Indirect evidence that maternal microchimerism in cord blood mediates a graft-versus-leukemia effect in cord blood transplantation

Haplo-cord transplant. Realizing the potential of umbilical cord blood grafts. - A review of techniques and analysis of outcomes

The combination of cord blood transplant with progenitor cells from partially HLA-matched adult donors (haplo-cord transplant) has been used over the past two decades. In Europe and the US the adult donor graft is CD34 selected and provides early hematopoiesis, but durable engraftment derives from the cord blood graft (CD34 selected haplo-cord). Neutrophil recovery is prompt and rates of acute and chronic GVHD are low. Recent Chinese studies combine cord blood grafts with T-replete haplo-identical grafts (unmodified haplo-cord). The haplo graft usually establishes dominance and UCB chimerism is rarely detected. Comparison studies suggest considerably decreased rates of relapse and improved outcomes, compared with either haplo-identical transplant or CBU transplant, particularly in patients with advanced leukemia. A recent prospective randomized study confirms this. Haplo-cord mitigates the engraftment delay of UCB transplant. The unique biology of UCB grafts results in low GVHD and improved GVL especially beneficial in high-risk disease.

Haploidentical Cord Blood Transplantation with 8 mg/kg Antithymocyte Globulin as Graft-versus-Host Disease Prophylaxis Compared to Haploidentical Transplantation with 10 mg/kg Antithymocyte Globulin in the Treatment of Acute Leukemia

Clinical outcomes of the transplantation strategy combined with a haploidentical stem cell graft and an unrelated umbilical cord blood unit (haplo-cord HSCT) with low-dose antithymocyte globulin (ATG) as graft-versus-host disease (GVHD) prophylaxis for the treatment of acute leukemia remains unclear. This study aimed to explore the clinical outcomes of haplo-cord HSCT in acute leukemia patients with the GVHD prevention strategy of 8 mg/kg ATG compared with haploidentical transplantation with 10 mg/kg ATG. A total of 130 patients with acute leukemia who underwent allogeneic HSCT between January 2016 and December 2020 were included in this study, including 70 patients who received haploidentical stem cell grafts and unrelated umbilical cord blood units (haplo-cord HSCT) with 8 mg/kg ATG (haplo-cord-ATG8 group) and haploidentical HSCT with 10 mg/kg ATG (haplo-ATG10 group) in 60 patients. Clinical data were collected and analyzed retrospectively. Patients in the haplo-cord-ATG8 group were significantly older compared with the haplo-ATG10 group (P = .000). Haplo-cord HSCT with reduced ATG to 8 mg/kg results in more rapid neutrophil recovery (P = .036). No between-group differences were observed in platelet recovery or the incidences of Epstein-Barr virus viremia, bloodstream infection, or hemorrhagic cystitis. The rate of grade II-IV acute GVHD by day 100 post-transplantation was higher in the haplo-ATG10 group (27.16% versus 11.48%; P = .033), as was the rate of chronic GVHD at 1 year (14.60% versus 3.36%; P = .048). The rate of cytomegalovirus reaction was higher in the haplo-ATG10 group (48.31% versus 26.30%; P = .022). With a median follow-up of 27.4 months for the haplo-cord-ATG8 group and 27.5 months for the haplo-ATG10 group, overall survival (OS) at 2 years was 79.4% versus 62.8% (P = .005), event-free survival (EFS) was 76.3% versus 55.9% (P = .001), the cumulative incidence of relapse was 10.11% versus 25.97% (P = .164), and nonrelapse mortality (NRM) was 14.33% versus 24.43% (P = .0040). Multivariate analysis identified Center for International Blood and Marrow Transplant Research Disease Risk Index was the sole significant predictor of relapse, NRM, OS, and EFS. Haplo-cord HSCT supported by cord blood with 8 mg/kg ATG as GVHD prophylaxis results in better outcomes compared with haplo-HSCT with 10 mg/kg ATG.

Clinical Outcomes of Umbilical Cord Blood Transplantation Using Ex Vivo Expansion: A Systematic Review and Meta-Analysis of Controlled Studies

Greater use of umbilical cord blood (UCB) for hematopoietic cell transplantation (HCT) is limited by the number of cells in banked units. Ex vivo culture strategies have been increasingly evaluated in controlled studies, but their impact on transplantation-related outcomes remains uncertain owing to the small patient numbers in these studies, necessitating an updated systematic review and meta-analysis. A systematic literature search was conducted using the MEDLINE, Embase, and Cochrane databases to March 18, 2022. Nine cohort-controlled phase I to III trials were identified, and data of 1146 patients undergoing umbilical cord blood transplantation (UCBT) were analyzed (308 ex vivo expanded and 838 unmanipulated controls). Expansion strategies involved cytokine cocktails plus the addition of small molecules (UM171, nicotinamide [NiCord], copper chelation, Notch ligand, or Stem regenin-1 [SR-1]) and coculture with mesenchymal stromal cells in a single-unit transplant strategy (5 studies) or a double-unit transplant strategy with 1 unmanipulated unit (4 studies). The included trials reported a median ex vivo expansion of CD34⁺ cells from 28-fold to 330-fold. Eight of the 9 studies demonstrated a significantly faster time to initial neutrophil and platelet engraftment using expanded cells compared with controls. Studies using UM171 and NiCord in single-unit UCBT and SR-1 or NiCord double-unit UCBT demonstrated long-term donor chimerism of the expanded unit at 100 days to 36 months post-transplantation in all single-unit recipients and in 35% to 78% of double-unit recipients. Our meta-analysis revealed a lower risk of death at the study endpoint in patients who received ex vivo expanded grafts (odds ratio [OR], .66; 95% confidence interval [CI], .47 to .95; P = .02), while the risk of grade II-IV acute graft-versus-host disease was unchanged (OR, .79; 95% CI, .58 to 1.08; P = .14). This review indicates that UCBT following ex vivo expansion can accelerate initial engraftment. Durable donor chimerism can be achieved after transplanting cord blood units expanded using NiCord, UM171, or SR-1; however, long term outcomes remain unclear. Larger studies with longer-term outcomes are needed to better understand the merits of specific expansion strategies on survival.

