National Marrow Donor Program Registry Research Articles

HLA-Matched Unrelated Donors for Patients with Sickle Cell Disease: Results of International Donor Searches.

Sickle cell disease (SCD) is the most common inherited hemoglobinopathy. Hematopoietic stem cell transplantation (HCT) is the sole curative therapy for SCD, but few patients will have a matched sibling donor. Patients with SCD are mostly of African origin and thus are less likely to find a matched unrelated donor in international registries. Using HaploStats, we estimated HLA haplotypes for 185 patients with SCD (116 from a Brazilian center and 69 from European Society for Blood and Marrow Transplantation [EBMT] centers) and classified the ethnic origin of haplotypes. Then we assessed the probability of finding an HLA-matched unrelated adult donor (MUD), considering loci A, B, and DRB1 (6/6), in international registries. Most haplotypes were African, but Brazilians showed a greater ethnic admixture than EBMT patients. Nevertheless, the chance of finding at least one 6/6 potential allelic donor was 47% for both groups. Most potential allelic donors were from the US National Marrow Donor Program registry and from the Brazilian REDOME donor registry. Although the probability of finding a donor is higher than previously reported, strategies are needed to improve ethnic diversity in registries. Moreover, predicting the likelihood of having an MUD might influence SCD management.

Frequencies and haplotype associations of non-expressed HLA alleles in ethnically diverse populations on the National Marrow Donor Program’s Be The Match Registry

HLA allele matching is critical to successful bone marrow transplantation between a patient and donor. Non-functional HLA alleles, so called ‘null alleles’, are not well described within a large population of well HLA-typed ethnically diverse individuals despite their impact on donor selection. A retrospective analysis was performed on 833,789 unrelated donors (URDs) in the National Marrow Donor Program’s Be The Match Registry® typed for HLA-A, -B, -C, -DRB1, -DQB1, and -DPB1 by next-generation DNA sequencing. Results showed that null alleles occur in low frequency (2.30E−04) compared to expressed alleles. Their overall frequency ranged from 6.00E−07 to 9.25E−04 with a median of 1.20E-06. The expected allele associations were commonly observed for HLA-A*24:09N, HLA-B*51:11N, and HLA-C*04:09N; however, associations outside of the expected were also observed. Notably, 82% of the National Marrow Donor Program Registry URDs carrying HLA-A*24:11N showed a different HLA-C allele association, HLA-C*05:01, compared to the allele described by prior published work characterizing German donor populations, HLA-C*04:01. The frequencies of these observed null alleles and linkage disequilibrium information could be invaluable and helpful in guiding the HLA testing decisions.

Human Leukocyte Antigen Matched Unrelated Donors for Patients with Sickle Cell Disease According to Geographic Origin: Results of International Donor Searches

