Impact of donor NKG2D and MICA gene polymorphism on clinical outcomes of adult and paediatric allogeneic cord blood transplantation for malignant diseases.

OBJECTIVES: NKG2D is an activating receptor expressed by natural killer (NK) and CD8+ T cells and activation intensity varies by NKG2D expression level or nature of its ligand. An NKG2D gene polymorphism determines high (HNK1) or low (LNK1) expression. MICA is the most polymorphic NKG2D ligand and stronger effector cell activation associates with methionine rather than valine at residue 129. We investigated correlation between cord blood (CB) NKG2D and MICA genotypes and haematopoietic stem cell (HSC) transplant outcome. METHODS: We retrospectively studied 267 CB HSC recipients (178 adult and 87 paediatric) who underwent transplant for malignant disease between 2007 and 2018, analysing CB graft DNA for NKG2D and MICA polymorphisms using Sanger sequencing. Multivariate analysis was used to correlate these results with transplant outcomes. RESULTS: In adult patients, LNK1 homozygous CB significantly improved 60-day neutrophil engraftment (hazard ratio (HR) 0.6; 95% confidence interval (CI) 0.4-0.9; p = .003). In paediatrics, HNK1 homozygous CB improved 60-day engraftment (HR 0.4; 95% CI 0.2-0.7; p = .003), as did MICA-129 methionine+ CB grafts (HR 1.7 95% CI 1.1-2.6; p = .02). CONCLUSION: CB NKG2D and MICA genotypes potentially improve CB HSC engraftment. However, results contrast between adult and paediatric recipients and may reflect transplant procedure disparities between cohorts.

Advanced Cell Therapy: Beyond the last Frontier in the Treatment of Cancer. A Historical Perspective Emphasizing the Work of Nobel Prize Laureates.

During the last five decades different therapies have been developed for the treatment of cancer, and as a result, patients can now live longer and better lives. Among such therapies, hematopoietic cell transplantation and immunotherapy have played key roles. In this short article, we present our particular point of view on the development of these two cellular therapies. We have focused on a historical perspective emphasizing the work of some of the Nobel Prize winners whose studies constituted cornerstones in our knowledge of the biology of cancer and in our fight against this devastating disease.

Enumerating regulatory T cells in cryopreserved umbilical cord blood samples using FOXP3 methylation specific quantitative PCR.

BACKGROUND: Allogeneic haematopoietic cell transplantation (HCT) is a curative therapy for severe haematological disorders. However, it carries significant risk of morbidity and mortality. To improve patient outcomes, better graft selection strategies are needed, incorporating HLA matching with clinically important graft characteristics. Studies have shown that the cellular content of HCT grafts, specifically higher ratios of T regulatory (Tregs)/T cells, are important factors influencing outcomes when using adult peripheral blood mobilised grafts. So far, no equivalent study exists in umbilical cord blood (CB) transplantation due to the limitations of cryopreserved CB samples. STUDY DESIGN AND METHODS: To establish the most robust and efficient way to measure the Treg content of previously cryopreserved CB units, we compared the enumeration of Treg and CD3+ cells using flow cytometry and an epigenetic, DNA-based methodology. The two methods were assessed for their agreement, consistency and susceptibility to error when enumerating Treg and CD3+ cell numbers in both fresh and cryopreserved CB samples. RESULTS: Epigenetic enumeration gave consistent and comparable results in both fresh and frozen CB samples. By contrast, assessment of Tregs and CD3+ cells by flow cytometry was only possible in fresh samples due to significant cell death following cryopreservation and thawing. CONCLUSION: Epigenetic assessment offers significant advantages over flow cytometry for analysing cryopreserved CB; similar cell numbers were observed both in fresh and frozen samples. Furthermore, multiple epigenetic assessments can be performed from DNA extracted from small cryopreserved CB segments; often the only CB sample available for clinical studies.

Role of HLA-DP Expression in Graft-Versus-Host Disease After Unrelated Donor Transplantation.