Haplo-Peripheral Blood Stem Cell Plus Cord Blood Grafts for Hematologic Malignancies Might Lead to Lower Relapse Compared with Haplo-Peripheral Blood Stem Cell Plus Bone Marrow Grafts

To compare the outcomes between peripheral blood stem cell (PBSC)+cord blood and PBSC+bone marrow (BM) grafts in the setting of haploidentical donor (HID) transplantation, 110 patients were enrolled in this retrospective study, including 54 recipients of haplo-PBSC+cord transplants and 56 recipients of haplo-PBSC+BM transplants. Chimerism analyses revealed that by day 30 post-transplantation, 94.3% of surviving patients in the haplo-PBSC+cord group had achieved full haploidentical chimerism and 5.7% had <10% cord chimerism, whereas 100% of surviving patients in the haplo-PBSC+BM group had achieved full donor chimerism. The cumulative incidence of platelet engraftment at 30 days was 92.6% in the haplo-PBSC+cord group versus 89.3% in the haplo-PBSC+BM group (P =.024), that of grade II-IV acute graft-versus-host disease (GVHD) at 100 days was 31.5% versus 48.2% (P =.060), and 1-year relapse was 13.0% versus 25.0% (P =.027), nonrelapse mortality was 9.3% versus 12.5% (P =.76), disease-free survival (DFS) was 77.7% versus 62.5% (P =.028), and overall survival (OS) was 81.4% versus 69.6% (P =.046). Multivariate analysis identified haplo-PBSC+cord transplantation as a protective factor for relapse (hazard ratio [HR], .31; P =.007), DFS (HR, .40; P =.007), and OS (HR, .44; P =.016). Overall, haplo-PBSC+cord transplantation led to faster platelet engraftment, lower relapse, and superior DFS and OS compared with haplo-PBSC+BM transplantation and thus might be a better transplant mode in the setting of HID transplantation.

Meiotic drive in chronic lymphocytic leukemia compared with other malignant blood disorders

The heredity of the malignant blood disorders, leukemias, lymphomas and myeloma, has so far been largely unknown. The present study comprises genealogical investigations of one hundred and twelve Scandinavian families with unrelated parents and two or more cases of malignant blood disease. For comparison, one large family with related family members and three hundred and forty-one cases of malignant blood disease from the Faroese population was included. The inheritance is non-Mendelian, a combination of genomic parental imprinting and feto-maternal microchimerism. There is significantly more segregation in maternal than in paternal lines, predominance of mother-daughter combinations in maternal lines, and father-son combinations in paternal lines. Chronic lymphocytic leukemia is the most frequent diagnosis in the family material, and chronic lymphocytic leukemia has a transgenerational segregation that is unique in that inheritance of susceptibility to chronic lymphocytic leukemia is predominant in males of paternal lines. Male offspring with chronic lymphocytic leukemia in paternal lines have a birth-order effect, which is manifest by the fact that there are significantly more male patients late in the sibling line. In addition, there is contravariation in chronic lymphocytic leukemia, i.e. lower occurrence than expected in relation to other diagnoses, interpreted in such a way that chronic lymphocytic leukemia remains isolated in the pedigree in relation to other diagnoses of malignant blood disease. Another non-Mendelian function appears in the form of anticipation, i.e. increased intensity of malignancy down through the generations and a lower age at onset of disease than otherwise seen in cases from the Cancer Registers, in acute lymphoblastic leukemia, for example. It is discussed that this non-Mendelian segregation seems to spread the susceptibility genes depending on the gender of the parents and not equally to all children in the sibling line, with some remaining unaffected by susceptibility i.e. "healthy and unaffected", due to a birth order effect. In addition, anticipation is regarded as a non-Mendelian mechanism that can amplify, «preserve» these vital susceptibility genes in the family. Perhaps this segregation also results in a sorting of the susceptibility, as the percentage of follicular lymphoma and diffuse large B-cell lymphoma is lower in the family material than in an unselected material. Although leukemias, lymphomas and myelomas are potentially fatal diseases, this non-Mendelian distribution and amplification hardly play any quantitative role in the survival of Homo sapiens, because these diseases mostly occur after fertile age.

Tools for optimizing risk assessment in hematopoietic cell transplant - What can we get away with?

Unrelated allogeneic hematopoietic cell transplant (HCT) is a critical modality to treat hematologic malignancies. The current objective of donor selection is to match donor and recipient at the HLA (human leukocyte antigen) peptide-binding region which should lower the risk of graft-versus-host disease. However, depending on the patient's ethnicity/race, finding a matched donor is challenging, especially for HLA-DPB1 which is due to the weak linkage disequilibrium between HLA-DPB1 and the other HLA class II loci. Recent evidence, on the molecular level, has shown that certain HLA mismatches carry lower clinical risk. More specifically, there is an increasing understanding of polymorphisms of the innate and adaptive immune systems and their impact on transplant outcomes, allowing us to expand our "toolkit" for optimization of donor selection in HCT. Therefore, in this review we discuss matching strategies based on comparing donor and recipient polymorphisms that may influence innate and adaptive immune response genes in allorecognition and the role of single nucleotide polymorphisms in non-HLA genes that have the potential for providing additional tools to refine risk stratification.

The clinical outcomes of B-cell Acute Lymphoblastic Leukemia Patients Treated with Haploidentical Stem Cells Combined with Umbilical Cord Blood Transplantation

BACKGROUND

Clinical outcomes of the transplantation strategy combined with a haploidentical stem cell graft and an unrelated umbilical cord blood unit (haplo-cord HSCT) for the treatment of B-cell acute lymphoblastic leukemia (B-ALL) remain unclear.

OBJECTIVE

To explore the clinical outcomes of haplo-cord HSCT in B-ALL patients.

STUDY DESIGN

A total of 112 B-ALL patients who received haplo-cord HSCT and 64 patients who received haploidentical hematopoietic stem cell transplantation (haplo-HSCT) in our center from 2010 to 2020 were retrospectively included in this study, and clinical outcomes and prognostic factors were further analyzed.

RESULTS

A total of 94.6% (106/112) of the haplo-cord patients achieved complete haploidentical chimerism, while 5.4% (6/112) of patients had mixed cord blood chimerism. No differences were observed in neutrophil and platelet recovery or the incidences of GVHD, CMV/EBV viremia, bloodstream infection or hemorrhagic cystitis between the haplo-cord HSCT and haplo-HSCT groups. Compared to haplo-HSCT group, the haplo-cord HSCT group had a higher absolute number of CD3⁺ cells (P=0.029) and a lower ratio of CD3⁺CD4⁺ /CD3⁺CD8⁺ cells (P=0.049) at 1 month after transplantation. Moreover, Haplo-cord HSCT patients showed lower minimal residual disease (MRD) levels at 1 month (P=0.020) and 100 days (P=0.038) after transplantation and better 3-year prognoses than the haplo-HSCT group (OS: P=0.016; DFS: P=0.041; cumulative incidence of relapse (CIR): P=0.016). The CIRs in patients with adverse genomic features (P=0.040) or flow cytometry-based minimal residual disease (FCM-MRD)≥1 × 10^-4 (P=0.033) were improved by haplo-cord HSCT. By multivariate analysis, we found that haplo-cord HSCT could independently improve the 3-year OS, DFS and CIR of B-ALL patients (OS: P=0.029; DFS: P=0.024; CIR: P=0.024). Additionally, allo-HSCT at CR1 was an independent parameter associated with 3-year OS for B-ALL patients (P=0.014). FCM-MRD≥1 × 10^-4 pre-HSCT could independently predict unfavorable 3-year DFS and CIR (DFS: P=0.020; CIR: P=0.036) in B-ALL patients.

CONCLUSION

Haplo-cord HSCT could independently improve survival in B-ALL patients.

Male microchimerism in females: a quantitative study of twin pedigrees to investigate mechanisms

STUDY QUESTION

Does having a male co-twin, older brothers, or sons lead to an increased probability of persistent male microchimerism in female members of twin pedigrees?

