Haematopoietic stem cell transplantation in haemophagocytic lymphohistiocytosis

The opposing effects of two gene defects in STX11 and SLP76 on the disease in a patient with an inborn error of immunity

BACKGROUND

Inborn errors of immunity are mostly monogenic. However, disease phenotype and outcome may be modified by the coexistence of a second gene defect.

OBJECTIVE

We sought to identify the genetic basis of the disease in a patient who experienced bleeding episodes, pancytopenia, hepatosplenomegaly, and recurrent pneumonia that resulted in death.

METHODS

Genetic analysis was done using next-generation sequencing. Protein expression and phosphorylation were determined by immunoblotting. T-cell proliferation and F-actin levels were studied by flow cytometry.

RESULTS

The patient harbored 2 homozygous deletions in STX11 (c.369_370del, c.374_376del; p.V124fs60∗) previously associated with familial hemophagocytic lymphohistiocytosis and a novel homozygous missense variant in SLP76 (c.767C>T; p.T256I) that resulted in an approximately 85% decrease in SLP76 levels and absent T-cell proliferation. The patient's heterozygous family members showed an approximately 50% decrease in SLP76 levels but normal immune function. SLP76-deficient J14 Jurkat cells did not express SLP76 and had decreased extracellular signal-regulated kinase signaling, basal F-actin levels, and polymerization following T-cell receptor stimulation. Reconstitution of J14 cells with T256I mutant SLP76 resulted in low protein expression and abnormal extracellular signal-regulated kinase phosphorylation and F-actin polymerization after T-cell receptor activation compared with normal expression and J14 function when wild-type SLP76 was introduced.

CONCLUSIONS

The hypomorphic mutation in SLP76 tones down the hyperinflammation due to STX11 deletion, resulting in a combined immunodeficiency that overshadows the hemophagocytic lymphohistiocytosis phenotype. To our knowledge, this study represents the first report of the opposing effects of 2 gene defects on the disease in a patient with an inborn error of immunity.

Combined IFN-γ and JAK inhibition to treat hemophagocytic lymphohistiocytosis in mice

BACKGROUND

Familial hemophagocytic lymphohistiocytosis is a life-threatening hyperinflammatory disease caused by genetic defects in the granule-mediated cytotoxic pathway. Success of hematopoietic cell transplantation, the only cure, is correlated with the extent of disease control before transplantation. Unfortunately, disease refractoriness and toxicities to standard chemotherapy-based regimens are fatal in a fraction of patients. Novel targeted immunotherapies, such as IFN-γ blocking antibodies or ruxolitinib, a Janus kinase (JAK) 1/2 inhibitor, are promising but only partially effective at controlling disease.

OBJECTIVE

We asked whether combinations of cytokine-targeted therapies, using antibodies or JAK inhibitor, work synergistically to counteract HLH.

METHODS

Genetically predisposed mice were infected and treated with distinct combinations of immunotherapies. Disease outcome was monitored and compared to monotherapies.

RESULTS

We showed that inhibiting IL-6 or IL-18 signaling in combination with IFN-γ blockade or ruxolitinib did not increase disease control compared to anti-IFN-γ antibodies or ruxolitinib monotherapies. In contrast, clinically relevant doses of ruxolitinib combined with low doses of anti-IFN-γ blocking antibodies corrected cytopenias, prevented overt neutrophilia, limited cytokinemia, and resolved HLH immunopathology and symptomatology.

CONCLUSIONS

Our findings demonstrate that IFN-γ blockade and ruxolitinib act synergistically to suppress HLH progression. This supports the use of combined cytokine-targeted therapies as a bridge to hematopoietic cell transplantation in severe familial hemophagocytic lymphohistiocytosis.

Second Allogeneic Hematopoietic Stem Cell Transplantation for Hemophagocytic Syndrome with Engraftment Failure

This study aims to assess the efficacy of second allogeneic hemopoietic stem cell transplantation (allo-HSCT) for treating hemophagocytic syndrome with first engraftment failure. Among a total of 35 patients who underwent allo-HSCT between June 2015 and July 2021 for HLH, 10 patients who underwent a second HSCT following graft rejection were retrospectively analyzed. Various factors, such as the treatment course and outcome, the remission status, donor selection, and the conditioning regimen of patients before second allo-HSCT, were scrutinized for transplant-related complications and transplant-related mortality, as well as transplant outcomes. All the subjects have achieved complete donor engraftment, in which the neutrophils and platelets engraftment occurred in a median time of 12 d (range 10–19 d) and 24 d (range 11–97 d), respectively. Among the selected subjects, 20% of patients are diseased due to transplant-related thrombotic microangiopathy. Further, 90% of patients are diagnosed with aGVHD, in which 3 of them with grade I aGVHD, one patient with grade II aGVHD, two patients with grade III GVHD, and three patients with localized chronic GVHD. Moreover, 70% of patients showed signs of combined viral infections. Despite the complex symptoms, the overall survival rate is around 80%, with transplant-related mortality and the incidence of post-transplant GVHD of 20% and 60%, respectively. Together, our findings indicated that the second allo-HSCT showed great potential in treating hemophagocytic syndrome with engraftment failure.

