Reduced intensity HLA-haploidentical BMT with post transplantation cyclophosphamide in nonmalignant hematologic diseases

Hematopoietic stem cell transplantation in inborn errors of metabolism-a retrospective analysis on behalf of the pediatric disease working party from the Brazilian Society of Bone Marrow Transplantation and Cellular Therapy

Hematopoietic stem cell transplantation (HSCT) is an established treatment for selected patients with inborn errors of metabolism. In this first report from the PDWP-SBTMO, we included 105 patients transplanted between 1988 and 2021 across six Brazilian HSCT centers. The most prevalent diseases were X-linked adrenoleukodystrophy (n = 61) and mucopolysaccharidosis (type I n = 20; type II n = 10), with a median age at HSCT of 8.7 years and 2.1 years, respectively. Most conditioning regimens were myeloablative and busulfan-based. With a median follow-up of 6.7 years, the 5-years overall survival (OS) was 75% (95% CI, 0.65-0.82) with a superior 5-years OS for those transplanted after 2010 (87% vs. 63%, p = 0.01). Higher risk of death was associated with the use of haploidentical donor (HR8.86, p 0.021), unrelated cord blood (HR 8.76, p 0.005), unrelated donor (HR 5.91, p 0.02), and for HSCT performed before 2010 (HR 4.16, p = 0.0015). The CI of acute GVHD was 24.8%, while chronic GVHD was 9.5%. Major causes of death were infections (n = 8), GVHD (n = 6), and neurologic progression (n = 3). Despite improvements in transplant outcomes since 2011, challenges persist, emphasizing the need for early diagnosis, timely transplantation and expanding HSCT centers with expertise in the field.

Is allogeneic transplantation for sickle cell disease still relevant in the era of gene therapy?

ABSTRACT

Sickle cell disease (SCD) is the most common inherited blood disease. Disease-modifying therapy and supportive care have improved the survival of children with SCD in the United States and Europe. Yet, adults with SCD continue to have high risks of morbidity and early death. Recently, 2 US Food and Drug Administration-approved genetic therapies offer the potential for a short-term decrease in acute vaso-occlusive pain events if not cure. Allogeneic hematopoietic cell transplantation (allo-HCT) is also curative but, until recently, was constrained by limited donor availability and the risks of graft-versus-host disease, graft rejection, and death. Importantly, recent advances have attenuated these barriers. Here, we discuss the current state of therapies with curative intent for SCD. Both genetic therapy and allo-HCT offer the potential for cure for most with SCD. However, the cost (∼5 times higher), the current need for myeloablation, and associated late-health effects may make genetic therapies less favorable choices than allo-HCT.

Lee P, Cao Viet T, Tran Minh D. Haploidentical stem cell transplantation with posttransplant cyclophosphamide in children with Wiskott-Aldrich syndrome: a case report

Wiskott-Aldrich syndrome (WAS) is a condition characterized by a low platelet count, eczema, and a weakened immune system. Hematopoietic stem cell transplantation (HSCT) is the only curative treatment option. Haploidentical HSCT with posttransplant cyclophosphamide (PTCy) is an emerging approach for children with noncancerous conditions. This case describes a WAS patient who was early diagnosed and successfully treated with haploidentical HSCT. A 3-month-old boy presented with widespread eczema, a low platelet count, and severe infections in infancy. The diagnosis of WAS was quickly confirmed by genetic test. He received immunoglobulin replacement therapy and antimicrobial prophylaxis and underwent HSCT at 4 years 3 months of age. After failed unrelated cord blood HSCT, second rescue haploidentical HSCT had been performed using the patient's mother as the donor, with stem cells collected from peripheral blood. The conditioning regimen included anti-thymocyte globulin, melphalan, and fludarabine. The stem cell dose was 2.63 × 106 CD34+ cells/kg. GVHD prevention included PTCy, mycophenolat mofetil, and tacrolimus. The patient had no significant complications after the transplant. Neutrophil and platelet engraftment occurred promptly. At 32 months post-HSCT, the patient had complete hematological and immune reconstitution, with full donor chimerism and no GVHD. In conclusion, the PTCy approach to haploidentical HSCT was a safe and effective treatment for this WAS patient.

Autologous stem cell transplantation in adult patients with intermediate-risk acute myeloid leukemia in first complete remission and no detectable minimal residual disease. A comparative retrospective study with haploidentical transplants of the global committee and the ALWP of the EBMT

In patients with acute myeloid leukemia (AML) of intermediate-risk (IR) in first remission (CR1) with no measurable residual disease (MRD negative), the choice of the best consolidation is questionable. 1122 adult patients from 196 centers, transplanted in 2010-21 were analyzed: 547 received an autologous stem cell transplantation (ASCT) and 575 a Haploidentical donor transplant. Because of a significant interaction, comparisons were done separately for patients with wild-type FLT3 (FLT3-wt) and FLT3-ITD mutation (FLT3-ITD). In FLT3-wt patients, haploidentical transplants had two year lower relapse incidence (RI) (16.9% versus 32.6%; HR = 0.40, p < 0.001), higher NRM higher (17.2% vs 3.5%; HR = 7.02, p < 0.001), similar LFS (65.9% vs 63.8%; p = 0.37) and lower OS (73.2% vs 80.6%; HR = 1.69, p = 0.018). In FLT3-ITD patients, haploidentical transplants had two year lower RI (8.2% vs 47.8%; HR = 0.14, p < 0.001) higher NRM (20.2% vs 5.6%; HR = 3.43, p = 0.002), better LFS (71.5% vs 46.6%; HR = 0.53, p = 0.007) and similar OS (73.5% vs 61.9%; p = 0.44). In IR AML patients with FLT3-wt in MRD negative CR1, autologous stem cell transplantation is a valid option, while in patients with FLT3-ITD, haploidentical transplant is better. Whether autologous transplantation is superior to chemotherapy in FLT3-wt patients and the role of maintenance therapy with FLT3 inhibitors remain to be studied.

Chimerism-based Tolerance Induction in Clinical Transplantation: Its Foundations and Mechanisms

Hematopoietic chimerism remains the most promising strategy to bring transplantation tolerance into clinical routine. The concept of chimerism-based tolerance aims to extend the recipient's mechanisms of self-tolerance (ie, clonal deletion, anergy, and regulation) to include the tolerization of donor antigens that are introduced through the cotransplantation of donor hematopoietic cells. For this to be successful, donor hematopoietic cells need to engraft in the recipient at least temporarily. Three pioneering clinical trials inducing chimerism-based tolerance in kidney transplantation have been published to date. Within this review, we discuss the mechanisms of tolerance that are associated with the specific therapeutic protocols of each trial. Recent data highlight the importance of regulation as a mechanism that maintains tolerance. Insufficient regulatory mechanisms are also a likely explanation for situations of tolerance failure despite persisting donor chimerism. After decades of preclinical development of chimerism protocols, mechanistic data from clinical trials have recently become increasingly important. Better understanding of the required mechanisms for tolerance to be induced in humans will be a key to design more reliable and less invasive chimerism protocols in the future.

