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

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

Haematopoietic stem cell transplantation after reduced intensity conditioning in children and adolescents with chronic myeloid leukaemia: A prospective multicentre trial of the I-BFM Study Group.

This prospective multicentre trial evaluated the safety and the efficacy of a thiotepa/melphalan-based reduced intensity conditioning (RIC) haematopoietic stem cell transplantation (HSCT) in children and adolescents with chronic myeloid leukaemia (CML) in chronic phase (CP). Thirty-two patients were transplanted from matched siblings or matched unrelated donors. In 22 patients, HSCT was performed due to insufficient molecular response or loss of response to first- or second-generation tyrosine kinase inhibitor (TKI), with pretransplant BCR::ABL1 transcripts ranging between 0.001% and 33%. The protocol included a BCR::ABL1-guided intervention with TKI retreatment in the first year and donor lymphocyte infusions (DLI) in the second-year post-transplant. All patients engrafted. The 1-year transplant-related mortality was 3% (confidence interval [CI]: 0%-6%). After a median follow-up of 6.3 years, 5-year overall survival and event-free survival are 97% (CI: 93%-100%) and 91% (CI: 79%-100%) respectively. The current 5-year leukaemia-free survival with BCR::ABL1 <0.01% is 97% (CI: 88%-100%) and the current TKI- and DLI-free survival is 95% (CI: 85%-100%). The incidence of chronic graft-versus-host disease (GvHD) was 32%, being severe in four patients (13%). At last follow-up, 31 patients are GvHD-free and have stopped immunosuppression. RIC HSCT following pretreatment with TKI is feasible and effective in children and adolescents with CP-CML with an excellent disease-free and TKI-free 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.

Spontaneous remission and loss of monosomy 7: a window of opportunity for young children with SAMD9L syndrome.

Monosomy 7 is the most common cytogenetic abnormality in pediatric myelodysplastic syndrome (MDS) and associated with a high risk of disease progression. However, in young children, spontaneous loss of monosomy 7 with concomitant hematologic recovery has been described, especially in the presence of germline mutations in SAMD9 and SAMD9L genes. Here, we report on our experience of close surveillance instead of upfront hematopoietic stem cell transplantation (HSCT) in seven patients diagnosed with SAMD9L syndrome and monosomy 7 at a median age of 0.6 years (range, 0.4-2.9). Within 14 months from diagnosis, three children experienced spontaneous hematological remission accompanied by a decrease in monosomy 7 clone size. Subclones with somatic SAMD9L mutations in cis were identified in five patients, three of whom attained hematological remission. Two patients acquired RUNX1 and EZH2 mutations during the observation period, of whom one progressed to myelodysplastic syndrome with excess of blasts (MDS-EB). Four patients underwent allogeneic HSCT at a median time of 26 months (range, 14-40) from diagnosis for MDSEB, necrotizing granulomatous lymphadenitis, persistent monosomy 7, and severe neutropenia. At last follow-up, six patients were alive, while one passed away due to transplant-related causes. These data confirm previous observations that monosomy 7 can be transient in young children with SAMD9L syndrome. However, they also indicate that delaying HSCT poses a substantial risk of severe infection and disease progression. Finally, surveillance of patients with SAMD9L syndrome and monosomy 7 is critical to define the evolving genetic landscape and to determine the appropriate timing of HSCT (clinicaltrials gov. Identifier: NCT00662090).

Variable Clinical Courses of Varicella Zoster Virus Infection-related or Vaccination-related Bone Marrow Failure.

We report 5 children with bone marrow failure (BMF) after primary varicella zoster virus (VZV) infection or VZV vaccination, highlighting the highly variable course. Two patients were treated with intravenous immunoglobulins; one had a slow hematologic recovery, and the other was rescued by allogeneic hematopoietic stem cell transplantation (HSCT). Of the 2 patients treated with immunosuppressive therapy with antithymocyte globulin and cyclosporine, one had a complete response, and the other was transplanted for nonresponse. One patient underwent a primary allograft. All patients are alive. This study demonstrated that VZV-associated BMF is a life-threatening disorder that often requires HSCT.

