Germline-activating mutations in PIK3CD compromise B cell development and function

Gain-of-function (GOF) mutations in PIK3CD, encoding the p110δ subunit of phosphatidylinositide 3-kinase (PI3K), cause a primary immunodeficiency. Affected individuals display impaired humoral immune responses following infection or immunization. To establish mechanisms underlying these immune defects, we studied a large cohort of patients with PIK3CD GOF mutations and established a novel mouse model using CRISPR/Cas9-mediated gene editing to introduce a common pathogenic mutation in Pik3cd In both species, hyperactive PI3K severely affected B cell development and differentiation in the bone marrow and the periphery. Furthermore, PI3K GOF B cells exhibited intrinsic defects in class-switch recombination (CSR) due to impaired induction of activation-induced cytidine deaminase (AID) and failure to acquire a plasmablast gene signature and phenotype. Importantly, defects in CSR, AID expression, and Ig secretion were restored by leniolisib, a specific p110δ inhibitor. Our findings reveal key roles for balanced PI3K signaling in B cell development and long-lived humoral immunity and memory and establish the validity of treating affected individuals with p110δ inhibitors.

Activating PIK3CD mutations impair human cytotoxic lymphocyte differentiation and function and EBV immunity

BACKGROUND

Germline gain-of function (GOF) mutations in PIK3CD, encoding the catalytic p110δ subunit of phosphoinositide 3-kinase (PI3K), result in hyperactivation of the PI3K-AKT-mechanistic target of rapamycin pathway and underlie a novel inborn error of immunity. Affected subjects exhibit perturbed humoral and cellular immunity, manifesting as recurrent infections, autoimmunity, hepatosplenomegaly, uncontrolled EBV and/or cytomegalovirus infection, and increased incidence of B-cell lymphoproliferation, lymphoma, or both. Mechanisms underlying disease pathogenesis remain unknown.

OBJECTIVE

Understanding the cellular and molecular mechanisms underpinning inefficient surveillance of EBV-infected B cells is required to understand disease in patients with PIK3CD GOF mutations, identify key molecules required for cell-mediated immunity against EBV, and develop immunotherapeutic interventions for the treatment of this and other EBV-opathies.

METHODS

We studied the consequences of PIK3CD GOF mutations on the generation, differentiation, and function of CD8⁺ T cells and natural killer (NK) cells, which are implicated in host defense against infection with herpesviruses, including EBV.

RESULTS

PIK3CD GOF total and EBV-specific CD8⁺ T cells were skewed toward an effector phenotype, with exaggerated expression of markers associated with premature immunosenescence/exhaustion and increased susceptibility to reactivation-induced cell death. These findings were recapitulated in a novel mouse model of PI3K GOF mutations. NK cells in patients with PIK3CD GOF mutations also exhibited perturbed expression of differentiation-associated molecules. Both CD8⁺ T and NK cells had reduced capacity to kill EBV-infected B cells. PIK3CD GOF B cells had increased expression of CD48, programmed death ligand 1/2, and CD70.

CONCLUSIONS

PIK3CD GOF mutations aberrantly induce exhaustion, senescence, or both and impair cytotoxicity of CD8⁺ T and NK cells. These defects might contribute to clinical features of affected subjects, such as impaired immunity to herpesviruses and tumor surveillance.

Newborn screening for severe combined immunodeficiency: Evaluation of a commercial T-cell receptor excision circle-based method in Victorian dried blood spots

AIM

Severe combined immunodeficiency (SCID) is the most severe form of primary immunodeficiency and is fatal in infancy if untreated. As early diagnosis is associated with improved outcomes, SCID is an ideal condition to consider for inclusion in a newborn screening (NBS) programme in Australia. In this feasibility study, we evaluated the EnLite Neonatal TREC kit for detection of T-cell receptor excision circles (TRECs) from NBS dried blood spots for the identification of known SCID patients in Victoria.

METHODS

TREC copies/μL were measured retrospectively in 14 children diagnosed with SCID or complete DiGeorge syndrome (CDGS) from 2005 to 2015 at the Royal Children's Hospital, Melbourne. In addition, TREC copies/μL were measured for 501 prospective de-identified NBS cards.

RESULTS

Of 14 known SCID or CDGS samples, 11 were correctly identified as presumptive positive samples with low or undetectable TREC on duplicate testing. The remaining three samples also had low or undetectable TREC on duplicate testing but were considered invalid due to insufficient β-actin DNA amplification. Of the 501 prospective NBS samples, none were identified as presumptive positive samples on duplicate testing.

