Background/aim: Adult T-cell leukemia (ATL) is a hematological malignancy caused by infection with human T-cell leukemia virus type 1 (HTLV-1). Chemotherapy, antibody therapy, and bone marrow transplantation are used to treat this disease, however, median survival time has not been significantly improved. Our aim was to develop and evaluate a novel antibody-drug conjugate (ADC) with regards to cell cytotoxicity and target specificity. Materials and methods: In this study, we have constructed a novel ADC, which is composed of an anti-CD70 single chain Fv-Fc antibody conjugated with the anticancer agent emtansine using a novel antibody modification method. Cell cytotoxicity and target specificity were assessed using a cell proliferation assay. Results: The anti-CD70 ADC selectively killed HTLV-1-infected cells and ATL cells without affecting other cells. Conclusion: The anti-CD70 ADC offers some chemotherapeutic potential for the treatment of ATL.Keywords: ATL; HTLV-1; antibody drug conjugate; cancer chemotherapy; immunotherapy.