In vitro cytostatic effect of TNF (tumor necrosis factor) entrapped in immunoliposomes on cells normally insensitive to TNF.

The cytostatic activity of TNF entrapped in novel immunoliposomes with a specific antibody against target cells is described. A two step conjugation method was used for the preparation of these targeted immunoliposomes. In the first step, liposomes containing N-4-(p-maleimidophenyl)butyryl phosphatidylethanolamine (MPB-PE) were conjugated with a goat anti-mouse IgG Fab' fragment which recognizes the Fc portion of a mouse antibody against the target cell markers. In the second step, the mouse antibody against human tumor cells was conjugated to the liposomes. Using these targeted immunoliposomes, we demonstrated that cells usually insensitive to TNF such as Daudi cells, MT-2 cells and T-24 cells could become sensitive to TNF in vitro. The cytostatic activity of these immunoliposomes was blocked by the addition of a lysosomotropic agent such as NH4Cl or chloroquine. Significant uptake of 125I-TNF into T-24 cells was observed when these immunoliposomes were used, and this uptake of TNF was inhibited by cytochalasin B or chloroquine. Free 125I-TNF was not taken up by these cells.