Interleukin-2 mutant and fusion protein thereof

An immunoconjugate, comprising (i) an antibody binding to PD-1 and (ii) an IL-2 mutant protein, wherein the mutant protein, compared to wild-type IL-2 (preferably human IL-2, and more preferably IL-2 comprising a sequence set forth in SEQ ID NO:

• 3), comprises mutations:
• (i) a mutation that eliminates or reduces the binding affinity for an IL-2Rα receptor, at a binding interface of IL-2 to IL-2Rα, particularly at positions 35 and/or 42;
• and/or
• (ii) a mutation that weakens the binding to an IL-2Rβγ receptor, at a binding interface of IL-2 to IL-2Rβγ, particularly at at least one position selected from positions 88, 127 and/or 130;
• and
• (iii) a shortened B′C′ loop region (i.e., a sequence linking amino acid residues aa72 and aa84), wherein preferably, the shortened loop region has less than 10, 9, 8, 7, 6 or 5 amino acids in length, and more preferably has 7 amino acids in length;
• preferably, the shortened B′C′ loop region leads to an improved protein expression yield and/or purity;
• and the amino acid positions are numbered according to SEQ ID NO:
• 3.