Combining PTCy and ATG for GvHD prophylaxis in non-malignant diseases

Bone marrow transplantation for non-malignant diseases such as aplastic anemia and hemoglobinopathies is a burgeoning clinical area. The goal of these transplants is to correct the hematopoietic defect with as little toxicity as possible. This requires mitigation of transplant-specific toxicities such as graft versus host disease, given this is not needed in non-malignant disorders. This review details current clinical outcomes in the field with a focus on post-transplantation cyclophosphamide and anti-thymoglobulin as intensive graft versus host disease prophylaxis to achieve that goal.

Allogeneic hematopoietic stem cell transplantation to cure sickle cell disease: A review

Sickle cell disease (SCD) had first been mentioned in the literature a century ago. Advancement in the molecular basis of the pathophysiology of the disease opens the door for various therapeutic options. Though life-extending treatments are available for treating patients with SCD, allogeneic hematopoietic stem cell transplantation (HSCT) is the only option as of yet. A major obstacle before HSCT to cure patients with SCD is the availability of donors. Matched sibling donors are available only for a small percentage of patients. To expand the donor pool, different contrasting approaches of allogeneic HSCT like T-cell replete and deplete have been tested. None of those tested approaches have been without the risk of GvHD and graft rejection. Other limitations such as transplantation-related infections and organ dysfunction caused by the harsh conditioning regimen need to be addressed on a priority basis. In this review, we will discuss available allogeneic HSCT approaches to cure SCD, as well as recent advancements to make the approach safer. The center of interest is using megadose T-cell-depleted bone marrow in conjugation with donor-derived CD8 veto T cells to achieve engraftment and tolerance across MHC barriers, under reduced intensity conditioning (RIC). This approach is in phase I/II clinical trial at the MD Anderson Cancer Centre and is open to patients with hemoglobinopathies.

Debating the Future of Sickle Cell Disease Curative Therapy: Haploidentical Hematopoietic Stem Cell Transplantation vs. Gene Therapy

Hematopoietic stem cell transplantation (HSCT) is a well-established curative therapy for patients with sickle cell disease (SCD) when using a human leukocyte antigen (HLA)-matched sibling donor. Most patients with SCD do not have a matched sibling donor, thereby significantly limiting the accessibility of this curative option to most patients. HLA-haploidentical HSCT with post-transplant cyclophosphamide expands the donor pool, with current approaches now demonstrating high overall survival, reduced toxicity, and an effective reduction in acute and chronic graft-vs.-host disease (GvHD). Alternatively, autologous genetic therapies appear promising and have the potential to overcome significant barriers associated with allogeneic HSCT, such as donor availability and GvHD. Here the authors each take a viewpoint and discuss what will be the future of curative options for patients with SCD outside of a matched sibling transplantation, specifically haploidentical HSCT vs. gene therapy.

Feasibility and Efficacy of Partially Replacing Post-Transplantation Cyclophosphamide with Bendamustine in Pediatric and Young Adult Patients Undergoing Haploidentical Bone Marrow Transplantation

Post-transplantation cyclophosphamide (PT-CY) is the most widely applied graft-versus-host disease (GVHD) prophylaxis regimen in T-cell replete haploidentical bone marrow transplantation (haplo-BMT). Although PT-CY has met with great success in the haplo-BMT arena by suppressing GVHD, patients without acute GVHD have high relapse rates. One strategy to reduce relapse rates being explored by others is a dosage reduction of PT-CY. We have taken a different approach in evaluating whether partially replacing PT-CY with post-transplantation bendamustine (PT-BEN) would be advantageous, an idea based on our preclinical research identifying several beneficial immunomodulatory properties of BEN. We therefore initiated and completed a Phase Ia trial to evaluate the progressive substitution of PT-CY with PT-BEN (ClinicalTrials.gov identifier NCT02996773). We compared outcomes between 13 patients with high-risk hematologic malignancies who received PT-CY/BEN and 31 contemporaneous haplo-BMT recipients treated with the same myeloablative conditioning regimens but receiving only PT-CY. We found that partial replacement of PT-CY with PT-BEN (PT-CY/BEN) on day +4 was well tolerated and associated with significantly earlier trilineage engraftment. We also report favorable trends toward significant improvements on univariate and multivariate analyses with PT-CY/BEN compared with PT-CY with respect to rates of chronic GVHD (hazard ratio [HR], .08; 95% confidence interval [CI], .005 to 1.11; P = .06), and GVHD-free relapse-free survival (GRFS) (HR, .22; 95% CI, .05 to .86; P = .039). Our human trial has now transitioned to Phase Ib, which will further evaluate the safety and potential benefits of PT-CY/BEN. Herein we also expand our pediatric, adolescent, and young adult experience to 31 patients, demonstrating overall survival, progression-free survival, and GRFS at 3 years of 85.6%, 76.1%, and 58.2%, respectively, in a largely racial/ethnic minority cohort. PT-CY/BEN appears to be a promising treatment option that requires further evaluation.

Incidence and Outcomes of Respiratory Failure After Non-Myeloablative Related Haploidentical Blood or Marrow Transplant

BACKGROUND

Respiratory failure is a devastating complication of allogenic blood or marrow transplant (BMT). Prior data suggest 20% and 15% of BMT patients develop respiratory failure and ARDS, respectively. Non-myeloablative (NMA) haploidentical BMT allows donor pool expansion and may decrease complications. Incidence, outcomes, and risk factors for respiratory failure after NMA haploidentical BMT are unknown.

RESEARCH QUESTION

Determine the incidence of respiratory failure after NMA haploidentical BMT and explore outcomes and risk factors for respiratory failure.

STUDY DESIGN AND METHODS

Single-center, retrospective study of all patients > 18 years old undergoing NMA haploidentical BMT from 2004-2016. The primary outcome was respiratory failure (high-flow nasal cannula oxygen, non-invasive ventilation [NIV], or invasive mechanical ventilation [IMV]) within 2 years after BMT. Respiratory failure incidence is reported as incidence rate ratios (IRR) with 95% confidence intervals. Unadjusted and multivariable Cox proportional hazards models with adjustment for a priori identified patient-level characteristics were used. Results are presented as hazard ratios (HR) with 95% CIs.

RESULTS

520 patients underwent NMA haploidentical BMT; 82 (15.8%) developed respiratory failure (IRR 0.114/person-year) at a median of 0.34 years (25^th, 75^th percentiles 0.06, 0.75 years) after BMT. Older age (HR 1.04, 1.02, 1.07), transplant for MDS (HR 1.99, 1.07, 3.72), and parent donor (HR 3.49, 1.32, 9.26) were associated with increased risk of respiratory failure; higher pre-transplant DLCO (% pred) was associated with lower risk (HR 0.98, 0.77, 0.99). Sixty-one (11.7%) patients required IMV; 30 were successfully extubated. Only 37 (7%) patients had ARDS. Of the 82 with respiratory failure, 43 (52.4%) and 61 (77.2%) died during index hospitalization and by 2 years, respectively. Only 40 (49%) had non-relapse mortality.

INTERPRETATION

Incidence of respiratory failure and ARDS after NMA haploidentical BMT is modest at 15% by 2 years after transplant. Despite successful extubation in more than 50% of patients, respiratory failure, regardless of cause, is associated with a high rate of death by 2 years, from both relapse and non-relapse causes. Age, BMT for MDS, parental donor, and pre-transplant DLCO were risk factors for respiratory failure.

