Functional analysis of isolated CD4+ T-cell clones. Reactivity of all CD4+ T-cell clones isolated during acute skin and colonic GVHD from patient 1 (A) and patient 2 (B) was tested against patient and donor EBV-LCL with IFN-γ ELISA. Allo-reactive CD4+ T-cell clones produced significant levels of IFN-γ (>200 pg/mL) upon incubation with patient, but not donor, EBV-LCL, whereas EBV-reactive CD4+ T-cell clones produced IFN-γ upon incubation with both patient and donor EBV-LCL, and CMV-reactive CD4+ T-cell clones upon incubation with donor EBV-LCL pulsed with CMV lysate. Each symbol represents the release of IFN-γ (pg/mL) in 10 µL supernatants by a single CD4+ T-cell clone.