PURPOSE: The main aim of this study was to evaluate the significance of HLA-DPB1 expression in acute graft-versus-host disease (GVHD) after hematopoietic cell transplantation (HCT) from HLA-A, -B, -C, -DRB1, -DQB1-matched and -mismatched unrelated donors. PATIENTS AND METHODS: Between January 1, 2017, and January 10, 2019, we assessed 19,136 patients who received HCT from an HLA-A, -B, -C, -DRB1, -DQB1-matched or -mismatched unrelated donor performed in Australia, the European Union, Japan, North America, and the United Kingdom between 1988 and 2016. Among transplant recipients with one HLA-DPB1 mismatch, the patient's mismatched HLA-DPB1 allotype was defined as low or high expression. Multivariable regression models were used to assess risks of GVHD associated with high expression relative to low expression HLA-DPB1 mismatches. The effect of increasing numbers of HLA-DPB1 mismatches on clinical outcome was assessed in HLA-mismatched transplant recipients. RESULTS: In HLA-A, -B, -C, -DRB1,-DQB1-matched transplant recipients, donor mismatching against one high-expression patient HLA-DPB1 increased moderate (odds ratio [OR], 1.36; P = .001) and severe acute GVHD (OR, 1.32; P = .0016) relative to low-expression patient mismatches, regardless of the expression level of the donor's mismatched HLA-DPB1. Among transplant recipients with one HLA-A, -B, -C, -DRB1, or -DQB1 mismatch, the odds of acute GVHD increased with increasing numbers of HLA-DPB1 mismatches (OR, 1.23 for one; OR, 1.40 for two mismatches relative to zero mismatches for moderate GVHD; OR, 1.19 for one; OR, 1.40 for two mismatches relative to zero for severe GVHD), but not with the level of expression of the patient's mismatched HLA-DPB1 allotype. CONCLUSION: The level of expression of patient HLA-DPB1 mismatches informs the risk of GVHD after HLA-A, -B, -C, -DRB1, -DQB1-matched unrelated HCT, and the total number of HLA-DPB1 mismatches informs the risk of GVHD after HLA-mismatched unrelated HCT. Prospective consideration of HLA-DPB1 may help to lower GVHD risks after transplantation.

HLA-B leader and survivorship after HLA-mismatched unrelated donor transplantation.

Hematopoietic cell transplantation (HCT) from HLA-mismatched unrelated donors can cure life-threatening blood disorders, but its success is limited by graft-versus-host disease (GVHD). HLA-B leaders encode methionine (M) or threonine (T) at position 2 and give rise to TT, MT, or MM genotypes. The dimorphic HLA-B leader informs GVHD risk in HLA-B-mismatched HCT. If the leader influences outcome in other HLA-mismatched transplant settings, the success of HCT could be improved for future patients. We determined leader genotypes for 10 415 patients receiving a transplant between 1988 and 2016 from unrelated donors with one HLA-A, HLA-B, HLA-C, HLA-DRB1, or HLA-DQB1 mismatch. Multivariate regression methods were used to evaluate risks associated with patient leader genotype according to the mismatched HLA locus and with HLA-A, HLA-B, HLA-C, HLA-DRB1, or HLA-DQB1 mismatching according to patient leader genotype. The impact of the patient leader genotype on acute GVHD and mortality varied across different mismatched HLA loci. Nonrelapse mortality was higher among HLA-DQB1-mismatched MM patients compared with HLA-DQB1-mismatched TT patients (hazard ratio, 1.35; P = .01). Grades III to IV GVHD risk was higher among HLA-DRB1-mismatched MM or MT patients compared with HLA-DRB1-mismatched TT patients (odds ratio, 2.52 and 1.51, respectively). Patients tolerated a single HLA-DQB1 mismatch better than mismatches at other loci. Outcome after HLA-mismatched transplantation depends on the HLA-B leader dimorphism and the mismatched HLA locus. The patient's leader variant provides new information on the limits of HLA mismatching. The success of HLA-mismatched unrelated transplantation might be enhanced through the judicious selection of mismatched donors for a patient's leader genotype.

Presence of donor-encoded centromeric KIR B content increases the risk of infectious mortality in recipients of myeloablative, T-cell deplete, HLA-matched HCT to treat AML.

The reported influence of donor Killer-cell Immunoglobulin-like Receptor (KIR) genes on the outcomes of haematopoietic cell transplantation (HCT) are contradictory, in part due to diversity of disease, donor sources, era and conditioning regimens within and between different studies. Here, we describe the results of a retrospective clinical analysis establishing the effect of donor KIR motifs on the outcomes of 119 HLA-matched, unrelated donor HCT for adult acute myeloid leukaemia (AML) using myeloablative conditioning (MAC) in a predominantly T-cell deplete (TCD) cohort. We observed that HCT involving donors with at least one KIR B haplotype were more likely to result in non-relapse mortality (NRM) than HCT involving donors with two KIR A haplotypes (p = 0.019). Upon separation of KIR haplotypes into their centromeric (Cen) and telomeric (Tel) motif structures, we demonstrated that the Cen-B motif was largely responsible for this effect (p = 0.001). When the cause of NRM was investigated further, infection was the dominant cause of death (p = 0.006). No evidence correlating donor KIR B haplotype with relapse risk was observed. The results from this analysis confirm previous findings in the unrelated, TCD, MAC transplant setting and imply a protective role for donor-encoded Cen-A motifs against infection in allogeneic HCT recipients.