Prospective Newborn Screening for SCID in Germany: A First Analysis by the Pediatric Immunology Working Group (API).

BACKGR OUND: T-cell receptor excision circle (TREC)-based newborn screening (NBS) for severe combined immunodeficiencies (SCID) was introduced in Germany in August 2019. METHODS: Children with abnormal TREC-NBS were referred to a newly established network of Combined Immunodeficiency (CID) Clinics and Centers. The Working Group for Pediatric Immunology (API) and German Society for Newborn Screening (DGNS) performed 6-monthly surveys to assess the TREC-NBS process after 2.5 years. RESULTS: Among 1.9 million screened newborns, 88 patients with congenital T-cell lymphocytopenia were identified (25 SCID, 17 leaky SCID/Omenn syndrome (OS)/idiopathic T-cell lymphocytopenia, and 46 syndromic disorders). A genetic diagnosis was established in 88%. Twenty-six patients underwent hematopoietic stem cell transplantation (HSCT), 23/26 within 4 months of life. Of these, 25/26 (96%) were alive at last follow-up. Two patients presented with in utero onset OS and died after birth. Five patients with syndromic disorders underwent thymus transplantation. Eight syndromic patients deceased, all from non-immunological complications. TREC-NBS missed one patient, who later presented clinically, and one tracking failure occurred after an inconclusive screening result. CONCLUSION: The German TREC-NBS represents the largest European SCID screening at this point. The incidence of SCID/leaky SCID/OS in Germany is approximately 1:54,000, very similar to previous observations from North American and European regions and countries where TREC-NBS was implemented. The newly founded API-CID network facilitates tracking and treatment of identified patients. Short-term HSCT outcome was excellent, but NBS and transplant registries will remain essential to evaluate the long-term outcome and to compare results across the rising numbers of TREC-NBS programs across Europe.

CTLA-4 Insufficiency due to a Novel CTLA-4 Deletion, Identified through Copy Number Variation Analysis.

BACKGROUND: The diagnostic yield of next-generation sequencing (NGS) technologies in the diagnosis of monogenic inborn errors of immunity (IEI) remains limited, rarely exceeding 30%. Monoallelic pathogenic germline variants in cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) result in variable immunodeficiency and immune dysregulation. The genetic diagnosis of CTLA-4 insufficiency can affect follow-up procedures and may lead to consideration of treatment with CTLA-4-Ig. OBJECTIVES: The aim of the study was to identify the genetic cause of familial immunodeficiency and immune dysregulation in cases where single nucleotide variant analysis of short-read NGS data yielded no diagnostic result. METHODS: Analysis of copy number variants (CNVs) was applied on short-read NGS data. RESULTS: We identified a novel monoallelic deletion-insertion variant in CTLA-4 (c.445_568-544delinsTTTGCGATTG) resulting in familial autoimmunity. This is the second larger scale variant in CTLA-4, which despite consistently reduced expression of CTLA-4 displayed variable expressivity, ranging from typical juvenile idiopathic arthritis to common variable immunodeficiency-like immunodeficiency. CONCLUSIONS: Our report suggests the significance of integration of CNV analysis in routine evaluation of NGS, which may increase its diagnostic yield in IEI.

Interleukin-10 receptor signaling in innate immune cells regulates mucosal immune tolerance and anti-inflammatory macrophage function.

Intact interleukin-10 receptor (IL-10R) signaling on effector and T regulatory (Treg) cells are each independently required to maintain immune tolerance. Here we show that IL-10 sensing by innate immune cells, independent of its effects on T cells, was critical for regulating mucosal homeostasis. Following wild-type (WT) CD4(+) T cell transfer, Rag2(-/-)Il10rb(-/-) mice developed severe colitis in association with profound defects in generation and function of Treg cells. Moreover, loss of IL-10R signaling impaired the generation and function of anti-inflammatory intestinal and bone-marrow-derived macrophages and their ability to secrete IL-10. Importantly, transfer of WT but not Il10rb(-/-) anti-inflammatory macrophages ameliorated colitis induction by WT CD4(+) T cells in Rag2(-/-)Il10rb(-/-) mice. Similar alterations in the generation and function of anti-inflammatory macrophages were observed in IL-10R-deficient patients with very early onset inflammatory bowel disease. Collectively, our studies define innate immune IL-10R signaling as a key factor regulating mucosal immune homeostasis in mice and humans.

