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.

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.

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.

Activated phosphoinositide 3-kinase δ syndrome: Update from the ESID Registry and comparison with other autoimmune-lymphoproliferative inborn errors of immunity

BACKGROUND

Activated phosphoinositide-3-kinase δ syndrome (APDS) is an inborn error of immunity (IEI) with infection susceptibility and immune dysregulation, clinically overlapping with other conditions. Management depends on disease evolution, but predictors of severe disease are lacking.

OBJECTIVES

This study sought to report the extended spectrum of disease manifestations in APDS1 versus APDS2; compare these to CTLA4 deficiency, NFKB1 deficiency, and STAT3 gain-of-function (GOF) disease; and identify predictors of severity in APDS.

METHODS

Data was collected from the ESID (European Society for Immunodeficiencies)-APDS registry and was compared with published cohorts of the other IEIs.

RESULTS

The analysis of 170 patients with APDS outlines high penetrance and early onset of APDS compared to the other IEIs. The large clinical heterogeneity even in individuals with the same PIK3CD variant E1021K illustrates how poorly the genotype predicts the disease phenotype and course. The high clinical overlap between APDS and the other investigated IEIs suggests relevant pathophysiological convergence of the affected pathways. Preferentially affected organ systems indicate specific pathophysiology: bronchiectasis is typical of APDS1; interstitial lung disease and enteropathy are more common in STAT3 GOF and CTLA4 deficiency. Endocrinopathies are most frequent in STAT3 GOF, but growth impairment is also common, particularly in APDS2. Early clinical presentation is a risk factor for severe disease in APDS.

CONCLUSIONS

APDS illustrates how a single genetic variant can result in a diverse autoimmune-lymphoproliferative phenotype. Overlap with other IEIs is substantial. Some specific features distinguish APDS1 from APDS2. Early onset is a risk factor for severe disease course calling for specific treatment studies in younger patients.

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.

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.

Impact of Graft Function on Health Status and Quality of Life in Very Long-Term Survivors Who Received an HSCT for Inborn Errors of Immunity, a Prospective Study of the CEREDIH

The overall survival rate after hematopoietic stem cell transplantation (HSCT) for inborn errors of immunity (IEI) has improved considerably, and its indications have broadened. As a consequence, addressing the issue of long-term health-related quality of life (HRQoL) has become crucial. Our study focuses on the health and HRQoL of post-HSCT survivors. We conducted a multicenter prospective follow-up study enrolling IEI patients who underwent transplantation in childhood before 2009. Self-reported data from the French Childhood Immune Deficiency Long-term Cohort and the 36-item Short Form questionnaires were compiled. One hundred twelve survivors were included with a median duration period from HSCT of 15 years (range 5-37), of whom 55 underwent transplantation for a combined immunodeficiency. We show that in patients evaluated at least 5 years after HSCT, 55% are still affected by a poor or very poor health status. Poor and very poor health status correlated with an abnormal graft function, defined as host or mixed chimerism, abnormal CD3+ count, or diagnosis of chronic graft-versus-host disease (poor health: odds ratio [OR] = 2.6, 95% confidence interval [CI], 1.1-5.9, P = .028; very poor health: OR = 3.6, 95% CI, 1.1-13, P = .049). Poor health was directly linked to a poorer HRQoL. Significant improvements in graft procedures have translated into better survival rates, but we show here that about half of the transplanted patients remain affected by an altered health status with a correlation to both abnormal graft function and impaired HRQoL. Additional studies are needed to confirm the impact of those improvements on long-term health status and HRQoL.

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.

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.

Late-onset enteric virus infection associated with hepatitis (EVAH) in transplanted SCID patients

BACKGROUND

Allogenic hematopoietic stem cell transplantation (HSCT) and gene therapy (GT) are potentially curative treatments for severe combined immunodeficiency (SCID). Late-onset posttreatment manifestations (such as persistent hepatitis) are not uncommon.

OBJECTIVE

We sought to characterize the prevalence and pathophysiology of persistent hepatitis in transplanted SCID patients (SCIDH+) and to evaluate risk factors and treatments.

METHODS

We used various techniques (including pathology assessments, metagenomics, single-cell transcriptomics, and cytometry by time of flight) to perform an in-depth study of different tissues from patients in the SCIDH+ group and corresponding asymptomatic similarly transplanted SCID patients without hepatitis (SCIDH-).

RESULTS

Eleven patients developed persistent hepatitis (median of 6 years after HSCT or GT). This condition was associated with the chronic detection of enteric viruses (human Aichi virus, norovirus, and sapovirus) in liver and/or stools, which were not found in stools from the SCIDH- group (n = 12). Multiomics analysis identified an expansion of effector memory CD8+ T cells with high type I and II interferon signatures. Hepatitis was associated with absence of myeloablation during conditioning, split chimerism, and defective B-cell function, representing 25% of the 44 patients with SCID having these characteristics. Partially myeloablative retransplantation or GT of patients with this condition (which we have named as "enteric virus infection associated with hepatitis") led to the reconstitution of T- and B-cell immunity and remission of hepatitis in 5 patients, concomitantly with viral clearance.

CONCLUSIONS

Enteric virus infection associated with hepatitis is related to chronic enteric viral infection and immune dysregulation and is an important risk for transplanted SCID patients with defective B-cell function.

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.