SUMMARY ANSWER

The presence of a male co-twin did not increase risk of male microchimerism and the prevalence of male microchimerism was not explained by having male offspring or by having an older brother.

WHAT IS KNOWN ALREADY

Microchimerism describes the presence of cells within an organism that originate from another zygote and is commonly described as resulting from pregnancy in placental mammals. It is associated with diseases with a female predilection including autoimmune diseases and pregnancy-related complications. However, microchimerism also occurs in nulliparous women; signifying gaps in the understanding of risk factors contributing to persistent microchimerism and the origin of the minor cell population.

STUDY DESIGN, SIZE, DURATION

This cross-sectional study composed of 446 adult female participants of the Netherlands Twin Register (NTR).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Participants included in the study were female monozygotic (MZ) twins, female dizygotic same-sex twins and females of dizygotic opposite-sex twin pairs, along with the mothers and sisters of these twins. Peripheral blood samples collected from adult female participants underwent DNA extraction and were biobanked prior to the study. To detect the presence of male-origin microchimerism, DNA samples were tested for the relative quantity of male specific Y chromosome gene DYS14 compared to a common β-globin gene using a highly sensitive quantitative PCR assay.

MAIN RESULTS AND THE ROLE OF CHANCE

We observed a large number of women (26.9%) having detectable male microchimerism in their peripheral blood samples. The presence of a male co-twin did not increase risk of male microchimerism (odds ratio (OR) = 1.23: SE 0.40, P = 0.61) and the prevalence of male microchimerism was not explained by having male offspring (OR 0.90: SE 0.19, P = 0.63) or by having an older brother (OR = 1.46: SE 0.32, P = 0.09). The resemblance (correlation) for the presence of microchimerism was similar (P = 0.66) in MZ pairs (0.27; SE 0.37) and in first-degree relatives (0.091; SE 0.092). However, age had a positive relationship with the presence of male microchimerism (P = 0.02).

LIMITATIONS, REASONS FOR CAUTION

After stratifying for variables of interest, some participant groups resulted in a low numbers of subjects. We investigated microchimerism in peripheral blood due to the proposed mechanism of cell acquisition via transplacental blood exchange; however, this does not represent global chimerism in the individual and microchimerism may localize to numerous other tissues.

WIDER IMPLICATIONS OF THE FINDINGS

Immune regulation during pregnancy is known to mitigate allosensitization and support tolerance to non-inherited antigens found on donor cells. While unable to identify a specific source that promotes microchimerism prevalence within pedigrees, this study points to the underlying complexities of natural microchimerism in the general population. These findings support previous studies which have identified the presence of male microchimerism among women with no history of pregnancy, suggesting alternative sources of microchimerism. The association of detectable male microchimerism with age is suggestive of additional factors including time, molecular characteristics and environment playing a critical role in the prevalence of persistent microchimerism. The present study necessitates investigation into the molecular underpinnings of natural chimerism to provide insight into women’s health, transplant medicine and immunology.

STUDY FUNDING/COMPETING INTEREST(S)

This work is funded by Royal Netherlands Academy of Science Professor Award (PAH/6635 to D.I.B.); The Netherlands Organisation for Health Research and Development (ZonMw)—Genotype/phenotype database for behavior genetic and genetic epidemiological studies (ZonMw 911-09-032); Biobanking and Biomolecular Research Infrastructure (BBMRI–NL, 184.021.007; 184.033.111); The Netherlands Organisation for Scientific Research (NWO)—Netherlands Twin Registry Repository (NWO-Groot 480-15-001/674); the National Institutes of Health—The Rutgers University Cell and DNA Repository cooperative agreement (NIMH U24 MH068457-06), Grand Opportunity grants Integration of genomics and transcriptomics in normal twins and major depression (NIMH 1RC2 MH089951-01), and Developmental trajectories of psychopathology (NIMH 1RC2 MH089995); and European Research Council—Genetics of Mental Illness (ERC 230374). C.B.L. declares a competing interest as editor-in-chief of Human Reproduction and his department receives unrestricted research grants from Ferring, Merck and Guerbet. All remaining authors have no conflict-of-interest to declare in regards to this work.

TRIAL REGISTRATION NUMBER

N/A.

Adoptive immunotherapy with CB following chemotherapy for patients with refractory myeloid malignancy: chimerism and response

We conducted a prospective evaluation of cord blood (CB)-derived adoptive cell therapy, after salvage chemotherapy, for patients with advanced myeloid malignancies and poor prognosis. Previously, we reported safety, feasibility, and preliminary efficacy of this approach. We present updated results in 31 patients who received intensive chemotherapy followed by CB infusion and identify predictors of response. To enhance the antileukemic effect, we selected CB units (CBU) with shared inherited paternal antigens and/or noninherited maternal antigens with the recipients. Twenty-eight patients with acute myeloid leukemia (AML), 2 with myelodysplastic syndrome, and 1 in chronic myeloid leukemia myeloid blast crisis were enrolled; 9 had relapsed after allogeneic transplant. Response was defined as <5% blasts in hypocellular bone marrow at 2 weeks after treatment. Thirteen patients (42%) responded; a rate higher than historical data with chemotherapy only. Twelve had CBU-derived chimerism detected; chimerism was a powerful predictor of response (P < .001). CBU lymphocyte content and a prior transplant were associated with chimerism (P < .01). Safety was acceptable: 3 patients developed mild cytokine release syndrome, 2 had grade 1 and 2 had grade 4 graft-versus-host disease. Seven responders and 6 nonresponders (after additional therapy) received subsequent transplant; 5 are alive (follow-up, 5-47 months). The most common cause of death for nonresponders was disease progression, whereas for responders it was infection. CB-derived adoptive cell therapy is feasible and efficacious for refractory AML. Banked CBU are readily available for treatment. Response depends on chimerism, highlighting the graft-versus-leukemia effect of CB cell therapy. This trial was registered at www.clinicaltrials.gov as #NCT02508324.

Factors Predicting the Presence of Maternal Cells in Cord Blood and Associated Changes in Immune Cell Composition

Background

Cord blood (CB) samples are increasingly used as a source of hematopoietic stem cells in transplantation settings. Maternal cells have been detected in CB samples and their presence is associated with a better graft outcome. However, we still do not know what influences the presence of maternal microchimerism (MMc) in CB samples and whether their presence influences CB hematopoietic cell composition.

Patients and Methods

Here we test whether genetic, biological, anthropometric and/or obstetrical parameters influence the frequency and/or quantity of maternal Mc in CB samples from 55 healthy primigravid women. Mc was evaluated by targeting non-shared, non-inherited Human Leukocyte Antigen (HLA)-specific real-time quantitative PCR in whole blood and four cell subsets (T, B lymphocytes, granulocytes and/or hematopoietic progenitor cells). Furthermore CB samples were analyzed for their cell composition by flow cytometry and categorized according to their microchimeric status.

