The possible mode of escape of adult T-cell leukaemia cells from antibody-dependent cellular cytotoxicity.

Antibody-dependent cellular cytotoxicity (ADCC) was measured using 51Cr-labelled ATL derived cell lines as the target, peripheral mononuclear cells (PMNCs) from disease-free persons as the effector cells and heat-inactivated serum from patients with ATL or the IgG purified from this. The release of 51Cr was not usually demonstrated in the HTLV-1 non-producing ATL derived cell line (MT-1), but was evident in the HTLV-1 producing ATL derived cell lines (KT 252 and IT 607). The 51Cr-labelled MT-1 cells after induction of HTLV-1 retrovirus by 5-iodo-2'-deoxyuridine (IdUr), showed a remarkable target sensitivity in the ADCC assay. On the other hand, the 51Cr-labelled MT-1 cells after culture with IdUr and ATL patient's serum, had no ADCC sensitivity. The fresh ATL cells immediately separated from ATL patient's blood did not express HTLV-1 virus in the cell and had no ADCC sensitivity as the target. Based on these findings, an antigenic modulation on the ATL cell surface by ATL patient's serum is considered to be the possible mode of escape of ATL cells from ADCC.