Case report and literature review: Hemophagocytic lymphohistiocytosis in a pregnant woman with systemic lupus erythematosus with Syntaxin 11 gene defect

Hemophagocytic lymphohistiocytosis is an extremely rare occurrence during pregnancy. Early recognition of its signs and symptoms is critical for early intervention, and delays in diagnosis may be life-threatening. A 23-year-old nulliparous woman presented with a persistent fever as high as 39°C with bilateral edema of the lower limbs at 24 weeks of gestation. Typical laboratory findings included pancytopenia, high triglycerides, ferritin, transaminases, bilirubin, and hypoproteinemia. Active systemic lupus erythematosus was diagnosed using an autoimmune work-up and a Systemic Lupus Erythematosus Disease Activity Index 2000 score of 17 points. Her bone marrow aspirate revealed prominent hemophagocytosis; hence, HLH was confirmed. Genetic tests showed mutations in Syntaxin 11 mutations. Considering the potential impact of drugs on the fetus, the patient and her family members chose to terminate the pregnancy through medical induction of labor. Afterwards, her condition improved with immunosuppressive therapy.

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.

Hematopoietic Cell Transplantation for Inborn Errors of Immunity Other than Severe Combined Immunodeficiency in Japan: Retrospective Analysis for 1985-2016

PURPOSE

Hematopoietic cell transplantation (HCT) is a curative therapy for most patients with inborn errors of immunity (IEI). We conducted a nationwide study on HCT for patients with IEI other than severe combined immunodeficiency (non-SCID) in Japan.

METHODS

Data from the Japanese national database (Transplant Registry Unified Management Program, TRUMP) for 566 patients with non-SCID IEI, who underwent their first HCT between 1985 and 2016, were retrospectively analyzed.

RESULTS

The 10-year overall survival (OS) and event-free survival (EFS) were 74% and 64%, respectively. The 10-year OS for HCT from unrelated bone marrow (URBM), accounting for 39% of HCTs, was comparable to that for HCT from matched sibling donor (MSD), 79% and 81%, respectively. HCT from unrelated cord blood (URCB), accounting for 28% of HCTs, was also common, with a 10-year OS of 69% but less robust engraftment. The intensity of conditioning was not associated with OS or neutrophil recovery; however, myeloablative conditioning was more frequently associated with infection-related death. Patients who received myeloablative irradiation showed poor OS. Multivariate analyses revealed that HCT in 1985-1995 (hazard ratio [HR], 2.0; P = 0.03), URCB (HR, 2.0; P = 0.01), and related donor other than MSD (ORD) (HR, 2.9; P < 0.001) were associated with poor OS, and URCB (HR, 3.6; P < 0.001) and ORD (HR, 2.7; P = 0.02) showed a higher incidence of retransplantation.

CONCLUSIONS

We present the 1985-2016 status of HCT for non-SCID IEI in Japan with sufficient statistical power, highlighting the potential of URBM as an alternative donor and the feasibility of reduced intensity conditioning.

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.

Clinical features, diagnosis and therapy of familial haemophagocytic lymphohistiocytosis

Familial haemophagocytic lymphohistiocytosis (FHL) is an inherited immune deficiency with defective cytotoxicity of natural killer cells and cytotoxic T lymphocytes. A highly stimulated, but ineffective immune response leads to severe hyperinflammation. Clinical and laboratory features are characteristic, but unspecific; thus awareness of FHL is important for early diagnosis. FHL is rapidly fatal without treatment. Standard-of-care therapy is etoposide and corticosteroids, followed by haematopoietic stem cell transplantation (HSCT). CONCLUSION: FHL has become a curable disease with present treatment. Additional cytokine-directed therapy still has to prove its value. Earlier HSCT and less toxic conditioning regimens will lead to improved cure rates.

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.

Hemophagocytic Lymphohistiocytosis

CONTEXT.—

Hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening disorder of immune regulation that can eventually result in end-organ damage and death. HLH is characterized by uncontrolled activation of cytotoxic T lymphocytes, natural killer cells, and macrophages that can lead to a cytokine storm. The diagnosis of HLH is often challenging due to the diverse clinical manifestations and the presence of several diagnostic mimics. The prognosis is generally poor, warranting rapid diagnosis and aggressive management.

OBJECTIVE.—

To provide a comprehensive review of the pathogenesis, clinical features, diagnosis, and management of HLH.

DATA SOURCES.—

Peer-reviewed literature.

CONCLUSIONS.—

HLH is a condition where a complete understanding of the pathogenesis, early diagnosis, and proper management has an important role in determining patient outcome. Genetic mutations causing impairment in the function of cytotoxic T lymphocytes and natural killer cells have been identified as the root cause of familial HLH; however, the specific pathogenesis of acquired HLH is unclear. The HLH-2004 protocol used in the diagnosis of HLH was originally developed for the pediatric population. The HLH-2004 protocol still forms the basis of the diagnosis of HLH in adults, although its use in adults has not been formally validated yet. Treatment of HLH is primarily based on the HLH-94 protocol, which involves suppressing the inflammatory response, but the treatment needs to be modified in adults depending on the underlying cause and comorbidities.

