DC-rich AML cell cultures from a trisomy 8 patient show +8 chromosome in their nuclei. Fluorescein-labeled chromosome 8–specific alpha satellite DNA probe was used to perform FISH analysis on freshly isolated PBMNC or cells cultured for 14 days in GM-CSF + IL-4 + TNF-, or GM-CSF + IL-4 + CD40L. Results depicted were obtained with cells cultured in GM-CSF + IL-4 + TNF-. At least 400 interphase nuclei were examined in each sample to quantitate the percentage of cells with three hybridization signals for chromosome 8. Cells from patient 7 and patient 14 were used for this study. The number of +8 positive cells in the three groups of cells were 93%, 92%, and 88%, respectively. With patient 14, only DC generated with GM-CSF + IL-4 + TNF- were analyzed. Eighty-eight percent of the cells were observed to express trisomy 8.