CD45-Directed CAR-T Cells with CD45 Knockout Efficiently Kill Myeloid Leukemia and Lymphoma Cells In-Vitro Even After Extended Culture

Abstract

Until today, allogeneic stem cell transplantation (allo-SCT) is the only curative therapy for relapsed/refractory acute myeloid leukemia (AML). Despite major progress made in the last decades a significant risk of therapy-related complications and mortality as well as relapse of AML remains. A targeted conditioning may enable potent anti-malignancy effects while lowering the toxicity. CD45 is expressed on most normal and malignant hematopoietic cells and thus represents an ideal target for this approach. In this work different therapeutic approaches targeting the CD45 protein were tested in vitro. Knockout of CD45 was established to avoid fratricide of effector cells. Both CD45koCD45-CAR-T and CD45koCD45CAR-KHYG-1 NK cells showed efficient and specific cytotoxic activity in luciferase- and flow-cytometry based co-culture assays, even after prolonged in vitro culture of the CAR-T cells. In addition, killing assays with bispecific antibodies directed against CD45 showed effective elimination of CD45pos target cells using NK and T cells as effector cells. Both the CD45koCD45CAR-KHYG-1 and the bispecific antibodies would be available off-the-shelf.