Impact of mother donor, peripheral blood stem cells and measurable residual disease on outcomes after haploidentical hematopoietic cell transplantation with post-transplant cyclophosphamide in children with acute leukaemia

Haploidentical hematopoietic-cell transplantation using post-transplant cyclophosphamide(Haplo-PTCy) is a feasible procedure in children with haematologic malignancies. However, data of a large series of children with acute leukaemia(AL) in this setting is missing. We analysed 144 AL Haplo-PTCy paediatric recipients; median age was 10 years. Patients had acute lymphoblastic(ALL; n = 86) or myeloblastic leukaemia(AML; n = 58) and were transplanted in remission(CR1: n = 40; CR2: n = 57; CR3+: n = 27) or relapse (n = 20). Bone marrow was the graft source in 57%; donors were father (54%), mother (35%), or sibling (11%). Myeloablative conditioning was used in 87%. Median follow-up was 31 months. At day +100, cumulative incidence (CI) of neutrophil recovery and acute GVHD (II-IV) were 94% and 40%, respectively. At 2-years, CI of chronic GVHD and relapse, were 31%, 40%, and estimated 2-year overall survival (OS), leukaemia-free survival (LFS) and graft-versus-host-relapse-free survival (GRFS) were 52%, 44% and 34% respectively. For patients transplanted in remission, positive measurable residual disease (MRD) prior to transplant was associated with decreased LFS (p = 0.05) and GRFS (p = 0.003) and increased risk of relapse (p = 0.02). Mother donor was associated with increased risk of chronic GVHD (p = 0.001), decreased OS (p = 0.03) and GRFS (p = 0.004). Use of PBSC was associated with increased risk of chronic GVHD (p = 0.04). In conclusion, achieving MRD negativity pre-transplant, avoiding use of mother donors and PBSC as graft source may improve outcomes of Haplo-PTCy in children with AL.

Haploidentical Hematopoietic Cell Transplantation Using Post-transplant Cyclophosphamide for Children with Non-malignant Diseases

Haploidentical hematopoietic cell transplantation (HCT) is a valuable curative option for children with non-malignant diseases. Haploidentical HCT using post-transplant cyclophosphamide (PTCy) is a readily available option in the absence of an HLA-matched donor. We conducted a retrospective single-center study on the outcome of haploidentical HCT in children with non-malignant diseases. We gathered data from 44 patients underwent HCT in the period 2015 to 2020. The indications for HCT were bone marrow failure, primary immunodeficiency, metabolic disorders, and hemoglobinopathy. Median age at HCT was 4 years (range 0.7-20). The conditioning regimens were myeloablative (n = 17) or reduced intensity (n = 27). After a median follow-up of 20 months (range 4-71), 2-year overall survival was 89% and 2-year GvHD-free relapse-free survival (GRFS) was 66%. Incidence of primary graft failure was 13.6%. Cumulative incidence of grade II-IV acute and moderate/severe chronic GvHD were 20% and 6.4%, respectively. Younger age at HCT (< 4 years) and primary immunodeficiency were significantly associated with better GRFS (p < 0.05). In conclusion, haploidentical HCT using PTCy is feasible and curative in children with non-malignant diseases lacking an HLA-matched donor. Early diagnosis and referral in addition to timely treatment can further improve outcomes.

Have CD19-directed immunotherapy and haploidentical hematopoietic cell transplantation transformed pediatric B-cell acute lymphoblastic leukemia into a chronic disease?

The treatment of pediatric B-cell acute lymphoblastic leukemia (B-ALL) has undergone several recent advancements, leading to an increased amount of treatment options for relapsed patients. The development of immunotherapies such as anti-CD19 chimeric antigen receptor(CAR) T cells and bispecific T-cell engagers has given clinicians therapeutic options with less expected toxicity when compared to standard re-induction chemotherapy. This is especially beneficial in patients with toxicities from their prior treatment. Along with this, the emergence of haploidentical hematopoietic cell transplantation (HCT) has increased opportunity for patients to receive HCT who may not have had an available matched donor. We present four patients who have received all of these therapies in different combinations to treat multiple relapses. Because of the success of achieving remission as well as decreasing toxicity, the patients are alive and well up to 15 y after the original B-ALL diagnosis, rendering this as a chronic disease for them.

Immunomodulatory Effects of Bendamustine in Hematopoietic Cell Transplantation

Bendamustine (BEN) is a unique alkylating agent with efficacy against a broad range of hematological malignancies, although investigations have only recently started to delve into its immunomodulatory effects. These immunomodulatory properties of BEN in the context of hematopoietic cell transplantation (HCT) are reviewed here. Pre- and post-transplant use of BEN in multiple murine models have consistently resulted in reduced GvHD and enhanced GvL, with significant changes to key immunological cell populations, including T-cells, myeloid derived suppressor cells (MDSCs), and dendritic cells (DCs). Further, in vitro studies find that BEN enhances the suppressive function of MDSCs, skews DCs toward cDC1s, enhances Flt3 expression on DCs, increases B-cell production of IL-10, inhibits STAT3 activation, and suppresses proliferation of T- and B-cells. Overall, BEN has a broad range of immunomodulatory effects that, as they are further elucidated, may be exploited to improve clinical outcomes. As such, clinical trials are currently underway investigating new potential applications of BEN in the setting of allogeneic HCT.

Correction of murine sickle cell disease by allogeneic haematopoietic cell transplantation with anti-3rd party veto cells

Despite advances in gene therapy allogeneic hematopoietic stem cell transplants (HSCT) remains the most effective way to cure sickle cell disease (SCD). However, there are substantial challenges including lack of suitable donors, therapy-related toxicity (TRM) and risk of graft-versus-host disease (GvHD). Perhaps the most critical question is when to do a transplant for SCD. Safer transplant protocols for HLA-disparate HSCT is needed before transplants are widely accepted for SCD. Although risk of GvHD and TRM are less with T-cell-deplete HSCT and reduced-intensity conditioning (RIC), transplant rejection is a challenge. We have reported graft rejection of T cell-depleted non-myeloablative HSCT can be overcome in wild type fully mis-matched recipient mice, using donor-derived anti-3rd party central memory CD8-positive veto cells combined with short-term low-dose rapamycin. Here, we report safety and efficacy of this approach in a murine model for SCD. Durable donor-derived chimerism was achieved using this strategy with reversal of pathological parameters of SCD, including complete conversion to normal donor-derived red cells, and correction of splenomegaly and the levels of circulating reticulocytes, hematocrit, and hemoglobin.

Allogenic hematopoietic stem cell transplantation in sickle cell disease

Sickle cell disease (SCD) is one of the most common monogenic disorders worldwide and affects approximately 100,000 people in the United States alone. SCD can cause numerous complications, including anemia, pain, stroke, and organ failure, which can lead to death. Although there are a few disease-modifying treatments available to patients with SCD, the only current curative option is a hematopoietic stem cell transplant (HSCT). In this review, we will discuss the different approaches to allogeneic HSCT in the treatment of SCD and the outcomes of these approaches.