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.

Antiviral T-Cell Frequencies in a Healthy Population: Reference Values for Evaluating Antiviral Immune Cell Profiles in Immunocompromised Patients.

Viral infections and reactivations are major causes of morbidity and mortality after hematopoietic stem cell (HSCT) and solid organ transplantation (SOT) as well as in patients with immunodeficiencies. Latent herpesviruses (e.g., cytomegalovirus, Epstein-Barr virus, and human herpesvirus 6), lytic viruses (e.g., adenovirus), and polyomaviruses (e.g., BK virus, JC virus) can cause severe complications. Antiviral drugs form the mainstay of treatment for viral infections and reactivations after transplantation, but they have side effects and cannot achieve complete viral clearance without prior reconstitution of functional antiviral T-cell immunity. The aim of this study was to establish normal ranges for virus-specific T-cell (VST) frequencies in healthy donors. Such data are needed for better interpretation of VST frequencies observed in immunocompromised patients. Therefore, we measured the frequencies of VSTs against 23 viral protein-derived peptide pools from 11 clinically relevant human viruses in blood from healthy donors (n = 151). Specifically, we determined the VST frequencies by interferon-gamma enzyme-linked immunospot assay and classified their distribution according to age and gender to allow for a more specific evaluation and prediction of antiviral immune responses. The reference values established here provide an invaluable tool for immune response evaluation, intensity of therapeutic drugs and treatment decision-making in immunosuppressed patients. This data should make an important contribution to improving the assessment of immune responses in immunocompromised patients.

Plasma levels of osteopontin from birth to adulthood.

AIM: Osteopontin (OPN) has been investigated as a biomarker for cancer and nonmalignant diseases during the last decades. Data about OPN as a potential biomarker in childhood diseases are still sparse, and reference values are not available in children. We aimed to establish reference values for children from birth to young adulthood and evaluate whether there are age-, gender-, and weight-specific differences. METHOD: Umbilical cord blood and blood plasma samples of 117 children were collected in the Children's Hospital of Saarland University in Homburg/Saar. OPN levels were measured by ELISA, and statistical analysis was performed using SPSS software. RESULTS: Neonates, infants, toddlers, young children, adolescents, and adults were divided into the following six age groups: newborns (birth), infancy and toddlers (0-24 months), early childhood (3-6 years), middle childhood (7-11 years), adolescence (12-18 years), and adults (> 18 years). Highest blood OPN levels were found in the group of 0-1 years of age. OPN blood levels declined significantly with age (Spearman r = -0.874; P < 0.001). CONCLUSION: Our work is the first prospective and systematic study analyzing OPN cord blood and blood plasma levels in children of all ages. It is the first study yielding reference values for different age groups from birth to young adulthood. Our data give insight on how OPN in umbilical cord blood and OPN in blood plasma are physiologically influenced during childhood development and growth with high OPN levels after birth and a constant age-related decline until the age of 14, when OPN levels reach similar values to those measured in adults.

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

BACKGROUND: Reduced toxicity conditioning for hematopoietic stem cell transplantation of patients with hemophagocyticlymphohistiocytosis (HLH) results in favorable survival, however at the expense of relevant rates of mixed chimerism. Factors predisposing to mixed chimerism remain to be determined. PROCEDURE: Patients with primary HLH transplanted 2009-2016 after treosulfan- or melphalan-based conditioning regimens were analyzed in a retrospective multicenter study for survival, engraftment, chimerism, and adverse events. Mixed chimerism was considered substantial if < 25% donor chimerism occurred and/or if secondary cell therapy was administered. Donor type, graft source, type of alkylating agent, type of serotherapy, and remission status were analyzed as potential risk factors in a multivariable logistic regression model. RESULTS: Among 60 patients, engraftment was achieved in 95%, and the five-year estimated overall survival rate was 75%. Prevalence of any recipient chimerism was 48%. Substantial recipient chimerism was recorded in 32% of patients. Secondary post-HSCT cell therapy was administered in 30% of patients. A human leukocyte antigen (HLA)-mismatched donor (< 10/10) was the only significant risk factor for the occurrence of substantial recipient chimerism (P = 0.01; odds ratio, 5.8; CI 95%, 1.5-26.3). CONCLUSION: The use of an HLA-matched donor is the most important factor to avoid substantial recipient chimerism following treosulfan -or melphalan-based conditioning in primary HLH.