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

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

Hematopoietic stem cell transplantation, a curative approach in infantile osteopetrosis

Most patients with osteopetrosis (OPT) can be causally and curatively treated with allogeneic hematopoietic stem cell transplantation (HSCT) because osteoclasts are derived from the HSC. However, HSCT is contraindicated in some forms of OPT, namely OPT with neurodegeneration (in all patients with OSTM1 and about half of patients with CLCN7 mutations) and OPT caused by an osteoblast defect (patients with RANKL mutations). HSCT for OPT risks serious side effects, such as transplant failure, venous occlusive disease, pulmonary hypertension, and hypercalcemic crises. Nevertheless, the success rate of HSCT has improved significantly in recent decades. This applies, in particular, to HSCT from non-HLA compatible (haploidentical) donors. Therefore, nowadays an HSCT can be discussed for intermediate OPT forms. After a successful HSCT, most patients have very good quality of life, but about two-thirds are visually impaired, and in rarer cases show motor and neurological disabilities. Early diagnosis, further improvements in transplantation procedures, and advances to improve quality-of-life after transplantation are challenges for the future.

An evolutionarily conserved coronin-dependent pathway defines cell population size

Maintenance of cell population size is fundamental to the proper functioning of multicellular organisms. Here, we describe a cell-intrinsic cell density–sensing pathway that enabled T cells to reach and maintain an appropriate population size. This pathway operated “kin-to-kin” or between identical or similar T cell populations occupying a niche within a tissue or organ, such as the lymph nodes, spleen, and blood. We showed that this pathway depended on the cell density–dependent abundance of the evolutionarily conserved protein coronin 1, which coordinated prosurvival signaling with the inhibition of cell death until the cell population reached threshold densities. At or above threshold densities, coronin 1 expression peaked and remained stable, thereby resulting in the initiation of apoptosis through kin-to-kin intercellular signaling to return the cell population to the appropriate cell density. This cell population size-controlling pathway was conserved from amoeba to humans, thus providing evidence for the existence of a coronin-regulated, evolutionarily conserved mechanism by which cells are informed of and coordinate their relative population size.

Child Neurology: Familial Hemophagocytic Lymphohistiocytosis Underlying Isolated Central Nervous System Inflammation

Encephalitis and encephalopathy in children represent a diagnostic challenge. We describe a patient with relapsing encephalitis in whom the differential diagnosis included acute disseminated encephalomyelitis (ADEM), human herpesvirus 6 (HHV-6) encephalitis, and hemophagocytic lymphohistiocytosis (HLH). Because of its rarity, HLH is often overlooked as a differential diagnosis in encephalitis, especially in the isolated central nervous system (CNS) forms. As this case illustrates, inborn errors of immunity (IEIs) can underlie isolated encephalitis and should be included in the differential diagnosis of these presentations.

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.

Patients with partial recombination-activating gene (RAG) deficiency (pRD) present variable late-onset autoimmune clinical phenotypes. Walter and colleagues identified a restricted primary B cell antigen receptor repertoire enriched for autoreactivity and clonal persistence in pRD. They described dysregulated B cell maturation with expansion of T-bet⁺ B cells revealing how RAG impacts stringency of tolerance and B cell fate in the periphery.

Curative allogeneic hematopoietic stem cell transplantation following reduced toxicity conditioning in adults with primary immunodeficiency

Primary immunodeficiencies (PID) are heterogeneous inborn errors of the immune system. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is curative and safe at the pediatric age but remains underperformed in adults. We report our experience on 32 consecutive adult patients with various PID including 17 (53%) with a combined immune deficiency, six (19%) with a disease of immune dysregulation and nine (28%) with a chronic granulomatous disease (CGD) who underwent an allo-HSCT between 2011 and 2020. The median age at transplant was 27 years (17-41). All assessable patients engrafted. The majority of patients received a fludarabine-Busulfan (FB) based regimen (FB2-3 in 16, FB4 in 12). Overall survival (OS) was 80.4% (100% for CGD and 74% for other PID patients) at 9 months and beyond (median follow-up 51.6 months). Six patients died, all in the first-year post-transplant. Cumulative incidences of grade II-IV acute GVHD/chronic GVHD were 18%/22%. Stem cell source, GVHD prophylaxis and conditioning intensity had no impact on OS. All surviving patients had over 90% donor chimerism, immune reconstitution, no sign of active PID related complications and were clinically improved. Allo-HSCT is effective in young adults PID patients with an acceptable toxicity and should be discussed in case of life-threatening PID.

Inherited TNFSF9 deficiency causes broad Epstein-Barr virus infection with EBV+ smooth muscle tumors

Epstein-Barr virus (EBV) can infect smooth muscle cells causing smooth muscle tumors (SMTs) or leiomyoma. Here, we report a patient with a heterozygous 22q11.2 deletion/DiGeorge syndrome who developed a unique, broad, and lethal susceptibility to EBV characterized by EBV-infected T and B cells and disseminated EBV+SMT. The patient also harbored a homozygous missense mutation (p.V140G) in TNFSF9 coding for CD137L/4-1BBL, the ligand of the T cell co-stimulatory molecule CD137/4-1BB, whose deficiency predisposes to EBV infection. We show that wild-type CD137L was up-regulated on activated monocytes and dendritic cells, EBV-infected B cells, and SMT. The CD137LV140G mutant was weakly expressed on patient cells or when ectopically expressed in HEK and P815 cells. Importantly, patient EBV-infected B cells failed to trigger the expansion of EBV-specific T cells, resulting in decreased T cell effector responses. T cell expansion was recovered when CD137L expression was restored on B cells. Therefore, these results highlight the critical role of the CD137-CD137L pathway in anti-EBV immunity, in particular in the control of EBV+SMT.