Timing of Alemtuzumab With Respect to Day of Bone Marrow Infusion and its Effects Upon Engraftment and Graft-Versus-Host Disease in Patients With Sickle Cell Disease: A Single-Institutional Study

The possible impact of "late" alemtuzumab (administered on days -10 to -8) versus "early" alemtuzumab (-19 to -17) with respect to engraftment and acute/chronic graft-versus-host disease (GvHD) in a group of 25 pediatric patients with sickle cell disease undergoing bone marrow transplantation following conditioning with alemtuzumab, fludarabine, and melphalan is reported. The first 9 patients received "late" alemtuzumab followed by bone marrow transplantation from HLA-matched sibling donors. The next 16 patients undergoing matched sibling transplants received "early" alemtuzumab. In the "late" group, 1 patient (11%) developed acute GvHD. Six patients (67%) achieved sustained engraftment. Three patients (33%) experienced graft rejection, leading to termination of enrollment of patients on this regimen. In the "early" alemtuzumab group, acute and chronic GvHD developed in 43% and 25% patients, respectively. None of the patients experienced graft rejection in this group of patients. Three patients developed stable mixed chimerism and 13 patients demonstrated 100% donor chimerism at 1 year post-transplant and beyond. These results suggest a benefit with respect to engraftment of administering "early" versus "late" alemtuzumab in this reduced-intensity conditioning regimen, however, with the possible cost of an increase in acute, and possibly chronic GvHD.

Pre-transplant myeloid and immune suppression, upfront plerixafor mobilization and post-transplant cyclophosphamide: novel strategy for haploidentical transplant in sickle cell disease

Allogenic hematopoietic stem cell transplant is the only curative option for symptomatic sickle cell disease (SCD). HLA haploidentical related donor transplants are associated with high graft failure rates. We conceptualized a novel protocol (APOLLO protocol) using pre-transplant immune and myelosuppression (PTIS) using fludarabine, cyclophosphamide, and dexamethasone followed by augmented John Hopkins protocol by adding thiotepa to conditioning. Twenty-five consecutive patients suffering from symptomatic SCD were enrolled into the study. We added upfront plerixafor to granulocyte colony stimulating factor (GCSF) for mobilization of healthy donors. Graft versus host disease (GvHD) prophylaxis was done using post-transplant cyclophosphamide, sirolimus, and mycophenolate mofetil. Graft failure was not seen in any of our patients. Five patients developed acute grade II/IV GvHD (4 classical acute, 1 late onset), 3 had limited chronic GvHD. Out of 25 evaluable patients, 22 are alive and disease free, making an overall survival (OS) and disease-free survival (DFS) of 88% with a median follow up of 485 days (range 198-802). T-cell-replete haploidentical transplant with PTIS, augmented John Hopkins conditioning and plerixafor based mobilization is a safe and effective way of treating patients suffering from SCD with minimal or no risk of graft failure and acceptable GvHD rates.

Post-transplantation cyclophosphamide for chimerism-based tolerance

High-dose cyclophosphamide given post-transplant (PTCy) successfully enables tolerance induction in HLA-mismatched related blood or marrow transplantation (haploBMT) manifested by low rates of graft failure, severe acute graft-versus-host disease (GVHD), and chronic GVHD. When proceeded by nonmyeloablative conditioning, PTCy has also been associated with a low incidence of nonrelapse mortality. The safety of this platform has garnered interest in expanding its use to non-malignant indications for allogeneic blood or marrow transplantation (alloBMT). After success in a preliminary Phase I/II trial, use of a PTCy-based haploBMT platform is now being explored in a large Blood and Marrow Transplant Clinical Trials Network (BMT CTN) study for sickle cell disease. These emerging data in patients with hemoglobinopathies provided the rationale for exploring the use of PTCy in combined solid organ and BM transplantation as a means of tolerance induction through donor hematopoietic chimerism with a goal to obviate the need for a lifetime of immunosuppression. Several case reports, series, and small clinical trials have now been published of combined solid organ and alloBMT in patients with hematologic malignancies who had organ failure that would have been preclusive of alloBMT in the absence of solid organ transplantation. Here we will review the pre-clinical and clinical studies supporting the use of PTCy for chimerism-based tolerance induction.

Outcomes after Haploidentical Stem Cell Transplantation with Post-Transplantation Cyclophosphamide in Patients with Primary Immunodeficiency Diseases

Allogeneic hematopoietic stem cell transplantation (HCT) can cure primary immunodeficiency diseases (PID). When a HLA-matched donor is not available, a haploidentical family donor may be considered. The use of T cell-replete haploidentical HCT with post-transplantation cyclophosphamide (haplo-PTCy) in children with PID has been reported in few case series. A donor is usually readily available, and haplo-PTCy can be used in urgent cases. We studied the outcomes of 73 patients with PID who underwent haplo-PTCy, including 55 patients who did so as a first transplantation and 18 who did so as a salvage transplantation after graft failure of previous HCT. The median patient age was 1.6 years. Most of the children were male (n = 54) and had active infection at the time of transplantation (n = 50); 10 children had severe organ damage. The diagnosis was severe combined immunodeficiency (SCID) in 34 patients and non-SCID in 39 (Wiskott-Aldrich syndrome; n = 14; chronic granulomatous disease, n = 10; other PID, n = 15). The median duration of follow-up of survivors was 2 years. The cumulative incidence of neutrophil recovery was 88% in the SCID group and 84% in non-SCID group and was 81% for first transplantations and 83% after a salvage graft. At 100 days, the cumulative incidence of acute GVHD grade II-IV and III-IV was 33% and 14%, respectively. The majority of patients reached 200/μL CD4⁺ and 1000/μL CD3⁺ cell counts between 3 and 6 months. The estimated 2-year overall survival was 66%; it was 64% for SCID patients and 65% for non-SCID patients and 63% for first HCT and 77% for salvage transplantations. Twenty-five patients died, most of them due to infection early after transplantation (before 100 days). In conclusion, haplo-PTCy is a feasible procedure, can cure two-thirds of children with PID, and can be used as rescue treatment for previous graft failure. © 2020 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Second Allogeneic Hematopoietic Stem Cell Transplantation After Donor Replacement in Children With Severe Aplastic Anemia

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective measure for the treatment of severe aplastic anemia (SAA). While infection, graft failure, and graft-vs-host disease (GVHD) are the main causes of allo-HSCT failure, a second HSCT is needed to eliminate the dependence of blood transfusion and maintain disease-free survival. We applied low-dose total body irradiation (TBI) + fludarabine (FLU) + cyclophosphamide (CTX) + antilymphocyte globulin (ALG) + busulfan (BU) as a conditioning regimen of second HSCT after a transplantation with an HLA-mismatched donor. As for retransplantation donors, 1 child had an unrelated HLA-matched donor, and 2 children had related HLA-mismatched ones. The latter underwent more serious GVHD with a relatively high cytokine level, and the former had no obvious GVHD after the second HSCT. All 3 patients achieved a desirable effect within 1 month and received satisfactory therapeutic effect during the subsequent follow-up, indicating the convincing effectiveness and safety of this method.

