Reduced-intensity conditioning for hematopoietic cell transplant for HLH and primary immune deficiencies

Late effects after allogeneic haematopoietic cell transplantation in children and adolescents with non-malignant disorders: a retrospective cohort study

BACKGROUND

Continued advances in haematopoietic cell transplantation (HCT) for children with non-malignant diseases (NMDs) have led to a growing population of survivors in whom late occurring toxic effects remain a challenge. We investigated the incidence of and risk factors for post-transplant toxicities in a contemporary cohort of children and adolescents undergoing HCT for NMDs.

METHODS

In this retrospective cohort study, we extracted data from the Center for International Blood and Marrow Transplantation Research (CIBMTR) database to analyse timing and incidence of effects and risk factors associated with late effects of HCT for treatment of NMDs at age 21 years or younger. Late effects of interest were avascular necrosis, cataracts, congestive heart failure, myocardial infarction, diabetes, gonadal dysfunction, growth hormone deficiency, hypothyroidism, renal failure requiring dialysis, and neurological events (stroke and seizure). Cumulative incidence of each late effect was calculated at 5 years and 7 years after HCT. Risk factors were evaluated in Cox proportional hazards regression analyses. Main exposures were primary NMD, age, sex, ethnicity and race, insurance, donor and graft type, myoablative conditioning, total-body irradiation exposure, graft-versus-host disease (GVHD), and transplant year. Primary outcomes were rates, cumulative incidence probability (95% CI), and risk-factors for organ-specific late effects.

FINDINGS

Between Jan 1, 2000, and Dec 31, 2017, 7785 patients aged 21 years or younger underwent HCT. 1995 patients were ineligible or did not consent to be included. 5790 patients from 171 centres were included in the analysis. 3505 (60·5%) of 5790 patients were male and 2285 (39·5%) were female. 2106 (36·4%) patients were White, 771 (13·3%) were Hispanic, and 773 (12·7%) were Black. 1790 (30·9%) patients were non-USA residents. Median age at HCT was 5·5 years (range 0·0-21·0). 1127 (19%) of 5790 patients had one late effect, and 381 (7%) had at least two. At 7 years post-HCT, the cumulative incidence probability was 1·9 (95% CI 1·5-2·3) for cataracts, 4·9 (4·3-5·6) for diabetes, 2·6 (2·1-3·1) for gonadal dysfunction, 3·2 (2·7-3·8) for hypothyroidism, 5·0 (4·4-5·7) for growth disturbance, 8·1 (7·4-8·9) for renal failure, 1·6 (1·3-2·0) for avascular necrosis, 0·6 (0·4-0·8) for congestive heart failure, 0·2 (0·1-0·3) for myocardial infarction, and 9·4 (8·6-10·2) for neurological effects. Age 10 years or older at HCT, unrelated donor source, total-body irradiation, and GVHD were identified as risk factors for long-term effects.

INTERPRETATION

The findings highlight the need for, and access to, multidisciplinary and lifelong follow-up for children undergoing HCT for NMDs. As more children undergo treatment with cellular therapies for non-malignant conditions, further analyses of post-transplant data could increasingly guide treatment decisions and subsequent long-term surveillance.

FUNDING

National Cancer Institute, National Heart, Lung and Blood Institute, National Institute of Allergy and Infectious Diseases, Health Resources and Services Administration, and Office of Naval Research.

Hematopoietic stem cell transplantation for B-thalassemia major with alemtuzumab

While matched related donor (MRD) allogeneic hematopoietic stem cell transplantation (HSCT) is a curative option for transfusion-dependent beta-thalassemia (TDT), the use of alternative sources has increased, resulting in the exploration of novel transplant-conditioning regimens to reduce the contribution of graft-versus-host disease (GVHD) and graft failure (GF) to transplant-related morbidity and mortality. Alemtuzumab is a CD52 monoclonal antibody that has been successfully incorporated into myeloablative conditioning regimens for other hematologic conditions, yet there have been limited studies regarding the use of alemtuzumab in HSCT for TDT. The purpose of this study was to evaluate engraftment, incidence of GVHD, and transplant related morbidity and mortality in patients with TDT who received alemtuzumab in addition to standard busulfan-based conditioning. The primary endpoint was severe GVHD-free, event-free survival (GEFS). Our cohort included 24 patients with a median age of 6.8 years (range 1.5-14.9). Eleven patients received a 10/10 MRD HSCT, eleven 10/10 unrelated donor (UD), and two mismatched UD. All patients achieved primary engraftment. For all patients, 5-year GEFS was 77.4% and 5-year overall survival (OS) was 91%. The 5-year cumulative incidence of GF (attributed to poor graft function) without loss of donor chimerism was 13.8% (95% CI: 4.5, 35.3). We report low rates of significant acute GVHD grade II-IV (12.5%) and chronic GVHD (4.4%). Younger age and MRD were associated with significantly improved GEFS, OS and EFS. Our results show that the use of alemtuzumab promotes stable engraftment, may reduce rates of severe GVHD, and results in acceptable GEFS, OS, and EFS.

Sequential haplo-identical conditioning transplant regimen for pediatric patients with relapsed or refractory hemophagocytic lymphohistiocytosis

Allogeneic hematopoietic stem cell transplantation (HSCT) currently stands as the sole remedy for individuals afflicted with hemophagocytic lymphohistiocytosis (HLH). In this study, we retrospectively evaluated how pediatric patients with relapsed or refractory (R/R) HLH responded to our institution's cocktail conditioning regimen. The disease was diagnosed according to criteria applicable to patients with familial/genetic, relapsing, or severe/persistent HLH. All donors were HLA haplo-identical family donors. In our cohort, sixty-five patients (P-HLH), including 28 with familial/genetic HLH, 36 with secondary HLH, and 1 with an unknown cause, underwent haplo-identical family donor HSCT. The conditioning regimen consisted of intravenous administration of etoposide (VP-16), busulfan, fludarabine, rabbit anti-human thymocyte globulin (r-ATG), and cyclophosphamide (Cy). Tacrolimus and mycophenolate mofetil were used for graft-versus-host disease (GvHD) prevention. We observed that the median time for neutrophil recovery was 11 days (range, 8-24), and for platelet counts to exceed 20 × 109/L, it was 14 days (range, 7-130). There were 5 patients (7.7%) who experienced grades III to IV acute GvHD, and 6 patients (9.2%) developed extensive chronic GvHD. The estimated 3- and 5-year overall survival rates were 78.1% (95% CI, 65.8-84.6%) and 74.9% (95% CI, 61.2-84.4%), respectively. The estimated 3- and 5-year event-free survival rates were 73.5% (95% CI, 60.8-82.6%) and 70.3% (95% CI, 56.4-80.5%), respectively. Our findings demonstrate that our innovative conditioning regimen is both effective and safe, offering valuable insights for healthcare professionals evaluating the merits of existing therapies.

