Partial RAG deficiency in humans induces dysregulated peripheral lymphocyte development and humoral tolerance defect with accumulation of T-bet+ B cells.

The recombination-activating genes (RAG) 1 and 2 are indispensable for diversifying the primary B cell receptor repertoire and pruning self-reactive clones via receptor editing in the bone marrow; however, the impact of RAG1/RAG2 on peripheral tolerance is unknown. Partial RAG deficiency (pRD) manifesting with late-onset immune dysregulation represents an 'experiment of nature' to explore this conundrum. By studying B cell development and subset-specific repertoires in pRD, we demonstrate that reduced RAG activity impinges on peripheral tolerance through the generation of a restricted primary B cell repertoire, persistent antigenic stimulation and an inflammatory milieu with elevated B cell-activating factor. This unique environment gradually provokes profound B cell dysregulation with widespread activation, remarkable extrafollicular maturation and persistence, expansion and somatic diversification of self-reactive clones. Through the model of pRD, we reveal a RAG-dependent 'domino effect' that impacts stringency of tolerance and B cell fate in the periphery.

Evidence of innate lymphoid cell redundancy in humans.

Innate lymphoid cells (ILCs) have potent immunological functions in experimental conditions in mice, but their contributions to immunity in natural conditions in humans have remained unclear. We investigated the presence of ILCs in a cohort of patients with severe combined immunodeficiency (SCID). All ILC subsets were absent in patients with SCID who had mutation of the gene encoding the common γ-chain cytokine receptor subunit IL-2Rγ or the gene encoding the tyrosine kinase JAK3. T cell reconstitution was observed in patients with SCID after hematopoietic stem cell transplantation (HSCT), but the patients still had considerably fewer ILCs in the absence of myeloablation than did healthy control subjects, with the exception of rare cases of reconstitution of the ILC1 subset of ILCs. Notably, the ILC deficiencies observed were not associated with any particular susceptibility to disease, with follow-up extending from 7 years to 39 years after HSCT. We thus report here selective ILC deficiency in humans and show that ILCs might be dispensable in natural conditions, if T cells are present and B cell function is preserved.

Disruption of Coronin 1 Signaling in T Cells Promotes Allograft Tolerance while Maintaining Anti-Pathogen Immunity.

The ability of the immune system to discriminate self from non-self is essential for eradicating microbial pathogens but is also responsible for allograft rejection. Whether it is possible to selectively suppress alloresponses while maintaining anti-pathogen immunity remains unknown. We found that mice deficient in coronin 1, a regulator of naive T cell homeostasis, fully retained allografts while maintaining T cell-specific responses against microbial pathogens. Mechanistically, coronin 1-deficiency increased cyclic adenosine monophosphate (cAMP) concentrations to suppress allo-specific T cell responses. Costimulation induced on microbe-infected antigen presenting cells was able to overcome cAMP-mediated immunosuppression to maintain anti-pathogen immunity. In vivo pharmacological modulation of this pathway or a prior transfer of coronin 1-deficient T cells actively suppressed allograft rejection. These results define a coronin 1-dependent regulatory axis in T cells important for allograft rejection and suggest that modulation of this pathway may be a promising approach to achieve long-term acceptance of mismatched allografts.

Characterization of novel mutations in the TEL-patch domain of the telomeric factor TPP1 associated with telomere biology disorders.