Inborn errors of immunity caused by defects in the DNA damage response pathways: Importance of minimizing treatment-related genotoxicity

Several primary immunodeficiencies are caused by defects in the general DNA repair machinery as exemplified by the T-B- radiosensitive SCID condition owing to impaired resolution of programmed DNA double-strand breaks introduced by RAG1/2 during V(D)J recombination. The genome instability generally associated with these conditions results in an increased propensity to develop malignancies requiring genotoxic-based anti-cancer treatments. Moreover, the extent of immune deficiency often calls for hematopoietic stem cell transplantation as a definitive treatment, also requiring genotoxic-based conditioning regimen prior to transplantation. In both cases, the underlying general DNA repair defect may result in catastrophic iatrogenic consequences. It is, therefore, of paramount importance to assess the functionality of the DNA repair apparatus prior to any genotoxic treatment when the exact molecular cause of the disease is unknown. For this purpose, two simple assays can be used on patients derived peripheral blood lymphocytes: (1) the PROMIDISα biomarker, based on the next-generation sequencing analysis of the TCRα repertoire, will highlight specific signatures of DNA repair deficiencies; (2) direct analysis of the sensitivity of peripheral lymphocytes to ionizing radiation will formally identify patients at risk to develop toxicity toward genotoxic-based treatments.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Hematopoietic Cell Transplantation Cures Adenosine Deaminase 2 Deficiency: Report on 30 Patients

PURPOSE

Deficiency of adenosine deaminase 2 (DADA2) is an inherited inborn error of immunity, characterized by autoinflammation (recurrent fever), vasculopathy (livedo racemosa, polyarteritis nodosa, lacunar ischemic strokes, and intracranial hemorrhages), immunodeficiency, lymphoproliferation, immune cytopenias, and bone marrow failure (BMF). Tumor necrosis factor (TNF-α) blockade is the treatment of choice for the vasculopathy, but often fails to reverse refractory cytopenia. We aimed to study the outcome of hematopoietic cell transplantation (HCT) in patients with DADA2.

METHODS

We conducted a retrospective study on the outcome of HCT in patients with DADA2. The primary outcome was overall survival (OS).

RESULTS

Thirty DADA2 patients from 12 countries received a total of 38 HCTs. The indications for HCT were BMF, immune cytopenia, malignancy, or immunodeficiency. Median age at HCT was 9 years (range: 2-28 years). The conditioning regimens for the final transplants were myeloablative (n = 20), reduced intensity (n = 8), or non-myeloablative (n = 2). Donors were HLA-matched related (n = 4), HLA-matched unrelated (n = 16), HLA-haploidentical (n = 2), or HLA-mismatched unrelated (n = 8). After a median follow-up of 2 years (range: 0.5-16 years), 2-year OS was 97%, and 2-year GvHD-free relapse-free survival was 73%. The hematological and immunological phenotypes resolved, and there were no new vascular events. Plasma ADA2 enzyme activity normalized in 16/17 patients tested. Six patients required more than one HCT.

CONCLUSION

HCT was an effective treatment for DADA2, successfully reversing the refractory cytopenia, as well as the vasculopathy and immunodeficiency.

CLINICAL IMPLICATIONS

HCT is a definitive cure for DADA2 with > 95% survival.

Neurological involvement in secondary hemophagocytic lymphohistiocytosis in children

OBJECTIVES

To describe neurological characteristics and CNS involvement on MRI in secondary hemophagocytic lymphohistiocytosis (sHLH) and differentiate it from primary hemophagocytic lymphohistiocytosis (pHLH) and acute disseminated encephalomyelitis (ADEM).

METHODS

Nine children with sHLH who had neurological symptoms were retrospectively included. Characteristics of brain MRI were compared to those of 15 children with pHLH and neurological involvement and 44 children with ADEM.

RESULTS

Three children (33%) presented with isolated neurological symptoms. Neurological signs occurred within one month following Epstein-Barr virus primary infection or systemic juvenile arthritis exacerbation in 8 patients (89%). Eight children (89%) had MRI lesions. sHLH MRI lesions were distinct of those of pHLH by morphology and signal with more frequent hyposignal intensities on T1-weighted sequences (p = 0.01) and well-defined and less fuzzy lesions (p = 0.03). All patients survived and one patient presented severe motor and cognitive disability.

CONCLUSION

Neurological symptoms of sHLH are non-specific and their outcome is favorable in most of the children. MRI at onset may help to differentiate this condition from pHLH.

Different Clinical Presentations and Outcomes of Disseminated Varicella in Children With Primary and Acquired Immunodeficiencies

Primary infection with varicella-zoster virus (VZV) causes chickenpox, a benign and self-limited disease in healthy children. In patients with primary or acquired immunodeficiencies, primary infection can be life-threatening, due to rapid dissemination of the virus to various organs [lung, gastrointestinal tract, liver, eye, central nervous system (CNS)]. We retrospectively described and compared the clinical presentations and outcomes of disseminated varicella infection (DV) in patients with acquired (AID) (n= 7) and primary (PID) (n= 12) immunodeficiencies. Patients with AID were on immunosuppression (mostly steroids) for nephrotic syndrome, solid organ transplantation or the treatment of hemopathies, whereas those with PID had combined immunodeficiency (CID) or severe CID (SCID). The course of the disease was severe and fulminant in patients with AID, with multiple organ failure, no rash or a delayed rash, whereas patients with CID and SICD presented typical signs of chickenpox, including a rash, with dissemination to other organs, including the lungs and CNS. In the PID group, antiviral treatment was prolonged until immune reconstitution after bone marrow transplantation, which was performed in 10/12 patients. Four patients died, and three experienced neurological sequelae. SCID patients had the worst outcome. Our findings highlight substantial differences in the clinical presentation and course of DV between children with AID and PID, suggesting differences in pathophysiology. Prevention, early diagnosis and treatment are required to improve outcome.