Results

MMc was present in 55% of CB samples in at least one cell subset or whole blood, with levels reaching up to 0.3% of hematopoietic progenitor cells. Two factors were predictive of the presence of MMc in CB samples: high concentrations of maternal serological Pregnancy-Associated-Protein-A at first trimester of pregnancy (p=0.018) and feto-maternal HLA-A and/or –DR compatibility (p=0.009 and p=0.01 respectively). Finally, CB samples positive for MMc were significantly enriched in CD56+ cells compared to CB negative for MMc.

Conclusions

We have identified two factors, measurable at early pregnancy, predicting the presence of maternal cells in CB samples at delivery. We have shown that MMc in CB samples could have an influence on the hematopoietic composition of fetal cells. CD56 is the phenotypic marker of natural killer cells (NK) and NK cells are known to be the main effector for graft versus leukemia reactions early after hematopoietic stem cell transplantation. These results emphasize the importance of MMc investigation for CB banking strategies.

BSHI guideline: HLA matching and donor selection for haematopoietic progenitor cell transplantation

A review of the British Society for Histocompatibility and Immunogenetics (BSHI) Guideline 'HLA matching and donor selection for haematopoietic progenitor cell transplantation' published in 2016 was undertaken by a BSHI appointed writing committee. Literature searches were performed and the data extracted were presented as recommendations according to the GRADE nomenclature.

Cord blood maternal microchimerism following unrelated cord blood transplantation

Cord blood transplantation (CBT) is associated with low risk of leukemia relapse. Mechanisms underlying antileukemia benefit of CBT are not well understood, however a previous study strongly but indirectly implicated cells from the mother of the cord blood (CB) donor. A fetus acquires a small number of maternal cells referred to as maternal microchimerism (MMc) and MMc is sometimes detectable in CB. From a series of 95 patients who underwent double or single CBT at our center, we obtained or generated HLA-genotyping of CB mothers in 68. We employed a technique of highly sensitive HLA-specific quantitative-PCR assays targeting polymorphisms unique to the CB mother to assay CB-MMc in patients post-CBT. After additional exclusion criteria, CB-MMc was evaluated at multiple timepoints in 36 patients (529 specimens). CB-MMc was present in 7 (19.4%) patients in bone marrow, peripheral blood, innate and adaptive immune cell subsets, and was detected up to 1-year post-CBT. Statistical trends to lower relapse, mortality, and treatment failure were observed for patients with vs. without CB-MMc post-CBT. Our study provides proof-of-concept that maternal cells of the CB graft can be tracked in recipients post-CBT, and underscore the importance of further investigating CB-MMc in sustained remission from leukemia following CBT.

Guidelines for Cord Blood Unit Selection

Optimal cord blood (CB) unit selection is critical to maximize the likelihood of successful engraftment and survival after CB transplantation (CBT). However, unit selection can be complex because multiple characteristics must be considered including unit cell dose, donor-recipient human leukocyte antigen (HLA) match, and unit quality. This review provides evidence-based and experience-based comprehensive guidelines for CB unit selection. Topics addressed include the use of both the TNC and the CD34⁺ cell dose, as well as the CD34⁺ cell to TNC content ratio to evaluate unit progenitor cell content and engraftment potential, the acceptable TNC and CD34⁺ cell dose criteria that define an adequate single-unit graft, and the indication and acceptable cell dose criteria for double-unit grafts. The acceptable criteria for 6-loci (HLA-A, -B antigen, -DRB1 allele) and 8-allele (HLA-A, -B, -C, -DRB1) donor-recipient HLA match, the evaluation of patients with donor-specific HLA antibodies, and the multiple determinants of unit quality are also reviewed in detail. Finally, a practical step-by-step guide to CB searches and the principles that guide ultimate graft selection are outlined.

A Bird's-Eye View of Cell Sources for Cell-Based Therapies in Blood Cancers

: Hematological malignancies comprise over a hundred different types of cancers and account for around 6.5% of all cancers. Despite the significant improvements in diagnosis and treatment, many of those cancers remain incurable. In recent years, cancer cell-based therapy has become a promising approach to treat those incurable hematological malignancies with striking results in different clinical trials. The most investigated, and the one that has advanced the most, is the cell-based therapy with T lymphocytes modified with chimeric antigen receptors. Those promising initial results prepared the ground to explore other cell-based therapies to treat patients with blood cancer. In this review, we want to provide an overview of the different types of cell-based therapies in blood cancer, describing them according to the cell source.

Haploidentical vs haplo-cord transplant in adults under 60 years receiving fludarabine and melphalan conditioning

Haplo-identical transplant with posttransplant cyclophosphamide (haplo) and umbilical cord blood transplant supported by third-party CD34 cells (haplo-cord) are competing approaches to alternative donor transplant. We compared, in adults younger than age 60 years, the outcomes of 170 haplo at 1 institution with that of 137 haplo-cord at 2 other institutions. All received reduced intensity conditioning with fludarabine and melphalan ± total body irradiation. GVHD prophylaxis for haplo consisted of cyclophosphamide, tacrolimus, and mycophenolate, whereas haplo-cord received antithymocyte globulin, tacrolimus, and mycophenolate. Haplo transplant used mostly bone marrow, and peripheral blood stem cells were used in haplo-cord transplants. Haplo-cord were older and had more advanced disease. Haplo-cord hastened median time to neutrophil (11 vs 18 days, P = .001) and platelet recovery (22 vs 25 days, P = .03). At 4 years, overall survival (OS) was 50% for haplo-cord vs 49% for haplo. Progression-free survival (PFS) was 40% for haplo-cord vs 45% for haplo. In multivariate analysis, the disease risk index was significant for OS (hazard ratio, 1.8; 95% confidence interval, 1.48-2.17; P = .00) and PFS. Total body irradiation was associated with decreased recurrence and improved PFS, age >40 with increased nonrelapse mortality. The type of transplant had no effect on OS, PFS, relapse, or nonrelapse mortality. Cumulative incidence of grade 2-4 acute graft-versus-host disease (GVHD) by day 100 was 16% after haplo-cord vs 33% after haplo (P < .0001), but grade 3-4 GVHD was similar. Chronic GVHD at 1 year was 4% after haplo-cord vs 16% after haplo (P < .0001). Haplo or haplo-cord results in similar and encouraging outcomes. Haplo-cord is associated with more rapid neutrophil and platelet recovery and lower acute and chronic GVHD. Institutional review board authorization for this retrospective study was obtained at each institution. Some patients participated in trials registered at www.clinicaltrials.gov as #NCT01810588 and NCT01050946.

Determining the extent of maternal-foetal chimerism in cord blood

During pregnancy, maternal T cells can enter the foetus, leading to maternal-foetal chimerism. This phenomenon may affect how leukaemia patients respond to transplantation therapy using stem cells from cord blood (CB). It has been proposed that maternal T cells, primed to inherited paternal HLAs, are present in CB transplants and help to suppress leukaemic relapse. Several studies have reported evidence for the presence of maternal T cells in most CBs at sufficiently high numbers to lend credence to this idea. We here aimed to functionally characterise maternal T cells from CB. To our surprise, we could not isolate viable maternal cells from CB even after using state-of-the-art enrichment techniques that allow detection of viable cells in heterologous populations at frequencies that were several orders of magnitude lower than reported frequencies of maternal T cells in CB. In support of these results, we could only detect maternal DNA in a minority of samples and at insufficient amounts for reliable quantification through a sensitive PCR-based assay to measure In/Del polymorphisms. We conclude that maternal microchimerism is far less prominent than reported, at least in our cohort of CBs, and discuss possible explanations and implications.

