Antitumor effect of unprimed human lymphocytes in SCID mice. Tumors were initiated by inoculation of 2 × 10⁷ K562 cells (○) or K562DR1 cells (•) through SC injection. PBMC were administered by tail vein injection 24 hours later and tumor size (maximum tumor diameter) was measured after 14 days. Each data point in the graph represents the mean and one standard deviation (SD) of 8 to 12 tumors.