TPO and thyroid gland papillary carcinoma: Before testing anti-TPO Abs in in vivo trials, we compared the in vitro cytotoxic activities of baculovirus-expressed, CHO-expressed human IgG1 anti-TPO aAbs named B4 and B4′ with those of purified anti-TPO IgG of patients' sera, on papillary thyroid cancer cells expressing TPO.