Haploidentical hematopoietic transplantation for the cure of leukemia: from its biology to clinical translation

Donor matters: Donor selection impact on hematopoietic stem cell transplantation outcomes in Hispanic patients with B-cell acute lymphocytic leukemia: Insights from a myeloablative HSCT study

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is a pivotal treatment for high-risk acute lymphocytic leukemia (ALL), although limited by suitable human leukocyte antigen (HLA)-matched sibling donors (MSD). This study evaluates the impact of donor selection on outcomes in post-HSCT Hispanic B-cell ALL patients.

METHODOLOGY

This single-center retrospective study evaluates outcomes in 88 adult Hispanic B-cell ALL patients who underwent haploidentical, MSD, or MUD myeloablative HSCT between 2013 and 2023.

RESULTS

Compared to Haploidentical transplants, MSD exhibited worse cumulative incidence of relapse (CIR) (HR = 3.39; P = 0.014) and disease-free survival (DFS) (HR = 2.44; P = 0.048) whereas MUD outcomes did not differ. This effect persisted even when controlling for pre-HSCT stage and Minimal residual disease (MRD) status. In addition, Ph-like was a significant predictor of worse DFS (HR = 3.60; P=0.014) and CIR (HR = 2.97; P=0.035) on multivariate analysis. Older donor age correlated with worse GVHD-free, relapse-free survival (GRFS) in haploidentical transplants (HR = 1.05; P=0.036).

CONCLUSION

Our data highlights improved outcomes with younger, haploidentical donors among Hispanic B-cell ALL patients undergoing myeloablative HSCT. This underscores the importance of donor selection in optimizing outcomes for ALL patients.

The Role of Natural Killer Cells in the Tumor Immune Microenvironment of EBV-Associated Nasopharyngeal Carcinoma

Endemic nasopharyngeal carcinoma (NPC) is closely associated with the Epstein-Barr virus (EBV), which contributes to tumor development and influences the tumor immune microenvironment (TIME) in NPC. Natural killer (NK) cells, as part of the innate immune system, play a crucial role in responding to viral infections and malignant cell transformations. Notably, NK cells possess a unique ability to target tumor cells independent of major histocompatibility complex class I (MHC I) expression. This means that MHC I-deficient tumor cells, which can escape from effective T cell attack, are susceptible to NK-cell-mediated killing. The activation of NK cells is determined by the signals generated through inhibitory and activating receptors expressed on their surface. Understanding the role of NK cells in the complex TIME of EBV+ NPC is of utmost importance. In this review, we provide a comprehensive summary of the current understanding of NK cells in NPC, focusing on their subpopulations, interactions, and cytotoxicity within the TIME. Moreover, we discuss the potential translational therapeutic applications of NK cells in NPC. This review aims to enhance our knowledge of the role of NK cells in NPC and provide valuable insights for future investigations.

How adoptive transfer of components of the donor immune system boosts GvL and prevents GvHD in HLA-haploidentical hematopoietic transplantation for acute leukemia

Why a new Perspective in allogeneic hematopoietic transplantation? A summary. Nowadays, for high-risk acute leukemia patients without an HLA-matched donor (sibling or volunteer), hematopoietic transplants that use HLA-haploidentical grafts combined with enhanced post transplant immune suppression (i.e., high-dose cyclophosphamide) are widely used. They are associated with low TRM rates. However, they are also associated with significant chronic GvHD while they only partially abrogate leukemia relapse rates. One may speculate that post-transplant immune suppression, required for GvHD prophylaxis, weakens the anti-leukemic potential of the graft. Historically, haploidentical transplants became feasible for the first time through transplantation of T cell-depleted peripheral blood hematopoietic progenitor cells. Lack of post-transplant immune suppression allowed the emergence of donor-versus-recipient NK-cell alloreactions that eradicated AML. In an attempt to improve these results we recently combined an age-adapted, irradiation-based conditioning regimen with transplant of T-cell-depleted grafts and infusion of regulatory and conventional T cells, without any post transplant immune suppression. With the obvious limitations of a single center experience, this protocol resulted in extremely low relapse and chronic GvHD rates and, consequently, in a remarkable 75% chronic GvHD/relapse-free survival in over 50 AML patients up to the age of 65 many of whom at high risk of relapse.

Cationic nanoparticles-based approaches for immune tolerance induction in vivo

The development of autoimmune diseases and the rejection of transplanted organs are primarily caused by an exaggerated immune response to autoantigens or graft antigens. Achieving immune tolerance is crucial for the effective treatment of these conditions. However, traditional therapies often have limited therapeutic efficacy and can result in systemic toxic effects. The emergence of nanomedicine offers a promising avenue for addressing immune-related diseases. Among the various nanoparticle formulations, cationic nanoparticles have demonstrated significant potential in inducing immune tolerance. In this review, we provide an overview of the underlying mechanism of autoimmune disease and organ transplantation rejection. We then highlight the recent advancements and advantages of utilizing cationic nanoparticles for inducing immune tolerance in the treatment of autoimmune diseases and the prevention of transplant rejection.

Autoimmune Limbic Encephalitis in Patients with Hematologic Malignancies after Haploidentical Hematopoietic Stem Cell Transplantation with Post-Transplant Cyclophosphamide

Autoimmune limbic encephalitis (LE) is a rare, but devastating complication of allogeneic hematopoietic stem cell transplantation (HSCT). There is currently limited evidence describing the risk factors, laboratory features, and underlying mechanisms of this neurologic adverse event. We retrospectively reviewed available clinical, imaging, and laboratory data from adult patients with hematological malignancies who underwent haploidentical HSCT with post-transplant cyclophosphamide (PTCy) at Chungnam National University Hospital from June 2016 to May 2020. Patients who developed LE were compared to those who did not based on clinical assessment, serum inflammatory biomarkers, and reconstitution of various T cell populations. Of 35 patients, 4 developed LE. There were no differences in patient demographics, donor demographics, or treatment conditions between patients that did and did not develop LE. Overall, patients with LE had worse clinical outcomes and overall survival than those without. In addition, they tended to have higher markers of systemic inflammation in the early post-transplant period, including fever, C-reactive protein (CRP), and cytokines. Remarkably, baseline interleukin-6 levels before HSCT were found to be higher in patients who developed LE than those who did not. In addition, analysis of T cell subsets showed impaired expansion of CD25+FOXP3+ regulatory T (Treg) cells in LE compared to non-LE patients despite appropriate reconstitution of the total CD4+ T cell population. Patients that developed LE within the first 30 days of HSCT were likely to have high serum IL-6 among other inflammatory cytokines coupled with suppression of regulatory T cell differentiation. Further work is needed on the mechanisms underlying impaired Treg expansion following HSCT and potential therapies.

Roles of natural killer cells in immunity to cancer, and applications to immunotherapy

Great strides have been made in recent years towards understanding the roles of natural killer (NK) cells in immunity to tumours and viruses. NK cells are cytotoxic innate lymphoid cells that produce inflammatory cytokines and chemokines. By lysing transformed or infected cells, they limit tumour growth and viral infections. Whereas T cells recognize peptides presented by MHC molecules, NK cells display receptors that recognize stress-induced autologous proteins on cancer cells. At the same time, their functional activity is inhibited by MHC molecules displayed on such cells. The enormous potential of NK cells for immunotherapy for cancer is illustrated by their broad recognition of stressed cells regardless of neoantigen presentation, and enhanced activity against tumours that have lost expression of MHC class I owing to acquired resistance mechanisms. As a result, many efforts are under way to mobilize endogenous NK cells with therapeutics, or to provide populations of ex vivo-expanded NK cells as a cellular therapy, in some cases by equipping the NK cells with chimeric antigen receptors. Here we consider the key features that underlie why NK cells are emerging as important new additions to the cancer therapeutic arsenal.

