Hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening, hyperinflammatory syndrome. Emapalumab, a fully human monoclonal antibody that neutralizes the proinflammatory cytokine interferon gamma, is approved in the United States to treat primary HLH (pHLH) in patients with refractory, recurrent, or progressive disease, or intolerance with conventional HLH treatments. REAL-HLH, a retrospective study, conducted across 33 US hospitals, evaluated real-world treatment patterns and outcomes in patients treated with ≥1 dose of emapalumab between 20 November 2018 and 31 October 2021. In total, 46 patients met the pHLH classification criteria. Median age at diagnosis was 1.0 year (range, 0.3-21.0). Emapalumab was initiated for treating refractory (19/46), recurrent (14/46), or progressive (7/46) pHLH. At initiation, 15 of 46 patients were in the intensive care unit, and 35 of 46 had received prior HLH-related therapies. Emapalumab treatment resulted in normalization of key laboratory parameters, including chemokine ligand 9 (24/33, 72.7%), ferritin (20/45, 44.4%), fibrinogen (37/38, 97.4%), platelets (39/46, 84.8%), and absolute neutrophil count (40/45, 88.9%). Forty-two (91.3%) patients were considered eligible for transplant. Pretransplant survival was 38 of 42 (90.5%). Thirty-one (73.8%) transplant-eligible patients proceeded to transplant, and 23 of 31 (74.2%) of those who received transplant were alive at the end of the follow-up period. Twelve-month survival probability from emapalumab initiation for the entire cohort (N = 46) was 73.1%. There were no discontinuations because of adverse events. In conclusion, results from the REAL-HLH study, which describes treatment patterns, effectiveness, and outcomes in patients with pHLH treated with emapalumab in real-world settings, are consistent with the emapalumab pivotal phase 2/3 pHLH trial.

Human recombination-activating gene (RAG) deficiency can manifest with distinct clinical and immunological phenotypes. By applying a multiomics approach to a large group of RAG -mutated patients, we aimed at characterizing the immunopathology associated with each phenotype. Although defective T and B cell development is common to all phenotypes, patients with hypomorphic RAG variants can generate T and B cells with signatures of immune dysregulation and produce autoantibodies to a broad range of self-antigens, including type I interferons. T helper 2 (T _H 2) cell skewing and a prominent inflammatory signature characterize Omenn syndrome, whereas more hypomorphic forms of RAG deficiency are associated with a type 1 immune profile both in blood and tissues. We used cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) analysis to define the cell lineage–specific contribution to the immunopathology of the distinct RAG phenotypes. These insights may help improve the diagnosis and clinical management of the various forms of the disease.

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.

Chronic granulomatous disease (CGD) is a primary immunodeficiency characterized by life-threatening infections and inflammatory conditions. Hematopoietic cell transplantation (HCT) is the definitive treatment for CGD, but questions remain regarding patient selection and impact of active disease on transplant outcomes. We performed a multi-institutional retrospective and prospective study of 391 patients with CGD treated either conventionally (non-HCT) enrolled from 2004 to 2018 or with HCT from 1996 to 2018. Median follow-up after HCT was 3.7 years with a 3-year overall survival of 82% and event-free survival of 69%. In a multivariate analysis, a Lansky/Karnofsky score <90 and use of HLA-mismatched donors negatively affected survival. Age, genotype, and oxidase status did not affect outcomes. Before HCT, patients had higher infection density, higher frequency of noninfectious lung and liver diseases, and more steroid use than conventionally treated patients; however, these issues did not adversely affect HCT survival. Presence of pre-HCT inflammatory conditions was associated with chronic graft-versus-host disease. Graft failure or receipt of a second HCT occurred in 17.6% of the patients and was associated with melphalan-based conditioning and/or early mixed chimerism. At 3 to 5 years after HCT, patients had improved growth and nutrition, resolved infections and inflammatory disease, and lower rates of antimicrobial prophylaxis or corticosteroid use compared with both their baseline and those of conventionally treated patients. HCT leads to durable resolution of CGD symptoms and lowers the burden of the disease. Patients with active infection or inflammation are candidates for transplants; HCT should be considered before the development of comorbidities that could affect performance status. This trial was registered at www.clinicaltrials.gov as #NCT02082353.

Germline gain-of-function (GOF) mutations in signal transducer and activator of transcription 1 (STAT1) are associated with infections, including chronic mucocutaneous candidiasis and autoimmunity. Morbidity is high, and disease manifestations can be life-threatening. Curative allogeneic hematopoietic stem cell transplantation (HSCT) historically has had poor outcomes. We identified 36 patients with STAT1 GOF disease, receiving 40 HSCT procedures in 2010–2023, in a combined effort of the EBMT-IEWP and the PIDTC. Median age at first transplant was 11 years (range 1–33). Indications for HSCT were combined immunodeficiency, severe and/or refractory infections, and autoimmunity. Acute GvHD occurred in 22/40 HSCT procedures; 5 patients suffered from grade III/IV acute GvHD. One patient had chronic GvHD. Overall survival was 72.2%, and event-free survival was 55.6%, markedly improved from an earlier report on HSCT for STAT1 GOF disease. Patients with an HCT-CI score of 1 or higher had worse outcome. Pre-treatment with Janus kinase (JAK) inhibitors was associated with better event-free survival.