Stem cell transplantation for children with hemophagocytic lymphohistiocytosis: results from the HLH-2004 study

We report the largest prospective study thus far on hematopoietic stem cell transplantation (HSCT) in hemophagocytic lymphohistiocytosis (HLH), a life-threatening hyperinflammatory syndrome comprising familial/genetic HLH (FHL) and secondary HLH. Although all patients with HLH typically need intensive anti-inflammatory therapy, patients with FHL also need HSCT to be cured. In the international HLH-2004 study, 187 children aged <18 years fulfilling the study inclusion criteria (5 of 8 diagnostic criteria, affected sibling, or molecular diagnosis in FHL-causative genes) underwent 209 transplants (2004-2012), defined as indicated in patients with familial/genetic, relapsing, or severe/persistent disease. Five-year overall survival (OS) post-HSCT was 66% (95% confidence interval [CI], 59-72); event-free survival (EFS) was 60% (95% CI, 52-67). Five-year OS was 81% (95% CI, 65-90) for children with a complete response and 59% (95% CI, 48-69) for those with a partial response (hazard ratio [HR], 2.12; 95% CI, 1.06-4.27; P = .035). For children with verified FHL (family history/genetically verified, n = 134), 5-year OS was 71% (95% CI, 62-78) and EFS was 62% (95% CI, 54-70); 5-year OS for children without verified FHL (n = 53) was significantly lower (52%; 95% CI, 38-65) (P = .040; HR, 1.69; 95% CI, 1.03-2.77); they were also significantly older. Notably, 20 (38%) of 53 patients without verified FHL had natural killer cell activity reported as normal at diagnosis, after 2 months, or at HSCT, suggestive of secondary HLH; and in addition 14 (26%) of these 53 children had no evidence of biallelic mutations despite having 3 or 4 FHL genes analyzed (natural killer cell activity not analyzed after 2 months or at HSCT). We conclude that post-HSCT survival in FHL remains suboptimal, and that the FHL diagnosis should be carefully investigated before HSCT. Pretransplant complete remission is beneficial but not mandatory to achieve post-HSCT survival. This trial was registered at www.clinicaltrials.gov as #NCT00426101.

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.

Current status of the diagnosis and treatment of hemophagocytic lymphohistiocytosis in adults

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of defective apoptosis, a disruption of the regulatory pathway that terminates immune and inflammatory responses. Fever, cytopenia, splenomegaly, and/or hemophagocytosis are typical findings of this syndrome. HLH can be induced by genetic disorders (familial) or secondary causes. Familial HLH is rare, while secondary causes in adults include infection, autoimmunity, and malignancy. HLH in adults tends to be confused with or misdiagnosed as sepsis, mainly due to similar clinical manifestations and laboratory findings, which make it difficult to diagnose HLH rapidly and adopt immunosuppressive agents and/or chemotherapy adequately. Treatment of pediatric HLH using HLH-2004 or multi-agent chemotherapy can be applied in adult patients, although the dose and type of drug need to be adjusted. It is highly recommended that allogenic hematopoietic stem cell transplantation should be used in patients who become reactivated or are refractory to the initial treatment as soon as possible to improve survival. Future clinical trials are warranted to determine more suitable treatments for adult patients with HLH.

Clinical Management of Relapsed/Refractory Hemophagocytic Lymphohistiocytosis in Adult Patients: A Review of Current Strategies and Emerging Therapies

Introduction

Haemophagocytic lymphohistiocytosis (HLH) is a severe disorder with high mortality. The aim of this review is to update clinical management of relapsed/refractory HLH in adults, with a focus on current and new therapies.

Methods

We searched relevant articles in Embase and PUBMED with the MESH term “hemophagocytic lymphohistiocytosis; refractory; relapsing; adult.”

Results

One hundred eight papers were found; of these, 22 were retained for this review. The treatment of HLH in adult is based on the HLH-94 regimen. The response rate is lower than in pediatric patients, and 20–30% are refractory to this therapy. DEP regimen and allogenic hematopoietic stem cell transplantation (HSCT) are associated with complete response and partial response in 27% and 49.2%, respectively. However, many patients fail to achieve a stable condition before HSCT, and mortality is higher in them. New drugs have been developed, such as emapalumab, ruxolitinib, and alemtuzumab, and they may be used as bridges to the curative HSCT. They are relatively well tolerated and have few or mild side effects. With these agents, the rate of partial response ranges from 14.2% to 100%, while the rate of complete response is highly variable according to study and medication used. The number of patients who achieved HSCT ranged from 44.8% to 77%, with a survival rate of 55.9% to 100%. However, the populations in these studies are mainly composed of mixed-age patients (pediatric and adult patients), and studies including only adult patients are scarce.

Conclusion

Relapsed or refractory HLH in adult patients is associated with poor outcome, and consolidation with HSCT may be required in some cases. Mortality related to HSCT is mainly due to active HLH disease before HSCT and post HSCT complications. New drugs, such as empalumab, ruxolitinib, and alemtuzumab are interesting since these agents may be used as bridges to HSCT with increases in the numbers of patients proceeding to HSCT and survival rate.

Hemophagocytic Lymphohistiocytosis Occurring in Inflammatory Bowel Disease: Systematic Review

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is a rare and aggressive syndrome of excessive cytokine requiring prompt recognition and aggressive therapy.

AIMS

We aimed to systematically characterize HLH in moderate-to-severe inflammatory bowel disease (IBD).

METHODS

We performed a systematic review of the literature (PubMED; EMBASE) and FDA Adverse Event Reporting System in accordance with the PRISMA statement. Use of biologics was used as a surrogate definition for disease severity (consistent with usual and contemporary clinical management), to enable identification of rare HLH cases with the highest fidelity.