Donor natural killer cells trigger production of β-2-microglobulin to enhance post-bone marrow transplant immunity

Allogeneic hematopoietic transplantation is a powerful treatment for hematologic malignancies. Posttransplant immune incompetence exposes patients to disease relapse and infections. We previously demonstrated that donor alloreactive natural killer (NK) cells ablate recipient hematopoietic targets, including leukemia. Here, in murine models, we show that infusion of donor alloreactive NK cells triggers recipient dendritic cells (DCs) to synthesize β-2-microglobulin (B2M) that elicits the release of c-KIT ligand and interleukin-7 that greatly accelerate posttransplant immune reconstitution. An identical chain of events was reproduced by infusing supernatants of alloreactive NK/DC cocultures. Similarly, human alloreactive NK cells triggered human DCs to synthesize B2M that induced interleukin-7 production by thymic epithelial cells and thereby supported thymocyte cellularity in vitro. Chromatography fractionation of murine and human alloreactive NK/DC coculture supernatants identified a protein with molecular weight and isoelectric point of B2M, and mass spectrometry identified amino acid sequences specific of B2M. Anti-B2M antibody depletion of NK/DC coculture supernatants abrogated their immune-rebuilding effect. B2M knock-out mice were unable to undergo accelerated immune reconstitution, but infusion of (wild-type) NK/DC coculture supernatants restored their ability to undergo accelerated immune reconstitution. Similarly, silencing the B2M gene in human DCs, before coculture with alloreactive NK cells, prevented the increase in thymocyte cellularity in vitro. Finally, human recombinant B2M increased thymocyte cellularity in a thymic epithelial cells/thymocyte culture system. Our studies uncover a novel therapeutic principle for treating posttransplant immune incompetence and suggest that, upon its translation to the clinic, patients may benefit from adoptive transfer of large numbers of cytokine-activated, ex vivo-expanded donor alloreactive NK cells.

Infusion of haploidentical HSCs combined with allogenic MSCs for the treatment of ALL patients

Although haploidentical stem cell transplantation (haplo-HSCT) offers almost all acute lymphoblastic leukaemia (ALL) patients an opportunity for immediate transplantation, it exhibits a higher incidence of graft failure and graft versus host disease (GVHD). Mesenchymal stem cells (MSCs) are characterised by their haematopoiesis-promoting and immunomodulatory capacity. Thus, we designed a combination of haplo-HSCT and MSCs for ALL patients. ALL patients (n = 110) were given haploidentical HSCs combined with allogenic MSCs, and ALL patients without MSC infusion (n = 56) were included as controls. The 100-day cumulative incidences of grade ≥2 acute GVHD (aGVHD) and grade ≥3 aGVHD were 40.00% and 9.09% compared to 42.32% (P = 0.79) and 22.79% (P = 0.03) in patients without MSC infusion, respectively. The 3-year cumulative incidences of chronic GVHD (cGVHD) and extensive cGVHD were 22.27% and 10.27% compared to 32.14% (P = 0.19) and 22.21% (P = 0.04) in patients without MSC infusion, respectively. No significant differences in the 3-year relapse incidence, nonrelapse mortality, leukaemia-free survival or overall survival in groups with and without MSC cotransplantation were observed. Multivariate analysis showed that MSC infusion contributed to a lower risk of developing extensive cGVHD. Our data suggested that haplo-HSCT combined with MSCs may provide an effective and safe treatment for ALL patients.

Mother donors improve outcomes after HLA haploidentical transplantation: A Study by the Cellular Therapy and Immunobiology Working Party of the EBMT

BACKGROUND

Trans-placental trafficking of maternal and foetal cells during pregnancy establishes long-term, reciprocal micro-chimerism in both mother and child. As a consequence, the immune system of the mother may become sensitized to paternal histocompatibility antigens. It has been hypothesized that mother's "exposure" to paternal HLA haplotype antigens during pregnancy may affect transplantation outcomes when the mother acts as donor for the child. In T-cell depleted HLA haploidentical hematopoietic transplants, maternal donors have been shown to improve transplantation outcomes (Stern et al. Blood, 2008;112: 2990-2995).

OBJECTIVES AND STUDY DESIGN

The present retrospective multicenter study was conducted on behalf of Cellular Therapy and Immunobiology Working Party of the EBMT. It involved 409 patients (102 pediatric and 307 adult) with acute leukemia who were given HLA-haploidentical hematopoietic transplants. The goal of the study was to evaluate the role of maternal donors in a large cohort of haploidentical transplants.

RESULTS

Transplants from maternal donors were associated with lower relapse incidence in T-cell depleted (HR: 2.13 (1.16-3.92), p= 0.018) as well as in a limited series of unmanipulated, in vivo T-cell depleted transplants (HR: 4.15 (0.94-18.35), P=0.06) and also better graft-vs-host disease/relapse-free survival in T-cell depleted transplants (HR: 1.67 (1.02-2.73), p = 0.04).

CONCLUSION

These results indicate that the mother should be the preferred donor in order to provide better graft-vs-host disease/relapse-free survival in T-cell depleted HLA-haploidentical transplants for acute leukemia.

Post-transplant cyclophosphamide versus anti-thymocyte globulin for graft-versus-host disease prevention in haploidentical transplantation for adult acute lymphoblastic leukemia

Graft-versus-host disease (GVHD) prophylaxis for unmanipulated haploidentical hematopoietic cell transplantation (haplo-HCT) include post-transplant cyclophosphamide (PTCy) and anti-thymocyte globulin (ATG). Utilizing EBMT registry, we compared ATG versus PTCy based GVHD prophylaxis in adult acute lymphoblastic leukemia (ALL) patients undergoing haplo-HCT. Included were 434 patients; ATG (n=98) and PTCy (n=336). Median follow-up was ~2 years. Baseline characteristics were similar between the groups except that the ATG-group was more likely to have relapsed/refractory ALL (P=0.008), non-TBI conditioning (P<0.001), peripheral blood graft source (P=<0.001) and transplanted at an earlier time-period (median year of HCT 2011 vs. 2015). The 100-day grade II-IV and III-IV acute-GVHD was similar between ATG and PTCy, as was 2-year chronic-GVHD. On multivariate analysis (MVA), leukemia-free survival (LFS) and overall survival (OS) was better with PTCy compared to ATG prophylaxis. Relapse incidence (RI) was lower in the PTCy group (P=0.03), while non-relapse mortality (NRM) was not different. Advanced disease and lower performance score were associated with poorer LFS and OS and advanced disease with inferior GVHD-free/relapse-free survival (GRFS). Peripheral grafts were associated with higher GVHD compared to bone marrow grafts. In ALL patients undergoing unmanipulated haplo-HCT, PTCy for GVHD prevention resulted in lower RI and improved LFS and OS compared to ATG.

Haploidentical age-adapted myeloablative transplant and regulatory and effector T cells for acute myeloid leukemia

Allogeneic hematopoietic stem cell transplantation (HSCT) is the most effective treatment in eradicating high-risk acute myeloid leukemia (AML). Here, we present data from a novel HLA-haploidentical HSCT protocol that addressed the 2 remaining major unmet medical needs: leukemia relapse and chronic graft-versus-host disease (cGVHD). Fifty AML patients were enrolled in the study. The conditioning regimen included total body irradiation for patients up to age 50 years and total marrow/lymphoid irradiation for patients age 51 to 65 years. Irradiation was followed by thiotepa, fludarabine, and cyclophosphamide. Patients received an infusion of 2 × 106/kg donor regulatory T cells on day -4 followed by 1 × 106/kg donor conventional T cells on day -1 and a mean of 10.7 × 106 ± 3.4 × 106/kgpurified CD34+ hematopoietic progenitor cells on day 0. No pharmacological GVHD prophylaxis was administered posttransplantation. Patients achieved full donor-type engraftment. Fifteen patients developed grade ≥2 acute GVHD (aGVHD). Twelve of the 15 patients with aGVHD were alive and no longer receiving immunosuppressive therapy. Moderate/severe cGVHD occurred in only 1 patient. Nonrelapse mortality occurred in 10 patients. Only 2 patients relapsed. Consequently, at a median follow-up of 29 months, the probability of moderate/severe cGVHD/relapse-free survival was 75% (95% confidence interval, 71%-78%). A novel HLA-haploidentical HSCT strategy that combines an age-adapted myeloablative conditioning regimen with regulatory and conventional T-cell adoptive immunotherapy resulted in an unprecedented cGVHD/relapse-free survival rate in 50 AML patients with a median age of 53 years. This trial was registered with the Umbria Region Institutional Review Board Public Registry as identification code 02/14 and public registry #2384/14 and at www.clinicaltrials.gov as #NCT03977103.

