INTRODUCTION: The JAK family comprises of the four non-receptor tyrosine kinases 
JAK1, JAK2, JAK3 and Tyk2, which play key, but differing, roles in cytokine 
receptor signal transduction. A non-selective JAK inhibitor, ruxolitinib, has 
recently been approved to treat myelofibrosis whereas tofacitinib is poised for 
approval to treat rheumatoid arthritis. Selective inhibition of JAK3, JAK1 or 
Tyk2 provides the opportunity to achieve clinical efficacy in the treatment of 
inflammatory diseases while reducing the risk of dose-limiting effects 
attributable to JAK2 inhibition.
AREAS COVERED: This review considers the small number of published patent 
filings that claim either selective JAK1 or selective Tyk2 inhibitors. These are 
considered in the context of the considerably larger number of disclosures and 
patent filings claiming selective JAK2 or JAK3 inhibitors.
EXPERT OPINION: The recent disclosure of the clinical efficacy of a selective 
JAK1 inhibitor (GLPG-0634) in rheumatoid arthritis and detailed disclosure of 
the some potent and highly selective JAK1 inhibitors provide a clear stimulus 
for further activity in this area. The availability of a selective Tyk2 
inhibitor will provide the opportunity for better understanding of the 
physiological role of this kinase. Recent patent applications indicate that Tyk2 
selectivity is achievable and Tyk2 inhibitors have potential in the treatment of 
multiple sclerosis.