Survival in primary hemophagocytic lymphohistiocytosis, 2016 to 2021: etoposide is better than its reputation

ABSTRACT

Primary hemophagocytic lymphohistiocytosis (pHLH) is a life-threatening hyperinflammatory syndrome that develops mainly in patients with genetic disorders of lymphocyte cytotoxicity and X-linked lymphoproliferative syndromes. Previous studies with etoposide-based treatment followed by hematopoetic stem cell transplantation (HSCT) resulted in 5-year survival of 50% to 59%. Contemporary data are lacking. We evaluated 88 patients with pHLH documented in the international HLH registry from 2016-2021. In 12 of 88 patients, diagnosis was made without HLH activity, based on siblings or albinism. Major HLH-directed drugs (etoposide, antithymocyte globulin, alemtuzumab, emapalumab, ruxolitinib) were administered to 66 of 76 patients who were symptomatic (86% first-line etoposide); 16 of 57 patients treated with etoposide and 3 of 9 with other first-line treatment received salvage therapy. HSCT was performed in 75 patients; 7 patients died before HSCT. Three-year probability of survival (pSU) was 82% (confidence interval [CI], 72%-88%) for the entire cohort and 77% (CI, 64%-86%) for patients receiving first-line etoposide. Compared with the HLH-2004 study, both pre-HSCT and post-HSCT survival of patients receiving first-line etoposide improved, 83% to 91% and 70% to 88%. Differences to HLH-2004 included preferential use of reduced-toxicity conditioning and reduced time from diagnosis to HSCT (from 148 to 88 days). Three-year pSU was lower with haploidentical (4 of 9 patients [44%]) than with other donors (62 of 66 [94%]; P < .001). Importantly, early HSCT for patients who were asymptomatic resulted in 100% survival, emphasizing the potential benefit of newborn screening. This contemporary standard-of-care study of patients with pHLH reveals that first-line etoposide-based therapy is better than previously reported, providing a benchmark for novel treatment regimes.

Hematopoietic Bone Marrow Transplant to Treat Systemic EBV-positive T-cell Lymphoma of Childhood

Systemic Epstein-Barr virus-positive T-cell lymphoma of childhood (S-EBV-TCL) is a rare disease for which there is no standard of care. S-EBV-TCL is often associated with hemophagocytic lymphohistiocytosis and is generally thought of on the spectrum of EBV-related disease. For the few reported cases of cure in the literature, hematopoietic stem cell transplant has been required because it is the only treatment that has induced complete remission in patients suffering from EBV-associated T-cell or natural killer cell lymphoproliferative diseases, except hemophagocytic lymphohistiocytosis. Here, we present the case of one patient who was successfully cured with a modified regimen of dose-adjusted EPOCH (etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin), followed by hematopoietic stem cell transplant using a reduced-intensity conditioning regimen.

Salvage Therapy and Allogeneic Hematopoietic Cell Transplantation for the Severe Cytokine Storm Syndrome of Hemophagocytic Lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) can be considered as a severe cytokine storm syndrome disorder. HLH typically manifests as a life-threatening inflammatory syndrome characterized by fevers, cytopenias, hepatosplenomegaly, and various other accompanying manifestations such as coagulopathy, hepatitis or liver failure, seizures or altered mental status, and even multi-organ failure. Standard up-front treatments do not always bring HLH into remission or maintain adequate response, and salvage or alternative therapies are often needed. For patients with genetic diseases that cause HLH, curative allogeneic hematopoietic cell transplantation is usually offered to prevent future episodes of life-threatening HLH. Here, we will discuss the options and approaches for salvage therapy and hematopoietic cell transplantation for patients with HLH.

Age Impacts Risk of Mixed Chimerism Following Reduced-Intensity Conditioning Hematopoietic Cell Transplantation for Non-Severe Combined Immune Deficiency Inborn Errors of Immunity

Alemtuzumab, fludarabine, and melphalan containing-reduced intensity conditioning (RIC) is commonly used in patients undergoing allogeneic hematopoietic cell transplantation (HCT) for definitive treatment of high-risk inborn errors of immunity (IEI). Although survival is favorable, there is an increased risk of mixed chimerism leading to secondary graft failure. This study evaluated factors associated with the risk of developing mixed chimerism, particularly the influence of age in patients undergoing allogeneic HCT for non-severe combined immune deficiency (SCID) IEI who received a uniform RIC regimen that included intermediate schedule alemtuzumab, fludarabine, and melphalan. We hypothesized that age would impact the incidence of mixed chimerism. We retrospectively reviewed records of patients who underwent HCT for non-SCID IEI with a uniform RIC regimen that included intermediate schedule alemtuzumab (1 mg/kg divided over days -14 to -10), fludarabine (150 mg/m2 or 5 mg/kg if weight <10 kg divided over days -9 to -4), and melphalan (140 mg/m2 or 4.7 mg/kg if weight <10 kg on day -3) between 2010 and 2020 at our institution. Mixed chimerism was defined as <95% donor chimerism on 2 or more consecutive occasions in whole blood. Ninety-three patients who underwent RIC-HCT for non-SCID IEI using intermediate schedule alemtuzumab, fludarabine, and melphalan were categorized into 3 groups: age <1 year, age 1 to 5 years, and age >5 years. Forty-nine patients (52.7%) developed mixed chimerism, at a median of 34 days post-HCT (range, 10 to 1396 days). Mixed chimerism developed in 88.9% (n = 16/18) of the age <1 year group, in 57.1% (n = 20/35) of the age 1 to 5 years group, and in 35% (n =14/40) of the age >5 years group. Patients age <5 years were significantly more likely to develop mixed chimerism (χ2 (3, N = 93) = 14.8; P = .001). We observed a significantly increased cumulative incidence of developing mixed chimerism associated with age <1 year (P = .0002). Competing risk regression analysis showed a 3-fold higher risk of developing mixed chimerism for age <1 year (subdistribution hazard ratio (HR), 3.05; 95% confidence interval [CI], 1.11 to 8.38; P = .031,) compared to age >5 years and a significantly decreased risk of mixed chimerism in patients who developed acute GVHD prior to any intervention (OR, .24; 95% CI, .09 to .65; P = .005) There were no significant associations between mixed chimerism and graft source, graft type, CD34+ or CD3+ cell dose, HLA match, or underlying disease (hemophagocytic lymphohistiocytosis [HLH] versus non-HLH). Additionally, the need for secondary intervention was evaluated; 27 patients (29.0%) required 1 or more secondary interventions (donor lymphocyte infusion, CD34 boost, or second HCT). Patients age <1 year with mixed chimerism were significantly more likely than patients age >5 years to require secondary intervention for mixed chimerism (P = .004). Our study demonstrates that age <5 years, especially age <1 year, is associated with an increased risk of developing mixed chimerism in patients undergoing RIC-HCT for non-SCID IEI using intermediate-schedule alemtuzumab, fludarabine, and melphalan. Our data suggest tailoring regimen intensity based on age to reduce the incidence of mixed chimerism. Children age <5 years, particularly those age <1 year, require a higher-intensity regimen. Possible strategies include adding thiotepa or using a busulfan-based reduced toxicity regimen.

