recipient pairs on outcome of haploidentical hematopoietic stem cell transplantation with a third part cord blood unit]

OBJECTIVE

To analyze allele mismatches of HLA- A, - B, - C, - DRB1, - DQB1 and haplotype mismatch of donor- recipient pairs on the outcome of haploidentical transplantation combined with a third part cord blood unit.

METHODS

230 pairs of donor-recipient were performed HLA-A, B, C, DRB1, DQB1 typing using SBT and SSOP methods from January 2012 to December 2014.

RESULTS

Pairs were divided into HLA- 5/10、6/10、7/10 and ≥8/10 groups according to HLA- A, B, C and DRB1 highresolution typing and matched degrees, the 3-year probability of overall survival (OS) for each group were 48.7%, 59.3%, 71.1%, 38.3% (P=0.068) respectively. HLA-6/10 matched group associated with significant favorable effect on OS compared with HLA- 5/10 matched one (P=0.041).When the HLA class I antigen matched on the recipient and donor, improved OS and event free survival (EFS) in HLA- 6/10 matched group than in HLA-5/10 matched one (P=0.017,P=0.088), especially in single HLA-A loci allele matched one (P=0.013,P=0.013), were observed. As to the third part cord blood unit, sharing the same haplotype with the recipient-donor pairs produced better platelet recovery than the misfit one (95.3%vs 86.2%,P= 0.007), similar result was found in terms of neutrophil recovery (98.8%vs 96.1% ,P=0.022).

CONCLUSIONS

HLA locus mismatch and haplotype mismatch of the donor and recipient should be useful for selection of the most optimum donor. Co- infused of an unrelated cord blood unit sharing the same haplotype with the recipient-donor pairs could improve hematopoietic recovery.

HLA-C expression levels define permissible mismatches in hematopoietic cell transplantation

Life-threatening graft-versus-host disease (GVHD) limits the use of HLA-C-mismatched unrelated donors in transplantation. Clinicians lack criteria for donor selection when HLA-C-mismatched donors are a patient's only option for cure. We examined the role for HLA-C expression levels to identify permissible HLA-C mismatches. The median fluorescence intensity, a proxy of HLA-C expression, was assigned to each HLA-C allotype in 1975 patients and their HLA-C-mismatched unrelated transplant donors. The association of outcome with the level of expression of patients' and donors' HLA-C allotypes was evaluated in multivariable models. Increasing expression level of the patient's mismatched HLA-C allotype was associated with increased risks of grades III to IV acute GVHD, nonrelapse mortality, and mortality. Increasing expression level among HLA-C mismatches with residue 116 or residue 77/80 mismatching was associated with increased nonrelapse mortality. The immunogenicity of HLA-C mismatches in unrelated donor transplantation is influenced by the expression level of the patient's mismatched HLA-C allotype. HLA-C expression levels provide new information on mismatches that should be avoided and extend understanding of HLA-C-mediated immune responses in human disease.

Biological significance of HLA locus matching in unrelated donor bone marrow transplantation

We hypothesized that the compatibility of each HLA loci between donor and patient induced divergent transplant-related immunologic responses, which attributed to the individualized manifestation of clinical outcomes. Here, we analyzed 7898 Japanese pairs transplanted with T-cell-replete marrow from an unrelated donor with complete HLA allele typing data. Multivariable competing risk regression analyses were conducted to evaluate the relative risk (RR) of clinical outcomes after transplantation. A significant RR of HLA allele mismatch compared with match was seen with HLA-A, -B, -C, and -DPB1 for grade III-IV acute graft-versus-host disease (GVHD), and HLA-C for chronic GVHD. Of note, only HLA-C and HLA-DPB1 mismatch reduced leukemia relapse, and this graft-versus-leukemia effect of HLA-DPB1 was independent of chronic GVHD. HLA-DRB1 and HLA-DQB1 double (DRB1_DQB1) mismatch was revealed to be a significant RR for acute GVHD and mortality, whereas single mismatch was not. Thus, the number of HLA-A, -B, -C, -DPB1, and DRB1_DQB1 mismatches showed a clear-cut risk difference for acute GVHD, whereas the number of mismatches for HLA-A, -B, -C, and DRB1_DQB1 showed the same for mortality. In conclusion, we determined the biological response to HLA locus mismatch in transplant-related immunologic events, and provide a rationale for use of a personalized algorithm for unrelated donor selection.

