Multi-arm linker for treating rejection reaction in transplantation

A linker unit comprising, a center core, a plurality of linking arms, a plurality of first elements, optionally, a coupling arm, and, optionally, a second element, wherein,

• the center core is (1) a first polypeptide comprising 2 to 15 K resides and one or more filler sequences separating each K residue and its next K residue, wherein the filler sequence comprises glycine (G) and serine (S) residues;
• or (2) a second polypeptide comprising the sequence of (Xaa-K)2-15, where Xaa is a PEGylated amino acid having 2 to 12 repeats of ethylene glycol (EG) unit;
• the plurality of linking arms are respectively linked to the K residues of the center core;
• the amino acid residue at the N- or C-terminus of the center core has an azide or alkyne group;
• or the amino acid residue at the N- or C-terminus of the center core is a cysteine residue, and the thiol group of the cysteine residue is linked with the coupling arm;
• and
• the coupling arm has an azide, alkyne, tetrazine, cyclooctene, or cyclooctyne group at the free terminus thereof,
• the plurality of first elements are respectively linked to the plurality of linking arms via forming an amide bound therebetween, or via thiol-maleimide reaction, copper catalyzed azide-alkyne cycloaddition (CuAAC) reaction, strained-promoted azide-alkyne click chemistry (SPAAC) reaction, or inverse electron demand Diels-Alder (iEDDA) reaction;
• the second element, if present, is linked to the center core or the coupling arm via CuAAC reaction, SPAAC reaction, or iEDDA reaction;
• each of the first elements is a targeting element and the second elements is an effector element, or vice versa, wherein the targeting element is a single-chain variable fragment (scFv) that is specific for a human leukocyte antigen (HLA) allotype present only on cells of a donor transplant, and comprises the amino acid sequence of SEQ ID NO:
• 32 or 34;
• and
• the effector element is sirolimus, everolimus, tacrolimus, fingolimod, fingolimod phosphate, an ectodomain or extracellular domain of cytotoxic T lymphocyte associated protein 4 (CTLA-4), an ectodomain or extracellular domain of programmed death-ligand 1 (PD-L1), or an scFv that is specific for CD25, and comprises the amino acid sequence of SEQ ID NO:
• 33;
• wherein,
• when the plurality of first elements are respectively linked to the plurality of linking arms via CuAAC or SPAAC reaction, then the amino acid residue at the N- or C-terminus of the center core is a cysteine residue, and the free terminus of the coupling arm is the tetrazine or the cyclooctene group;
• or
• when the plurality of first elements are respectively linked to the plurality of linking arms via iEDDA reaction, then the amino acid residue at the N- or C-terminus of the center core has the azide or the alkyne group, or the amino acid residue at the N- or C-terminus of the center core is a cysteine residue, and the free terminus of the coupling arm is the azide, the alkyne, or the cyclooctyne group.