Thymic Epithelial Cell Alterations and Defective Thymopoiesis Lead to Central and Peripheral Tolerance Perturbation in MHCII Deficiency

Major Histocompatibility Complex (MHC) class II (MHCII) deficiency (MHCII-D), also known as Bare Lymphocyte Syndrome (BLS), is a rare combined immunodeficiency due to mutations in genes regulating expression of MHCII molecules. MHCII deficiency results in impaired cellular and humoral immune responses, leading to severe infections and autoimmunity. Abnormal cross-talk with developing T cells due to the absence of MHCII expression likely leads to defects in thymic epithelial cells (TEC). However, the contribution of TEC alterations to the pathogenesis of this primary immunodeficiency has not been well characterized to date, in particular in regard to immune dysregulation. To this aim, we have performed an in-depth cellular and molecular characterization of TEC in this disease. We observed an overall perturbation of thymic structure and function in both MHCII-/- mice and patients. Transcriptomic and proteomic profiling of murine TEC revealed several alterations. In particular, we demonstrated that impairment of lymphostromal cross-talk in the thymus of MHCII-/- mice affects mTEC maturation and promiscuous gene expression and causes defects of central tolerance. Furthermore, we observed peripheral tolerance impairment, likely due to defective Treg cell generation and/or function and B cell tolerance breakdown. Overall, our findings reveal disease-specific TEC defects resulting in perturbation of central tolerance and limiting the potential benefits of hematopoietic stem cell transplantation in MHCII deficiency.

International retrospective study of allogeneic hematopoietic cell transplantation for activated PI3K-delta syndrome

Background:

Activated phosphoinositide 3-kinase delta syndrome (APDS) is a combined immunodeficiency with a heterogeneous phenotype considered reversible by allogeneic hematopoietic cell transplantation (HCT).

Objectives:

This study sought to characterize HCT outcomes in APDS.

Methods:

Retrospective data were collected on 57 patients with APDS1/2 (median age, 13 years; range, 2–66 years) who underwent HCT.

Results:

Pre-HCT comorbidities such as lung, gastrointestinal, and liver pathology were common, with hematologic malignancy in 26%. With median follow-up of 2.3 years, 2-year overall and graft failure–free survival probabilities were 86% and 68%, respectively, and did not differ significantly by APDS1 versus APDS2, donor type, or conditioning intensity. The 2-year cumulative incidence of graft failure following first HCT was 17% overall but 42% if mammalian target of rapamycin inhibitor(s) (mTORi) were used in the first year post-HCT, compared with 9% without mTORi. Similarly, 2-year cumulative incidence of unplanned donor cell infusion was overall 28%, but 65% in the context of mTORi receipt and 23% without. Phenotype reversal occurred in 96% of evaluable patients, of whom 17% had mixed chimerism. Vulnerability to renal complications continued post-HCT, adding new insights into potential nonimmunologic roles of phosphoinositide 3-kinase not correctable through HCT.

Conclusions:

Graft failure, graft instability, and poor graft function requiring unplanned donor cell infusion were major barriers to successful HCT. Post-HCT mTORi use may confer an advantage to residual host cells, promoting graft instability. Longer-term post-HCT follow-up of more patients is needed to elucidate the kinetics of immune reconstitution and donor chimerism, establish approaches that reduce graft instability, and assess the completeness of phenotype reversal over time.

Current Spectrum of Infections in Patients with X-Linked Agammaglobulinemia

Outcome of patients with X-linked agammaglobulinemia (XLA) has improved with the widespread use of immunoglobulin replacement therapy (IgRT). There are few data on the spectrum of infections experienced by patients undergoing IgRT. We carried out a retrospective cross-sectional analysis of the records of XLA patients seen at Necker-Enfants Malades Hospital, Paris. For each infection, we evaluated infection site, microbial etiology, antibiotic prophylaxis, immunosuppressive treatment, IgRT route, and last known IgG trough level. Sixty patients were included, who cumulated a follow-up of 1470 patient-years. We recorded 188 infections, including 97 after initiation of IgRT. The rate of infection was highest before IgRT (0.66 vs. 0.06 per person-year (ppy), p < 0.001) and was higher after the age of 16 compared to before (0.14 vs. 0.05 ppy, p = 0.048). It was similar for patients receiving intravenous or subcutaneous Ig (0.09 vs 0.05 ppy, p = 0.54). The lungs and gastrointestinal tract accounted for 71% of infection sites. Forty-six (47%) infections occurred in patients receiving antibiotic prophylaxis. Sixteen (16.5%) infections occurred in patients receiving immunosuppressive therapy, which more frequently occurred after age 16 (35% vs. 2.4%, p < 0.001). The median IgG trough level prior to all infections was 8.4 g/L. Almost half (44.3%) of infections occurred with prior IgG trough levels > 8 g/L, and 16/97 (16.7%) in patients with trough levels > 10 g/L. Infection remains a significant issue in patients with XLA undergoing IgRT despite adequate IgG trough levels. Chronic inflammatory manifestations of X-linked agammaglobulinemia and immunosuppressive therapies may be significant drivers of infection during adulthood.

