Activatable masked anti-CTLA4 binding proteins

A masked antibody, comprising:

• a) an anti-CTLA4 antibody or antigen-binding fragment thereof comprising a light chain variable (VL) domain and a heavy chain variable (VH) domain;
• and
• b) a masking peptide comprising the amino acid sequence of SEQ ID NO:
• 5;
• wherein the masking peptide is linked via a linker comprising a cleavable peptide to
• an amino-terminus of the VL domain;
• wherein the linker comprising a cleavable peptide comprises a cleavable peptide comprising the amino acid sequence of SEQ ID NO:
• 86;
• wherein (a) the VL domain comprises a CDR-L1 comprising the amino acid sequence of SEQ ID NO:
• 408, a CDR-L2 comprising the amino acid sequence of SEQ ID NO:
• 409, and a CDR-L3 comprising the amino acid sequence of SEQ ID NO:
• 410;
• and the VH domain comprises a CDR-H1 comprising the amino acid sequence of SEQ ID NO:
• 411, a CDR-H2 comprising the amino acid sequence of SEQ ID NO:
• 412, and a CDR-H3 comprising the amino acid sequence of SEQ ID NO:
• 413;
• or (b) the VL domain comprises a CDR-L1 comprising the amino acid sequence of SEQ ID NO:
• 438, a CDR-L2 comprising the amino acid sequence of SEQ ID NO:
• 439, and a CDR-L3 comprising the amino acid sequence of SEQ ID NO:
• 440;
• and the VH domain comprises a CDR-H1 comprising the amino acid sequence of SEQ ID NO:
• 441, a CDR-H2 comprising the amino acid sequence of SEQ ID NO:
• 442, and a CDR-H3 comprising the amino acid sequence of SEQ ID NO:
• 443.