Activated PI3K-delta Syndrome Research Articles

FDA approves leniolisib (Joenja) as the first treatment for APDS: A breaththrough in the field of immunology

Activated PI3K delta Syndrome (APDS) is a rare genetic heterogeneous disorder initially identified in 2013. The primary cause of APDS is an immune imbalance leading to immune deficiency and dysregulation. Symptoms of APDS are diverse primarily including recurrent respiratory infections and increased predisposition to lymphoma. The disease is challenging to diagnose as patients are often misdiagnosed. Genetic testing can be used to make a confirmatory diagnosis. There were no FDA-approved treatments specifically targeting the root cause of APDS, PI3Kδ until the recent promising outcomes seen in the clinical trials of leniolisib. However, long term effects of the drug remain a concern as further research is required.

Somatic Mutational Landscape and Transcriptomic Profiles of Lymphoproliferative Disorders with Epstein-Barr Virus Infection in Activated PI3K Delta Syndrome

Introduction: Germline gain-of-function variants in PIK3CD and PIK3R1 cause activated PI3K delta syndrome (APDS) types 1 and 2, respectively. Lymphoproliferative disorder (LPD) and susceptibility to various infections, including Epstein-Barr virus (EBV), are well-known features of APDS. EBV-associated LPDs are frequently observed in patients with APDS, and oligoclonal LPD might transform malignant lymphoma (ML). However, somatic molecular alterations in LPD and ML are not fully elucidated. Here, we report clinical characteristics and somatic mutational landscape and transcriptomic profiles of LPDs with EBV infection in APDS. Methods: LPD and ML in APDS diagnosed during 2011-2022 were recruited all over Japan. Clinical characteristics and outcomes were analyzed. EBV infection status was analyzed by EBER ISH and RNA sequencing (RNA-seq). Whole-exome sequencing (WES), RNA-seq, and single cell RNA-seq (scRNA-seq) were also performed. Results: Five LPD and 5 ML (borderline ML: n = 2, diffuse large B-cell lymphoma (DLBCL): n = 2, classical Hodgkin lymphoma: n = 1) cases were enrolled. Seven cases were APDS1 and 3 cases were APDS2. The median follow-up period was 2.9 (0.5-8.4) years. LPD cases were treated with rituximab monotherapy (n = 1), prednisolone (n = 3), and hematopoietic cell transplantation (HCT) (n = 1). Rituximab-combined chemotherapy was performed in borderline ML and DLBCL (n = 4) or ABVD regimen in Hodgkin lymphoma cases (n = 1). Sirolimus was used in two ML cases. HCT was performed in 9 cases. Two-year overall survival and event-free survival (events: relapse and death) were 78.8% and 70.0% in total LPDs, respectively, and 60% and 40% in ML cases. EBV was negative in 3 cases and positive in 2 cases of LPD cases, and positive in 4 cases, and negative in 1 case of ML cases. The median of 18 (10-48) and 42 (18-189) somatic variants were detected by tumor/germline pair WES in LPD (n = 5) and ML (n = 7, 2 samples were from the same patient at different time points), respectively. The recurrent variants were identified in ZFHX3 (n = 4), TRPM2 (n = 3), BEND3, CDH23, UBR4, ARAF, TET2, FBXO10, MAP4K1, KMT2C, KMT2D and PIK3R1 (n = 2) in LPD and ML cases. In transcriptome analysis, genes associated with lymphocyte activation including B-cell receptor signaling were upregulated in LPD, cell-cell adhesion, cellular response to TNF, and IL-18 signaling pathway were upregulated in ML samples. We performed correlation analysis to elucidate a relationship between EBV infection status and host transcriptomic profiles using RNA-seq data. Interestingly, in addition to cell-cell adhesion and inflammatory machinery, the upregulated molecules of the p53 pathway and negative regulation of the immune system were correlated with transcripts associated with EBV latency, such as EBNA, LMP-1, and LMP-2. In single-cell transcriptome analysis, LPD sample consisted of two large clusters of T cells and B cells with 10 subsets, and EBV-positive DLBCL sample consisted of one independent large cluster with 9 subsets. In LPD sample, components indicative of the normal lymphocyte differentiation process, including the germinal center, were preserved. The molecules involved in lymphocyte activation were upregulated in LPD subsets. In DLBCL sample, the genes associated with mitotic G2-M phases, chromatin organization and RNA metabolism were upregulated in the subsets in which EBV transcripts were more actively transcribed. Discussion and Conclusions: Our retrospective analysis demonstrated that the outcome of LPD and ML in APDS is not satisfactory. scRNA-seq data revealed that cells in LPD still retain the signature of normal lymph node. However, once transformed with EBV, EBV infection may affect epigenetic machineries including chromatin organizer followed by active RNA transcription involved in cell-cell adhesion, inflammatory machineries, molecules of p53 pathway and negative regulation of immune system in the host genome. As the outcome of ML is inferior to LPD, preemptive HCT would be an option for LPD cases.

