Trispecific molecule combining specific tumor targeting and local immune checkpoint inhibition

A trispecific protein comprising:

• (i) a first domain, wherein said first domain is formed by a Fab domain that specifically binds to a cell surface molecule at the cell surface of a tumor cell, wherein said cell surface molecule at the cell surface of the tumor cell is CD33, wherein the first domain comprises light chain CDR1 having an amino acid sequence of RASESLDNYGIRFLT (SEQ ID NO:
• 29), light chain CDR2 having an amino acid sequence of AASNQGS (SEQ ID NO:
• 30), light chain CDR3 having an amino acid sequence of QQTKEVPWS (SEQ ID NO:
• 31), heavy chain CDR1 having an amino acid sequence of DSNIH (SEQ ID NO:
• 32), heavy chain CDR2 having an amino acid sequence of YIYPYNGGTDYNQKFKN (SEQ ID NO:
• 33), and heavy chain CDR3 having an amino acid sequence of GNPWLAY (SEQ ID NO:
• 34);
• (ii) a second domain, wherein said second domain is formed by an IgG Fc domain and specifically binds to a cell surface molecule at the cell surface of an immune cell/immune cells;
• and
• (iii) a third domain, wherein said third domain is formed by one or more SirpIg domains that specifically bind to a checkpoint molecule at the cell surface of said tumor cell, wherein said checkpoint molecule at the cell surface of said tumor cell is CD47, wherein said third domain is formed by an immunoglobulin-like domain of SIRPα (signal regulatory protein alpha),
• and wherein said trispecific protein does not comprise any other part of said immune cell checkpoint receptor besides said immunoglobulin-like domain of SIRPα;
• wherein two copies of the first domain and the second domain form an IgG and wherein the third domain is fused on its C-terminus to the N-terminus of each first domain by a flexible linker;
• wherein the flexible linker comprises two to eight tandem repeats, each tandem repeat consisting of four or five amino acids with the amino acid sequence GGGS (SEQ ID NO:
• 6 or GGGGS (SEQ ID NO:
• 14).