High affinity Sirp-alpha reagents and methods of using
High affinity SIRP-α reagent are provided, which (i) comprise at least one amino acid change relative to the wild-type protein; and (ii) have an increased affinity for CD47 relative to the wild-type protein. Compositions and methods are provided for modulating phagocytosis in a mammal by administering a therapeutic dose of a pharmaceutical composition comprising a high affinity SIRPα reagent, which blocks the physiological binding interaction between SIRPα and its ligand CD47.
1. A soluble high affinity SIRPα polypeptide comprising an amino acid sequence set forth in SEQ ID NO: 10, wherein the high affinity SIRPα polypeptide lacks a SIRPα transmembrane domain.
2. The soluble high affinity SIRPα polypeptide of claim 1 , wherein the high affinity SIRPα polypeptide has a K D less than 279 nM for human CD47.
3. The soluble high affinity SIRPα polypeptide of claim 1 , wherein the high affinity SIRPα polypeptide comprises amino acid sequences from SIRPα outside of the d1 domain.
4. The soluble high affinity SIRPα polypeptide of claim 1 , wherein the high affinity SIRPα polypeptide is multimeric.
5. The soluble high affinity SIRPα polypeptide of claim 1 , wherein the high affinity SIRPα polypeptide is monomeric.
6. A therapeutic formulation comprising the soluble high affinity SIRPα polypeptide of claim 1 and a pharmaceutically acceptable excipient.
7. The soluble high affinity SIRPα polypeptide of claim 1 , further comprising a detectable label.
8. A method of imaging a tumor, the method comprising contacting cancer cells expressing CD47 with a polypeptide as set forth in claim 7 .
9. The soluble high affinity SIRPα polypeptide of claim 1 , wherein the high affinity SIRPα polypeptide is fused to an immunoglobulin Fc sequence.
10. A therapeutic formulation comprising the soluble high affinity SIRPα polypeptide of claim 9 and a pharmaceutically acceptable excipient.
11. A method of increasing phagocytosis of a cell expressing human CD47, the method comprising contacting the cell with a formulation of claim 10 .
12. The method of claim 11 , further comprising contacting the cell with a tumor specific antibody.
13. The method of claim 11 , wherein the contacting is in vitro.
14. The method of claim 11 , wherein the contacting is in vivo.
15. The method of claim 11 , wherein the cell expressing human CD47 is a cancer cell.