Electron microscopic observation of killer cells induced by mixed culture of lymphocytes with autologous cancer cells and further culture with recombinant interleukin-2.

Peripheral blood lymphocytes obtained from 2 patients with hypopharyngeal cancer were cultured with mitomycin C treated autologous tumor cells (autologous MLTC) for 10 days and further cultured with recombinant interleukin 2 (rIL-2). In one case 10-day MLTC induced increase of CD25-positive lymphocyte count, indicating that IL-2 receptors were expressed dominantly by the autologous tumor stimulation, and further culture with rIL-2 differentiated killing activity against autologous tumor cells. In the other case, however, MLTC alone induced killing activity against autologous tumor cells, indicating that the tumor cells from this patient might possess stimulatory activity sufficient to induce mature killer cells. Electron microscopic observation of the morphological features of lymphocytes cultured for 10 days revealed mostly small lymphocytes with low incidence of cytoplasmic granules. Further culture with rIL-2, however, induced slightly larger lymphocytes with well-developed microvilli, and cytoplasmic granules were found in many of the cells. Lymphokine activated killer (LAK) cells induced by culture of lymphocytes with rIL-2 alone were much larger and had long microvilli and abundant cytoplasmic granules, and were apparently morphologically different from the killer cells initiated by MLTC. The small lymphocytes induced by autologous MLTC alone might be autologous tumor specific cytotoxic T lymphocytes (CTL) and/or CTL precursors. Further culture with rIL-2 induced maturation of the CTL. However, the nature of the cytoplasmic granules remains obscure.