Bendamustine with total body irradiation conditioning yields tolerant T-cells while preserving T-cell-dependent graft-versus-leukemia

Graft-versus-host disease (GvHD) remains a significant impediment to allogeneic hematopoietic cell transplantation (HCT) success, necessitating studies focused on alleviating GvHD, while preserving the graft-versus-leukemia (GvL) effect. Based on our previous studies showing bendamustine with total body irradiation (BEN-TBI) conditioning reduces GvHD compared to the current clinical standard of care cyclophosphamide (CY)-TBI in a murine MHC-mismatched bone marrow transplantation (BMT) model, this study aimed to evaluate the role and fate of donor T-cells following BEN-TBI conditioning. We demonstrate that BEN-TBI reduces GvHD compared to CY-TBI independently of T regulatory cells (Tregs). BEN-TBI conditioned mice have a smaller proportion and less activated donor T-cells, with lower CD47 expression, early post-transplant, but no sustained phenotypic differences in T-cells. In BEN-TBI conditioned mice, donor T-cells gain tolerance specific to host MHC antigens. Though these T-cells are tolerant to host antigens, we demonstrate that BEN-TBI preserves a T-cell-dependent GvL effect. These findings indicate that BEN-TBI conditioning reduces GvHD without compromising GvL, warranting its further investigation as a potentially safer and more efficacious clinical alternative to CY-TBI.

Haploidentical bone marrow transplant with posttransplant cyclophosphamide for sickle cell disease: An update

Hematopoietic cell transplant (HCT) can cure both children and adults with sickle cell disease. Outcomes have historically been poor for the vast majority of patients who lack a matched sibling donor. However, the development of haploidentical HCT (haplo-HCT) with high doses of posttransplant cyclophosphamide (PTCy) has allowed for curative long-term potential with favorable transplant-related outcomes, though this has not obviated the potential for graft rejection from human leukocyte antigen mismatch and repeated red blood cell transfusions. Accordingly, multiple strategies have been developed to improve outcomes, the majority of which are based on the Johns Hopkins platform from 2012. Presently, we aim to discuss results from pertinent studies and compare outcomes with the two most recent approaches involving either thiotepa plus 200-cGy total body irradiation or 400-cGy total body irradiation. Direct comparisons are required to determine the optimized curative potential. Transplant-eligible patients must be referred to tertiary medical centers for consideration of haplo-HCT.

Granulocyte Colony-Stimulating Factor-Primed Unmanipulated Haploidentical Blood and Marrow Transplantation

Granulocyte colony-stimulating factor (G-CSF), a growth factor for neutrophils, has been successfully used for stem cell mobilization and T cell immune tolerance induction. The establishment of G-CSF-primed unmanipulated haploidentical blood and marrow transplantation (The Beijing Protocol) has achieved outcomes for the treatment of acute leukemia, myelodysplastic syndrome, and severe aplastic anemia with haploidentical allografts comparable to those of human leukocyte antigen (HLA)-matched sibling donor transplantation. Currently, G-CSF-mobilized bone marrow and/or peripheral blood stem cell sources have been widely used in unmanipulated haploidentical transplant settings. In this review, we summarize the roles of G-CSF in inducing T cell immune tolerance. We discuss the recent advances in the Beijing Protocol, mainly focusing on strategies that have been used to improve transplant outcomes in cases of poor graft function, virus infections, and relapse. The application of G-CSF-primed allografts in other haploidentical modalities is also discussed.

Outcomes of Related and Unrelated Donor Searches Among Patients with Primary Immunodeficiency Diseases Referred for Allogeneic Hematopoietic Cell Transplantation

Patients with primary immunodeficiencies (PIDs) are potentially cured by allogeneic hematopoietic cell transplantation (HCT). The spectrum of PIDs has expanded greatly beyond those that present in infancy or are diagnosed on newborn screening and require urgent, preemptive HCT. Many PID diagnoses are now made later in life, and the role of HCT is only considered for severe disease manifestations; in these cases, the kinetics and goals of a donor search may be different than for severe combined immunodeficiency. Across all PIDs, related donor searches have the additional selection factor of the inherited disease, and such searches may yield more limited options than searches for patients with hematologic malignancies; thus, unrelated donor options often become more critical in these patients. We retrospectively evaluated the outcomes of donor searches among patents with PIDs referred for HCT at the National Institutes of Health, where the minimum patient age for evaluation is 3 years and where donor options include matched sibling donors or matched related donors, HLA-haploidentical (haplo), or 7-8/8 HLA matched unrelated donors (mMUDs/MUDs). Patient (n = 161) and donor demographics, MUD search results, HLA typing, pedigrees, mutation testing, and donor selection data were collected. The National Marrow Donor Program HapLogic 8/8 HLA match algorithm was used to predict the likelihood of a successful MUD search and categorized as very good, good, fair, poor, very poor, or futile per the Memorial Sloan Kettering Cancer Center (MSKCC) Search Prognosis method. There were significant differences by PID mode of inheritance in patient age, disposition (receipt of HCT or not), donor source, and donor relatedness. A related or unrelated donor option could be identified for 94% of patients. Of living first-degree relatives (median, 3; range, 0 to 12 per patient), a median of 1 donor remained for autosomal dominant and X-linked (XL) diseases after HLA typing, mutation testing, and other exclusions, and a median of 2 donors remained for autosomal recessive (AR) diseases. Among patients with a PID of known mode of inheritance (n = 142), the best related donor was haplo for 99 (70%) patients, with 56 (39%) haplos age 40 years or older and 5 (4%) second-degree haplos; 13 (9%) had no family donor options. The best related donor was a heterozygote/asymptomatic carrier of the PID mutation in 36 (49%) patients with AR or XL disease (n = 73). Among patients with MUD search performed (n = 139), 53 (38%) had very poor/futile 8/8 MUD searches, including 6 (32%) of those with unknown PID mutation and therefore no family donor options. The MSKCC Search Prognosis was less favorable for those of non-European ancestry compared with European ancestry (P = .002). Most patients of Hispanic or African ancestry had very poor/futile MUD searches, 71% and 63%, respectively. No HCT recipients with very poor/futile MUD searches (n = 38) received 8/8 MUD grafts. Alternative donor options, including haplo and unrelated donors, are critical to enable HCT for patients with PIDs. MUD search success remains low for those of non-European ancestry, and this is of particular concern for patients with PIDs caused by an unknown genetic defect. Among patients with PIDs, related donor options are reduced and haplos age 40 years and older and/or mutation carriers are often the best family option.