Background: Hematopoietic stem cell transplantation (HSCT), the only available curative therapy for sickle cell disease (SCD), remains hampered by the lack of histocompatible stem cell donors. Most patients will not have a suitable human leukocyte antigen(HLA) matched sibling donor. In addition, SCD affects ethnic groups that are underrepresented in stem cell donor registries worldwide. Objective: to assess the probability of having a potential allelic HLA matched unrelated donor(MUD) for HLA-A,B and DRB1 loci (6/6) in international donor registries for patients with SCD. Methods: 185 patients with SCD were included, 116 from Brazil, of whom 23 underwent HSCT, and 69 patients who underwent HSCT in centers reporting to the European Society for Blood and Marrow Transplantation (EBMT). All patients had HLA typing available at intermediate or high resolution. For intermediate resolution, using the National Marrow Donor Program (NMDP) code, we assigned alleles based on allele frequencies.We performed HLA haplotype estimation using the HaploStats website, which describes HLA haplotype frequency from the NMDP registry for the following ethnic groups: Caucasian, African-American, Asian, Hispanic and Native American. Because Hispanic is not a primary ethnicity, we did not consider this group in our analyses. Based on haplotype frequency of each ethnic group, we defined the most likely ethnicity for each estimated haplotype; those with frequency >1:1000 in all ethnic groups were named common. Unrelated donor search was done using the World Marrow Donor Association (WMDA) algorithm, which is based on haplotype matching. A potential allelic donor was defined as a full match high resolution 6/6 donor. Because it is described that testing at least 5 potential allelic donors simultaneously increases the chances of having a real donor, we assessed the probability of finding at least 1 and at least 5 potential allelic donors. Patients who received HSCT from MUD were excluded from donor searches (n=10).Comparisons of probabilities of having potential allelic donors between Brazilian and EBMT cohorts were performed by chi-square. Results: In the Brazilian cohort, from 181 HLA haplotypes, 45% were classified as African-American, 18% common, 12% Caucasian, 9% Amerindian and 16% could not be classified. In the EBMT cohort, from 116 HLA haplotypes, 70% were classified as African-American, 8% common, 6% Caucasian, 3% Amerindian and 13% were not classified. Although Brazilians showed greater genetic admixture, chances of finding at least one potential allelic MUD were 47% in both groups (p-value not significant) and chances of having at least 5 potential allelic MUD were 24% for Brazilians and 15% for EBMT (p-value not significant). Overall, most potential allelic MUD were found in the NMDP registry, followed by the Brazilian registry (REDOME) and by the German registry (ZKMD); for the Brazilian cohort, most potential allelic MUD were found in REDOME. Discussion: Migration from Africa to Brazil started at the colonial period, and interethnic admixture have been occurring since then, explaining the higher diversity observed in the Brazilian cohort. Despite differences in ethnic composition, chances of having at least one potential allelic MUD are identical, probably because carrying at least one African or Amerindian haplotype decreases the chances of a full HLA matching. Although we demonstrated higher probabilities of finding a potential allelic MUD in SCD than previous studies, the chances are still low, therefore further strategies are required to increase donor representativeness for SCD. In this setting, alternative sources, such as haploidentical HSCT and cord blood, should be considered. Also, our study might help to predict the probabilities of finding a MUD for patients with SCD. This is important because given that HSCT in SCD has better results if performed at earlier age, knowing which patients are less likely to find a MUD might influence therapy management. Disclosures No relevant conflicts of interest to declare.

Multiplicative fitness, rapid haplotype discovery, and fitness decay explain evolution of human MHC

The major histocompatibility complex (MHC) is a central component of the vertebrate immune system and hence evolves in the regime of a host-pathogen evolutionary race. The MHC is associated with quantitative traits which directly affect fitness and are subject to selection pressure. The evolution of haplotypes at the MHC HLA (HLA) locus is generally thought to be governed by selection for increased diversity that is manifested in overdominance and/or negative frequency-dependent selection (FDS). However, recently, a model combining purifying selection on haplotypes and balancing selection on alleles has been proposed. We compare the predictions of several population dynamics models of haplotype frequency evolution to the distributions derived from 6.59-million-donor HLA typings from the National Marrow Donor Program registry. We show that models that combine a multiplicative fitness function, extremely high haplotype discovery rates, and exponential fitness decay over time produce the best fit to the data for most of the analyzed populations. In contrast, overdominance is not supported, and population substructure does not explain the observed haplotype frequencies. Furthermore, there is no evidence of negative FDS. Thus, multiplicative fitness, rapid haplotype discovery, and rapid fitness decay appear to be the major factors shaping the HLA haplotype frequency distribution in the human population.

Next-generation sequencing characterization of HLA in multi-generation families of Kuwaiti descent

The frequency of HLA genes in one population may not accurately represent frequencies in other populations. In this study, we characterized extended human leukocyte antigen (HLA) haplotypes in several families of Kuwaiti descent by high-resolution typing using next-generation technology. A total 81 members (including patients and related donors) from 21 families were enrolled. No haplotypes were shared among multiple families. Of 77 haplotypes identified, 23 were not listed in the HaploStats database. Two haplotypes were most common in African Americans, six in Asian Pacific Islanders, three in Caucasians, three in Hispanics, and three in Native Americans. The remaining identified haplotypes were not among the most common 200 HLA haplotypes in any of the five major populations. This cohort had 202 (19%) unique alleles, including 20 rare alleles, 16 very rare alleles, and 2 novel ones. Furthermore, no frequency data were available for 30% (23/77) of the observed haplotypes, and 6% (3/49) of B ∼ C blocks identified were not available in the HaploStats database. Kuwaiti individuals carry unique HLA haplotypes that are not shared by the majority of individuals historically reported to the US National Marrow Donor Program registry.

