Effect of phytohemagglutinin and interleukin-2 on malignant and nonmalignant B and T lymphocytes

Peripheral blood mononuclear cells (PBMC) from patients with acute myeloid leukemia (AML) or non-Hodgkin lymphoma (NHL) and healthy controls were stimulated with phytohemagglutinin (PHA) and interleukin-2 (IL-2). PHA (1 microgram/ml) induced higher 3H-thymidine incorporation than 800 U/ml IL-2 in PBMC from both controls and patients with AML in complete remission. A synergistic effect between PHA and IL-2 was found. Malignant B cells from 5/12 NHL expressed IL-2 receptors and showed proliferative response to IL-2, but not to PHA. PHA induced higher cytotoxicity toward AML blasts in lymphocytes from healthy controls than did IL-2. In addition, PHA induced higher cytotoxicity in lymphocytes from healthy controls than in those from patients with AML in remission. In contrast, no difference in cytotoxicity between controls' and patients' lymphocytes was found after stimulation with IL-2. No HLA restriction could be demonstrated. Normal peripheral blood mononuclear cells and leukemic blasts from 2/12 AML were completely resistant to cytotoxic cells even at effector:target ratios four times as high as those otherwise required.