The increase of the global donor inventory is of limited benefit to patients of non-Northwestern European descent

Permissible HLA mismatches in 9/10 unrelated donor pediatric stem cell transplants using HLA-EMMA: an EBMT Inborn Errors Working Party study

ABSTRACT

Allogeneic hematopoietic stem cell transplantation (HSCT) with mismatched unrelated donors (MMUD) is associated with inferior outcome compared with matched unrelated donors (MUDs). We aimed to identify permissible mismatches using HLA epitope mismatch algorithm, which determines permissibility by analyzing amino acid sequences, in a single-center cohort of 70 pediatric 9/10 MMUD HSCTs and 157 10/10 MUDs for comparison. Amino acid matching was evaluated for the whole HLA protein, the α-helices, and the β-sheets, in both host vs graft (HvG) and graft vs host (GvH) direction. Superior event-free survival (EFS) was found in 13 patients permissibly mismatched in the HvG direction (totalHvG, 92% vs 58% at 1 year; P = .009) and in 21 patients matched on the α-helices (αHvG, 90% vs 53%; P = .002). These rates were similar to EFS rates in patients with 10/10 MUDs (90% vs 80%; P = .60). EFS was not related to β-sheet amino acid matching, nor to matching in the GvH direction. Overall survival (OS) rates trended similarly to those of EFS for amino acid mismatches (totalHvG, 92% vs 74%; P = .075; αHvG, 90% vs 71%; P = .072). These findings were reproduced in an EBMT Registry inborn errors cohort of 271 pediatric 9/10 MMUD HSCTs and 929 10/10 MUD HSCTs, showing a significant effect of αHvG matching on both OS and EFS and similar OS and EFS between αHvG matched MMUDs and 10/10 MUDs. In summary, HvG amino acid matching on the α-helices identifies 9/10 MMUDs with permissible mismatches, which are correlated with favorable transplant outcomes similar to those of matched donors.

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.

Utilization and outcome disparities in allogeneic hematopoietic stem cell transplant in the United States

Allogeneic hematopoietic stem cell transplant (allo-HSCT) is increasingly being used in the United States (US) and across the world as a curative therapeutic option for patients with certain high-risk hematologic malignancies and non-malignant diseases. However, racial and ethnic disparities in utilization of the procedure and in outcome following transplant remain major problems. Racial and ethnic minority patients are consistently under-represented in the proportion of patients who undergo allo-HSCT in the US. The transplant outcomes in these patients are also inferior. The interrelated driving forces responsible for the differences in the utilization and transplant outcome of the medical intervention are socioeconomic status, complexity of the procedure, geographical barriers, and the results of differences in the genetics and comorbidities across different races. Bridging the disparity gaps is important not only to provide equity and inclusion in the utilization of this potentially life-saving procedure but also in ensuring that minority groups are well represented for research studies about allo-HSCT. This is required to determine interventions that may be more efficacious in particular racial and ethnic groups. Various strategies at the Federal, State, and Program levels have been designed to bridge the disparity gaps with varying successes. In this review paper, we will examine the disparities and discuss the strategies currently available to address the utilization and outcome gaps between patients of different races in the US.

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.

Novel Human Umbilical Di-Chimeric (HUDC) cell therapy for transplantation without life-long immunosuppression

Background

Cell-based therapies are promising for tolerance induction in bone marrow (BM), solid organs, and vascularized composite allotransplantation (VCA). The toxicity of bone marrow transplantation (BMT) protocols precludes this approach from routine clinical applications. To address this problem, we developed a new therapy of Human Umbilical Di-Chimeric (HUDC) cells for tolerance induction in transplantation. This study established in vitro characterization of the created HUDC cells.

Methods

We performed sixteen ex vivo polyethylene glycol (PEG)-mediated fusions of human umbilical cord blood (UCB) cells from two unrelated donors. Fusion feasibility was confirmed in vitro by flow cytometry (FC) and confocal microscopy (CM). The HUDC cells' genotype was assessed by lymphocytotoxicity test and short tandem repeat-polymerase chain reaction (STR-PCR) analysis, phenotype by FC, viability by LIVE/DEAD® assay, and apoptosis level by Annexin V staining. We used COMET assay to assess HUDC cells' genotoxicity after the fusion procedure. Clonogenic properties of HUDC cells were evaluated by colony forming unit (CFU) assay. Mixed lymphocyte reaction (MLR) assay assessed immunogenic and tolerogenic properties of HUDC cells.

