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

Hematopoietic stem cell transplantation in children with chronic granulomatous disease: the Spanish experience

Introduction

Hematopoietic stem cell transplantation (HCT) can cure chronic granulomatous disease (CGD). However, transplant-associated morbidity or mortality may occur, and it is still controversial which patients benefit from this procedure. The aim of this retrospective study was to evaluate the outcome of pediatric patients who received HCT in one of the Spanish pediatric transplant units.

Results

Thirty children with a median age of 6.9 years (range 0.6-12.7) were evaluated: 8 patients received a transplant from a sibling donor (MSD), 21 received a transplant from an unrelated donor (UD), and 1 received a haploidentical transplant. The majority of the patients received reduced-intensity conditioning regimens based on either busulfan plus fludarabine or treosulfan. Relevant post-HCT complications were as follows: i) graft failure (GF), with a global incidence of 28.26% (CI: 15.15-48.88), 11.1% in patients with MSD (1.64-56.70) and 37.08% in unrelated donors (19.33-63.17); and ii) chronic graft-versus-host disease (GVHD), with an incidence of 20.5% (8.9-43.2), 11.1% in patients with MSD (1.64-56.70) and 26.7% in unrelated donors (10.42-58.44). Post-HCT infections were usually manageable, but two episodes of pulmonary aspergillosis were diagnosed in the context of graft rejection. The 2-year OS was 77.3% (55.92-89.23). There were no statistically significant differences among donor types.

Discussion

HCT in patients with CGD is a complex procedure with significant morbidity and mortality, especially in patients who receive grafts from unrelated donors. These factors need to be considered in the decision-making process and when discussing conditioning and GVHD prophylaxis.

Outcome of Second Allogeneic HSCT for Patients with Inborn Errors of Immunity: Retrospective Study of 20 Years' Experience

A significant complication of HSCT is graft failure, although few studies focus on this problem in patients with inborn errors of immunity (IE). We explored outcome of second HSCT for IEI by a retrospective, single-centre study between 2002 and 2022. Four hundred ninety-three patients underwent allogeneic HSCT for severe combined immunodeficiency (SCID; n = 113, 22.9%) or non-SCID IEI (n = 380, 77.1%). Thirty patients (6.0%) required second HSCT. Unconditioned infusion or no serotherapy at first HSCT was more common in patients who required second transplant. Median interval between first and second HSCT was 0.97 years (range: 0.19-8.60 years); a different donor was selected for second HSCT in 24/30 (80.0%) patients. Conditioning regimens for second HSCT were predominately treosulfan-based (with thiotepa: n = 18, 60.0%; without, n = 6, 20.0%). Patients received grafts from peripheral blood stem cell (n = 25, 83.3%) or bone marrow (n = 5, 16.7%) with median stem cell dose 9.5 × 106 CD34 + cells/kilogram (range: 1.4-32.3). Median follow-up was 1.92 years (0.22-16.0). Overall survival was 80.8% and event-free survival was 64.7%. Four patients died, two of early-transplant related complications, and two of late sepsis post-second HSCT. Three patients required third HSCT; all are alive with 100% donor chimerism. Cumulative incidence of acute graft-versus-host disease was 28.4%, (all grade I-II). Viral reactivation was seen in 13/30 (43.3%) patients, including HHV6 (n = 6), CMV (n = 4), and adenovirus (n = 2). At latest follow-up, 25/26 surviving patients have donor chimerism ≥ 90% and 16/25 (64.0%) have discontinued immunoglobulin replacement. Second HSCT offers IEI patients with graft failure curative treatment with good overall survival and immunological recovery.

Post-transplantation cyclophosphamide as GVHD prophylaxis in allogenic hematopoietic stem cell transplantation: Recent advances and modification

Allogenic hematopoietic stem cell transplantation (allo-HSCT) is the most important therapeutic option for hematological disorders, although graft-versus-host disease (GVHD) remains the main cause of mortality. Post-transplantation cyclophosphamide (PTCY) induces immune tolerance and is associated with a low incidence of GVHD and non-relapse mortality. Therefore, PTCY has emerged as a safe and effective GVHD prophylaxis in haploidentical transplantation and has been expanded to matched related or unrelated donor and mismatched unrelated donor HSCT. On the basis of current understanding of the mechanisms of PTCY and antithymocyte globulin (ATG) in the prevention of GVHD, growing evidence suggests that the combination of ATG and PTCY could improve allo-HSCT clinical outcomes. Further research will focus on optimizing PTCY regimens by modifying the timing of administration or adding other immunosuppressive agents.