A Micropolymorphism Altering the Residue Triad 97/114/156 Determines the Relative Levels of Tapasin Independence and Distinct Peptide Profiles for HLA-A(*)24 Allotypes

While many HLA class I molecules interact directly with the peptide loading complex (PLC) for conventional loading of peptides certain class I molecules are able to present peptides in a way that circumvents the PLC components. We investigated micropolymorphisms at position 156 of HLA-A(*)24 allotypes and their effects on PLC dependence for assembly and peptide binding specificities. HLA-A(*)24:06(156Trp) and HLA-A(*)24:13(156Leu) showed high levels of cell surface expression while HLA-A(*)24:02(156Gln) was expressed at low levels in tapasin deficient cells. Peptides presented by these allelic variants showed distinct differences in features and repertoire. Immunoprecipitation experiments demonstrated all the HLA-A(*)24/156 variants to associate at similar levels with tapasin when present. Structurally, HLA-A(*)24:02 contains the residue triad Met97/His114/Gln156 and a Trp156 or Leu156 polymorphism provides tapasin independence by stabilizing these triad residues, thus generating an energetically stable and a more peptide receptive environment. Micropolymorphisms at position 156 can influence the generic peptide loading pathway for HLA-A(*)24 by altering their tapasin dependence for peptide selection. The trade-off for this tapasin independence could be the presentation of unusual ligands by these alleles, imposing significant risk following hematopoietic stem cell transplantation (HSCT).

Soluble HLA technology as a strategy to evaluate the impact of HLA mismatches

HLA class I incompatibilities still remain one of the main barriers for unrelated bone marrow transplantation (BMT); hence the molecular understanding of how to mismatch patients and donors and still have successful clinical outcomes will guide towards the future of unrelated BMT. One way to estimate the magnitude of polymorphisms within the PBR is to determine which peptides can be selected by individual HLA alleles and subsequently presented for recognition by T cells. The features (structure, length, and sequence) of different peptides each confer an individual pHLA landscape and thus directly shape the individual immune response. The elution and sequencing of peptides by mass spectrometric analysis enable determining the bona fide repertoire of presented peptides for a given allele. This is an effective and simple way to compare the functions of allelic variants and make a first assessment of their degree of permissivity. We describe the methodology used for peptide sequencing and the limitations of peptide prediction tools compared to experimental methods. We highlight the altered peptide features that are observed between allelic variants and the need to discover the altered peptide repertoire in situations of "artificial" graft versus host disease (GvHD) that occur in HLA-specific hypersensitive immune responses to drugs.

Graft-versus-host disease and survival after cord blood transplantation for acute leukemia: a comparison of Japanese versus White populations

An earlier report identified higher risks of acute and chronic graft-versus-host disease (GVHD) in White children compared with the Japanese after HLA-matched sibling transplantations. The current analysis explored whether racial differences are associated with GVHD risks after unrelated umbilical cord blood transplantation. Included are patients of Japanese descent (n = 257) and Whites (n = 260; 168 of 260 received antithymocyte globulin [ATG]). Transplants were performed in the United States or Japan between 2000 and 2009; patients were aged 16 years or younger, had acute leukemia, were in complete remission, and received a myeloablative conditioning regimen. The median ages of the Japanese and Whites who received ATG were younger at 5 years compared with 8 years for Whites who did not receive ATG. In all groups most transplants were mismatched at 1 or 2 HLA loci. Multivariate analysis found no differences in risks of acute GVHD between the Japanese and Whites. However, chronic GVHD was higher in Whites who did not receive ATG compared with the Japanese (hazard ratio, 2.16; P < .001), and treatment-related mortality was higher in Whites who received ATG compared with the Japanese (relative risk, 1.81; P = .01). Nevertheless, there were no significant differences in overall survival between the 3 groups.