IFN-γ protects short-term ovarian carcinomas from CTL lysis. The effect of IFN-γ on CTL recognition of OVACs was evaluated in 4-hour 51Cr-release assays. (a) K562 and untreated or IFN-γ–treated OVAC 16 (HLA-A11+) were used as targets for the HLA-A11–specific, CD8+ CTL clone KV109. (b) OVAC 16 was untreated or treated with IFN-γ and then pulsed or not pulsed with the HLA-A11–restricted, EBNA4-derived epitope IVT at a concentration of 1 μg/ml and used as a target for the IVT-specific, CD8+ T cell clone BK289. (c) C1R/A11 was untreated or treated with IFN-γ and then pulsed or not pulsed with the IVT peptide (1 μg/ml) and used as a target for BK289. (d) Untreated or IFN-γ–treated OVAC 16 was prepulsed with IVT peptide at concentrations ranging from 10–12 to 10–6 g/ml and used as a target for BK289 at an effector-to-target ratio of 3:1. Recognition of non-pulsed targets was below 7%. Results from one of at least three experiments are shown. (e) K562 and untreated or IFN-γ–treated OVAC 16 was used as a target for autologous TALs.