Telomeres are nucleoprotein structures that protect the chromosome ends from degradation and fusion. Telomerase is a ribonucleoprotein complex essential to maintain the length of telomeres. Germline defects that lead to short and/or dysfunctional telomeres cause telomere biology disorders (TBDs), a group of rare and heterogeneous Mendelian diseases including pulmonary fibrosis, dyskeratosis congenita, and Høyeraal-Hreidarsson syndrome. TPP1, a telomeric factor encoded by the gene ACD, recruits telomerase at telomere and stimulates its activity via its TEL-patch domain that directly interacts with TERT, the catalytic subunit of telomerase. TBDs due to TPP1 deficiency have been reported only in 11 individuals. We here report four unrelated individuals with a wide spectrum of TBD manifestations carrying either heterozygous or homozygous ACD variants consisting in the recurrent and previously described in-frame deletion of K170 (K170∆) and three novel missense mutations G179D, L184R, and E215V. Structural and functional analyses demonstrated that the four variants affect the TEL-patch domain of TPP1 and impair telomerase activity. In addition, we identified in the ACD gene several motifs associated with small deletion hotspots that could explain the recurrence of the K170∆ mutation. Finally, we detected in a subset of blood cells from one patient, a somatic TERT promoter-activating mutation that likely provides a selective advantage over non-modified cells, a phenomenon known as indirect somatic genetic rescue. Together, our results broaden the genetic and clinical spectrum of TPP1 deficiency and specify new residues in the TEL-patch domain that are crucial for length maintenance and stability of human telomeres in vivo.

Outcomes of HLA-mismatched HSCT with TCRαß/CD19 depletion or post-HSCT cyclophosphamide for inborn errors of immunity.

ABSTRACT: HLA-mismatched transplants with either in vitro depletion of CD3+ T-cell receptor (TCR)αß/CD19 (TCRαß) cells or in vivo T-cell depletion using posttransplant cyclophosphamide (PTCY) have been increasingly used for patients with inborn errors of immunity (IEIs). We performed a retrospective multicenter study via the EBMT registry on 306 children with IEIs undergoing their first transplant between 2010 and 2019 from an HLA-mismatched donor using TCRαß (n = 167) or PTCY (n = 139). The median age for hematopoietic stem cell transplantation (HSCT) was 1.2 years (range, 0.03-19.6 years). The 3-year overall survival (OS) was 78% (95% confidence interval (CI), 71-84) after TCRαß and 66% (57-74) after PTCY (P = .013). Pre-HSCT morbidity score (hazard ratio [HR], 2.27; 1.07-4.80, P = .032) and non-busulfan/treosulfan conditioning (HR, 3.12; 1.98-4.92, P < .001) were the only independent predictors of unfavorable OS. The 3-year event-free survival (EFS) was 58% (50%-66%) after TCRαß and 57% (48%-66%) after PTCY (P = .804). The cumulative incidence of severe acute graft-versus-host disease (GvHD) was higher after PTCY (15%, 9%-21%) than TCRαß (6%, 2%-9%, P = .007), with no difference in chronic GvHD (PTCY, 11%, 6%-17%; TCRαß, 7%, 3%-11%, P = .173). The 3-year GvHD-free EFS was 53% (44%-61%) after TCRαß and 41% (32%-50%) after PTCY (P = .080). PTCY had significantly higher rates of veno-occlusive disease (14.4% vs TCRαß 4.9%, P = .009), acute kidney injury (12.7% vs 4.6%, P = .032), and pulmonary complications (38.2% vs 24.1%, P = .017). Adenoviremia (18.3% vs PTCY 8.0%, P = .015), primary graft failure (10% vs 5%, P = .048), and second HSCT (17.4% vs 7.9%, P = .023) were significantly higher in TCRαß. In conclusion, this study demonstrates that both approaches are suitable options in patients with IEIs, although they are characterized by different advantages and outcomes.

Clinical and functional spectrum of RAC2-related immunodeficiency.