Dynamic of plasma IL-22 level is an indicator of thymic output after allogeneic hematopoietic cell transplantation

AIMS

Interleukin-22 (IL-22) promotes thymus recovery and improves T-cell recovery in preclinical allogeneic hematopoietic cell transplant models. However, the correlation between IL-22 and thymus recovery is unknown in human transplant.

MATERIALS AND METHODS

In this study, plasma IL-22 levels of transplanted humans were analyzed peri-transplant. Thymic output was assessed by detecting blood signal joint T-cell receptor excision circles (TRECs). Flow cytometry was applied to measure T-cell subsets.

KEY FINDINGS

Plasma IL-22 level positively correlated with blood TRECs level at days 14 and 28 posttransplant. Multiple linear regression analysis showed plasma IL-22 level, occurrence of acute graft-versus-host disease (aGVHD) and age were significantly associated with blood TRECs level at day 28 after allotransplant. An increase of plasma IL-22 level during day 14 and day 28 correlated with faster recovery of blood TRECs and naïve T-cell levels in allotransplant recipients. Recipients with high TRECs levels at day 28 had lower incidence of aGVHD comparing with those who with low TRECs levels according to a median split of their TRECs levels, an effect also seen in the high IL-22 level and low IL-22 level cohorts. Other factors such as age and infection had impacts on plasma IL-22 level in allotransplants.

SIGNIFICANCE

Our findings suggest that dynamic change of plasma IL-22 level is an indicator of thymic output and occurrence of aGVHD. Monitoring plasma IL-22 level might help to assess recovery of thymus function in human allotransplants.

Impact of access to care on 1-year mortality following allogeneic blood or marrow transplantation

Mortality is highest in the first year following an allogeneic hematopoietic stem cell transplant. With recent advancements, we have expanded the pool of patients to whom we are able to offer transplant as a treatment option. In this context, we analyzed socioeconomic, patient, disease and transplant-related variables that predicted for 1-year all-cause, relapse-related (RRM) and non-relapse related mortality (NRM) in 304 patients at the University of Alabama at Birmingham. The 1-year overall survival, RRM and NRM rates were 60.5%, 13.5% and 22.7% respectively. A KPS score < 80, pre-transplant infection and hypertension and non-complete remission disease status adversely effected all-cause mortality. For NRM, increasing age, pre-transplant infection and diabetes, and poor access to care were associated with higher mortality whereas haploidentical donor type was associated with improved survival. For RRM, a KPS score <80, high/very high disease risk index and the presence of comorbidities were risk factors for higher mortality. Poor access to care, in addition to individual comorbidities, performance status and high-risk disease characteristics, is associated with adverse outcomes following transplant. We propose the incorporation of socioeconomic variables with patient, disease, and transplant-related variables to predict 1-year NRM.

The role of the thymus in allogeneic bone marrow transplantation and the recovery of the peripheral T-cell compartment

As the thymus represents the primary site of T-cell development, optimal thymic function is of paramount importance for the successful reconstitution of the adaptive immunity after allogeneic hematopoietic stem cell transplantation. Thymus involutes as part of the aging process and several factors, including previous chemotherapy treatments, conditioning regimen used in preparation to the allograft, occurrence of graft-versus-host disease, and steroid therapy that impair the integrity of the thymus, thus affecting its role in supporting T-cell neogenesis. Although the pathways governing its regeneration are still poorly understood, the thymus has a remarkable capacity to recover its function after damage. Measurement of both recent thymic emigrants and T-cell receptor excision circles is valuable tools to assess thymic output and gain insights on its function. In this review, we will extensively discuss available data on factors regulating thymic function after allogeneic hematopoietic stem cell transplantation, as well as the strategies and therapeutic approaches under investigation to promote thymic reconstitution and accelerate immune recovery in transplanted patients, including the use of cytokines, sex-steroid ablation, precursor T-cells, and thymus bioengineering. Although none of them is routinely used in the clinic, these approaches have the potential to enhance thymic function and immune recovery, not only in patients given an allograft but also in other conditions characterized by immune deficiencies related to a defective function of the thymus.

Haploidentical vs matched unrelated donor transplantation for acute myeloid leukemia in remission: A prospective comparative study

Despite comparable outcomes of haploidentical transplants (Haplo-HSCT) with HLA-matched unrelated transplants (MUD-HSCT) in retrospective comparisons, few studies have prospectively compared Haplo-HSCT with MUD-HSCT in AML. Here, we prospectively compared the outcomes of Haplo-HSCT with MUD-HSCT for AML in remission (n = 110) to prove non-inferiority of overall survival in Haplo-HSCT. Both groups were well balanced in factors related to biological features of AML and measurable residual disease (MRD) status by Wilms' tumor gene 1 (WT1) assay. A unique, reduced-toxicity preparative regimen was used for Haplo-HSCT, whereas mostly-myeloablative regimen was for MUD-HSCT. Both groups showed similar patterns of neutrophil and platelet recovery, whereas delayed T-cell reconstitution in Haplo-HSCT was found compared with MUD-HSCT. No significant differences were found in acute or chronic graft-vs-host-disease (GVHD) and post-transplant infectious events with an exception of EBV or CMV infection, which occurred more frequently in Haplo-HSCT. After a median follow-up of 47 months, no significant differences in overall survival (65% vs 54%, P = .146), disease-free survival (67% vs 53%, P = .142), relapse (20% vs 21%, P = .858), non-relapse mortality (14% vs 26%, P = .103), or GVHD-free/relapse-free survival (54% vs 41%, P = .138) were observed for Haplo-HSCT vs MUD-HSCT. In multivariate analysis, WT1 expression before transplantation independently predicted relapse, resulting in inferior survival. Separate analysis of unenrolled patients (n = 110) who were excluded or refused to participate in this study showed consistent results with enrolled patients. This prospective study demonstrated the non-inferiority of Haplo-HSCT to MUD-HSCT for AML in remission, and validated the role of WT1 quantification as an MRD marker (ClinicalTrial.gov identifier: NCT01751997).

T-Cell-Replete Versus ex vivo T-Cell-Depleted Haploidentical Haematopoietic Stem Cell Transplantation in Children With Acute Lymphoblastic Leukaemia and Other Haematological Malignancies

Allogeneic haematopoietic stem cell transplantation (HSCT) represents a potentially curative option for children with high-risk or refractory/relapsed leukaemias. Traditional donor hierarchy favours a human leukocyte antigen (HLA)-matched sibling donor (MSD) over an HLA-matched unrelated donor (MUD), followed by alternative donors such as haploidentical donors or unrelated cord blood. However, haploidentical HSCT (hHSCT) may be entailed with significant advantages: besides a potentially increased graft-vs.-leukaemia effect, the immediate availability of a relative as well as the possibility of a second donation for additional cellular therapies may impact on outcome. The key question in hHSCT is how, and how deeply, to deplete donor T-cells. More T cells in the graft confer faster immune reconstitution with consecutively lower infection rates, however, greater numbers of T-cells might be associated with higher rates of graft-vs.-host disease (GvHD). Two different methods for reduction of alloreactivity have been established: in vivo T-cell suppression and ex vivo T-cell depletion (TCD). Ex vivo TCD of the graft uses either positive selection or negative depletion of graft cells before infusion. In contrast, T-cell-repleted grafts consisting of non-manipulated bone marrow or peripheral blood grafts require intense in vivo GvHD prophylaxis. There are two major T-cell replete protocols: one is based on post-transplantation cyclophosphamide (PTCy), while the other is based on anti-thymocyte globulin (ATG; Beijing protocol). Published data do not show an unequivocal benefit for one of these three platforms in terms of overall survival, non-relapse mortality or disease recurrence. In this review, we discuss the pros and cons of these three different approaches to hHSCT with an emphasis on the significance of the existing data for children with acute lymphoblastic leukaemia.

HLA-Haploidentical Family Donors: The New Promise for Childhood Acute Lymphoblastic Leukaemia?