Rapid identification and characterization of infected cells in blood during chronic active Epstein-Barr virus infection

Epstein-Barr virus (EBV) preferentially infects epithelial cells and B lymphocytes and sometimes T and NK lymphocytes. Persistence of EBV-infected cells results in severe lymphoproliferative disorders (LPDs). Diagnosis of EBV-driven T or NK cell LPD and chronic active EBV diseases (CAEBV) is difficult, often requiring biopsies. Herein, we report a flow-FISH cytometry assay that detects cells expressing EBV-encoded small RNAs (EBERs), allowing rapid identification of EBV-infected cells among PBMCs. EBV-infected B, T, and/or NK cells were detectable in various LPD conditions. Diagnosis of CAEBV in 22 patients of Caucasian and African origins was established. All exhibited circulating EBV-infected T and/or NK cells, highlighting that CAEBV is not restricted to native American and Asian populations. Proportions of EBV-infected cells correlated with blood EBV loads. We showed that EBV-infected T cells had an effector memory activated phenotype, whereas EBV-infected B cells expressed plasma cell differentiation markers. Thus, this method achieves accurate and unambiguous diagnoses of different forms of EBV-driven LPD and represents a powerful tool to study their pathophysiological mechanisms.

Two Novel Homozygous Mutations in Phosphoglucomutase 3 Leading to Severe Combined Immunodeficiency, Skeletal Dysplasia, and Malformations

Phosphoglucomutase 3 (PGM3) deficiency is a rare congenital disorder of glycosylation. Most of patients with autosomal recessive hypomorphic mutations in PGM3 encoding for phosphoglucomutase 3 present with eczema, skin and lung infections, elevated serum IgE, as well as neurological and skeletal features. A few PGM3-deficient patients suffer from a more severe disease with nearly absent T cells and severe skeletal dysplasia. We performed targeted next-generation sequencing on two kindred to identify the underlying genetic etiology of a severe combined immunodeficiency with developmental defect. We report here two novel homozygous missense variants (p.Gly359Asp and p.Met423Thr) in PGM3 identified in three patients from two unrelated kindreds with severe combined immunodeficiency, neurological impairment, and skeletal dysplasia. Both variants segregated with the disease in the two families. They were predicted to be deleterious by in silico analysis. PGM3 enzymatic activity was found to be severely impaired in primary fibroblasts and Epstein-Barr virus immortalized B cells from the kindred carrying the p.Met423Thr variant. Our findings support the pathogenicity of these two novel variants in severe PGM3 deficiency.

Overview of STING-Associated Vasculopathy with Onset in Infancy (SAVI) Among 21 Patients

BACKGROUND

Gain-of-function mutations in STING1 underlie a type I interferonopathy termed SAVI (STING-associated vasculopathy with onset in infancy). This severe disease is variably characterized by early-onset systemic inflammation, skin vasculopathy, and interstitial lung disease (ILD).

OBJECTIVE

To describe a cohort of patients with SAVI.

METHODS

Assessment of clinical, radiological and immunological data from 21 patients (17 families) was carried out.

RESULTS

Patients carried heterozygous substitutions in STING1 previously described in SAVI, mainly the p.V155M. Most were symptomatic from infancy, but late onset in adulthood occurred in 1 patient. Systemic inflammation, skin vasculopathy, and ILD were observed in 19, 18, and 21 patients, respectively. Extensive tissue loss occurred in 4 patients. Severity of ILD was highly variable with insidious progression up to end-stage respiratory failure reached at teenage in 6 patients. Lung imaging revealed early fibrotic lesions. Failure to thrive was almost constant, with severe growth failure seen in 4 patients. Seven patients presented polyarthritis, and the phenotype in 1 infant mimicked a combined immunodeficiency. Extended features reminiscent of other interferonopathies were also found, including intracranial calcification, glaucoma and glomerular nephropathy. Increased expression of interferon-stimulated genes and interferon α protein was constant. Autoantibodies were frequently found, in particular rheumatoid factor. Most patients presented with a T-cell defect, with low counts of memory CD8+ cells and impaired T-cell proliferation in response to antigens. Long-term follow-up described in 8 children confirmed the clinical benefit of ruxolitinib in SAVI where the treatment was started early in the disease course, underlying the need for early diagnosis. Tolerance was reasonably good.

CONCLUSION

The largest worldwide cohort of SAVI patients yet described, illustrates the core features of the disease and extends the clinical and immunological phenotype to include overlap with other monogenic interferonopathies.

A gain-of-function RAC2 mutation is associated with bone-marrow hypoplasia and an autosomal dominant form of severe combined immunodeficiency

Severe combined immunodeficiencies (SCIDs) constitute a heterogeneous group of life-threatening genetic disorders that typically present in the first year of life. They are defined by the absence of autologous T cells and the presence of an intrinsic or extrinsic defect in the B-cell compartment. In three newborns presenting with frequent infections and profound leukopenia, we identified a private, heterozygous mutation in the RAC2 gene (p.G12R). This mutation was de novo in the index case, who had been cured by hematopoietic stem cell transplantation but had transmitted the mutation to her sick daughter. Biochemical assays showed that the mutation was associated with a gain of function. The results of in vitro differentiation assays showed that RAC2 is essential for the survival and differentiation of hematopoietic stem/progenitor cells. Therefore, screening for RAC2 gain-of-function mutations should be considered in patients with a SCID phenotype and who lack a molecular diagnosis.

