Anti-her2/cd3 bispecific antibody specifically activated in tumor microenvironment

A mutant CD3 antibody, wherein one or more mutations are introduced in the complementary determining regions (CDR regions) of the heavy chain variable region and/or light chain variable region of the mutant CD3 antibody relative to a wild-type CD3 antibody sequence, wherein the mutation is selected from the group consisting of:

• a mutation where one or more amino acids are replaced with cysteine (Cys) at the position of M34, S53, Y61, D68, F104, Will, or F112 in the heavy chain variable region;
• and/or at the position of N54, K55, R56, W93, Y94 or N96 in the light chain variable region;
• wherein, the affinity of the wild-type CD3 antibody for binding to CD3 is E0, the affinity of the mutant CD3 antibody for binding to CD3 is E1, and E1/E0≤5.5 (preferably E1/E0≤3, preferably ≤1.5, more preferably E1/E0≤1);
• wherein the heavy chain variable region of the wild-type CD3 antibody comprises the following three complementary determining regions (CDRs):
• VH-CDR1 as shown in SEQ ID NO.1,
• VH-CDR2 as shown in SEQ ID NO.2, and
• VH-CDR3 as shown in SEQ ID NO.3;
• and
• the light chain variable region of the wild-type CD3 antibody comprises the following three complementary determining regions (CDRs):
• VL-CDR1 as shown in SEQ ID NO.5,
• VL-CDR2 as shown in SEQ ID NO.6, and
• VL-CDR3 as shown in SEQ ID NO.7.