A somatic splice-site variant in PIK3R1 in a patient with vascular overgrowth and low immunoglobulin levels: A case report.

The PI3K/AKT pathway, extensively studied in cancer, is vital for regulating cell metabolism, differentiation, and proliferation. Pathogenic variants in the PIK3R1 gene, which encodes three regulatory units of class IA PI3Ks, have been found in affected tissue of individuals with vascular lesions. These variants predominantly occur in the iSH2 domain, disrupting inhibitory contacts with the catalytic unit and leading to PI3K activation. Germline variants in this gene are also linked to an immunological condition called Activated PI3K delta syndrome type 2 (APDS2). This is a case report and literature review. Clinical data were retrieved from medical records. A male patient presented with extensive vascular malformation covering over 90% of his body, along with complete 2-3 toe syndactyly, suggesting a vascular malformation syndrome called PROS. Low levels of IgA and IgG were detected. The patient achieved his developmental milestones and had above-average weight, height, and head circumference. Exome sequencing of skin and blood DNA revealed a de novo variant in PIK3R1 (c.1746-2A>G, p.?) in 9% of the patient's blood cells and 25% of cultured fibroblasts. Initially, classified as a variant of uncertain significance, this variant was later confirmed to be the cause. This is the first intronic SNV in a canonical splice site within iSH2 described, highlighting the importance of iSH2 in the regulation of the PI3K/AKT pathway and its involvement in the development of vascular overgrowth and antibody deficiency.

EE308 Estimated Annual Costs Among Patients with Activated PI3K Delta Syndrome

To our knowledge, the economic burden of activated PI3K delta syndrome (APDS) is not well characterized. We designed a cost model to estimate the annual direct medical costs associated with APDS.

COVID-19-Related Encephalitis in a Child with PIK3CD Defect

IntroductionCOVID-19 related encephalitis has been reported in pediatric patients; however, there are no reports in patients with inborn errors of immunity (IEI). Activated PI3K Delta Syndrome (APDS) is a disease of immune dysregulation with immunodeficiency, autoimmunity, and abnormal lymphoproliferation resulting from autosomal dominant gain-offunction variants in PIK3CD or PIK3R1 genes. We investigate a family with APDS, one mother and three children, one of whom developed COVID-19 related encephalitis. MethodsPatients were consented to an IRB-approved protocol at our institution. Medical records and detailed immunophenotyping were reviewed. Family members were sequenced for IEI with a targeted gene panel. ResultsThe index case is a 10-year-old female with a known pathogenic variant in PIK3CD (c.3061 G > A, p.Glu1021Lys), who contracted SARS-COV-2 despite one COVID-19 vaccination in the series. Her disease course included COVID-related encephalitis with cerebellitis and compression of the pons, resulting in lasting truncal ataxia and cerebellar mutism. At that time, the patient was not on immunoglobulin replacement therapy (IgRT), but was receiving Sirolimus. Besides the index case, 3 family members (2 brothers, 1 mother) also share the same PIK3CD variant with variable clinical and immunological phenotypes. All children exhibited high transitional B-cells, consistent with developmental block to follicular B cell stage. Increased non-class switched IgM+ memory B cells and skewing towards CD21lo B cell subset, which is considered autoreactive-like, was observed in all patients. Of note, the patient had low plasmablasts, but normal immunoglobulins. Of her family members, only one was receiving both sirolimus and IgRT. ConclusionsWe describe a rare case of COVID-19-related encephalitis in a patient with inborn error of immunity while not on IgRT. This may indicate infection susceptibility because of a lack of sufficient immunity to SARS-CoV-2, unlike the rest of her family with the same PIK3CD variant.

