Autoimmunity, hypogammaglobulinemia, lymphoproliferation, and mycobacterial disease in patients with activating mutations in STAT3

Abstract

The signal transducer and activator of transcription (STAT) family of transcription factors orchestrate hematopoietic cell differentiation. Recently, mutations in STAT1, STAT5B, and STAT3 have been linked to development of immunodysregulation polyendocrinopathy enteropathy X-linked-like syndrome. Here, we immunologically characterized 3 patients with de novo activating mutations in the DNA binding or dimerization domains of STAT3 (p.K392R, p.M394T, and p.K658N, respectively). The patients displayed multiorgan autoimmunity, lymphoproliferation, and delayed-onset mycobacterial disease. Immunologically, we noted hypogammaglobulinemia with terminal B-cell maturation arrest, dendritic cell deficiency, peripheral eosinopenia, increased double-negative (CD4(-)CD8(-)) T cells, and decreased natural killer, T helper 17, and regulatory T-cell numbers. Notably, the patient harboring the K392R mutation developed T-cell large granular lymphocytic leukemia at age 14 years. Our results broaden the spectrum of phenotypes caused by activating STAT3 mutations, highlight the role of STAT3 in the development and differentiation of multiple immune cell lineages, and strengthen the link between the STAT family of transcription factors and autoimmunity.

Figure 1

Clinical characteristics of patients. (A) Livedo-like generalized exfoliating dermatitis in patient 1. The rash culminates in limb extensor areas. (B) High-resolution computed tomography of patient 2 showing ground-glass opacity, bronchoalveolar thickening, and increased nodularity. (C) BM biopsy from patient 1 showing modest BM eosinophilia despite observed peripheral eosinopenia (yellow asterisks). Hematoxylin and eosin stain, original magnification ×40.

Figure 2

STAT3 mutations K658N, K392R, and M394T in studied patients. (A) Schematic representation of STAT3 protein domains with the observed mutations marked as black lines. Germ-line and somatic mutation hotspots for HIES^, and LGL leukemia^- are indicated as green and blue bars, respectively, at top. (B) Crystallographic structure of STAT3 dimer (RCSB Protein Data Bank code 1BG1). K658N, K392R, and M394T mutations are indicated as red dots. (C-D) HEK293 cells containing STAT3-responsive luciferase were transfected with empty, WT, and mutant STAT3 overexpression plasmids with or without IL-6 stimulation. K392R and M394T significantly increased STAT3 transcriptional activity in basal and stimulated conditions. Error bars represent standard error of the mean (n = 6; C). The K658N mutant showed hypersensitivity to IL-6 stimulation in low concentrations. Error bars represent standard error of the mean (n = 3; D). Two-way analysis of variance, *P < .05, **P < .01, and ***P < .001. (E) No significant increase in pSTAT3^Y705 phosphorylation was observed when HEK293 cells were transfected with mutant STAT3-overexpression constructs. Equal amounts of parallel-derived whole cell lysates were loaded per condition. α-tubulin and STAT3 were used as loading and expression controls, respectively. +, presence of IL-6 stimulation; –, absence of IL-6 stimulation. (F) In peripheral blood, no significant increase in STAT3 phosphorylation was noted in studied patients. Color change indicates relative pSTAT3^Y705 expression. Forward panel, K392R; middle panel, K658N; back panel, healthy control (n = 3, value range presented in parentheses).

Figure 3

Abnormal lymphocyte populations detected in STAT3-mutated patients. (A-C) BM biopsy shows abnormally high number of phospho-STAT3–positive lymphocytes both in patient 2 (p.K392R) (A) and, to a lesser extent, in patient 1 (p.K658N) (B). Patient 3 (M394T) was not available for study. In healthy BM, no phospho-STAT3 cells are present (C). (D-F) Flow cytometry results from patient 2 (p. K392R). The majority of lymphocytes were CD3⁺ (A), with 57% of the population expressing TCR-γδ (B). The TCR-γδ⁺ population consisted of CD4⁻CD8⁻ and CD4⁻CD8⁺ T cells. The expression of TCR-γδ was considerably lower in CD4⁻CD8⁻ cells than in CD4⁻CD8⁺ T cells; therefore, 2 populations are seen in the scatter plot. (C). In healthy individuals, TCR-γδ–expressing T cells account less than 6% of all CD3⁺ T cells and the TCR-γδ expression is normally uniform. ×40 magnification, hematoxylin and eosin stain.