Life-Threatening Influenza, Hemophagocytic Lymphohistiocytosis and Probable Vaccine-Strain Varicella in a Novel Case of Homozygous STAT2 Deficiency

Abstract

STAT2 is a transcription factor that plays an essential role in antiviral immunity by mediating the activity of type I and III interferons (IFN-I and IFN-III). It also has a recently established function in the negative regulation of IFN-I signaling. Homozygous STAT2 deficiency is an ultra-rare inborn error of immunity which provides unique insight into the pathologic consequence of STAT2 dysfunction. We report here a novel genetic cause of homozygous STAT2 deficiency with several notable clinical features. The proband presented aged 12 months with hemophagocytic lymphohistiocytosis (HLH) closely followed by clinical varicella, both occurring within three weeks of measles, mumps, and rubella (MMR) and varicella vaccinations. There was a history of life-threatening influenza A virus (IAV) disease 2 months previously. Genetic investigation uncovered homozygosity for a novel nonsense variant in STAT2 (c. 1999C>T, p. Arg667Ter) that abrogated STAT2 protein expression. Compatible with STAT2 deficiency, dermal fibroblasts from the child demonstrated a defect of interferon-stimulated gene expression and a failure to mount an antiviral state in response to treatment with IFN-I, a phenotype that was rescued by lentiviral complementation by wild type STAT2. This case significantly expands the phenotypic spectrum of STAT2 deficiency. The occurrence of life-threatening influenza, which has not previously been reported in this condition, adds STAT2 to the list of monogenetic causes of this phenotype and underscores the critical importance of IFN-I and IFN-III to influenza immunity. The development of probable vaccine-strain varicella is also a novel occurrence in STAT2 deficiency, implying a role for IFN-I/III immunity in control of attenuated varicella zoster virus in vivo and reinforcing the susceptibility to pathologic effects of live-attenuated viral vaccines in disorders of IFN-I immunity. Finally, the occurrence of HLH in this case reinforces emerging links to hyperinflammation in patients with STAT2 deficiency and other related defects of IFN-I signaling-highlighting an important avenue for further scientific enquiry.

Keywords: JAK-STAT signaling pathway; hyperinflammation; inborn errors of antiviral immunity; interferon stimulated gene; type I and type III interferon signaling; type I interferon; varicella zoster virus; viral disease.

Figure 1

A novel Arg677Ter variant causing autosomal recessive STAT2 deficiency. (A) Family pedigree. (B) STAT2 protein domains, showing the Arg677Ter variant.

Figure 2

Impaired type I but preserved type II IFN signaling in patient cells. Immunoblot of whole-cell lysates prepared from primary dermal fibroblasts from patient II:3 or a healthy control treated with 1000 IU/ml of IFNα2b or IFNγ for 30 mins, showing absence of STAT2 using N-terminal and C-terminal antibodies. Signaling to IFNγ was preserved. Representative of n=3 repeat experiments.

Figure 3

Defective induction of the type I IFN dependent antiviral state. (A) Immunoblot analysis of whole cell lysates prepared from patient II:3 and control fibroblasts following overnight treatment with IFNα2b (1000 IU/ml) demonstrating the failure to induce the ISG products of MX1, RSAD2, and IFIT1 in patient fibroblasts. Stars represent non-specific bands. Representative of n=3 repeat experiments. (B) Encephalomyocarditis virus (EMCV) cytopathic effect reduction bioassay demonstrating the failure of IFNα2b pre-treatment (1000 IU/ml) to induce the antiviral state in patient but not control fibroblasts. Displayed are mean ± SEM of n=3 repeat experiments ****P<0.001 ANOVA with Sidak’s post-test.

Figure 4

STAT2 complementation rescues the defect of type I IFN signaling. Fibroblasts from patient II:3 were transduced by lentiviruses expressing either empty vector (GFP) or STAT2. Immunoblot analysis of whole cell lysates prepared from transduced fibroblasts demonstrating (A) restoration of STAT2 protein expression and tyrosine phosphorylation in response to 30 min IFNα2b 1000 IU/ml and (B) restoration of ISG expression in response to 16h treatment with IFNα2b (1000 IU/ml) in STAT2 complemented patient fibroblasts. (C) EMCV cytopathic effect reduction bioassay demonstrating the failure of IFNα2b pre-treatment (1000 IU/ml) to induce the antiviral state in GFP complemented but not STAT2- complemented II:3 fibroblasts. Displayed are mean ± SEM of n=3 repeat experiments ****P<0.001 ANOVA with Sidak’s post-test.