Hematopoietic stem cell transplants from unrelated donors

Case Series Using Salvage Haplo-Identical Stem Cells for Secondary Transplantation

In order to expand the donor pool and accessibility of the transplant procedure, it was necessary to introduce haplo-identical stem cell transplants in the Fundeni Clinical Institute from 2015. Even if the Romanian population is an ethnically compact white population, many of the patients referred for bone marrow transplant lack a suitable donor. Hematopoietic stem cell transplant from a haplo-identical donor is an alternative option for those patients without an HLA (Human Leucocyte Antigen)-matched donor (sibling or matched unrelated). This procedure was used also as a salvage option for those who experienced engraftment failure or the rejection of the first stem cell graft. In this case series, we present three such cases, with a haplo-transplant used as a salvage protocol (after an engraftment failure or rejection of the first transplanted cells). The patients we present were diagnosed with AML (acute myeloid leukemia) with MDS (myelodysplastic syndrome), MDS-RAEB 2 (myelodysplastic syndrome-refractory anemia with excess blasts 2), and SAA (severe aplastic anemia). In two of the three cases, the engraftment failure may have been due to the conditioning Fludarabine/Busulfan/Cyclophosphamide (Flu/Bu/CFA) used, combined with marrow grafts. In all three cases, the second transplant was of haplo-identical peripheral blood stem cells using Melphalan/Fludarabine (Mel/Flu) conditioning, the cells engrafted properly and the patients experienced complete chimerism, and two of them are alive with an excellent quality of life.

Cell therapy in transplantation: A comprehensive review of the current applications of cell therapy in transplant patients with the focus on Tregs, CAR Tregs, and Mesenchymal stem cells

Organ transplantation is a practical treatment for patients with end-stage organ failure. Despite the advances in short-term graft survival, long-term graft survival remains the main challenge considering the increased mortality and morbidity associated with chronic rejection and the toxicity of immunosuppressive drugs. Since a novel therapeutic strategy to induce allograft tolerance seems urgent, focusing on developing novel and safe approaches to prolong graft survival is one of the main goals of transplant investigators. Researchers in the field of organ transplantation are interested in suppressing or optimizing the immune responses by focusing on immune cells including mesenchymal stem cells (MSCs), polyclonal regulatory Tcells (Tregs), and antigen-specific Tregs engineered with chimeric antigen receptors (CAR Tregs). We review the mechanistic pathways, phenotypic and functional characteristics of these cells, and their promising application in organ transplantation.

Luminex-Based Methods in High-Resolution HLA Typing

Luminex-based technology has been applied to discriminate between the different Human Leukocyte Antigens (HLA) alleles. The typing method consists in a reverse-SSO assay: Target DNA is PCR-amplified using biotinylated group-specific primers. A single PCR reaction is used for each HLA locus. The biotinylated PCR product is chemically denatured using a pH change and allowed to rehybridize to complementary DNA probes conjugated to microspheres. These beads are characterized by two internal fluorescent dyes that create a unique combination of color, make them identifiable. Washes are performed to eliminate any additional PCR product that does not exactly match the sequence detected by the probe. The biotinylated PCR product bound to the microsphere is labelled with streptavidin conjugated with R-phycoerythrin (SAPE). A flow analyzer identifies the fluorescent intensity SAPE on each microsphere. Software is used to assign positive or negative reactions based on the strength of the fluorescent signal. The assignment of the HLA typing is based on positive and negative probe reactions compared with published HLA gene sequences. Recently kits characterized by an extensive number of probes/beads designed to potentially reduce the number of ambiguities or to directly lead to an allele level typing, have been made available.

Advances and perspectives on cellular therapy in acquired bone marrow failure diseases

Acquired bone marrow failure diseases (ABMFD) are a class of hematopoietic stem cell diseases with a commonality of non-inherited disruption of hematopoiesis that results in pancytopenia. ABMFDs also are a group of heterogeneous diseases with different etiologies and treatment options. The three most common ABMFDs are aplastic anemia, myelodysplastic syndrome, and paroxysmal nocturnal hemoglobinuria. Stem cell transplantation is the only treatment that can cure these diseases. However, due to high therapy-related mortality, stem cell transplantation has rarely been used as a first line treatment in treating ABMFD. With the advance of personalized medicine and precision medicine, various novel cellular therapy strategies are in trial to increase the efficiency and efficacy of ABMFD treatment. This article aims to review current available stem cell transplantation protocols and promising cellular therapy research in treating ABMFD.

Effect of ATG-F on B-cell reconstitution after hematopoietic stem cell transplantation

Antithymocyte globulin Fresenius (ATG-F) is used before hematopoietic stem cell transplantation to prevent graft rejection and graft-versus-host disease in patients with HLA-matched unrelated donors or mismatched volunteers. However, little is known about the effect of ATG-F on the reconstitution of B-cell subsets. Sixty-seven patients were longitudinally studied at day 15, day 30, and then monthly after hematopoietic stem cell transplantation. Conditioning regimes included ATG-F, which was infused at days 3, 2 and 1 at a dosage of 10 mg/kg/d. Twenty-seven patients received conditioning regimes without ATG. ATG-treated patients showed a significant delay of CD19+ B cells in the early recovery period. The absolute numbers of circulating CD19+ B cells were significantly lower (P < 0.05) up to 5 months post-transplantation compared to non-ATG patients. The recovery of the memory compartment was delayed in both groups and did not reach normal values 1-year post-transplantation. ATG-treated patient showed significantly lower absolute numbers of circulating CD27+ memory B cells in the first-month after transplantation compared to non-ATG patients. In conclusion, treatment with ATG in the conditioning regime of patients undergoing allogeneic hematopoietic stem cell transplantation leads to a significant delay of CD19+ B cells. Thus, ATG seems also to negatively influence B-cell immune reconstitution.

Unrelated cord blood compared with haploidentical grafts in patients with hematological malignancies

BACKGROUND

Alternative donors, such as unrelated umbilical cord blood (UCB) and related haploidentical (haplo) donors, are more and more frequently searched for and used for patients who are candidates for allogeneic hematopoietic stem cell transplantation but are without a suitable related or unrelated donor. The aim of the current retrospective study was to compare the outcome of patients after haplo and UCB grafts prepared using a nonmyeloablative conditioning regimen.