RESULTS

58 cases of HLH occurring in IBD patients are known (mean age: 26.0 years, 70% male, 83% with Crohn's disease, mean disease duration 7.0 years). 34.5% of patients were undergoing induction therapy at HLH diagnosis. All cases occurred on patients exposed to anti-TNF agents, but cases with anti-integrin or anti-IL-12/23 exposure were reported. 2/3 of cases did not report prior AZA/6MP exposure. Underlying opportunistic infection or lymphoma was found in > 80% of cases. Survival was 70% if promptly recognized and treated. Five patients restarted biologics after HLH resolved, and one patient developed recurrent HLH.

CONCLUSIONS

HLH is rare among IBD patients exposed to biologic therapy. Most cases had an identifiable infection or malignancy at the time of diagnosis as well as history of immunomodulator use. Risk factors may include younger age, male gender, presence of Crohn's disease, and induction phase of treatment. Our study is not intended to assess risk of HLH with specific IBD therapies.

Coronavirus disease 2019: investigational therapies in the prevention and treatment of hyperinflammation

Introduction: The mortality of coronavirus disease 2019 (COVID-19) is frequently driven by an injurious immune response characterized by the development of acute respiratory distress syndrome (ARDS), endotheliitis, coagulopathy, and multi-organ failure. This spectrum of hyperinflammation in COVID-19 is commonly referred to as cytokine storm syndrome (CSS). Areas covered: Medline and Google Scholar were searched up until 15th of August 2020 for relevant literature. Evidence supports a role of dysregulated immune responses in the immunopathogenesis of severe COVID-19. CSS associated with SARS-CoV-2 shows similarities to the exuberant cytokine production in some patients with viral infection (e.g.SARS-CoV-1) and may be confused with other syndromes of hyperinflammation like the cytokine release syndrome (CRS) in CAR-T cell therapy. Interleukin (IL)-6, IL-8, and tumor necrosis factor-alpha have emerged as predictors of COVID-19 severity and in-hospital mortality. Expert opinion: Despite similarities, COVID-19-CSS appears to be distinct from HLH, MAS, and CRS, and the application of HLH diagnostic scores and criteria to COVID-19 is not supported by emerging data. While immunosuppressive therapy with glucocorticoids has shown a mortality benefit, cytokine inhibitors may hold promise as 'rescue therapies' in severe COVID-19. Given the arguably limited benefit in advanced disease, strategies to prevent the development of COVID-19-CSS are needed.

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.

An Intriguing Presentation of Epstein-Barr Virus-Associated Hemophagocytic Lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is an immune related clinical syndrome with protean manifestations, varying presentation, clinically complex, with diverse causes, and is an under-recognized entity which carries high morbidity and mortality. It is precipitated by an immunological trigger in a susceptible host resulting in immune activation and dysregulation leading to disruption of immune homeostasis, cytokine storm and multi-organ failure. We describe a case of Epstein-Barr virus (EBV) associated HLH with its typical diagnostic challenges and associated high mortality rate. Certain diagnostic criteria and online tools may help to arrive at an earlier presumptive diagnosis which, in turn, may expedite treatment and lead to better clinical outcomes.

Hematopoietic stem cell transplantation in children with Griscelli syndrome type 2: a single-center report on 35 patients

In 2010, we reported the outcome of hematopoietic stem cell transplantation (HSCT) in 11 children with Griscelli syndrome type 2 (GS2). We report here the update on this cohort to include 35 patients. Twenty-seven (77%) patients received conditioning regimen including busulfan, cyclophosphamide with etoposide. Eight (23%) were given busulfan, fludarabine. Thiotepa was added to busulfan and fludarabine regimen in two patients; one received haploidentical marrow and one unrelated cord blood. Posttransplant clinical events included veno-occlusive disease (n = 7), acute (n = 8), or chronic (n = 1) graft-versus-host disease II-IV. With a mortality rate of 37.1% (n = 13) and a median follow-up of 87.7 months of the survivors, 5-year cumulative probability of overall survival (OS) for our cohort of patients was 62.7% (±8.2%). Cumulative probability of 5-year OS was significantly better in those who did not have hemophagocytic lymphohistiocytosis (HLH) prior to HSCT (100% vs. 53.3 ± 9.5%, P value: 0.042). Of the 16 patients with neurologic involvement before HSCT, 8 survived and 3 presented sequelae. OS at 5-year was 50 ± 12.5% and 73.3 ± 10.2% (P value: 0.320) in patients with and without CNS involvement, respectively. In conclusion, HSCT in patients with GS2 is potentially curative with long-term disease-free survival. Early HSCT before the development of the accelerated phase is associated with a better outcome.

Impact of graft-versus-host disease on the clinical outcome of allogeneic hematopoietic stem cell transplantation for non-malignant diseases

The impact of acute and chronic graft-versus-host disease (GVHD) on clinical outcomes was retrospectively analyzed in 960 patients with non-malignant diseases (NMD) who underwent a first allogeneic hematopoietic stem cell transplantation (HSCT). Grade III-IV acute GVHD (but not grade I-II) was significantly associated with a lower rate of overall survival (OS), and higher non-relapse mortality (NRM) than that seen in patients without acute GVHD. Extensive (but not limited) GVHD was significantly associated with a lower OS rate and higher NRM than that seen in patients without chronic GVHD. Any grade of acute (but not chronic) GVHD was significantly associated with a lower incidence of relapse and a lower proportion of patients requiring a second HSCT or donor lymphocyte infusion for graft failure or mixed chimerism, but its impact on OS was almost negligible. Acute GVHD was significantly associated with lower OS rates in all disease groups, whereas chronic GVHD was significantly associated with lower OS rates in the primary immunodeficiency and histiocytosis groups. In conclusion, acute and chronic GVHD, even if mild, was associated with reduced OS in patients receiving HSCT for NMD and effective strategies should, therefore, be implemented to minimize GVHD.