Successful treatment of DOCK8 deficiency by allogeneic hematopoietic cell transplantation from alternative donors

Dedicator of cytokinesis 8 (DOCK8) deficiency is a rare autosomal recessive inborn error of immunity (IEI) characterized by eczematous dermatitis, elevated serum IgE, and recurrent infections, comprising a seemingly hyper-IgE syndrome (HIES). DOCK8 deficiency is only curable with allogeneic hematopoietic cell transplantation (HCT), but the outcome of HCT from alternative donors is not fully understood. Here, we describe the cases of two Japanese patients with DOCK8 deficiency who were successfully treated by allogeneic HCT from alternative donors. Patient 1 underwent cord blood transplantation at the age of 16 years, and Patient 2 underwent haploidentical peripheral blood stem cell transplantation with post-transplant cyclophosphamide at the age of 22 years. Each patient received a fludarabine-based conditioning regimen. Their clinical manifestations, including refractory molluscum contagiosum, promptly improved post-HCT. They achieved successful engraftment and immune reconstitution without serious complications. Alternative donor sources such as cord blood and haploidentical donors can be options for allogeneic HCT for DOCK8 deficiency.

Fatal Severe Cytokine Release Syndrome Post-haploidentical Stem Cell Transplant With Post-transplant Cyclophosphamide in an Infant With Severe Combined Immunodeficiency and Disseminated Bacille Calmette-Guérin Infection

INTRODUCTION

Severe Combined Immunodeficiency (SCID) is a primary immunodeficiency disorder characterized by absent or dysfunctional T lymphocytes, leading to defective cellular and humoral immunity requiring urgent hematopoietic stem cell transplantation (HSCT). We report a case of SCID with disseminated Bacille Calmette-Guérin (BCG) infection who developed cytokine release syndrome (CRS) and possible Immune reconstitution inflammatory syndrome (IRIS) after Haploidentical HSCT with post-transplant cyclophosphamide.

METHODS

Data were retrospectively retrieved from electronic medical records.

RESULT

A 5-month-old male infant was referred with fever, cough, and generalized maculopapular rash for 15 days, and had pallor without hepatosplenomegaly or lymphadenopathy. He had a history of previous male sibling death at 6 months of age due to pneumonia. Investigations: hemoglobin: 4.7 g/dL, TLC-6.37×103/uL, absolute lymphocytes: 0.98×103/uL, platelets: 319×103/uL, bilateral patchy opacities in both lung fields, and low immunoglobulin levels. Lymphocyte subset analysis revealed T-, B+, NK- SCID. Genetic analysis showed a hemizygous mutation in IL2RG (c.314A>G). The child received intravenous (IV) antibiotics, antifungal, antitubercular drugs, irradiated blood products, and IV immunoglobulins. Urgent haploidentical HSCT from the mother was planned. Conditioning was Fludarabine-40 mg/m2/d for 4 days, cyclophosphamide: 14.5 mg/kg/d for 2 days. He received peripheral blood hematopoietic stem cells with CD34- 15×106 cells/kg and CD3- 805×106 cells/kg. Within 2 hours of stem cell infusion, he developed respiratory distress, fever, shock, and flaring of rash. Methylprednisolone was started in view of CRS. On day+2, he had sudden desaturation and bradycardia needing mechanical ventilation and inotropes. His inflammatory markers were elevated (Ferritin: 3640 ng/mL, IL-6:5000 pg/mL, CRP:255 mg/L). In view of high-grade CRS, he received an injection of tocilizumab 8 mg/kg on day +2 and day +4. He received post-transplant cyclophosphamide 5 mg/kg on day +3. The endotracheal secretion GeneXpert was positive for Mycobacterium supporting the diagnosis of disseminated tuberculosis. Our patient had disseminated BCG infection which could also be contributory in the initiation of IRIS as the mother was immunized with the BCG vaccine in childhood so she must be having cytotoxic T cells specific for BCG, which were transferred to the infant with peripheral blood stem cell product. He succumbed to severe acute respiratory distress syndrome and multiorgan dysfunction on day +5 post-transplant.