CONCLUSIONS

The EnLite Neonatal TREC kit correctly identified known SCID or CDGS patients as presumptive positive samples, and initial cut-offs for TREC and β-actin in the Victorian NBS population were determined. A larger pilot study is required to confirm these proposed cut-offs and to evaluate the cost and implementation of this screening programme in Victoria, Australia. Overall, this study provides preliminary data to support the introduction of this assay to the NBS programme in Victoria.

Characterization of T and B cell repertoire diversity in patients with RAG deficiency

Recombination-activating genes 1 and 2 (RAG1 and RAG2) play a critical role in T and B cell development by initiating the recombination process that controls the expression of T cell receptor (TCR) and immunoglobulin genes. Mutations in the RAG1 and RAG2 genes in humans cause a broad spectrum of phenotypes, including severe combined immunodeficiency (SCID) with lack of T and B cells, Omenn syndrome, leaky SCID, and combined immunodeficiency with granulomas or autoimmunity (CID-G/AI). Using next-generation sequencing, we analyzed the TCR and B cell receptor (BCR) repertoire in 12 patients with RAG mutations presenting with Omenn syndrome (n = 5), leaky SCID (n = 3), or CID-G/AI (n = 4). Restriction of repertoire diversity skewed usage of variable (V), diversity (D), and joining (J) segment genes, and abnormalities of CDR3 length distribution were progressively more prominent in patients with a more severe phenotype. Skewed usage of V, D, and J segment genes was present also within unique sequences, indicating a primary restriction of repertoire. Patients with Omenn syndrome had a high proportion of class-switched immunoglobulin heavy chain transcripts and increased somatic hypermutation rate, suggesting in vivo activation of these B cells. These data provide a framework to better understand the phenotypic heterogeneity of RAG deficiency.

Carboplatin Hypersensitivity Reactions in Pediatric Low Grade Glioma Are Protocol Specific and Desensitization Shows Poor Efficacy

BACKGROUND

The use of carboplatin for the treatment of pediatric low grade gliomas (PLGG) is often limited by the development of carboplatin hypersensitivity. Reported rates of carboplatin hypersensitivity reactions vary between 6% and 32% in these patients. Here we report the frequency of carboplatin hypersensitivity reactions depending on the treatment regimen used, and outcomes of carboplatin desensitization.

METHODS

The records of all patients in a single institution who were treated with carboplatin for PLGG were accessed and all patients receiving more than one dose of carboplatin are reported.

RESULTS

Thirty four patients with PLGG were treated with carboplatin according to one of the two different regimens. Carboplatin hypersensitivity was documented in 47% of patients, but the frequency differed by treatment protocol. Those patients treated with 4-weekly single agent carboplatin had carboplatin allergy in 8% of cases whereas 68% of those treated with combined carboplatin and vincristine (every three weeks, according to the SIOP 2004 low grade glioma protocol) had carboplatin reactions (OR 23.6, P < 0.01). Desensitization was only successful in two out of 10 patients in whom it was attempted.

CONCLUSIONS

Hypersensitivity reactions to carboplatin are more common in this cohort than previously reported and rates are protocol-dependent. Desensitization showed limited effectiveness in this cohort.

Cerebral Vasculitis in X-linked Lymphoproliferative Disease Cured by Matched Unrelated Cord Blood Transplant

Vasculitis occurs rarely in association with X-linked lymphoproliferative disease (XLP). There are four published cases of non-EBV XLP-associated cerebral vasculitis reported, none of whom have survived without major cognitive impairment.

CASE

A 9-year old boy initially presented aged 5 years with a restrictive joint disease. He subsequently developed dysgammaglobulinemia, episodic severe pneumonitis, aplastic anaemia, gastritis and cerebral vasculitis. A diagnosis of XLP was made, based on flow cytometric analysis and the identification of a novel mutation in SH2D1A, c.96G>C. No peripheral blood lymphocyte clonal proliferation was identified and he was EBV negative, although human herpes virus-7 (HHV7) was detected repeatedly in his cerebrospinal fluid. He underwent a reduced intensity unrelated umbilical cord blood transplant, but failed to engraft. A second 5/6 matched cord gave 100 % donor engraftment. Complications included BK virus-associated haemorrhagic cystitis, a possible NK-cell mediated immune reconstitution syndrome and post-transplant anti-glomerular basement membrane disease, the latter treated with cyclophosphamide and rituximab. At +450 days post-transplant he is in remission from his vasculitis and anti-glomerular basement membrane disease, and HHV-7 has remained undetectable.