Modeling coverage gaps in haplotype frequencies via Bayesian inference to improve stem cell donor selection.

Regardless of sampling depth, accurate genotype imputation is limited in regions of high polymorphism which often have a heavy-tailed haplotype frequency distribution. Many rare haplotypes are thus unobserved. Statistical methods to improve imputation by extending reference haplotype distributions using linkage disequilibrium patterns that relate allele and haplotype frequencies have not yet been explored. In the field of unrelated stem cell transplantation, imputation of highly polymorphic human leukocyte antigen (HLA) genes has an important application in identifying the best-matched stem cell donor when searching large registries totaling over 28,000,000 donors worldwide. Despite these large registry sizes, a significant proportion of searched patients present novel HLA haplotypes. Supporting this observation, HLA population genetic models have indicated that many extant HLA haplotypes remain unobserved. The absent haplotypes are a significant cause of error in haplotype matching. We have applied a Bayesian inference methodology for extending haplotype frequency distributions, using a model where new haplotypes are created by recombination of observed alleles. Applications of this joint probability model offer significant improvement in frequency distribution estimates over the best existing alternative methods, as we illustrate using five-locus HLA frequency data from the National Marrow Donor Program registry. Transplant matching algorithms and disease association studies involving phasing and imputation of rare variants may benefit from this statistical inference framework.

P011 Advances in HLA clinical relevant exon novelty detection from over 21,000 donor recruitment samples

Aim The assignment of exon novel alleles is clinically relevant in hematopoietic stem cell transplantation (HSCT), in particular for donor selection. Here we investigate the exon novelty in over 21,000 National Marrow Donor Program (NMDP) registry donors by using next generation sequencing (NGS) approach on buccal swab DNA. Methods Multiplex long-range PCR primers amplified the full-length of HLA class I genes (HLA-A, -B, -C) from promoter to 3’ UTR. Class II genes (-DQB1, -DRB1) were amplified from exon 2 through part of exon 4. PCR amplicons were pooled and sheared using Covaris fragmentation. Library preparation was performed using the Illumina TruSeq Nano kit on the Beckman FX automated platform. Each sample was tagged with a unique barcode, followed by 2 × 250 bp paired-end sequencing on the Illumina MiSeq. Exon novelty was assigned using GenDx NGSengine v2.4.0 and Omixon Twin v1.0.7 software to ensure high confidence in allele calling. Exon novelties were confirmed by Sanger sequencing and 3D protein structure was predicted using Phyre2. Results Using this automated workflow, over 21,000 NMDP registry donors were successfully typed using high-resolution by NGS. NGS-HLA typing identified 94 exon novelties (0.044%) at five loci (HLA-A = 33, -B = 16, -C = 18, -DQB1 = 12, and -DRB1 = 15). We discerned 29 synonymous and 65 non-synonymous mutations. Among them 17 novel alleles (HLA-A = 3, -B = 5, -C = 2, -DQB1 = 4, and -DRB1 = 3) were detected within key exons involved in antigen recognition (exon 2 and 3 for Class I, and exon 2 for Class II). Interestingly, there are three frameshift novelties: A∗33:01:01NEW (1598InsC), A∗66:03NEW (1598delC), and B∗38:01:01NEW (9 bp del 1705-1713). Based on the 3D protein structure, these three proteins are truncated on α 3. Future experiments will determine if these proteins lose function or have lower cell surface expression. Conclusion Long-range, unambiguous HLA genotyping is achievable on clinical buccal swab-extracted DNA. High resolution HLA typing provides more accurate matching of the HLA-A, -B, -C, -DQB1, and -DRB1 alleles to improve patient survival. This work is the first step to define permissive mismatches in the context of HSCT, and it emphasize the need to improve our knowledge on donor selection.

HLA class I haplotype diversity is consistent with selection for frequent existing haplotypes.