Allogeneic haematopoietic stem cell transplantation (HSCT) is indicated in children with high-risk, relapsed or refractory acute lymphoblastic leukaemia (ALL). HLA-matched grafts from cord blood and stem cell repositories have allowed patients without suitable sibling donors to undergo HSCT. However, challenges in procuring matched unrelated donor (MUD) grafts due to high cost, ethnic disparity and time constraints have led to the exponential rise in the use of stem cells from human leukocyte antigen (HLA)-haploidentical family donors. Whilst HLA-haploidentical HSCT (hHSCT) performed in adult patients with acute leukaemia has produced outcomes similar to MUD transplants, experience in children is limited. Over the last 5 years, more data have emerged on hHSCT in the childhood ALL setting, allowing comparisons with matched donor transplants. The feasibility of hHSCT using adult family donors in childhood ALL may also address the ethical issues related to selection of minor siblings in matched sibling donor transplants. Here, we review hHSCT in paediatric recipients with ALL and highlight the emergence of hHSCT as a promising therapeutic option for patients lacking a suitable matched donor. Recent issues related to conditioning regimens, donor selection and graft-vs.-host disease prophylaxis are discussed. We also identify areas for future research to address transplant-related complications and improve post-transplant disease-free survival.

NK cell alloreactivity in acute myeloid leukemia in the post-transplant cyclophosphamide era

Allogeneic hematopoietic stem cell transplantation (alloSCT) for myeloid leukemia remains one of the most effective anti-tumor treatments available, capable of curing an increasingly higher proportion of patients. Alloreactivity generated by T cells has limited efficacy in the early post-transplant period while most patients will relapse within 6 months after transplantation. Prior studies in T cell depleted grafts showed that, with the elimination of T cells, natural killer (NK) cells provide most of the anti-tumor effect in the early post-transplant period. Administration of unmodified T cells to mitigate infections and relapse will expose the patient to a high risk of graft-vs-host disease (GvHD). Post-transplant cyclophosphamide (PTCy), initially used for haploidentical (haplo) donor transplants, is now also increasingly utilized in HLA matched donor transplants to prevent GvHD. In most patients, PTCy eliminates, at least in part, alloreactive T and NK cells early post-transplant. Administration of modified NK cells in the early post-transplant period makes intuitive sense to enhance the anti-tumor effect of the graft and thereby prevent relapse. Effective application of cellular therapy early after transplant has opened a new direction and could revolutionize the field of hematopoietic stem cell transplantation.

Hematopoietic stem cell transplantation in children and adolescents with nonremission acute lymphoblastic leukemia

BACKGROUND

The appropriateness of allogeneic hematopoietic stem cell transplantation (HSCT) in children and adolescents with leukemia in whom complete remission is not possible remains unclear. This retrospective analysis aimed to investigate the outcomes associated with HSCT, and the risks of HSCT in children and adolescents with nonremission acute lymphoblastic leukemia (ALL).

PROCEDURE

Data from the Japan Society for Hematopoietic Cell Transplantation registry on 325 patients with nonremission ALL (aged <21 years, with blasts in the peripheral blood and/or bone marrow) who had undergone HSCT between January 2001 and December 2015 were evaluated. To assess survival, we developed a scoring system using significant adverse pre-HSCT variables.

RESULTS

Overall, 247 patients died. The median length of follow up among survivors was 1145 days, and the 3-year overall survival was 22% (95% confidence interval [CI]: 18-27%). A low performance score, presence of >25% bone marrow blasts, T-cell phenotype, poor-risk or normal cytogenetics, and history of HSCT were predictors of a poor outcome. Patients scoring 0-1 (n = 109), 2 (n = 91), and 3-7 (n = 125) had a 3-year overall survival of 41% (95% CI: 31-51%), 21% (95% CI: 13-31%), and 7% (95% CI: 3-12%), respectively.

CONCLUSION

These results support HSCT in certain nonremission patients. Even in patients without complete remission, outcomes differed according to pre-HSCT factors. A scoring system could help determine the appropriateness of HSCT in children and adolescents with nonremission ALL.

Notch Regulates Innate Lymphoid Cell Plasticity during Human NK Cell Development

Human NK cells develop in tonsils through discrete NK cell developmental intermediates (NKDIs), yet the mechanistic regulation of this process is unclear. We demonstrate that Notch activation in human tonsil-derived stage 3 (CD34^-CD117⁺CD94^-NKp80^-) and 4A (CD34^-CD117^+/-CD94⁺NKp80^-) NKDIs promoted non-NK innate lymphoid cell differentiation at the expense of NK cell differentiation. In contrast, stage 4B (CD34^-CD117^+/-CD94⁺NKp80⁺) NKDIs were NK cell lineage committed despite Notch activation. Interestingly, whereas NK cell functional maturation from stage 3 and 4A NKDIs was independent of Notch activation, the latter was required for high NKp80 expression and a stage 4B-like phenotype by the NKDI-derived NK cells. The Notch-dependent effects required simultaneous engagement with OP9 stromal cells and were also stage-specific, with NOTCH1 and NOTCH2 receptors regulating stage 3 NKDIs and NOTCH1 primarily regulating stage 4A NKDIs. These data establish stage-specific and stromal-dependent roles for Notch in regulating human NK cell developmental plasticity and maturation.

Phenotypic and Functional Characterization of NK Cells in αβT-Cell and B-Cell Depleted Haplo-HSCT to Cure Pediatric Patients with Acute Leukemia

NK cells can exert remarkable graft-versus-leukemia (GvL) effect in HLA-haploidentical hematopoietic stem cell transplantation (haplo-HSCT). Here, we dissected the NK-cell repertoire of 80 pediatric acute leukemia patients previously reported to have an excellent clinical outcome after αβT/B-depleted haplo-HSCT. This graft manipulation strategy allows the co-infusion of mature immune cells, mainly NK and γδT cells, and hematopoietic stem cells (HSCs). To promote NK-cell based antileukemia activity, 36/80 patients were transplanted with an NK alloreactive donor, defined according to the KIR/KIR-Ligand mismatch in the graft-versus-host direction. The analysis of the reconstituted NK-cell repertoire in these patients showed relatively high proportions of mature and functional KIR⁺NKG2A^-CD57⁺ NK cells, including the alloreactive NK cell subset, one month after HSCT. Thus, the NK cells adoptively transfused with the graft persist as a mature source of effector cells while new NK cells differentiate from the donor HSCs. Notably, the alloreactive NK cell subset was endowed with the highest anti-leukemia activity and its size in the reconstituted repertoire could be influenced by human cytomegalovirus (HCMV) reactivation. While the phenotypic pattern of donor NK cells did not impact on post-transplant HCMV reactivation, in the recipients, HCMV infection/reactivation fostered a more differentiated NK-cell phenotype. In this cohort, no significant correlation between differentiated NK cells and relapse-free survival was observed.

Genetic and Molecular Basis of Heterogeneous NK Cell Responses against Acute Leukemia

Natural killer (NK) cells are key cytotoxic effectors against malignant cells. Polygenic and polymorphic Killer cell Immunoglobulin-like Receptor (KIR) and HLA genes participate in the structural and functional formation of the NK cell repertoire. In this study, we extensively investigated the anti-leukemic potential of NK cell subsets, taking into account these genetic parameters and cytomegalovirus (CMV) status. Hierarchical clustering analysis of NK cell subsets based on NKG2A, KIR, CD57 and NKG2C markers from 68 blood donors identified donor clusters characterized by a specific phenotypic NK cell repertoire linked to a particular immunogenetic KIR and HLA profile and CMV status. On the functional side, acute lymphoblastic leukemia (ALL) was better recognized by NK cells than acute myeloid leukemia (AML). However, a broad inter-individual disparity of NK cell responses exists against the same leukemic target, highlighting bad and good NK responders. The most effective NK cell subsets against different ALLs expressed NKG2A and represented the most frequent subset in the NK cell repertoire. In contrast, minority CD57+ or/and KIR+ NK cell subsets were more efficient against AML. Overall, our data may help to optimize the selection of hematopoietic stem cell donors on the basis of immunogenetic KIR/HLA for ALL patients and identify the best NK cell candidates in immunotherapy for AML.

HLA antibodies in haematopoietic stem cell transplantation

The negative impact of donor specific HLA alloantibodies in solid organ transplantation is well known and understood within the histocompatibility and immunogenetics community. However the influence of donor-specific antibodies in the outcome of haematopoietic stem cell transplantation is less well regarded. As donor choices have evolved from HLA matched siblings and extremely well matched unrelated donors to mismatched cord blood and haplo-identical-related donors, we are now identifying more patients with antibodies reactive against their donor mismatches. The clinical significance of the antibodies that can be detected has not yet been fully elucidated.