Results

We confirmed the creation of HUDC cells from two unrelated human donors of UCB cells by FC and CM. Human leukocyte antigen (HLA) class I and II typing, and STR-PCR analysis of HUDC cells confirmed the presence of alleles and loci from both unrelated UCB donors (donor chimerism: 49%±8.3%, n=4). FC confirmed the hematopoietic phenotype of HUDC cells. We confirmed high HUDC cells' viability (0.47% of dead cells) and a low apoptosis level of fused HUDC cells (15.9%) compared to positive control of PKH-stained UCB cells (20.4%) before fusion. COMET assay of HUDC cells revealed a lack of DNA damage. CFU assay confirmed clonogenic properties of HUDC cells, and MLR assay revealed a low immunogenicity of HUDC cells.

Conclusions

This study confirmed creation of a novel HUDC cell line by ex vivo PEG-mediated fusion of UCB cells from two unrelated donors. The unique concept of creating a HUDC cell line, representing the genotype and phenotype of both, transplant donor and the recipient, introduces a promising approach for tolerance induction in BM, solid organs, and VCA transplantation.

Comparison of clinical outcomes between peripheral blood stem cells and peripheral blood stem cells plus bone marrow in myelodysplastic syndrome patients with haploidentical transplantation

The comparison of haploidentical G-CSF-mobilized peripheral blood and bone marrow transplantation (HBMT) for patients with myelodysplastic syndrome (MDS) and haploidentical G-CSF-primed peripheral blood stem cell transplantation (HPBSCT) remains unclear. We performed a retrospective analysis using a propensity score method on 140 MDS patients who received HPBSCT (n = 46) or HBMT (n = 94) with BU/CY as a conditioning regimen prior to transplantation at our center between June 2016 and June 2021. HBMT recipients were associated with a reduced incidence of grade III-IV acute GVHD (17.22% vs. 30.57%, p = 0.019) within 100 days, reduced 2-year transplant-related mortality (TRM) (14.29% vs. 28.94%, p = 0.045) and superior 2-year overall survival (OS) (81.6% vs. 66.0%, p = 0.027), progression-free survival (PFS) (80.9% vs. 61.2%, p = 0.015), and GVHD relapse-free survival (GRFS) (64.6% vs. 53.3%, p = 0.062) compared with HPBSCT, but 2-year relapse incidence (RI) (5.96% vs. 9.39%, p = 0.445) was not affected. Multivariate analysis revealed that a GPB/GBM mixture was the independent factor for a reduced incidence of grade III-IV acute GVHD (p = 0.018) and TRM (p = 0.048), improved OS (p = 0.029), PFS (p = 0.019) and GRFS (p = 0.072). Collectively, the use of a GPB/GBM mixture as stem cell grafts for haplo-HSCT in patients with MDS appears to be an optimal choice.

Impact of the combination of donor age and HLA disparity on the outcomes of unrelated bone marrow transplantation

Impact of donor age considering HLA disparity on hematopoietic cell transplantation (HCT) outcomes has not been fully evaluated. We evaluated 8486 patients who received unrelated bone marrow transplantation (UR-BMT) from 8/8 or 7/8 HLA-matched donors. Compared to 8/8 HLA-matched younger donors (<40 years), 8/8 HLA-matched older donors (subdistribution hazard ratio [SHR], 1.16; 95% CI, 0.97-1.38) and 7/8 HLA-matched younger donors (SHR, 1.33; 95% CI, 1.11-1.58) were associated with increased risk of grade III-IV acute graft-versus-host disease (aGVHD). 7/8 HLA-matched older donors had further increased risk (SHR, 2.00; 95% CI, 1.68-2.38) due to interaction between donor age and HLA disparity (p for interaction = 0.038). Progression-free survival (PFS) after UR-BMT with 8/8 HLA-matched younger donors was comparable to that after UR-BMT with 8/8 HLA-matched older donors, whereas UR-BMT with 7/8 HLA-matched younger or older donors was significantly associated with lower PFS than UR-BMT with 8/8 HLA-matched younger donors (younger donor; HR, 1.12; 95% CI, 1.04-1.21, older donor; HR, 1.28; 95% CI, 1.17-1.40; p for interaction = 0.079). In conclusion, adverse effect of increased donor age requires attention, especially in HLA-mismatched UR-BMT due to interaction between donor age and HLA disparity. Intensive aGVHD prophylaxis may be required to improve outcomes after HCT with mismatched older donors.