Use of TCR α+β+/CD19+-Depleted Haploidentical Hematopoietic Stem Cell Transplant Is a Viable Option in Patients With Primary Immune Deficiency Without Matched Sibling Donor

Allogeneic hematopoietic stem cell transplantation (HSCT) is curative for many patients with primary immune deficiency (PID). Haploidentical donors have historically been associated with higher rates of graft-versus-host disease (GvHD) and graft failure. Use of T cell receptor (TCR) α⁺β⁺/CD19⁺-depleted grafts has resulted in improved haploidentical HSCT outcomes. We sought to evaluate outcomes of TCR α⁺β⁺/CD19⁺-depleted haploidentical HSCT in pediatric patients with PID at a single center in Australia. Specifically, we evaluated immune reconstitution, looking at time to T cell and B cell reconstitution, and B cell function post-HSCT. Eleven patients with a mean age of 7.92 years (range 0.33-17.17 years) were included. The median time to B cell recovery was 93 days (range 41-205 days), and the median time to cessation of immunoglobulin replacement was 281.5 days (range 41-205 days). All patients who had ceased immunoglobulin replacement had an adequate response to pneumococcal conjugate (Prevenar 13) vaccine. The median time to CD4⁺ recovery was 132 days (range 30-296 days), and naive T cells were present in all surviving patients by 4 months post-HSCT. Eight of 11 patients are surviving, with six patients having whole blood chimerism greater than 95%, one patient with whole blood chimerism of 82.8%, and another with 76.0%. All of these patients clinically had no evidence of underlying immunodeficiency. Likelihood of overall survival at 2 years post-HSCT was 81.8%. Cumulative incidence of acute GvHD was 27.3%. Cumulative incidence of CMV viremia was 63.6%. All patients previously exposed to CMV had reactivation post-HSCT, but were controlled with pre-emptive CMV treatment. Assuming most children with PID have a haploidentical donor available, use of this technique is likely to result in good outcomes for patients who do not have a suitable matched sibling or matched unrelated donor.

Haploidentical transplantation outcomes are comparable with those obtained with identical human leukocyte antigen allogeneic transplantation in Chilean patients with benign and malignant hemopathies

Introduction

Patients with benign or malignant blood disorders, who require allogeneic stem cell transplantation and lack an identical human leukocyte antigen HLA identicalHL sibling donor, could be transplanted with hematopoietic stem cells from unrelated adult or umbilical cord donors. However, in our country, both approaches are costly and time-consuming options.

Methods

Over the last few years, haploidentical modalities have been investigated as an alternative donor source, showing similar results to those obtained with identical HLA donors. We started using T-cell-replete haploidentical with post-transplant cyclophosphamide in 2012 and we presented our experience with patients undergoing haploidentical ransplantation compared to SIB.

Results

Since January 2012 to date, 91 allogeneic transplants have been performed, of which 49 were haploidentical and 42 were HLA identical. The mean age of the patients was 35 years (range: 17–62). The mean CD34/kg × 10⁶ infused per group was 5.93 and 5.89, respectively. Time to granulocyte and platelet engraftment was 11 and 15 days, respectively, for haploidentical, and 12 and 14 days, respectively, for HLA identical (p = 0.10). The 100-day cumulative incidence of global acute GVHD was 34% for haploidentical and 29% for SIHLA identical (p = 0.9). The 2-year overall global graft-versus-host disease was 43% for haploidentical and 41% for HLA identical (p = 0.8). Overall survival, relapse, and transplant and relapse-related mortality were similar between both groups.

Conclusion

Our experience showed that haploidentical has similar outcomes to those obtained with HLA idential and can be performed in our country safely.

Effect of increased dose of total body irradiation on graft failure associated with HLA-haploidentical transplantation in patients with severe haemoglobinopathies: a prospective clinical trial

BACKGROUND

Although severe haemoglobinopathies can be cured with allogeneic blood or bone marrow transplantation, availability of matched donors and toxic effects can be problematic. We previously found that non-myeloablative haploidentical related bone marrow transplantation with post-transplantation cyclophosphamide expanded the donor pool while limiting graft-versus-host disease (GVHD). However, graft failure-albeit with full host haemopoietic recovery-occurred in 50% of patients. In this study, we investigated whether increasing total body irradiation from 200 cGy to 400 cGy would improve engraftment while maintaining the safety profile.

METHODS

This study was done at Johns Hopkins Hospital (Baltimore, MD, USA). Patients aged 2-70 years receiving their first bone marrow transplant were eligible for inclusion in the study. Patients received rabbit-derived intravenous anti-thymocyte globulin 0·5 mg/kg on day -9 and 2 mg/kg on days -8 and -7, intravenous fludarabine 30 mg/m² on days -6 to -2, intravenous cyclophosphamide 14·5 mg/kg on days -6 and -5, and total body irradiation 400 cGy administered as a single fraction on day -1. We collected unmanipulated bone marrow and infused on day 0. GVHD prophylaxis comprised intravenous cyclophosphamide 50 mg/kg per day on days 3 and 4 after transplantation, oral mycophenolate mofetil 15 mg/kg per dose (maximum 1 g) every 8 h on days 5 to 35, and oral sirolimus to maintain a level of 5-15 ng/dL for at least 1 year starting on day 5. The original planned primary objectives of this phase 2 clinical trial were transplant-related mortality and progression-free survival. However, the coverage decision by the Centers for Medicare and Medicaid Services to only provide payment for allogeneic bone marrow transplantation for patients with sickle cell disease on a clinical trial that had a comparison arm with patients not receiving bone marrow transplantation prompted the closure of this trial to accrual in 2017. Therefore, as we were unable to perform our planned statistical analysis, the primary objective was modified to evaluate engraftment, assessed by chimerism. This trial is registered with ClinicalTrials.gov, number NCT00489281. The study is closed to new participants and this is the primary analysis.

FINDINGS

Between Sept 24, 2014, and Aug 1, 2017, we enrolled 17 consecutive patients: 12 (71%) with sickle cell disease and 5 (29%) with β-thalassaemia major. The median patient age was 16 years (range 6-31, IQR 7·7-27·5). One (6%) of 17 patients had primary graft failure with recovery of host haemopoiesis. 13 (76%) of 17 patients achieved full donor chimerism and three (18%) had mixed donor-host chimerism. Five (29%) of 17 patients developed grade 2-4 acute GVHD, including four (24%) with maximal grade 2 GVHD and one (6%) with grade 3 GVHD. Chronic GVHD developed in three (18%) patients. As of their last follow-up visit, GVHD had resolved in all patients and no patients were receiving systemic GVHD therapy. All patients remained alive as of Aug 4, 2019, and the median follow-up duration was 705 days (range 355-1294; IQR 398-943). Only one (6%) of the 16 engrafted patients remained transfusion dependent, and 14 (88%) discontinued immunosuppression.

INTERPRETATION

Increasing total body irradiation to 400 cGy substantially reduced graft failure while maintaining the safety of haploidentical bone marrow transplantation with post-transplantation cyclophosphamide. These results suggest that engraftment after haploidentical bone marrow transplantation for haemoglobinopathies is possible, and primary graft failure-the main problem previously reported-might be addressed by this strategy. Therefore, this curative approach should no longer be restricted to patients with HLA-matched donors.

FUNDING

Maryland Stem Cell Research Fund and US National Institutes of Health.