The major histocompatibility complex (MHC) contains the most polymorphic genetic system in humans, the human leukocyte antigen (HLA) genes of the adaptive immune system. High allelic diversity in HLA is argued to be maintained by balancing selection, such as negative frequency-dependent selection or heterozygote advantage. Selective pressure against immune escape by pathogens can maintain appreciable frequencies of many different HLA alleles. The selection pressures operating on combinations of HLA alleles across loci, or haplotypes, have not been extensively evaluated since the high HLA polymorphism necessitates very large sample sizes, which have not been available until recently. We aimed to evaluate the effect of selection operating at the HLA haplotype level by analyzing HLA A~C~B~DRB1~DQB1 haplotype frequencies derived from over six million individuals genotyped by the National Marrow Donor Program registry. In contrast with alleles, HLA haplotype diversity patterns suggest purifying selection, as certain HLA allele combinations co-occur in high linkage disequilibrium. Linkage disequilibrium is positive (Dij'>0) among frequent haplotypes and negative (Dij'<0) among rare haplotypes. Fitting the haplotype frequency distribution to several population dynamics models, we found that the best fit was obtained when significant positive frequency-dependent selection (FDS) was incorporated. Finally, the Ewens-Watterson test of homozygosity showed excess homozygosity for 5-locus haplotypes within 23 US populations studied, with an average Fnd of 28.43. Haplotype diversity is most consistent with purifying selection for HLA Class I haplotypes (HLA-A, -B, -C), and was not inferred for HLA Class II haplotypes (-DRB1 and—DQB1). We discuss our empirical results in the context of evolutionary theory, exploring potential mechanisms of selection that maintain high linkage disequilibrium in MHC haplotype blocks.

Application of High-Throughput Next-Generation Sequencing for HLA Typing on Buccal Extracted DNA: Results from over 10,000 Donor Recruitment Samples.

BackgroundUnambiguous HLA typing is important in hematopoietic stem cell transplantation (HSCT), HLA disease association studies, and solid organ transplantation. However, current molecular typing methods only interrogate the antigen recognition site (ARS) of HLA genes, resulting in many cis-trans ambiguities that require additional typing methods to resolve. Here we report high-resolution HLA typing of 10,063 National Marrow Donor Program (NMDP) registry donors using long-range PCR by next generation sequencing (NGS) approach on buccal swab DNA.MethodsMultiplex long-range PCR primers amplified the full-length of HLA class I genes (A, B, C) from promotor to 3’ UTR. Class II genes (DRB1, DQB1) were amplified from exon 2 through part of exon 4. PCR amplicons were pooled and sheared using Covaris fragmentation. Library preparation was performed using the Illumina TruSeq Nano kit on the Beckman FX automated platform. Each sample was tagged with a unique barcode, followed by 2×250 bp paired-end sequencing on the Illumina MiSeq. HLA typing was assigned using Omixon Twin software that combines two independent computational algorithms to ensure high confidence in allele calling. Consensus sequence and typing results were reported in Histoimmunogenetics Markup Language (HML) format. All homozygous alleles were confirmed by Luminex SSO typing and exon novelties were confirmed by Sanger sequencing.ResultsUsing this automated workflow, over 10,063 NMDP registry donors were successfully typed under high-resolution by NGS. Despite known challenges of nucleic acid degradation and low DNA concentration commonly associated with buccal-based specimens, 97.8% of samples were successfully amplified using long-range PCR. Among these, 98.2% were successfully reported by NGS, with an accuracy rate of 99.84% in an independent blind Quality Control audit performed by the NDMP. In this study, NGS-HLA typing identified 23 null alleles (0.023%), 92 rare alleles (0.091%) and 42 exon novelties (0.042%).ConclusionLong-range, unambiguous HLA genotyping is achievable on clinical buccal swab-extracted DNA. Importantly, full-length gene sequencing and the ability to curate full sequence data will permit future interrogation of the impact of introns, expanded exons, and other gene regulatory sequences on clinical outcomes in transplantation.