Multimedia resources to support the recruitment of committed hematopoietic stem cell donors: Perspectives of the most-needed donors

BACKGROUND

Recruitment of committed unrelated hematopoietic stem cell donors from the most-needed demographics remains a challenge for donor recruitment organizations worldwide. Multimedia resources are gaining attention as a modality to support recruitment efforts; however, there is a lack of guidance for the development of such tools. This qualitative study explores the perspectives of eligible stem cell donors on an educational whiteboard video about stem cell donation, generating insights into how whiteboard videos and related multimedia may be optimized for donor recruitment.

STUDY DESIGN AND METHODS

Eight semistructured focus groups were conducted with 38 potential donors from the most-needed demographics (young, male, and non-Caucasian) after they had watched a 3.5-minute whiteboard video explaining key concepts in stem cell donation (https://youtu.be/V4fVBtxnWfM). Constructivist grounded theory was used to identify themes and to develop a framework for understanding participants' preferred features of recruitment multimedia.

RESULTS

Participants identified a range of features contributing to the effectiveness of recruitment multimedia, adding that the whiteboard video is an effective, integrated, and readily accessible format for supporting donor recruitment. Topics that participants felt are important to address include knowledge gaps regarding donation procedures, concerns about donor safety, and the particular need for specific donor demographics. Suggested avenues for improvement include the addition of donor/recipient/patient personal experiences, attention-grabbing hooks, and a call to action including opportunities for further learning.

CONCLUSIONS

Several considerations were generated to inform the development of future multimedia for donor education/recruitment and are relevant to donor recruitment organizations worldwide.

Development and evaluation of stem cell collection procedure diagrams to support the education and recruitment of committed stem cell donors

BACKGROUND

Diagrams which allow potential unrelated stem cell donors to visualize the stem cell collection process were hypothesized to support the recruitment and education of committed stem cell donors.

STUDY DESIGN AND METHODS

A series of bone marrow and peripheral blood stem cell collection procedure diagrams were developed, featuring young adult male donors of varied ethnic backgrounds. Post-implementation, surveys were conducted to evaluate stakeholder perspective on the diagrams' utility. A quality improvement project was conducted at five stem cell drives from 2017 to 2018 at which recruiters did or did not show the diagrams to potential donors. Following the drives, registrants were invited to complete a survey exploring their experience, knowledge and attitude towards donation.

RESULTS

The diagrams were implemented in Canada in 07/2016. Of 293 participating registrants (24·7% non-Caucasian males) recruited at five drives between 2017 and 2018, 76% (n = 197) were shown the diagrams. Participants who were shown the diagrams were significantly more likely to report that the recruiters appeared very knowledgeable (89% vs. 76%, P = 0·019) and to report improved self-reported knowledge of stem cell donation (P = 0·010) compared to participants not shown the diagram. Data are also shown demonstrating that stakeholders in donor recruitment used and valued the diagrams and that use of the diagrams was associated with improved donor recruitment outcomes in Canada.

CONCLUSION

This report is the first evaluation of stem cell collection diagrams in the literature. The diagrams are relevant to donor registries, recruitment organizations and transplant centres worldwide, and their use may support efforts to educate and recruit committed, ethnically diverse donors.

Why are hypomethylating agents or low-dose cytarabine and venetoclax so effective?

PURPOSE OF REVIEW

Venetoclax with backbone therapies have shown promising efficacy for newly diagnosed, previously untreated, older, unfit acute myeloid leukemia patients. This review discusses this data and potential reasons for the efficacy of these venetoclax-based combinations.

RECENT FINDINGS

Venetoclax with hypomethylators and low-dose cytarabine have resulted in high response rates, promising response durations, and significant overall survival in relatively small, uncontrolled studies. There is emerging data that these responses are due to the effective targeting of leukemia stem cells through an alteration of the metabolic environment that is poorly tolerated by this population.

SUMMARY

Venetoclax with a backbone therapy in older, untreated patients with acute myeloid leukemia has shown promising efficacy in preliminary clinical trials, and at least partially works through a novel mechanism that can target the leukemia stem cell population. Future investigations will help elucidate the mechanism and the contributions being made by each agent in the regimen.

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.