METHODS

A total of 150 adult patients with high-risk hematologic diseases who underwent allogeneic hematopoietic stem cell transplantation from alternative donors at 2 centers (Paoli-Calmettes Institute [Marseille, France] and Humanitas Cancer Center [Milan, Italy]) were analyzed. Sixty-nine patients had haplo donors and 81 patients had UCB donors.

RESULTS

The cumulative incidence of nonrecurrence mortality at 1 year was 23% in the UCB group versus 17% in the haplo group (P = .39). The incidence of grade 2 to 4 acute graft-versus-host disease and extensive chronic graft-versus-host disease in the UCB group versus the haplo group was 52% versus 29% (P = .05) and 12% versus 6% (P<.0001), respectively. The overall survival rate at 2 years was 45% in the UCB group (95% confidence interval [95% CI], 34%-56%) versus 69% in the haplo group (95% CI, 58%-80%) (P = .10). The progression-free survival rate at 2 years was 36% in the UCB group (95% CI, 25%-47%) versus 65% in the haplo group (95% CI, 53%-77%) (P = .01).

CONCLUSIONS

The results of the current study suggest that for patients with high-risk hematological diseases without a related or unrelated donor, haploidentical transplants are a promising alternative option that deserves further investigation.

A well-tolerated regimen of 800 cGy TBI-fludarabine-busulfan-ATG for reliable engraftment after unmanipulated haploidentical peripheral blood stem cell transplantation in adult patients with acute myeloid leukemia

Eighty adult patients with acute myeloid leukemia (AML) received peripheral blood T cell-replete HLA haploidentical hematopoietic stem cell transplantation (haplo-HSCT). Disease status at transplantation was either first or second complete remission (CR, n = 69) or relapse/refractory (n = 11). Identical transplant-related procedures with conditioning regimen consisting of fractionated 800 cGy total body irradiation (TBI), fludarabine (30 mg/m(2)/day for 5 days), busulfan (3.2 mg/kg/day for 2 days), and antithymocyte globulin (1.25 mg/kg/day on days -4 to -1) and graft-versus-host disease (GVHD) prophylaxis with tacrolimus and methotrexate were used in all patients. Recovery of neutrophil (median, 11 days) and platelet (median, 10 days) counts was achieved in all patients with full donor chimerism (≥ 99%), and no delayed engraftment failure was observed. The cumulative incidence of grades III to IV acute GVHD and moderate to severe chronic GVHD was 11.2% and 26.3%, respectively. A donor CD8(+) and CD4(+) T cell dose above the median value was significantly associated with the incidences of grades II to IV acute GHVD and moderate to severe chronic GVHD, respectively. After a median follow-up of 28 months for survivors, the 2-year cumulative incidences of relapse (n = 20) and nonrelapse mortality (n = 10) were 26.6% and 12.2%, respectively. Although all but 1 patient in relapse/refractory status died, the 2-year overall and progression-free survival of patients in first CR was 82.5% and 75.1%, respectively. We suggest the strategy of fractionated 800 cGy TBI-based conditioning with unmanipulated peripheral blood stem cell grafts seems feasible with favorable outcomes for adult patients with AML undergoing haplo-HSCT in CR.

Exogenous endothelial cells as accelerators of hematopoietic reconstitution

Despite the successes of recombinant hematopoietic-stimulatory factors at accelerating bone marrow reconstitution and shortening the neutropenic period post-transplantation, significant challenges remain such as cost, inability to reconstitute thrombocytic lineages, and lack of efficacy in conditions such as aplastic anemia. A possible means of accelerating hematopoietic reconstitution would be administration of cells capable of secreting hematopoietic growth factors. Advantages of this approach would include: a) ability to regulate secretion of cytokines based on biological need; b) long term, localized production of growth factors, alleviating need for systemic administration of factors that possess unintended adverse effects; and c) potential to actively repair the hematopoietic stem cell niche. Here we overview the field of hematopoietic growth factors, discuss previous experiences with mesenchymal stem cells (MSC) in accelerating hematopoiesis, and conclude by putting forth the rationale of utilizing exogenous endothelial cells as a novel cellular therapy for acceleration of hematopoietic recovery.

Clinical tolerance in allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) has been a curative therapeutic option for a wide range of immune hematologic malignant and non-malignant disorders including genetic diseases and inborn errors. Once in the host, allogeneic transplanted cells have not only to ensure myeloid repopulation and immunological reconstitution but also to acquire tolerance to host human leukocyte antigens via central or peripheral mechanisms. Peripheral tolerance after allogeneic HSCT depends on several regulatory mechanisms aimed at blocking alloimmune reactivity while preserving immune responses to pathogens and tumor antigens. Patients transplanted with HSCT represent an ideal model system in humans to identify and characterize the key cellular and molecular players underlying these mechanisms. The knowledge gained from these studies has allowed the development of novel therapeutic strategies aimed at inducing long-term peripheral tolerance, which can be applicable not only in allogeneic HSCT but also in autoimmune diseases and solid-organ transplantation. In the present review, we describe Type 1 regulatory T cells, initially discovered and characterized in chimeric patients transplanted with human leukocyte antigen-mismatched HSCT, and how their presence correlates to tolerance induction and maintenance. Furthermore, we summarize different cell therapy approaches with regulatory T cells, designed to facilitate tolerance induction, minimizing pharmaceutical interventions.

Adoptive Immunotherapy after Allogeneic Hematopoietic Progenitor Cell Transplantation: New Perspectives for Transfusion Medicine

SUMMARY: Allogeneic hematopoietic progenitor cell transplantation (HPCT) is a crucial therapeutic option in hematological malignancies, and the graft-versus-leukemia (GvL) effect builds the cornerstone of a long-lasting remission. Cyto-toxic T cells are known to be the primary effector cells in GvL. They recognize minor histocompatibility antigens (mHags) and tumor/leukemia-associated antigens. In case of disease relapse after HPCT, donor lymphocyte infusion (DLI) is an important treatment option for re-induction of remission. However, both treatments, HPCT and DLI carry the risk of morbidity and mortality due to graft-versus-host disease (GvHD) and severe infections. Therefore, the development of targeted adoptive immunotherapy with a lower risk of GvHD is needed, and several study groups are working on that topic.