CONCLUSION

This is the second published description of joint disease in XLP, and only the fourth case of non-EBV associated cerebral vasculitis in XLP, as well as being the first to be successfully treated for this manifestation. This case raises specific questions about vasculitis in XLP, in particular the potential relevance of HHV-7 to the pathogenesis.

Evaluation of Severe Combined Immunodeficiency and Combined Immunodeficiency Pediatric Patients on the Basis of Cellular Radiosensitivity

Pediatric patients with severe or nonsevere combined immunodeficiency have increased susceptibility to severe, life-threatening infections and, without hematopoietic stem cell transplantation, may fail to thrive. A subset of these patients have the radiosensitive (RS) phenotype, which may necessitate conditioning before hematopoietic stem cell transplantation, and this conditioning includes radiomimetic drugs, which may significantly affect treatment response. To provide statistical criteria for classifying cellular response to ionizing radiation as the measure of functional RS screening, we analyzed the repair capacity and survival of ex vivo irradiated primary skin fibroblasts from five dysmorphic and/or developmentally delayed pediatric patients with severe combined immunodeficiency and combined immunodeficiency. We developed a mathematical framework for the analysis of γ histone 2A isoform X foci kinetics to quantitate DNA-repair capacity, thus establishing crucial criteria for identifying RS. The results, presented in a diagram showing each patient as a point in a 2D RS map, were in agreement with findings from the assessment of cellular RS by clonogenic survival and from the genetic analysis of factors involved in the nonhomologous end-joining repair pathway. We provide recommendations for incorporating into clinical practice the functional assays and genetic analysis used for establishing RS status before conditioning. This knowledge would enable the selection of the most appropriate treatment regimen, reducing the risk for severe therapy-related adverse effects.

Pediatric anaphylactic adverse events following immunization in Victoria, Australia from 2007 to 2013

BACKGROUND

Anaphylaxis is a rare life-threatening adverse event following immunization (AEFI). Variability in presentation can make differentiation between anaphylaxis and other AEFI difficult. This study summarizes pediatric anaphylaxis AEFI reported to an Australian state-based passive surveillance system.

METHODS

All suspected and reported pediatric (<18 years) anaphylaxis AEFI notified to SAEFVIC (Surveillance of Adverse Events Following Vaccination In the Community) Melbourne, Australia, between May 2007 to May 2013 were analyzed. Clinical descriptions of the AEFI, using the internationally recognized Brighton Collaboration case definition (BCCD) and final outcome were documented.

RESULTS

93% (25/27) of AEFI classified as anaphylaxis met BCCD criteria, with 36% (9/25), assessed as the highest level of diagnostic certainty (Level 1). Median age was 4.7 years (range 0.3-16.2); 48% of cases were male. The vaccine antigens administered included: diphtheria, tetanus, acellular pertussis (DTaP) alone or in combination vaccines containing other antigens in 11 of 25 cases (44%); and live attenuated measles mumps rubella (MMR) vaccine for six (five also had other vaccines concomitantly administered). The estimated incidence rate of anaphylaxis for DTaP vaccines was 0.36 cases per 100,000 doses, and 1.25 per 100,000 doses for MMR vaccines. The majority of cases had rapid onset, but in 24% (6/25) of cases, first symptoms of anaphylaxis developed ≥30 min after immunization. In 60% (15/25) of cases, symptoms resolved ≤60 min of presentation. Intramuscular adrenaline was administered in 90% (18/25) of cases. All cases made a full recovery with no sequelae identified.

CONCLUSION

This comprehensive case series of pediatric anaphylaxis as an AEFI identified that diagnostic criteria are useful when applied to a passive vaccine surveillance system when adequate clinical information is available. Anaphylaxis as an AEFI is rare and usually begins within 30 min of vaccination. However, healthcare professionals and vaccinees/parents should be aware that onset of anaphylaxis can be delayed beyond 30 min following immunization and that medical attention should be sought promptly if anaphylaxis is suspected.

