Characterization of BIS20x3, a bi-specific antibody activating and retargeting T-cells to CD20-positive B-cells

This paper describes a bi-specific antibody, which was called BIS20x3. It r etargets CD3 epsilon -positive cells (T-cells) to CD20-positive cells and w as obtained by hybrid-hybridoma fusion. BIS20x3 could be isolated readily f rom quadroma culture supernatant and retained all the signalling characteri stics associated with both of its chains. Cross-linking of BIS20x3 on Ramos cells leads to DNA fragmentation percentages similar to those obtained aft er Rituximab-cross-linking. Cross-linking of BIS20x3 on T-cells using cross -linking F(ab')2-fragments induced T-cell activation. Indirect cross-linkin g of T-cell-bound BIS20x3 via Ramos cells hyper-activated the T-cells. Furt hermore, it was demonstrated that BIS20x3 effectively re-targets T-cells to B-cells, leading to high B-cell cytotoxicity. The results presented in thi s paper show that BIS20x3 is fully functional in retargeting T-cells to B-c ells and suggest that B-cell lymphomas may represent ideal targets for T-ce ll retargeting bi-specific antibodies, because the retargeted T-cell is max imally stimulated in the presence of B-cells. Additionally, since B-cells m ay up-regulate CD95/Fas expression upon binding of CD20-directed antibodies , B-cells will become even more sensitive for T-cell mediated killing via C D95L/FasL, and therefore supports the intention to use T-cell retargeting b i-specific antibodies recognizing CD20 on B-cell malignancies as a treatmen t modality for these diseases. (C) 2001 Cancer Research Campaign.