Fc-engineered anti-CD33 monoclonal antibody potentiates cytotoxicity of membrane-bound interleukin-21 expanded natural killer cells in acute myeloid leukemia

BACKGROUND

Qualitative and quantitative defects in natural killer (NK) cells have been noted in patients with acute myeloid leukemia (AML), providing rationale for infusion of donor-derived NK cells. We previously showed that decitabine enhances expression of NKG2D ligands in AML with additive cytotoxicity when NK cells and Fc (fragment crystallizable region)-engineered CD33 monoclonal antibody (CD33mAb) was used. We conducted a phase 1 study evaluating decitabine and haploidentical NK cells in relapsed AML. Using patient samples from this study, we evaluated whether ex vivo donor-derived expanded NK cells with or without CD33mAb was effective in decitabine-treated AML.

METHODS

Bone marrow aspirates were collected from patients at pre- and post-NK cell infusion. NK cells from healthy donors were expanded for 14 days using irradiated K562 feeder cells displaying membrane-bound IL-21 (mbIL-21). Patient samples were used to test in vitro activity of mbIL-21 NK cells ± CD33m Ab-dependent cellular cytotoxicity (ADCC) and AML patient derived xenograft (PDX) mice were developed to test in vivo activity.

RESULTS

Upon incubation with primary AML blasts, mbIL-21 NK cells showed variable donor-dependent intra-cellular interferon-γ production, which increased with CD33mAb-coated AML. ADCC assays revealed mbIL-21 NK cells effectively lysed primary AML blasts with higher activity on CD33mAb-coated AML. Importantly, CD33mAb-dependent enhanced cytotoxicity by mbIL-21 NK cells was maintained in AML cells from patients even 24 days post-decitabine treatment. In vivo infusion of mbIL-21 NK cells in AML PDX mice, treated with CD33mAb, reduced the tumor burden.

DISCUSSION

These data show the therapeutic utility of mbIL-21 NK cells that can be further potentiated by addition of CD33mAb in AML.

CD4+FOXP3+ Regulatory T Cell Therapies in HLA Haploidentical Hematopoietic Transplantation

Since their discovery CD4⁺FOXP3⁺ regulatory T cells (Tregs) represented a promising tool to induce tolerance in allogeneic hematopoietic cell transplantation. Preclinical models proved that adoptive transfer of Tregs or the use of compounds that can favor their function in vivo are effective for prevention and treatment of graft-vs.-host disease (GvHD). Following these findings, Treg-based therapies have been employed in clinical trials. Adoptive immunotherapy with Tregs effectively prevents GvHD induced by alloreactive T cells in the setting of one HLA haplotype mismatched hematopoietic transplantation. The absence of post transplant pharmacologic immunosuppression unleashes T-cell mediated graft-vs.-tumor (GvT) effect, which results in an unprecedented, almost complete control of leukemia relapse in this setting. In the present review, we will report preclinical studies and clinical trials that demonstrate Treg ability to promote donor engraftment, protect from GvHD and improve GvT effect. We will also discuss new strategies to further enhance in vivo efficacy of Treg-based therapies.

Innate Immune Responses in the Outcome of Haploidentical Hematopoietic Stem Cell Transplantation to Cure Hematologic Malignancies

In the context of allogeneic transplant platforms, human leukocyte antigen (HLA)-haploidentical hematopoietic stem cell transplantation (haplo-HSCT) represents one of the latest and most promising curative strategies for patients affected by high-risk hematologic malignancies. Indeed, this platform ensures a suitable stem cell source immediately available for virtually any patents in need. Moreover, the establishment in recipients of a state of immunologic tolerance toward grafted hematopoietic stem cells (HSCs) remarkably improves the clinical outcome of this transplant procedure in terms of overall and disease free survival. However, the HLA-mismatch between donors and recipients has not been yet fully exploited in order to optimize the Graft vs. Leukemia effect. Furthermore, the efficacy of haplo-HSCT is currently hampered by several life-threatening side effects including the onset of Graft vs. Host Disease (GvHD) and the occurrence of opportunistic viral infections. In this context, the quality and the kinetic of the immune cell reconstitution (IR) certainly play a major role and several experimental efforts have been greatly endorsed to better understand and accelerate the post-transplant recovery of a fully competent immune system in haplo-HSCT. In particular, the IR of innate immune system is receiving a growing interest, as it recovers much earlier than T and B cells and it is able to rapidly exert protective effects against both tumor relapses, GvHD and the onset of life-threatening opportunistic infections. Herein, we review our current knowledge in regard to the kinetic and clinical impact of Natural Killer (NK), γδ and Innate lymphoid cells (ILCs) IRs in both allogeneic and haplo-HSCT. The present paper also provides an overview of those new therapeutic strategies currently being implemented to boost the alloreactivity of the above-mentioned innate immune effectors in order to ameliorate the prognosis of patients affected by hematologic malignancies and undergone transplant procedures.

Graft Engineering and Adoptive Immunotherapy: New Approaches to Promote Immune Tolerance After Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative therapeutic option for a wide range of immune and hematologic malignant and non-malignant disorders. Once transplanted, allogeneic cells have to support myeloid repopulation and immunological reconstitution, but also need to become tolerant to the host via central or peripheral mechanisms to achieve the desired therapeutic effect. Peripheral tolerance after allogeneic HSCT may be achieved by several mechanisms, though blocking alloreactivity to the host human leukocyte antigens while preserving immune responses to pathogens and tumor antigens remains a challenge. Recently uncovered evidence on the mechanisms of post-HSCT immune reconstitution and tolerance in transplanted patients has allowed for the development of novel cell-based therapeutic approaches. These therapies are aimed at inducing long-term peripheral tolerance and reducing the risk of graft-vs-host disease (GvHD), while sparing the graft-vs-leukemia (GvL) effect. Thus, ensuring effective long term remission in hematologic malignancies. Today, haploidentical stem cell transplants have become a widely used treatment for patients with hematological malignancies. A myriad of ex vivo and in vivo T-cell depletion strategies have been adopted, with the goal of preventing GvHD while preserving GvL in the context of immunogenetic disparity. αβ T-cell/CD19 B-cell depletion techniques, in particular, has gained significant momentum, because of the high rate of leukemia-free survival and the low risk of severe GvHD. Despite progress, better treatments are still needed in a portion of patients to further reduce the incidence of relapse and achieve long-term tolerance. Current post-HSCT cell therapy approaches designed to induce tolerance and minimizing GvHD occurrence include the use of (i) γδ T cells, (ii) regulatory Type 1 T (Tr1) cells, and (iii) engineered FOXP3+ regulatory T cells. Future protocols may include post-HSCT infusion of allogeneic effector or regulatory T cells engineered with a chimeric antigen receptor (CAR). In the present review, we describe the most recent advances in graft engineering and post-HSCT adoptive immunotherapy.

Effectiveness and safety of direct oral anticoagulants compared to warfarin in treatment naïve non-valvular atrial fibrillation patients in the US Department of defense population

BACKGROUND

Clinical trials have demonstrated that direct oral anticoagulants (DOACs) are at least non-inferior to warfarin in reducing the risk of stroke/systemic embolism (SE) among patients with non-valvular atrial fibrillation (NVAF), but the comparative risk of major bleeding varies between DOACs and warfarin. Using US Department of Defense (DOD) data, this study compared the risk of stroke/SE and major bleeding for DOACs relative to warfarin.

METHODS

Adult patients with ≥1 pharmacy claim for apixaban, dabigatran, rivaroxaban, or warfarin from 01 Jan 2013-30 Sep 2015 were selected. Patients were required to have ≥1 medical claim for atrial fibrillation during the 12-month baseline period. Patients with a warfarin or DOAC claim during the 12-month baseline period were excluded. Each DOAC cohort was matched to the warfarin cohort using propensity score matching (PSM). Cox proportional hazards models were conducted to evaluate the risk of stroke/SE and major bleeding of each DOAC vs warfarin.