ABSTRACT: Mutations in the small Rho-family guanosine triphosphate hydrolase RAC2, critical for actin cytoskeleton remodeling and intracellular signal transduction, are associated with neonatal severe combined immunodeficiency (SCID), infantile neutrophilic disorder resembling leukocyte adhesion deficiency (LAD), and later-onset combined immune deficiency (CID). We investigated 54 patients (23 previously reported) from 37 families yielding 15 novel RAC2 missense mutations, including one present only in homozygosity. Data were collected from referring physicians and literature reports with updated clinical information. Patients were grouped by presentation: neonatal SCID (n = 5), infantile LAD-like disease (n = 5), or CID (n = 44). Disease correlated to RAC2 activity: constitutively active RAS-like mutations caused neonatal SCID, dominant-negative mutations caused LAD-like disease, whereas dominant-activating mutations caused CID. Significant T- and B-lymphopenia with low immunoglobulins were seen in most patients; myeloid abnormalities included neutropenia, altered oxidative burst, impaired neutrophil migration, and visible neutrophil macropinosomes. Among 42 patients with CID with clinical data, upper and lower respiratory infections and viral infections were common. Twenty-three distinct RAC2 mutations, including 15 novel variants, were identified. Using heterologous expression systems, we assessed downstream effector functions including superoxide production, p21-activated kinase 1 binding, AKT activation, and protein stability. Confocal microscopy showed altered actin assembly evidenced by membrane ruffling and macropinosomes. Altered protein localization and aggregation were observed. All tested RAC2 mutant proteins exhibited aberrant function; no single assay was sufficient to determine functional consequence. Most mutants produced elevated superoxide; mutations unable to support superoxide formation were associated with bacterial infections. RAC2 mutations cause a spectrum of immune dysfunction, ranging from early onset SCID to later-onset combined immunodeficiencies depending on RAC2 activity. This trial was registered at www.clinicaltrials.gov as #NCT00001355 and #NCT00001467.

Allogeneic stem cell transplantation compared to conservative management in adults with inborn errors of immunity.

Allogeneic hematopoietic stem cell transplantation (alloSCT) is curative for severe inborn errors of immunity (IEIs), with recent data suggesting alloSCT in adulthood is safe and effective in selected patients. However, questions remain regarding the indications for and optimal timing of transplant. We retrospectively compared outcomes of transplanted vs matched nontransplanted adults with severe IEIs. Seventy-nine patients (aged ≥ 15 years) underwent alloSCT between 2008 and 2018 for IEIs such as chronic granulomatous disease (n = 20) and various combined immune deficiencies (n = 59). A cohort of nontransplanted patients from the French Centre de Référence Déficits Immunitaires Héréditaires registry was identified blindly for case-control analysis, with ≤3 matched controls per index patient, without replacement. The nontransplanted patients were matched for birth decade, age at last review greater than index patient age at alloSCT, chronic granulomatous disease or combined immune deficiencies, and autoimmune/lymphoproliferative complications. A total of 281 patients were included (79 transplanted, 202 nontransplanted). Median age at transplant was 21 years. Transplant indications were mainly lymphoproliferative disease (n = 23) or colitis (n = 15). Median follow-up was 4.8 years (interquartile range, 2.5-7.2). One-year transplant-related mortality rate was 13%. Estimated disease-free survival at 5 years was higher in transplanted patients (58% vs 33%; P = .007). Nontransplanted patients had an ongoing risk of severe events, with an increased mean cumulative number of recurrent events compared with transplanted patients. Sensitivity analyses removing patients with common variable immune deficiency and their matched transplanted patients confirm these results. AlloSCT prevents progressive morbidity associated with IEIs in adults, which may outweigh the negative impact of transplant-related mortality.

DOCK11 deficiency in patients with X-linked actinopathy and autoimmunity.