Corrigendum: Functional Characterisation and Analysis of the Soluble NKG2D Ligand Repertoire Detected in Umbilical Cord Blood Plasma.

[This corrects the article DOI: 10.3389/fimmu.2018.01282.].

Autoimmune cytopenias (AIC) following allogeneic haematopoietic stem cell transplant for acquired aplastic anaemia: a joint study of the Autoimmune Diseases and Severe Aplastic Anaemia Working Parties (ADWP/SAAWP) of the European Society for Blood and Marrow Transplantation (EBMT).

This retrospective study explored the incidence of autoimmune cytopenia (AIC) in 530 paediatric and adult patients with acquired aplastic anaemia (aAA) who underwent first allogeneic HSCT between 2002 and 2012. AIC was a rare complication with a cumulative incidence of AIC at 1, 3, 5 and 10 years post HSCT of 2.5% (1.2-3.9 95% CI), 4.4% (2.6-6.2 95% CI), 4.6% (2.8-6.5 95% CI) and 5.1% (3.1-7.2 95% CI). Overall survival at 5 years after diagnosis of AIC was 85.9% (71-100 95% CI). Twenty-five patients were diagnosed with AIC at a median of 10.6 (2.6-91.5) months post HSCT. Eight (32%) patients were diagnosed with immune thrombocytopenia (ITP), seven (28%) with autoimmune haemolytic anaemia (AIHA), seven (24%) with Evans syndrome and four (16%) with autoimmune neutropenia (AIN). Treatment strategies were heterogeneous. Complete responses were seen in 12 of 25 patients, with death in three patients. In multivariable Cox analysis of a subgroup of 475 patients, peripheral blood stem cell (PBSC) transplant was associated with higher risk of AIC compared with bone marrow (BM) when conditioning regimens contained fludarabine and/or alemtuzumab (2.81 [1.06-7.49 95% CI]; p = 0.038), or anti-thymocyte globulin (ATG) (2.86 [1.11-7.37 95% CI]; p = 0.029). Myeloablative conditioning was associated with a lower risk of AIC compared with reduced intensity conditioning (RIC) in fludarabine and/or alemtuzumab (0.34 [0.12-0.98 95% CI]; p = 0.046) and ATG containing regimens (0.34 [0.12-0.95 95% CI]; p = 0.04). These findings provide clinically useful information regarding the incidence of a rare and potentially life-threatening complication of allogeneic HSCT for aAA, and further support for BM as the preferred stem cell source for transplant of patients with aAA.

Role of HLA-B exon 1 in graft-versus-host disease after unrelated haemopoietic cell transplantation: a retrospective cohort study.