PI3Kδ: a key driver of effector differentiation under conditions of T cell exhaustion

Abstract In chronic infection and cancer, prolonged antigen exposure drives a state of T cell hyporesponsiveness, called exhaustion. A small subset of TCF1 +progenitor exhausted stem-like T cells (pTex) cells, is required to maintain exhausted T (Tex) cells and respond to checkpoint blockade. Understanding mechanisms regulating these populations may help identify approaches to counter exhaustion. Phosphatidylinositol 3-kinase-d (PI3Kd) is an important component of T cell signaling. We have found that TCF-1 is repressed in CD8 +T cells from patients with Activated PI3K Delta Syndrome and in a mouse model (Pik3cd E1020K/+mice) in acute viral infections. How activated-PI3Kδ affects T cell exhaustion is unknown. Using chronic LCMV clone 13 infection, we found that Pik3cd E1020K/+mice rapidly die, yet surviving mice recover faster than WT. RNA sequencing revealed decreased expression of Tcf7, encoding TCF-1, in antigen-specific CD8 +T cells, along with loss of TCF-1 +Tim3 −CD8 +pTex cells in Pik3cd E1020K/+mice upon cl13 infection. Tex cells that were maintained during chronic infection in Pik3cd E1020K/+mice displayed an effector-like phenotype, with expression of CX3CR1 +and KLRG1 +, and increased effector functions, suggesting that these cells might induce early immunopathology yet increase viral clearance. P14 cell transfers, in conjunction with CRISPR-mediated gene disruption, revealed that loss of FoxO1 leads to loss of TCF-1 +cells, whereas the increase of effector cells is at least partially cell-extrinsic. Our findings suggest that PI3Kδ is a critical rheostat that balances effector vs exhaustion differentiation, providing insight for therapeutic strategies for exhaustion.

Resolution of IgA vasculitis nephritis in patient with activated PI3Kdelta syndrome after treatment with leniolisib

IntroductionActivated PI3K-delta syndrome is a combined immunodeficiency disease with a heterogenous immune phenotype. Common clinical manifestations include recurrent respiratory infections, persistent herpesvirus infections, lymphoproliferative disease, and autoimmunity. We describe the case of a patient with APDS who developed IgA vasculitis nephritis that responded to steroids, plasmapheresis, rituximab, and initiation of a new selective PI3Kdelta inhibitor, leniolisib. Case description19-year-old male with APDS (pathogenic variant in PI3KCD, p.E81K) complicated by recurrent ear and sinus infections, marginal zone B-cell hyperplasia, and EBV lymphadenitis who presented to the hospital with hematuria and fatigue. Initial work-up revealed acute kidney injury (Cr 1.72 mg/dL) with gross hematuria and nephrotic range proteinuria. A renal biopsy was performed which demonstrated IgA dominant immune complex glomerulonephritis (10% focal cellular crescents). The patient was started on empiric high-dose steroids. However, due to worsening renal injury (Cr peak to 4.1 mg/dL) and proteinuria, plasmapheresis and rituximab were administered. Additionally, leniolisib, a new oral PI3Kdelta inhibitor, was initiated at 70 mg twice daily. The patient’s renal function began to stabilize after administration of these therapies, and he was discharged on daily prednisone and leniolisib. On outpatient follow-up over the course of six months, he demonstrated normalization of his creatinine and improvement of his proteinuria. ConclusionsGlomerulonephritis has been reported as an autoimmune renal manifestation in APDS. This case highlights the first reported instance of treatment response to leniolisib and immunomodulatory agents in an APDS patient with IgA vasculitis nephritis. While leniolisib is an unapproved selective PI3K-delta inhibitor, its use should be considered in the management of APDS patients with significant autoimmune complications.

