Cysteine engineered antibodies and conjugates

An antibody-drug conjugate compound comprising a cysteine engineered antibody (Ab) comprising a free cysteine amino acid having a thiol reactivity value in the range of 0.6 to 1.0;

• and a sequence in the heavy chain selected from SEQ ID NOS:
• 11, 12, 13, and 15:
• LVTVCSASTKGPS
• SEQ ID NO:11
• LVTVSCASTKGPS
• SEQ ID NO:12
• LVTVSSCSTKGPS
• SEQ ID NO:13
• HTFPCVLQSSGLYS
• SEQ ID NO:15
• where the cysteine in SEQ ID NOS:
• 11, 12, 13, and 15 are the free cysteine amino acid, and a drug moiety (D) selected from a maytansinoid, an auristatin, a dolastatin, and a calicheamicin, wherein the cysteine engineered antibody is attached through one or more free cysteine amino acids by a linker moiety (L) to D;
• the compound having Formula I:
• Ab-(L-D)p
• where p is 1, 2, 3, or 4;
• and wherein the cysteine engineered antibody is prepared by a process comprising replacing one or more amino acid residues of a parent antibody with the one or more free cysteine amino acids, where the parent antibody selectively binds to an antigen and the cysteine engineered antibody selectively binds to the same antigen as the parent antibody.