ANTI-BCMA CAR ANTIBODIES, CONJUGATES, AND METHODS OF USE

1 . A polynucleotide encoding an antibody or antigen binding fragment thereof that binds an anti-BCMA scFv domain of an anti-BCMA CAR, wherein the antibody or antigen binding fragment comprises a variable light chain comprising CDRL1-CDRL3 sequences set forth in SEQ ID NOs: 1-3, 9-11, or 17-19; and a variable heavy chain comprising CDRH1-CDRH3 sequences set forth in SEQ ID NOs: 4-6, 12-14, or 20-22.

2 . A method of detecting expression of an anti-BCMA CAR on a T cell or population of T cells, comprising:

contacting a T cell or population of T cells with an antibody or antigen-binding fragment thereof that binds an anti-BCMA scFv domain of an anti-BCMA CAR, wherein the antibody or antigen binding fragment comprises a variable light chain comprising CDRL1-CDRL3 sequences set forth in SEQ ID NOs: 1-3, 9-11, or 17-19;

and a variable heavy chain comprising CDRH1-CDRH3 sequences set forth in SEQ ID NOs: 4-6, 12-14, or 20-22, and detecting the formation of an antibody: anti-BCMA CAR complex.

3 . A method of determining the expression of an anti-BCMA CAR on a T cell or population of T cells comprising:

contacting a T cell or population of T cells with an antibody or antigen-binding fragment thereof that binds an anti-BCMA scFv domain of an anti-BCMA CAR, wherein the antibody or antigen binding fragment comprises a variable light chain comprising CDRL1-CDRL3 sequences set forth in SEQ ID NOs: 1-3, 9-11, or 17-19;

and a variable heavy chain comprising CDRH1-CDRH3 sequences set forth in SEQ ID NOs: 4-6, 12-14, or 20-22; detecting the formation of an antibody: anti-BCMA CAR complex; and measuring the amount of the complex to determine the expression of the anti-BCMA CAR on the T cell.

4 . A method of determining a number of anti-BCMA CAR+ T cells in a population of T cells, comprising:

contacting a population of T cells with an antibody or antigen-binding fragment thereof that binds an anti-BCMA scFv domain of an anti-BCMA CAR, wherein the antibody or antigen binding fragment comprises a variable light chain comprising CDRL1-CDRL3 sequences set forth in SEQ ID NOs: 1-3, 9-11, or 17-19; and a variable heavy chain comprising CDRH1-CDRH3 sequences set forth in SEQ ID NOs: 4-6, 12-14, or 20-22;

detecting the formation of an antibody: anti-BCMA CAR complex on one or more T cells; and enumerating the T cells that express the anti-BCMA CAR.

5 . The polynucleotide of claim 1 , wherein the antibody or antigen binding fragment thereof binds one or more epitopes of an anti-BCMA scFv sequence set forth in SEQ ID NO: 25.

6 . The polynucleotide of claim 1 , wherein the antibody or antigen binding fragment thereof comprises a variable light chain sequence having 90% amino acid identity to an amino acid sequence as set forth in SEQ ID NO: 7 or 15.

7 . The polynucleotide of claim 1 , wherein the antibody or antigen binding fragment thereof comprises a variable heavy chain sequence having 90% amino acid identity to an amino acid sequence as set forth in SEQ ID NO: 8, 16, or 24.

8 . The polynucleotide of claim 1 , wherein the antibody or antigen binding fragment thereof comprises a variable light chain sequence having 90% amino acid identity to an amino acid sequence as set forth in SEQ ID NO: 7 or 15; and a variable heavy chain sequence having 90% amino acid identity to an amino acid sequence as set forth in SEQ ID NO: 8, 16, or 24.

9 . The polynucleotide of claim 1 , wherein the antibody or antigen binding fragment thereof is murine, human, humanized, or chimeric.

10 . The polynucleotide of claim 1 , wherein the antibody or antigen binding fragment thereof is monoclonal.

11 . The polynucleotide of claim 1 , wherein the antibody or antigen binding fragment thereof is selected from the group consisting of: a Fab′ fragments, F(ab′) 2 fragments, bispecific Fab dimers (Fab2), trispecific Fab trimers (Fab3), Fv, single chain Fv proteins (“scFv”), bis-scFv, (scFv) 2 , minibodies, diabodies, triabodies, tetrabodies, disulfide stabilized Fv proteins (“dsFv”), and single-domain antibody (sdAb).

12 . The method of claim 2 , wherein the antibody or antigen binding fragment thereof binds one or more epitopes of an anti-BCMA scFv sequence set forth in SEQ ID NO: 25.

13 . The method of claim 2 , wherein the antibody or antigen binding fragment thereof comprises a variable light chain sequence having 90% amino acid identity to an amino acid sequence as set forth in SEQ ID NO: 7 or 15; and a variable heavy chain sequence having 90% amino acid identity to an amino acid sequence as set forth in SEQ ID NO: 8, 16, or 24.

14 . The method of claim 2 , wherein the antibody or antigen binding fragment thereof is murine, human, humanized, or chimeric.

15 . The method of claim 2 , wherein the antibody or antigen binding fragment thereof is monoclonal.

16 . The method of claim 2 , wherein the antibody or antigen binding fragment thereof is selected from the group consisting of: a Fab′ fragments, F(ab′) 2 fragments, bispecific Fab dimers (Fab2), trispecific Fab trimers (Fab3), Fv, single chain Fv proteins (“scFv”), bis-scFv, (scFv) 2 , minibodies, diabodies, triabodies, tetrabodies, disulfide stabilized Fv proteins (“dsFv”), and single-domain antibody (sdAb).

17 . The method of claim 2 , wherein the antibody or antigen binding fragment comprises a detectable label.

18 . The method of claim 17 , wherein the detectable label is selected from the group consisting of: a hapten, a fluorescent dye, a fluorescent protein, a chromophore, a metal ion, a gold particle, a silver particle, a magnetic particle, a polypeptide, an enzyme, a luminescent compound, or an oligonucleotide.

19 . The method of claim 18 , wherein the detectable label is a dye selected from the group consisting of: AF350, AF405, AF488, AF500, AF514, AF532, AF546, AF555, AF568, AF594, AF610, AF633, AF635, AF647, AF680, AF700, AF710, AF750, AF790, and AF800.

20 . The method of claim 19 , wherein the detectable label is AF488.