Familial Hemophagocytic Lymphohistiocytosis: A Rare Mutation of STXBP2 in Exon 19

Familial hemophagocytic lymphohistiocytosis (FHLH) is a fulminant rapidly progressive disorder characterized by uncontrolled immune system activation. Over the last decade, STXBP2 mutations have been reported as causative. We report a baby with typical clinical features and supportive laboratory findings, who had a homozygous missense variation in exon 19 of STXBP2 that results in an amino acid substitution of aspartic acid for glycine. Adding to the currently scant literature on this variation may contribute to the database pool and help to confirm assertion of pathogenicity in FHLH.

Haematopoietic Stem Cell Transplantation for Primary Haemophagocytic Lymphohistiocytosis

Haematopoietic stem cell transplantation currently remains the only curative treatment of primary forms of haemophagocytic lymphohistiocytosis (HLH). Rapid diagnosis, efficient primary treatment of hyperinflammation, and conditioning regimens tailored to this demanding condition have substantially improved prognosis in the past 40 years. However, refractory hyperinflammation, central nervous system (CNS) involvement, unavailability of matched donors, susceptibility to conditioning-related toxicities, and a high frequency of mixed chimaerism remain a challenge in a substantial proportion of patients. Gene therapeutic approaches for several genetic defects of primary HLH are being developed at pre-clinical and translational levels.

Fludarabine/Melphalan 100 mg/m2 Conditioning Therapy Followed by Allogeneic Hematopoietic Cell Transplantation for Adult Patients with Secondary Hemophagocytic Lymphohistiocytosis

Our previous research indicated that a reduced-intensity conditioning regimen (fludarabine and melphalan at 100 mg/m²) was useful in allogeneic hematopoietic cell transplantation (HCT) for patients with lymphoma. This retrospective study evaluated the reduced-intensity conditioning regimen in allogeneic HCT for adult patients with hemophagocytic lymphohistiocytosis (HLH). Sixteen patients with HLH were evaluated, including 6 patients who were enrolled in a prospective clinical trial (NCT00772811) and 10 patients who received the same conditioning regimen (fludarabine at 30 mg/m²/day on days -6 to -2 and melphalan at 100 mg/m² on day -2). The median age was 42 years (range, 18 to 64), and 12 patients had Epstein-Barr virus (EBV)-associated HLH. Donors were an HLA matched sibling for 10 patients, an unrelated matched volunteer for 4 patients, and a mismatched family member for 2 patients. After excluding 3 patients who died soon after HCT, 12 patients achieved an engraftment (neutrophil median, day 12; platelet median, day 16). Five patients experienced acute graft-versus-host disease (GVHD), including 1 case of grade II and 4 cases of grades III to IV. Chronic GVHD occurred in 3 patients (moderate, 1 case; severe, 2 cases). After a median follow-up of 33.8 months 1 patient progressed, 3 patients relapsed, and 9 patients died. Five deaths were unrelated to relapse or progression and were caused by infection (n = 3), bleeding (n = 1), and GVHD (n = 1). No deaths or relapses were observed at >124 days post-transplant. The overall survival rate was 48.6%, and significant differences were observed according to pretransplant ferritin level (P = .007) and cytopenia lineage (P = .021). Before allogeneic HCT 10 of 12 patients still tested positive for EBV DNA: 6 patients tested negative for EBV DNA after HCT, 2 patients had persistent EBV DNA, and 2 patients were unassessable because of early death. Conditioning therapy using a lower dose of melphalan combined with fludarabine appears to be promising in allogeneic HCT for adults with HLH. However, strategies are needed to reduce the risk of early death.

Risk factors affecting outcome of unrelated cord blood transplantation for children with familial haemophagocytic lymphohistiocytosis

Allogeneic haematopoietic stem cell transplantation is still the only available curative option for Familial Haemophagocytic Lymphohistiocytosis (FHLH). Most studies report outcomes after bone marrow or peripheral blood stem cell transplantation. We analysed the outcomes of 118 children with FHLH undergoing single-unit umbilical cord blood transplantation performed from 1996 to 2014. Myeloablative conditioning regimen was given to 90% of the patients, and was mostly busulfan-based (n = 81, 76%), including anti-thymocyte globulin or alemtuzumab (n = 102, 86%). The cumulative incidence of Day 60 neutrophil engraftment was 85%; and that of non-relapse mortality and acute graft-versus-host disease (GvHD) was 21% and 33% at 100 days, respectively. The 6-year cumulative incidence of chronic GvHD was 17% and the 6-year probability of overall survival was 55%. In multivariate analysis, children receiving a graft with a total nucleated cell dose greater than 9·9 × 10⁷ /kg had a better overall survival (hazard ratio [HR]: 0·49, 95% CI: 0·27-0·88, P = 0·02). Degree of human leucocyte antigen (HLA) matching was associated with improved disease-free survival (5/6 vs. 6/6 HR: 2·11, 95% confidence interval [CI]: 1·01-4·4, P = 0·05 and ≤4/6 vs. 6/6, HR: 2·82, CI: 1·27-6·23, P = 0·01). Umbilical cord blood transplantation with a high cell dose and good HLA match is a suitable alternative option to haematopoietic stem cell transplantation in children with FHLH who lack a HLA-matched donor.

