Elsevier

Clinical Immunology

Volume 191, June 2018, Pages 52-58
Clinical Immunology

IPEX due to an exon 7 skipping FOXP3 mutation with autoimmune diabetes mellitus cured by selective TReg cell engraftment

https://doi.org/10.1016/j.clim.2018.03.008Get rights and content

Highlights

  • IPEX caused by hemizygous FOXP3 mutations leads to severe but after timely treatment reversible organ-specific autoimmunity

  • FOXP3 c.816+2T>A impairs exon 7 splicing and TReg cell biology by altering the transcriptome and causes delayed-onset IPEX

  • Timely HSCT with selective TReg cell engraftment can lead to remission of autoimune diabetes despite reamining autoantibodies

Abstract

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare inherited disorder leading to severe organ-specific autoimmunity. IPEX is caused by hemizygous mutations in FOXP3, which codes for a master transcription factor of regulatory T (TReg) cell development and function.

We describe a four-year-old boy with typical but slightly delayed-onset of IPEX with autoimmune diabetes mellitus, enteropathy, hepatitis and skin disease. We found the unreported FOXP3 splice site mutation c.816+2T>A that leads to the loss of leucine-zipper coding exon 7. RNA-Seq revealed that FOXP3Δ7 leads to differential expression of FOXP3 regulated genes. After myeloablative conditioning the patient underwent allogeneic HSCT from a matched unrelated donor. HSCT led to the resolution of all IPEX symptoms including insulin requirement despite persisting autoantibody levels. After initial full donor engraftment nearly complete autologous reconstitution was documented, but donor-derived TReg cells persisted with a lineage-specific chimerism of >70% and the patient remained in clinical remission.

Introduction

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is an inborn error of immunity particularly characterized by severe immune dysregulation [1]. IPEX is caused by hemizygous mutations of the FOXP3 gene, which codes for the FOXP3 master transcription factor of regulatory T (TReg) cell development and function [2]. Thus in IPEX, missing or dysfunctional TReg cells lead to destructive organ-specific autoimmunity [3]. Typical symptoms include autoimmune enteropathy, diabetes mellitus, thyroiditis and skin disease alone or in combination with further autoimmune manifestations [4]. Treatment by pharmacological immune suppression is often insufficient to control autoimmunity and causes side effects and complications. IPEX patients are also prone to infections that are partially attributable to concomitant immunosuppressive treatment [5]. The only curative treatment available at present is allogeneic hematopoietic stem cell transplantation (HSCT) [6,7]. While especially enteropathy and skin disease resolve when donor engraftment is established, damage to other organs can be permanent especially with persistence of diabetes mellitus if post-mitotic pancreatic islet beta cells are lost [4,8]. Systematic evaluation of HSCT outcome is lacking for larger patient cohorts, but several case reports and small cohorts have reported results after myeloablative and reduced intensity conditioning [4,6,9]. It has been shown that mixed chimerism can cure IPEX and that even selective engraftment of donor regulatory T cells may suffice [10]. However, outcome is still not universally good with a persistent risk of severe complications, especially in older patients [6]. It is therefore mandatory to establish an early diagnosis. However, this can be demanding since there is no clear genotype-phenotype correlation and similar mutations can lead to differential clinical outcomes [5]. Furthermore, dysfunctional FOXP3 proteins can be expressed and phenotypically unsuspicious TReg cells can be detected by flow cytometry that still are devoid of proper function [5,11]. Therefore, in-depth analysis of individual FOXP3 variants and their consequences for TReg cell phenotype and function are necessary to truly establish the diagnosis of IPEX. Over 60 mutations have been described with the majority of them clustering around the FOXP3 forkhead domain necessary for DNA binding [2]. The ongoing discovery of new mutations still increases our knowledge about the physiological importance of other FOXP3 domains [12,13].

Section snippets

Subjects

Blood from patient and healthy donors was obtained after written informed consent in accordance with the Declaration of Helsinki. The study was approved by the local ethics committee of the LMU München.

Isolation and stimulation of peripheral blood T cell populations

Human peripheral blood mononuclear cells (PBMC) were isolated from heparinized blood samples by Biocoll (Biochrom, Berlin, Germany) density gradient centrifugation. Untouched CD4+ T cells were separated using the CD4+ T cell Isolation Kit II (Miltenyi Biotec, Bergisch Gladbach, Germany) according

IPEX-related autoimmunity is cured by selective TReg cell engraftment

We report a male patient with skin disease resembling atopic dermatitis, recurrent pulmonary infections and systemic CMV infection initially presenting at the age of ten months. At three years of age, episodes of protracted diarrhea with enteral villous atrophy and elevated anti-AIE75 (autoimmune enteropathy-related 75 kDa antigen) autoantibodies lead to the diagnosis of autoimmune enteropathy. Simultaneously, the patient developed an autoimmune overlap-syndrome with hepatitis type 2 and

Discussion

It is well accepted that FOPX3 is essential for the development and function of TReg cells and that its absence leads to IPEX syndrome [27]. Four naturally occurring FOXP3 splice variants, i.e. FOXP3fl, FOXP3Δ2, FOXP3Δ7 and FOXP3Δ2Δ7, have been described in humans [28,29]. However, little is known about their individual involvement in human TReg cell development and function. We here report the FOXP3 splice site mutation c.861+2T>A that only leads to expression of FOXP3 transcripts and FOXP3

Conflict of interest

The authors declare that they have no conflict of interest.

Acknowledgments

We value the personal contribution of the patient and his family as well as the excellent clinical care by the medical and nursing teams. We thank Eva Eisl, Mayumi Hofmann and Irmgard Eckerlein for technical assistance. T.M., M.A. and F.H. have been funded by the Wilhelm Sander-Foundation (Grant numbers.: 2009.095.1, 2009.095.2 and 2014.040.1). The project was further supported by the German Research Foundation (CRC 914 projects A4/A8, Gottfried-Wilhelm-Leibniz Program, Grant number: KL 877-11-1

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