Clinical features and treatment of activated PI3K-delta syndrome in Peruvian children: A case series

IntroductionActivated phosphoinositide 3-kinase δ (PI3Kδ) syndrome (APDS) is an inborn error of immunity (IEI) caused by a gain-of-function mutation in the PIK3CD gene. It is characterized by recurrent respiratory infections, chronic herpes infections, lymphoproliferation, mucosal lymphoid hyperplasia, enteropathy and immune dysregulation. This condition can be misdiagnosed with other diseases, such as lymphoma or other IEI. Additionally, limited knowledge of APDS in physicians could generate delay in diagnosis, treatment and lead to worse outcomes, especially in developing countries. This study aimed to describe the clinical features and treatment of APDS in Peruvian children evaluated in two centers. MethodsWe retrospectively analyzed data from eight patients with APDS evaluated in the two main Peruvian clinical immunology centers. Demographics, clinical features, laboratory analysis, and treatment data were included. ResultsAll patients were female. At the onset of symptoms and diagnosis, the mean age was 1.4 (SD: 0.98) and 6 (SD: 2.1) years, respectively. The mean delay in diagnosis was 4.5 (SD: 2.7) years. No consanguinity was reported, and only one patient had a family history of IEI. The mortality rate was 25% (2 patients). The main clinical manifestations were lymphadenopathy and hepatomegaly (100%), chronic diarrhea and recurrent pneumonia (87.5%), and splenomegaly (62.5%). All the patients had E1021K mutation. Seven patients (87.5%) had elevated IgG and 50% had elevated IgM. Regarding treatment, all the patients received intravenous immunoglobulin (IVIG), 50% were treated with everolimus and only one patient received hematopoietic stem cell transplantation. ConclusionLymphadenopathy, hepatosplenomegaly, chronic diarrhea, pneumonia, and IVIG treatment were the main features. Our cohort had limited treatment options with calcineurin inhibitors and transplantation and laboratory testing such as lymphocyte population and functional antibody tests. Although genetic testing was done on all the patients, it was supported by international collaboration. Therefore, further studies are needed to evaluate the diagnosis and management impact on patients with APDS in our setting.

Activated PI3K delta syndrome 1 mutations cause neutrophilia in zebrafish larvae.

People with activated PI3 kinase delta syndrome 1 (APDS1) suffer from immune deficiency and severe bronchiectasis. APDS1 is caused by dominant activating mutations of the PIK3CD gene that encodes the PI3 kinase delta (PI3Kδ) catalytic subunit. Despite the importance of innate immunity defects in bronchiectasis, there has been limited investigation of neutrophils or macrophages in APDS1 patients or mouse models. Zebrafish embryos provide an ideal system to study neutrophils and macrophages. We used CRISPR-Cas9 and CRISPR-Cpf1, with oligonucleotide-directed homologous repair, to engineer zebrafish equivalents of the two most prevalent human APDS1 disease mutations. These zebrafish pik3cd alleles dominantly caused excessive neutrophilic inflammation in a tail-fin injury model. They also resulted in total body neutrophilia in the absence of any inflammatory stimulus but normal numbers of macrophages. Exposure of zebrafish to the PI3Kδ inhibitor CAL-101 reversed the total body neutrophilia. There was no apparent defect in neutrophil maturation or migration, and tail-fin regeneration was unimpaired. Overall, the finding is of enhanced granulopoeisis, in the absence of notable phenotypic change in neutrophils and macrophages.

Expanded Autoreactive Transitional B Cells in Monogenic Common Variable Immunodeficiency