Dedicator of cytokinesis (DOCK) proteins play a central role in actin cytoskeleton regulation. This is highlighted by the DOCK2 and DOCK8 deficiencies leading to actinopathies and immune deficiencies. DOCK8 and DOCK11 activate CDC42, a Rho-guanosine triphosphate hydrolases involved in actin cytoskeleton dynamics, among many cellular functions. The role of DOCK11 in human immune disease has been long suspected but, to the best of our knowledge, has never been described to date. We studied 8 male patients, from 7 unrelated families, with hemizygous DOCK11 missense variants leading to reduced DOCK11 expression. The patients were presenting with early-onset autoimmunity, including cytopenia, systemic lupus erythematosus, skin, and digestive manifestations. Patients' platelets exhibited abnormal ultrastructural morphology and spreading as well as impaired CDC42 activity. In vitro activated T cells and B-lymphoblastoid cell lines from patients exhibited aberrant protrusions and abnormal migration speed in confined channels concomitant with altered actin polymerization during migration. Knock down of DOCK11 recapitulated these abnormal cellular phenotypes in monocytes-derived dendritic cells and primary activated T cells from healthy controls. Lastly, in line with the patients' autoimmune manifestations, we also observed abnormal regulatory T-cell (Treg) phenotype with profoundly reduced FOXP3 and IKZF2 expression. Moreover, we found reduced T-cell proliferation and impaired STAT5B phosphorylation upon interleukin-2 stimulation of the patients' lymphocytes. In conclusion, DOCK11 deficiency is a new X-linked immune-related actinopathy leading to impaired CDC42 activity and STAT5 activation, and is associated with abnormal actin cytoskeleton remodeling as well as Treg phenotype, culminating in immune dysregulation and severe early-onset autoimmunity.

Long-term assessment of haematological recovery following somatic genetic rescue in a MYSM1-deficient patient: Implications for in vivo gene therapy.

MYSM1 deficiency causes inherited bone marrow failure syndrome (IBMFS). We have previously identified an IBMFS patient with a homozygous pathogenic variant in MYSM1 who recovered from cytopenia due to spontaneous correction of one MYSM1 variant in the haematopoietic compartment, an event called somatic genetic rescue (SGR). The study of the genetic and biological aspects of the patient's haematopoietic/lymphopoietic system over a decade after SGR shows that one genetically corrected haematopoietic stem cell (HSC) can restore a healthy and stable haematopoietic system. This supports in vivo gene correction of HSCs as a promising treatment for IBMFS, including MYSM1 deficiency.

Determinants of long-term outcomes of splenectomy in pediatric autoimmune cytopenias.

Splenectomy is effective in ∼70% to 80% of pediatric chronic immune thrombocytopenia (cITP) cases, and few data exist about it in autoimmune hemolytic anemia (AIHA) and Evans syndrome (ES). Because of the irreversibility of the procedure and the lack of predictions regarding long-term outcomes, the decision to undertake splenectomy is difficult in children. We report here factors associated with splenectomy outcomes from the OBS'CEREVANCE cohort, which prospectively includes French children with autoimmune cytopenia (AIC) since 2004. The primary outcome was failure-free survival (FFS), defined as the time from splenectomy to the initiation of a second-line treatment (other than steroids and intravenous immunoglobulins) or death. We included 161 patients (cITP, n = 120; AIHA, n = 19; ES, n = 22) with a median (minimum-maximum) follow-up of 6.8 years (1.0-33.3) after splenectomy. AIC subtype was not associated with FFS. We found that immunopathological manifestations (IMs) were strongly associated with unfavorable outcomes. Diagnosis of an IM before splenectomy was associated with a lower FFS (hazard ratio [HR], 0.39; 95% confidence interval [CI], 0.21-0.72, P = .003, adjusted for AIC subtype). Diagnosis of an IM at any timepoint during follow-up was associated with an even lower FFS (HR, 0.22; 95% CI, 0.12-0.39; P = 2.8 × 10-7, adjusted for AIC subtype) as well as with higher risk of recurrent or severe bacterial infections and thrombosis. In conclusion, our results support the search for associated IMs when considering a splenectomy to refine the risk-benefit ratio. After the procedure, monitoring IMs helps to identify patients with higher risk of unfavorable outcomes.

Hematopoietic stem cell transplantation for Wiskott-Aldrich syndrome: an EBMT Inborn Errors Working Party analysis.