C∗08:02/16:02 versus C∗05:01/16:01, ambiguous pairs particularly susceptible to typing error

We present four individuals initially determined to be C∗08:02:01:01 & 16:02:01 but subsequently typed as C∗05:01:01:01 & 16:01:01. These consist of a patient typed in our laboratory as well as three unrelated donors (URDs). The URDs had initial typing performed at National Marrow Donor Program (NMDP) laboratories and confirmatory typing performed in our lab. Typing for our patient was performed by sequence specific oligonucleotide probe (SSOP, One Lambda) and sequence based typing (SBT, Conexio) techniques. SBT included both the C∗08:02/16:02 and C∗05:01/16:01 types as ambiguous pairs. These were resolved by SSOP showing the apparent patient C∗ locus types as 08:02 and 16:02. The patient had a diagnosis of mantle cell lymphoma and an unrelated donor search was conducted based on the type of A∗02:01/29:02, B∗44:02/44:03, C∗08:02/16:02, DRB1∗04:01/07:01. Samples from three potentially matched URDs were received. All were listed in the NMDP registry as C∗08:02/16:02. Confirmatory typing on the URDs in our laboratory by SBT showed the same ambiguous pair as expected. However, SSOP appeared to rule out the C∗08:02/16:02 combination listed by the NMDP and indicated that C∗05:01/16:01 was the correct type for all three donors. To better confirm the C∗ locus types, sequencing with an allele-specific sequencing primer (HARP) was performed on all four individuals. C∗ locus typing by sequence specific primers was also performed for three. These methods identified C∗05:01 and 16:01 as the correct type in the patient and all three URDs. Review of the initial patient typing showed a single false negative DNA probe. This probe in the One Lambda SSOP kit separates the ambiguous pairs and is susceptible to false negative results. It was near the cut-off value in our patient as well as one of the donors. Laboratories using the techniques of One Lambda SSOP with SBT for high resolution typing should be aware of the possibility of an incorrect type when the C∗08:02/16:02 pair is identified. Close attention to B∗/C∗ associations is also warranted as the C∗05:01/16:01 pair is expected to be considerably more frequent than C∗08:02/16:02 in association with B∗44:02/44:03. Additional potential C∗08:02/16:02 URDs were listed in the initial search. The NMDP was notified that investigation of those donors might be useful.

F8 and HLA-II Haplotypes in the Hispanic Population: Implications for Inhibitor Risk Development in Hispanic Hemophilia A Patients

AbstractAbstract 3365 Background:A recent study suggested an increased rate of inhibitor development among Hispanic compared to White hemophilia A (HA) patients; however, a possible mechanism was not proposed or explored. In light of findings implicating a role for race-specific distributions of factor VIII (F8) and class-II human-leukocyte antigen (HLA-II) haplotypes on the disparate risk of inhibitor development in the Black HA population, we sought to determine the distributions of F8 and HLA-II haplotypes among Hispanic Americans and compare them to that of Black and White Americans. Methods:Using archived genomic DNA samples from the 194 unrelated founders of the San Antonio Family Heart Study (SAFHS), a collection of 1431 people from 41 large Mexican American families, we re-sequenced all exons of F8 to genotype the known nonsynonymous-single nucleotide polymorphisms (ns-SNPs) and identify any novel ns-SNPs. We then performed high-resolution HLA-II genotyping to identify each founders' pair of HLA-DRB1 alleles to compare them against those found in other ethnic groups. Results:Among the 291 potentially distinct Mexican American X-chromosomes evaluated, we identified the H2 F8 haplotype, defined by D1241E, in 25.0% of the subjects, which is in between that observed in the White (7.4%) and Black (37.4%) populations. We also found H3 F8, defined by D1241E and M2238V, in two subjects, who represent the first non-Black individuals reported to carry this haplotype. Furthermore, we discovered a previously unreported ns-SNP (H1919N), whose minor allele was found in only one male and defines a ninth wild-type F8 haplotype (H9). Regarding HLA-II alleles, the distribution among Mexican Americans in the present study was quite different from those found in Black and White individuals in the National Marrow Donor Program registry (see Figure). Three of the 4 most common HLA-II alleles in the Mexican Americans (DRB1*0802, DRB1*0407 and DRB1*1406) were seen in < 1% of both Blacks and Whites. Discussion:This is the first study to report the haplotypic prevalence of F8 and HLA-II alleles in Mexican Americans, the largest Hispanic ethnic group in the United States. By informing specific wild-type factor VIII (FVIII) peptides for use in HLA-II binding and T-cell stimulation assays, these results may help to identify high risk combinations of FVIII therapeutics and individual HLA-II repertoires that contribute to the higher rate of inhibitor development observed in Mexican versus Caucasian American HA patients. [Display omitted] Disclosures:Viel:Histonis, Incorporated: Employment. Howard:Haplomics, Inc.: Equity Ownership.

