Pegylated t cell engager with dual specificities to cd3 and cd19

A method of treating an autoimmune disease in a subject, comprising:

• administering an effective amount of a compound of formula (Ib), or a pharmaceutically acceptable salt thereof to said subject,
• wherein:
• P is a non-immunogenic polymer;
• B is H or a capping group selected from C1-10 alkyl and aryl, wherein one or more carbons of said alkyl or aryl are optionally replaced with a heteroatom;
• T is a tri-functional linker having one, two, or more functional groups that, after derivatization and/or extension with a bifunctional spacer, are capable of site-specific conjugation with A1 and A2 or their derivatives, wherein the linkage between T and (L1)a and the linkage between T and (L2)b can be same or different;
• each of L1 and L2 is independently a bifunctional linker;
• each of a and b is an integer selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10;
• each of A1 and A2 is independently selected from an antibody or an antigen-binding fragment thereof, in which one of A1 and A2 recognizes and binds to the antigen CD3 and the other recognizes and binds the antigen CD19;
• and
• y is an integer selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10;
• or
• administering an effective amount of a compound of formula (Ia), or a pharmaceutically acceptable salt thereof to the subject
• wherein
• P is a non-immunogenic polymer;
• T is a multifunctional small molecule linker moiety and has one, two, or more functional groups that are capable of site-specific conjugation with one, two or more the same or different polypeptides;
• Each of A1 and A2 is independently selected from an antibody or an antigen-binding fragment thereof, in which one of A1 and A2 recognizes and binds to the antigen CD3 and the other recognizes and binds the antigen CD19.