To overcome the lack of a specific targetable antigen in acute myeloid leukemia (AML), Kim et al. turned CD33 (expressed on normal and cancerous myeloid cells) into a targetable antigen for AML by genetically knocking out CD33 on human hematopoietic stem and progenitor cells (HSPCs). Engraftment of the CD33- HSPCs into mice and non-human primates showed normal myeloid function and long-term multilineage survival with no measurable off-target effects. In mice, treatment of AML with CD33-targeted CAR T cells eliminated the leukemic cells while preserving HSPC-driven myeloid cells, allowing for elimination of AML without myelotoxicity.
The absence of cancer-restricted surface markers is a major impediment to antigen-specific immunotherapy using chimeric antigen receptor (CAR) T cells. For example, targeting the canonical myeloid marker CD33 in acute myeloid leukemia (AML) results in toxicity from destruction of normal myeloid cells. We hypothesized that a leukemia-specific antigen could be created by deleting CD33 from normal hematopoietic stem and progenitor cells (HSPCs), thereby generating a hematopoietic system resistant to CD33-targeted therapy and enabling specific targeting of AML with CAR T cells. We generated CD33-deficient human HSPCs and demonstrated normal engraftment and differentiation in immunodeficient mice. Autologous CD33 KO HSPC transplantation in rhesus macaques demonstrated long-term multilineage engraftment of gene-edited cells with normal myeloid function. CD33-deficient cells were impervious to CD33-targeting CAR T cells, allowing for efficient elimination of leukemia without myelotoxicity. These studies illuminate a novel approach to antigen-specific immunotherapy by genetically engineering the host to avoid on-target, off-tumor toxicity.
Author Info: (1) Center for Cellular Immunotherapies, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. (2) Hematology Branch, National Heart, Lung, and Blood Institut
Author Info: (1) Center for Cellular Immunotherapies, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. (2) Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. (3) Division of Hematology, Mayo Clinic, Rochester, MN 55905, USA. (4) Center for Cellular Immunotherapies, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. (5) Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. (6) Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. (7) Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA; Department of Chemistry and Molecular & Cellular Biology, Georgetown University, Washington, D.C. 20057, USA. (8) Division of Hematology-Oncology, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. (9) Center for Cellular Immunotherapies, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. (10) Center for Cellular Immunotherapies, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. (11) Center for Cellular Immunotherapies, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. (12) Center for Cellular Immunotherapies, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. (13) Center for Cellular Immunotherapies, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. (14) Genomics and Computational Biology Graduate Group, University of Pennsylvania, Philadelphia, PA 19104, USA. (15) Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. (16) Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. (17) The Ohio State University Comprehensive Cancer Center, Ohio State University, Columbus, OH 43210, USA. (18) Department of Hematology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA. (19) Department of Laboratory Medicine, Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA. (20) Clinical Services Program, Leidos Biomedical Research, Frederick National Laboratory for Cancer Research, Frederick, MD 21701, USA. (21) Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. (22) The Ohio State University Comprehensive Cancer Center, Ohio State University, Columbus, OH 43210, USA; Division of Hematology, Department of Medicine, Ohio State University, Columbus, OH 43210, USA. (23) Department of Hematology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA. (24) Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. Electronic address: dunbarc@nhlbi.nih.gov. (25) Center for Cellular Immunotherapies, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA; Division of Hematology-Oncology, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. Electronic address: saargill@pennmedicine.upenn.edu.