Sickle cell disease in Germany: Results from a national registry.

BACKGROUND: Limited data on the prevalence and medical care of sickle cell disease (SCD) in Germany are available. Here, we make use of a patient registry to characterize the burden of disease and the treatment modalities for patients with SCD in Germany. PROCEDURE: A nationwide German registry for patients with SCD documents basic data on diagnosis and patient history retrospectively at the time of registration. A prospective annual documentation provides more details on complications and treatment of SCD. For the current analyses, data of 439 patients were available. RESULTS: Most patients had homozygous SCD (HbSS 75.1%, HbS/ß-thalassemia 13.2%, and HbSC 11.3%). The median age at diagnosis was 1.9 years (interquartile range, 0.6-4.4 years), most patients were diagnosed when characteristic symptoms occurred. Sepsis and stroke had affected 3.2% and 4.2% of patients, respectively. During the first year of observation, 48.3% of patients were admitted to a hospital and 10.1% required intensive care. Prophylactic penicillin was prescribed to 95.6% of patients with homozygous SCD or HbS/ß thalassemia below the age of six and hydroxycarbamide to 90.4% of patients above the age of two years. At least one annual transcranial Doppler ultrasound was documented for 74.8% of patients between 2 and 18 years. CONCLUSION: With an estimated number of at least 2000, the prevalence of SCD in Germany remains low. Prospectively, we expect that the quality of care for children with SCD will be further improved by an earlier diagnosis after the anticipated introduction of a newborn screening program for SCD.

Treosulfan-based conditioning for allogeneic HSCT in children with chronic granulomatous disease: a multicenter experience.

Chronic granulomatous disease (CGD) can be cured by allogeneic hemopoietic stem cell transplantation (HSCT). Complications include graft failure, graft-versus-host disease (GVHD), infection, and transplant-related mortality; therefore, reduced-intensity conditioning regimens are being used to improve outcomes. In this retrospective study, the aim was to determine the outcome of treosulfan-based conditioning in HSCT for pediatric patients with CGD. The following data were collected: risk features pre-HSCT, additional conditioning agents, donor type and stem cell source, toxicity, engraftment, GVHD, chimerism, viral reactivation, post-HSCT complications, length of follow-up, and outcome. Seventy patients (median age, 107 months; interquartile range [IQR], 46-232 months) from 16 centers worldwide were transplanted between 2006 and 2015. Ninety-one percent had high-risk features. Fifty-seven HLA-matched donors, 12 HLA-mismatched donors, and 1 CD3(+)TCR αß/CD19 depleted parental haploidentical transplants were performed. No major toxicity was reported. Median times to neutrophil and platelet engraftment were 17 (IQR, 15-35) and 16 (IQR, 13-50) days. At a median follow-up of 34 months (IQR, 13-102 months), the overall survival was 91.4%, and event-free survival was 81.4%. The cumulative incidence of acute grade III-IV GVHD was 12%. Nine patients developed chronic GVHD. When split cell chimerism was available, 95% or more myeloid donor chimerism was documented in 80% of surviving patients. Secondary graft failure occurred in 12% of patients. Treosulfan-containing conditioning regimens can be used safely in HSCT for children with CGD and high-risk clinical features, achieving excellent survival with high myeloid chimerism. Further studies are needed to compare with other regimens and evaluate the long-term outcome, particularly on fertility.

Dexamethasone vs prednisone in induction treatment of pediatric ALL: results of the randomized trial AIEOP-BFM ALL 2000.