Exposure-response analysis of alemtuzumab in pediatric allogeneic HSCT for nonmalignant diseases: the ARTIC study

Alemtuzumab (anti-CD52 antibody) is frequently prescribed to children with nonmalignant diseases undergoing allogeneic hematopoietic stem cell transplantation (HSCT) to prevent graft failure (GF) and acute graft-versus-host disease (aGVHD). The aim of this multicenter study was the characterization of alemtuzumab population pharmacokinetics to perform a novel model-based exposure-response analysis in 53 children with nonmalignant immunological or hematological disease and a median age of 4.4 years (interquartile range [IQR], 0.8-8.7). The median cumulative alemtuzumab dose was 0.6 mg/kg (IQR, 0.6-1) administered over 2 to 7 days. A 2-compartment population pharmacokinetics model with parallel linear and nonlinear elimination including allometrically scaled bodyweight (median, 17.50 kg; IQR, 8.76-33.00) and lymphocyte count at baseline (mean, 2.24 × 109/L; standard deviation ± 1.87) as significant pharmacokinetic predictors was developed using nonlinear mixed effects modeling. Based on the model-estimated median concentration at day of HSCT (0.77 μg/mL; IQR, 0.33-1.82), patients were grouped into a low- (≤0.77 μg/mL) or high- (>0.77 μg/mL) exposure groups. High alemtuzumab exposure at day of HSCT correlated with delayed CD4+ and CD8+ T-cell reconstitution (P value < .0001) and increased risk of GF (P value = .043). In contrast, alemtuzumab exposure did not significantly influence the incidence of aGVHD grade ≥2, mortality, chimerism at 1 year, viral reactivations, and autoimmunity at a median follow-up of 3.3 years (IQR, 2.5-8.0). In conclusion, this novel population pharmacokinetics model is suitable for individualized intravenous precision dosing to predict alemtuzumab exposure in pediatric allogeneic HSCT for nonmalignant diseases, aiming at the achievement of early T-cell reconstitution and prevention of GF in future prospective studies.

Personalized hematopoietic stem cell transplantation for inborn errors of immunity

Patients with inborn errors of immunity (IEI) have been transplanted for more than 50 years. Many long-term survivors have ongoing medical issues showing the need for further improvements in how hematopoietic stem cell transplantation (HSCT) is performed if patients in the future are to have a normal quality of life. Precise genetic diagnosis enables early treatment before recurrent infection, autoimmunity and organ impairment occur. Newborn screening for severe combined immunodeficiency (SCID) is established in many countries. For newly described disorders the decision to transplant is not straight-forward. Specific biologic therapies are effective for some diseases and can be used as a bridge to HSCT to improve outcome. Developments in reduced toxicity conditioning and methods of T-cell depletion for mismatched donors have made transplant an option for all eligible patients. Further refinements in conditioning plus precise graft composition and additional cellular therapy are emerging as techniques to personalize the approach to HSCT for each patient.

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.

Favorable outcomes with durable chimerism after hematopoietic cell transplantation using busulfan and fludarabine-based reduced-intensity conditioning for pediatric patients with hemophagocytic lymphohistiocytosis

Background

The incorporation of a reduced-intensity conditioning (RIC) regimen in hematopoietic cell transplantation (HCT) for patients with hemophagocytic lymphohistiocytosis (HLH) has decreased early mortality but is associated with a high rate of mixed chimerism and graft failure. Here, we present a successful single-center experience using busulfan and a fludarabine-based RIC regimen for the treatment of HLH.

Methods

The medical records of pediatric patients with HLH who underwent HCT using a busulfan/fludarabine-based RIC regimen between January 2008 and December 2017 were reviewed retrospectively.

Results

Nine patients received HCT with a busulfan/fludarabine-based RIC regimen. Three patients had primary HLH, and the other six patients had secondary HLH with multiple reactivations. All three patients with primary HLH had UNC13D mutations. All patients achieved neutrophil and platelet engraftment at a median of 11 days (range, 10‒21) and 19 days (range, 13‒32), and all eight evaluable patients had sustained complete donor chimerism at the last follow-up. Two patients (22%) experienced grade 2 acute graft-versus-host disease (GVHD). Two patients (22%) developed chronic GVHD, and one died from chronic GVHD. One patient (11%) experienced reactivation 4 months after HCT from a syngeneic donor and died of the disease. The 8-year overall survival and event-free survival rates were 78%. No early treatment-related mortality within 100 days after HCT was observed.

Conclusion

Our experience suggests that a busulfan/fludarabine-based RIC regimen is a viable option for pediatric patients with HLH who require HCT.

Emerging approaches to improve allogeneic hematopoietic cell transplantation outcomes for nonmalignant diseases

Many congenital or acquired nonmalignant diseases (NMDs) of the hematopoietic system can be potentially cured by allogeneic hematopoietic cell transplantation (HCT) with varying types of donor grafts, degrees of HLA matching, and intensity of conditioning regimens. Unique features that distinguish the use of allogeneic HCT in this population include higher rates of graft failure, immune-mediated cytopenias, and the potential to achieve long-term disease-free survival in a mixed chimerism state. Additionally, in contrast to patients with hematologic malignancies, a priority is to completely avoid graft-versus-host disease in patients with NMD because there is no theoretical beneficial graft-versus-leukemia effect that can accompany graft-versus-host responses. In this review, we discuss the current approach to each of these clinical issues and how emerging novel therapeutics hold promise to advance transplant care for patients with NMDs.

The significance of mixed chimaerism and cell lineage chimaerism monitoring in paediatric patients post haematopoietic stem cell transplant

Haematopoietic stem cell transplants (HSCTs) are carried out across the world to treat haematological and immunological diseases which would otherwise prove fatal. Certain diseases are predominantly encountered in paediatric patients, such severe primary immunodeficiencies (PID) and diseases of inborn errors of metabolism (IEM). Chimaerism testing for these disorders has different considerations compared to adult diseases. This review focuses on the importance of cell-lineage-specific chimaerism testing and examines the appropriate cell populations to be assessed in individual paediatric patient groups. By analysing disease-associated subpopulations, abnormalities are identified significantly earlier than in whole samples and targeted clinical decisions can be made. Chimaerism methods have evolved over time and lead to an ever-increasing level of sensitivity and biomarker arrays to distinguish between recipient and donor cells. Short tandem repeat (STR) is still the gold standard for routine chimaerism assessment, and hypersensitive methods such as quantitative and digital polymerase chain reaction (PCR) are leading the forefront of microchimaerism testing. The rise of molecular methods operating with minute DNA amounts has been hugely beneficial to chimaerism testing of paediatric samples. As HSCTs are becoming increasingly personalised and risk-adjusted towards a child's individual needs, chimaerism testing needs to adapt alongside these medical advances ensuring the best possible care.