Treatment dilemmas in asymptomatic children with primary hemophagocytic lymphohistiocytosis

Asymptomatic carriers (ACs) of pathogenic biallelic mutations in causative genes for primary hemophagocytic lymphohistiocytosis (HLH) are at high risk of developing life-threatening HLH, which requires allogeneic hematopoietic stem cell transplantation (HSCT) to be cured. There are no guidelines on the management of these asymptomatic patients. We analyzed the outcomes of pairs of index cases (ICs) and subsequently diagnosed asymptomatic family members carrying the same genetic defect. We collected data from 22 HSCT centers worldwide. Sixty-four children were evaluable. ICs presented with HLH at a median age of 16 months. Seven of 32 ICs died during first-line therapy, and 2 are alive after chemotherapy only. In all, 23/32 underwent HSCT, and 16 of them are alive. At a median follow-up of 36 months from diagnosis, 18/32 ICs are alive. Median age of ACs at diagnosis was 5 months. Ten of 32 ACs activated HLH while being observed, and all underwent HSCT: 6/10 are alive and in complete remission (CR). 22/32 ACs remained asymptomatic, and 6/22 have received no treatment and are in CR at a median follow-up of 39 months. Sixteen of 22 underwent preemptive HSCT: 15/16 are alive and in CR. Eight-year probability of overall survival (pOS) in ACs who did not have activated HLH was significantly higher than that in ICs (95% vs 45%; P = .02), and pOS in ACs receiving HSCT before disease activation was significantly higher than in ACs receiving HSCT after HLH activation (93% vs 64%; P = .03). Preemptive HSCT in ACs proved to be safe and should be considered.

Recommendations for the Use of Etoposide-Based Therapy and Bone Marrow Transplantation for the Treatment of HLH: Consensus Statements by the HLH Steering Committee of the Histiocyte Society

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome requiring aggressive immunosuppressive therapy. Following 2 large international studies mainly targeting pediatric patients with familial disease and patients without underlying chronic or malignant disease, the HLH-94 protocol is recommended as the standard of care when using etoposide-based therapy by the Histiocyte Society. However, in clinical practice, etoposide-based therapy has been widely used beyond the study inclusion criteria, including older patients and patients with underlying diseases (secondary HLH). Many questions remain around these extended indications and published reports do not address several practical issues. To tackle these concerns, the HLH Steering Committee of the Histiocyte Society decided to issue guidance for use of the HLH-94 protocol. The group convened in a structured consensus finding process to define recommendations that are based largely on expert opinion backed up by available data from the literature. The recommendations address all main elements of HLH-94 including corticosteroids, cyclosporin, etoposide, intrathecal therapy, and hematopoietic stem cell transplantation (HSCT) and consider various forms of HLH and all age groups. Aspects covered include indications, applications, dosing, side effects, duration of therapy, salvage therapy, and HSCT. These recommendations aim to provide a framework to guide treatment decisions in this severe disease.

Epstein-Barr Virus and Hemophagocytic Lymphohistiocytosis

Epstein–Barr virus (EBV) is a ubiquitous virus that infects nearly all people worldwide without serious sequela. However, for patients who have genetic diseases which predispose them to the development of hemophagocytic lymphohistiocytosis (HLH), EBV infection is a life-threatening problem. As a part of a themed collection of articles on EBV infection and human primary immune deficiencies, we will review key concepts related to the understanding and treatment of HLH.

Hematopoietic stem cell transplantation in children with Griscelli syndrome: A single-center experience

GS2 is a rare autosomal recessive disease characterized by hypopigmentation, variable immunodeficiency with HLH. HSCT is the only curative treatment for GS2. We analyzed the outcome of 10 children with GS2 who underwent HSCT at our center between October 1997 and September 2013. The median age of the patients at transplant was 13.5 months (range, 6-58 months). All of the patients developed HLH before HSCT and received HLH 94 or HLH 2004 protocols. Donors were HLA-identical relatives in 8 patients, HLA-mismatched relatives in 2 patients. Engraftment was achieved in all except one patient. None of the patients developed acute GVHD. Chronic GVHD occurred in one and veno-occlusive disease occurred in four patients. Eight of the patients are under remission without any neurologic sequelae-median time of disease-free survival is 92.4 months. The present study shows successful transplant outcome without long-term neurologic sequelae in patients with GS2 who underwent HSCT from HLA-related donors.

Confirmed efficacy of etoposide and dexamethasone in HLH treatment: long-term results of the cooperative HLH-2004 study

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome comprising familial/genetic HLH (FHL) and secondary HLH. In the HLH-94 study, with an estimated 5-year probability of survival (pSu) of 54% (95% confidence interval, 48%-60%), systemic therapy included etoposide, dexamethasone, and, from week 9, cyclosporine A (CSA). Hematopoietic stem cell transplantation (HSCT) was indicated in patients with familial/genetic, relapsing, or severe/persistent disease. In HLH-2004, CSA was instead administered upfront, aiming to reduce pre-HSCT mortality and morbidity. From 2004 to 2011, 369 children aged <18 years fulfilled HLH-2004 inclusion criteria (5 of 8 diagnostic criteria, affected siblings, and/or molecular diagnosis in FHL-causative genes). At median follow-up of 5.2 years, 230 of 369 patients (62%) were alive (5-year pSu, 61%; 56%-67%). Five-year pSu in children with (n = 168) and without (n = 201) family history/genetically verified FHL was 59% (52%-67%) and 64% (57%-71%), respectively (familial occurrence [n = 47], 58% [45%-75%]). Comparing with historical data (HLH-94), using HLH-94 inclusion criteria, pre-HSCT mortality was nonsignificantly reduced from 27% to 19% (P = .064 adjusted for age and sex). Time from start of therapy to HSCT was shorter compared with HLH-94 (P =020 adjusted for age and sex) and reported neurological alterations at HSCT were 22% in HLH-94 and 17% in HLH-2004 (using HLH-94 inclusion criteria). Five-year pSu post-HSCT overall was 66% (verified FHL, 70% [63%-78%]). Additional analyses provided specific suggestions on potential pre-HSCT treatment improvements. HLH-2004 confirms that a majority of patients may be rescued by the etoposide/dexamethasone combination but intensification with CSA upfront, adding corticosteroids to intrathecal therapy, and reduced time to HSCT did not improve outcome significantly.