Allelic and haplotypic HLA frequency distribution in Spanish hematopoietic patients. Implications for unrelated donor searching

Histocompatibility criteria for unrelated donor selection are based on high-resolution definition of HLA genes. In spite of the expansion of the unrelated donor registries, HLA matching remains a problem for many patients because of the great diversity of HLA alleles and haplotypes. The availability of matched donors at an allelic level depends on the frequency of the patient's alleles and haplotypes. Therefore, data regarding HLA distribution for each population are needed in order to evaluate the donor searching approach and, may be, even the therapeutic strategy. In the present report, we have analyzed 253 haematological Spanish patients awaiting unrelated haematopoietic stem cell (HSC) donors. HLA allele and haplotype frequencies have been defined at high resolution for the first time in this population. Significant differences in HLA distribution have been reported when comparing two patient groups, one that received full-match (10/10) unrelated donors and one that did not. Factors like rare alleles, presence of B*510101 (because of the association with multiple HLA-C alleles), as well as infrequent B-C and DRB1-DQB1 associations, showed a negative value for finding a suitable donor, whereas the presence of one of the six-gene haplotypes with a frequency ≥ 0.9% in our sample was a positive factor influencing donor searching. These differences will be useful in donor searching advising and in the use of different therapeutic strategies.

Haploidentical hematopoietic stem-cell transplantation in adults

Haploidentical hematopoietic stem-cell transplantation is an alternative transplant strategy for patients without an HLA-matched donor. Still, only half of patients who might benefit from transplantation are able to find an HLA-matched related or unrelated donor. Haploidentical donor is readily available for many patients in need of immediate stem-cell transplantation. Historical experience with haploidentical stem-cell transplantation has been characterised by a high rejection rate, graft-versus-host disease, and transplant-related mortality. Important advances have been made in this field during the last 20 years. Many drawbacks of haploidentical transplants such as graft failure and significant GVHD have been overcome due to the development of new extensive T cell depletion methods with mega dose stem-cell administration. However, prolonged immune deficiency and an increased relapse rate remain unresolved problems of T cell depletion. New approaches such as partial ex vivo or in vivo alloreactive T cell depletion and posttransplant cell therapy will allow to improve immune reconstitution in haploidentical transplants. Results of unmanipulated stem-cell transplantation with using ATG and combined immunosuppression in mismatched/haploidentical transplant setting are promising. This paper focuses on recent advances in haploidentical hematopoietic stem-cell transplantation for hematologic malignancies.

T-cell precursor frequencies and long-term outcome following unrelated hematopoietic stem cell transplantation

Functional assays measuring alloreactivity of donor cells are desired to detect either cryptic epitopes inducing graft-vs.-host disease (GvHD) after human leukocyte antigen (HLA)-identical hematopoietic stem cell transplantation (HSCT) or permissible HLA mismatches. However, their value in predicting GvHD and survival is still limited. We determined the cytotoxic and helper T-cell precursor (CTLp and HTLp) frequencies by limiting dilution analysis (LDA) in 40 unrelated recipient/donor combinations. The median observation period at the time of this writing was 4.44 years (range from 0.1 to 11.28). Better overall survival was observed in patients with rather low host-specific CTLp and HTLp frequencies, whereas a trend toward high CTLp frequencies was seen in patients with higher incidence of acute GvHD, especially in patients mismatched in HLA-C. CTLp and HTLp frequencies did not correlate with the incidence of chronic GvHD and relapse. In conclusion, we detected a trend toward better overall survival of patient/donor pairs with low CTLp and HTLp frequencies, however, recommend to use LDA as an additional tool for identifying the most suitable donor when more than one fully HLA-matched stem cell donor is available.

Current status of haploidentical stem cell transplantation for leukemia

Haploidentical hematopoietic stem cell transplantation has made tremendous progress over the past 20 years and has become a feasible option for leukemia patients without a HLA identical sibling donor. The early complications of severe graft-versus-host disease (GVHD), graft failure and delayed engraftment, as well as disease recurrence have limited the use of this approach. Newer strategies have been applied and overcome some of the problems, including the use of T-cell depleted graft, "mega" dose of stem cells, intensive post-transplant immunosuppression and manipulation of the graft. These have decreased the transplant related mortality and GVHD associated with haploidentical transplantation, however, the major problems of disease relapse and infection, which related to late immune reconstitution, limit the development of haploidentical HSCT. Future challenges remain in improving post-transplant immune reconstitution and finding the best approach to reduce the incidence and severity of GVHD, while preserving graft-versus-leukemia effect to prevent the recurrence of underlying malignancy.

Haploidentical hematopoietic cell transplantation

Haploidentical hematopoietic stem cell transplantation (HSCT) provides an opportunity for nearly all patients to benefit from HCT when a HLA genotypically matched sibling is not available. Initial results with the use of mismatched allografts led to limited enthusiasm due to GVHD and infectious complications resulting in unacceptable treatment-related morbidity and mortality. Recent advances with effective T-cell depletion, the use of 'megadoses' of stem cells, better antimicrobial therapy and reduced intensity conditioning has significantly decreased the early transplant-related mortality and GVHD. These modifications also enabled robust and prompt engraftment and led to enhancing the therapeutic benefits of haploidentical transplantation. However, the cardinal problems related to delayed immune reconstitution causing post-transplant infectious complications and relapse remain, limiting the efficacy of haploidentical transplant. Preliminary data have demonstrated the great potential in the use of adoptive cellular immunity and selective allodepletion in rapidly reconstituting immunity without GVHD. The encouraging reports from haploidentical transplant using noninherited maternal antigen (NIMA)-mismatched donors or natural killer (NK) alloreactive donors may greatly increase the donor availability and open a way to more appropriate donor selection in HLA-haploidentical HSCT. Future challenges remain in determining the safest approach for haploidentical transplant with minimal risk of GVHD, while preserving effective GVL activity and promoting prompt immune reconstitution.