Ensuring HLA-matched platelet support requires an ethnic diverse donor population

BACKGROUND

Patients refractory for platelet transfusions benefit from human leukocyte antigen (HLA)‐matched platelet transfusions. Differences in ethnic background of patients and donors could hamper the availability of sufficient numbers of HLA‐matched donors for all patients. We evaluated our HLA‐matched donor program and explored the role of ethnic background of patients related to the number of available donors.

METHODS

We performed a cohort study among consecutive patients who received HLA‐matched platelet concentrates in the Netherlands between 1994 and 2017. The number of available matched donors was determined per patient. Haplotypes were constructed from genotypes with computer software (PyPop). Based on haplotypes, HaploStats, an algorithm from the National Marrow Donor Program, was used to assess the most likely ethnic background for patients with 5 or fewer and 30 or more donors.

RESULTS

HLA typing was available for 19,478 donors in September 2017. A total of 1206 patients received 12,350 HLA‐matched transfusions. A median of 83 (interquartile range, 18‐266) donors were available per patient. For 95 (10.3%) patients, 5 or fewer donors were available. These patients were more likely to have an African American background, whereas patients with 30 or more donors were more often from Caucasian origin, compared with Caucasian origin for patients with 30 donors.

CONCLUSION

Adequate transfusion support could be guaranteed for most but not all refractory patients. More non‐Caucasian donors are required to ensure the availability of HLA‐matched donors for all patients in the Netherlands.

Exploratory Study of Predicted Indirectly ReCognizable HLA Epitopes in Mismatched Hematopoietic Cell Transplantations

HLA-mismatches in hematopoietic stem-cell transplantation are associated with an impaired overall survival (OS). The aim of this study is to explore whether the Predicted Indirectly ReCognizable HLA-Epitopes (PIRCHE) algorithm can be used to identify HLA-mismatches that are related to an impaired transplant outcome. PIRCHE are computationally predicted peptides derived from the patient's mismatched-HLA molecules that can be presented by donor-patient shared HLA. We retrospectively scored PIRCHE numbers either presented on HLA class-I (PIRCHE-I) or class-II (PIRCHE-II) for a Dutch multicenter cohort of 103 patients who received a single HLA-mismatched (9/10) unrelated donor transplant in an early phase of their disease. These patients were divided into low and high PIRCHE-I and PIRCHE-II groups, based on their PIRCHE scores, and compared using multivariate statistical analysis methods. The high PIRCHE-II group had a significantly impaired OS compared to the low PIRCHE-II group and the 10/10 reference group (HR: 1.86, 95%-CI: 1.02–3.40; and HR: 2.65, 95%-CI: 1.53–4.60, respectively). Overall, PIRCHE-II seem to have a more prominent effect on OS than PIRCHE-I. This impaired OS is probably due to an increased risk for severe acute graft-vs.-host disease. These data suggest that high PIRCHE-II scores may be used to identify non-permissible HLA mismatches within single HLA-mismatched hematopoietic stem-cell transplantations.

Haploidentical versus matched donor stem cell transplantation for patients with hematological malignancies: a systemic review and meta-analysis

We compared the safety and efficacy of haploidentical stem cell transplantation (haplo-SCT) to matched donor SCT (matched-SCT) in treating hematological malignancies. The Medline, Cochrane, EMBASE, and Google Scholar databases were searched through 21 June 2017 using the search term "(hematological disease) AND matched AND (haploidentical OR haplo-identical OR haplo identical OR haplo transplantation OR haplo transplant OR haplo-SCT OR haplo-HSCT OR haplo-HCT)." Twenty-five studies enrolling 11,359 patients (haplo-SCT: 2677; matched-SCT: 8682) were included. The primary outcomes were acute and chronic graft-versus-host disease (GVHD), non-relapse mortality, and 1-year cumulative incidence of relapse. Haplo-SCT was associated with similar risks as matched-SCT for all primary endpoints. Subgroup analysis of patients who received a matched-SCT from a related donor revealed that patients who received haplo-SCT had a lower risk of acute GVHD. Among patients who received reduced-intensity conditioning (RIC), those who received haplo-SCT had a higher risk of acute grade II-IV GVHD and non-relapse mortality than did patients who received a matched-SCT from a related or unrelated donor. Haplo-SCT should continue to be considered as a safe and effective transplant option when a matched donor is unavailable, but it may not be suitable for patients who receive RIC.