CD4 and cancer: Despite the fact that TR-CD4 did not show immediate cytotoxicity, we observed that SK37 underwent apoptosis after 1–2 days of co-culture with TR-CD4 but not NTR-CD4 to a similar level as observed with ESO-CD8 (Fig. 1E), raising the possibility that TR-CD4 may mediate delayed cancer cell death rather than immediate cytotoxicity.