Immunogenetics in stem cell donor registry work: The DKMS example (Part 1)

Unrelated hematopoietic stem cell donor registries: present reality and future prospects

PURPOSE OF REVIEW

Stem cell donor registries play an important role in providing stem cell products from unrelated donors to patients with severe blood diseases. In this review, important aspects of donor registry work, current challenges and possible future developments are discussed.

RECENT FINDINGS

The current growth in global unrelated stem cell donations is in line with the long-term trend, indicating that donor registries have overcome the COVID-19 pandemic. A key challenge for donor registries is the recruitment of donors from disadvantaged populations to create greater equity in access to unrelated stem cell transplantation. In addition, recruiting young donors and increasing the availability of donors who are already registered are important goals. In recent years, numerous studies have looked at the context of these themes and the development of possible solutions.

SUMMARY

The international community of donor registries, together with the World Marrow Donor Association, has helped many patients in need of a stem cell transplant over the past decades and is, therefore, a bright example of international collaboration for a good cause. It is currently addressing a number of challenges to effectively help as many patients as possible from various populations also in the future.

Optimisation of global stem cell donor recruitment based on analysis of unsuccessful donor searches

Despite over 41 million registered potential volunteer stem cell donors worldwide, many patients in need of a transplant do not find an HLA-matched unrelated donor or cord blood units, with the respective odds differing significantly between various populations. In this study, we analysed data of 2205 unsuccessful real-life donor searches sent to the DKMS Registry to identify populations in which further donor recruitment would be associated with particularly large patient benefits. For that purpose, we estimated haplotype frequencies of 67 donor populations at various sample sizes and entered them into two different mathematical models. These models assessed patient benefits from population-specific donor recruitment, operationalised by the number of originally unsuccessful searches that may become successful due to new donors. Consistently, across the different mathematical models and sample sizes, we obtained several countries from East and Southeast Asia (Thailand, Vietnam, China, and the Philippines) and the population of Asians in the USA as countries/populations where donor recruitment activities would be particularly beneficial for patients. We also identified various countries in Southeast and Central Europe as possible target regions for donor recruitment with above-average patient benefits. The results presented are registry-specific in the sense that they were obtained by optimising unsuccessful searches that had been sent to the DKMS Registry. Therefore, it would be desirable to apply the presented methods to a global data set that includes all unsuccessful stem cell donor searches worldwide and uses population-specific haplotype frequencies based on all donors available in the WMDA Search & Match Service.

Racial/ethnic disparities in availability of volunteer unrelated donors for allogeneic transplantation

ABSTRACT

Despite the global unrelated donor (URD) registry size, the degree to which URD availability is a transplant barrier is not established. We evaluated the availability of 3,843 URDs requested for 455 diverse adult patients (predominantly with acute leukemia). URDs for non-Europeans were more likely to be domestic and had markedly lower Donor Readiness scores. Of URDs requested for confirmatory HLA-typing (CT) alone (ie, without simultaneous workup), 1,894 of 3,529 (54%) were available. Availability of domestic URDs was 45%. Donor Readiness score was highly predictive of CT availability. More non-European patients (n = 120) than Europeans (n = 335) had >10 URDs requested and <5 available. Of workup requests (after CT or CT-workup), <70% (604/889 [68%]) were available. More non-Europeans had <2 URDs available. URD availability for CT was markedly worse for non-Europeans, with availabilities for African, non-Black Hispanic, and Asian patients being 150/458 (33%), 120/258 (47%), and 119/270 (44%), respectively, with further decrements in URD workup availability. Our data suggest the functional size of the URD pool is much smaller than appreciated, mandating major operational changes for transplant centers and donor registries. Likelihood of donor availability should have a high priority in donor selection. Considering patient ancestry and URD Donor Readiness scores, centers should pursue, and registries permit, simultaneous pursuit of many URDs and abandon futile searches. Patients should be informed about their likelihood of donor availability and alternative options. Finally, although registries should address high URD attrition and speed procurement, use of all HLA-disparate graft types is needed to facilitate timely transplant for all.

