A novel human IL2RB mutation results in T and NK cell-driven immune dysregulation

Abstract

The pleiotropic actions of interleukin-2 (IL-2) are essential for regulation of immune responses and maintenance of immune tolerance. The IL-2 receptor (IL-2R) is composed of IL-2Rα, IL-2Rβ, and IL-2Rγ subunits, with defects in IL-2Rα and IL-2Rγ and their downstream signaling effectors resulting in known primary immunodeficiency disorders. Here, we report the first human defect in IL-2Rβ, occurring in two infant siblings with a homozygous IL2RB mutation in the WSXWS motif, manifesting as multisystem autoimmunity and susceptibility to CMV infection. The hypomorphic mutation results in diminished IL-2Rβ surface expression and dysregulated IL-2/15 signaling, with an anticipated reduction in regulatory T cells. However, in contrast to the IL-2Rβ^-/- animal model, which lacks NK cells, these siblings demonstrate an expansion of NK cells, particularly the CD56^bright subset, and a lack of terminally differentiated NK cells. Thus, the early-onset autoimmunity and immunodeficiency are linked to functional deficits arising from altered IL-2Rβ expression and signaling in T and NK cells.

Graphical abstract

Figure 1.

Identification of an IL2RB homozygous mutation in patients with lymphoproliferation and autoimmunity. (A) Pedigree of the consanguineous parents with two affected children and chromatogram showing the 9-nucleotide deletion in the IL2RB gene. (B) Patient II.1 endoscopy of the (i) esophagus with severe nodularity with the submucosal lymphoid hyperplasia; (ii) stomach with edema of the antrum with chronic active gastritis; (iii) duodenum with erythema, edema, and loss of villous profile; and (iv) colon with small superficial aphthous ulcerations with chronic active colitis. Bars, 100 µm. (C) Patient II.2 bronchoscopy shows (i) lymphocytic interstitial pneumonia pattern; (ii) patchy peri-airway and intraalveolar macrophage accumulation, with a predominant CD8⁺ and CD4⁺ T lymphocyte infiltrate (iii and iv). Bars, 500 or 100 µm. (D) IL2RB gene expression quantification relative to actin (HA in black, n = 3, 1 ± 0.35; one experiment). Cartoon shows primer position (black arrows) relative to deletion (asterisk). RQ, relative quantification. (E) 3D modeling of the IL-2Rβ protein structure, with disruption of the WSXWS motif in the patients (from left to right): the IL-2R complex is shown in ribbons. The WSXWS motif is shown in red and orange. In the expanded view of the IL-2Rβ protein D2 domain with the WSXWS motif, the three residues that are deleted in the patient are shown in red (translucent in patient). Adjacent residues involved in the π cation-stacking ladder are shown in dark gray. (F) Normalized surface IL-2Rβ protein expression mean fluorescence intensity (MFI) in CD56^bright NK, CD56^dim NK, and CD8⁺ T cells. The MFI is calculated as IL-2Rβ MFI − isotype control MFI normalized to the mean for each cell type. Healthy cord (H. cord) and pediatric controls (H. Ped; age 12–30 mo) were normalized independently. For cord comparisons, two experiments with different healthy cord donors are shown. For pediatric comparisons, one experiment with four healthy pediatric controls is shown. Ped, pediatric. (G) Representative bright-field and immunofluorescence images of CD56 and IL-2Rβ staining are shown for healthy adult (H. Adult; top) and patient II.2 (bottom). Number of IL-2Rβ clusters per cell in one healthy adult (18.43 ± 15.16, cells = 30), three pediatric controls (25.38 ± 12, cells = 16), patient II.1 (2.567 ± 3.256, cells = 30), and patient II.2 (2.8 ± 2.497, cells = 30) is shown as a dot graph where each dot represents one cell. Bars, 1 µm. Two experiments were performed. Mean ± SD is shown.

Figure 2.

IL2RB homozygous patients have increased IL-2 and IL-15c plasma levels, dysregulated STAT5 phosphorylation, and IL-15c–induced NK cell survival. (A) Plasma levels of IL-2 and IL-15c in patients (IL-2 = 83.08 ± 15.1, IL-15c = 246 ± 40.1, n = 3 for II.1 and n = 2 for II.2), and healthy controls (HC; IL-2 = 16.72 ± 5.8, Il-15c = 62.5 ± 0). For IL-2 ELISA measurements, there were n = 5 adult, n = 3 pediatric (age 12–30 mo), n = 7 cord controls, and four experiments; for IL-15c, ELISA, there were n = 3 adult and n = 2 pediatric (age 12–30 mo) controls, and two experiments. Ped, pediatric. (B) Basal pSTAT5 MFI (no stimulation [unstim], filled) and maximal response (IL-2 at 10 µg/ml for 30 min, unfilled) in CD56^bright and CD56^dim NK, CD8⁺, and CD4⁺ T cells. (C) Percentage of CD56^bright and CD56^dim NK, CD8⁺, and CD4⁺ T cells with pSTAT5 signal above unstimulated level in response to 30-min stimulation with IL-2 (0.1, 1.0, or 10 µg/ml, left to right, filled bar), IL-15c (0.1, 10, or 1,000 ng/ml, left to right, hashed bar), or IL-7 (1 µg/ml, unfilled bar). Unstimulated %pSTAT5⁺ level is set with 95% of cells below threshold (dashed line). For B and C, one experiment with II.1 age 24 mo and II.2 age 8 mo compared with healthy adults (H. adult, n = 3) and pediatric controls (age 12–30 mo, H. ped, n = 3) is shown. (D) Total number of live NK cells cultured with no cytokines, IL-2, IL-15c or IL-2, and IL-15c for 100 h from healthy adults (n = 2) and patient II.2 (n = 2, two experiments). (E) Percentage of Annexin V-7⁻AAD⁻ (live), Annexin V⁺7-AAD⁻ (early apoptotic), and Annexin V⁺7-AAD⁺ (dead) NK cells cultured with no cytokine or with IL-15c (0.3 or 30 ng/ml) for 110 h. One experiment with healthy adults (n = 2) and pediatric controls (age 12–30 mo, n = 3) shown. Mean ± SD is shown.

