Bispecific single chain molecules (Janusins) target cytotoxic lymphocytes on HIV infected cells.

The human immunodeficiency virus type 1 (HIV-1) uses cell surface CD4 as a receptor to infect susceptible cells. Therefore, different forms of soluble CD4 (sCD4) molecules have been developed recently for potential therapeutic purposes. Here we describe a novel design of sCD4 molecules which exploit cytotoxic T cells as their effector function. The principle of bispecific antibodies was exploited and further developed to create new bispecific reagents which could retarget cytotoxic T cells of any specificity and thus, induce killing of HIV-1 infected cells. The most advanced molecules, Janusins, contain in one polypeptide chain the first two N-terminal CD4 domains and single chain combining site against the human CD3 complex (FvCD3).