Naive and memory human B cells have distinct requirements for STAT3 activation to differentiate into antibody-secreting plasma cells

Long-lived antibody memory is mediated by the combined effects of long-lived plasma cells (PCs) and memory B cells generated in response to T cell-dependent antigens (Ags). IL-10 and IL-21 can activate multiple signaling pathways, including STAT1, STAT3, and STAT5; ERK; PI3K/Akt, and potently promote human B cell differentiation. We previously showed that loss-of-function mutations in STAT3, but not STAT1, abrogate IL-10- and IL-21-mediated differentiation of human naive B cells into plasmablasts. We report here that, in contrast to naive B cells, STAT3-deficient memory B cells responded to these STAT3-activating cytokines, differentiating into plasmablasts and secreting high levels of IgM, IgG, and IgA, as well as Ag-specific IgG. This was associated with the induction of the molecular machinery necessary for PC formation. Mutations in IL21R, however, abolished IL-21-induced responses of both naive and memory human B cells and compromised memory B cell formation in vivo. These findings reveal a key role for IL-21R/STAT3 signaling in regulating human B cell function. Furthermore, our results indicate that the threshold of STAT3 activation required for differentiation is lower in memory compared with naive B cells, thereby identifying an intrinsic difference in the mechanism underlying differentiation of naive versus memory B cells.

Signal transducer and activator of transcription 3 (STAT3) mutations underlying autosomal dominant hyper-IgE syndrome impair human CD8(+) T-cell memory formation and function

BACKGROUND

The capacity of CD8(+) T cells to control infections and mediate antitumor immunity requires the development and survival of effector and memory cells. IL-21 has emerged as a potent inducer of CD8(+) T-cell effector function and memory development in mouse models of infectious disease. However, the role of IL-21 and associated signaling pathways in protective CD8(+) T-cell immunity in human subjects is unknown.

OBJECTIVE

We sought to determine which signaling pathways mediate the effects of IL-21 on human CD8(+) T cells and whether defects in these pathways contribute to disease pathogenesis in patients with primary immunodeficiencies caused by mutations in components of the IL-21 signaling cascade.

METHODS

Human primary immunodeficiencies resulting from monogenic mutations provide a unique opportunity to assess the requirement for particular molecules in regulating human lymphocyte function. Lymphocytes from patients with loss-of-function mutations in signal transducer and activator of transcription 1 (STAT1), STAT3, or IL-21 receptor (IL21R) were used to assess the respective roles of these genes in human CD8(+) T-cell differentiation in vivo and in vitro.

RESULTS

Mutations in STAT3 and IL21R, but not STAT1, led to a decrease in multiple memory CD8(+) T-cell subsets in vivo, indicating that STAT3 signaling, possibly downstream of IL-21R, regulates the memory cell pool. Furthermore, STAT3 was important for inducing the lytic machinery in IL-21-stimulated naive CD8(+) T cells. However, this defect was overcome by T-cell receptor engagement.

CONCLUSION

The IL-21R/STAT3 pathway is required for many aspects of human CD8(+) T-cell behavior but in some cases can be compensated by other signals. This helps explain the relatively mild susceptibility to viral disease observed in STAT3- and IL-21R-deficient subjects.

Statistical analysis of kinetics, distribution and co-localisation of DNA repair foci in irradiated cells: cell cycle effect and implications for prediction of radiosensitivity

Detection of γ-H2AX foci as a measure of DNA double strand break induction and repair provides the basis of a rapid approach to establish individual radiosensitivity. However, the assignment of criteria to define increased radiosensitivity is not straightforward. Experimental end points, analytical methods and proliferative status of the cells sampled for analysis are important. All these issues are addressed in the present study, which was prompted by a clinical request to assess the radiosensitivity status of an SCID paediatric patient being considered for bone marrow transplantation. We investigated the kinetics of repair of radiation-induced γ-H2AX foci in proliferating and confluent cultures of skin fibroblasts obtained from the patient, and from normal and radiosensitive (Artemis-deficient) controls. As well as the standard approach of averaging foci per cell over the entire population ("standard average"), we also examined foci per cell frequency distributions and calculated average foci per cell values in the major Poisson-distributed subpopulation ("principal average"). This approach allowed to avoid distortions such as that due to the S/G2 population in proliferating cells, with focus numbers approaching twice the normal, and to detect subpopulations of cells with defects in focus formation and repair. From the "standard average" analysis and co-localisation of γ-H2AX foci with 53BP1 we assigned the patient's repair status as close-to-normal. However, analysis of "principal average", foci per cell frequency distributions and survival curves challenged this initial conclusion. These studies indicate new dimensions of the γ-H2AX assay that, with further elaboration and exemplification, have the potential to augment its power to predict radiosensitivity.