Providing hematopoietic stem cell products from unrelated donors to the world: DKMS donor centers and DKMS Registry

Allogeneic hematopoietic stem cell (HSC) transplantation is a curative therapy for many severe blood diseases. As many patients have no suitable family donor, large unrelated donor registries and donor centers have been established in many countries, along with an international system for the provision of unrelated donor HSC products. As an essential part of this system, DKMS operates donor centers in 7 countries with a total of 12.2 million donors and over 114,000 donations so far, and a multinational donor registry. In 2022, DKMS donors contributed 57.5% of all cross-border donations worldwide. In this review, we describe the international system for the provision of unrelated donor HSC products as well as tasks and responsibilities of donor registries and donor centers. We also discuss relevant aspects of DKMS donor centers, namely donor file composition, matching and donation probabilities and actual donations, and the unique multinational approach of the DKMS Registry.

HLA haplotype frequencies and diversity in patients with hemoglobinopathies

The genetic diversity of the human leukocyte antigen (HLA) system was shaped by evolutionary constraints exerted by environmental factors. Analyzing HLA diversity may allow understanding of the underlying pathways and offer useful tools in transplant setting. The aim of this study was to investigate the HLA haplotype diversity in patients with sickle cell disease (SCD, N = 282) or β-thalassemia (β-Thal, N = 60), who received hematopoietic cell transplantation (HCT) reported to Eurocord and the Société Francophone de Greffe de Moelle et de Thérapie Cellulaire (SFGM-TC). We identified 405 different HLA-A-B-DRB1 haplotypes in SCD and 108 in β-Thal patients. Using data from African and European populations of the "1000 Genomes Project" for comparison with SCD and β-Thal, respectively, we found that the haplotypes HLA-A*30-B*14-DRB1*15 (OR 7.87, 95% CI: 1.66-37.3, p b = 0.035), HLA-A*23-B*08 (OR 6.59, 95% CI: 1.8-24.13, p b = 0.023), and HLA-B*14-DRB1*15 (OR 10.74, 95% CI: 3.66-31.57, p b = 0.000) were associated with SCD, and the partial haplotypes HLA-A*30-B*13 and HLA-A*68-B*53 were associated with β-Thal (OR 4.810, 95% CI: 1.55-14.91, p b = 0.033, and OR 17.52, 95% CI: 2.81-184.95, p b = 0.011). Our results confirm the extreme HLA genetic diversity in SCD patients likely due to their African ancestry. This diversity seems less accentuated in patients with β-Thal. Our findings emphasize the need to expand inclusion of donors of African descent in HCT donor registries and cord blood banks.

5 years DKMS Chile: approach, results and impact of the first unrelated stem cell donor center in Chile

Introduction

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is performed worldwide to treat blood cancer and other life-threatening blood disorders. As successful transplantation requires an HLA-compatible donor, unrelated donor centers and registries have been established worldwide to identify donors for patients without a family match. Ethnic minorities are underrepresented in large donor registries. Matching probabilities are higher when donors and patients share the same ethnic background, making it desirable to increase the diversity of the global donor pool by recruiting donors in new regions. Here, we report the establishment and the first 5 years of operation of the first unrelated stem cell donor center in Chile, a high-income country in South America with a population of over 19 million.

Methods

We used online and in-person donor recruitment practices through patient appeals and donor drives in companies, universities, the armed forces, and public services. After confirmatory typing donors were subjected to medical work-up and cleared for donation.

Results

We recruited almost 170,000 donors in 5 years. There were 1,488 requests received for confirmatory typing and donor availability checks, of which 333 resulted in medical work-up, leading to 194 stem cell collections. Products were shipped to Chile (48.5%) and abroad. Even when the COVID-19 pandemic challenged our activities, the number of donors recruited and shipped stem cell products remained steady. In Chile there was an almost 8-fold increase in unrelated donor transplantation activity from 16 procedures in 2016-2018 to 124 procedures in 2019-2021, mainly for pediatric patients following the center's establishment. We estimate that 49.6% of Chilean patients would find at least one matched unrelated donor in the global DKMS donor pool.