CONCLUSIONS

In haploidentical HSCT of SCID, post-transplant course can be complicated by CRS and IRIS as these patients are inefficient in mounting any response to infused donor lymphocytes resulting in their unregulated growth.

Chronic graft-versus-host-disease treatment in Brazil: analyses of failure-free survival

Failure-free survival (FFS), defined as the absence of new systemic treatment, recurrence of original malignancy and mortality not associated with recurrence after allogeneic hematopoietic stem cell transplantation (HCT), is a robust clinical measure to interpret results of initial systemic treatment of chronic graft-versus-host disease (cGVHD). We evaluate FFS after initial treatment of cGVHD in a mixed-race cohort from a resource-constrained country. This retrospective study included 354 consecutive patients after their first HCT between January 2014 and August 2020, who received initial systemic treatment for moderate or severe cGVHD at 13 Brazilian centers. Cox regression models were used to identify risk factors for treatment failure. The overall median follow-up among survivors was 28 months (range 1-71) after initial treatment. FFS was 89% at 6 months, 71% at 1 year and 52% at 2 years. New systemic treatment was the major cause of failure. In multivariable models, prior grades II-IV acute GVHD, a National Institutes of Health severity score of 3 in liver, gastrointestinal tract or lung involvement, and onset of initial treatment of cGVHD within 12 months after transplantation were all associated with an increased risk of treatment failure. Our results could serve as a benchmark for the design of future clinical trials evaluating initial treatment of cGVHD in resource-constrained locations.

Second allogeneic hematopoietic stem cell transplantation in patients with inborn errors of immunity

Graft failure (GF) remains a serious issue of hematopoietic stem cell transplantation (HSCT) in inborn errors of immunity (IEI). Second HSCT is the only salvage therapy for GF. There are no uniform strategies for the second HSCTs and limited data are available on the second HSCT outcomes. 48 patients with various IEI received second allogeneic HSCT from 2013 to 2020. Different conditioning regimens were used, divided into two main groups: containing myeloablative doses of busulfan/treosulfan (n = 19) and lymphoid irradiation 2-6 Gy (n = 22). Irradiation-containing conditioning was predominantly used in suspected immune-mediated rejection of the first graft. Matched unrelated donor was used in 28 patients, mismatched related in 18, and matched related in 1. 35 patients received TCRαβ/CD19 graft depletion. The median follow-up time was 2.4 years post-HSCT. One patient died at conditioning. The OS was 0.63 (95% CI: 0.41-0.85) after busulfan/treosulfan and 0.68 (95% CI: 0.48-0.88) after irradiation-based conditioning, p = 0.66. Active infection at HSCT significantly influenced OS: 0.43 (95% CI: 0.17-0.69) versus 0.73 (95% CI: 0.58-0.88) without infection, p = 0.004. The cumulative incidence of GF was 0.15 (95% CI: 0.08-0.29). To conclude, an individualized approach is required for the second HSCT in IEI. Low-dose lymphoid irradiation in suspected immune-mediated GF may be a feasible option.

Hypomorphic RAG deficiency: impact of disease burden on survival and thymic recovery argues for early diagnosis and HSCT

