Assays to monitor bleeding disorders

1. A method of treating a hemophilia A in a human subject wherein the subject is administered with a Factor VIII (FVIII) chimeric polypeptide, the method comprising

measuring the subject's thrombin generation activity using a thrombin generation assay (TGA) in a blood sample from the human subject, wherein the assay is performed in the presence of an exogenous thrombin at a concentration of about 5 nM, but in the absence of exogenous tissue factor;

comparing the subject's thrombin generation activity with a corresponding standard, wherein the standard correlates with a therapeutically efficacious treatment;

determining an optimized dose or dosing interval of the FVIII chimeric polypeptide based on the relative difference between the subject's thrombin generation activity and the corresponding standard; and

administering the FVIII chimeric polypeptide to the subject at the determined optimized dose or dosing interval during subsequent administrations,

wherein the FVIII chimeric polypeptide comprises a FVIII and an FcRn binding partner, and wherein the FcRn binding partner comprises an Fc region or albumin.

2. The method of claim 1 , wherein the determined optimized dosing interval for the FVIII chimeric polypeptide is at least about 2 days or longer than the dosing interval required for an equivalent amount of a reference FVIII polypeptide.

3. The method of claim 2 , wherein the determined optimized dosing interval for the FVIII chimeric polypeptide is at least every 3-8 days and the determined dose for the FVIII chimeric polypeptide is at least about 10-150 IU/kg.

4. The method of claim 1 , wherein the standard is constructed by

a. providing at least two reference samples, each containing a different, known concentration of activated FVIII reference protein; and

b. measuring thrombin generation activity for each reference sample in the presence of FVIII-deficient plasma or FVIII-deficient blood and in the presence of exogenous thrombin at a concentration of about 5 nM, but in the absence of exogenous tissue factor.

5. The method of claim 4 , wherein the reference samples comprise from about 0 pM to about 200 pM of activated FVIII protein.

6. The method of claim 1 , wherein the FcRn binding partner comprises an Fc.

7. The method of claim 6 , wherein the determined optimized dose of the FVIII chimeric polypeptide is 25 IU/kg to 65 IU/kg and wherein the determined optimized dosing interval is once every 3 or more days.

8. The method of claim 6 , wherein the determined optimized dose of the FVIII chimeric polypeptide is 65 IU/kg and wherein the determined dosing interval is once every 6-7 days.

9. The method of claim 6 , wherein the subject exhibits at least one of the following properties after administration of the FVIII chimeric polypeptide at the determined optimized dose or dosing interval during subsequent administrations:

a) a mean residence time (MRT) (activity) in the subject of about 14-41.3 hours;

b) a clearance (CL) (activity) in the subject of about 1.22-5.19 mL/hour/kg or less;

c) a t 1/2beta (activity) in the subject of about 11-26.4 hours;

d) an incremental recovery (K value) (activity; observed) in the subject of about 1.38-2.88 IU/dL per IU/kg;

e) a Vss (activity) in the subject of about 37.7-79.4 mL/kg; and

f) an AUC/dose in the subject of about 19.2-81.7 IU*h/dL per IU/kg.

10. The method of claim 1 , wherein after administering the FVIII chimeric polypeptide during the subsequent administrations to the subject at the determined optimized dose and dosing interval, a trough level of the plasma FVIII in the subject is maintained above 3 IU/dL.

11. The method of claim 1 , wherein the FVIII comprises a full-length FVIII, mature FVIII, or FVIII with a full or partial deletion of the B domain.

12. The method of claim 1 , wherein the determined optimized dose or determined dosing interval is for a prophylactic treatment or an on-demand treatment.

13. The method of claim 1 , wherein the FcRn binding partner comprises albumin.