Inheritance of Susceptibility to Malignant Blood Disorders

Malignant blood disorders depend on heritable susceptibility genes and occur in familial aggregations. We suggest a model of transgenerational segregation of the susceptibility genes based on the study of malignant blood disorders in Norwegian and Danish families with unrelated parents, and in the inbred Faroese population with related parents. This model, consisting of parental genomic imprinting and mother-son microchimerism, can explain the male predominance in most of the diseases, the predominance of affected parent-offspring when parents are not related, and the different modes of segregation in males and females. The model displays a specific pattern in the distribution of affected relatives for each diagnosis, viz. a characteristic distribution in the pedigrees of family members with malignant blood disorder related to the proband. Three such patterns, each reflecting a specific transgenerational passage, were identified: (1) alterations in the number of affected relatives in paternal lines alone, e.g. in patterns for probands with multiple myeloma; (2) alterations in the number of affected relatives in both paternal and maternal lines for probands with chronic lymphocytic leukemia; and (3) no alterations in the numbers of male and female affected relatives in the parental lines, e.g. for probands with some types of malignant lymphoma.

Primary Immunodeficiency and Cancer Predisposition Revisited: Embedding Two Closely Related Concepts Into an Integrative Conceptual Framework

Common understanding suggests that the normal function of a "healthy" immune system safe-guards and protects against the development of malignancies, whereas a genetically impaired one might increase the likelihood of their manifestation. This view is primarily based on and apparently supported by an increased incidence of such diseases in patients with specific forms of immunodeficiencies that are caused by high penetrant gene defects. As I will review and discuss herein, such constellations merely represent the tip of an iceberg. The overall situation is by far more varied and complex, especially if one takes into account the growing difficulties to define what actually constitutes an immunodeficiency and what defines a cancer predisposition. The enormous advances in genome sequencing, in bioinformatic analyses and in the functional in vitro and in vivo assessment of novel findings together with the availability of large databases provide us with a wealth of information that steadily increases the number of sequence variants that concur with clinically more or less recognizable immunological problems and their consequences. Since many of the newly identified hard-core defects are exceedingly rare, their tumor predisposing effect is difficult to ascertain. The analyses of large data sets, on the other hand, continuously supply us with low penetrant variants that, at least in statistical terms, are clearly tumor predisposing, although their specific relevance for the respective carriers still needs to be carefully assessed on an individual basis. Finally, defects and variants that affect the same gene families and pathways in both a constitutional and somatic setting underscore the fact that immunodeficiencies and cancer predisposition can be viewed as two closely related errors of development. Depending on the particular genetic and/or environmental context as well as the respective stage of development, the same changes can have either a neutral, predisposing and, in some instances, even a protective effect. To understand the interaction between the immune system, be it "normal" or "deficient" and tumor predisposition and development on a systemic level, one therefore needs to focus on the structure and dynamic functional organization of the entire immune system rather than on its isolated individual components alone.

Jon van Rood: The pioneer and his personal view on the early developments of HLA and immunogenetics

A single observation in a patient with an unusual transfusion reaction led to a life-long fascination with immunogenetics, and a strong wish to improve the care for patients needing a transplantation. In 2017, Jon van Rood, one of the pioneers in the field of HLA and immunogenetics of transplantation, passed away. Several obituaries have appeared describing some of the highlights of his career. However, the details of the early developments leading among others to the routine use of HLA as an important parameter for donor selection in organ- and hematopoietic stem cell transplantation are largely unknown to the community. After his retirement as Chair of the Department of Immunohaematology and Blood Transfusion (IHB) in 1991, Jon van Rood wrote regularly in the "Crosstalk", the departmental journal, and gave his personal view on the history of the discovery and implications of HLA. These autobiographic descriptions were originally written in Dutch and have been translated, while texts from other sources and the relevant references have been added to illustrate the historical perspective. This special issue of Transplant Immunology combines the autobiographic part, Jon's own version of the history, with other facts of his scientific life and the impact of his findings on the field of clinical transplantation. Hopefully, this knowledge of the history will be of benefit for future developments in transplantation immunology.

Adoptive Immunotherapy with Cord Blood for the Treatment of Refractory Acute Myelogenous Leukemia: Feasibility, Safety, and Preliminary Outcomes

Adoptive immunotherapy has shown efficacy in patients with relapsed/refractory acute myelogenous leukemia (AML). We conducted a prospective evaluation of cord blood (CB)-based adoptive cell therapy following salvage chemotherapy in patients with AML or myelodysplastic syndrome (MDS) and describe the safety and early outcomes of this approach. To enhance the antileukemic effect, we selected CB units (CBUs) with a shared inherited paternal antigen (IPA) and/or noninherited maternal antigen (NIMA) match with the recipients. Furthermore, the CBUs had total nucleated cell (TNC) dose <2.5 × 10⁷/kg and were at least 4/6 HLA-matched with the patients; a higher allele-level match was preferred. Heavily pretreated adult patients with AML/MDS were enrolled. CBU searches were performed for 50 patients. CBUs with shared IPA targets were identified for all, and CBUs with NIMA matches were found for 80%. Twenty-one patients underwent treatment (AML, primary induction failure, n = 8; refractory relapse, n = 10, including 7 recipients of previous allogeneic HSCT; blast crisis chronic myelogenous leukemia, n = 1; MDS, n = 2). Most received combination chemotherapy; those not fit for intensive treatment received a hypomethylating agent. Response was defined as <10% residual blasts in hypocellular bone marrow at approximately 2 weeks after treatment. Ten of the 19 evaluable patients responded, including 5 of the 7 recipients of previous transplant. Response was seen in 4 of 4 patients with full CBU-derived chimerism, 2 of 2 of those with partial, low-level chimerism and 4 of 12 of the recipients with no detectable CBU chimerism. The most common adverse events were infections (bacterial, n = 5; viral, n = 2; fungal, n = 5). Grade IV acute graft-versus-host disease (GVHD) developed in 2 patients with full CBU chimerism; 2 other patients had grade 1 skin GVHD. A total of 11 patients died, 7 from disease recurrence and 4 from infections (1 early death; the other 3 in remission at the time of death). Overall, 12 patients proceeded to allogeneic HSCT; of those, 7 had responded to treatment, 3 had not (and had received additional therapy), and 2 had persistent minimal residual disease. In conclusion, the use of CB as adoptive immunotherapy in combination with salvage chemotherapy for patients with refractory AML/MDS is feasible, can induce disease control, can serve as a bridge to allogeneic HSCT, and has an acceptable incidence of adverse events. Alloreactivity was enhanced through the selection of CBUs targeting a shared IPA and/or NIMA match with the patients. CBUs with lower cell doses, already available in the CB bank and unlikely to be adequate grafts for adult transplants, can be used for cell therapy within a short time frame.

