Comparison of total PBMC expansion with and without feeder cells. CD3^dep PBMC cells were cocultured with IL-2 and with feeder cells (PBMC, K562, and Jurkat) for 15 days. The total numbers of cells were counted on Days 0, 3, 5, 7, 9, 11, 13, and 15. The data from four independent experiments performed in triplicate are expressed as mean±SD.