Allogeneic hematopoietic stem cell transplantation for adult HLH: a retrospective study by the chronic malignancies and inborn errors working parties of EBMT

Hemophagocytic lymphohistiocytosis (HLH; hemophagocytic syndrome) is a rare syndrome of potentially fatal, uncontrolled hyperinflammation. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is indicated in primary, recurrent or progressive HLH, but information about its outcomes in the adult population is limited. We obtained data about 87 adult (≥18 years of age) patients retrospectively reported to the EBMT. The median survival time was 13.9 months. The three and five-year overall survival (OS) was 44% (95% CI 33-54%). Among 39 patients with a follow-up longer than 15 months, only three died. Relapse rate was 21% (95% CI 13-30%), while NRM reached 36% (95% CI 25-46%). Younger patients (<30 years of age) had better prognosis, with an OS of 59% (95% CI 45-73%) at three and five years vs 23% (95% CI 8-37%) for older ones. No difference in survival between reduced and myeloablative conditioning was found. To our knowledge, this is the largest report of adult HLH patients who underwent allo-HSCT. Patients who survive the first period after this procedure can expect a long disease-free survival. Both reduced intensity and myeloablative conditioning have therapeutic potential in adult HLH.

Comparison of hematopoietic cell transplant conditioning regimens for hemophagocytic lymphohistiocytosis disorders

BACKGROUND

Allogeneic hematopoietic cell transplantation for hemophagocytic lymphohistiocytosis (HLH) disorders is associated with substantial morbidity and mortality.

OBJECTIVE

The effect of conditioning regimen groups of varying intensity on outcomes after transplantation was examined to identify an optimal regimen or regimens for HLH disorders.

METHODS

We studied 261 patients with HLH disorders transplanted between 2005 and 2018. Risk factors for transplantation outcomes by conditioning regimen groups were studied by Cox regression models.

RESULTS

Four regimen groups were studied: (1) fludarabine (Flu) and melphalan (Mel) in 123 subjects; (2) Flu, Mel, and thiotepa (TT) in 28 subjects; (3) Flu and busulfan (Bu) in 14 subjects; and (4) Bu and cyclophosphamide (Cy) in 96 subjects. The day 100 incidence of veno-occlusive disease was lower with Flu/Mel (4%) and Flu/Mel/TT (0%) compared to Flu/Bu (14%) and Bu/Cy (22%) (P < .001). The 6-month incidence of viral infections was highest after Flu/Mel (72%) and Flu/Mel/TT (64%) compared to Flu/Bu (39%) and Bu/Cy (38%) (P < .001). Five-year event-free survival (alive and engrafted without additional cell product administration) was lower with Flu/Mel (44%) compared to Flu/Mel/TT (70%), Flu/Bu (79%), and Bu/Cy (61%) (P = .002). The corresponding 5-year overall survival values were 68%, 75%, 86%, and 64%, and did not differ by conditioning regimen (P = .19). Low event-free survival with Flu/Mel is attributed to high graft failure (42%) compared to Flu/Mel/TT (15%), Flu/Bu (7%), and Bu/Cy (18%) (P < .001).

CONCLUSIONS

Given the high rate of graft failure with Flu/Mel and the high rate of veno-occlusive disease with Bu/Cy and Flu/Bu, Flu/Mel/TT may be preferred for HLH disorders. Prospective studies are warranted.

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.

Treosulfan-Based Conditioning in Matched Family, Unrelated and Haploidentical Hematopoietic Stem Cell Transplantation for Genetic Hemophagocytic Lymphohistiocytosis: Experience and Outcomes over 10 Years from India

We aimed to analyze data in children with primary hemophagocytic lymphohistiocytosis (HLH) who underwent hematopoietic stem cell transplantation (HSCT). We performed a retrospective study where children up to 18 years, with primary HLH and who underwent HSCT from January 2011 to December 2019, were included. Twenty-five children with genetic HLH underwent HSCT, including variants (Griscelli syndrome (GS2) 7, Chediak-Higashi syndrome (CHS) 2, XIAP mutation 2). Donors were matched family 8 (32%), umbilical cord blood unit 3 (12%), matched unrelated 2 (8%), haploidentical HSCT 12 (48%), (TCR alpha/beta depletion 2 and post-transplant cyclophosphamide 10). With treosulfan-based conditioning, engraftment was achieved in 23/25 (92%) transplants (100% in haplo-HSCT), with sustained complete chimerism in 87%. Disease-free survival was noted in 2/3 children with stable mixed chimerism. Graft-versus-host disease (GVHD) of grade I/II was noted in 6 (24%), grade III in 3 (13%); chronic limited skin GVHD in 2 (12%) children. Overall survival was 72% (87.5% in matched donor, 66.7% in the haplo-HSCT), 71% in GS2, 50% in CHS, 100% in XIAP. HSCT is curative in primary HLH with acceptable disease-free survival with mixed chimerism. Haplo-HSCT is a viable option for those without matched family or unrelated donors.

High risk of relapsed disease in patients with NK/T cell chronic active Epstein-Barr virus disease outside of Asia

Stem cell transplant improves long-term survival in T/NK CAEBV, though mortality remains high.

Development of T/NK lymphoma showed a trend with increased mortality.

Chronic active Epstein-Barr virus (EBV) disease (CAEBV) is characterized by high levels of EBV predominantly in T and/or natural killer cells with lymphoproliferation, organ failure due to infiltration of tissues with virus-infected cells, hemophagocytic lymphohistiocytosis, and/or lymphoma. The disease is more common in Asia than in the United States and Europe. Although allogeneic hematopoietic stem cell transplantation (HSCT) is considered the only curative therapy for CAEBV, its efficacy and the best treatment modality to reduce disease severity prior to HSCT is unknown. Here, we retrospectively assessed an international cohort of 57 patients outside of Asia. Treatment of the disease varied widely, although most patients ultimately proceeded to HSCT. Though patients undergoing HSCT had better survival than those who did not (55% vs 25%, P < .01), there was still a high rate of death in both groups. Mortality was largely not affected by age, ethnicity, cell-type involvement, or disease complications, but development of lymphoma showed a trend with increased mortality (56% vs 35%, P = .1). The overwhelming majority (75%) of patients who died after HSCT succumbed to relapsed disease. CAEBV remains challenging to treat when advanced disease is present. Outcomes would likely improve with better disease control strategies, earlier referral for HSCT, and close follow-up after HSCT including aggressive management of rising EBV DNA levels in the blood.