Expanded circulating hematopoietic stem/progenitor cells as novel cell source for the treatment of TCIRG1 osteopetrosis

Allogeneic hematopoietic stem cell transplantation is the treatment of choice for autosomal recessive osteopetrosis caused by defects in the TCIRG1 gene. Despite recent progress in conditioning, a relevant number of patients are not eligible for allogeneic stem cell transplantation because of the severity of the disease and significant transplant-related morbidity. We exploited peripheral CD34+ cells, known to circulate at high frequency in the peripheral blood of TCIRG1-deficient patients, as a novel cell source for autologous transplantation of gene corrected cells. Detailed phenotypical analysis showed that circulating CD34+ cells have a cellular composition that resembles bone marrow, supporting their use in gene therapy protocols. Transcriptomic profile revealed enrichment in genes expressed by hematopoietic stem and progenitor cells (HSPCs). To overcome the limit of bone marrow harvest/ HSPC mobilization and serial blood drawings in TCIRG1 patients, we applied UM171-based ex-vivo expansion of HSPCs coupled with lentiviral gene transfer. Circulating CD34+ cells from TCIRG1-defective patients were transduced with a clinically-optimized lentiviral vector (LV) expressing TCIRG1 under the control of phosphoglycerate promoter and expanded ex vivo. Expanded cells maintained long-term engraftment capacity and multi-lineage repopulating potential when transplanted in vivo both in primary and secondary NSG recipients. Moreover, when CD34+ cells were differentiated in vitro, genetically corrected osteoclasts resorbed the bone efficiently. Overall, we provide evidence that expansion of circulating HSPCs coupled to gene therapy can overcome the limit of stem cell harvest in osteopetrotic patients, thus opening the way to future gene-based treatment of skeletal diseases caused by bone marrow fibrosis.

Bayesian Modeling Immune Reconstitution Apply to CD34+ Selected Stem Cell Transplantation for Severe Combined Immunodeficiency

Severe combined immunodeficiencies (SCIDs) correspond to the most severe form of primary immunodeficiency. Allogeneic hematopoietic stem cell transplantation (HSCT) and gene therapy are curative treatments, depending on the donor's availability and molecular diagnostics. A partially human leukocyte antigen (HLA)-compatible donor used has been developed for this specific HSCT indication in the absence of a matched donor. However, the CD34+ selected process induces prolonged post-transplant T-cell immunodeficiency. The aim here was to investigate a modeling approach to predict the time course and the extent of CD4+ T-cell immune reconstitution after CD34+ selected transplantation. We performed a Bayesian approach based on the age-related changes in thymic output and the cell proliferation/loss model. For that purpose, we defined specific individual covariates from the data collected from 10 years of clinical practice and then evaluated the model's predicted performances and accuracy. We have shown that this Bayesian modeling approach predicted the time course and extent of CD4+ T-cell immune reconstitution after SCID transplantation.

Seletalisib for Activated PI3Kδ Syndromes: Open-Label Phase 1b and Extension Studies

Mutations in two genes can result in activated PI3Kδ syndrome (APDS), a rare immunodeficiency disease with limited therapeutic options. Seletalisib, a potent, selective PI3Kδ inhibitor, was evaluated in patients with APDS1 and APDS2. In the phase 1b study (European Clinical Trials Database 2015-002900-10) patients with genetic and clinical confirmation of APDS1 or APDS2 received 15-25 mg/d seletalisib for 12 wk. Patients could enter an extension study (European Clinical Trials Database 2015-005541). Primary endpoints were safety and tolerability, with exploratory efficacy and immunology endpoints. Seven patients (median age 15 years; APDS1 n = 3; APDS2 n = 4) received seletalisib; five completed the phase 1b study. For the extension study, four patients entered, one withdrew consent (week 24), three completed ≥84 wk of treatment. In the phase 1b study, patients had improved peripheral lymphadenopathy (n = 2), lung function (n = 1), thrombocyte counts (n = 1), and chronic enteropathy (n = 1). Overall, effects were maintained in the extension. In the phase 1b study, percentages of transitional B cells decreased, naive B cells increased, and senescent CD8 T cells decreased (human cells); effects were generally maintained in the extension. Seletalisib-related adverse events occurred in four of seven patients (phase 1b study: hepatic enzyme increased, dizziness, aphthous ulcer, arthralgia, arthritis, increased appetite, increased weight, restlessness, tendon disorder, and potential drug-induced liver injury) and one of four patients had adverse events in the extension (aphthous ulcer). Serious adverse events occurred in three of seven patients (phase 1b study: hospitalization, colitis, and potential drug-induced liver injury) and one of four patients had adverse events in the extension (stomatitis). Patients with APDS receiving seletalisib had improvements in variable clinical and immunological features, and a favorable risk-benefit profile was maintained for ≤96 wk.