Hematopoietic SCT from partially HLA-mismatched (HLA-haploidentical) related donors

Hematopoietic SCT from a partially HLA-mismatched (HLA-haploidentical) first-degree relative offers the benefits of rapid and near universal donor availability but also the risks that result from traversing the HLA barrier; namely, graft failure, severe GVHD and prolonged immunodeficiency. Improvements over the last 10 years in conditioning regimens, graft engineering and pharmacological immunoprophylaxis of GVHD have substantially reduced the morbidity and mortality of HLA-haploidentical SCT. Highly immunosuppressive but nonmyeloablative conditioning extends the availability of HLA-haploidentical SCT to elderly hematologic malignancy patients lacking HLA-matched donors and permits recovery of autologous hematopoiesis in the event of graft failure. Current regimens for HLA-haploidentical SCT are associated with a 2-year non-relapse mortality of 20+/-5%, relapse of 35+/-15% and overall survival of 50+/-20%. Major developmental areas include harnessing natural killer cell alloreactivity to reduce the risk of disease relapse and improving immune reconstitution by delayed infusions of lymphocytes selectively depleted of alloreactive cells. Hematologic malignancy patients who lack suitably matched related or unrelated donors can now be treated with HLA-haploidentical related donor or unrelated umbilical cord blood SCT. Future clinical trials will assess the relative risks and benefits of these two graft sources.

Haploidentical haematopoietic stem cell transplantation for acute leukaemia in adults: experience in Europe and the United States

Work on one haplotype-mismatched transplants has been proceeding for over 20 years all over the world and novel transplant techniques have been developed. Some centres have focused on the conditioning regimens and post transplant immune suppression; others have concentrated on manipulating the graft. Haploidentical transplant modalities are based mainly on high-intensity conditioning regimen, but reduced intensity regimens have recently been introduced. The graft may be a megadose of extensively T cell-depleted or unmanipulated progenitor cells. Excellent engraftment rates are associated with a very low incidence of GVHD- and regimen-related mortality even in patients who are over 50 years old. Overall, event-free survival and transplant-related mortality compare favourably with reports on transplants from sources of stem cells other than the matched sibling. Improvements will come with successful implementation of strategies to accelerate and strengthen post transplant immune reconstitution as well as transplantation of patients in early stage disease.

Anti-leukaemic role of acute GvHD after unrelated haematopoietic stem cell transplantation in intermediate- to high-risk acute myelogenous leukaemia

Little is known about the role of acute GvHD (aGvHD) based on the concept of graft-versus-leukaemia effect (GVLE) after unrelated donor haematopoietic stem cell transplantation (uHSCT). We evaluated 67 uHSCTs performed with multinational unrelated donors for patients with AML. The median follow-up duration was 18 months (range 7-61). The majority of patients had intermediate- or high-risk cytogenetic findings. The conditioning regimen for most patients consisted of cyclophosphamide plus total body irradiation (n=56) with our standard GvHD prophylaxis containing tacrolimus plus a short course of methotrexate. The incidence of aGvHD and chronic GvHD was 50 and 52%, respectively. Eight patients (12%) have relapsed to date. The estimated overall disease-free survival (DFS) rate at 5 years was 67%. Notably fewer relapses were seen when aGvHD developed (P=0.008). Specifically, high-risk AML patients had a much lower relapse rate when they developed aGvHD (P=0.01), compared with the intermediate-risk group. Therefore, the development of aGvHD after uHSCT in AML patients is closely related to a lower relapse rate, probably in association with GVLE.

Nonmyeloablative allogeneic hematopoietic stem cell transplant using mismatched/haploidentical donors: a review

Haploidentical hematopoietic stem cell transplantation (HSCT) provides an opportunity for patients to benefit from HCT when a human leukocyte antigen (HLA) genotypically matched sibling is not available. Initial results with the use of mismatched allograft has been disappointing due to the high incidence of graft-versus-host disease (GVHD) and infectious complications resulting in an unacceptable treatment-related morbidity and mortality. Recent advances with effective T-cell depletion, the use of 'megadose' of stem cells and reduced intensity conditioning has significantly decreased the early transplant related mortality and GvHD, while enabling robust and prompt engraftment, and hence enhancing the therapeutic benefits of haploidentical transplantation. However, the cardinal problems related to delayed immune reconstitution causing posttransplant infectious complications and relapse remain, limiting the efficacy of haploidentical transplant. Preliminary data have demonstrated the great potential in the use of adoptive cellular immunity and selective allodepletion in rapidly reconstituting immunity without GvHD. The encouraging reports from haploidentical transplant using noninherited maternal antigen (NIMA)-mismatched donors or natural killer alloreactive donors may greatly increase the donor availability and open a way to more appropriate donor selection in HLA-haploidentical HSCT. Future challenges remain in determining the safest approach for haploidentical transplant to be performed with minimal risk of GvHD, while preserving effective graft-versus-leukemia activity and promoting prompt immune reconstitution.

KIR ligands and prediction of relapse after unrelated donor hematopoietic cell transplantation for hematologic malignancy

Recurrent malignancy remains a significant complication after allogeneic hematopoietic cell transplantation (HCT). Efforts to decrease relapse have included donor lymphocyte infusion to stimulate donor anti-recipient T-cell allorecognition of major and minor histocompatibility differences. Recently, alloreactive effects of donor natural killer cell-mediated inhibitory killer immunoglobulin-like receptor (KIR) recognition of recipient HLA-C and -B ligands have been described. We examined KIR ligand effects on risk of relapse in 1770 patients undergoing myeloablative T-replete HCT from HLA-matched or -mismatched unrelated donors for the treatment of myeloid and lymphoid leukemias. KIR ligands defined by HLA-B and -C genotypes were used to determine donor-recipient ligand incompatibility or recipient lack of KIR ligand. Among HLA-mismatched transplantations, recipient homozygosity for HLA-B or -C KIR epitopes predicted lack of KIR ligand and was associated with a decreased hazard of relapse (hazard ratio, 0.61; 95% confidence interval, .043-0.85; P = .004). Absence of HLA-C group 2 or HLA-Bw4 KIR ligands was associated with lower hazards of relapse (hazard ratio, 0.47; 95% confidence interval, 0.28-0.79, P = .004; hazard ratio, 0.56; 95% confidence interval, 0.33-0.97; P = .04, respectively). The decrease in hazard of relapse in patients with acute myelogenous leukemia was similar to that in patients with chronic myelogenous leukemia and acute lymphoblastic leukemia (P = .95). Recipient homozygosity for HLA-B or -C epitopes that define KIR ligands is likely to be a predictive factor for leukemia relapse after myeloablative HCT from HLA-mismatched unrelated donors. This effect was not observed in HLA-identical unrelated transplants.