Discussion

Establishing a DKMS donor center in Chile has significantly increased donor availability for Chilean patients and contributed to an increase of unrelated donor stem cell transplant activity.

Small volume bone marrow aspirates with high progenitor cell concentrations maximize cell therapy dose manufacture and substantially reduce donor hemoglobin loss

BACKGROUND

Bone marrow (BM) transplantation is a life-saving therapy for hematological diseases, and the BM harbors also highly useful (progenitor) cell types for novel cell therapies manufacture. Yet, the BM collection technique is not standardized.

METHODS

Benchmarking our collection efficiency to BM collections worldwide (N = 1248), we noted a great variability of total nucleated cell (TNC) yields in BM products (HPC-M) with superior performance of our center, where we have implemented a small volume aspirate policy. Thus, we next prospectively aimed to assess the impact of BM collection technique on HPC-M quality. For each BM collection (N = 20 donors), small volume (3 mL) and large volume (10 mL) BM aspirates were sampled at 3 time points and analyzed for cell composition.

RESULTS

Compared to large volume aspirates, small volume aspirates concentrated more TNCs, immune cells, platelets, hematopoietic stem/progenitor cells, mesenchymal stromal cells (MSCs), and endothelial progenitors. Inversely, the hemoglobin concentration was higher in large volume aspirates indicating more hemoglobin loss. Manufacturing and dosing scenarios showed that small volume aspirates save up to 42% BM volume and 44% hemoglobin for HPC-M donors. Moreover, MSC production efficiency can be increased by more than 150%.

CONCLUSIONS

We propose to consider small volume BM aspiration as standard technique for BM collection.

Genotype List String 1.1: Extending the Genotype List String grammar for describing HLA and Killer-cell Immunoglobulin-like Receptor genotypes

The Genotype List (GL) String grammar for reporting HLA and Killer-cell Immunoglobulin-like Receptor (KIR) genotypes in a text string was described in 2013. Since this initial description, GL Strings have been used to describe HLA and KIR genotypes for more than 40 million subjects, allowing these data to be recorded, stored and transmitted in an easily parsed, text-based format. After a decade of working with HLA and KIR data in GL String format, with advances in HLA and KIR genotyping technologies that have fostered the generation of full-gene sequence data, the need for an extension of the GL String system has become clear. Here, we introduce the new GL String delimiter "?," which addresses the need to describe ambiguity in assigning a gene sequence to gene paralogs. GL Strings that do not include a "?" delimiter continue to be interpreted as originally described. This extension represents version 1.1 of the GL String grammar.

Post-COVID-19 condition in the German working population: A cross-sectional study of 200,000 registered stem cell donors

BACKGROUND

The SARS-CoV-2 pandemic has strained health systems worldwide, and infection numbers continue to rise. While previous data have already shown that many patients suffer from symptoms for months after an acute infection, data on risk factors and long-term outcomes are incomplete, particularly for the working population.

OBJECTIVES

We aimed to provide information on the prevalence of post-COVID-19 conditions in a subset of the German working-age population (18-61 years old) and to analyze risk factors.

METHODS

We conducted an online survey with a health questionnaire among registered potential stem cell donors with or without a self-reported history of polymerase chain reaction (PCR)-confirmed SARS-CoV-2 infection. Logistic regression models were used to examine the risks of severity of acute infection, sex, age, body mass index, diabetes mellitus, and arterial hypertension medication on post-COVID-19 symptoms.

RESULTS

A total of 199,377 donors reported evaluable survey questionnaires-12,609 cases had a history of SARS-CoV-2 infection and 186,768 controls had none. Overall, cases reported physical, cognitive, and psychological complaints more frequently compared to controls. Increased rates of complaints persisted throughout 15 months postinfection, for example, 28.4%/19.3% of cases/controls reported fatigue (p <0.0001) and 9.5%/3.6% of cases/controls reported loss of concentration (p <0.0001). No significant differences were observed in the frequency of reported symptoms between 3 and 15 months postinfection. Multivariate analysis revealed a strong influence of the severity of the acute SARS-CoV-2 infection episode and age on the risk for post-COVID-19 conditions.

