CD20-Specific Engineered Toxin Body Demonstrates Direct Cell Kill Of Multiple B-Cell Non-Hodgkin's Lymphoma Types

The B-cell membrane protein CD20 is expressed by both benign and neoplastic lymphocytes. It has been a superb target for immunotherapies targeting B-cell derived diseases. There are several anti-CD20 antibodies which have been developed for B-cell lymphoma therapy. The most successful example of this targeted approach is rituximab, which is approved for front and second line therapy of Non-Hodgkin lymphoma (NHL). However, rituximab has limited direct cell-kill effects, acting primarily through indirect immune responses induced by antibody-dependent cell-mediated cytotoxicity (ADCC) and/or complement dependent cytotoxicity (CDC). While CD20-targeted radiotherapeutics have shown promise, their administrative challenges have curtailed their clinical utility. Thus, a therapeutic approach with direct cell-kill activity against CD20-expressing cells would be clinically useful. We have developed an engineered toxin body (ETB) comprising a CD20 specific scFv and a modified Shiga-like Toxin A (3F7) capable of specifically recognizing and killing CD20 expressing cells. 3F7 is selectively cytotoxic against B-cell NHL cell lines and against NHL cells obtained from patients. It demonstrated potent cytotoxicity against Burkitt’s lymphoma, diffuse large B-cell lymphoma, follicular lymphoma, and mantle cell lymphoma with IC (50) values ranging from 1.4 nM to 12 nM. Through immunofluorescent tracking, 3F7 internalizes within one hour after binding to CD20 (+) B cells. Consistent with the in vitro activity, 3F7 demonstrated anti-tumor efficacy in mice bearing Raji xenograft tumors. These results show that 3F7 is a promising targeted therapeutic agent against CD20 positive B-cell lymphomas and is currently under further development.