BTK and autoimmune disease: BTK is a key factor in B-cell development, differentiation, survival, and signal transduction, and has been used as a target for treating B-cell malignancies.13 Furthermore, BTK has also been validated as a therapeutic target for potential treatment of multiple sclerosis14 and several other autoimmune diseases.15 To date, six small-molecule BTK inhibitors have been approved for treating various haematological cancers; where five of them are covalent inhibitors targeting the non-catalytic Cys481 residue at the vicinity of its ATP-binding pocket.16