Successful treatment of JAK1-associated inflammatory disease

BACKGROUND

Gain-of-function variants of JAK1 drive a rare immune dysregulation syndrome associated with atopic dermatitis, allergy, and eosinophilia.

OBJECTIVES

This study sought to describe the clinical and immunological characteristics associated with a new gain-of-function variant of JAK1 and report the therapeutic efficacy of Janus kinase (JAK) inhibition.

METHODS

The investigators identified a family affected by JAK1-associated autoinflammatory disease and performed clinical assessment and immunological monitoring on 9 patients. JAK1 signaling was studied by flow and mass cytometry in patients' cells at basal state or after immune stimulation. A molecular disease signature in the blood was studied at the transcriptomic level. Patients were treated with 1 of 2 JAK inhibitors: either baricitinib or upadacitinib. Clinical, cellular, and molecular response were evaluated over a 2-year period.

RESULTS

Affected individuals displayed a syndromic disease with prominent allergy including atopic dermatitis, ichthyosis, arthralgia, chronic diarrhea, disseminated calcifying fibrous tumors, and elevated whole blood histamine levels. A variant of JAK1 localized in the pseudokinase domain was identified in all 9 affected, tested patients. Hyper-phosphorylation of STAT3 was found in 5 of 6 patients tested. Treatment of patients' cells with baricitinib controlled most of the atypical hyper-phosphorylation of STAT3. Administration of baricitinib to patients led to rapid improvement of the disease in all adults and was associated with reduction of systemic inflammation.

CONCLUSIONS

Patients with this new JAK1 gain-of-function pathogenic variant displayed very high levels of blood histamine and showed a variable combination of atopy with articular and gastrointestinal manifestations as well as calcifying fibrous tumors. The disease, which appears to be linked to STAT3 hyperactivation, was well controlled under treatment by JAK inhibitors in adult patients.

How many JAK inhibitors in myelofibrosis?

The discovery of the activating mutation JAK2 V617F ushered a new era in MPN which included new diagnostic and prognostic criteria as well as a potential therapeutic target. JAK2 inhibition became a reality with first patients receiving drugs that targeted JAK2 in 2007 and was marked by the first approval in 2011 of Ruxolitinib a JAK 1 and 2-inhibitor to treat myelofibrosis (MF). In this article entitled "How many JAK inhibitors for myelofibrosis" we discuss JAK2 as a target, review briefly the benefits to patients with MF of JAK inhibition and highlight some of the differences between the number of JAK inhibitors currently being evaluated. Reflecting upon what we have learnt from the chronic myeloid leukaemia field and for MF regarding disease complexity as well as individual patient factors including resistance we discuss why it is likely we will need several different agents with JAK inhibitory activity. The next chapter discusses combination therapies for myelofibrosis which is a logical step in both trying to cure this disease and improve patient outcome and toxicities with JAK inhibitors.