CONCLUSION

We report the prevalence of post-COVID-19 conditions in mainly unvaccinated individuals with SARS-CoV-2 infections between February 2020 and August 2021. The severity of the acute course and age were major risk factors. Vaccinations may reduce the risk of post-COVID-19 conditions by reducing the risk of severe infections.

Approaching Genetics Through the MHC Lens: Tools and Methods for HLA Research

The current SARS-CoV-2 pandemic era launched an immediate and broad response of the research community with studies both about the virus and host genetics. Research in genetics investigated HLA association with COVID-19 based on in silico, population, and individual data. However, they were conducted with variable scale and success; convincing results were mostly obtained with broader whole-genome association studies. Here, we propose a technical review of HLA analysis, including basic HLA knowledge as well as available tools and advice. We notably describe recent algorithms to infer and call HLA genotypes from GWAS SNPs and NGS data, respectively, which opens the possibility to investigate HLA from large datasets without a specific initial focus on this region. We thus hope this overview will empower geneticists who were unfamiliar with HLA to run MHC-focused analyses following the footsteps of the Covid-19|HLA & Immunogenetics Consortium.

Noninvasive Determination of CMV Serostatus From Dried Buccal Swab Samples: Assay Development, Validation, and Application to 1.2 Million Samples

BACKGROUND

Buccal swab sampling constitutes an attractive noninvasive alternative to blood drawings for antibody serostatus assays. Here we describe a method to determine the cytomegalovirus immunoglobulin G (CMV IgG) serostatus from dried buccal swab samples.

METHODS

Upon solubilization, CMV IgG is determined by an ELISA assay specifically adapted to cope with low IgG concentrations. The derived CMV titer is normalized against the total protein concentration to adjust for incorrectly or less efficiently sampled buccal swabs. Assay parameters were optimized on a set of 713 samples.

RESULTS

Validation with 1784 samples revealed distinct results for > 80% of samples with 98.6% specificity and 99.1% sensitivity. Based on the analysis of 1.2 million samples we derived age- and sex-stratified CMV prevalence statistics for Germany, Poland, United Kingdom, and Chile. To confirm accuracy of the assay in routine operation, the CMV status of 6518 donors was reassessed by independent laboratories based on conventional blood samples revealing 96.9% specificity and 97.4% sensitivity.

CONCLUSIONS

The assay accurately delivers the CMV IgG serostatus from dried buccal swab samples for > 80% of the participants. Thereby it provides a noninvasive alternative to plasma-based CMV monitoring for nondiagnostic purposes such as hematopoietic stem cell transplantation donor screening or population studies.

Estimating HLA haplotype frequencies from homozygous individuals - A Technical Report

We estimated HLA haplotype frequencies based on individuals homozygous for 4, 5 or 6 loci. Validation of our approach using a sample of over 3.4 million German individuals was successful. Compared to an expectation‐maximization algorithm, the errors were larger. However, our approach allows the unequivocal detection of rare haplotypes.

Individual HLA-A, -B, -C, and -DRB1 Genotypes Are No Major Factors Which Determine COVID-19 Severity

HLA molecules are key restrictive elements to present intracellular antigens at the crossroads of an effective T-cell response against SARS-CoV-2. To determine the impact of the HLA genotype on the severity of SARS-CoV-2 courses, we investigated data from 6,919 infected individuals. HLA-A, -B, and -DRB1 allotypes grouped into HLA supertypes by functional or predicted structural similarities of the peptide-binding grooves did not predict COVID-19 severity. Further, we did not observe a heterozygote advantage or a benefit from HLA diplotypes with more divergent physicochemical peptide-binding properties. Finally, numbers of in silico predicted viral T-cell epitopes did not correlate with the severity of SARS-CoV-2 infections. These findings suggest that the HLA genotype is no major factor determining COVID-19 severity. Moreover, our data suggest that the spike glycoprotein alone may allow for abundant T-cell epitopes to mount robust T-cell responses not limited by the HLA genotype.

