Isolated anti-human CD73 antibody includes two heavy chains each including a hinge region comprising an amino acid sequence of that allow site-specific conjugation of cytotoxic drugs. Each heavy chain can include a human CH1 domain located upstream of and connected to the hinge region. The CH1 domain comprising a cysteine at the position of 142 according to the IMGT numbering scheme. ADCs containing the antibody conjugated with a cytotoxic drug are also provided. Pharmaceutical compositions including the antibody or the ADCs, and methods of treating cancer using the pharmaceutical compositions are also provided.