RECOMBINANT HUMAN SINGLE-CHAIN FV ANTIBODIES RECOGNIZING HUMAN INTERLEUKIN-6 - SPECIFIC TARGETING OF CYTOKINE-SECRETING CELLS

A human antibody library was displayed on the surface of filamentous b acteriophage and screened for binding to human interleukin-6 (IL-6). T wo antibody-bearing phages were selected that bound IL-6. The compleme ntary-determining region 3 loops of the variable heavy chains of these two antibodies differed in length and sequence and recognized two dis tinct epitopes. One of the single chain Fv fragments isolated (H1) was found to bind human (but not murine) IL-6 with an affinity comparable to that of the human IL-6 receptor. HI also recognized newly synthesi zed human IL-6 intracellularly, as shown by indirect immunofluorescenc e. H1 did not neutralize human IL-6, and the H1 epitope was mapped to a region of IL-6 not involved in interactions with IL-6, IL-6 receptor , or the signal-transducing protein gp130. To target IL-6-secreting ce lls, we then constructed a bispecific antibody fragment (a diabody) co mprising H1 and the antigen binding site of the T-cell activating mono clonal antibody OKT3. The diabody led to T-cell-mediated killing of ce lls secreting IL-6.