HLA-E typing of more than 2.5 million potential hematopoietic stem cell donors: Methods and population-specific allele frequencies

We developed a cost-efficient workflow for genotyping HLA-E by NGS and applied it for genotyping more than 2.5 million potential stem cell donors. The data obtained were used to determine HLA-E allele frequency distributions for 104 populations. Our results confirm the known dominance of the alleles E*01:01 and E*01:03, which have a combined frequency of more than 0.99 in 97 of the 104 populations. E*01:01 is more frequent in Africa and the western part of South America, E*01:03 in Southeast and East Asia. E*01:03 shows a pronounced regional substructure at the high-resolution level with E*01:03:01G being particularly common in a large connected region extending from Turkey to China, E*01:03:02G in Northwestern Europe and E*01:03:03 in Central and Eastern Europe as well as Central Asia. The presented results are relevant both as a basis for further population genetics studies and for optimizing stem cell donor searches.

Mapping the Human Leukocyte Antigen Diversity among Croatian Regions: Implication in Transplantation

In the present study, HLA allele and haplotype frequencies were studied using the HLA data of 9277 Croatian unrelated individuals, typed using high-resolution methods for the HLA-A, -B, -C, and -DRB1 loci. The total numbers of observed alleles were 47 for HLA-A, 88 for HLA-B, 34 for HLA-C, and 53 for HLA-DRB1. HLA-A^∗02:01 (29.5%), B^∗51:01 (10.5%), C^∗04:01 (15.8%), and DRB1^∗16:01 (10.4%) were the most frequent alleles in the Croatian general population. The three most frequent haplotypes were HLA-A^∗01:01~C^∗07:01~B^∗08:01~DRB1^∗03:01 (4.7%), HLA-A^∗03:01~C^∗07:02~B^∗07:02~DRB1^∗15:01 (1.7%), and HLA-A^∗02:01~C^∗07:01~B^∗18:01~DRB1^∗11:04 (1.5%). Allele and haplotype frequencies were compared between national and regional data, and differences were observed, particularly in the North Croatia region. The data has potential use in refining donor recruitment strategies for national registries of volunteer hematopoietic stem cell donors, solid organ allocation schemes, and the design of future disease and anthropological studies.

Stem cell donor registry activities during the COVID-19 pandemic: a field report by DKMS

The COVID-19 pandemic has serious implications also for patients with other diseases. Here, we describe the effects of the pandemic on unrelated hematopoietic stem cell donation and transplantation from the perspective of DKMS, a large international donor registry. Especially, we cover the development of PBSC and bone marrow collection figures, donor management including Health and Availability Check (HAC), transport and cryopreservation of stem cell products, donor recruitment and business continuity measures. The total number of stem cell products provided declined by around 15% during the crisis with a particularly strong decrease in bone marrow products. We modified donor management processes to ensure donor and product safety. HAC instead of confirmatory typing was helpful especially in countries with strict lockdowns. New transport modes were developed so that stem cell products could be safely delivered despite COVID-19-related travel restrictions. Cryopreservation of stem cell products became the new temporary standard during the pandemic to minimize risks related to transport logistics and donor availability. However, many products from unrelated donors will never be transfused. DKMS discontinued public offline donor recruitment, leading to a 40% decline in new donors during the crisis. Most DKMS employees worked from home to ensure business continuity during the crisis.

Haplotype Motif-Based Models for KIR-Genotype Informed Selection of Hematopoietic Cell Donors Fail to Predict Outcome of Patients With Myelodysplastic Syndromes or Secondary Acute Myeloid Leukemia