The effect of NIMA matching in adult unrelated mismatched hematopoietic stem cell transplantation - a joint study of the Acute Leukemia Working Party of the EBMT and the CIBMTR

Hematological malignancies can be cured by unrelated donor allogeneic HSCT and outcomes are optimized by high-resolution HLA matching at HLA-A, -B, -C, -DRB1 and -DQB1 (10/10 match). If a 10/10 match is unavailable, 9/10 matches may be suitable. Fetal exposure to non-inherited maternal antigens (NIMA) may impart lifelong NIMA tolerance modulating the immune response, as shown in adult haploidentical transplantation. In cord blood transplantation, NIMA matching lowered rates of aGvHD and TRM; in haploidentical transplantation, sibling donors with non-shared maternal antigens showed less grade II-IV aGvHD. This retrospective analysis examined if 9/10 matched unrelated donor HSCT benefits from NIMA matching. DKMS contacted 1,735 donors and obtained 733 (42%) maternal samples. NIMA-matched and -mismatched cases with a minimum follow-up of 1 year were compared by univariate and multivariate analyses adjusted for co-variates for OS, DFS, relapse, TRM and a/cGvHD. The study population (N = 445) comprised 31 NIMA-matched and 414 NIMA-mismatched cases. No significant differences between NIMA-matched and NIMA-mismatched groups were found for any outcomes with similar OS and TRM rates within both groups. This study provides the proof of principle that NIMA matching is possible in the unrelated donor HSCT setting; larger studies may be able to provide significant results.

Cellular Subsets of Maternal Microchimerism in Umbilical Cord Blood

Maternal microchimerism may arise in the offspring during pregnancy, and may be favorable or unfavorable. Additionally, maternal cells present in umbilical cord blood used for stem cell transplantation may affect the outcome after transplantation. The aim of this study was to evaluate the cellular subset and frequency of maternal cells in umbilical cord blood following vaginal deliveries and elective Cesarean sections where the umbilical cord clamping time was measured. A total of 44 healthy women with normal pregnancies were included in the study. Of these, 24 delivered vaginally and 20 by elective Cesarean sections. In the fresh umbilical cord blood, cellular subsets of CD3+ (T-cells), CD19+ (B-cells), CD33+ (myeloid cells), CD34+ (hematopoietic progenitor cells) and CD56+ (natural killer cells) cells were isolated and DNA extracted. A single-nucleotide polymorphism unique to the mother was identified and maternal microchimerism in the different cellular fractions was detected using quantitative real-time polymerase chain reaction with a sensitivity of 0.01%. Overall, 5 out of the 44 (11%) umbilical cord blood samples contained maternal microchimerism. The positive fractions were total DNA (whole blood, n = 3), CD34+ (n = 1), CD56+ (n = 1) and CD34+/CD56+ (n = 1). Overall, four of the five (80%) positive samples were from Cesarean sections and one was from a vaginal delivery. The conclusion from this study is that maternal microchimerism in umbilical cord blood is not a common phenomenon but includes both lymphoid and hematopoietic progenitor lineages.

Simulation of non-inherited maternal antigens acceptable HLA mismatches to increase the chance of matched cord blood units: Hong Kong's experience

In Cord blood transplantation (CBT), the non-inherited maternal antigen (NIMA) virtual six HLA matched CB is found to have similar outcomes to six HLA inherited matched CB. Such virtual HLA matched CB units can be generated by substituting the inherited alleles with one to three NIMAs. In Hong Kong Cord Blood Bank, CB units have no NIMA defined. 100 CB samples were collected with NIMA defined. Retrospective searches of Hong Kong patients (n = 520) were matched against the inherited and virtual HLA phenotypes of NIMA CB file. One to three NIMA matches was analyzed, virtual six HLA matches were identified for 31.7% patients, 29.4% from CB units with 5/6 HLA match with 1 NIMA match and 1.7% CB units with a 4/6 HLA match and 2 NIMA matches. However, searches in the 167,201 Bone Marrow Donors Worldwide CB units with defined NIMA did not yield similar increases, possibly due to the ethnicity differences between populations. The match performance rises from 26% to 60% after including the NIMA match. Comparing the match performance of 32% in a previous Dutch study, we calculated with 60% matching in this smaller size study. This provides a solid ground to considering NIMA in stem cell donor selection which was adopted in some centers, to be extended to Asian and local CB registries to increase the chance for matches and also to improve patient outcomes, increase the utilization of CB units, enhance clinical flexibility and signify economic intelligence.

Infectious Agents in Childhood Leukemia

Acute leukemia is the most common pediatric cancer, representing one-third of all cancers that occurs in under 15 year olds, with a varied incidence worldwide. Although a number of advances have increased the knowledge of leukemia pathophysiology, its etiology remains less well understood. The role of infectious agents, such as viruses, bacteria, or parasites, in the pathogenesis of leukemia has been discussed. To date, several cellular mechanisms involving infectious agents have been proposed to cause leukemia following infections. However, although leukemia can be triggered by contact with such agents, they can also be beneficial in developing immune stimulation and protection despite the risk of leukemic clones. In this review, we analyze the proposed hypotheses concerning how infectious agents may play a role in the origin and development of leukemia, as well as in a possible mechanism of protection following infections. We review reported clinical observations associated with vaccination or breastfeeding, that support hypotheses such as early life exposure and the resulting early immune stimulation that lead to protection.

Microchimerism: Defining and redefining the prepregnancy context - A review

Bidirectional transplacental exchange characterizes human pregnancy. Cells exchanged between mother and fetus can durably persist as microchimerism and may have both short- and long-term consequences for the recipient. The amount, type, and persistence of microchimerism are influenced by obstetric characteristics, pregnancy complications, exposures to infection, and other factors. A reproductive-aged woman enters pregnancy harboring previously acquired microchimeric "grafts," which may influence her preconception health and her subsequent pregnancy outcomes. Many questions remain to be answered about microchimerism with broad-ranging implications. This review will summarize key aspects of this field of research and propose important questions to be addressed moving forward.

Graft predominance after double umbilical cord blood transplantation: a review

Several parameters are involved in graft predominance after double umbilical cord blood transplantation (dUCBT), of which T-cell alloreactivity between the grafts is now considered to be the major denominator. We recently showed that alloreactive CD4+ T-cells originating from the predominant CBU recognize HLA-class II allele mismatches and can readily be detected in the majority of patients. In addition, it was shown that HLA-class II allele-specific CD4+ T-cells were able to recognize primary leukemic cells when the mismatched HLA-class II allele was shared between the rejected CBU and the patient. These results further underscored the role of alloreactive T-cells, notably class II specific CD4+ T-cells, in graft-versus-graft reactions and in graft-versus-leukemia after dUCBT.