BACKGROUND: The success of unrelated haemopoietic cell transplantation (HCT) is limited by graft-versus-host disease (GVHD), which is the main post-transplantation challenge when HLA-matched donors are unavailable. A sequence dimorphism in exon 1 of HLA-B gives rise to leader peptides containing methionine (Met; M) or threonine (Thr; T), which differentially influence natural killer and T-cell alloresponses. The main aim of the study was to evaluate the role of the leader dimorphism in GVHD after HLA-B-mismatched unrelated HCT. METHODS: We did a retrospective cohort study of 33 982 patients who received an unrelated HCT done in Australia, Europe, Japan, North America, and the UK between Jan 1, 1988, and Dec 31, 2016. Data were contributed by participants of the International Histocompatibility Working Group in Hematopoietic Cell Transplantation. All cases were included and there were no exclusion criteria. Multivariate regression models were used to assess risks associated with HLA-A, HLA-B, HLA-C, HLA-DRB1, and HLA-DQB1 mismatching. Among the 33 982 transplantations, the risks of GVHD associated with HLA-B M and T leaders were established in 17 100 (50·3%) HLA-matched and 1457 (4·3%) single HLA-B-mismatched transplantations using multivariate regression models. Leader frequencies were defined in 2 004 742 BeTheMatch US registry donors. FINDINGS: Between Jan 20, 2017, and March 11, 2019, we assessed 33 982 HCTs using multivariate regression models for the role of HLA mismatching on outcome. Median follow-up was 1841 days (IQR 909-2963). Mortality and GVHD increased with increasing numbers of HLA mismatches. A single HLA-B mismatch increased grade 3-4 acute GVHD (odds ratio [OR] 1·89, 95% CI 1·53-2·33; p<0·0001). Among the single HLA-B-mismatched transplantations, acute GVHD risk was higher with leader mismatching than with leader matching (OR 1·73, 1·02-2·94; p=0·042 for grade 2-4) and with an M leader shared allotype compared with a T leader shared allotype (OR 1·98, 1·39-2·81; p=0·0001 for grade 3-4). The preferred HLA-B-mismatched donor is leader-matched and shares a T leader allotype. The majority (1 836 939 [91·6%]) of the 2 004 742 US registry donors have the TT or MT genotype. INTERPRETATION: The HLA-B leader informs GVHD risk after HLA-B-mismatched unrelated HCT and differentiates high-risk HLA-B mismatches from those with lower risk. The leader of the matched allotype could be considered to be as important as the leader of the mismatched allotype for GVHD. Prospective identification of leader-matched donors is feasible for most patients in need of a HCT, and could lower GVHD and increase availability of HCT therapy. These findings are being independently validated and warrant further research in prospective trials. FUNDING: The National Institutes of Health, USA.

5-Locus high-resolution HLA allele and haplotype frequencies in Costa Ricans from the Central Valley.

A total of 221 Costa Rican Mestizos from the Central Valley were genotyped at high-resolution for the human leukocyte antigen loci HLA-A, -B, -C, -DRB1, and -DQB1 using sequence-based typing methods. The respective allele and extended haplotype frequencies, as well as Hardy-Weinberg proportions were calculated. The most frequent extended haplotype identified was A*24:02:01-B*40:02:01-C*03:05-DRB1*08:02:01-DQB1*04:02:01, with an estimated frequency of 2.04%. No deviation from Hardy-Weinberg Equilibrium was detected at any of the loci studied. The HLA genotypic data of the population sample reported here are available publicly in the Allele Frequencies Net Database under the population name "Costa Rica Central Valley Mestizo" and the identifier AFN3606.

4-Locus high-resolution HLA allele and haplotype frequencies in Amerindians from Costa Rica.

A total of 125 Costa Ricans of Amerindian descent were genotyped at high-resolution for the human leukocyte antigen loci HLA-A, -B, -C, and -DRB1 using sequence-based typing methods. The respective allele and extended haplotype frequencies, as well as Hardy-Weinberg proportions were calculated. The most frequent extended haplotype identified was A*24:02:01-B*40:02:01-C*03:05-DRB1*04:07:01G, with an estimated frequency of 8.26%. A deviation from Hardy-Weinberg Equilibrium was detected at the DRB1 locus (p = 0.099). The HLA genotypic data of the population sample reported here are available publicly in the Allele Frequencies Net Database under the population name "Costa Rica Amerindians" and the identifier AFN3608.

4-Locus high-resolution HLA allele and haplotype frequencies in admixed population from Nicaragua.

A total of 155 Nicaraguan Mestizos from across the country were genotyped at high-resolution for the human leukocyte antigen loci HLA-A, -B, -C, and -DRB1 using sequence-based typing methods. The respective allele and extended haplotype frequencies, as well as Hardy-Weinberg proportions were calculated. The most frequent extended haplotype identified was A*24:02:01-B*40:02:01-C*03:05-DRB1*04:07:01G, with an estimated frequency of 2.26%. No deviation from Hardy-Weinberg Equilibrium was detected at any of the loci studied. The HLA genotypic data of the population sample reported here are available publicly in the Allele Frequencies Net Database under the population name "Nicaragua Mestizo" and the identifier AFN3610.

4-Locus high-resolution HLA allele and haplotype frequencies in Costa Ricans from African-Caribbean descent.

A total of 102 Costa Ricans of African-Caribbean descent were genotyped at high-resolution for the human leukocyte antigen loci HLA-A, -B, -C, and -DRB1 using sequence-based typing methods. The respective allele and extended haplotype frequencies, as well as Hardy-Weinberg proportions were calculated. The most frequent extended haplotype identified was A*01:01:01-B*08:01:01-C*07:01:01-DRB1*03:01:01G, with an estimated frequency of 1.96%. No deviation from Hardy-Weinberg Equilibrium was detected at any of the loci studied. The HLA genotypic data of the population sample reported here are available publicly in the Allele Frequencies Net Database under the population name "Costa Rica African-Caribbeans" and the identifier AFN3607.