Histiocytic disorders

The historic term 'histiocytosis' meaning 'tissue cell' is used as a unifying concept for diseases characterized by pathogenic myeloid cells that share histological features with macrophages or dendritic cells. These cells may arise from the embryonic yolk sac, fetal liver or postnatal bone marrow. Prior classification schemes align disease designation with terminal phenotype: for example, Langerhans cell histiocytosis (LCH) shares CD207+ antigen with physiological epidermal Langerhans cells. LCH, Erdheim-Chester disease (ECD), juvenile xanthogranuloma (JXG) and Rosai-Dorfman disease (RDD) are all characterized by pathological ERK activation driven by activating somatic mutations in MAPK pathway genes. The title of this Primer (Histiocytic disorders) was chosen to differentiate the above diseases from Langerhans cell sarcoma and malignant histiocytosis, which are hyperproliferative lesions typical of cancer. By comparison LCH, ECD, RDD and JXG share some features of malignant cells including activating MAPK pathway mutations, but are not hyperproliferative. 'Inflammatory myeloproliferative neoplasm' may be a more precise nomenclature. By contrast, haemophagocytic lymphohistiocytosis is associated with macrophage activation and extreme inflammation, and represents a syndrome of immune dysregulation. These diseases affect children and adults in varying proportions depending on which of the entities is involved.

American Society for Transplantation and Cellular Therapy Series: #3-Prevention of Cytomegalovirus Infection and Disease After Hematopoietic Cell Transplantation

The Practice Guidelines Committee of the American Society for Transplantation and Cellular Therapy partnered with its Transplant Infectious Disease Special Interest Group to update its 2009 compendium-style infectious diseases guidelines for the care of hematopoietic cell transplant (HCT) recipients. A new approach was taken with the goal of better serving clinical providers by publishing each standalone topic in the infectious disease series as a concise format of frequently asked questions (FAQ), tables, and figures. Adult and pediatric infectious disease and HCT content experts developed and answered FAQs. Topics were finalized with harmonized recommendations that were made by assigning an A through E strength of recommendation paired with a level of supporting evidence graded I through III. The third topic in the series focuses on the prevention of cytomegalovirus infection and disease in HCT recipients by reviewing prophylaxis and preemptive therapy approaches; key definitions, relevant risk factors, and diagnostic monitoring considerations are also reviewed.

Improved transplant outcomes with myeloablative conditioning for hemophagocytic lymphohistiocytosis in HLA-matched and mismatched donors: a national multicenter retrospective study

We report the results of national retrospective study of 45 children with hemophagocytic lymphohistiocytosis (HLH) who underwent allogeneic hematopoietic stem-cell transplantation (HSCT) in Israel between the years 2000-2018. Donors were either HLA-matched (n = 26), partially mismatched (n = 7), haploidentical (n = 8), or cord-blood (n = 4). Myeloablative conditioning (MAC) was used in 20 procedures, and reduced-intensity conditioning (RIC) in 25. Forty-two patients engrafted, two had primary graft failure (one successfully retransplanted), one died prior to engraftment, and two developed secondary graft failure. Of the eight patients who had mixed donor chimerism at day 30 (5-95%), five achieved stable mixed or full donor chimerism. The 5-year probabilities of overall survival and event-free survival (EFS) were 86% and 82%, respectively. Five-year EFS was lower for patients receiving RIC compared to MAC (72% vs. 100%, p = 0.018) and following alternative-donor transplant (68% vs. 92% for HLA-matched donors, p = 0.034), mostly due to increased transplant-related mortality (TRM). Thus, both HLA-matched and alternative donor transplant procedures may benefit form a myeloablative conditioning regimen.

Lentiviral Gene Therapy for Familial Hemophagocytic Lymphohistiocytosis Type 3, Caused by UNC13D Genetic Defects

Familial hemophagocytic lymphohistiocytosis type 3 (FHL3) is a rare disease caused by mutations to the UNC13D gene and the subsequent absence or decreased activity of the Munc13-4 protein. Munc13-4 is essential for the exocytosis of perforin and granzyme containing granules from cytotoxic cells. Without it, these cells are able to recognize an immunological insult but are unable to execute their cytotoxic functions. The result is a hyperinflammatory state that, if left untreated, is fatal. At present, the only curative treatment is hematopoietic stem cell transplantation (HSCT), but eligibility and response to this treatment are largely dependent on the ability to control inflammation before HSCT. In this study, we describe an optimized lentiviral vector that can restore Munc13-4 expression and degranulation capacity in both transduced FHL3 patient T cells and transduced hematopoietic stem cells from the FHL3 (Jinx) disease model.

Haemophagocytic lymphohistiocytosis and Epstein-Barr virus: a complex relationship with diverse origins, expression and outcomes

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus with rare but severe potential for lymphoproliferative complications. EBV is associated with a variety of presentations of haemophagocytic lymphohistiocytosis (HLH). HLH is a life-threatening hyperinflammatory syndrome that can occur in patients with genetic defects associated with dysregulation of the immune response (familial HLH) or arise in patients with underlying infection or malignancy (non-familial or secondary HLH). EBV can both serve as the incidental trigger of familial HLH or as the driving factor in patients with selective inherited vulnerability (e.g. X-linked lymphoproliferative disease). Alternatively, acute infection can idiosyncratically cause non-neoplastic HLH in patients without inherited predisposition (i.e. secondary HLH), while EBV-associated T/natural killer (NK)-cell lymphoproliferative disorders and lymphomas can cause neoplasia-associated HLH. The present review will discern between EBV-associated familial and non-familial HLH and highlight diagnostic and therapeutic considerations. Non-familial EBV-associated HLH is a major diagnostic dilemma, as it represents a diverse spectrum of disease ranging from highly curable (non-neoplastic EBV-HLH) to indolent but incurable (chronic active EBV) to acutely fatal (systemic EBV-positive T-cell lymphoma of childhood). Increased clinical awareness and understanding of this rare and potentially devastating subset of EBV-related complications is desperately needed to improve survival for patients with neoplasia-associated HLH.

How I Treat: Allogeneic HSCT for adults with Inborn Errors of Immunity

Inborn Errors of Immunity (IEI) are rare inherited disorders arising from monogenic germline mutations in genes that regulate the immune system. The majority of IEI are Primary Immunodeficiencies characterised by severe infection often associated with autoimmunity, autoinflammation and/or malignancy. Allogeneic hematopoietic stem cell transplant (HSCT) has been the corrective treatment of choice for many IEI presenting with severe disease in early childhood and experience has made this a successful and comparatively safe treatment in affected children. Early HSCT outcomes in adults were poor, resulting in extremely limited use worldwide. This is changing due to a combination of improved IEI diagnosis to inform patient selection, better understanding of the natural history of specific IEI and improvements in transplant practice. Recently published HSCT outcomes for adults with IEI have been comparable with pediatric data, making HSCT an important option for correction of clinically severe IEI in adulthood. Here we discuss our practice for patient selection, timing of HSCT, donor selection and conditioning, peri- and post HSCT management and our approach to long term follow up. We stress the importance of multidisciplinary involvement in the complex decision-making process that we believe is required for successful outcomes in this rapidly emerging area.