Results from registry studies suggest that harnessing Natural Killer (NK) cell reactivity mediated through Killer cell Immunoglobulin-like Receptors (KIR) could reduce the risk of relapse after allogeneic Hematopoietic Cell Transplantation (HCT). Several competing models have been developed to classify donors as KIR-advantageous or disadvantageous. Basically, these models differ by grouping donors based on distinct KIR–KIR–ligand combinations or by haplotype motif assignment. This study aimed to validate different models for unrelated donor selection for patients with Myelodysplatic Syndromes (MDS) or secondary Acute Myeloid Leukemia (sAML). In a joint retrospective study of the European Society for Blood and Marrow Transplantation (EBMT) and the Center for International Blood and Marrow Transplant Research (CIBMTR) registry data from 1704 patients with secondary AML or MDS were analysed. The cohort consisted mainly of older patients (median age 61 years) with high risk disease who had received chemotherapy-based reduced intensity conditioning and anti-thymocyte globulin prior to allogeneic HCT from well-matched unrelated stem cell donors. The impact of the predictors on Overall Survival (OS) and relapse incidence was tested in Cox regression models adjusted for patient age, a modified disease risk index, performance status, donor age, HLA-match, sex-match, CMV-match, conditioning intensity, type of T-cell depletion and graft type. KIR genes were typed using high-resolution amplicon-based next generation sequencing. In univariable and multivariable analyses none of the models predicted OS and the risk of relapse consistently. Our results do not support the hypothesis that optimizing NK-mediated alloreactivity is possible by KIR-genotype informed selection of HLA-matched unrelated donors. However, in the context of allogeneic transplantation, NK-cell biology is complex and only partly understood. KIR-genes are highly diverse and current assignment of haplotype motifs based on the presence or absence of selected KIR genes is over-simplistic. As a consequence, further research is highly warranted and should integrate cutting edge knowledge on KIR genetics, and NK-cell biology into future studies focused on homogeneous groups of patients and treatment modalities.

High-resolution HLA allele and haplotype frequencies of the Saudi Arabian population based on 45,457 individuals and corresponding stem cell donor matching probabilities

We estimated HLA allele and haplotype frequencies of the Saudi Arabian population from a sample of 45,457 registered stem cell donors. The most frequent HLA alleles were A*02:01g (18.5%), C*06:02g (16.1%), B*51:01g (14.1%), DRB1*07:01g (16.2%), DQB1*02:01g (30.5%), and DPB1*04:01g (33.6%). The most frequent 5-locus haplotypes were A*02:05g~C*06:02g~B*50:01g~DRB1*07:01g~DQB1*02:01g (1.73%), A*02:01g~C*06:02g~B*50:01g~DRB1*07:01g~DQB1*02:01g (1.66%), and A*26:01g~C*07:02g~B*08:01g~DRB1*03:01g~DQB1*02:01g (1.38%). Furthermore, we used the calculated haplotype frequencies to estimate stem cell donor matching probabilities for Saudi Arabian donor and patient populations under various matching requirements. These results are relevant for strategic donor registry planning in the Kingdom of Saudi Arabia.

Immunogenetics in stem cell donor registry work: The DKMS example (Part 2)

DKMS is a leading stem cell donor registry with more than 9 million donors. Donor registry activities share many touch points with topics from immunogenetics or population genetics. In this two-part review article, we deal with these aspects of donor registry work by using the example of DKMS. In the second part of the review, we focus on donor typing of non-HLA genes, the impact of donor age, gender and CMV serostatus on donation probabilities, the identification of novel HLA, KIR and MIC alleles by high-throughput donor typing, the activities of the Collaborative Biobank and pharmacogenetics in the donor registry context.

Immunogenetics in stem cell donor registry work: The DKMS example (Part 1)

Currently, stem cell donor registries include more than 35 million potential donors worldwide to provide HLA-matched stem cell products for patients in need of an unrelated donor transplant. DKMS is a leading stem cell donor registry with more than 9 million donors from Germany, Poland, the United States, the United Kingdom, India and Chile. DKMS donors have donated hematopoietic stem cells more than 80,000 times. Many aspects of donor registry work are closely related to topics from immunogenetics or population genetics. In this two-part review article, we describe, analyse and discuss these areas of donor registry work by using the example of DKMS. Part 1 of the review gives a general overview on DKMS and includes typical donor registry activities with special focus on the HLA system: high-throughput HLA typing of potential stem cell donors, HLA haplotype frequencies and resulting matching probabilities, and donor file optimization with regard to HLA diversity.