S.G.E. Marsh

Diverging effects of HLA–DPB1 matching status on outcome following unrelated donor transplantation depending on disease stage and the degree of matching for other HLA alleles

Disease stage and recipient/donor human leukocyte antigen (HLA) matching are important determinants of outcome in transplantation using volunteer-unrelated donors (VUD). Matching for HLA-A, -B, -C, -DRB1, -DQB1 is beneficial, whereas the importance of DPB1 matching is more controversial. The impact of HLA matching status may differ dependent on disease stage. We investigated the outcome according to the degree of HLA matching at 6 loci, in 488 recipients of predominantly T-cell depleted bone marrow VUD transplants for leukaemia. Survival was significantly better in 12/12-matched transplants in those with early leukaemia (5 years: 63 versus 41% in 10/10 matched, P=0.006), but not late stage disease. Conversely, within the HLA-mismatched group (⩽9/10), there was a significant survival advantage to DPB1 mismatching (5 years: 39 versus 21% in DPB1 matched, P=0.008), particularly in late leukaemia (P=0.01), persisting in multivariate analysis (odds ratio 0.478; 95% confidence interval 0.30, 0.75; P=0.001). These novel findings suggest that the best outcome for patients with early leukaemia, with a 10/10-matched donor, is achieved by matching for DPB1. Conversely, our results suggest that in patients receiving an HLA-mismatched graft, the outcome is significantly better if they are also mismatched for DPB1. We recommend validation of these results in independent datasets.

Cord blood stem cells for hematopoietic stem cell transplantation in the UK: how big should the bank be?

The need for umbilical cord blood units as an alternative source of hematopoietic stem cells for transplantation is increasing. This study defines the optimal size of a cord blood bank for a population of various ethnic background. See related perspective article on page 451. Background A stored cord blood donation may be a valuable source of hemopoietic stem cells for allogeneic transplantation when a matched sibling donor is not available. We carried out a study to define the optimal size of a national cord blood bank for the UK. Design and Methods We calculated the actual numbers of possible donors and the chance of finding at least one donor for 2,000 unselected and for 722 non-North Western European patients for whom searches had been initiated as a function of three levels of HLA matching (4, 5 and 6 out of 6 alleles by HLA-A, -B low and -DRB1 high resolution HLA typing) according to various donor bank sizes. Results With a bank size of 50,000, 80% of patients will have at least one donor unit available at the 5 out of 6 HLA allele match level (median 9 donors per patient), and 98% will have at least one donor at the 4 out of 6 allele match level (median 261). Doubling the size of the bank yields at least one donor for only an additional 6% of patients at the 5 of 6 allele match level. Moreover, for non-North Western European patients a 50,000 unit bank provides a donor for 50% at the 5 allele match level, and for 96% at the 4 allele match level. Conclusions A bank containing 50,000 units is optimal for the UK and larger banks would only marginally increase the chance of finding suitable units.

Translating the HLA-DPB1 T-cell epitope-matching algorithm into clinical practice

A simple online tool can predict HLA-DPB1 T-cell epitope (TCE) matching. At least a quarter of hematopoietic SCT recipients could benefit from a better outcome by including HLA-DPB1 in unrelated donor (UD) selection algorithms.

Single molecule real-time DNA sequencing of HLA genes at ultra-high resolution from 126 International HLA and Immunogenetics Workshop cell lines

The hyperpolymorphic HLA genes play important roles in disease and transplantation and act as genetic markers of migration and evolution. A panel of 107 B‐lymphoblastoid cell lines (B‐LCLs) was established in 1987 at the 10th International Histocompatibility Workshop as a resource for the immunogenetics community. These B‐LCLs are well characterised and represent diverse ethnicities and HLA haplotypes. Here we have applied Pacific Biosciences’ Single Molecule Real‐Time (SMRT) DNA sequencing to HLA type 126 B‐LCL, including the 107 International HLA and Immunogenetics Workshop (IHIW) cells, to ultra‐high resolution. Amplicon sequencing of full‐length HLA class I genes (HLA‐A, ‐B and ‐C) and partial length HLA class II genes (HLA‐DRB1, ‐DQB1 and ‐DPB1) was performed. We typed a total of 931 HLA alleles, 895 (96%) of which were consistent with the typing in the IPD‐IMGT/HLA Database (Release 3.27.0, January 20, 2017), with 595 (64%) typed at a higher resolution. Discrepant types, including novel alleles (n = 10) and changes in zygosity (n = 13), as well as previously unreported types (n = 34) were observed. In addition, patterns of linkage disequilibrium were distinguished by four‐field resolution typing of HLA‐B and HLA‐C. By improving and standardising the HLA typing of these B‐LCLs, we have ensured their continued usefulness as a resource for the immunogenetics community in the age of next generation DNA sequencing.