Patients with hypomorphic mutations in the RAG1 or RAG2 gene present with either Omenn syndrome or atypical combined immunodeficiency with a wide phenotypic range. Hematopoietic stem cell transplantation (HSCT) is potentially curative, but data are scarce. We report on a worldwide cohort of 60 patients with hypomorphic RAG variants who underwent HSCT, 78% of whom experienced infections (29% active at HSCT), 72% had autoimmunity, and 18% had granulomas pretransplant. These complications are frequently associated with organ damage. Eight individuals (13%) were diagnosed by newborn screening or family history. HSCT was performed at a median of 3.4 years (range 0.3-42.9 years) from matched unrelated donors, matched sibling or matched family donors, or mismatched donors in 48%, 22%, and 30% of the patients, respectively. Grafts were T-cell depleted in 15 cases (25%). Overall survival at 1 and 4 years was 77.5% and 67.5% (median follow-up of 39 months). Infection was the main cause of death. In univariable analysis, active infection, organ damage pre-HSCT, T-cell depletion of the graft, and transplant from a mismatched family donor were predictive of worse outcome, whereas organ damage and T-cell depletion remained significant in multivariable analysis (hazard ratio [HR] = 6.01, HR = 8.46, respectively). All patients diagnosed by newborn screening or family history survived. Cumulative incidences of acute and chronic graft-versus-host disease were 35% and 22%, respectively. Cumulative incidences of new-onset autoimmunity was 15%. Immune reconstitution, particularly recovery of naïve CD4+ T cells, was faster and more robust in patients transplanted before 3.5 years of age, and without organ damage. These findings support the indication for early transplantation.

Transplant for non-malignant disorders: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee report on the role of alternative donors, stem cell sources and graft engineering

Hematopoietic stem cell transplantation (HSCT) is curative for many non-malignant disorders. As HSCT and supportive care technologies improve, this life-saving treatment may be offered to more and more patients. With the development of new preparative regimens, expanded alternative donor availability, and graft manipulation techniques, there are many options when choosing the best regimen for patients. Herein the authors review transplant considerations, transplant goals, conditioning regimens, donor choice, and graft manipulation strategies for patients with non-malignant disorders undergoing HSCT.

How I prevent GVHD in high-risk patients: posttransplant cyclophosphamide and beyond

Advances in conditioning, graft-versus-host disease (GVHD) prophylaxis and antimicrobial prophylaxis have improved the safety of allogeneic hematopoietic cell transplantation (HCT), leading to a substantial increase in the number of patients transplanted each year. This influx of patients along with progress in remission-inducing and posttransplant maintenance strategies for hematologic malignancies has led to new GVHD risk factors and high-risk groups: HLA-mismatched related (haplo) and unrelated (MMUD) donors; older recipient age; posttransplant maintenance; prior checkpoint inhibitor and autologous HCT exposure; and patients with benign hematologic disorders. Along with the changing transplant population, the field of HCT has dramatically shifted in the past decade because of the widespread adoption of posttransplantation cyclophosphamide (PTCy), which has increased the use of HLA-mismatched related donors to levels comparable to HLA-matched related donors. Its success has led investigators to explore PTCy's utility for HLA-matched HCT, where we predict it will be embraced as well. Additionally, combinations of promising new agents for GVHD prophylaxis such as abatacept and JAK inhibitors with PTCy inspire hope for an even safer transplant platform. Using 3 illustrative cases, we review our current approach to transplantation of patients at high risk of GVHD using our modern armamentarium.

Controversies and expectations for the prevention of GVHD: A biological and clinical perspective

Severe acute and chronic graft versus host disease (GVHD) remains a major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation. Historically, cord blood and matched sibling transplantation has been associated with the lowest rates of GVHD. Newer methods have modified the lymphocyte components to minimize alloimmunity, including: anti-thymocyte globulin, post-transplant cyclophosphamide, alpha/beta T cell depletion, and abatacept. These agents have shown promise in reducing severe GVHD, however, can be associated with increased risks of relapse, graft failure, infections, and delayed immune reconstitution. Nonetheless, these GVHD prophylaxis strategies have permitted expansion of donor sources, especially critical for those of non-Caucasian decent who previously lacked transplant options. This review will focus on the biologic mechanisms driving GVHD, the method by which each agent impacts these activated pathways, and the clinical consequences of these modern prophylaxis approaches. In addition, emerging novel targeted strategies will be described. These GVHD prophylaxis approaches have revolutionized our ability to increase access to transplant and have provided important insights into the biology of GVHD and immune reconstitution.