Vasculitis as a Major Morbidity Factor in Patients With Partial RAG Deficiency

Vasculitis can be a life-threatening complication associated with high mortality and morbidity among patients with primary immunodeficiencies (PIDs), including variants of severe and combined immunodeficiencies ((S)CID). Our understanding of vasculitis in partial defects in recombination activating gene (RAG) deficiency, a prototype of (S)CIDs, is limited with no published systematic evaluation of diagnostic and therapeutic modalities. In this report, we sought to establish the clinical, laboratory features, and treatment outcome of patients with vasculitis due to partial RAG deficiency. Vasculitis was a major complication in eight (13%) of 62 patients in our cohort with partial RAG deficiency with features of infections and immune dysregulation. Vasculitis occurred early in life, often as first sign of disease (50%) and was complicated by significant end organ damage. Viral infections often preceded the onset of predominately non-granulomatous-small vessel vasculitis. Autoantibodies against cytokines (IFN-α, -ω, and IL-12) were detected in a large fraction of the cases tested (80%), whereas the majority of patients were anti-neutrophil cytoplasmic antibodies (ANCA) negative (>80%). Genetic diagnosis of RAG deficiency was delayed up to 2 years from the onset of vasculitis. Clinical cases with sole skin manifestation responded well to first-line steroid treatment, whereas systemic vasculitis with severe end-organ complications required second-line immunosuppression and/or hematopoietic stem cell transplantation (HSCT) for definitive management. In conclusion, our data suggest that vasculitis in partial RAG deficiency is prevalent among patients with partial RAG deficiency and is associated with high morbidity. Therefore, partial RAG deficiency should be included in the differential diagnosis of patients with early-onset systemic vasculitis. Diagnostic serology may be misleading with ANCA negative findings, and search for conventional autoantibodies should be extended to include those targeting cytokines.

New dosing nomogram and population pharmacokinetic model for young and very young children receiving busulfan for hematopoietic stem cell transplantation conditioning

BACKGROUND

Busulfan (Bu) is the cornerstone of conditioning regimens prior to hematopoietic stem cell transplantation, widely used in both adults and children for the treatment of malignant and nonmalignant diseases. Despite an intravenous formulation, interindividual variability (IIV) remains high and optimal exposure difficult to achieve, especially in neonates and infants.

PROCEDURE

To ensure both efficacy and safety, we set up in 2005 an observational study designed for children not fully assessed during the drug registration procedure. From a large cohort of 540 patients, we developed a Bu population pharmacokinetic model based on body weight (BW) and maturation concepts to reduce IIV and optimize exposure. A new dosing nomogram was evaluated to better fit the population pharmacokinetic model.

RESULTS

Bu clearance IIV was significantly decreased from 61.3% (covariate-free model) to 28.6% when combining BW and maturation function. Median Bu area under the curve (AUC) was 1179 µmol/L × min compared to 1025 with the EMA dosing nomogram for children <9 kg. The target AUC was reached for each BW strata, significantly increasing the percentages of patients achieving reaching the targeted AUC as compared to FDA schedule.

CONCLUSION

This new model made it possible to propose a novel dosing nomogram that better considered children below 16 kg of BW and allowed better initial exposure as compared to existing dosing schedules. This nomogram, which would be easy to use to determine an optimal dosing schedule in daily practice, will need to be validated in clinical routine. Therapeutic drug monitoring remains strongly advisable for small children and those with specific diseases.

Childhood Langerhans cell histiocytosis with severe lung involvement: a nationwide cohort study

BACKGROUND

Lung involvement in childhood Langerhans cell histiocytosis (LCH) is infrequent and rarely life threatening, but occasionally, severe presentations are observed.

METHODS

Among 1482 children (< 15 years) registered in the French LCH registry (1994-2018), 111 (7.4%) had lung involvement. This retrospective study included data for 17 (1.1%) patients that required one or more intensive care unit (ICU) admissions for respiratory failure.

RESULTS

The median age was 1.3 years at the first ICU hospitalization. Of the 17 patients, 14 presented with lung involvement at the LCH diagnosis, and 7 patients (41%) had concomitant involvement of risk-organ (hematologic, spleen, or liver). Thirty-five ICU hospitalizations were analysed. Among these, 22 (63%) were secondary to a pneumothorax, 5 (14%) were associated with important cystic lesions without pneumothorax, and 8 (23%) included a diffuse micronodular lung infiltration in the context of multisystem disease. First-line vinblastine-corticosteroid combination therapy was administered to 16 patients; 12 patients required a second-line therapy (cladribine: n = 7; etoposide-aracytine: n = 3; targeted therapy n = 2). A total of 6 children (35%) died (repeated pneumothorax: n = 3; diffuse micronodular lung infiltration in the context of multisystem disease: n = 2; following lung transplantation: n = 1). For survivors, the median follow-up after ICU was 11.2 years. Among these, 9 patients remain asymptomatic despite abnormal chest imaging.

CONCLUSIONS

Severe lung involvement is unusual in childhood LCH, but it is associated with high mortality. Treatment guidelines should be improved for this group of patients: viral infection prophylaxis and early administration of a new LCH therapy, such as targeted therapy.

Chronic Granulomatous Disease with the McLeod Phenotype: a French National Retrospective Case Series

BACKGROUND

X-linked chronic granulomatous disease (CGD) is a primary immunodeficiency caused by mutations in the CYBB gene (located on Xp21.1). Patients with large deletions on chromosome Xp21.1 can present with the McLeod phenotype and also Duchenne muscular dystrophy or retinitis pigmentosa. The objective of the present study was to describe a series of French patients with CGD and the McLeod phenotype.

METHODS

We retrospectively collected data from the medical records of 8 patients with CGD and the McLeod phenotype registered at the French National Reference Center for blood types.