Impact of high-resolution matching in allogeneic unrelated donor stem cell transplantation in Switzerland

It is currently unknown what degree of human leukocyte antigen (HLA)-mismatching is acceptable in unrelated donor hematopoietic stem cell transplantation (UD-HSCT). Mismatches at some loci may be more permissive than others. We have analyzed the effect of high-resolution HLA-matching on outcome of all 214 consecutive recipients of UD-HSCT carried out in Switzerland. All typing was by the Swiss reference laboratory. Donor-recipient pairs were HLA-10/10 matched (n=130) or mismatched for either HLA-A/-B/-DRB1/multiple loci (n=33; (HLA-A/-B=10); (-DRB1=8); (multiple=15)); HLA-C (n=29) or HLA-DQ/-DRB3 (n=22; (DQ=16); (-DRB1=6)). The median follow-up was 32 months. Survival probabilities (+/-95% confidence interval) at 3 years were 57 (+/-10)% for recipients of HLA 10/10-matched transplants, 53 (+/-22)% for recipients of HLA-DQ/-DRB3-mismatched transplants, 44 (+/-20)% for recipients of HLA-C-mismatched transplants and 0% for recipients of transplants mismatched at HLA-A/-B/-DRB1/multiple loci (P<0.0001). In multivariate analyses, HLA compatibility was the variable most significantly associated with survival and treatment-related mortality. We found important differences in survival in recipients of UD-HSCT with best results for transplants from 10/10 matched donors. Single mismatches at HLA-DQ/-DRB3 were well tolerated, mismatches at HLA-C had intermediate results and mismatches at HLA-A/-B/-DRB1/multiple loci resulted in poor survival.

Hematopoietic Stem Cell Donor Selection: the Europdonor Experience

International collaboration is essential for the optimal selection of unrelated hematopoietic stem cell donors. This review focuses on the benefit of a joint worldwide donor file called Bone Marrow Donors Worldwide and the experience of the Europdonor Foundation in selecting strategies to identify the best human leukocyte antigen-matched donor in the shortest time.

Class-, gene-, and group-specific HLA silencing by lentiviral shRNA delivery

HLA incompatibility is the most relevant immunologic barrier to cell-based therapies. Improvement of histocompatibility is essential to achieving better survival of allogeneic cells in the foreign organism. RNA interference technology can be used to selectively and stably reduce cellular HLA class I expression. In the present study, we designed small interfering RNA (siRNA) molecules that target either beta2-microglobulin (beta2m) or HLA-A heavy chain transcripts and identified sensitive sites on the target RNAs using an in vitro transcription/translation (IVTT) system. Transfection of siRNA into B-lymphocyte cell lines (B-LCLs) resulted in specific reduction of HLA class I or HLA-A antigen expression by 79% at the mRNA and protein levels. An allele-specific HLA silencing rate of 65% was achieved in a B-LCL heterozygous for HLA-A*24,*68 allospecificities using HLA-A*68-specific siRNA. Lentiviral delivery of short hairpin RNA into HeLa and B-LCL cells resulted in selective and permanent silencing of HLA class I or HLA-A by up to 90% even under inflammatory conditions. In cytotoxicity and proliferation assays, it was demonstrated that HLA class I knockdown was effective in preventing antibody-mediated cell lysis and CD8+ T cell response, while the residual HLA expression in HLA-silenced cells was protective against NK-cell-mediated lysis. The present data strongly suggest that silencing of HLA expression in a class-, gene-, and group-specific manner is an effective approach that may provide a new basis for developing new immunotherapies in the field of regenerative medicine.

Improving immune reconstitution while preventing GvHD in allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of choice for many hematologic malignancies and inherited disorders of the hematopoietic system. Ex vivo T-cell depletion (TCD) of the graft and post-transplantation immunosuppression efficiently prevents the development of GvHD in no- MHC-identical settings. However, the consequence of these non-specific strategies is a long-lasting immunodeficiency associated with increased incidence of disease relapse, graft rejection and reactivation of viral infections. Donor lymphocyte infusion, which is used for treating leukemic relapse after allogeneic HSCT, can result in severe GvHD. Several strategies are being optimized specifically to inactivate anti-host T cells while preserving anti-leukemic or anti-microbial immunocompetence. Based on the ex vivo or in vivo elimination of anti-host T cells, or on the modulation of their anti-host activity, these approaches, which have been explored extensively in pre-clinical studies and tested in some preliminary clinical trials, are discussed in this paper.

Antigen-dependent suppression of alloresponses byFoxp3-induced regulatory T cells in transplantation

Adoptive transfer of polyclonal CD4+CD25+ regulatory T cells (Treg) can tolerize transplantation alloresponses. Treg are activated via their specific TCR, but the antigen specificity of wild-type Treg remains elusive, and therefore controlling potency and duration of Treg activity in the transplantation setting is still not feasible. In this study, we used murine graft-versus-host disease (GVHD) as a model system to show that antigen-specific Treg suppress the response of T effector cells to alloantigens in vitro and prevent GVHD in vivo. The suppressive potential of antigen-specific Treg was much greater than that of polyclonal Treg. To acquire large numbers of antigen-specific Treg, we transduced CD4+CD25- cells with foxp3, and found that these foxp3-induced Treg suppress alloresponses in vitro and prevent GVHD in vivo as effectively as naturally derived CD4+CD25+ Treg. Furthermore, we used an antigen-specific CD4 Th1 clone as a source of foxp3-induced Treg after transduction with foxp3, and found those Treg to effectively prevent GVHD in an antigen-dependent manner. The findings of this study provide a basis for the concept that the onset and potency of the suppression by Treg can be regulated, and suggest a novel approach to enhance the feasibility and effectiveness of inducing tolerance by Treg as an adoptive immunotherapy in transplantation.

