Tyrosine kinase inhibitors show great promise as clinical therapies, but small molecule inhibitors that are available
in the clinic and under development bind to the adenosine triphosphate binding domain of the kinase, potentially limiting
efficacy and selectivity. The development of antisense peptide inhibitors is a relatively unexplored area of research,
and here we investigate inhibitory peptides specific for the Janus-associated kinase (JAK) family member, tyrosine kinase
2 (TYK2). We have developed peptides that are 2–3 times more selective for TYK2 than other JAK family members, with
a TYK2 IC50 of 1.2 μM. In addition, TYK2 inhibitory peptides show specificity for TYK2-mediated functions over JAK1
functions in cell-based assays. These peptides provide a new tool for the development of specific peptide inhibitors for
closely related tyrosine kinases.