Haploidentical Hematopoietic Stem Cell Transplantation with Post-Transplant Cyclophosphamide for Primary Immunodeficiencies and Inherited Disorders in Children

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative treatment for some inherited disorders, including selected primary immunodeficiencies (PIDs). In the absence of a well-matched donor, HSCT from a haploidentical family donor (HIFD) may be considered. In adult recipients high-dose post-transplant cyclophosphamide (PTCY) is increasingly used to mitigate the risks of graft failure and graft-versus-host disease (GVHD). However, data on the use of PTCY in children (and especially those with inherited disorders) are scarce. We reviewed the outcomes of 27 children transplanted with an HIFD and PTCY for a PID (n = 22) or osteopetrosis (n = 5) in a single center. The median age was 1.5 years (range, .2 to 17). HSCT with PTCY was a primary procedure (n = 21) or a rescue procedure after graft failure (n = 6). The conditioning regimen was myeloablative in most primary HSCTs and nonmyeloablative in rescue procedures. After a median follow-up of 25.6 months, 24 of 27 patients had engrafted. Twenty-one patients are alive and have been cured of the underlying disease. The 2-year overall survival rate was 77.7%. The cumulative incidences of acute GVHD grade ≥ II, chronic GVHD, and autoimmune disease were 45.8%, 24.2%, and 29.6%, respectively. There were 2 cases of grade III acute GVHD and no extensive cGVHD. The cumulative incidences of blood viral replication and life-threatening viral events were 58% and 15.6%, respectively. There was evidence of early T cell immune reconstitution. In the absence of an HLA-identical donor, HIFD HSCT with PTCY is a viable option for patients with life-threatening inherited disorders.

Excellent Outcomes of Allogeneic Hematopoietic Stem Cell Transplantation in Patients with Paroxysmal Nocturnal Hemoglobinuria: A Single-Center Study

We analyzed the outcomes of 44 patients with paroxysmal nocturnal hemoglobinuria (PNH) who received allogeneic hematopoietic stem cell transplantation (allo-HSCT) (haploidentical [haplo]-donors, 25; matched sibling donors [MSDs], 15; and matched unrelated donors, 4) between July 2007 and May 2018. All patients achieved successful donor engraftment. The median time was 12 days (range, 7 to 26) for myeloid engraftment and 13 days (range, 11 to 75) for platelets. The cumulative incidences were 15.91% and 2.27% for grades II to IV and grades III to IV acute graft-versus-host disease (GVHD), respectively, with a median follow-up time of 36 months (range, 4 to 132). The cumulative incidences were 26.73% for chronic GVHD and 9.70% for moderate to severe chronic GVHD. No patients relapsed. The probabilities of 3-year overall survival (OS) and GVHD-free, failure-free survival (GFFS) were 90.4% ± 4.6% and 85.6% ± 5.4%, respectively. The 3-year OS rates of the haplo-donor and MSD groups were 86.5% ± 7.3% versus 93.3% ± 6.4% (P = .520). The 3-year GFFS rates of the haplo-donor and MSD groups were 78.3% ± 8.6% versus 92.9% ± 6.9% (P = .250). The preliminary results indicated that allo-HSCT is a feasible option for patients with PNH; however, this should not be considered as a first-choice therapy, because the results seemed to only suggest rather than confirm that haplo-HSCT and MSD-HSCT exerted similar therapeutic efficacies.

Consensus approach for the management of severe combined immune deficiency caused by adenosine deaminase deficiency

Inherited defects in adenosine deaminase (ADA) cause a subtype of severe combined immunodeficiency (SCID) known as severe combined immune deficiency caused by adenosine deaminase defects (ADA-SCID). Most affected infants can receive a diagnosis while still asymptomatic by using an SCID newborn screening test, allowing early initiation of therapy. We review the evidence currently available and propose a consensus management strategy. In addition to treatment of the immune deficiency seen in patients with ADA-SCID, patients should be followed for specific noninfectious respiratory, neurological, and biochemical complications associated with ADA deficiency. All patients should initially receive enzyme replacement therapy (ERT), followed by definitive treatment with either of 2 equal first-line options. If an HLA-matched sibling donor or HLA-matched family donor is available, allogeneic hematopoietic stem cell transplantation (HSCT) should be pursued. The excellent safety and efficacy observed in more than 100 patients with ADA-SCID who received gammaretrovirus- or lentivirus-mediated autologous hematopoietic stem cell gene therapy (HSC-GT) since 2000 now positions HSC-GT as an equal alternative. If HLA-matched sibling donor/HLA-matched family donor HSCT or HSC-GT are not available or have failed, ERT can be continued or reinstituted, and HSCT with alternative donors should be considered. The outcomes of novel HSCT, ERT, and HSC-GT strategies should be evaluated prospectively in "real-life" conditions to further inform these management guidelines.

Transplantation of Hematopoietic Stem Cells for Primary Immunodeficiencies in Brazil: Challenges in Treating Rare Diseases in Developing Countries

The results of hematopoietic stem cell transplant (HSCT) for primary immunodeficiency diseases (PID) have been improving over time. Unfortunately, developing countries do not experience the same results. This first report of Brazilian experience of HSCT for PID describes the development and results in the field. We included data from transplants in 221 patients, performed at 11 centers which participated in the Brazilian collaborative group, from July 1990 to December 2015. The majority of transplants were concentrated in one center (n = 123). The median age at HSCT was 22 months, and the most common diseases were severe combined immunodeficiency (SCID) (n = 67) and Wiskott-Aldrich syndrome (WAS) (n = 67). Only 15 patients received unconditioned transplants. Cumulative incidence of GVHD grades II to IV was 23%, and GVHD grades III to IV was 10%. The 5-year overall survival was 71.6%. WAS patients had better survival compared to other diseases. Most deaths (n = 53) occurred in the first year after transplantation mainly due to infection (55%) and GVHD (13%). Although transplant for PID patients in Brazil has evolved since its beginning, we still face some challenges like delayed diagnosis and referral, severe infections before transplant, a limited number of transplant centers with expertise, and resources for more advanced techniques. Measures like newborn screening for SCID may hasten the diagnosis and ameliorate patients' conditions at the moment of transplant.

Bendamustine with Total Body Irradiation Limits Murine Graft-versus-Host Disease in Part Through Effects on Myeloid-Derived Suppressor Cells

Graft-versus-host disease (GVHD) remains a significant challenge in allogeneic hematopoietic cell transplantation (HCT). An underinvestigated strategy to reduce GVHD is the modification of the preparative conditioning regimen. In the present study, we aimed to evaluate GVHD associated with bendamustine (BEN) conditioning in conjunction with total body irradiation (TBI) as an alternative to the standard myeloablative regimen of cyclophosphamide (CY) and TBI. We demonstrate that BEN-TBI conditioning, although facilitating complete donor chimerism, results in significantly less GVHD compared with CY-TBI. In BEN-TBI-conditioned mice, suppressive CD11b⁺Gr-1^high myeloid cells are increased in the blood, bone marrow, spleen, and intestines. When Gr-1^high cells are depleted before transplantation, the beneficial effects of BEN-TBI are partially lost. Alternatively, administration of granulocyte colony-stimulating factor, which promotes CD11b⁺Gr-1⁺ myeloid cell expansion, is associated with a trend toward increased survival in BEN-TBI-conditioned mice. These findings indicate a potential role of myeloid-derived suppressor cells in the mechanism by which BEN allows engraftment with reduced GVHD. BEN-TBI conditioning may present a safer alternative to CY-TBI conditioning for allogeneic HCT.

