Efficient activation of human blood monocytes to a tumoricidal state by liposomes containing human recombinant gamma interferon

Human recombinant gamma interferon (INF-γ) activated human peripheral blood monocytes to a cytotoxic state capable of lysing adherent tumorigenic cells without harming normal cells. The efficiency of INF-γ activation of monocytes is enhanced by encapsulating INF-γ within liposomes: The minimum effective dose (MED) of free INF-γ for monocyte activation was found to be 1-10 U/ml, per 10⁵ monocytes, whereas the minimum dose for INF-γ encapsulated in liposomes was less than 0.0025 U. Monocytes treated with liposome-encapsulated INF-γ retained their cytotoxic phenotype for much longer than do monocytes treated with free INF-γ. Since liposomes can be passively targeted to cells of the reticuloendothelial system following IV administration, these findings suggest that liposome-encapsulated INF-γ may have therapeutic potential that should be evaluated in vivo.