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative treatment for patients affected by Wiskott-Aldrich syndrome (WAS). Reported HSCT outcomes have improved over time with respect to overall survival, but some studies have identified older age and HSCT from alternative donors as risk factors predicting poorer outcome. We analyzed 197 patients undergoing transplant at European Society for Blood and Marrow Transplantation centers between 2006 and 2017 who received conditioning as recommended by the Inborn Errors Working Party (IEWP): either busulfan (n = 103) or treosulfan (n = 94) combined with fludarabine ± thiotepa. After a median follow-up post-HSCT of 44.9 months, 176 patients were alive, resulting in a 3-year overall survival of 88.7% and chronic graft-versus-host disease (GVHD)-free survival (events include death, graft failure, and severe chronic GVHD) of 81.7%. Overall survival and chronic GVHD-free survival were not significantly affected by conditioning regimen (busulfan- vs treosulfan-based), donor type (matched sibling donor/matched family donor vs matched unrelated donor/mismatched unrelated donor vs mismatched family donor), or period of HSCT (2006-2013 vs 2014-2017). Patients aged <5 years at HSCT had a significantly better overall survival. The overall cumulative incidences of grade III to IV acute GVHD and extensive/moderate/severe chronic GVHD were 6.6% and 2.1%, respectively. Patients receiving treosulfan-based conditioning had a higher incidence of graft failure and mixed donor chimerism and more frequently underwent secondary procedures (second HSCT, unconditioned stem cell boost, donor lymphocyte infusion, or splenectomy). In summary, HSCT for WAS with conditioning regimens currently recommended by IEWP results in excellent survival and low rates of GVHD, regardless of donor or stem cell source, but age ≥5 years remains a risk factor for overall survival.

Hematopoietic stem cell transplantation for adolescents and adults with inborn errors of immunity: an EBMT IEWP study.

Allogeneic hematopoietic stem cell transplantation (HSCT) is the gold standard curative therapy for infants and children with many inborn errors of immunity (IEI), but adolescents and adults with IEI are rarely referred for transplant. Lack of published HSCT outcome data outside small, single-center studies and perceived high risk of transplant-related mortality have delayed the adoption of HSCT for IEI patients presenting or developing significant organ damage later in life. This large retrospective, multicenter HSCT outcome study reports on 329 IEI patients (age range, 15-62.5 years at HSCT). Patients underwent first HSCT between 2000 and 2019. Primary endpoints were overall survival (OS) and event-free survival (EFS). We also evaluated the influence of IEI-subgroup and IEI-specific risk factors at HSCT, including infections, bronchiectasis, colitis, malignancy, inflammatory lung disease, splenectomy, hepatic dysfunction, and systemic immunosuppression. At a median follow-up of 44.3 months, the estimated OS at 1 and 5 years post-HSCT for all patients was 78% and 71%, and EFS was 65% and 62%, respectively, with low rates of severe acute (8%) or extensive chronic (7%) graft-versus-host disease. On univariate analysis, OS and EFS were inferior in patients with primary antibody deficiency, bronchiectasis, prior splenectomy, hepatic comorbidity, and higher hematopoietic cell transplant comorbidity index scores. On multivariable analysis, EFS was inferior in those with a higher number of IEI-associated complications. Neither age nor donor had a significant effect on OS or EFS. We have identified age-independent risk factors for adverse outcome, providing much needed evidence to identify which patients are most likely to benefit from HSCT.

Actin dynamics regulation by TTC7A/PI4KIIIα limits DNA damage and cell death under confinement.