RESULTS

The median age at diagnosis of CGD was 1.2 years, the median age at diagnosis of the McLeod phenotype was 4.5 years, and the median length of follow-up was 15.2 years. Four patients displayed allo-immunization, with anti-KEL20 and anti-XK1 (formerly known as anti-KL) antibodies. Five of the 6 patients with available blood smears had acanthocytosis. Neuropsychiatric, muscle-related, and ocular manifestations were present in 4, 2, and 1 of the patients, respectively. Three of the 4 patients having undergone allogeneic hematopoietic stem cell transplantation (HSCT) are alive. Overall, 5 patients are alive, and 3 are alive and well.

CONCLUSION

This is the largest yet descriptive study of a series of patients with X-linked CGD and the McLeod phenotype. Although this disease combination is rare, the timely, accurate diagnosis of the McLeod phenotype is critical because of the serious post-transfusion complications. However, HSCT can be considered in these patients.

Cutaneous barrier leakage and gut inflammation drive skin disease in Omenn syndrome

Background

Severe early-onset erythroderma and gut inflammation, with massive tissue infiltration of oligoclonal activated T cells are the hallmark of Omenn syndrome (OS).

Objective

The impact of altered gut homeostasis in the cutaneous manifestations of OS remains to be clarified.

Methods

We analyzed a cohort of 15 patients with OS and the 129Sv/C57BL/6 knock-in Rag2^R229Q/R229Q (Rag2^R229Q) mouse model. Homing phenotypes of circulating lymphocytes were analyzed by flow cytometry. Inflammatory cytokines and chemokines were examined in the sera by ELISA and in skin biopsies by immunohistochemistry and in situ RNA hybridization. Experimental colitis was induced in mice by dextran sulfate sodium salt.

Results

We show that memory/activated T cells from patients with OS and from the Rag2^R229Q mouse model of OS abundantly express the skin homing receptors cutaneous lymphocyte associated antigen and CCR4 (Ccr4), associated with high levels of chemokine C-C motif ligands 17 and 22. Serum levels of LPS are also elevated. A broad T_h1/T_h2/T_h17 inflammatory signature is detected in the periphery and in the skin. Increased Tlr4 expression in the skin of Rag2^R229Q mice is associated with enhanced cutaneous inflammation on local and systemic administration of LPS. Likewise, boosting colitis in Rag2^R229Q mice results in increased frequency of Ccr4⁺ splenic T cells and worsening of skin inflammation, as indicated by epidermal thickening, enhanced epithelial cell activation, and dermal infiltration by T_h1 effector T cells.

Conclusions

These results support the existence of an interplay between gut and skin that can sustain skin inflammation in OS.

HSCT may lower leukemia risk in ELANE neutropenia: a before-after study from the French Severe Congenital Neutropenia Registry

ELANE neutropenia is associated with myelodysplasia and acute leukemia (MDS–AL), and severe infections. Because the MDS–AL risk has also been shown to be associated with exposure to GCSF, since 2005, in France, patients receiving high daily GCSF doses (>15 μg/kg/day) are eligible for HSCT, in addition to classic indications (MDS–AL or GCSF refractoriness). We analyzed the effect of this policy. Among 144 prospectively followed ELANE-neutropenia patients enrolled in the French Severe Congenital Neutropenia Registry, we defined two groups according to period: “before 2005” for those born before 2005 and followed until 31/12/2004 (1588 person-years); and “after 2005” comprised of those born after 2005 or born before 2005 but followed after 2005 until 31/03/2019 (1327 person-years). Sixteen of our cohort patients underwent HSCT (14 long-term survivors) and six developed MDS–ALs. Six leukemic transformations occurred in the before-2005 group and none after 2005 (respective frequencies 3.8 × 10^–3 vs. 0; P < 0.01), while four HSCTs were done before 2005 and 12 since 2005 (respective HSCT rates increased 2.5 × 10^–3 vs. 9 × 10^–3; P < 0.01). Our results support early HSCT for patients with ELANE mutations who received high GCSF doses, as it might lower the risk of leukemic transformation.

Bone Marrow Transplantation in Congenital Erythropoietic Porphyria: Sustained Efficacy but Unexpected Liver Dysfunction

Congenital erythropoietic porphyria (CEP) is a rare disease characterized by erosive photosensitivity and chronic hemolysis due to a defect of the enzyme uroporphyrinogen-III-synthase (UROS). To date, hematopoietic stem cell transplantation (HSCT) is the only curative therapy for the devastating early and severe form of the disease. We describe 6 patients with CEP treated with HSCT (3 of them twice after failure of a first graft) between 1994 and 2016 in our center, including 2 of the very first living patients treated more than 20 years ago. Four patients are doing well at 6 to 25 years post-HSCT, with near-normal biochemical parameters of porphyrin metabolism without the cutaneous or hematologic features of CEP. One patient died within the first year after HSCT from severe graft-versus-host disease (GVHD), and 1 child died of unexplained acute hepatic failure at 1 year after HSCT, despite full donor chimerism. Retrospectively, it appears that all but 1 child had increased transaminase activity with onset from the early postnatal period, which was significantly more marked in the child who died of liver failure. In contrast, liver function values progressively normalized after engraftment in all other children. Liver pathology before HSCT for 3 patients revealed varying degrees of portal, centrilobular, and perisinusoidal fibrosis; clarification of hepatocytes; and cytosolic porphyrin deposits. The liver porphyrin content in biopsy specimens was >60 times the normal values. Despite difficult engraftment, the long-term efficacy of HSCT in CEP appears to be favorable and reinforces its benefits for the severe form of CEP. Hepatic involvement requires careful evaluation before and after HSCT and further investigation into its pathophysiology and care.