Induction therapy for childhood acute lymphoblastic leukemia (ALL) traditionally includes prednisone; yet, dexamethasone may have higher antileukemic potency, leading to fewer relapses and improved survival. After a 7-day prednisone prephase, 3720 patients enrolled on trial Associazione Italiana di Ematologia e Oncologia Pediatrica and Berlin-Frankfurt-Münster (AIEOP-BFM) ALL 2000 were randomly selected to receive either dexamethasone (10 mg/m(2) per day) or prednisone (60 mg/m(2) per day) for 3 weeks plus tapering in induction. The 5-year cumulative incidence of relapse (± standard error) was 10.8 ± 0.7% in the dexamethasone and 15.6 ± 0.8% in the prednisone group (P < .0001), showing the largest effect on extramedullary relapses. The benefit of dexamethasone was partially counterbalanced by a significantly higher induction-related death rate (2.5% vs 0.9%, P = .00013), resulting in 5-year event-free survival rates of 83.9 ± 0.9% for dexamethasone and 80.8 ± 0.9% for prednisone (P = .024). No difference was seen in 5-year overall survival (OS) in the total cohort (dexamethasone, 90.3 ± 0.7%; prednisone, 90.5 ± 0.7%). Retrospective analyses of predefined subgroups revealed a significant survival benefit from dexamethasone only for patients with T-cell ALL and good response to the prednisone prephase (prednisone good-response [PGR]) (dexamethasone, 91.4 ± 2.4%; prednisone, 82.6 ± 3.2%; P = .036). In patients with precursor B-cell ALL and PGR, survival after relapse was found to be significantly worse if patients were previously assigned to the dexamethasone arm. We conclude that, for patients with PGR in the large subgroup of precursor B-cell ALL, dexamethasone especially reduced the incidence of better salvageable relapses, resulting in inferior survival after relapse. This explains the lack of benefit from dexamethasone in overall survival that we observed in the total cohort except in the subset of T-cell ALL patients with PGR. This trial was registered at www.clinicaltrials.gov (BFM: NCT00430118, AIEOP: NCT00613457).

The minimum required level of donor chimerism in hereditary hemophagocytic lymphohistiocytosis.

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

Monogenic mutations differentially affect the quantity and quality of T follicular helper cells in patients with human primary immunodeficiencies.

BACKGROUND: Follicular helper T (TFH) cells underpin T cell-dependent humoral immunity and the success of most vaccines. TFH cells also contribute to human immune disorders, such as autoimmunity, immunodeficiency, and malignancy. Understanding the molecular requirements for the generation and function of TFH cells will provide strategies for targeting these cells to modulate their behavior in the setting of these immunologic abnormalities. OBJECTIVE: We sought to determine the signaling pathways and cellular interactions required for the development and function of TFH cells in human subjects. METHODS: Human primary immunodeficiencies (PIDs) resulting from monogenic mutations provide a unique opportunity to assess the requirement for particular molecules in regulating human lymphocyte function. Circulating follicular helper T (cTFH) cell subsets, memory B cells, and serum immunoglobulin levels were quantified and functionally assessed in healthy control subjects, as well as in patients with PIDs resulting from mutations in STAT3, STAT1, TYK2, IL21, IL21R, IL10R, IFNGR1/2, IL12RB1, CD40LG, NEMO, ICOS, or BTK. RESULTS: Loss-of-function (LOF) mutations in STAT3, IL10R, CD40LG, NEMO, ICOS, or BTK reduced cTFH cell frequencies. STAT3 and IL21/R LOF and STAT1 gain-of-function mutations skewed cTFH cell differentiation toward a phenotype characterized by overexpression of IFN-γ and programmed death 1. IFN-γ inhibited cTFH cell function in vitro and in vivo, as corroborated by hypergammaglobulinemia in patients with IFNGR1/2, STAT1, and IL12RB1 LOF mutations. CONCLUSION: Specific mutations affect the quantity and quality of cTFH cells, highlighting the need to assess TFH cells in patients by using multiple criteria, including phenotype and function. Furthermore, IFN-γ functions in vivo to restrain TFH cell-induced B-cell differentiation. These findings shed new light on TFH cell biology and the integrated signaling pathways required for their generation, maintenance, and effector function and explain the compromised humoral immunity seen in patients with some PIDs.