Figure 3.

IL2RB patients possess a dysregulated NK cell compartment. (A) Representative dot plots show NK cell subsets dissected based on CD56 versus CD16 from the CD3⁻CD19⁻CD14⁻CD33⁻ gate. Bar graph shows the frequency of CD3⁻CD56^dim (unfilled) and CD3⁻CD56^bright (filled) NK cells from CMV⁺ (n = 5) or CMV⁻ (n = 5) healthy pediatric (H. Ped) donors and patients. Two experiments shown. (B) viSNE maps represent each cell from the CD3⁻CD19⁻CD14⁻CD33⁻HLADR⁻LILRB1^lo population as a dot. The location of the cell clusters for each healthy control in the 2D viSNE map represent the NK cell compartment in infancy (H. cord, cord blood, n = 6, 3 CMV⁺ and 3 CMV⁻), childhood (H. Ped, age 12 mo, n = 10, 5 CMV⁺ and 5 CMV⁻), and adulthood (H. Adult, n = 6, 3 CMV⁺ and 3 CMV⁻). The merge of these three viSNE maps illustrates a healthy “NK trajectory” (H. Trajectory). Below are each of the visNE maps described above colored by CD56 signal intensity. Two experiments with data merged and normalized together for analysis. (C) Representative dot plots for CD57 and NKG2C from the CD3⁻CD19⁻CD14⁻CD33⁻HLADR⁻LILRB1^lo parent gate (two experiments). Circles indicate CD57⁺NKG2C^hi cells. (D) Functional assay of CD3⁻CD56^dim and CD3⁻CD56^bright NK cells from CMV⁺ (closed circles) or CMV⁻ (open circles) healthy pediatric donors (age 12–30 mo) and patients II.1 (24 mo) and II.2 (10 mo). Intracellular expression of IFNγ and surface expression of CD107a were assessed after PBMC stimulation with K562 cells (n = 10), anti-CD20–coated Raji cells (n = 6), and IL-12/15 (10 ng/ml) and IL-18 (100 ng/ml; n = 4). Stimulated %CD107a⁺ and %IFNγ⁺ frequencies were based on a 5% positivity threshold set on the unstimulated samples. One experiment was performed. Mean ± SD is shown. Unstim, no stimulation.

Figure 4.

T cell immunophenotypic and functional characterization in patient II.1. (A) Production of IFNγ in response to PHA, EBV, and CMV ± IL-2/15c was measured by ELISPOT. Healthy adults (H. Adult; n = 7) and cord blood samples (H. Cord; n = 3) were used with patient samples (n = 1 for each) in one experiment. (B) TCR sequencing was performed in patients and healthy controls, and clonality scores are shown. Graphs show the frequency of the top 10 TCR rearrangements unique to patients and their respective age-matched healthy controls. Each numbered TCR rearrangement is different and unique for each patient and control. (C) Histograms of IL-2Rβ surface protein expression in patient II.1 post-HSCT and healthy control. (D) Normalized pSTAT5 responses in cell types as indicated. PBMCs were stimulated with IL-2 (1 µg/ml) or IL-15c (1 µg/ml) for 30 min. Fold change in MFI is calculated as pSTAT5 MFI for each condition normalized to the unstimulated (unstim) condition for each individual. Data merged from two experiments with II.1 pre- and post-HSCT compared with healthy adults (H. Adult, n = 7) and healthy 2 yr old (n = 1). (E) Representative dot plots show NK cell subsets dissected based on CD56 versus CD16 from the CD3⁻CD19⁻CD14⁻CD33⁻ gate from one experiment. (F) Representative dot plots show SSC versus CD45RA⁺ from the CD3⁺ gate in patient II.1 pre- and post-HSCT. Two experiments shown. (G) Percentage of lymphoid and myeloid chimerism in patients II.1 and II.2 post-HSCT. mo, months old; yo, years old. Mean ± SD is shown.