Case report: HLA-haploidentical hematopoietic cell transplant with posttransplant cyclophosphamide in a patient with leukocyte adhesion deficiency type I

Leukocyte adhesion deficiency type I (LAD-I) is a rare autosomal recessive inborn error of immunity (IEI) caused by the defects in CD18, encoded by the ITGB2 gene. LAD-I is characterized by defective leukocyte adhesion to the vascular endothelium and impaired migration of leukocytes. Allogeneic hematopoietic cell transplant (HCT) is the only curative treatment for LAD-I. In an absence of ideal donor for HCT, human leukocyte antigen (HLA)-haploidentical HCT is performed. Posttransplant cyclophosphamide (PT-CY) is a relatively new graft-versus-host disease (GVHD) prophylactic measure and has been increasingly used in HLA-haploidentical HCT for malignant and nonmalignant diseases. However, experience in using PT-CY for rare IEIs, such as LAD-I, is very limited. We report a case of LAD-I successfully treated with HLA-haploidentical HCT with PT-CY. Complete chimerism was achieved, and the patient was cured. Her transplant course was complicated by mild GVHD, cytomegalovirus reactivation and veno-occlusive disease/sinusoidal obstruction syndrome, which were successfully treated. HLA-haploidentical HCT with PT-CY is a safe and effective option for patients with LAD-I when HLA-matched donors are unavailable.

Haematopoietic stem cell transplantation for severe autoimmune diseases in children: A review of current literature, registry activity and future directions on behalf of the autoimmune diseases and paediatric diseases working parties of the European Society for Blood and Marrow Transplantation

Although modern clinical management strategies have improved the outcome of paediatric patients with severe autoimmune and inflammatory diseases over recent decades, a proportion will experience ongoing or recurrent/relapsing disease activity despite multiple therapies often leading to irreversible organ damage, and compromised quality of life, growth/development and long-term survival. Autologous and allogeneic haematopoietic stem cell transplantation (HSCT) have been used successfully to induce disease control and often apparent cure of severe treatment-refractory autoimmune diseases (ADs) in children. However, transplant-related outcomes are disease-dependent and long-term outcome data are limited in respect to efficacy and safety. Moreover, balancing risks of HSCT against AD prognosis with continually evolving non-transplant options is challenging. This review appraises published literature on HSCT strategies and outcomes in individual paediatric ADs. We also provide a summary of the European Society for Blood and Marrow Transplantation (EBMT) Registry, where 343 HSCT procedures (176 autologous and 167 allogeneic) have been reported in 326 children (<18 years) for a range of AD indications. HSCT is a promising treatment modality, with potential long-term disease control or cure, but therapy-related morbidity and mortality need to be reduced. Further research is warranted to establish the position of HSCT in paediatric ADs via registries and prospective clinical studies to support evidence-based interspeciality guidelines and recommendations.

Conditioning regimens for inborn errors of immunity: current perspectives and future strategies

Inborn errors of immunity (IEI) are caused by germline genetic mutations, resulting in defects of innate or acquired immunity. Hematopoietic cell transplantation (HCT) is indicated for curative therapy especially in patients with IEI who develop fatal opportunistic infections or severe manifestations of immune dysregulation. The first successful HCT for severe combined immunodeficiency (SCID) was reported in 1968. Since then, the indications for HCT have expanded from SCID to various non-SCID IEI. In general, HCT for IEI differs from that for other hematological malignancies in that the goal is not to eradicate certain immune cells but to achieve immune reconstitution. European Society for Blood and Marrow Transplantation/European Society for Immunodeficiencies guidelines recommend reduced-intensity conditioning to avoid treatment-related toxicity, and the optimal conditioning regimen should be considered for each IEI. We review conditioning regimens for some representative IEI disorders in Japanese and worldwide cohort studies, and future strategies for treating IEI.