Durable Chimerism and Long-Term Survival after Unrelated Umbilical Cord Blood Transplantation for Pediatric Hemophagocytic Lymphohistiocytosis: A Single-Center Experience

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening disorder of immune dysregulation characterized by fever, hepatosplenomegaly, cytopenias, central nervous system disease, increased inflammatory markers, and hemophagocytosis. Currently, allogeneic hematopoietic stem cell transplantation is the only curative approach for patients with HLH, with reported survival ranging from 50% to 70% with myeloablative conditioning (MAC) regimens. However, donor availability and transplantation-related mortality associated with conventional MAC are major barriers to success. Unrelated umbilical cord blood transplantation (UCBT) provides a readily available alternative donor source for patients lacking matched related donors. Accordingly, we report the results of UCBT in 14 children treated between 1998 and 2016. All children received standard HLH chemotherapy before UCBT. The median age at diagnosis was 2.7 months (range, .8 to 10.4) and at transplantation was 7.5 months (range, 3.8 to 17). Ten patients received MAC with busulfan/cyclophosphamide/etoposide /antithymocyte globulin (ATG) (n = 5), busulfan/cyclophosphamide /ATG (n = 4), or busulfan /melphalan/ATG (n = 1). Four patients received reduced-toxicity conditioning (RTC) with alemtuzumab/fludarabine/melphalan/hydroxyurea ± thiotepa. Cord blood units were mismatched at either 1 (n = 9) or 2 (n = 5) loci and delivered a median total nucleated cell dose of 11.9 × 10⁷/kg (range, 4.6 to 27.9) and CD34⁺ dose of 3.1 × 10⁵/kg (range, 1.1 to 6.8). The cumulative incidence of neutrophil engraftment by day 42 was 78.6% (95% confidence interval [CI], 42.9% to 93.4%) with a median of 19 days (range, 13 to 27), and that for platelet (50,000) engraftment by day 100 was 64.3% (95% CI, 28.2% to 85.7%) with a median of 51 days (range, 31 to 94). Six patients developed either grade II (n = 5) or grade IV (n = 1) acute graft-versus-host disease (GVHD); no extensive chronic GVHD was seen. Ten patients (71.4%) are alive and well at a median of 11.2 years after transplantation (range, .85 to 18.25), 9 of whom maintain sustained full donor chimerism after a single UCBT, whereas 1 patient with autologous recovery after first UCBT with RTC has achieved full donor chimerism after a second UCBT with MAC. This series demonstrates that, in combination with standard HLH therapy, UCBT after MAC or RTC conditioning can provide long-term survival with durable complete donor chimerism comparable to that of conventional donors. UCBT should be considered for patients with HLH lacking a fully matched related or unrelated adult donor.

Exome sequencing for simultaneous mutation screening in children with hemophagocytic lymphohistiocytosis

In the present study, we used exome sequencing to analyze PRF1, UNC13D, STX11, and STXBP2, as well as genes associated with primary immunodeficiency disease (RAB27A, LYST, AP3B1, SH2D1A, ITK, CD27, XIAP, and MAGT1) in Thai children with hemophagocytic lymphohistiocytosis (HLH). We performed mutation analysis of HLH-associated genes in 25 Thai children using an exome sequencing method. Genetic variations found within these target genes were compared to exome sequencing data from 133 healthy individuals. Variants identified with minor allele frequencies <5% and novel mutations were confirmed using Sanger sequencing. Exome sequencing data revealed 101 non-synonymous single nucleotide polymorphisms (SNPs) in all subjects. These SNPs were classified as pathogenic (n = 1), likely pathogenic (n = 16), variant of unknown significance (n = 12), or benign variant (n = 72). Homozygous, compound heterozygous, and double-gene heterozygous variants, involving mutations in PRF1 (n = 3), UNC13D (n = 2), STXBP2 (n = 3), LYST (n = 3), XIAP (n = 2), AP3B1 (n = 1), RAB27A (n = 1), and MAGT1 (n = 1), were demonstrated in 12 patients. Novel mutations were found in most patients in this study. In conclusion, exome sequencing demonstrated the ability to identify rare genetic variants in HLH patients. This method is useful in the detection of mutations in multi-gene associated diseases.

A retrospective analysis of 56 children with hemophagocytic lymphohistiocytosis

Aim

The aim of this study was to investigate the etiological factors, clinical features, and prognostic factors in children with hemophagocytic lymphohistiocytosis (HLH).

Methods

Fifty-six children with HLH in Wuhan Union Hospital, People’s Republic of China, were retrospectively analyzed in recent years. We reviewed the medical records of 56 HLH children hospitalized from 2000 to 2013 to identify the possible prognostic factors.