BACKGROUND: The actin cytoskeleton has a crucial role in the maintenance of the immune homeostasis by controlling various cellular processes, including cell migration. Mutations in TTC7A have been described as the cause of a primary immunodeficiency associated to different degrees of gut involvement and alterations in the actin cytoskeleton dynamics. OBJECTIVES: This study investigates the impact of TTC7A deficiency in immune homeostasis. In particular, the role of the TTC7A/phosphatidylinositol 4 kinase type III α pathway in the control of leukocyte migration and actin dynamics. METHODS: Microfabricated devices were leveraged to study cell migration and actin dynamics of murine and patient-derived leukocytes under confinement at the single-cell level. RESULTS: We show that TTC7A-deficient lymphocytes exhibit an altered cell migration and reduced capacity to deform through narrow gaps. Mechanistically, TTC7A-deficient phenotype resulted from impaired phosphoinositide signaling, leading to the downregulation of the phosphoinositide 3-kinase/AKT/RHOA regulatory axis and imbalanced actin cytoskeleton dynamics. TTC7A-associated phenotype resulted in impaired cell motility, accumulation of DNA damage, and increased cell death in dense 3-dimensional gels in the presence of chemokines. CONCLUSIONS: These results highlight a novel role of TTC7A as a critical regulator of lymphocyte migration. Impairment of this cellular function is likely to contribute to the pathophysiology underlying progressive immunodeficiency in patients.

Letermovir for CMV Prophylaxis in Very High-Risk Pediatric Hematopoietic Stem Cell Transplantation Recipients for Inborn Errors of Immunity.

The burden of CMV infection and disease is important in pediatric hematopoietic stem cell transplantation (HSCT), notably in the subgroup of patients with inborn errors of immunity (IEIs). Letermovir (LMV) is now a standard of care for CMV prophylaxis in adult sero-positive (R+) recipients, but is not yet labeled for children. Published pediatric studies are still scarce. We report a monocentric real-life use of LMV in 36 HSCT pediatric recipients with IEIs considered at high-risk of CMV infection including 14 patients between 2 and 12 months of age. A homogenous dosage proportional to the body surface area was used. Pharmacokinetic (PK) was performed in 8 patients with a median of 6 years of age (range 0,6;15). The cumulative incidence of clinically significant CMV infections (CS-CMVi) and the overall survival of patients under LMV were compared to a very similar historical cohort under (val)aciclovir prophylaxis. LMV tolerance was good. As compared to the historical cohort, the incidence of CS-CMVi was significantly lower in LMV group (5 out of 36 transplants (13.9%) versus 28 of the 62 HSCT (45.2%)) (p = 0.002). Plasma LMV exposures did not significantly differ with those reported in adult patients. In this high-risk pediatric HSCT cohort transplanted for IEIs, CMV prophylaxis with LMV at a homogenous dosage was well tolerated and effective in preventing CS-CMVi compared with a historical cohort.

JAK Inhibition in Aicardi-Goutières Syndrome: a Monocentric Multidisciplinary Real-World Approach Study.

The paradigm type I interferonopathy Aicardi-Goutières syndrome (AGS) is most typically characterized by severe neurological involvement. AGS is considered an immune-mediated disease, poorly responsive to conventional immunosuppression. Premised on a chronic enhancement of type I interferon signaling, JAK1/2 inhibition has been trialed in AGS, with clear improvements in cutaneous and systemic disease manifestations. Contrastingly, treatment efficacy at the level of the neurological system has been less conclusive. Here, we report our real-word approach study of JAK1/2 inhibition in 11 patients with AGS, providing extensive assessments of clinical and radiological status; interferon signaling, including in cerebrospinal fluid (CSF); and drug concentrations in blood and CSF. Over a median follow-up of 17 months, we observed a clear benefit of JAK1/2 inhibition on certain systemic features of AGS, and reproduced results reported using the AGS neurologic severity scale. In contrast, there was no change in other scales assessing neurological status; using the caregiver scale, only patient comfort, but no other domain of everyday-life care, was improved. Serious bacterial infections occurred in 4 out of the 11 patients. Overall, our data lead us to conclude that other approaches to treatment are urgently required for the neurologic features of AGS. We suggest that earlier diagnosis and adequate central nervous system penetration likely remain the major factors determining the efficacy of therapy in preventing irreversible brain damage, implying the importance of early and rapid genetic testing and the consideration of intrathecal drug delivery.