Introduction Autoimmune cytopenias (AIC) are prevalent in patients with primary immune deficiencies, including common variable immunodeficiency (CVID). They are often refractory and difficult to treat, and patients with autoimmune complications of CVID have a higher risk of mortality than those with an infectious phenotype (Farmer et al. Front Immnol 2017; Resnick et al. Blood 2021). The pathogenesis of AIC in CVID is not well understood, making diagnosis and prognostication challenging. We previously observed a block in development from transitional to follicular B cells in patients with activated PI3K delta syndrome (APDS), a monogenic form of CVID (Farmer et al. Sci Signal 2019). We have now investigated a larger cohort with various causes of monogenic CVID (45% with AIC). We sought to determine if a block in B cell development extended beyond APDS to other patients with monogenic CVID and autoimmunity. We aimed to identify a link between the transitional B cell block and a break in tolerance, as transitional B cells are immature cells with self-reactive properties prior to differentiating into mature follicular B cells (Allman et al. Curr Opin Immunol 2008). Thus, we performed flow cytometry using the 9G4 monoclonal antibody to identify B cells containing the 9G4 idiotope of the immunoglobulin heavy chain VH4-34 gene. This idiotope is associated with autoimmunity (Cappione et al. J Clin Invest 2005; Pugh-Bernard et al. J Clin Invest 2001). Utilizing single-cell Cellular Indexing of Transcriptomes and Epitopes by Sequencing (scCITE-Seq) and B cell receptor (BCR) repertoire, we analyzed patients with APDS to further define heterogeneous B cell populations. We leveraged our access to biospecimens and clinical data from patients with monogenic CVID to study pathologic B cells. Methods Patients were recruited in accordance with the Partners Institutional Review Board. The cohort was queried for cytopenias, including immune thrombocytopenia (ITP), autoimmune hemolytic anemia (AIHA), and autoimmune neutropenia (AIN), identified by positive history on physician chart review or otherwise captured by review of all clinical details in the Electronic Medical Record. We performed flow cytometry on peripheral blood mononuclear cells with a detailed B cell panel including the 9G4 antibody. We included 20 patients with monogenic CVID (PI3K (n=4), NFKB1 (n=5), and CTLA4 mutations (n=11)) and 12 healthy controls. Nine patients had AIC (ITP (n=3), ITP + AIHA (n=4), ITP + AIN (n=1), ITP + AIHA + AIN (n=1)). We sequenced total CD19+ B cells from 4 patients with APDS and 4 controls using scCITE-Seq. With the Immcantation software suite, we identified clonal clusters based on BCR sequences and constructed maximum parsimony lineage trees for clusters with >5 unique sequences. Results Patients with monogenic CVID and AIC had marked expansion of 9G4+ B cells compared to healthy controls. There was a statistically significant (p<0.05) increase in the percent of 9G4+ B cells in patients with AIC compared to controls in the transitional T1/2, T3a, and T3b B cell subsets, as well as double negative, follicular, activated naïve, marginal zone precursor, and marginal zone subsets. This expansion was particularly pronounced in the transitional B cell population (p<0.001). ScCITE-Seq identified 19 B cell clusters. Clonal B cell populations separated into three predominant IgM isotype clusters in healthy controls (5, 9, and 15), while in patients with APDS there were additional clusters identified, including IgM isotype clusters 0, 2, 3, 10, 13, 17 and IgG isotype clusters 4, 6, 10, 12, and 16 (Figure 1). This suggests that there are novel, isotype-switched B cell states present in patients with APDS that are not present in healthy controls. Conclusions In this study, we investigated B cell populations in patients with monogenic CVID and autoimmunity. We found expansion of transitional B cells characterized by 9G4 positivity. These transitional cells may fail to be eliminated because they are aberrantly activated and differentiate into self-reactive activated B cells and plasmablasts that secrete pathogenic autoantibodies. ScCITE-Seq revealed novel B cell subsets in patients with APDS and could represent an altered state of B cell biology that leads to pathologic autoantibody production and clinical autoimmunity. These results improve identification of heterogeneous B cell subsets and connectivity between subsets. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Interim Analysis of Safety and Hematological Parameters of an Ongoing Long-Term Open-Label Extension Study of Investigational PI3Kδ Inhibitor Leniolisib for Patients with Activated PI3K Delta Syndrome (APDS) through December 2021

Interim Analysis of Safety and Hematological Parameters of an Ongoing Long-Term Open-Label Extension Study of Investigational PI3Kδ Inhibitor Leniolisib for Patients with Activated PI3K Delta Syndrome (APDS) through December 2021

AKT Hyperphosphorylation and T Cell Exhaustion in Down Syndrome.