Unresolved issues in allogeneic hematopoietic cell transplantation for non-malignant diseases

Allogeneic hematopoietic cell transplantation (HCT) can be curative for a variety of non-malignant diseases (NMDs) as well as hematological malignancies. However, there are several fundamental differences between HCT for NMDs and hematological malignancies, which may necessitate the use of alternative HCT strategies. For example, these diseases differ in the intensity of conditioning regimen sufficient to improve disease. In addition, patients with NMDs are at higher risk of graft failure or mixed chimerism following HCT, and gain no or little survival benefit from graft-versus-host disease. Because more than 80% of patients with NMDs become long-term survivors, greater attention has been paid to late adverse effects and decreased of quality of life after HCT. This review addresses several unresolved issues in allogeneic HCT for patients with NMDs, such as (1) stem cell source, (2) conditioning regimen, (3) use of serotherapy or low-dose irradiation, and (4) therapeutic intervention for mixed chimerism. Resolving these issues may improve transplant outcomes in patients with NMDs.

HAPLOIDENTICAL STEM CELL TRANSPLANTATION AFTER TCR αβ+AND CD19+ CELLS DEPLETION IN CHILDREN WITH CONGENITAL NON-MALIGNANT DISEASE

BACKGROUND

. Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) represents a valuable alternative for children with non-malignant disease and ex-vivo negative selection of TCR αβ⁺-cells is an emerging graft manipulation option that carries several potential advantages in terms of reduced risk of Graft versus Host Disease (GvHD) and improved immune reconstitution.

METHODS

. We reported all consecutive patients with a diagnosis of non-malignant disease who received a TCR-αβ⁺ and CD19⁺depleted haplo-HSCT at "IRCCS Istituto Giannina Gaslini" from 2013 to 2019; the conditioning regimen was myeloablative or non-myeloablative, depending on underlying disease; all patients received anti-thymocyte globulin and rituximab. No post-transplant GvHD prophylaxis was given in presence of a TCR-αβ⁺ cell-dose in the graft lower than the threshold of 1 × 10⁵/kg of the recipient's weight.

RESULTS

. Among 20 HSCTs, engraftment occurred in 17 (85%) after a median of 14 and 12 days from graft infusion for neutrophils and platelets respectively. Primary graft failure was diagnosed in 3 (15%) patients, two (10%) experienced secondary rejection; all of these underwent a second HSCT. The cumulative incidence of a-GvHD and c-GvHD was 15% (2 grade 1, 1 grade 4) at 90 days and 5% (1 grade 1) at 7 months, respectively. Cytomegalovirus reactivation requiring pre-emptive treatment was observed in 9 patients (45%). One patient developed a JC virus-related progressive multifocal leukoencephalopathy, successfully managed with donor-derived virus-specific T-cell infusions. A complete immunological recovery was reached in most patients within 6 months. After a median follow-up of 4 years, 18 patients are alive, with a cumulative survival probability of 90%.

CONCLUSION

. Haplo-HSCT after ex-vivo TCR-αβ⁺/CD19⁺ negative selection may be considered a good option for children with non-malignant diseases since it ensures a high engraftment rate with an acceptable risk of graft failure, very low incidence of significant GvHD, and good immune reconstitution with low frequency of severe virus-related disease. However, the control of viral infection/reactivation should be kept high in order to promptly provide pre-emptive treatments and approaches of antiviral adoptive immunotherapy.

Increasing access to hematopoietic cell transplantation in Latin America: results of the 2018 LABMT activity survey and trends since 2012

A total of 5642 hematopoietic cell transplants (HCT) in 5445 patients (2196-40% allogeneic and 3249-60% autologous) were reported by 127 teams in 14 Latin American countries that answered the 2018 LABMT/WBMT Global Transplant Activity survey. The transplant rate (defined as the number of first transplants per 10 million inhabitants per year) was 85 (51 autologous and 34 allogeneic) in 2018. The main indications for allogeneic HCT were acute leukemias (60%), while plasma cell disorders and lymphomas were the most common conditions warranting autologous HCT (50 and 36%, respectively). In the allogeneic HCT, HLA-identical siblings were the main type of donor (44%) followed by related mismatched/haploidentical donors (32%). Peripheral blood stem cells were used in 98% of the autologous and in 64% of the allogeneic transplants. From 2012 to 2018, there was a 64% increase of reported HCT (54% in autologous and 80% in allogeneic). In the allogeneic setting, the most pronounced increase in donor type was observed in haploidentical relatives (from 94 procedures in 2012 up to 710 in 2018), surpassing unrelated donors as of 2017. Significant trends detected in Latin America include rising numbers of the procedures reported, a faster increase in allogeneic HCT compared with autologous HCT and a significant increase in family mismatched/haploidentical donors. The LABMT/WBMT activity survey provides useful data to understand the HCT activity and trends in Latin America.