Epstein-Barr Virus Genome Deletions in Epstein-Barr Virus-Positive T/NK Cell Lymphoproliferative Diseases.

The main target cells for Epstein-Barr virus (EBV) infection and persistence are B lymphocytes, although T and NK cells can also become infected. In this paper, we characterize the EBV present in 21 pediatric and adult patients who were treated in France for a range of diseases that involve infection of T or NK cells. Of these 21 cases, 5 pediatric patients (21%) and 11 adult patients (52%) were of Caucasian origin. In about 30% of the cases, some of the EBV genomes contain a large deletion. The deletions are different in every patient but tend to cluster near the BART region of the viral genome. Detailed investigation of a family in which several members have persistent T or NK cell infection by EBV indicates that the virus genome deletions arise or are selected independently in each individual patient. Genome sequence polymorphisms in the EBV in these T or NK cell diseases reflect the geographic origin of the patient and not a distinct type of EBV (the 21 cases studied included examples of both type 1 and type 2 EBV infection). Using virus produced from type 1 or type 2 EBV genomes cloned in bacterial artificial chromosome (BAC) vectors, we demonstrate infection of T cells in cord blood from healthy donors. Our results are consistent with transient infection of some T cells being part of normal asymptomatic infection by EBV in young children. IMPORTANCE EBV contributes to several types of human cancer. Some cancers and nonmalignant lymphoproliferative diseases involving T or NK cells contain EBV. These diseases are relatively frequent in Japan and China and have been shown sometimes to have deletions in the EBV genome in the disease cells. We identify further examples of deletions within the EBV genome associated with T or NK cell diseases, and we provide evidence that the virus genomes with these deletions are most likely selected in the individual cases, rather than being transmitted between people during infection. We demonstrate EBV infection of cord blood T cells by highly characterized, cloned EBV genomes and suggest that transient infection of T cells may be part of normal asymptomatic infection by EBV in young children.

Spectrum of neuroradiological manifestations in primary hemophagocytic lymphohistiocytosis: a comparative study of EBV-induced versus non-EBV-induced forms in 75 genetically confirmed pediatric cases.

OBJECTIVES: Hemophagocytic lymphohistiocytosis (HLH) is a rare and life-threatening condition affecting young children. It is potentially triggered by Epstein-Barr virus (EBV). This study describes the neuroradiological features observed in 75 children with genetically confirmed primary HLH, comparing EBV-induced with non-EBV-induced HLH forms. METHODS: Brain MRIs between 2007 and 2021 from 75 children with HLH according to the 2004 Histiocyte Society criteria and with a confirmed HLH-related mutation, were retrospectively reviewed by two pediatric neuroradiologists blinded to EBV status and to mutation status. At diagnosis, 17 children with EBV viremia above a threshold of 1000 copies/mL were included in the EBV-induced HLH group. The remaining 58 patients were included in the non-EBV-induced HLH group. RESULTS: Of the 75 children initially included, 21 had abnormal MRI (21/75 (28%); 9/17 in the EBV-induced HLH group and 12/58 in the non-EBV-induced HLH group). All patients with abnormal MRI had neurological symptoms. Abnormal MRIs showed white matter lesions; the posterior fossa was affected in all but one case. There was no significant difference between groups regarding the localization or morphology of white matter lesions. The striatum was more frequently affected in the EBV-induced HLH group (8/9 (89%) versus 1/12 (8%), p = 0.00037). All lesions, whether in the white matter or in the basal ganglia, presented increased ADC values on diffusion weighted imaging (DWI). CONCLUSION: In this study of 75 children with genetically confirmed HLH, only children with neurological signs had abnormal brain MRI. Bilateral striatum involvement suggested an EBV-induced form of HLH. KEY POINTS: • In children with genetically proven HLH, only those with neurological signs did have brain abnormalities at MRI. • All patients with abnormal brain MRI had multiple white matter lesions with increased ADC values, including in the posterior fossa in almost all cases. • Basal ganglia and in particular the striatum were bilaterally and symmetrically affected in almost all EBV-induced HLH patients, in contrast to the non-EBV-induced HLH patients.