RESULTS

Of 41,001 identified patients, there were 3691 dabigatran-warfarin, 8226 rivaroxaban-warfarin, and 7607 apixaban-warfarin matched patient pairs. Apixaban was the only DOAC found to be associated with a significantly lower risk of stroke/SE (hazard ratio [HR]: 0.55; 95% confidence interval [CI]: 0.39, 0.77; p < 0.001) and major bleeding (HR: 0.65; 95% CI: 0.53, 0.80; p < 0.001) compared to warfarin. Dabigatran and rivaroxaban initiation were associated with similar risk of stroke/SE (dabigatran: HR: 0.68; 95% CI: 0.43, 1.07; p = 0.096; rivaroxaban: HR: 0.83; 95% CI: 0.64, 1.09; p = 0.187) and major bleeding (dabigatran: HR: 1.05; 95% CI: 0.79, 1.40; p = 0.730; rivaroxaban: HR: 1.07; 95% CI: 0.91, 1.27; p = 0.423) compared to warfarin.

CONCLUSION

Among NVAF patients in the US DOD population, apixaban was associated with significantly lower risk of stroke/SE and major bleeding compared to warfarin. Dabigatran and rivaroxaban were associated with similar risk of stroke/SE and major bleeding compared to warfarin.

Hematopoietic stem cell transplantation with unrelated cord blood or haploidentical donor grafts in adult patients with secondary acute myeloid leukemia, a comparative study from Eurocord and the ALWP EBMT

Survival of patients with secondary acute myeloid leukemia (sAML) is poor. Cord blood transplantation (UCBT) and non-T-cell-depleted stem cell transplantation from haploidentical donors (HAPLO) are both strategies that have shown encouraging results in patients who do not have an human leukocyte antigen (HLA)-matched sibling or unrelated donor. We retrospectively analyzed outcomes of 409 adults with sAML receiving either UCBT (n = 163) or HAPLO (n = 246) in EBMT centers. Myelodysplastic syndrome (MDS) or myeloproliferative disorder (MPD) was the antecedent diagnosis in 79% of UCBT and 85% of HAPLO recipients. In multivariate analysis, UCBT was associated with higher risk of grade II-IV acute GVHD (HR 1.9, p = 0.009) and lower GHVD-free-relapse-free-survival (GRFS) (HR 1.57, p = 0.007) compared to HAPLO. Chronic-GVHD, RI, NRM, LFS, and OS were not statistically different between the two. Early disease stage at transplant was independently associated with lower RI and NRM and higher OS and LFS. These results indicate that HAPLO is associated with better GRFS and lower aGvHD compared to UCBT in patients with sAML and that UCBT can be a valid alternative for sAML patients who lack a matched sibling, a proper haploidentical or an unrelated donor.

Alpha-1 Antitrypsin-Expressing Mesenchymal Stromal Cells Confer a Long-Term Survival Benefit in a Mouse Model of Lethal GvHD

Acute graft-versus-host disease is a frequent complication associated with allogeneic hematopoietic stem cell transplantation. Patients that become refractory to initial steroid treatment have a poor prognosis. apceth-201 consists of human allogeneic mesenchymal stromal cells, engineered by lentiviral transduction to express the protease inhibitor alpha-1 antitrypsin, to augment the anti-inflammatory potential of the mesenchymal stromal cells. We show that apceth-201 mesenchymal stromal cells efficiently suppress T cell proliferation and polarize macrophages to an anti-inflammatory M2 type, in vitro. To assess the in vivo efficacy of apceth-201, it was tested in two different mouse models of acute graft-versus-host disease. Control animals in a humanized model succumbed quickly to disease, whereas median survival was doubled in apceth-201-treated animals. The product was also tested in a graft-versus-host disease model system that closely mimics haploidentical hematopoietic stem cell transplantation, an approach that is now being evaluated for use in the clinic. Control animals succumbed quickly to disease, whereas treatment with apceth-201 resulted in long-term survival of 57% of the animals. Within 25 days after the second injection, clinical scores returned to baseline in responding animals, indicating complete resolution of graft-versus-host disease. These promising data have led to planning of a phase I study using apceth-201.

TNFR2 signaling modulates immunity after allogeneic hematopoietic cell transplantation

Tumor necrosis factor-α (TNF-α) signaling through TNF receptor 2 (TNFR2) plays a complex immune regulatory role in allogeneic hematopoietic cell transplantation (HCT). TNF-α is rapidly released in the circulation after the conditioning regimen with chemotherapy and/or radiotherapy. It activates the function of donor alloreactive T cells and donor Natural Killer cells and promotes graft versus tumor effects. However, donor alloreactive T cells also attack host tissues and cause graft versus host disease (GVHD), a life-threatening complication of HCT. Indeed, anti-TNF-α therapy has been used to treat steroid-refractory GVHD. Recent studies have highlighted another role for TNFR2 signaling, as it enhances the function of immune cells with suppressive properties, in particular CD4⁺Foxp3⁺ regulatory T cells (Tregs). Various clinical trials are employing Treg-based treatments to prevent or treat GVHD. The present review will discuss the effects of TNFR2 signaling in the setting of allogeneic HCT, the implications for the use of anti-TNF-α therapy to treat GVHD and the clinical perspectives of strategies that specifically target this pathway.

Depletion of αβ+ T and B Cells Using the CliniMACS Prodigy: Results of 10 Graft-Processing Procedures from Haploidentical Donors

Background

Depletion of TCRαβ+ T cells and B cells with the CliniMACS Plus® has been used for haploidentical hematopoietic stem cell transplantation for a decade. The depletion procedure is time and labour demanding and with variable reported efficiencies. Recently, an automated procedure was launched for the CliniMACS Prodigy® (Miltenyi Biotec) but reported data are scarce. Here, we report the results of the first ten TCRαβ+ and B cell depletion procedures for clinical use performed at our centre.

Materials and Methods

All transplants were from a parent to a child. Collection of peripheral blood stem cells was performed after filgrastim mobilisation by use of the Spectra Optia® (TerumoBCT) set on the MNC program. Because of insufficient hematopoietic stem cell mobilisation, 1 donor received additional plerixafor.

Results

We performed ten uncomplicated processes with the CliniMACS Prodigy. We found the results of the depletion procedures satisfactory with a median log reduction of TCRαβ+ cells of -4.21 (range -3.98 to -4.74), resulting in a median number of TCRαβ+ cells in the depleted product of 28.6 × 10³/kg recipient weight (range 14.9-69.7 × 10³/kg). The median CD34 recovery was 83% (range 70-100). To achieve a sufficient number of CD34+ cells, we performed an additional CD34+ enrichment procedure using the CliniMACS Plus for 3 patients. The B cell depletion was slightly less efficient with a median log reduction of -3.72 (range -2.83 to -4.20).

Conclusion

Overall, we found the TCRαβ and CD19 depletion procedure on the CliniMACS Prodigy easy to handle and reliable, providing reproducible good results.

Recipient-derived IL-22 alleviates murine acute graft-versus-host disease in association with reduced activation of antigen presenting cells

Acute graft-versus-host disease (aGVHD) remains a major challenging complication of patients receiving allogeneic hematopoietic cell transplantation (allo-HCT). CD4+ effector T cells and their related cytokines mediate pathogenesis of aGVHD, in which donor-T-cell derived interleukin-22 (IL-22) was recently indicated to play a role. The role of recipient-derived IL-22 in aGVHD remains to be elucidated. By applying IL-22 knock out (IL-22KO) mice as recipients of allotransplant, we found recipient derived IL-22 alleviated aGVHD and improved survival of allotransplant recipients. Knock out of IL-22 in recipient increased levels of T-helper (Th1) 1 cells but decreased levels of regulatory T cells (Tregs) in target tissues of aGVHD. Levels of IL-22 increased in aGVHD mice. Recipient antigen presenting cells (APCs) are important sources of IL-22. IL-22 reduced activation of APCs in vitro. Defect of IL-22 in APCs resulted in increased polarization of Th1 cells but decreased level of Tregs in an in vitro co-culture system. Our data highlight an immunoregulatory function of recipient-derived IL-22 in aGVHD.