Increased HLA class I and II diversity as 72 novel alleles are identified in volunteers for the National Marrow Donor Program Registry in 2010

Seventy-two novel human leukocyte antigen (HLA) class I and class II alleles are described from volunteers for the 'Be The Match Registry®': 17 HLA-A alleles, 12 HLA-C alleles, 31 HLA-B alleles and 12 HLA-DRB1 alleles. Forty-six (≈ 64%) of the 72 novel alleles are single-nucleotide substitution variants when compared with their most homologous allele. Five of these single-nucleotide variants are silent substitutions and one creates a non-expressed allele (B*44:108N). The remaining novel alleles differ from their most similar allele by two to five nucleotide substitutions. One of the novel HLA-C alleles (C*07:150Q) is of questionable expression due to an insertion of 21 nucleotides starting at codon 143 that adds seven amino acids to exon 3. An inter-locus gene conversion may have created the novel allele HLA-A*23:31 that shares its codon differences with HLA-B*07:28. Some of the new alleles encode novel codons and unique amino acid changes at polymorphic positions in the HLA-A (codons 116 and 150), HLA-C (codon 114), HLA-B (codons 11, 21, 35, 42, 48, 73, 98 and 170) and HLA-DRB1 (codon 29) loci.

Ninety‐six novel HLA class I and II alleles identified in volunteers for the National Marrow Donor Program Registry in 2009

Ninety-six novel human leukocyte antigen (HLA) class I and class II alleles are described from volunteers for the 'Be The Match Registry®': 15 HLA-A alleles, 11 HLA-C alleles, 36 HLA-B alleles and 34 HLA-DRB1 alleles. Sixty-eight (∼71%) of the 96 novel alleles are single nucleotide substitution variants when compared with their most homologous allele. Twenty-three of these single nucleotide variants are silent substitutions and one creates a non-expressed allele (B(*) 27:59N). The remaining novel alleles differ from their most similar allele by two to five nucleotide substitutions. One of the novel HLA-A alleles (A(*) 11:52Q) is of questionable expression because of a deletion of codon 11. Three of the novel alleles encode amino acid changes at codons 63 (HLA-C), 88 (HLA-B) and 79 (HLA-DRB1) which have not previously been reported to be polymorphic in these loci. Some of the new alleles encode novel codons and unique amino acid changes at polymorphic positions in the HLA-A (codons 115, 149 and 168), HLA-C (codon 90), HLA-B (codons 23, 44, 70, 120 and 153) and HLA-DRB1 (codon 88) loci.

HLA-C Antigen Mismatch Is Associated with Worse Outcome in Unrelated Donor Peripheral Blood Stem Cell Transplantation

The association between HLA matching and outcome in unrelated-donor peripheral blood stem cell (PBSC) transplantation has not yet been established. In the present study, a total of 1933 unrelated donor-recipient pairs who underwent PBSC transplantation between 1999 and 2006 for acute myelogenous leukemia, acute lymphoblastic leukemia, myelodysplastic syndrome, or chronic myelogenous leukemia and received high-resolution HLA typing for HLA-A, -B, -C, -DRB1, -DQA1, and -DQB1 were included in the analysis. Outcomes were compared between HLA-matched and HLA-mismatched pairs, adjusting for patient and transplant characteristics. Matching for HLA-A, -B, -C, and -DRB1 alleles (8/8 match) was associated with better survival at 1 year compared with 7/8 HLA-matched pairs (56% vs 47%). Using 8/8 HLA-matched patients as the baseline (n = 1243), HLA-C antigen mismatches (n = 189) were statistically significantly associated with lower leukemia-free survival (relative risk [RR], 1.36; 95% confidence interval [CI], 1.13-1.64; P = .0010), and increased risk for mortality (RR, 1.41; 95% CI, 1.16-1.70; P = .0005), treatment-related mortality (RR, 1.61; 95% CI, 1.25-2.08; P = .0002), and grade III-IV graft-versus-host disease (RR, 1.98; 95% CI, 1.50-2.62; P < .0001). HLA-B antigen or allele mismatching was associated with an increased risk for acute GVHD grade III-IV. No statistically significant differences in outcome were observed for HLA-C allele (n = 61), HLA-A antigen/allele (n = 136), HLA-DRB1 allele (n = 39), or HLA-DQ antigen/allele (n = 114) mismatches compared with 8/8 HLA-matched pairs. HLA mismatch was not associated with relapse or chronic GVHD. HLA-C antigen-mismatched unrelated PBSC donors were associated with worse outcomes compared with 8/8 HLA-matched donors. The study's limited power due to small sample size precludesconclusions about other mismatches.

