Correspondence

FOXP3 Forkhead Domain Mutation and Regulatory T Cells in the IPEX Syndrome

N Engl J Med 2009; 361:1710-1713October 22, 2009

Article

To the Editor:

The immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome, a rare disorder characterized by multiorgan autoimmunity, often results in death in infancy.1 The IPEX syndrome results from mutations in the forkhead box P3 (FOXP3) gene, which encodes a transcriptional repressor considered to be the master regulator of differentiation in CD4+ regulatory T (Treg) cells.2,3 Multiple FOXP3 mutations resulting in a range of clinical outcomes have been characterized.1-3 Since neither genetic sequencing nor protein expression correlates reliably with clinical manifestations in the IPEX syndrome,4 identification of the functional consequences of individual mutations is critical to gain insights into the prognosis of and possible treatments for this syndrome.

We report on a preterm male infant with clinical features and laboratory findings that were consistent with a severe phenotype of the IPEX syndrome (see the Supplementary Appendix, available with the full text of this letter at NEJM.org). Sequencing of the FOXP3 gene revealed an 1150G→A missense mutation in exon 11 resulting in a substitution of alanine for threonine at residue 384 (A384T), within the forkhead DNA-binding domain of FOXP3. This mutation is commonly associated with mild phenotypes of the IPEX syndrome1,5; however, this patient died at 7 weeks of age, despite treatment with sirolimus.

Despite the severe clinical presentation, FOXP3-expressing CD4+ T cells were readily detectable in the patient, although at a slightly reduced level as compared with these cells in a control patient (Figure 1AFigure 1Evaluation of the Phenotype and Function of Regulatory T Cells in the IPEX Syndrome.). Nonetheless, the proportions of CD4+ T cells that secreted interleukin-10, interleukin-17, or interferon-γ in the blood of the patient with the IPEX syndrome were approximately 8, 15, and 4 times as high, respectively, as the proportions in the blood of the control patient (Figure 1B), and this cytokine production is largely restricted to FOXP3− T cells (data not shown). The increased production of inflammatory cytokines in T cells in the patient with the IPEX syndrome who had the A384T mutation strongly suggests that effector T-cell inflammatory responses are dysregulated and that FOXP3+ Treg cells with the A384T mutation are probably defective in their function (Figure 1B).

We next used a multiparametric, single-cell strategy to directly assess the consequences of the A384T mutation on FOXP3 expression, relative to CD4+ Treg functional parameters, in primary clonal CD4+ T-cell lines. Despite detectable frequencies of FOXP3+ Treg cells in peripheral-blood mononuclear cells, the suppressive function was almost absent in FOXP3+ clones in the patient with the IPEX syndrome as compared with Treg cells in the control patient (Figure 1C); this was consistent with the dysregulated T-cell responses and severe phenotype of the IPEX syndrome.

Although the A384T mutation in FOXP3 does not affect FOXP3 expression, it abolishes the suppressive function in Treg cells. The systemic autoimmunity in this patient with the IPEX syndrome is probably the consequence of defective Treg-cell–mediated control of immune responses. Further studies are required to unravel the molecular basis underlying the effect of the A384T mutation in FOXP3. The severe course in our patient, as compared with the course in most patients with the IPEX syndrome who have this mutation, may be the consequence of different environmental, genetic, and epigenetic factors; thus, there is a diverse clinical and immunologic spectrum. Our results emphasize the need to go beyond simple mutation analysis and FOXP3 detection and to perform functional studies of Treg cells in patients in whom the IPEX syndrome is suspected. Such studies will help us to understand and improve the prognosis in affected patients.

Eva d'Hennezel, M.Sc.
Moshe Ben-Shoshan, M.D.
McGill University Health Center, Montreal, QC, Canada

Hans D. Ochs, M.D.
Troy R. Torgerson, M.D., Ph.D.
University of Washington School of Medicine, Seattle, WA

Laura J. Russell, M.D.
Christine Lejtenyi, M.D.
Francisco J. Noya, M.D.
Nada Jabado, M.D., Ph.D.
Bruce Mazer, M.D.
Ciriaco A. Piccirillo, Ph.D.
McGill University Health Center, Montreal, QC, Canada
ciro.piccirillo@mcgill.ca

Supported by grants (MOP67211 and MOP84041, to Dr. Piccirillo) from the New Emerging Team in Clinical Autoimmunity: Immune Regulation and Biomarker Development in Pediatric and Adult Onset Autoimmune Diseases of the Canadian Institutes of Health Research.

Dr. Noya reports receiving grant support from Sanofi Pasteur Canada and GlaxoSmithKline; Dr. Mazer, consulting fees from Novartis Canada, King Pharmaceuticals Canada, and Paladin Laboratories, lecture fees from Novartis Canada and King Pharmaceuticals Canada, and grant support from Novartis Canada and Talecris Biotherapeutics; and Dr. Ochs, consulting fees from CSL Behring and Baxter and grant support from Flebogamma. No other potential conflict of interest relevant to this letter was reported.

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   D. Zennaro, E. Scala, D. Pomponi, E. Caprini, D. Arcelli, E. Gambineri, G. Russo, A. Mari. (2012) Proteomics plus genomics approaches in primary immunodeficiency: the case of immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome. Clinical & Experimental Immunology 167:1, 120-128
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    Anthony L Guerrerio, Pamela A Frischmeyer-Guerrerio, Howard M Lederman, Maria Oliva-Hemker. (2010) Recognizing Gastrointestinal and Hepatic Manifestations of Primary Immunodeficiency Diseases. Journal of Pediatric Gastroenterology and Nutrition 51:5, 548-555
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