Unrelated donor vs HLA-haploidentical α/β T-cell- and B-cell-depleted HSCT in children with acute leukemia

Traditionally, hematopoietic stem cell transplantation (HSCT) from both HLA-matched related and unrelated donors (UD) has been used for treating children with acute leukemia (AL) in need of an allograft. Recently, HLA-haploidentical HSCT after αβ T-cell/B-cell depletion (αβhaplo-HSCT) was shown to be effective in single-center studies. Here, we report the first multicenter retrospective analysis of 127 matched UD (MUD), 118 mismatched UD (MMUD), and 98 αβhaplo-HSCT recipients, transplanted between 2010 and 2015, in 13 Italian centers. All these AL children were transplanted in morphological remission after a myeloablative conditioning regimen. Graft failure occurred in 2% each of UD-HSCT and αβhaplo-HSCT groups. In MUD vs MMUD-HSCT recipients, the cumulative incidence of grade II to IV and grade III to IV acute graft-versus-host disease (GVHD) was 35% vs 44% and 6% vs 18%, respectively, compared with 16% and 0% in αβhaplo-HSCT recipients (P < .001). Children treated with αβhaplo-HSCT also had a significantly lower incidence of overall and extensive chronic GVHD (P < .01). Eight (6%) MUD, 32 (28%) MMUD, and 9 (9%) αβhaplo-HSCT patients died of transplant-related complications. With a median follow-up of 3.3 years, the 5-year probability of leukemia-free survival in the 3 groups was 67%, 55%, and 62%, respectively. In the 3 groups, chronic GVHD-free/relapse-free (GRFS) probability of survival was 61%, 34%, and 58%, respectively (P < .001). When compared with patients given MMUD-HSCT, αβhaplo-HSCT recipients had a lower cumulative incidence of nonrelapse mortality and a better GRFS (P < .001). These data indicate that αβhaplo-HSCT is a suitable therapeutic option for children with AL in need of transplantation, especially when an allele-matched UD is not available.

Killer cell immunoglobulin-like receptor ligand mismatching and outcome after haploidentical transplantation with post-transplant cyclophosphamide

Haploidentical stem cell transplantation with T cell-replete grafts and post-transplant cyclophosphamide (PTCy) is increasingly used with encouraging outcome. Natural killer (NK) cell alloreactivity, predicted by missing killer cell immunoglobulin-like receptor (KIR) ligands in the recipient that are present in their donor improves outcome of T cell-depleted haploidentical transplants. We explored the role of KIR ligand mismatching in 444 acute leukemia patients after T cell-replete transplants with PTCy. Thirty-seven percent of all patients had KIR ligand mismatching. Patients were in first remission (CR1) (39%), second remission (CR2) (26%), or active disease (35%). Stem cell source was peripheral blood (PBSC, 46%) or bone marrow (54%). The 2-year relapse, non-relapse mortality (NRM), and survival rates were 36.0% (95% confidence interval (CI), 31.4-40.7), 23.9% (20.0-28.0), and 45.9% (40.8-51.0), respectively. Multivariate analysis identified acute myeloid leukemia compared with acute lymphoblastic leukemia (hazard ratio (HR) 0.55, P = 0.002), female gender (HR 0.72, P = 0.04), and good performance status (HR 0.71, P = 0.04) as factors associated with better survival, while advanced age (HR 1.13, P = 0.04), active disease (HR 3.38, P < 0.0001), and KIR ligand mismatching (HR 1.41, P = 0.03) as associated with worse survival. KIR ligand mismatching was associated with a trend for higher relapse but not with graft-versus-host disease or NRM. The KIR ligand-mismatching effect was more prominent in patients given PBSC. In conclusion, there is no evidence that KIR ligand mismatching results in better outcome in the PTCy setting.

Haploidentical transplantation outcomes for secondary acute myeloid leukemia: Acute Leukemia Working Party (ALWP) of the European Society for Blood and Marrow Transplantation (EBMT) study

Secondary acute myeloid leukemia (sAML) traditionally has inferior outcomes compared to de novo AML. Allogeneic hematopoietic cell transplantation (HCT) is the sole potentially curative therapy. This study analyzes the outcomes for unmanipulated haploidentical HCT (haploHCT) for sAML using the Acute Leukemia Working Party (ALWP) registry of the European Society for Blood and Marrow Transplantation (EBMT). We identified 154 patients with sAML who underwent haploHCT from 2006 to 2016. Median age at HCT was 60 years with time from diagnosis to HCT 5 months. At transplantation, 69 patients were in first CR and 85 had active disease. Fifty-seven (38.0%) patients underwent myeloablative conditioning and 97 (62.0%) reduced intensity conditioning (RIC) conditioning. Multivariate analysis showed that there was no difference in RI, nonrelapse mortality (NRM), leukemia free survival (LFS), overall survival (OS), or GVHD-free/relapse free survival (GRFS) for conditioning intensity, age, performance status, or graft source. Active disease was associated with higher RI and inferior LFS, OS, and GRFS compared with patients in CR at time of transplant. T-cell depletion with anti-thymoglobulin resulted in higher NRM and inferior LFS, OS, and GRFS compared to post-transplant cyclophosphamide (PTCy) (HR 2.25, 2.01, 2.16, and 1.73, respectively with P values <.05). Our data shows that haploHCT is a feasible alternative for sAML when matched transplantation is unavailable.

Emerging stem cell based strategies for treatment of childhood diseases

Cell therapy is an important regenerative medicine approach, in which either differentiated cells or stem cells capable of differentiation are transplanted into an individual with the objective of yielding specific cell types in the damaged tissue and consequently restoring its function. The most successful example of cell therapy is hematopoietic stem cell transplantation, leading to regeneration of patient's blood cells, now a widely established procedure for many hematopoietic diseases. Development of cellular therapies for other tissues then followed in the footsteps of the hematopoietic experience. Nowadays, there are numerous ongoing clinical trials using various types of stem cells and some of them become approved cell-based products for use by patients. The aim of this review is to highlight some of advances and challenges of cell-based therapies including.

Outcomes of hematopoietic stem cell transplantation from unmanipulated haploidentical versus matched sibling donor in patients with acute myeloid leukemia in first complete remission with intermediate or high-risk cytogenetics: a study from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

Allogeneic hematopoietic stem cell transplantation is the optimal care for patients with high-risk or intermediate - acute myeloid leukemia. In patients lacking matched sibling donor, haploidentical donors are an option. We compared outcomes of unmanipulated (Haplo) to matched sibling donor transplant in acute myeloid leukemia patients in first complete remission. Included were intermediate and high-risk acute myeloid leukemia in first complete remission undergoing Haplo and matched sibling donor transplant from 2007-2015, and reported to the ALWP of the EBMT. A propensity score technique was used to confirm results of main analysis: 2 matched sibling donors were matched with 1 Haplo. We identified 2654 pts (Haplo =185; matched sibling donor =2469), 2010 with intermediate acute myeloid leukemia (Haplo=122; matched sibling donor =1888) and 644 with high-risk acute myeloid leukemia (Haplo =63; matched sibling donor =581). Median follow up was 30 (range 1-116) months. In multivariate analysis, in intermediate - acute myeloid leukemia patients, Haplo resulted in lower leukemia-free survival (Hazard Ratio 1.74; P<0.01), overall-survival (HR 1.80; P<0.01) and GvHD-free-relapse-free survival (Hazard Ratio 1.32; P<0.05) and higher graft-versus-host disease (GvHD) non-relapse mortality (Hazard Ratio 3.03; P<0.01) as compared to matched sibling donor. In high-risk acute myeloid leukemia, no differences were found in leukemia-free survival, overall-survival, and GvHD-free- relapse-free survival according to donor type. Higher grade II-IV acute GvHD was observed for Haplo in both high-risk (Hazard Ratio 2.20; P<0.01) and intermediate risk (Hazard Ratio 1.84; P<0.01). A trend for a lower Relapse-Incidence was observed in Haplo among high-risk acute myeloid leukemia (Hazard Ratio 0.56; P=0.06). The propensity score analysis confirmed results. Our results underline that matched sibling donor is the first choice for acute myeloid leukemia patients in first complete remission. On the other hand, results of Haplo transplants are similar to matched sibling donor transplants in acute myeloid leukemia patients with high risk cytogenetics.

