Purification of acidic proteins using ceramic hydroxyapatite chromatography

1. A method of purifying at least one acidic protein of interest from a protein preparation containing impurities, comprising:

(a) applying an equilibration buffer comprising CaCl 2 to hydroxyapatite resin;

(b) contacting the hydroxyapatite resin with the protein preparation in a load buffer;

(c) washing the hydroxyapatite resin with a wash buffer comprising CaCl 2 ; and

(d) eluting at least one acidic protein from the hydroxyapatite resin with an elution buffer comprising about 2 to about 50 mM phosphate.

2. The method of claim 1 , wherein the equilibration buffer comprises from about 1 to about 20 mM CaCl 2 , the load buffer comprises about 1 to about 20 mM CaCl 2 , and the wash buffer comprises about 1 to about 20 mM CaCl 2 .

3. The method of claim 2 , wherein the equilibration buffer, the load buffer, and the wash buffer comprise about 5 mM CaCl 2 , and the elution buffer comprises about 6 mM phosphate.

4. The method of claim 1 , wherein the impurities are inactive or partially active species of the at least one acidic protein.

5. The method of claim 1 , wherein the impurities are high molecular weight aggregates.

6. The method of claim 5 , wherein the method results in at least about 60% reduction in high molecular weight aggregates.

7. The method of claim 6 , wherein the method results in at least about 90% reduction in high molecular weight aggregates.

8. The method of claim 1 , wherein the hydroxyapatite resin is ceramic hydroxyapatite Type I or Type II.

9. The method of claim 1 , wherein the phosphate is sodium phosphate or potassium phosphate.

10. The method of claim 9 , wherein the phosphate is sodium phosphate.

11. The method of claim 1 , wherein at least one of the equilibration buffer, the wash buffer, or the elution buffer further comprise about 10 mM to about 200 mM HEPES.

12. The method of claim 11 , wherein at least one of the equilibration buffer, the wash buffer, or the elution buffer further comprise about 10 mM HEPES.

13. The method of claim 1 , wherein at least one of the equilibration buffer, the wash buffer, or the elution buffer have a pH of about 6.1 to about 8.1.

14. The method of claim 13 , wherein at least one of the equilibration buffer, the wash buffer, or the elution buffer have a pH of about 7.2.

15. The method of claim 1 , wherein the acidic protein is an immunoglobulin fusion protein.

16. The method of claim 15 , wherein the immunoglobulin fusion protein is a receptor fusion protein.

17. The method of claim 16 , wherein the receptor fusion protein is ActRIIB-Fc.

18. The method of claim 15 , wherein the fusion protein is sIL21r-Fc.

19. The method of claim 18 , wherein the load buffer comprises a monovalent cation.

20. The method of claim 19 , wherein the monovalent cation is NaCI.

21. The method of claim 1 , wherein the impurities are protein A or host cell proteins.

22. The method of claim 1 , wherein the method further comprises, prior to the step of applying the equilibration buffer, the step of subjecting the protein preparation to a purification method selected from the group consisting of Protein A chromatography, affinity chromatography, hydrophobic interaction chromatography, immobilized metal affinity chromatography, size exclusion chromatography, diafiltration, ultrafiltration, viral removal filtration, ion exchange chromatography, and combinations thereof.

23. A method of purifying at least one acidic protein of interest from a protein preparation containing inactive or partially active species of the at least one acidic protein, comprising:

(a) applying an equilibration buffer comprising CaCl 2 to hydroxyapatite resin;

(b) contacting the hydroxyapatite resin with the protein preparation;

(c) washing the hydroxyapatite resin with a wash buffer comprising CaCl 2 ; and

(d) eluting the at least one acidic protein of interest separately from the inactive or partially active species.