2016 - GENE EDITED STEM CELLS COMBINED WITH TARGETED IMMUNOTHERAPY: A NOVEL APPROACH TO TREAT MYELOID MALIGNANCIES

Despite improvements in supportive care and bone marrow transplantation, only 25% of patients diagnosed with Acute Myeloid Leukemia will survive beyond 5 years. While the emergence of targeted immunotherapy has opened new possibilities, clinical studies with chimeric antigen T-cells (CAR-T) cells have shown limited success beyond CD19-targeted immunotherapy, due to lack of unique targetable cell surface antigens and the possible management of B cell aplasia with immunoglobulin supplements. To be an ideal candidate for immunotherapy, an antigen should be unique to cancer cells, indispensable for their survival and not expressed on normal cells. Frequent expression of CD33 on AML blasts and leukemic stem cells have made it an attractive target for AML therapy. The recently reapproved anti-CD33 drug conjugate gemtuzumab ozogamicin (GO) shows promising results but leads to neutropenia and low platelets because of its off-tumor effects targeting CD33 expressed on normal cells. We have designed a novel approach combining immunotherapy targeting a lineage specific antigen expressed by cancer cells with the transplantation of hematopoietic stem cells (HSCs) lacking that lineage specific antigen. As a proof of concept, using CRISPR/Cas 9 technology, we have deleted all CD33 isoforms in human CD34+ stem cells, generating CD34+33Del human stem cells. After confirming in vivo, that the deletion of CD33 in HSCs doesn't impair their ability to engraft and to repopulate a fully functional hematopoietic system overtime, we demonstrate that leukemic humanized mice transplanted with CD34+33Del stem cells and treated with CD33-targeted immunotherapy (anti-CD33-CART cells and/or GO) show full remission and full engraftment of CD34+33- stem cells overtime. With the present study, we have demonstrated a pioneering new approach to improve targeted immunotherapies to treat blood disorders