Natural killer cell receptors: regulating innate immune responses to hematologic malignancy

Critical to innate immunity, the natural killer (NK) cell performs its function of immunosurveillance through its recognition of altered or missing self on damaged, infected, or transformed malignant cells. NK cell receptors responsible for detection of human leukocyte antigen (HLA) class I and class I-like proteins on potential target cells transmit inhibitory and activating signals that integrate to determine NK cell function. Advances in the fields of NK cell receptor biology and immunogenetics have enhanced our understanding of NK cell target recognition and may now guide studies to determine NK cell effects in the clinical setting. Analysis of NK cell receptor-ligand relationships, such as the inhibitory killer immunoglobulin-like receptors (KIRs) and their HLA class I ligands, has revealed the potential for NK cell-mediated benefit in allogeneic hematopoietic stem cell transplantation for hematologic malignancies.

Factors influencing late allograft valve failure

Allograft valves are a valuable valve replacement substitute in the surgical management of heart valve disease. It remains the valve substitute of choice in the reconstruction of the right ventricular outflow tract in children with congenital heart disease and in the Ross procedure. However, its durability remains suboptimal, particularly in children. This article reviews the mechanisms and factors implicated in late allograft dysfunction, with a focus on the evidence for an immunological cause for allograft valve failure. Unravelling the mechanisms of allograft valve failure may allow modification of the allograft to improve its long-term durability.

Listing of Common HLA Alleles and Haplotypes Based on the Study of 356 Families Residing in the Paris, France, Area: Implications for Unrelated Hematopoietic Stem Cell Donor Selection

In this study we have identified frequent human leukocyte antigen (HLA)-A, -B, -C,-DRB1, and -DQB1 alleles, frequent HLA-B/C, HLA-DRB1/DQB1 two-allele associations, and the most common HLA-A/B/C/DRB1/DQB1 five-locus haplotypes in a population residing in the Paris, France, area. The study was carried out in 356 families of children awaiting hematopoietic stem-cell transplantation (HSCT), with the selection criterion that haplotypes could be assigned with certainty to both the patient and at least one parent. Parental haplotypes were HLA-A, -B serologically typed, and HLA-C, -DRB1, -DQB1 broadly typed by polymerase chain reaction-sequence-specific oligonucleotide probe. The alleles of the most frequent haplotypes were subsequently defined at a high-resolution level by polymerase chain reaction-sequence-specific primer. The results on the distribution of common alleles and common allele associations demonstrated similarities with the previously published data in Caucasian populations, as expected from the geographic origin of the studied population. More importantly, this study provides the largest listing of common B/C and DRB1/DQB1 associations and of common five-allele haplotypes defined with certainty in a Caucasian population to date. These results can be used to help estimate the likelihood of finding a suitable donor in unrelated HSCT and to delineate search strategies for potential donors.

Hematopoietic stem cell transplantation from alternative sources in adults with high-risk acute leukemia

Since 75% of patients with high-risk acute leukemia do not have a human leukocyte antigen (HLA)-identical sibling, alternative sources for hematopoietic stem cell transplantation (HSCT) are matched unrelated donors (MUD), unrelated umbilical cord blood (UD-UCB) and one HLA haplotype mismatched family members (haploidentical). The chance of finding a suitable donor in the international voluntary donor registries is limited by frequency of the HLA phenotype and the time required to identify the right donor from a potential panel, to establish eligibility and to harvest the cells. In adult MUD recipients, event-free survival ranges up to 50% and refers only to patients who undergo transplant, without taking into account those who do not find a donor. Umbilical cord blood offers the advantages of easy procurement, the absence of risks to donors, the reduced risk of transmitting infections, immediate availability of cryopreserved samples and acceptance of mismatches at two of the six antigens. Although UD-UCB transplantation is a viable option for children, it is seldom considered for adults. The great divergency between body weight and the number of hematopoietic cells in a standard cord blood unit, particularly if associated with a two-antigen mismatch, increases the risk of graft failure and delays hematopoietic reconstitution. Work on full-haplotype mismatched transplants has been proceeding for over 20 years. Originally, outcome in leukemia patients was disappointing because of high incidence of severe graft-vs.-host disease in T-replete transplants and high rejection rates in T-cell-depleted transplants. The breakthrough came with the use of a megadose of T-cell-depleted progenitor cells after a high-intensity conditioning regimen. Treating end-stage patients inevitably confounded clinical outcome in the early pilot studies. Today, high-risk acute leukemia patients are treated at less advanced stages of disease, receive a reasonably well tolerated conditioning regimen, and benefit from advances in post-transplant immunological reconstitution. All these factors contribute to markedly reduce transplant-related mortality. Overall, event-free survival and transplant-related mortality compare favorably with reports from unrelated matched transplants. T-cell-depleted megadose stem cell transplant from a mismatched family member, who is immediately available, can be offered as a viable option to candidates with high-risk acute leukemias.

The beneficial role of inhibitory KIR genes of HLA class I NK epitopes in haploidentically mismatched stem cell allografts may be masked by residual donor-alloreactive T cells causing GVHD

HLA allele mismatches will provoke T-cell alloreactivity after allogeneic stem cell transplantation. As donors and recipients are usually HLA matched, the public HLA epitopes that are recognized by natural killer (NK) cells (NK epitopes) are rarely mismatched, and therefore there is rarely potential for NK alloreactivity arising from the absence of ligands for inhibitory killer immunoglobulin-like receptors (KIR). Transplants using related donors sharing only one haplotype (haploidentical donors) represent a setting in which NK epitopes are often mismatched, thus resulting in the potential for NK alloreactivity. We have analyzed engraftment, acute graft vs host disease (GVHD), leukemia relapse, and survival in 62 haploidentical transplants in relationship with potential NK alloreactivity, inhibitory, and activating KIR genes of class I HLA NK epitopes. Potential NK alloreactivity in the rejection direction was not associated with any outcome variable. Potential NK alloreactivity in the GVHD direction was associated with an increased incidence of severe GVHD and poorer patient survival but not with non-engraftment nor leukemia relapse. A higher number of activating KIR receptors in the genome of the donor was associated with a higher prevalence of GVHD. These results suggest that lack of extensive T-cell depletion in haploidentical transplantation is associated with high GVHD rates and diminishes the benefits of NK-cell alloreactivity.