Targeted busulfan-based reduced-intensity conditioning and HLA-matched HSCT cure hemophagocytic lymphohistiocytosis

Reduced-intensity/reduced-toxicity conditioning and allogeneic T-cell replete hematopoietic stem cell transplantation are curative in patients with hemophagocytic lymphohistiocytosis (HLH). Unstable donor chimerism (DC) and relapses are clinical challenges . We examined the effect of a reduced-intensity conditioning regimen based on targeted busulfan to enhance myeloid DC in HLH. The European Society for Bone and Marrow Transplantation-approved reduced-intensity conditioning protocol comprised targeted submyeloablative IV busulfan, IV fludarabine, and serotherapy comprising IV alemtuzumab (0.5-0.8 mg/kg) for unrelated-donor and IV rabbit anti-T-cell globulin for related-donor transplants. We assessed toxicity, engraftment, graft-versus-host disease (GHVD), DC in blood cell subtypes, and overall survival/event-free survival. Twenty-five patients from 7 centers were treated (median age, 0.68 year). The median total dose and cumulative area under the curve of busulfan was 13.1 mg/kg (6.4-26.4) and 63.1 mg/L × h (48-77), respectively. Bone marrow, peripheral blood stem cell, or cord blood transplants from HLA-matched related (n = 7) or unrelated (n = 18) donors were administered. Donor cells engrafted in all patients (median: neutrophils d+20/platelets d+28). At last follow-up (median, 36 months; range, 8-111 months), the median DC of CD15+ neutrophils, CD3+ T cells, and CD16+56+ natural killer cells was 99.5% (10-100), 97% (30-100), and 97.5% (30-100), respectively. Eight patients (32%) developed sinusoidal obstruction syndrome, resolving after defibrotide treatment. The 3-year overall survival and event-free survival rates were both 100%. None of the patients developed acute grade III to IV GHVD. Limited chronic GVHD was encountered in 4%. This regimen achieves excellent results with stable DC in patients with HLH.

Reduced-intensity single-unit unrelated cord blood transplant with optional immune boost for nonmalignant disorders

Children with many inherited nonmalignant disorders can be cured or their condition alleviated by hematopoietic stem cell transplantation (HSCT). Umbilical cord blood (UCB) units are a rapidly available stem cell source and offer great flexibility in HLA matching, allowing nearly uniform access to HSCT. Although reduced-intensity conditioning (RIC) regimens promise decreased treatment-related morbidity and mortality, graft failure and infections have limited their use in chemotherapy-naive patients. We prospectively evaluated a novel RIC regimen of alemtuzumab, hydroxyurea, fludarabine, melphalan, and thiotepa with a single-unit UCB graft in 44 consecutive patients with inborn errors of metabolism, immunity, or hematopoiesis. In addition, 5% of the UCB graft was re-cryopreserved and reserved for cord donor leukocyte infusion (cDLI) posttransplant. All patients engrafted at a median of 15 days posttransplant, and chimerism was >90% donor in the majority of patients at 1-year posttransplant with only 1 secondary graft failure. The incidence of grade II to IV graft-versus-host disease (GVHD) was 27% (95% confidence interval [CI], 17-43) with no extensive chronic GVHD. Overall survival was 95% (95% CI, 83-99) and 85% (95% CI, 64-93) at 1 and 5 years posttransplant, respectively. No significant end-organ toxicities were observed. The use of cDLI did not affect GVHD and showed signals of efficacy for infection control or donor chimerism. This RIC transplant regimen using single-unit UCB graft resulted in outstanding survival and remarkably low rates of graft failure. Implementation of the protocol not requiring pharmacokinetic monitoring would be feasible and applicable worldwide for children with inherited disorders of metabolism, immunity, or hematopoiesis. This trial was registered at www.clinicaltrials.gov as #NCT01962415.

Emapalumab for adult and pediatric patients with hemophagocytic lymphohistiocytosis

INTRODUCTION

Hemophagocytic lymphohistiocytosis (HLH) is a rare life-threatening hyperinflammatory syndrome. Standard treatment is based on immunosuppressive, cytotoxic drugs and hematopoietic stem cell transplantation (HSCT) in primary HLH. Interferon-gamma (IFN-γ) plays a key pathogenic role. Emapalumab, a monoclonal antibody directed against IFN-γ, is the first target therapy approved for primary HLH with refractory, recurrent or progressive disease or intolerance to conventional therapy.

AREAS COVERED

We reviewed the pharmacological characteristics, safety, efficacy and clinical uses of emapalumab. We summarized the results of current standard treatment based on chemo-immunosuppressive protocols and outlined the alternative options available.

EXPERT OPINION

Emapalumab is an effective treatment for HLH with a good safety profile. Its efficacy was demonstrated in a phase II/III study on primary HLH pediatric patients with refractory, relapsing HLH or intolerance to first-line treatment. The use of emapalumab allowed most patients to proceed to HSCT, with a high estimated probability of survival 12 months after transplantation. The outcomes in patients who underwent transplantation compare favorably with those reported previously with either myeloablative or reduced-intensity conditioning regimens. The potential role of emapalumab in the treatment of secondary HLH and as a prevention of graft failure after HSCT deserves to be further assessed.

Considerations in Preparative Regimen Selection to Minimize Rejection in Pediatric Hematopoietic Transplantation in Non-Malignant Diseases

The variables that influence the selection of a preparative regimen for a pediatric hematopoietic stem cell transplant procedure encompasses many issues. When one considers this procedure for non-malignant diseases, components in a preparative regimen that were historically developed to reduce malignant tumor burden may be unnecessary. The primary goal of the procedure in this instance becomes engraftment with the establishment of normal hematopoiesis and a normal immune system. Overcoming rejection becomes the primary priority, but pursuit of this goal cannot neglect organ toxicity, or post-transplant morbidity such as graft-versus-host disease or life threatening infections. With the improvements in supportive care, newborn screening techniques for early disease detection, and the expansion of viable donor sources, we have reached a stage where hematopoietic stem cell transplantation can be considered for virtually any patient with a hematopoietic based disease. Advancing preparative regiments that minimize rejection and transplant related toxicity will thus dictate to what extent this medical technology is fully utilized. This mini-review will provide an overview of the origins of conditioning regimens for transplantation and how agents and techniques have evolved to make hematopoietic stem cell transplantation a viable option for children with non-malignant diseases of the hematopoietic system. We will summarize the current state of this facet of the transplant procedure and describe the considerations that come into play in selecting a particular preparative regimen. Decisions within this realm must tailor the treatment to the primary disease condition to ideally achieve an optimal outcome. Finally, we will project forward where advances are needed to overcome the persistent engraftment obstacles that currently limit the utilization of transplantation for haematopoietically based diseases in children.

