title: SIRPα-Antibody Fusion Proteins Selectively Bind and Eliminate Dual Antigen-Expressing Tumor Cells.
abstract: OBJECTIVE
  CD47 is highly expressed on a variety of tumor cells. The interaction of CD47 with signal regulatory protein alpha (SIRPα), a protein on phagocytic cells, transmits a "don't eat me" signal that negatively regulates phagocytosis. CD47-SIRPα antagonists enable phagocytosis by disrupting the inhibitory signal and can synergize with Fc-mediated pro-phagocytic signals for potent elimination of tumor cells. A potential limitation of therapeutic CD47-SIRPα antagonists is that expression of CD47 on normal cells may create sites of toxicity or an "antigen sink." To overcome these limitations and address selective tumor targeting, we developed SIRPabodies to improve the therapeutic benefits of CD47-SIRPα blockade specifically toward tumor.
  
  
  METHODS
  SIRPabodies were generated by grafting the wild-type SIRPα either to the N-terminus or to the C-terminus of the heavy chain of rituximab. Selective tumor binding was tested using CFSE-labeled human primary CLL cells in the presence of 20-fold excess of human RBCs. NSG mice were transplanted with Raji-luciferase cells and were assigned to controls versus SIRPabody treatment. Cynomolgus nonhuman primates were administered a single intravenous infusion of SIRPabody at 3, 10, or 30 mg/kg.
  
  
  RESULTS
  SIRPabodies selectively bound to dual antigen-expressing tumor cells in the presence of a large antigen sink. SIRPabody reduced tumor burden and extended survival in mouse xenograft lymphoma models. SIRPabody caused no significant toxicity in nonhuman primates.
  
  
  CONCLUSIONS
  These findings establish SIRPabodies as a promising approach to deliver the therapeutic benefit of CD47-SIRPα blockade specifically toward tumor cells. SIRPabodies may be applied to additional cancer types by grafting SIRPα onto other tumor-specific therapeutic antibodies. Clin Cancer Res; 22(20); 5109-19. ©2016 AACR.
authors.affiliation: Division of Hematology, Department of Medicine, Cancer Institute, and Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, California.
authors.forename: Emily C
authors.initials: EC
authors.lastname: Piccione
authors.affiliation: Division of Hematology, Department of Medicine, Cancer Institute, and Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, California.
authors.forename: Silvia
authors.initials: S
authors.lastname: Juarez
authors.affiliation: Division of Hematology, Department of Medicine, Cancer Institute, and Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, California.
authors.forename: Serena
authors.initials: S
authors.lastname: Tseng
authors.affiliation: Division of Hematology, Department of Medicine, Cancer Institute, and Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, California.
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.affiliation: Division of Hematology, Department of Medicine, Cancer Institute, and Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, California.
authors.forename: Melissa
authors.initials: M
authors.lastname: Stafford
authors.affiliation: Division of Hematology, Department of Medicine, Cancer Institute, and Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, California.
authors.forename: Cyndhavi
authors.initials: C
authors.lastname: Narayanan
authors.affiliation: Division of Hematology, Department of Medicine, Cancer Institute, and Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, California.
authors.forename: Lijuan
authors.initials: L
authors.lastname: Wang
authors.affiliation: Division of Hematology, Department of Medicine, Cancer Institute, and Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, California.
authors.forename: Kipp
authors.initials: K
authors.lastname: Weiskopf
authors.affiliation: Division of Hematology, Department of Medicine, Cancer Institute, and Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, California. rmajeti@stanford.edu.
authors.forename: Ravindra
authors.initials: R
authors.lastname: Majeti
mesh_terms: D000818:Animals; D018033:Antibodies, Bispecific / Q000276:immunology / Q000494:pharmacology*; D000943:Antigens, Differentiation / Q000737:chemistry / Q000276:immunology; D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology*; D051928:CD47 Antigen / Q000037:antagonists & inhibitors* / Q000276:immunology; D045744:Cell Line, Tumor; D006801:Humans; D008252:Macaca fascicularis; D008297:Male; D051379:Mice; D010587:Phagocytosis; D011971:Receptors, Immunologic / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000276:immunology; D000069283:Rituximab / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D018033:Antibodies, Bispecific; D000943:Antigens, Differentiation; D000970:Antineoplastic Agents; D051928:CD47 Antigen; C497894:CD47 protein, human; D011971:Receptors, Immunologic; C501920:SIRPA protein, human; D000069283:Rituximab