Pediatric immune deficiencies: current treatment approaches

PURPOSE OF REVIEW

To summarize the currently available definitive therapies for patients with inborn errors of immunity (IEIs) with a strong focus on recent advances in allogeneic hematopoietic cell transplantation (HCT) and gene therapy, including the use of alternative donors, graft manipulation techniques, less toxic approaches for pretransplant conditioning and gene transfer using autologous hematopoietic stem cells.

RECENT FINDINGS

In the absence of a matched sibling or a matched related donor, therapeutic alternatives for patients with IEIs include alternative donor transplantation or autologous gene therapy, which is only available for selected IEIs. In recent years, several groups have published their experience with haploidentical hematopoietic cell transplantation (HHCT) using different T-cell depletion strategies. Overall survival and event free survival results, although variable among centers, are encouraging. Preliminary results from autologous gene therapy trials with safer vectors and low-dose busulfan conditioning have shown reproducible and successful results. Both strategies have become valid therapeutic options for patients with IEIs. A new promising and less toxic conditioning regimen strategy is also discussed.

SUMMARY

Definitive therapies for IEIs with HCT and gene therapy are in stage of evolution, not only to refine their efficacy and safety but also their reach to a larger number of patients.

Gene Editing of Hematopoietic Stem Cells: Hopes and Hurdles Toward Clinical Translation

In the field of hematology, gene therapies based on integrating vectors have reached outstanding results for a number of human diseases. With the advent of novel programmable nucleases, such as CRISPR/Cas9, it has been possible to expand the applications of gene therapy beyond semi-random gene addition to site-specific modification of the genome, holding the promise for safer genetic manipulation. Here we review the state of the art of ex vivo gene editing with programmable nucleases in human hematopoietic stem and progenitor cells (HSPCs). We highlight the potential advantages and the current challenges toward safe and effective clinical translation of gene editing for the treatment of hematological diseases.

Case Report: Haploidentical Bone Marrow Transplantation in Two Brothers With Wiskott-Aldrich Syndrome Using Their Father as the Donor

Wiskott-Aldrich syndrome (WAS) is an X-linked genetic disorder with a variable phenotypic expression that includes thrombocytopenia, eczema, and immunodeficiency. Some patients may also exhibit autoimmune manifestations. Patients with WAS are at increased risk of developing malignancies such as lymphoma. Allogeneic hematopoietic cell transplantation remains the only curative treatment. Haploidentical bone marrow transplantation (haplo-BMT) with post-transplant cyclophosphamide (PT-CY) has more recently been applied in WAS. Here, we report two brothers who underwent successful T-cell replete haplo-BMT with PT-CY at ages 9 months and 4 years using their father as the donor. Our myeloablative regimen was well-tolerated with minimal organ toxicity and no acute or chronic graft vs. host disease (GvHD). Haplo-BMT may be considered as a safe and effective option for patients with WAS who do not have available human leukocyte antigen (HLA) matched donors.

Hematopoietic cell transplantation in severe combined immunodeficiency: The SCETIDE 2006-2014 European cohort

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) represents a curative treatment for patients with severe combined immunodeficiency (SCID), a group of monogenic immune disorders with an otherwise fatal outcome.

OBJECTIVE

We performed a comprehensive multicenter analysis of genotype-specific HSCT outcome, including detailed analysis of immune reconstitution (IR) and the predictive value for clinical outcome.

METHODS

HSCT outcome was studied in 338 patients with genetically confirmed SCID who underwent transplantation in 2006-2014 and who were registered in the SCETIDE registry. In a representative subgroup of 152 patients, data on IR and long-term clinical outcome were analyzed.