Results

In more than half of the cases (64.29%), the etiological factor was found to be infection. Clinical characteristics such as prolonged fever (100.00%), hepatosplenomegaly (95.24%), and pancytopenia (100.00%) were observed. Characteristic laboratory values presented with increased ferritin (64.29%), triglycerides (78.57%), transaminases (80.95%), bilirubin (67.54%), lactate dehydrogenase (95.23%), and decreased fibrinogen (61.90%), natrium (40.48%), and potassium (30.94%). Bone marrow aspiration showed hemophagocytosis in 48 cases (85.71%). Forty-two patients were treated according to HLH-2004 protocol. Out of the 42 patients, 19 cases acquired remission and 13 cases died. Ten cases lost follow-up. High lactate dehydrogenase (>2,000 U/L), high bilirubin (>2 mg/mL), and younger age (<2 years) at the time of diagnosis were adverse prognostic factors.

Conclusion

HLH is a life-threatening syndrome caused by complicated etiology. The level of lactate dehydrogenase and bilirubin accompanied with younger age were adverse factors.

Allogeneic hematopoietic stem-cell transplantation for adult and adolescent hemophagocytic lymphohistiocytosis: a single center analysis

Myeloablative conditioning-based allogeneic hematopoietic stem-cell transplantation (allo-HSCT) in the treatment of adult and adolescent hemophagocytic lymphohistiocytosis (HLH) is rarely reported. We conducted a retrospective study of 30 adult and adolescent HLH transplanted for primary HLH (n = 4), tumor-HLH (n = 8), EBV-HLH (n = 14), and underlying disease-unknown (UDU)-HLH (n = 4). Peripheral blood stem cells (PBSCs) were the stem-cell source in all patients. Twenty-three patients were transplanted from HLA-haploidentical family donors, six from HLA-identical sibling donors, and one from a matched unrelated donor. Four patients appeared with mixed chimerism (MC), and no patient presented with graft failure. There was a high risk for EBV reactivation with an incidence of 47 %. Two patients developed post-transplant lymphoproliferative disorder (PTLD) and three were considered primary disease recurrent. With a median follow-up of 26 months, 19 patients survived and 11 patients died. The estimated 2-year overall survival (OS) was 63.3 ± 8.8 % in all patients, 100 % in primary HLH, 64.3 ± 12.8 % in EBV-HLH, 50.0 ± 17.7 % in tumor-HLH, and 50.0 ± 25.0 % in UDU-HLH. Myeloablative conditioning-based allo-HSCT is an effective treatment for adult and adolescent HLH to achieve complete remission and long-term survival.

Understanding the spectrum of haemophagocytic lymphohistiocytosis: update on diagnostic challenges and therapeutic options

The cytokine storm syndrome 'haemophagocytic lymphohistiocytosis' (HLH) is an under-recognized hyperinflammatory disorder, causing high morbidity and mortality risk in children and adults. It can be subdivided into a primary, genetic form and a secondary, acquired form that complicates diverse infections, malignancies and autoimmune or autoinflammatory disorders. Both subtypes present with the same spectrum of non-specific symptoms, making accurate diagnosis and rapid treatment initiation challenging. In the last decade, increased awareness and international collaborative efforts fuelled a marked progress in diagnostic protocols and novel treatment strategies for HLH and new diagnostic guidelines are being tailored to specific secondary HLH subtypes. Therapy is gradually shifting its focus from overall immunosuppression towards targeting specific cytokines, cell types or signalling pathways underlying pathophysiology. Nevertheless, continued research efforts remain indispensable to customize therapy to individual patient needs.

The minimum required level of donor chimerism in hereditary hemophagocytic lymphohistiocytosis

Reduced-intensity conditioning has improved survival after hematopoietic stem cell transplantation (HSCT) for hemophagocytic lymphohistiocytosis (HLH) at the cost of more frequent mixed chimerism. The minimum level of donor chimerism (DC) required to prevent HLH reactivation in humans remains to be determined. In a multicenter retrospective study, 103 patients transplanted for hereditary HLH (2000-2013) and DC permanently or transiently <75% (overall, CD3(+), CD56(+)) were analyzed regarding DC, specific immunologic function, occurrence of systemic reactivations (≥5/8 HLH criteria), partial systemic flares (<5 criteria and HLH-directed treatment), isolated central nervous system reactivations, and management. Recurrence was reported in 18 patients (systemic reactivation n = 11, partial flare n = 3, isolated central nervous system reactivation n = 4). Ten events occurred during profound immune suppression before day 180 (median DC, 10%; range, 1-100%; CD3(+) if available, otherwise overall DC), which renders a differentiation between secondary post-HSCT HLH and HLH related to the genetic defect difficult. Eight events occurred between 0.5 and 6.7 years post-HSCT (median DC, 13%; range, 0-30%). In 5 patients, overall and lineage-specific DC were ≤10% for >6 months (median, 5.1; range, 1.1-10 years) without reactivation. A second HSCT was performed in 18 patients (median, DC 4%; range, 0-19%). Death from reactivation occurred in 4 patients (22% of recurrences). Six patients died of transplant complications following a second HSCT (33% of second HSCT). We conclude that a DC >20%-30% is protective against late reactivation. Lower levels do not, however, inescapably result in recurrences. The decision for or against second HSCT must be based on a thorough risk assessment.