4-Locus high-resolution HLA allele and haplotype frequencies in Costa Ricans from Guanacaste.

A total of 110 Costa Rican Mestizos from the province of Guanacaste were genotyped at high-resolution for the human leukocyte antigen loci HLA-A, -B, -C, and -DRB1 using sequence-based typing methods. The respective allele and extended haplotype frequencies, as well as Hardy-Weinberg proportions were calculated. The most frequent extended haplotype identified was A*24:02:01-B*35:12:01-C*04:01:01-DRB1*04:07:01G, with an estimated frequency of 2.73%. No deviation from Hardy-Weinberg Equilibrium was detected at any of the loci studied. The HLA genotypic data of the population sample reported here are available publicly in the Allele Frequencies Net Database under the population name "Costa Rica Guanacaste Mestizo" and the identifier AFN3609.

Recipients Receiving Better HLA-Matched Hematopoietic Cell Transplantation Grafts, Uncovered by a Novel HLA Typing Method, Have Superior Survival: A Retrospective Study.

HLA matching at an allelic-level resolution for volunteer unrelated donor (VUD) hematopoietic cell transplantation (HCT) results in improved survival and fewer post-transplant complications. Limitations in typing technologies used for the hyperpolymorphic HLA genes have meant that variations outside of the antigen recognition domain (ARD) have not been previously characterized in HCT. Our aim was to explore the extent of diversity outside of the ARD and determine the impact of this diversity on transplant outcome. Eight hundred ninety-one VUD-HCT donors and their recipients transplanted for a hematologic malignancy in the United Kingdom were retrospectively HLA typed at an ultra-high resolution (UHR) for HLA-A, -B, -C, -DRB1, -DQB1, and -DPB1 using next-generation sequencing technology. Matching was determined at full gene level for HLA class I and at a coding DNA sequence level for HLA class II genes. The HLA matching status changed in 29.1% of pairs after UHR HLA typing. The 12/12 UHR HLA matched patients had significantly improved 5-year overall survival when compared with those believed to be 12/12 HLA matches based on their original HLA typing but were found to be mismatched after UHR HLA typing (54.8% versus 30.1%, P = .022). Survival was also significantly better in 12/12 UHR HLA-matched patients when compared with those with any degree of mismatch at this level of resolution (55.1% versus 40.1%, P = .005). This study shows that better HLA matching, found when typing is done at UHR that includes exons outside of the ARD, introns, and untranslated regions, can significantly improve outcomes for recipients of a VUD-HCT for a hematologic malignancy and should be prospectively performed at donor selection.

Diversity and characterisation of polymorphic 3' untranslated region haplotypes of MICA and MICB genes.

MICA and MICB genes encode ligands that interact with the natural killer (NK) cell activating receptor, NKG2D. These ligands display a highly polymorphic allelic repertoire, although the true functional significance of this polymorphism remains elusive. We previously reported additional polymorphism in the 5' untranslated region (UTR) proximal promoter region of these genes by sequencing international histocompatibility workshop (IHW) cell line DNA promoter and coding regions. The present study extends this analysis by further characterising the 3'UTR region of the same IHW reference panel to achieve a more complete understanding of MICA and MICB haplotype diversity and possible functional relevance. We found 17 extended MICA haplotypes encompassing the coding region and 3'UTR, including four novel haplotypes identified in IHW cell line DNA. This increased to 21 when also considering the 5'UTR proximal promoter region. Analysis of the MICB 3'UTR revealed two novel sequences in cell lines KLO and WIN designated MICB-UTR8 and UTR9, respectively. A total of 11 MICB haplotypes were identified in this study and five were unique. The present study, characterising MICA/B 3'UTR polymorphism utilising IHW reference cell lines, could be useful for future studies investigating the role of microRNA in post-transcriptional repression of gene expression and for immunotherapy strategies to combat cancer progression.

Functional Characterisation and Analysis of the Soluble NKG2D Ligand Repertoire Detected in Umbilical Cord Blood Plasma.