Allogeneic hematopoietic stem cell transplant in rare hematologic disorders: a single center experience from Pakistan

Management of rare hematological disorders pose unique diagnostic and therapeutic challenges due to unusual occurrence and limited treatment options. We retrospectively identified 45 patients receiving matched related donor transplant for rare hematological disorders from 2006 to 2019. Patients were divided into two groups (1) malignant and (2) non malignant. The malignant disorder group included four patients while the nonmalignant group included 41 patients divided into immune dysregulation (n = 23), bone marrow failure (n = 10), metabolic (n = 5), and bleeding diathesis (n = 3). Twenty-six (57.8%) patients received myeloablative conditioning (MAC) and 16 (35.6%) received reduced intensity conditioning (RIC), while 3 (6.6%) patients with severe combined immunodeficiency received stem cell infusion alone without conditioning. The cumulative incidence (CI) of grade II-IV acute GVHD (aGVHD) was 39.1% (n = 18) and chronic GVHD (cGVHD) 15.2% (n = 7). There was no primary graft failure while CI of secondary graft failure was 9%. Overall survival (OS) and disease-free survival (DFS) was 82.2% and 77.8% respectively. Group wise OS was 75% in the malignant group, 82.6% in the immune dysregulation group, 80% in patients with metabolic disorders and bone marrow failure, while 100% in patients with bleeding diathesis. This retrospective analysis shows that hematopoietic stem cell transplant can be a feasible treatment option for rare hematological disorders.

Reduced Intensity Bone Marrow Transplantation with Post-Transplant Cyclophosphamide for Pediatric Inherited Immune Deficiencies and Bone Marrow Failure Syndromes

PURPOSE

Allogeneic bone marrow transplantation (alloBMT) is the only cure for many primary immune deficiency disorders (PIDD), primary immune regulatory disorders (PIRD), and inherited bone marrow failure syndromes (IBMFS).

METHODS

We report the results of 25 patients who underwent alloBMT using reduced intensity conditioning (RIC), alternative donors, and post-transplantation cyclophosphamide (PTCy). In an attempt to reduce regimen-related toxicities, we removed low-dose TBI from the prep and added mycophenolate mofetil and tacrolimus for graft-versus-host disease (GVHD) prophylaxis for all donor types in the latter 14 patients. Donors were haploidentical related (n = 14), matched unrelated (n = 9), or mismatched unrelated (n = 2). The median age was 9 years (range 5 months-21 years).

RESULTS

With a median follow-up of 26 months (range 7 months-9 years), the 2-year overall survival is 92%. There were two deaths, one from infection, and one from complications after a second myeloablative BMT. Three patients developed secondary graft failure, one at 2 years and two at >3 years, successfully treated with CD34 cell boost in one or second BMT in two. The remaining 20 patients have full or stable mixed donor chimerism and are disease-free. The incidence of mixed chimerism is increased since removing TBI from the prep. The 6-month cumulative incidence of grade II acute GVHD is 17%, with no grade III-IV. The 1-year cumulative incidence of chronic GVHD is 14%, with severe of 5%.

CONCLUSION

This alloBMT platform using alternative donors, RIC, and PTCy is associated with excellent rates of engraftment and low rates of GVHD and non-relapse mortality, and offers a curative option for patients with PIDD, PIRD, and IBMFS.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04232085.

Pediatric hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome describing patients with severe systemic hyperinflammation. Characteristic features include unremitting fever, cytopenias, hepatosplenomegaly, and elevation of typical HLH biomarkers. Patients can develop hepatitis, coagulopathy, liver failure, central nervous system involvement, multiorgan failure, and other manifestations. The syndrome has a high mortality rate. More and more, it is recognized that while HLH can be appropriately used as a broad summary diagnosis, many pediatric patients actually suffer from an expanding spectrum of genetic diseases that can be complicated by the syndrome of HLH. Classic genetic diseases in which HLH is a typical and common manifestation include pathogenic changes in familial HLH genes (PRF1, UNC13D, STXBP2, and STX11), several granule/pigment abnormality genes (RAB27A, LYST, and AP3B1), X-linked lymphoproliferative disease genes (SH2D1A and XIAP), and others such as NLRC4, CDC42, and the Epstein-Barr virus susceptibility diseases. There are many other genetic diseases in which HLH is an infrequent complication of the disorder as opposed to a prominent manifestation of the disease caused directly by the genetic defect, including other primary immune deficiencies and inborn errors of metabolism. HLH can also occur in patients with underlying rheumatologic or autoinflammatory disorders and is usually designated macrophage activation syndrome in those settings. Additionally, HLH can develop in patients during infections or malignancies without a known (or as-yet-identified) genetic predisposition. This article will attempt to summarize current concepts in the pediatric HLH field as well as offer a practical diagnostic and treatment overview.

Experience with a Reduced Toxicity Allogeneic Transplant Regimen for Non-CGD Primary Immune Deficiencies Requiring Myeloablation

PURPOSE

A need exists for reduced toxicity conditioning regimens that offer less toxicity while maintaining myeloablation, especially for primary immune deficiencies where myeloablation or high donor myeloid chimerism is required to achieve cure. We adapted a busulfan and fludarabine regimen by Gungor et al. for children and young adults undergoing allogeneic HCT for non-CGD primary immune deficiencies requiring myeloablation or high donor myeloid chimerism, and herein report our experience.

METHODS

We retrospectively reviewed records of 41 consecutive patients who underwent allogeneic HCT for Wiskott-Aldrich syndrome (n = 12), primary HLH/XLP (n = 10), CD40L deficiency (n = 7), or other (n = 12) primary immune deficiencies with a conditioning regimen containing pharmacokinetic-guided busulfan dosing which achieved a cumulative AUC between 57 and 74 mg/L × h (65-80% of conventional myeloablative exposure), along with fludarabine and alemtuzumab or anti-thymocyte globulin at 3 transplant centers between 2014 and 2019.

RESULTS

Forty-one patients underwent a first (n = 33) or second (n = 8) allogeneic HCT. Median age was 2.3 years (range, 0.3 years-19.8 years). All but one patient (97.5%) achieved neutrophil recovery at a median of 14 days (range, 11-34 days). One patient developed sinusoidal obstruction syndrome and two patients developed diffuse alveolar hemorrhage. Four patients developed grades II-IV acute GVHD. Three patients developed chronic GVHD. One-year overall survival was 90% (95% confidence interval [CI] 81-99%) and event-free survival was 83% (95% CI 71-94%).

CONCLUSIONS

Our experience suggests that a reduced toxicity busulfan-fludarabine regimen offers low toxicity, low incidence of grades 2-4 GVHD, durable myeloid engraftment, and excellent survival, and may be considered for a variety of primary immune deficiencies where myeloablative HCT is desired.

Risk factors for mixed chimerism in children with hemophagocytic lymphohistiocytosis after reduced toxicity conditioning

BACKGROUND

Reduced toxicity conditioning for hematopoietic stem cell transplantation of patients with hemophagocyticlymphohistiocytosis (HLH) results in favorable survival, however at the expense of relevant rates of mixed chimerism. Factors predisposing to mixed chimerism remain to be determined.

