We show here that anti-TPO aAb B4′ purified from CHO is able to induce a moderate cytotoxic activity, lower than that of patients' circulating anti-TPO aAbs on the papillary carcinoma cell line NPA, whatever the effector cells used (peripheral blood mononuclear cells (PBMC) or monocyte cell line). This evidence concerns the gene TPO and thyroid gland papillary carcinoma.