Down syndrome (DS) is associated with increased susceptibility to infections, auto-immunity, immunodeficiency and haematological malignancies. The exact underlying immunological pathophysiology is still unclear. The immunophenotype and clinical characteristics of DS resemble those of Activated PI3K Delta Syndrome (APDS), in which the PI3K/AKT/mTOR pathway is overactivated. We hypothesized that T cell exhaustion and the hyperactivation of the AKT signalling pathway is also present in immune cells of children with DS. In this observational non-interventional cohort study we collected blood samples of children with DS (n=22) and healthy age-matched controls (n=21) for flowcytometric immunophenotyping, phospho-flow AKT analysis and exhaustion analysis of T cells. The median age was 5 years (range 1-12y). Total T and NK cells were similar for both groups, but absolute values and transitional B cells, naive memory B cells and naive CD4+ and CD8+ T cells were lower in DS. pAKT and AKT were increased for CD3+ and CD4+ T cells and CD20+ B cells in children with DS. Total AKT was also increased in CD8+ T cells. Children with DS showed increased expression of inhibitory markers Programmed cell dealth-1 (PD-1), CD244 and CD160 on CD8+ T cells and increased PD-1 and CD244+ expression on CD4+ T cells, suggesting T cell exhaustion. Children with DS show increased pAKT and AKT and increased T cell exhaustion, which might contribute to their increased susceptibility to infections, auto immunity and haematological malignancies.

Dysregulated PI3K Signaling in B Cells of CVID Patients.

The altered wiring of signaling pathways downstream of antigen receptors of T and B cells contributes to the dysregulation of the adaptive immune system, potentially causing immunodeficiency and autoimmunity. In humans, the investigation of such complex systems benefits from nature’s experiments in patients with genetically defined primary immunodeficiencies. Disturbed B-cell receptor (BCR) signaling in a subgroup of common variable immunodeficiency (CVID) patients with immune dysregulation and expanded T-bethighCD21low B cells in peripheral blood has been previously reported. Here, we investigate PI3K signaling and its targets as crucial regulators of survival, proliferation and metabolism by intracellular flow cytometry, imaging flow cytometry and RNAseq. We observed increased basal but disturbed BCR-induced PI3K signaling, especially in T-bethighCD21low B cells from CVID patients, translating into impaired activation of crucial downstream molecules and affecting proliferation, survival and the metabolic profile. In contrast to CVID, increased basal activity of PI3K in patients with a gain-of-function mutation in PIK3CD and activated PI3K delta syndrome (APDS) did not result in impaired BCR-induced AKT-mTOR-S6 phosphorylation, highlighting that signaling defects in B cells in CVID and APDS patients are fundamentally different and that assessing responses to BCR stimulation is an appropriate confirmative diagnostic test for APDS. The active PI3K signaling in vivo may render autoreactive T-bethighCD21low B cells in CVID at the same time to be more sensitive to mTOR or PI3K inhibition.

Clinical and Cytometric Study of Immune Involvement in a Heterogeneous Cohort of Subjects With RASopathies and mTORopathies.

RASopathies and mTORopathies are groups of genetic syndromes associated with increased activation of the RAS-MAPK or the PI3K-AKT-mTOR pathway, resulting in altered cell proliferation during embryonic and postnatal development. The RAS-MAPK and the PI3K-AKT-mTOR pathways are connected to each other and play a crucial role in adaptive immunity. However, with the exception of Activated PI3K delta syndrome (APDS), immune function has not been deeply studied in these disorders. We collected clinical and immunophenotypic data of a cohort of patients with RASopathies and mTORopathies. Overall, we enrolled 47 patients (22 females, 25 males, age 2–40 years): 33 with neurofibromatosis type 1, 11 Noonan syndrome and 3 Bannayan-Riley-Ruvalcaba syndrome. 8 patients reported a history of invasive infections requiring hospitalization and intravenous antibiotic therapy. Only 3 patients reported a history of unusual, difficult-to-treat or deep-seated infection. Adenotonsillectomy was performed in 11 patients (24%). However, in most cases (83%) patients' parents did not perceive their child as more prone to infections than their peers. Lymphocyte subpopulations were analyzed in 37 of the 47 patients (16 female, 21 males, age 1–40 years). Among the studied lymphocyte subsets, the only consistent alteration regarded an increased percentage of immature B cells (recent bone marrow emigrants) in 34 out of 37 (91,9%) patients, and an increased percentage of double negative T cells in 9 patients. In conclusion, although borderline immune abnormalities were present in a significant proportion of subjects and adenotonsillectomy was performed more frequently than expected for the general population, no major immune disturbance was found in this cohort of patients.

PI3K in T Cell Adhesion and Trafficking.

