The present disclosure relates to CDR defined antibodies targeting the 5T4 oncofoetal antigen (TPBG, 5T4, Wnt Activated Inhibitory Factor 1, WAIF1) which exhibit a binding affinity for human 5T4 antigen which is in the same order of magnitude as their affinity for cynomolgus monkey 5T4. Antibody-drug conjugates (ADCs), and their use in the treatment of human solid tumours and haematological malignancies are claimed.