Update on current research into haploidentical hematopoietic stem cell transplantation

INTRODUCTION

Haploidentical stem cell transplantation (Haplo-SCT) is currently a suitable alternative worldwide for patients with hematological diseases, who lack human leukocyte antigen (HLA)-matched siblings or unrelated donors. Areas covered: This review summarizes the advancements in Haplo-SCT in recent years, primarily focusing on the global trends of haploidentical allograft, the comparison of outcomes between Haplo-SCT and other transplantation modalities, strategies for improving clinical outcomes, including donor selection, hematopoietic reconstitution promotion, and graft-versus-host disease, and relapse prevention/management, as well as the expanded indications of Haplo-SCT, such as severe aplastic anemia, myeloma and lymphoma. Expert commentary: Haploidentical allografts, including granulocyte colony-stimulating factor-based protocol and a post-transplant cyclophosphamide-based protocol, have been the mainstream strategy for Haplo-SCT. However, there are many unanswered questions in this field.

NK cell recovery after haploidentical HSCT with posttransplant cyclophosphamide: dynamics and clinical implications

The use of posttransplant cyclophosphamide (PT-Cy) as graft-versus-host disease (GVHD) prophylaxis has revolutionized haploidentical hematopoietic stem cell transplantation (HSCT), allowing safe infusion of unmanipulated T cell-replete grafts. PT-Cy selectively eliminates proliferating alloreactive T cells, but whether and how it affects natural killer (NK) cells and their alloreactivity is largely unknown. Here we characterized NK cell dynamics in 17 patients who received unmanipulated haploidentical grafts, containing high numbers of mature NK cells, according to PT-Cy-based protocols in 2 independent centers. In both series, we documented robust proliferation of donor-derived NK cells immediately after HSCT. After infusion of Cy, a marked reduction of proliferating NK cells was evident, suggesting selective purging of dividing cells. Supporting this hypothesis, proliferating NK cells did not express aldehyde dehydrogenase and were killed by Cy in vitro. After ablation of mature NK cells, starting from day 15 after HSCT and favored by the high levels of interleukin-15 present in patients' sera, immature NK cells (CD62L⁺NKG2A⁺KIR^-) became highly prevalent, possibly directly stemming from infused hematopoietic stem cells. Importantly, also putatively alloreactive single KIR⁺ NK cells were eliminated by PT-Cy and were thus decreased in numbers and antileukemic potential at day 30 after HSCT. As a consequence, in an extended series of 99 haplo-HSCT with PT-Cy, we found no significant difference in progression-free survival between patients with or without predicted NK alloreactivity (42% vs 52% at 1 year, P = NS). Our data suggest that the majority of mature NK cells infused with unmanipulated grafts are lost upon PT-Cy administration, blunting NK cell alloreactivity in this transplantation setting.

Clinical Studies in Hematologic Microtransplantation

The anti-tumor effects of allogeneic hematopoietic stem cell transplantation depend upon engraftment of donor cells followed by a graft-versus-tumor (GVT) effect. However, pre-clinical and clinical studies have established that under certain circumstances, anti-tumor responses can occur despite the absence of high levels of durable donor cell engraftment. Tumor response with little or no donor engraftment has been termed "microtransplantation." It has been hard to define conditions leading to tumor responses without donor cell persistence in humans because the degree of engraftment depends very heavily upon many patient-specific factors, including immune status and degree of prior therapy. Likewise, it is unknown to what degree donor chimerism in the blood or tissue is required for an anti-tumor effect under conditions of microtransplantation. In this review, we summarize some key studies supporting the concept of microtransplantation and emphasize the importance of recent large studies of microtransplantation in patients with acute myelogenous leukemia (AML). These AML studies provide the first evidence of the efficacy of microtransplantation as a therapeutic strategy and lay the foundation for additional pre-clinical studies and clinical trials that will refine the understanding of the mechanisms involved and guide its further development as a treatment modality.

Haploidentical hematopoietic cell transplantation for adult acute myeloid leukemia: a position statement from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

Allogeneic blood or marrow hematopoietic cell transplantation continues to be the most potent anti-leukemic treatment for adult patients with standard, high-risk, or chemo-refractory acute myeloid leukemia. Until recently, this procedure was generally limited to those recipients who had an available matched-sibling donor or matched-unrelated donor. Technical advances in graft cell processing and manipulation, control of bidirectional T cell alloreactivity, graft-versus-host disease prophylaxis, and other supportive measures in haploidentical transplantation now enable nearly all patients with acute myeloid leukemia to benefit from the graft-versus-leukemia effect with substantial reduction in procedure-related mortality. Over recent years, haploidentical donors have been increasingly adopted as a valid donor source in allogeneic hematopoietic cell transplantation for acute myeloid leukemia in the absence of an HLA-matched donor. Among centers of the European Society for Blood and Marrow Transplantation, the use of haploidentical related donor transplantation has increased by 250% since 2010, and 291% since 2005. On behalf of the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation, we summarize recent utilization trends in haploidentical transplantation for acute myeloid leukemia and describe the transformative changes in haploidentical hematopoietic cell transplantation techniques over the past decade, which have led to the current widespread use of this procedure. Furthermore, we review the efficacy of haploidentical hematopoietic cell transplantation for acute myeloid leukemia from available studies, including preliminary comparative studies, and bring attention to remaining unanswered questions and directions for future research. We conclude this report with our recommendations for the role of haploidentical hematopoietic cell transplantation in acute myeloid leukemia.

Outcome of children with acute leukemia given HLA-haploidentical HSCT after αβ T-cell and B-cell depletion

Children with AL given haplo-HSCT after αβ T- and B-cell depletion are exposed to a low risk of acute and chronic GVHD and NRM. The leukemia-free, GVHD-free survival of patients given this type of allograft is comparable to that of HLA-matched donor HSCT recipients.

Natural Killer Cell-Based Cancer Immunotherapies: From Immune Evasion to Promising Targeted Cellular Therapies

Immunotherapies based on natural killer (NK) cells are among the most promising therapies under development for the treatment of so far incurable forms of leukemia and other types of cancer. The importance of NK cells for the control of viral infections and cancer is supported among others by the findings that viruses and tumors use a multitude of mechanisms to subvert and evade the NK cell system. Infections and malignant diseases can further lead to the shaping of NK cell populations with altered reactivity. Counter measures of potential therapeutic impact include the blocking of inhibitory interactions between NK cell receptors and their cellular ligands, the enhancement of activating receptor signals, and the infusion of large numbers of ex vivo generated and selected NK cells. Moreover, the specific cross-linking of NK cells to their target cells using chimeric antigen receptors or therapeutic bi-/trispecific antibody reagents is a promising approach. In this context, NK cells stand out by their positive effects and safety demonstrated in most clinical trials so far. Based in part on results of the recent EC-sponsored project “NATURIMMUN” and considering additional published work in the field, we discuss below new developments and future directions that have the potential to further advance and establish NK cell-based therapies at the clinics on a broader scale.

Clinical impact of NK-cell reconstitution after reduced intensity conditioned unrelated cord blood transplantation in patients with acute myeloid leukemia: analysis of a prospective phase II multicenter trial on behalf of the Société Française de Greffe de Moelle Osseuse et Thérapie Cellulaire and Eurocord

Unrelated cord blood transplantation (UCBT) after a reduced intensity conditioning regimen (RIC) has extended the use of UCB in elderly patients and those with co-morbidities without an HLA-identical donor, although post-transplant relapse remains a concern in high-risk acute myeloid leukemia (AML) patients. HLA incompatibilities between donor and recipient might enhance the alloreactivity of natural killer (NK) cells after allogeneic hematopoietic stem-cell transplantation (HSCT). We studied the reconstitution of NK cells and KIR-L mismatch in 54 patients who underwent a RIC-UCBT for AML in CR in a prospective phase II clinical trial. After RIC-UCBT, NK cells displayed phenotypic features of both activation and immaturity. Restoration of their polyfunctional capacities depended on the timing of their acquisition of phenotypic markers of maturity. The incidence of treatment-related mortality (TRM) was correlated with low CD16 expression (P=0.043) and high HLA-DR expression (P=0.0008), whereas overall survival was associated with increased frequency of NK-cell degranulation (P=0.001). These features reflect a general impairment of the NK licensing process in HLA-mismatched HSCT and may aid the development of future strategies for selecting optimal UCB units and enhancing immune recovery.