Transplantation of haploidentically mismatched stem cells for the treatment of malignant diseases

Hematopoietic stem cell transplantation (HSCT) from HLA haploidentical mismatched donors has recently been developed for patients with high-risk acute leukemia who do not have a matched donor. After a high intensity conditioning regimen the HLA barrier is overcome by infusing a graft containing a megadose of T cell-depleted progenitor cells. Nowadays, for graft processing automated peripheral blood CD34(+) cell immunoselection is time and labor saving and ensures a high CD34(+) cell recovery rate. Besides providing 4.5 log T cell depletion of the graft, it guarantees a 3.5 log B cell depletion, which helps prevent EBV-related lymphoproliferative disorders. Excellent engraftment rates are associated with a very low incidence of graft-versus-host disease and regimen-related mortality even in patients who are over 40 years old. Overall, event-free survival and transplant-related mortality compare favorably with reports from unrelated matched transplants. Donor natural killer cell alloreactivity also plays a role in improving outcome in patients with acute myeloid leukemia. These results show the haploidentical transplant to be a viable, alternative source of stem cells for adults with acute leukemia at high-risk of relapse who do not have matched donors, and encourage extending it to patients with an indication to transplant.

IL-7 effect on immunological reconstitution after HSCT depends on MHC incompatibility

Considerable progress has been recently accomplished in the management of patients who have undergone haplo-incompatible haematopoietic stem cell transplantation (HSCT) in terms of intake and prevention of graft-versus-host disease. Nevertheless haplo-incompatible HSCT is a procedure limited to a small number of patients because of the long-lasting immunodeficiency that is responsible for more than 50% of deaths within the first 3 months. Interleukin (IL)-7, which plays a unique and key role in T-cell development both in the mouse and in the human, is particularly attractive for attempting to speed up T-cell reconstitution. However, controversial results have been obtained after bone marrow graft in murine and primate models. To elucidate the impact of IL-7 treatment, we have performed HSCT in irradiated murine recombination activating gene (RAG) immunodeficient recipients, using donors that exhibited increased major histocompatibilty complex (MHC) incompatibility. Although irradiation performed prior to HSCT lead to a profound defect in the thymic stromal cells responsible for IL-7 production, IL-7 treatment had no significant effect on immune reconstitution in the MHC compatible and partially compatible settings. Interestingly, in the MHC fully incompatible setting in which only one-third of the recipients demonstrated active thymopoiesis, probably because of the rejection of donor cells by host natural killer cells, IL-7 treatment had a beneficial effect on T-cell development.

Haploidentical stem cell transplantation with purified CD34 cells after a chemotherapy-alone conditioning regimen

We investigated whether a novel chemotherapy-alone conditioning regimen would permit durable engraftment of standard doses of CD34+ purified stem cell grafts from full-haplotype mismatched related donors. We also examined the role of infusing limited doses of donor leukocytes for prevention of leukemia relapse. Our conditioning regimen consisted of thiotepa, fludarabine, rabbit antithymocyte globulin, melphalan, cyclosporin, and prednisolone. Since October 1998, 14 patients with high-risk leukemia were treated; 13 donor-patient pairs shared 3 of 6 HLA antigens, and 1 pair shared 5 of 6 HLA antigens. A median of 5.4 x 10(6) CD34+ cells per kilogram, 1.62 x 10(4) CD3+ cells per kilogram, and 9.32 x 10(4) CD19+ cells per kilogram were infused. T-cell depletion was the only graft-versus-host disease (GVHD) prophylaxis. All patients had prompt engraftment, and no late graft rejections were observed. All surviving patients received at least 1 infusion of donor whole blood containing 5, 7, 10, 25, or 50 x 10(3) CD3+ cells per kilogram between days 25 and 95 after transplantation, after which 8 developed acute GVHD (3 grade I, 2 grade II, 2 grade III, and 1 grade IV) and 2 developed a bronchiolitis obliterans-like syndrome. After attaining complete remission, 5 patients relapsed and died with active leukemia. The estimated relapse-related mortality at 4 years is 38.1%. As of June 15, 2003, 6 of 14 patients have survived a median of 43.5 months after transplantation with 100% donor cells. All 6 surviving patients developed acute GVHD and had a natural killer cell mismatch with their donors in the direction of graft versus host. The estimated overall survival and event-free survival for the 14 patients at 4 years is 41.7% +/- 13.5%.

Impact of HLA matching on outcome of hematopoietic stem cell transplantation in children with inherited diseases: a single-center comparative analysis of genoidentical, haploidentical or unrelated donors

SUMMARY

Hematological inherited diseases can be cured by hematopoietic stem cell transplantation (HSCT) from an human leukocyte antigen (HLA)-identical sibling donor (MSD), but the outcome of unrelated donors (URD) or haploidentical donors (HMD) has been a cause of concern. In all, 94 children affected with inherited diseases underwent HSCT at a single center using MSD (group A, n=31), URD (group B, n=23) or HMD (group C, n=40). There was no difference in the rate of engraftment or in the incidence of grades III-IV acute graft-versus-host disease (GVHD) between the groups. Survival rate was 80.6% in group A, 62.5% in group B and 47.5% in group C (P=0.023). In group B, survival rate was 73.7% in the subgroup with zero or one class I mismatch, and 25% in the subgroup with two or more class I mismatches (P=0.04). In group C, survival rate was 83.3% in the 9/10-identical subgroup, 64.3% in the seven or 8/10 subgroup, and 25% in the five or 6/10 subgroup (P=0.0007). Thus, engraftment, incidence of GVHD and survival are similar in recipients of grafts from MSD, URD with 0-1 class I-mismatch, or HMD with at least 7/10 HLA matches. The low success of HSCT using more disparate donors suggests reserving them for patients with very poor prognosis.

