Labeling of antibodies

1. A radiolabeled binding protein comprising:

(i) a single domain antibody fragment VHH,

(ii) a polyethylene glycol (PEG) of a molecular weight of at least 15 kDa,

(iii) a radionuclide, wherein the radionuclide is rubidium-82, copper-61, copper-62, copper-64, yttrium-86, gallium-68 or zirconium-89, and

(iv) a chelating moiety, wherein the chelating moiety is 1,4,7-triazacyclononane-triacetic acid (NOTA), 1,4,7,10-tetraazacyclododecane-tetraacetic acid (DOTA), triazacyclononane-phosphinate (TRAP), or desferrioxamine (DFO), wherein the radionuclide is bound by the chelating moiety;

the chelating moiety and the antibody fragment VHH are joined by a first linker, wherein the first linker comprises an amino acid sequence comprising a sortase recognition motif;

the PEG of a molecular weight of at least 15 kDa and the first linker are joined together by a second linker;

the first linker and the second linker together comprise the structure:

wherein the chelating moiety is attached at the cysteine (Cys), the PEG of a molecular weight of at least 15 kDa is attached through the position indicated by an x, and the leucine (Leu) is at the C-terminus of the antibody fragment VHH;

the ratio of the antibody fragment VHH to the chelating moiety is 1:1;

and the ratio of the antibody fragment VHH to the PEG of a molecular weight of at least 15 kDa is 1:1.

2. The radiolabeled binding protein of claim 1 , wherein the antibody fragment VHH binds to a tumor cell, a tumor-associated cell, or a tumor antigen.

3. The radiolabeled binding protein of claim 1 , wherein the antibody fragment VHH binds to an immune cell.

4. The radiolabeled binding protein of claim 1 , wherein the antibody fragment VHH is from 10 kDa to 40 kDa in size.

5. The radiolabeled binding protein of claim 1 , wherein the PEG of a molecular weight of at least 15 kDa further has a molecular weight 20 kDa.

6. The radiolabeled binding protein of claim 1 , wherein the radionuclide is zirconium-89.

7. The radiolabeled binding protein of claim 1 , wherein the radionuclide is copper-61.

8. The radiolabeled binding protein of claim 1 , wherein the radionuclide is rubidium-82.

9. A method of diagnosing, monitoring, imaging, or treating a subject comprising: (a) administering the radiolabeled binding protein of claim 1 to the subject; and (b) detecting a radiolabel in the subject.

10. A method of obtaining a radiologic image of a subject comprising:

(i) administering the radiolabeled binding protein of claim 1 to the subject; and

(ii) obtaining a radiologic image of the subject by capturing the radiation emitted.

11. A method of treating a subject having a tumor, the method comprising:

(i) administering the radiolabeled binding protein of claim 1 to the subject;

(ii) obtaining a radiological image of the tumor;

(iii) determining an intensity or a pattern of the radiologic image; and

(iv) administering to the subject an agent intended to enhance or inhibit an immune response based on the intensity or the pattern of the radiologic image determined in step (iii).

12. A composition comprising the radiolabeled binding protein of claim 1 , and an excipient.

13. A method of diagnosing, monitoring, imaging, or treating a subject comprising: (a) administering the composition of claim 12 to the subject; and (b) detecting a radiolabel in the subject.

14. The radiolabeled binding protein of claim 1 , wherein the radionuclide is zirconium-89 which is bound by a desferrioxamine (DFO) chelating moiety.

15. The radiolabeled binding protein of claim 1 , wherein the chelating moiety is 1,4,7-triazacyclononane-triacetic acid (NOTA).

16. The radiolabeled binding protein of claim 1 , wherein the chelating moiety is desferrioxamine (DFO).