We recently reported that
low molecular weight B-cell growth factor (
LMW-BCGF) plus recombinant
interleukin-2 (rIL-2) synergistically induced lymphokine-activated killer (LAK) activity from the bone marrow (BM) cells of children with
acute lymphoblastic leukemia (ALL). The kinetics of cell growth, antigenic phenotype, and lytic activity of the generated effector cells were further analyzed in this study. BM cells from ALL patients with active disease and
in complete remission (CR) were cultured with a combination of
LMW-BCGF and rIL-2.
Monoclonal antibodies (anti-CD3 and anti-Leu 19) and immunomagnetic beads were used to separate LAK cells into three subsets: CD3+/Leu 19-, CD3+/Leu 19+, and CD3-/Leu 19+. Cytotoxicity assays with different subsets were performed versus K562, Raji, and autologous leukemic cells, using a 3-hour 51Cr release test. There was a significant cell expansion of 54-fold (mean value) for CD3+ cells and 15-fold for Leu 19+ cells in culture with
LMW-BCGF plus rIL-2 for 7 to 14 days, whereas no cell expansion was observed in culture with rIL-2 alone. Although NK activity (K562) was generated from leukemic BM cells in culture with rIL-2 alone, it is only about one third of that generated in culture with rIL-2 plus
LMW-BCGF. Analysis of lytic activity of cells generated in the latter cultures demonstrated that CD3-/Leu 19+ cells expressed highest lytic activity against NK-sensitive K562 cells as well as against NK-resistant Raji cells. CD3+/Leu 19+ cells showed median cytotoxicity, and CD3+Leu 19- cells mediated only minimal cytotoxic activity. Also, lytic activity of CD3-/Leu 19+ cells against autologous leukemic blasts was noted in patients with active disease. Our results demonstrate that LAK activity generated from BM cells by
LMW-BCGF and r-IL2 is mediated mainly by two types of Leu 19+ cells: CD3-/Leu 19+ NK cells and CD3-/Leu 19+ T cells. Although CD3+ T cells (both Leu 19+ and Leu 19-) mediated less antitumor cytotoxicity than CD3-/Leu 19+ cells, the former cells were the major expanding cell population in culture with
LMW-BCGF and rIL-2. The new culture system may be effective in generation of cells with LAK activity for
therapeutic use.