Which donor should be chosen for hematopoietic stem cell transplantation among unrelated HLA-A, -B, and -DRB1 genomically identical volunteers?

The aim of this study was to identify significant prognostic factors by using unrelated genomically HLA-A, -B and -DRB1-identical donors. Such data could help to choose the best donor. We studied 136 consecutive patients with hematologic malignancies and a median age of 32 years (range, 0-55 years) who received hematopoietic stem cell transplantation. Bone marrow grafts were given to 83 and peripheral blood stem cells to 53 patients. The cumulative incidence of grade II to IV acute graft-versus-host disease (GVHD) was 30% and of chronic GVHD was 54%. At 5 years, the overall transplant-related mortality (TRM) was 34%, and patient survival was 50%. In Cox multivariate analysis, 32 potential risk factors were analyzed. Monoclonal antibody OKT-3 during conditioning was correlated with grade II to IV acute GVHD, chronic GVHD, and TRM. HLA-DP mismatch was associated with poor TRM and poor survival. Cytomegalovirus-seropositive patients with a seronegative donor had a decreased leukemia-free survival. Five-year TRM was 14% with no risk factor, 38% with 1 risk factor, and 87% with 2 risk factors. The 5-year survival was 72%, 48%, and 30% with 0, 1, and 2 risk factors, respectively. We concluded that unrelated hematopoietic stem cell transplantation may be improved if an optimal donor and immunosuppression are chosen.

The role of haploidentical stem cell transplantation in the management of children with haematological disorders

The broader application of stem cell transplantation (SCT) for paediatric diseases has been limited by a lack of human leucocyte antigen (HLA)-matched donors. Virtually all children, however have at least one haploidentical parent who could serve as a donor. Such a donor is immediately available and the considerable costs of additional HLA typing, registry and banking expenditures that are necessary to procure an unrelated donor, could be reduced. Recent technological advances appear to have overcome the historical problems of graft rejection and severe graft versus host disease in the haploidentical setting, and in the latest studies the overall survival for children undergoing haploidentical SCT for leukaemia is now comparable with that following unrelated donor bone marrow or cord blood transplantation. Post-transplant infectious complications and leukaemia relapse remain the most important barriers yet to overcome, and new directions in the use of adoptive cellular immunity appear to be promising in this respect. Haploidentical SCT is now a viable option for those children who do not have an HLA compatible sibling or fully matched unrelated donor. The relative merits of a haploidentical family donor versus mismatched unrelated bone marrow or cord blood donation needs to be assessed in prospective, randomized clinical trials.

Successful haematopoietic stem cell transplantation from a matched unrelated donor following three graft failures from HLA-mismatched related donors

Graft rejection and graft failure are serious complications after allogeneic stem cell transplantation (SCT). We report a patient with CML in first chronic phase who finally engrafted with a transplant from an HLA-identical unrelated donor after graft failures from two related HLA-mismatched sibling donors. After failure of one BM and two PBSC grafts from two 1 HLA-antigen mismatched related donors, the patient was finally successfully transplanted from a subsequently identified HLA-identical unrelated donor (donor 3). At 5 years post transplant, the patient is in complete cytogenetic and molecular remission.

Roles of HLA-B, HLA-C and HLA-DPA1 incompatibilities in the outcome of unrelated stem-cell transplantation

In unrelated stem-cell transplantation, the value of matching at the HLA-A, -B and -DR loci between donor and recipient is well documented. The effect of HLA-C, DPB1 and DPA1 mismatches on transplantation outcome is unclear. In this study, 104 donor recipient-pairs, transplanted at Huddinge University Hospital between 1988 and 1999, were retrospectively HLA class I- and class II-typed by PCR-SSP. The samples were typed for HLA-A, -B and -C and HLA-DRB1, -DRB3, -DRB4, -DRB5, -DQA1, -DQB1, -DPB1 and -DPA1 with allele level resolution. Isolated HLA-B allele level mismatches were associated with an increased incidence of acute graft versus host disease grades II-IV and grades III-IV. HLA-C-mismatched, but killer cell immunoglobulin-like receptor (KIR) ligand motif-matched stem-cell grafts were significantly associated with improved survival rates and relapse-free survival (RFS). In patients receiving HLA-DPA1-mismatched stem cell grafts, reduced survival and shorter RFS were seen. These patients also had an increased frequency of relapses (64%vs 26%). We conclude that genomic HLA class I- and class II-typing may improve the outcome after unrelated stem-cell transplantation. The awareness of HLA class I- and II-mismatches in a recipient-donor pair makes it possible to give appropriate pre- and post-transplantation treatment.

Mono-allelic amplification of exons 2-4 using allele group-specific primers for sequence-based typing (SBT) of the HLA-A, -B and -C genes: preparation and validation of ready-to-use pre-SBT mini-kits

Class I allelic typing based on sequencing is reliable, immutable and easy to analyse when only one allele is amplified using a specific mono-allelic technique. A strategy has been developed to selectively amplify exons 2, 3 and 4 of each allele of the three class I loci, previously identified by generic typing, in order to sequence these alleles from their intronic parts in only one direction. This procedure is based mainly on the polymorphism of exon 1 and intron 1 of the HLA-A, -B and -C genes with allele group-specific forward primers and locus-specific reverse primers so as to perform mono-allelic amplification in a 'One Step' pre-sequence-based typing (pre-SBT) PCR. The 5' polymorphism found at each locus is nevertheless not sufficient to discriminate all allelic combinations. Hence exon 2 and exon 3 polymorphism had to be used in a 'Two Step' pre-SBT PCR method to selectively amplify the two alleles in the 1.8%, 7.6% and 0.9% of unresolved combinations found in our laboratory for, respectively, the HLA-A, -B and -C loci. Preparation and validation of 'ready-to-use' aliquots of primer-mixes, pre-SBT buffer and sets of Dye terminator reaction mixtures containing locus-specific intronic primers makes the procedure easy and efficient. The SBT method is the only allelic typing technique used in our laboratory (to date, 742 HLA-A*, 802 HLA-B* and 615 HLA-Cw* alleles have been sequenced) and our successful participation in the national and international quality controls of 4 years ago testifies to the accuracy of the results.