Immune reconstitution and outcomes after conditioning with anti-thymocyte-globulin in unrelated cord blood transplantation; the good, the bad, and the ugly

Unrelated umbilical cord blood transplantation (UCBT) exhibits a low risk of graft-versus-host-disease (GvHD) and has unique potent anti-virus and anti-leukemia effects. Anti-thymocyte globulin (ATG) in the conditioning regimen for UCBT is successful in reducing graft rejection and GvHD. Nevertheless, this beneficial effect of ATG coincides with its detrimental effect on immune reconstitution. The latter directly relates to a high incidence of viral infections and leukemia relapses. ATG has been used in transplant patients for over 30 years. In recent years, the knowledge on the mechanisms of action of ATG and its implementation in the UCBT setting has increased dramatically. Important data became available showing the highly variable pharmacokinetics (PK) of ATG and its consequence on outcome measures. Here, we review the effects of ATG on immune reconstitution and subsequent outcomes after UCBT, and describe the mechanisms causing these effects. We highlight the importance of optimizing ATG exposure before and after UCBT and discuss strategies to maintain the 'good' and overcome the 'bad and ugly' effects of ATG on UCBT outcome.

Maternal microchimerism is prevalent in cord blood in memory T cells and other cell subsets, and persists post-transplant

Among reported advantages of umbilical cord blood (CB) in transplantation is lower leukemia relapse probability. Underlying cellular mechanisms of graft-vs.-leukemia (GVL) are thought to include a prominent role for T cells. Cells of the CB's mother, maternal microchimerism (MMc), were recently strongly, but indirectly, implicated in this GVL benefit. We assayed MMc directly and hypothesized benefit accrues from CB maternal T cells. MMc was quantified in 51 CBs and, within memory T, naïve T, B, NK cells, and monocytes in 27 CBs. Polymorphism-specific quantitative-PCR assays targeted maternal genotypes non-shared with CBs. Overall MMc was common and often at substantial levels. It was present in 52.9% of CB and in 33.3-55.6% of tested subsets. Remarkably, MMc quantities were greater in memory T cells than other subsets (p < 0.001). Expressed as genome equivalents (gEq) per 10⁵ total gEq tested (gEq/10⁵), memory T cell MMc averaged 850.2 gEq/10⁵, while other subset mean quantities were 13.8-30.1 gEq/10⁵. After adjustment for proportionality in CB, MMc remained 6-17 times greater in memory T, and 3-9 times greater in naïve T, vs. non-T-cell subsets. Further, CB-origin MMc was detected in vivo in a patient up to 6 mo post-transplantation, including among T cells. Overall, results revealed levels and phenotypes of CB MMc with potential relevance to CB transplantation and, more broadly, to offspring health.

Modification of host dendritic cells by microchimerism-derived extracellular vesicles generates split tolerance

Maternal microchimerism (MMc) has been associated with development of allospecific transplant tolerance, antitumor immunity, and cross-generational reproductive fitness, but its mode of action is unknown. We found in a murine model that MMc caused exposure to the noninherited maternal antigens in all offspring, but in some, MMc magnitude was enough to cause membrane alloantigen acquisition (mAAQ; "cross-dressing") of host dendritic cells (DCs). Extracellular vesicle (EV)-enriched serum fractions from mAAQ⁺, but not from non-mAAQ, mice reproduced the DC cross-dressing phenomenon in vitro. In vivo, mAAQ was associated with increased expression of immune modulators PD-L1 (programmed death-ligand 1) and CD86 by myeloid DCs (mDCs) and decreased presentation of allopeptide+self-MHC complexes, along with increased PD-L1, on plasmacytoid DCs (pDCs). Remarkably, both serum EV-enriched fractions and membrane microdomains containing the acquired MHC alloantigens included CD86, but completely excluded PD-L1. In contrast, EV-enriched fractions and microdomains containing allopeptide+self-MHC did not exclude PD-L1. Adoptive transfer of allospecific transgenic CD4 T cells revealed a "split tolerance" status in mAAQ⁺ mice: T cells recognizing intact acquired MHC alloantigens proliferated, whereas those responding to allopeptide+self-MHC did not. Using isolated pDCs and mDCs for in vitro culture with allopeptide+self-MHC-specific CD4 T cells, we could replicate their normal activation in non-mAAQ mice, and PD-L1-dependent anergy in mAAQ⁺ hosts. We propose that EVs provide a physiologic link between microchimerism and split tolerance, with implications for tumor immunity, transplantation, autoimmunity, and reproductive success.

Milestones of Hematopoietic Stem Cell Transplantation - From First Human Studies to Current Developments

Since the early beginnings, in the 1950s, hematopoietic stem cell transplantation (HSCT) has become an established curative treatment for an increasing number of patients with life-threatening hematological, oncological, hereditary, and immunological diseases. This has become possible due to worldwide efforts of preclinical and clinical research focusing on issues of transplant immunology, reduction of transplant-associated morbidity, and mortality and efficient malignant disease eradication. The latter has been accomplished by potent graft-versus-leukemia (GvL) effector cells contained in the stem cell graft. Exciting insights into the genetics of the human leukocyte antigen (HLA) system allowed improved donor selection, including HLA-identical related and unrelated donors. Besides bone marrow, other stem cell sources like granulocyte-colony stimulating-mobilized peripheral blood stem cells and cord blood stem cells have been established in clinical routine. Use of reduced-intensity or non-myeloablative conditioning regimens has been associated with a marked reduction of non-hematological toxicities and eventually, non-relapse mortality allowing older patients and individuals with comorbidities to undergo allogeneic HSCT and to benefit from GvL or antitumor effects. Whereas in the early years, malignant disease eradication by high-dose chemotherapy or radiotherapy was the ultimate goal; nowadays, allogeneic HSCT has been recognized as cellular immunotherapy relying prominently on immune mechanisms and to a lesser extent on non-specific direct cellular toxicity. This chapter will summarize the key milestones of HSCT and introduce current developments.

Cord blood chimerism and relapse after haplo-cord transplantation

Haplo-cord stem cell transplantation combines the infusion of CD34 selected hematopoietic progenitors from a haplo-identical donor with an umbilical cord blood (UCB) graft from an unrelated donor and allows faster count recovery, with low rates of disease recurrence and chronic graft-versus-host disease (GVHD). But the contribution of the umbilical cord blood graft to long-term transplant outcome remains unclear. We analyzed 39 recipients of haplo-cord transplants with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS), engrafted and in remission at 2 months. Median age was 66 (18-72) and all had intermediate, high, or very-high risk disease. Less than 20% UCB chimerism in the CD33 lineage was associated with an increased rate of disease recurrence (54% versus 11% p < 0.0001) and decrease in one year progression-free (20% versus 55%, p = 0.004) and overall survival (30% versus 62%, p = 0.02). Less than 100% UCB chimerism in the CD3 lineage was associated with increase rate of disease recurrence (46% versus 12%, p = 0.007). Persistent haplo-chimerism in the CD3 lineage was associated with an increased rate of disease recurrence (40% versus 15%, p = 0.009) Chimerism did not predict for treatment related mortality. The cumulative incidence of acute GVHD by day 100 was 43%. The cumulative incidence of moderate/severe chronic GVHD was only 5%. Engraftment of the umbilical cord blood grafts provides powerful graft-versus-leukemia (GVL) effects which protect against disease recurrence and is associated with low risk of chronic GVHD. Engraftment of CD34 selected haplo-identical cells can lead to rapid development of circulating T-cells, but when these cells dominate, GVL-effects are limited and rates of disease recurrence are high.