Recipient/donor HLA and CMV matching in recipients of T-cell-depleted unrelated donor haematopoietic cell transplants

Improving haematopoietic cell transplantation outcomes by selection of an HLA-matched unrelated donor is best practice; however, donor selection by secondary characteristics is controversial. We studied 1271 recipients with haematological malignancies who underwent T-cell-depleted allografts and had complete data on HLA-matching status for six loci (HLA-A, -B, -C, -DRB1, -DQB1, -DPB1) and clinical outcome data. Five-year overall survival was 40.6%. HLA mismatching (at HLA-A, -B, -C, -DRB1, -DQB1) relative risk (RR) 1.22, 95% confidence interval (CI) 1.2–1.5, P=0.033 for 1 mismatch and RR 1.46, 95% CI 1.1–1.9, P=0.009 for >1 mismatch) and CMV mismatching (RR 1.37, 95% CI 1.2–1.6, P<0.001) were significantly associated with inferior survival. Donors aged <30 years showed a trend towards better survival. The multivariate model for mortality, combining CMV and HLA-match status, found an RR of 1.36 (95% CI 1.1–1.7, P=0.003) for HLA matched/CMV mismatched, an RR of 1.22 (95% CI 0.99–1.5, P=0.062) for HLA mismatched/CMV matched and an RR of 1.81 (95% CI 1.4–2.3, P=<0.001) for HLA/ CMV mismatched, compared with the HLA/CMV-matched recipients. These data suggest that HLA and CMV matching status should be considered when selecting unrelated donors and that CMV matching may abrogate the effect of an HLA mismatch.

The novel HLA‐B*44 allele, HLA‐B*44:220, identified by Single Molecule Real‐Time DNA sequencing in a British Caucasoid male

The genomic sequence of the novel HLA-B*44:220 allele identified in a British Caucasoid male.

No impact of NOD2/CARD15 on outcome after SCT: a reply.

In a recent issue of Bone Marrow Transplantation, Dr Sairafi et al. reported the results of a retrospective study to investigate the impact of NOD2/CARD15 single nucleotide polymorphisms (SNPs) on the outcome of allogeneic haematopoietic stem cell transplants (HSCT). They found no significant correlation between the presence of a NOD2/ CARD15 SNP and the incidence of acute GVHD, TRM, relapse-free survival or overall survival. We have recently reported the results of a retrospective analysis of the impact of NOD2/CARD15 SNPs on the outcome of 196 unrelated donor HSCT (UD-HSCT) pairs where the recipient was diagnosed with acute leukaemia. We found that the presence of a NOD2/CARD15 SNP correlated with a significant reduction in overall survival because of an increase in disease relapse. Numerous other studies have shown the presence of SNPs to have a detrimental effect on the outcome of HSCT although the actual complication observed varies between groups and is thought to be dependent on specific characteristics of the cohort itself. The authors discussed the possibility that differences in patient characteristics and transplant regimens between their cohort and those previously reported may explain why they failed to see significant effects on outcome where others have. Thus, we looked for any differences between the cohort described by Sairafi et al. and the patients in our study that might explain the divergent results. The most obvious difference is that their study comprised a mixture of related and UD sources, whereas our study focused solely on UD transplants. We found that the effect of NOD2/CARD15 SNPs was seen only in recipients with acute leukaemia and more specifically the effect was more pronounced in the ALL subgroup (Figure 1). This marked effect in acute leukaemia has also been reported in a related donor cohort, although, as previously, the outcome affected was different in the two studies based on differences in the clinical protocols used. As 37% of the cohort studied by Sairafi et al. were recipients whose diagnosis was not acute leukaemia, the lack of effect seen in these recipients may mask any effect of the NOD2/ CARD15 SNPs in this study. The use and method of T-cell depletion was noticeably different when compared with our data, which we and others believe contributes significantly to the effect of any polymorphisms. In addition, the majority of transplants in the Sairafi study occurred when the recipient was considered to be in a lowrisk stage of their disease, which in itself may predict for a reduced risk of disease relapse. Finally, the frequency of NOD2/CARD15 SNPs seen in their study were markedly lower than in our cohort and in other HSCT studies. (The reported overall SNP frequency was 18% as compared with 27–29% in other studies.) There is evidence to suggest that there is geographic variation in the prevalence of NOD2/CARD15 SNPs, which may explain the low frequency seen. Thus, the lack of correlation to transplant outcome may be due to a lower prevalence of SNPs in this cohort. It would be of interest to see if Sairafi et al. were able to see an effect in more homogeneous subgroups of their cohort, particularly in the acute leukaemia recipients and the UD pairs. This study adds much to the discussion that