Posttransplant Cyclophosphamide for HLA-haploidentical Transplantation in Patients With Mucopolysaccharidosis

We successfully used a haploidentical transplantation protocol with posttransplant cyclophosphamide (CY) (50 mg/kg/d on days +3 and +4) for in vivo T-cell depletion in patients with mucopolysaccharidosis using reduced-intensive conditioning regimens, followed by a busulfan-based conditioning regimen, which included busulfan (12 to 16 mg/kg) and fludarabine(150 to 200 mg/m)+rabbit antihuman thymocyte globulin (7.5 to 10 mg/kg) as a conditioning regimen. Cyclosporine or tacrolimus, methotrexate, mycophenolate mofetil, and methylprednisolone were administered to prevent graft-versus-host disease (GVHD). After follow-up for a median period of 1.5 years, all 8 patients without preexisting severe comorbidities and early transplant referrals are alive, with 100% donor chimerism and excellent performance status. Only 1 patient developed chronic GVHD(II). We conclude that posttransplant CY is effective in vivo for T-cell depletion to promote full donor engraftment in patients with mucopolysaccharidosis. In addition, with posttransplant CY, the procedure reduced the rate of GVHD and the cost of transplant and improved the patients' quality of life.

When there is no match, the game is not over: Alternative donor options for hematopoietic stem cell transplantation in sickle cell disease

Many patients with sickle cell disease experience severe morbidity and early mortality. The only curative option remains hematopoietic stem cell transplantation. Although HLA-matched sibling transplantation has been very successful for adults and children, the vast majority of patients with sickle cell disease do not have an HLA-matched sibling. Alternative donor options include haploidentical, unrelated umbilical cord blood, and matched unrelated donor transplantation. This report summarizes major alternative donor transplantation studies reported to date and ongoing and upcoming clinical trials. We conclude that when there is no HLA-match, all these approaches should be systematically considered before ruling out the option of hematopoietic stem cell transplantation.

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.

Haplotype Counting for Sensitive Chimerism Testing: Potential for Early Leukemia Relapse Detection

Fields of forensics, transplantation, and paternity rely on human identity testing. Currently, this is accomplished through amplification of microsatellites followed by capillary electrophoresis. An alternative and theoretically better approach uses multiple single-nucleotide polymorphisms located within a small region of DNA, a method we initially developed using HLA-A and called haplotype counting. Herein, we validated seven additional polymorphic loci, sequenced a total of 45 individuals from three of the 1000 Genomes populations (15 from each), and determined the number of haplotypes, heterozygosity, and polymorphic information content for each locus. In addition, we developed a multiplex PCR that amplifies five of these loci simultaneously. Using this strategy with a small cohort of leukemic patients who underwent allogeneic bone marrow transplantation, we first attempted to define a threshold (0.26% recipient) by examining seven patients who tested all donor and did not relapse. Although this initial threshold will need to be confirmed in a larger cohort, we detected increased recipient DNA above this threshold 90 to 145 days earlier than microsatellite positivity, and 127 to 142 days before clinical relapse in four of eight patients (50%). Haplotype counting using these novel loci may be useful for ultrasensitive detection in fields such as bone marrow transplantation, solid organ transplant rejection, patient identification, and forensics.

Transplantation Tolerance through Hematopoietic Chimerism: Progress and Challenges for Clinical Translation

The perception that transplantation of hematopoietic stem cells can confer tolerance to any tissue or organ from the same donor is widely accepted but it has not yet become a treatment option in clinical routine. The reasons for this are multifaceted but can generally be classified into safety and efficacy concerns that also became evident from the results of the first clinical pilot trials. In comparison to standard immunosuppressive therapies, the infection risk associated with the cytotoxic pre-conditioning necessary to allow allogeneic bone marrow engraftment and the risk of developing graft-vs.-host disease (GVHD) constitute the most prohibitive hurdles. However, several approaches have recently been developed at the experimental level to reduce or even overcome the necessity for cytoreductive conditioning, such as costimulation blockade, pro-apoptotic drugs, or Treg therapy. But even in the absence of any hazardous pretreatment, the recipients are exposed to the risk of developing GVHD as long as non-tolerant donor T cells are present. Total lymphoid irradiation and enriching the stem cell graft with facilitating cells emerged as potential strategies to reduce this peril. On the other hand, the long-lasting survival of kidney allografts, seen with transient chimerism in some clinical series, questions the need for durable chimerism for robust tolerance. From a safety point of view, loss of chimerism would indeed be favorable as it eliminates the risk of GVHD, but also complicates the assessment of tolerance. Therefore, other biomarkers are warranted to monitor tolerance and to identify those patients who can safely be weaned off immunosuppression. In addition to these safety concerns, the limited efficacy of the current pilot trials with approximately 40-60% patients becoming tolerant remains an important issue that needs to be resolved. Overall, the road ahead to clinical routine may still be rocky but the first successful long-term patients and progress in pre-clinical research provide encouraging evidence that deliberately inducing tolerance through hematopoietic chimerism might eventually make it from dream to reality.

HSCT-Based Approaches for Tolerance Induction in Renal Transplant

Renal transplantation has become the preferred treatment for end stage kidney failure. Although short-term graft survival has significantly improved as advances in immunosuppression have occurred, long-term patient and graft survival have not. Approximately only 50% of renal transplant recipients are alive at 10 years due to the toxicities of immunosuppression and alloimmunity. Emerging research on cell-based therapies is opening a new door for patients to receive the organs they need without sacrificing quality of life and longevity because of drug-based immunosuppression. Research has focused on inducing tolerance, a state in which the body accepts the transplant and graft function is stable. Cell-based therapies to facilitate chimerism and achieve tolerance in major histocompatibility disparate recipients have been developed in mouse, swine, canine, and nonhuman primate models. These findings are now being translated into the clinic in several trials currently underway. Protocols that use a combination of traditional therapeutic agents paired with cell populations including hematopoietic stem cells, regulatory T cells, and facilitating cells are being conducted with the objective to harness the donor immune system to protect the transplanted tissue. The benefits and feasibility of the clinical application of cell-based therapy has been demonstrated, and promising results have been achieved. Here we discuss the preclinical work that has led to the clinical application of the various approaches and a summary of the most current clinical data from groups throughout the world.

Outcomes of Unrelated Donor Stem Cell Transplantion with Post-Transplant Cyclophosphamide for Graft-versus-Host Disease Prophylaxis in Patients with Severe Sickle Cell Disease

Unrelated donor (URD) hematopoietic cell transplantation (HCT) in children with sickle cell disease (SCD) is associated with a high incidence of rejection and graft-versus-host disease (GVHD). We report on the first 4 patients with severe SCD who underwent URD HCT using a novel myeloablative and immunosuppressive regimen composed of busulfan, fludarabine, and antithymocyte globulin with a single dose of post-transplant cyclophosphamide along with tacrolimus and mycophenolate mofetil for GVHD prophylaxis. Three patients engrafted and remain disease-free after a median follow-up period of 2.5 years. One patient had primary graft failure attributed to low stem cell content of the graft. Of interest, none of the engrafted patients developed acute or chronic GVHD. This preparative regimen along with the use of post-transplant cyclophosphamide offers a promising approach for unrelated donor transplants in patients with SCD and needs further corroboration in larger number of patients.