Molecular and clinicopathologic characterization of pediatric histiocytoses.

The spectrum of somatic mutations in pediatric histiocytoses and their clinical implications are not fully characterized, especially for non-Langerhans cell histiocytosis (-LCH) subtypes. A cohort of 415 children with histiocytosis from the French histiocytosis registry was reviewed and analyzed for BRAFV600E . Most BRAFWT samples were analyzed by next-generation sequencing (NGS) with a custom panel of genes for histiocytosis and myeloid neoplasia. Of 415 case samples, there were 366 LCH, 1 Erdheim-Chester disease, 21 Rosai-Dorfman disease (RDD), 21 juvenile xanthogranuloma (JXG, mostly with severe presentation), and 6 malignant histiocytosis (MH). BRAFV600E was the most common mutation found in LCH (50.3%, n = 184). Among 105 non-BRAFV600E -mutated LCH case samples, NGS revealed mutations as follows: MAP2K1 (n = 44), BRAF exon 12 deletions (n = 26), and duplications (n = 8), other BRAF V600 codon mutation (n = 4), and non-MAP-kinase pathway genes (n = 5). Wild-type sequences were identified in 17.1% of samples. BRAFV600E was the only variant significantly correlated with critical presentations: organ-risk involvement and neurodegeneration. MAP-kinase pathway mutations were identified in seven RDD (mostly MAP2K1) and three JXG samples, but most samples were wild-type on NGS. Finally, two MH samples had KRAS mutations, and one had a novel BRAFG469R mutation. Rarely, we identified mutations unrelated to MAP-kinase pathway genes. In conclusion, we characterized the mutational spectrum of childhood LCH and clinical correlations of variants and subtypes. Variants responsible for JXG and RDD were not elucidated in more than half of the cases, calling for other sequencing approaches.

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

BACKGROUND: Hematopoietic stem cell transplantation (HSCT) represents a curative treatment for patients with severe combined immunodeficiency (SCID), a group of monogenic immune disorders with an otherwise fatal outcome. OBJECTIVE: We performed a comprehensive multicenter analysis of genotype-specific HSCT outcome, including detailed analysis of immune reconstitution (IR) and the predictive value for clinical outcome. METHODS: HSCT outcome was studied in 338 patients with genetically confirmed SCID who underwent transplantation in 2006-2014 and who were registered in the SCETIDE registry. In a representative subgroup of 152 patients, data on IR and long-term clinical outcome were analyzed. RESULTS: Two-year OS was similar with matched family and unrelated donors and better than mismatched donor HSCT (P < .001). The 2-year event-free survival (EFS) was similar in matched and mismatched unrelated donor and less favorable in mismatched related donor (MMRD) HSCT (P < .001). Genetic subgroups did not differ in 2-year OS (P = .1) and EFS (P = .073). In multivariate analysis, pretransplantation infections and use of MMRDs were associated with less favorable OS and EFS. With a median follow-up of 6.2 years (range, 2.0-11.8 years), 73 of 152 patients in the IR cohort were alive and well without Ig dependency. IL-2 receptor gamma chain/Janus kinase 3/IL-7 receptor-deficient SCID, myeloablative conditioning, matched donor HSCT, and naive CD4 T lymphocytes >0.5 × 10e3/µL at +1 year were identified as independent predictors of favorable clinical and immunologic outcome. CONCLUSION: Recent advances in HSCT in SCID patients have resulted in improved OS and EFS in all genotypes and donor types. To achieve a favorable long-term outcome, treatment strategies should aim for optimal naive CD4 T lymphocyte regeneration.