Elevated Serum Type I Interferon Activity and Type I Interferon Peripheral Blood Gene Signature In a Subset of Patients with Acquired ADAMTS13-Deficient Thrombotic Thrombocytopenic Purpura.

Current treatments for Thrombotic Thrombocytopenic Purpura (TTP) fail to successfully control this life-threatening syndrome in up to 20% of patients, and of those patients who survive the first episode, a substantial fraction experience at least one relapse. Genetic mutation or autoantibody inhibition of the ultra-large von-Willebrand factor protease, A Disintegrin And Metalloproteinase with a Thrombospondin Type 1 Motif (ADAMTS13), reduces its enzymatic activity and is an important factor that promotes TTP development. Case reports of acute TTP episodes following infections or Type I interferon (IFN) treatment, a phenomenon also observed in systemic lupus erythematosus (SLE), suggest that inflammatory dysregulation could be important in this disease. SLE patients have elevated serum Type I IFN activity and a peripheral blood Type I IFN gene signature, which are associated with the presence of autoantibodies specific for RNA-binding nuclear antigens.

This study was undertaken to determine whether, in the absence of SLE, Type I IFN is elevated in acquired TTP patients, and/or is associated with autoantibodies to RNA-binding proteins.

We obtained blood and serum samples from patients with acquired ADAMTS13-deficient TTP and matched healthy controls. Patient Inclusion Criteria: 1) ADAMTS13 activity <10% during either the initial episode or during a relapse, 2) at least six months follow-up after an initial or relapse episode; Exclusion criteria: 1) institutionalized or not alive at the time of study 2) previous diagnosis of an autoimmune disorder.

Blood samples were collected from 38 eligible TTP subjects during remission and from 38 age- (±5 years), race- and sex-matched healthy controls. While anti-nuclear autoantibody prevalence (titer ≥1:120) did not significantly differ between TTP patients and controls, specific autoantibodies against one or more of the following RNA-binding antigens: Ro, La, Sm or nRNP, were more frequent in TTP patients (31.6%) compared to controls (5.3%) (McNemar c2 p=0.0063). Using previously-banked serum samples from acute phase(s) of the disease obtained from the same patients, we observed no differences in the prevalence of these autoantibodies among TTP subjects in the acute phase of disease compared to remission. Serum Type I IFN activity was measured by the capacity of serum samples to induce expression of Type I IFN genes in the WISH epithelial cell line and was significantly increased in remission TTP samples compared to controls (McNemar c2 p=0.0313). Finally, global gene expression was examined (Illumina WG6 version 3 chips) in globin RNA-cleared total RNA taken from whole blood samples of the TTP patients in remission and controls. In initial analysis, 17 genes were found to be ≥ 1.5× differentially expressed in the peripheral blood of TTP patients compared to controls. Among the 7 genes exhibiting the greatest expression difference, 6 are recognized interferon-regulated genes. The relative expression of IFI44 effectively partitioned 13 of the TTP samples (34.2%) into a subset bearing a Type I interferon gene signature similar to that observed in SLE, compared to occurrence of a Type I interferon gene signature observed in 3 of the healthy controls (7.9%) (McNemar c2 p=0.0020). The Type I IFN gene signature was significantly associated with autoantibodies against specific RNA-binding nuclear antigens, defined as the presence of detectable IgG antibodies to one or more of the Ro, La, Sm, or nRNP antigens (Fisher p=0.0086) and correlated with serum Type I interferon activity in the WISH assay (r=.47, p=.0031). However, the Type I interferon gene signature did not associate with tendency of a patient to relapse after a first episode.

From these studies, we propose a new subset of acquired, ADAMTS13–deficient TTP patients characterized by elevated serum Type I interferon activity, Type I interferon gene signature and IgG antibodies directed to RNA-binding proteins.

Merrill:MedImmune: Consultancy, Honoraria; Genentech: Consultancy, Honoraria.