HA-1 CTLs infiltrate 3D microtumors, inhibit tumor growth, and release IFN-γ. (A-B) CD8 staining of MDA-MB 231 (A) and MCF-7 (B) microtumors after 3 days of coincubation with HA-1 or H-Y CTLs. Arrowheads indicate CD8⁺ CTLs; bar represents 50 μm. (C) Microtumor growth inhibition after addition of the anti–HA-1, H-Y, or HLA-A2 CTLs. X-axis represents CTL clones each in 3 different effector-target ratios (15:1, 5:1, 1:1) or medium; y-axis, ratio between the microtumor areas in photographs of day 7 and day 3. Bars correspond to means plus or minus SEM (data are pooled from 3 independent experiments resulting in median 3 [range, 2-8] microtumors per condition). (D) IFN-γ in the supernatant of microtumors after addition of anti–HA-1, H-Y CTL, and HLA-A2 CTLs in an effector to target ratio of 15:1. X-axis represents days 3, 5, and 7 after addition of different CTL clones; y-axis, IFN-γ in the supernatant. Bars correspond to means plus or minus SEM (4 measurements per sample). Asterisk indicates off-scale measurement.