PROCEDURE

Patients with primary HLH transplanted 2009-2016 after treosulfan- or melphalan-based conditioning regimens were analyzed in a retrospective multicenter study for survival, engraftment, chimerism, and adverse events. Mixed chimerism was considered substantial if < 25% donor chimerism occurred and/or if secondary cell therapy was administered. Donor type, graft source, type of alkylating agent, type of serotherapy, and remission status were analyzed as potential risk factors in a multivariable logistic regression model.

RESULTS

Among 60 patients, engraftment was achieved in 95%, and the five-year estimated overall survival rate was 75%. Prevalence of any recipient chimerism was 48%. Substantial recipient chimerism was recorded in 32% of patients. Secondary post-HSCT cell therapy was administered in 30% of patients. A human leukocyte antigen (HLA)-mismatched donor (< 10/10) was the only significant risk factor for the occurrence of substantial recipient chimerism (P = 0.01; odds ratio, 5.8; CI 95%, 1.5-26.3).

CONCLUSION

The use of an HLA-matched donor is the most important factor to avoid substantial recipient chimerism following treosulfan -or melphalan-based conditioning in primary HLH.

Effect of different conditioning regimens on survival and engraftment for children with hemophagocytic lymphohistiocytosis undergoing allogeneic hematopoeitic stem cell transplantation: A single institution experience

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH), a rare hyperinflammatory immuneregulatory disorder, is a challenge in hematopoietic stem cell transplantation (HSCT) because of the high rate of mixed chimerism, relapse, and graft failure (GF) unless intensive myeloablative regimens are used. However, historically conventional myeloablative regimens (conv MA) are associated with high toxicity and mortality.

PROCEDURE

We retrospectively compared transplant outcomes between three preparative regimens of varying intensities: Conv MA (n = 15), reduced-intensity conditioning (RIC, n = 12), and a treosulfan-based reduced-toxicity conditioning (RTC, n = 9).

RESULTS

Patients in the RIC cohort had a higher incidence of mixed donor chimerism and five patients (42%) developed secondary GF (P = .002) compared to the other two regimens. There was a higher incidence of veno-occlusive disease and intensive care unit (ICU) admissions in the Conv MA cohort. With the RTC regimen, there was a similar 2-year overall survival (89, 73, and 83%; P = .87), but improved compound EFS (lack of relapse, GF, second transplant or additional donor cell infusions, or death; 89, 73, and 42%, P = .041) in RTC, Conv MA, and RIC regimen, respectively.

CONCLUSIONS

The intensity of the preparative regimen has a significant impact on outcome of HSCT for HLH. The newly described treosulfan-based RTC provides for a stable graft with a reasonable toxicity profile.

Haploidentical stem cell transplantation with post-transplant cyclophosphamide for osteopetrosis and other nonmalignant diseases

Allogeneic hematopoietic stem cell transplantation (HSCT) is curative for a variety of nonmalignant disorders including osteopetrosis, bone marrow failures, and immune deficiencies. Haploidentical HSCT is a readily available option in the absence of a matched donor, but engraftment failure and other post-transplant complications are a concern. Post-transplant cyclophosphamide (PT-Cy) regimens are gaining popularity and recent reports show promising results. We report our experience with nine pediatric patients with nonmalignant diseases who were transplanted from a haploidentical donor with PT-Cy. From 2015 to 2019, nine children with nonmalignant diseases underwent haploidentical HSCT with PT-Cy, two as a second transplant and seven as primary grafts after upfront serotherapy and busulfan-based myeloablative conditioning. Patient’s diseases included osteopetrosis (n = 5), congenital amegakaryocytic thrombocytopenia (n = 2), hemophagocytic lymphohistiocytosis (n = 1), and Wiskott Aldrich syndrome (n = 1). Two patients failed to engraft following upfront PT-Cy transplants, one was salvaged with a second PT-Cy transplant, and the other with a CD34+ selected graft. None of the patients suffered from graft-versus-host disease. Three patients died from early posttransplant infectious complications and six patients are alive and well. In conclusion, haploidentical HSCT with PT-Cy is a feasible option for pediatric patients with nonmalignant diseases lacking a matched donor.

Chimerism in the Realm of Hematopoietic Stem Cell Transplantation for Non-malignant Disorders-A Perspective

Hematopoietic stem cell transplantation (HCT) is a curative intervention in non-malignant disorders (NMD) that benefit from donor-derived hematopoiesis, immunity, and establishment of vital cells or enzyme systems. Stability or reversal of disease symptoms depends on adequacy and long-term stability of donor cell engraftment in the compartment of interest. Unlike hematologic malignancies where complete replacement with donor derived hematopoiesis is desirable for a cure, NMD manifestations can often be controlled in the presence of mixed chimerism. This allows for exploration of reduced intensity conditioning regimens that can limit organ toxicity, late effects, and increase tolerability especially in young recipients or those with a large burden of disease related morbidity. However, the levels of donor chimerism conducive to disease control vary between NMD, need to focus on the hematopoietic lineage necessary to correct individual disorders, and need to be assessed for stability over time, i.e., a whole lifespan. An enhanced ability to reject grafts due to recipient immune competence, alloimmunization, and autoimmunity add to the complexity of this balance making NMD a highly diverse group of unrelated disorders. The addition of donor factors such as stem cell source and Human-Leukocyte-Antigen match extend the complexity such that 'one size does not fit all'. In this perspective, we will discuss current knowledge of the role of chimerism and goals, approach to HCT, and emerging methods of boosting engraftment and graft function, and monitoring recommendations. We draw attention to knowledge gaps and areas of necessity for further research and research support.

Autosomal dominant hyper-IgE syndrome: When hematopoietic stem cell transplantation should be considered?

AD-HIES or Job's syndrome is a primary immunodeficiency, caused by dominant negative mutations in signal transducer and activator of transcription (STAT) 3. The syndrome is characterized by infectious, immunologic, and non-immunologic manifestations and is associated with significant morbidity, mortality, and development of lymphomas. What has not yet been elucidated is the role of HSCT in the disease treatment spectrum. We review published cases of patients with AD-HIES that underwent HSCT and attempt to clarify at what stage HSCT should be considered and what are the complications.

Hemophagocytic Lymphohistiocytosis: Lessons Learned from the Dark Side

Hemophagocytic lymphohistiocytosis (HLH) is a rare but severe form of immune dysregulation often presenting as unremitting fever, cytopenia, hepatosplenomegaly, coagulopathy, and elevation of typical HLH biomarkers. HLH is universally fatal, if left untreated. The HLH-2004 criteria are widely used to diagnose this condition, but there is growing concerns across different settings that its application may result in undertreatment of certain patients. There is an expanding spectrum of genetic conditions that can be complicated by HLH. This review summarizes the current concepts in HLH, the lessons learned from the past, and provide an overview of the latest diagnostic and treatment modalities.