Impact of HLA in cord blood transplantation outcomes

Umbilical cord blood (UCB) emerged in the last 20 years as a valid alternative source of hematopoietic stem cell (HSC) in allogeneic transplantation setting, mainly in the absence of a fully human leucocyte antigen (HLA)-matched sibling. The probability of finding a matched unrelated donor through the registries varies from 20 to 70%, depending on the ethnicity of the patients. Therefore, patients in need may benefit of an HLA-mismatched hematopoietic stem cell transplantation from haploidentical donors or from UCB. One of the advantages of using UCB is the lower incidence of acute graft-versus-host-disease and allowance of greater HLA mismatch. Conversely, the low number of HSCs and lymphocytes and specific immunological features of T cells are associated with delayed engraftment and immune reconstitution and consequently, increased opportunistic infections. Nevertheless, retrospective studies showed similar results comparing UCB with other stem cell sources, both in pediatric and adult setting. The ability to use partially HLA-matched UCB units allows expanding the donor pool. Many UCB banks have strategies to increase their inventory including UCB grafts that have rare haplotypes. HLA and cell dose are very important factors associated with outcomes after umbilical cord blood transplantation (UCBT) that interact with each other. Increasing cell dose counterbalances the number of HLA disparities. Understanding those interactions, the role of HLA mismatches and other immunogenic factors, are important to allow clinicians to choose the best cord blood graft for patients. This review will describe the role of HLA in UCBT setting.

Frequency and Risk Factors Associated with Cord Graft Failure after Transplant with Single-Unit Umbilical Cord Cells Supplemented by Haploidentical Cells with Reduced-Intensity Conditioning

Delayed engraftment and cord graft failure (CGF) are serious complications after unrelated cord blood (UCB) hematopoietic stem cell transplantation (HSCT), particularly when using low-cell-dose UCB units. The haplo-cord HSCT approach allows the use of a lower dose single UCB unit by co-infusion of a CD34(+) selected haploidentical graft, which provides early transient engraftment while awaiting durable UCB engraftment. We describe the frequency, complications, and risk factors of CGF after reduced-intensity conditioning haplo-cord HSCT. Among 107 patients who underwent haplo-cord HSCT, 94 were assessable for CGF, defined as <5% cord blood chimerism at day 60 in the myeloid and CD3 compartments, irrespective of neutrophil and platelet counts. CGF occurred in 14 of 94 assessable patients (15%). Median survival after CGF was 12.7 months with haploidentical or mixed haploidentical-autologous hematopoiesis persisting in the 7 surviving. Median progression-free survival after CGF was 7.7 months and was not statistically different from those without CGF (10.47 months; P = .18). In univariate analyses, no UCB factors were associated with CGF, including cell dose, cell viability, recipient major ABO mismatch against the UCB unit, or degree of HLA match. We also found no association of CGF with recipient cytomegalovirus serostatus, haploidentical donor age, or day 30 haploidentical chimerism. However, higher haploidentical total nucleated and CD34(+) cell doses and day 30 UCB chimerism < 5% in either the myeloid or CD3 compartments were associated with greater risk of CGF. We conclude that assessing chimerism at day 30 may foretell impending CGF, and avoidance of high haploidentical cell doses may reduce risk of CGF after haplo-cord HSCT. However, long-term survival is possible after CGF because of predominant haploidentical or mixed chimerism and hematopoietic function.

Naturally acquired microchimerism: implications for transplantation outcome and novel methodologies for detection

Microchimerism represents a condition where one individual harbors genetically distinct cell populations, and the chimeric population constitutes <1% of the total number of cells. The most common natural source of microchimerism is pregnancy. The reciprocal cell exchange between a mother and her child often leads to the stable engraftment of hematopoietic and non-hematopoietic stem cells in both parties. Interaction between cells from the mother and those from the child may result in maternal immune cells becoming sensitized to inherited paternal alloantigens of the child, which are not expressed by the mother herself. Vice versa, immune cells of the child may become sensitized toward the non-inherited maternal alloantigens of the mother. The extent of microchimerism, its anatomical location, and the sensitivity of the techniques used for detecting its presence collectively determine whether microchimerism can be detected in an individual. In this review, we focus on the clinical consequences of microchimerism in solid organ and hematopoietic stem cell transplantation, and propose concepts derived from data of epidemiologic studies. Next, we elaborate on the latest molecular methodology, including digital PCR, for determining in a reliable and sensitive way the extent of microchimerism. For the first time, tools have become available to isolate viable chimeric cells from a host background, so that the challenges of establishing the biologic mechanisms and function of these cells may finally be tackled.

Patterns of Immune Regulation in Rhesus Macaque and Human Families

Supplemental digital content is available in the text.

Naturally acquired immune regulation amongst family members can result in mutual regulation between living related renal transplant donor and recipients. Pretransplant bidirectional regulation predisposed to superior renal allograft outcome in a CAMPATH-1H protocol. We tested whether Rhesus macaques, a large animal model of choice for preclinical transplant studies, share these immunoregulatory properties.

Topping it up: methods to improve cord blood transplantation outcomes by increasing the number of CD34+ cells

Cord blood is increasingly recognized for its excellent stem cell potential, lenient matching criteria, instant availability and clinical behavior in transplants when cell dose criteria can be met. However with 1-2 log fewer total (stem cell) numbers in the graft compared with other cell sources, the infused cell dose per kilogram is critical for engraftment and outcome, creating the need for development of stem cell support platforms. The co-transplant platforms of haplo cord and double unit cord blood (DUCB) transplantation are aimed toward increasing stem cell dose. Together with the optimization of reduced-intensity protocols, long-term sustained engraftment using cord blood has become available to most patients, including elderly patients. Haplo cord has a low incidence of both acute and chronic graft-versus-host disease but may require anti-thymocyte globulin ATG for effective neutrophil recovery. DUCB can be performed without anti-thymocyte globulin with excellent immune reconstitution and disease-free survival, but engraftment is considerably slower, and graft-versus-host disease incidence significant. Both haplo-cord and DUCB transplantation appear to both be valid alternatives to matched unrelated donors in adults.

Immunogenetic factors in the selection of cord blood units for transplantation: current search strategies and future perspectives

Hematopoietic stem cell transplantation is currently used as a curative treatment for patients with malignant and non-malignant hematologic diseases. Human leukocyte antigen (HLA) matching is a major determinant for hematopoietic stem cell transplantation outcome. For patients lacking a fully HLA-matched donor, umbilical cord blood (UCB) units are alternative sources of hematopoietic stem cells because UCB transplantation allows a less stringent HLA matching. However, selection of the optimal UCB units remains challenging. The current UCB donor selection strategies are based on both cell dose and HLA matching. This Review focuses on the immunogenetic factors that influence UCB donor selection and highlights the future perspectives in UCB donor search.