PI3K signalling is required for activation, differentiation, and trafficking of T cells. PI3Kδ, the dominant PI3K isoform in T cells, has been extensively characterised using PI3Kδ mutant mouse models and PI3K inhibitors. Furthermore, characterisation of patients with Activated PI3K Delta Syndrome (APDS) and mouse models with hyperactive PI3Kδ have shed light on how increased PI3Kδ activity affects T cell functions. An important function of PI3Kδ is that it acts downstream of TCR stimulation to activate the major T cell integrin, LFA-1, which controls transendothelial migration of T cells as well as their interaction with antigen-presenting cells. PI3Kδ also suppresses the cell surface expression of CD62L and CCR7 which controls the migration of T cells across high endothelial venules in the lymph nodes and S1PR1 which controls lymph node egress. Therefore, PI3Kδ can control both entry and exit of T cells from lymph nodes as well as the recruitment to and retention of T cells within inflamed tissues. This review will focus on the regulation of adhesion receptors by PI3Kδ and how this contributes to T cell trafficking and localisation. These findings are relevant for our understanding of how PI3Kδ inhibitors may affect T cell redistribution and function.

Phosphatidylinositol 3-kinase signalling and immune regulation: insights into disease pathogenesis and clinical implications

Introduction: Phosphatidylinositol 3-kinase (PI3K) is a lipid kinase that plays a key role in fundamental aspects of cell biology including survival, metabolism, proliferation and differentiation. Thus, balanced PI3K signalling is critical for multiple aspects of human health. The initial discovery that germline variants in genes in the PI3K pathway resulted in inborn errors of immunity highlighted the non-redundant role of these signalling proteins in the human immune system. The subsequent identification and characterisation of >250 individuals with a novel immune dysregulatory disorder, termed activated PI3K-delta syndrome (APDS), has reinforced the status of PI3K as a key pathway regulating immune function. Studies of APDS have demonstrated that dysregulated PI3K function is disruptive for many immune cell processes including development, activation, differentiation, effector function and self-tolerance, which are all important in supporting effective, long-term immune responses. Areas covered: In this review, we recount recent findings regarding humans with germline variants in PI3K genes and discuss the underlying cellular and molecular pathologies, with a focus on the implications of these findings for therapy in APDS patients. Expert Opinion: Fine tuning immune signalling by modulating PI3K offers opportunities for therapeutic interventions in settings of immunodeficiency, autoimmunity and malignancy, but also highlights potential adverse events that may result from overt pharmacological or intrinsic inhibition of PI3K function.

Infections in activated PI3K delta syndrome (APDS).

Activated PI3K-delta Syndrome (APDS), also called PI3K-delta activating mutation causing senescent T cells, lymphadenopathy, and immunodeficiency (PASLI), is an autosomal dominant disorder caused by inherited or de novo gain-of-function mutations in one of two genes encoding subunits of the phosphoinositide-3-kinase delta (PI3Kδ) complex. This largely leukocyte-restricted protein complex regulates cell growth, activation, proliferation, and survival. Patients who harbor these mutations have early onset immunodeficiency with recurrent infections, lymphadenopathy, and autoimmunity. The most common infection susceptibilities are sinopulmonary (encapsulated bacteria) and herpesviruses. Multiple defects in both innate and adaptive immune function are responsible for this phenotype. Apart from anti-microbial prophylaxis and immunoglobulin replacement, patients are treated with a variety of immunomodulatory agents and some have needed hematopoietic stem cell transplants. Here, we highlight the spectrum of infections, immune defects, and therapy options in this inborn error of immunity.

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.

Autoimmune Cytopenias in Nonmalignant Lymphoproliferative Disorders: Thinking Beyond ALPS(Autoimmune Lymphoproliferative Syndrome)