Efforts of the United States’ National Marrow Donor Program and Registry to improve utilization and representation of minority donors

Haematopoietic stem cell transplantation is often used as a therapy for patients with certain blood, metabolic or immune system disorders. The United States' National Marrow Donor Program (NMDP) works to facilitate such life-saving transplants by coordinating the donor search and match process. However, concern exists that the NMDP Registry is underutilized and under-representative of racial and ethnic minorities. African-Americans and Hispanics are somewhat under-represented within the total number of donors, and it is estimated that the Registry is used by only approximately one-third of patients needing transplants. The NMDP has instituted programmes that address such concerns, resulting in an increase in both the total number of donors and the minority representation on the Registry. It has also increased efforts to recruit donors of umbilical cord blood, often a viable alternative source of haematopoietic stem cells. Over the past 8 years, the Registry has grown by more than 30% to contain over seven million donors, and the proportional distribution of racial and ethnic groups on the Registry has steadily approached their proportional distribution in the US population. Continued efforts on the part of the NMDP to maintain a Registry that is large in number and ethnically diverse should help ensure access to haematopoietic stem cell transplants for all patients who need them. The procedures and experience of the NMDP and its Registry may have implications for registries elsewhere in the world as they confront similar issues of number and diversity.

The US National Marrow Donor Program role in unrelated donor hematopoietic cell transplantation

The National Marrow Donor Program (NMDP) is headquartered in Minneapolis, Minnesota, USA. Established in 1986, the NMDP currently operates the world's largest registry of unrelated adult donors and umbilical cord blood (UCB) units. Since its inception, the NMDP has benefited from continuous financial support provided by the US government through a series of contracts and grant awards. This funding has supported a large network of donor centers and the recruitment of millions of potential adult hematopoietic cell (HC) donors. More recently, the federal government has also supported a national registry for UCB units and expansion of the available UCB inventories. Today, the NMDP registry lists more than 6.7 million adult donors and 68,000 UCB units. Seventy-seven percent (5.2 million) of the adult donors and virtually all of the UCB units are fully typed for HLA A, B and DR. An additional 5 million donors are available for search through international collaborations. The NMDP currently facilitates more than 3600 recipients each year totaling more than 29,000 transplants since 1987.

Estimation of HLA-A, -B, -DRB1 Haplotype Frequencies Using Mixed Resolution Data from a National Registry with Selective Retyping of Volunteers

Large registries of volunteer hematopoietic stem cell donors typed for HLA contain potentially valuable data for studying haplotype frequencies in the general population. However the usual assumptions for use of the expectation-maximization (EM) algorithm are typically violated in these registries. To avoid this problem, previous studies using registry data have reduced the HLA typings to low-resolution and/or excluded subjects who were selected for testing on behalf of a specific patient ("patient-directed" typings). These restrictions, added to avoid bias from selection of nonrepresentative volunteers for higher-resolution typing, have limited previous results to haplotypes defined at low resolution. In this article we eliminate the need for such restrictions by formally relaxing the assumptions necessary for the EM algorithm. We show mathematically and through simulation that varying levels of resolution can be incorporated even if the level of typing resolution is chosen based on the HLA type. This allows use of intermediate and high resolution data from patient-directed typings to extend haplotype frequency estimates to the allele level for HLA-DRB1. We demonstrate the feasibility of using this computationally demanding algorithm on large datasets by applying it to more than 3 million volunteers listed in the National Marrow Donor Program Registry.