We previously reported that cord blood plasma (CBP) contains significantly more soluble NKG2D ligands (sNKG2DLs), such as sMICB and sULBP1, than healthy adult plasma. Viral infection or malignant transformation upregulates expression of NKG2D ligand on affected cells, leading to NK group 2, member D (NKG2D)-mediated natural killer (NK) cell lysis. Conversely, sNKG2DL engagement of NKG2D decreases NK cell cytotoxicity leading to viral or tumour immune escape. We hypothesised that sNKG2DLs detected in CBP may represent an additional fetal-maternal tolerance mechanism. To further understand the role of sNKG2DL in pregnancy and individual contributions of the various ligand types, we carried out functional analysis using 181 CBP samples. To test the ability of CBP to suppress the function of NK cells in vitro, we measured expression of NKG2D, CD107a, and IFN-γ in NK cells from control donors after exposure to 181 individual CBP samples and characterised the sMICA, sMICB, and sULBP1 content of each one. Furthermore, to detect possible allelic differences between samples that may also affect function, we carried out umbilical cord blood typing for MHC class I-related chain A (MICA) and MHC class I-related chain B (MICB) coding and promoter allelic types. Strongest functional correlations related to increasing concentration of exosomal sULBP1, which was present in all CBP samples tested. In addition, common MICB alleles, such as MICB*005:02, resulted in increased concentration of sMICB. Interestingly, MICB*005:02 uniquely associated with eight different promoter types. Among promoter polymorphisms, P2 resulted in the highest expression of sMICB and P9 the least and was confirmed using luciferase reporter assays. Higher levels of sMICB associated with lower IFN-γ production, indicating that sMICB also suppressed NK cell function. We also examined the MICA functional dimorphism encoding methionine (met) or valine (val) at residue 129 associated with strong or weak NKG2D binding, respectively. Most sMICA associated with val/val, some with met/val but none with met/met and, counter-intuitively, the presence of sMICA in CBP increased NK cell cytotoxicity. We propose a model for fetal-maternal tolerance, whereby NK cell activity is limited by sULBP1 and sMICB in CBP. The release of 129val sMICA with weak NKG2D signalling may reduce the overall net suppressive signal and break tolerance thus allowing fetal NK cells to overcome immunological threats in utero.

Clinical Grade Regulatory CD4+ T Cells (Tregs): Moving Toward Cellular-Based Immunomodulatory Therapies.

Regulatory T cells (Tregs) are CD4+ T cells that are key players of immune tolerance. They are powerful suppressor cells, able to impact the function of numerous immune cells, including key effectors of inflammation such as effector T cells. For this reason, Tregs are an ideal candidate for the development of cell therapy approaches to modulate immune responses. Treg therapy has shown promising results so far, providing key knowledge on the conditions in which these cells can provide protection and demonstrating that they could be an alternative to current pharmacological immunosuppressive therapies. However, a more comprehensive understanding of their characteristics, isolation, activation, and expansion is needed to be able design cost effective therapies. Here, we review the practicalities of making Tregs a viable cell therapy, in particular, discussing the challenges faced in isolating and manufacturing Tregs and defining what are the most appropriate applications for this new therapy.

Donation of peripheral blood stem cells to unrelated strangers: A thematic analysis.

BACKGROUND: Donation of haematopoietic stem cells, either through bone marrow (BM) or peripheral blood stem cell (PBSC) collection, is a generally safe procedure for healthy donors, although side effects are a known risk. Previous research, including our recent quantitative study, has shown that the psychosocial response to donating is usually a positive one and most donors would be willing to donate again in the future. This is often despite experiencing significant side effects during the donation process. Due to the relative recent introduction of PBSC, a comprehensive understanding of the range of physical and emotional issues donors may experience is lacking, as well as an understanding of specific donor characteristics Qualitative research can provide rich narrative data into these areas. This study was set up in order to identify specific donor characteristics and to further explore the relationship between pre-donation physical health and the donation experience, as previously identified in our quantitative study. METHODS: It involved in-depth telephone interviews with 14 PBSC donors who participated in our original quantitative study. Thematic analysis was used to analyse the findings and the results provide a summary of participants' characteristics using themes and constituent codes. RESULTS: We identified several donor characteristics, including strong intrinsic motivation, altruism, sense of duty, determination, low levels of ambivalence and the ability to develop a strong emotional relationship with an (unknown/anonymous) recipient whilst being able to manage strong feelings and emotions. CONCLUSIONS: These personality traits may explain the resilience that has been observed previously in haematopoietic stem cells donors. Significant feelings of grief were reported after a recipient's death. Possibilities to alleviate these symptoms may include raising awareness of potential poor outcomes in the recipient and offering improved counselling services if the recipient dies. We acknowledge several limitations including the sampling frame.