The ALPS Clinic at NIH has studied autoimmune lymphoproliferative disorders for over 30 years elucidating the genetic underpinnings and natural history of Autoimmune Lymphoproliferative Syndrome (ALPS) due to FAS gene defects (Blood 2014). Over the years, we continue to receive and work-up numerous referrals for diseases that masquerade like ALPS-FAS, presenting with multi-lineage cytopenias due to autoimmune peripheral destruction and splenic sequestration in the setting of non-malignant lymphoproliferation. In a review of 259 cases evaluated by our team, there were 150 ALPS-FAS, 54 Activated PI3K-delta Syndrome (APDS), 31 CTLA-4 Haploinsufficiency (CTLA4), 7 LRBA deficiency (LRBA), and 17 MAGT-1 deficiency (XMEN) patients. Non-malignant lymphadenopathy and splenomegaly occurred on average in 83% and 71% of all patients, respectively. Anemia, thrombocytopenia, and neutropenia were seen in 65%, 58%, and 46%, respectively. Thus, autoimmune cytopenias in the setting of non-malignant lymphoproliferation in themselves are not adequate to rule in or rule out a presumptive diagnosis of ALPS-FAS. Timely and accurate genetic diagnosis of ALPS-like conditions will improve the morbidity and mortality associated with these disease processes. Rapamycin, an m-TOR inhibitor provides salutary benefits for many of these conditions by restoring the TREG function and reversing immune-dysregulation. For example, in addition to lymphadenopathy and splenomegaly associated with an increased risk of malignant lymphoma like ALPS-FAS patients, APDS patients usually present with recurrent sinopulmonary and ear infections. Their serum IgM tends to be elevated with low IgG levels. Unlike for ALPS-FAS patients, a potential targeted treatment for APDS exists: Leniolisib, a targeted PI3Kinase p-110 delta inhibitor is currently undergoing clinical trials (Blood 2016). CTLA-4 is critical for T-cell activation and immune check-point regulation by tempering regulatory T cell function. Patients affected by CTLA4 and LRBA variants present with symptoms of lymphocytic infiltration of the bone marrow (often leading to hypoplastic anemia), gut (colitis, bowel obstruction), lungs (bronchiectasis, restrictive airway disease), and central nervous system (seizures and neurological deficits due to brain and spinal cord lesions). They also tend to have B cell lymphopenia, low IgG and IgM levels. CTLA4 and LRBA patients share pathophysiology as well as clinical phenotype because LRBA gene regulates intracellular lysosomal trafficking and recycling of CTLA-4 protein. Hence CTLA-4 haploinsufficiency or LRBA deficiency renders both patient types CTLA-4 deficient. This can be directly addressed with abatacept infusions, a CTLA-4 hybridized immunoglobulin given as a combination immunosuppressive therapy with rapamycin. Abatacept replaces the CTLA-4 molecule and reverses some of the immune dysregulation and thus morbidity associated with both CTLA4 and LRBA deficiency. Like APDS patients, XMEN patients are also prone to recurrent ear and sinopulmonary infection, but key differentiating features of this X-linked disorder are that only males are affected, these patients are unable to clear Epstein-Barr virus (EBV) once exposed, and they have a propensity to develop EBV-driven lymphomas. These patients also usually have a strong family history of multiple lymphomas in males. Even though a targeted treatment does not yet exist, steroid-sparing measures such as rituximab, rapamycin and mycophenolate mofetil are the first-line treatments often used in managing their refractory autoimmune cytopenias. Hence accurate early genetic diagnosis is key to accessing the appropriate treatment, thus decreasing the morbidity and mortality associated with these childhood onset ALPS-like rare inherited disorders (table). Table Disclosures No relevant conflicts of interest to declare. OffLabel Disclosure: Rapamycin, Abatacept, Mycophenolate Mofetil.

Activated PI3K-delta syndrome in an Egyptian pediatric cohort with primary immune deficiency

BackgroundActivated Phospho-Inositide 3 (PI3) Kinases Delta syndrome (APDS) can underlie primary immune deficiency. The prevalence and phenotypic characterization of these patients are not well described in Egypt. ObjectivesTo describe patients with APDS in hospitalized children with recurrent respiratory tract infections with suspected primary immune deficiency. Methods79 patients were included in the study. E1021K and E525K mutations of PI3K δ chain gene were screened by Sanger sequencing technique. Resultsone patient was heterozygous to E1021K mutation; a female child was diagnosed clinically as Combined Immune Deficiency with CD4 and B lymphopenia and markedly deficient IgG and increased IgM. The E525K mutation was not detected in our cohort. ConclusionsScreening for APDS in patients with recurrent respiratory tract infections with undefined antibody deficiency or combined immune deficiency with or without bronchiectasis is required. These patients need great attention to benefit from the available treatment. Further studies on the Egyptian population are recommended to increase the knowledge about the prevalence and phenotypic characterization of this disease in Egypt.