The polymorphism and haplotype analysis of HLA‐A, ‐B and ‐DRB1 genes of population in Jiangsu province of China

The polymorphism of human leucocyte antigen (HLA)-A, -B and -DRB1 genes and their computed haplotype analysis results from a population of Jiangsu province of China are presented here. The data consist of 20 248 unrelated peripheral blood stem cell donors in Jiangsu Branch of Chinese National Marrow Donor Program registry. In total, 18 different HLA-A alleles, 34 different HLA-B alleles and 13 different HLA-DRB1 alleles were found in Jiangsu Han population. The most frequent alleles in HLA-A, -B and -DRB1 loci were A*02 (29.55%), B*15 (14.40%), and DRB1*09 (16.15%), respectively. The most common haplotype in A-B-DRB1 loci was A*30-B*13- DRB1*07 (6.92%), in A-B loci was A*30-B*13 (8.05%), in B-DRB1 loci was B*13-DRB1*07 (8.17%), and in A-DRB1 loci was A*02-DRB1*09 (8.30%). The dendrogram study indicated that the distribution of HLA genes in Jiangsu Han population, as expected, represented a mixture of Northern and Southern Han population in China. These findings could shade new lights in population genetics and anthropology studies of Han-Chinese.

Advances in HLA: Practical Implications for Selecting Adult Donors and Cord Blood Units

HLA plays a critical role in hematopoietic cell ransplantation, but a full understanding of this role is onstantly in flux because of changing technologies nd burgeoning amounts of clinical transplantation esults. Today the clinician considering unrelated donor ransplantation must also consider stem cell source: an dult donor or an umbilical cord blood unit (CBU). In he context of cord blood, the task is further compliated by the strong interaction of cell dose. Each individual carries from 10 to 12 genes that ncode the HLA-A, HLA-B, HLA-C, HLA-DR, HLAQ, and HLA-DP molecules. Most of these genes are ighly polymorphic, ranging from 13 (HLA-DRB4) to 99 (HLA-B) alleles at a locus [1]. Most of the allelic ifferences result in changes in the HLA protein seuences, thus producing potential targets for allorecogition [2]. The frequency of alleles differs in different opulations: some are common in most populations, nd others are found predominantly in only 1 or a few opulations. The same is true for HLA haplotypes—the ollection of multiple HLA alleles within a short reion of chromosome 6—which are typically inherited s a single block of genetic information. Table 1 proides examples. DNA-based testing methods provide an accurate nd powerful approach to identify HLA diversity, and hese are replacing serologic testing [3,4]. DNA testng detects specific nucleotide differences that distinuish alleles or sets of alleles. The ability to distinuish among particular alleles at a locus (ie, the esolution) depends on the methodology, the set of ligonucleotide reagents used in the assay, or both. he choice of assay depends on the purpose of the yping, eg, initial testing of newly recruited volunteers r CBUs for a registry (low to intermediate resoluion) compared with testing of transplantation candiates and a few selected potential donors or CBUs high or allele-level resolution). C

Assessment of optimal size and composition of the U.S. National Registry of hematopoietic stem cell donors.

The National Marrow Donor Program (NMDP) receives federal funding to operate a registry of over 4 million volunteer donors for patients in need of a hematopoietic stem cell transplant. Because minority patients are less likely to find a suitably matched donor than whites, special efforts have been aimed toward recruitment of minorities. Significant financial resources are required to recruit and tissue type additional volunteer donors. Population genetics models have been constructed to project likelihoods of finding a human leukocyte antigen (HLA)-matched donor for patients of various racial/ethnic groups. These projections have been made under a variety of strategies for expansion of the NMDP Registry. Cost-effectiveness calculations incorporated donor unavailability and other barriers to transplantation. At current recruitment rates, the probability of an available HLA-A,B,DRB1 matched donor is projected to increase from 27% to 34%; 45% to 54%; 75% to 79%; and 48% to 55%, for blacks, Asians/Pacific Islanders, whites and Hispanics, respectively, by the year 2007. Substantial increases in minority recruitment would have only modest impacts on these projections. These projections are heavily affected by donor availability rates, which are less than 50% for minority volunteers. Continued recruitment of additional volunteers can improve the likelihood of finding an HLA-matched donor, but will still leave significant numbers of patients of all racial/ethnic groups without a match. Efforts to improve donor availability (especially among minorities) and to increase the number of patients with access to the NMDP Registry may prove to be more cost-effective means of increasing transplants.