RESULTS

Two-year OS was similar with matched family and unrelated donors and better than mismatched donor HSCT (P < .001). The 2-year event-free survival (EFS) was similar in matched and mismatched unrelated donor and less favorable in mismatched related donor (MMRD) HSCT (P < .001). Genetic subgroups did not differ in 2-year OS (P = .1) and EFS (P = .073). In multivariate analysis, pretransplantation infections and use of MMRDs were associated with less favorable OS and EFS. With a median follow-up of 6.2 years (range, 2.0-11.8 years), 73 of 152 patients in the IR cohort were alive and well without Ig dependency. IL-2 receptor gamma chain/Janus kinase 3/IL-7 receptor-deficient SCID, myeloablative conditioning, matched donor HSCT, and naive CD4 T lymphocytes >0.5 × 10^e3/μL at +1 year were identified as independent predictors of favorable clinical and immunologic outcome.

CONCLUSION

Recent advances in HSCT in SCID patients have resulted in improved OS and EFS in all genotypes and donor types. To achieve a favorable long-term outcome, treatment strategies should aim for optimal naive CD4 T lymphocyte regeneration.

TCRαβ/CD19 depleted HSCT from an HLA-haploidentical relative to treat children with different non-malignant disorders

Several non-malignant disorders (NMDs), either inherited or acquired, can be cured by allogeneic hematopoietic stem cell transplantation (HSCT). Between January 2012 and April 2020, 70 consecutive children affected by primary immunodeficiencies, inherited/acquired bone marrow failure syndromes, red blood cell disorders or metabolic diseases, lacking a fully-matched donor or requiring urgent transplantation, underwent TCRαβ/CD19-depleted haploidentical HSCT from an HLA-partially matched relative as part of a prospective study (#NCT01810120). Median age at transplant was 3.5 years (range 0.3-16.1); median time from diagnosis to transplant was 10.5 months (2.7 for SCID patients). Primary engraftment was obtained in 51 patients, while 19 and 2 patients experienced either primary or secondary graft failure (GF), the overall incidence of this complication being 30.4%. Most GFs were observed in children with disease at risk for this complication (e.g., aplastic anemia, thalassemia). All but 5 patients experiencing GF were successfully retransplanted. Six patients died of infectious complications (4 had active/recent infections at time of HSCT), the cumulative incidence of transplant-related mortality (TRM) being 8.5%. Cumulative incidence of grade I-II acute GvHD was 14.4% (no patient developed grade III-IV acute GVHD). Only one patient at risk developed mild chronic GvHD. With a median follow-up of 3.5 years, the 5-year probability of overall and disease-free survival was 91.4% and 86.8%, respectively. In conclusion, TCRαβ/CD19-depleted haploidentical HSCT from an HLA-partially matched relative is confirmed to be an effective treatment for children with NMDs. Prompt donor availability, low incidence of GvHD and TRM make this strategy an attractive option in NMDs patients.

Hematopoietic Stem Cell Therapy for Wiskott-Aldrich Syndrome: Improved Outcome and Quality of Life

The Wiskott-Aldrich syndrome (WAS) is an X-linked disorder caused by mutations in the WAS gene resulting in congenital thrombocytopenia, eczema, recurrent infections and an increased incidence of autoimmune diseases and malignancies. Without curative therapies, affected patients have diminished life expectancy and reduced quality of life. Since WAS protein (WASP) is constitutively expressed only in hematopoietic stem cell-derived lineages, hematopoietic stem cell transplantation (HSCT) and gene therapy (GT) are well suited to correct the hematologic and immunologic defects. Advances in high-resolution HLA typing, new techniques to prevent GvHD allowing the use of haploidentical donors, and the introduction of reduced intensity conditioning regimens with myeloablative features have increased overall survival (OS) to over 90%. The development of GT for WAS has provided basic knowledge into vector selection and random integration of various viral vectors into the genome, with the possibility of inducing leukemogenesis. After trials and errors, inactivating lentiviral vectors carrying the WAS gene were successfully evaluated in clinical trials, demonstrating cure of the disease except for insufficient resolution of the platelet defect. Thus, 50 years of clinical evaluation, genetic exploration and extensive clinical trials, a lethal syndrome has turned into a curable disorder.