Indirect homogeneous mobility shift assays for the detection of biologics in patient samples
The present invention provides a sensitive and specific indirect homogeneous mobility shift assay using size exclusion chromatography to measure biologics such as vedolizumab and ustekinumab in a patient sample. The assays of the present invention are particularly advantageous for detecting the presence or level of biologics that target complex or large antigens including cell surface proteins, transmembrane proteins, heavily glycosylated proteins, and multimeric proteins, as well as antigens that cannot be purified, impure antigens, and partially or substantially purified antigens. The present invention also provides isolated soluble α4β7 integrin heterodimers and isolated soluble IL-12p40 monomers that are suitable for use in the indirect assays described herein.
1. A method for determining the presence or level of a biologic in a sample, the method comprising:
(a) contacting the sample with an unlabeled soluble antigen that binds to the biologic to form an unlabeled complex between the antigen and the biologic in the sample;
(b) contacting the sample from step (a) with a labeled form of the biologic to form a labeled complex between the antigen and the labeled biologic;
(c) subjecting the unlabeled and labeled complexes to size exclusion chromatography to separate the unlabeled and labeled complexes from free labeled biologic and to detect an amount of the free labeled biologic; and
(d) comparing the amount of the free labeled biologic detected in step (c) to a standard curve of known amounts of the biologic, thereby determining the presence or level of the biologic in the sample.
2. The method of claim 1 , wherein the antigen comprises a soluble fragment, variant, or monomer of a membrane-bound protein, a glycosylated protein, a multimeric protein, an insoluble protein, and/or a large protein.
3. The method of claim 1 , wherein the antigen is a soluble fragment of a cell surface molecule.
4. The method of claim 3 , wherein the cell surface molecule is a cell adhesion molecule (CAM).
5. The method of claim 4 , wherein the cell adhesion molecule (CAM) is a member selected from the group consisting of an Ig superfamily CAM, an integrin, a cadherin, and a selectin.
6. The method of claim 5 , wherein the integrin is an α4β7 integrin.
7. The method of claim 6 , wherein the soluble fragment comprises an α4 fragment comprising an amino acid sequence having at least 80% identity to SEQ ID NO:1 or SEQ ID NO:3 and/or a β7 fragment comprising an amino acid sequence having at least 80% identity to SEQ ID NO: 2 or SEQ ID NO:4.
8. The method of claim 6 , wherein the biologic is vedolizumab.
9. The method of claim 1 , wherein the antigen is a cytokine or a monomer thereof.
10. The method of claim 9 , wherein the cytokine is a p40 subunit of IL-12 or IL-23.
11. The method of claim 10 , wherein the p40 subunit comprises an amino acid sequence having at least 80% identity to SEQ ID NOS:6, 7, 11, 12, or 13.
12. The method of claim 10 , wherein the biologic is ustekinumab.
13. The method of claim 1 , wherein the standard curve is generated by incubating the antigen and the labeled biologic with a serial dilution of known amounts of the biologic.
14. The method of claim 1 , wherein the area under the curve (AUC) of the free labeled biologic is plotted against the log of known amounts of the biologic and the level of the biologic in the sample is calculated by interpolation.
15. The method of claim 1 , wherein the sample is serum.
16. The method of claim 1 , wherein the labeled biologic is a fluorophore-labeled biologic.
17. The method of claim 1 , wherein the sample is obtained from a subject receiving therapy with the biologic.