Ethnicity, length of time on the register and sex predict donor availability at the confirmatory typing stage.

Despite over 20 million unrelated donors being listed worldwide, donor attrition at the confirmatory typing (CT) stage of donor acquisition is a key source of delay. Anthony Nolan undertook a study of CT requests from 2010 to 2011 to identify factors associated with attrition. Of 7541 CT requests, 38.2% were cancelled for donor reasons. Of these, 19.4% were personal, 34.1% medical, 36% no contact, 7.9% emigrated and 2.6% others. African (odds ratio (OR) 2.78, P<0.001), African-Caribbean (OR 3.07, P<0.001), Asian (OR 2.65, P<0.001), Jewish (OR 1.54, P=0.009) and Mediterranean (OR=2.38, P<0.001) donors were more likely not to be available compared to Caucasian donors. Female donors were also more likely not to be available (OR=1.32, P<0.001): primarily due to pregnancy. Older donors were less likely to be available in univariate analysis, but this association was not significant after controlling for other factors. Blood donors and those recruited within the past five years had lower rates of attrition. Accumulation of additional attrition-associated characteristics for a given donor was associated with progressively greater odds of attrition (OR 1.99, 2.52, 3.4 and 5.53, respectively, for 1, 2, 3 and 4 risk factors, P<0.001). Donor registries must develop evidence-driven strategies to recruit and retain the most reliable donors.

Caspase-8 polymorphisms result in reduced Alemtuzumab-induced T-cell apoptosis and worse survival after transplantation

Allo-SCT using unrelated donors is a curative treatment for patients with hematological disorders. The best donor is one matched for 10/10 HLA alleles, however studies have shown an additional survival benefit when considering other genetic factors. It has been shown that a six-nucleotide insertion/deletion polymorphism in the CASP8 gene promoter results in reduced susceptibility of T lymphocytes to undergo apoptosis. In 186 SCT recipients, we found a significantly better OS in those who received a transplant from a WT/WT donor compared with donors with a deletion (3 years: 52 vs 34%; P=0.03; multivariate analysis; RR 0.61; 95% CI 0.38–0.98, P=0.04). This was more marked when both the patient and the donor had a deletion (3 years OS: 62% compared with 36%, P=0.01). As the majority of these patients received Alemtuzumab during conditioning, we went on to analyze the in vitro effect of the polymorphism on Alemtuzumab-induced apoptosis. We showed statistically significantly higher percentages of apoptotic naïve CD4 (P<0.0005) and CD8 (P<0.0005) T cells in WT/WT donors in comparison with donors with a deletion. These data imply an unrecognized role for the CASP8 promoter polymorphism on survival following unrelated SCT particularly in the context of T-cell depletion with Alemtuzumab.

Nomenclature for factors of the HLA system, update July 2014

The following sequences have been submitted to the Nomenclature Committee since the June 2014 nomenclature update and, following agreed policy, have been assigned official allele designations (1). Complete details of all sequences will be published in a forthcoming report. Below are listed the newly assigned sequences (Table 1) and confirmations of previously reported sequences (Table 2). The accession number of each sequence is given and these can be used to retrieve the sequence files from the EMBL, GenBank or DDBJ data libraries. Although accession numbers have been assigned by the data-libraries and most sequences are already available, there is still the possibility