WO2022005991A1 - Platform for assessing in vivo and in vitro hapten-capture in a cell bound system - Google Patents

Abstract

The present disclosure provides compositions and methods for assaying the in vitro and in vivo properties of candidate DOTA-based hapten probes (e.g, radioactive or non-radioactive DOTA-based hapten probes) that may be useful for imaging, dosimetry, in vivo cell tracking, flow cytometry, cell sorting/purification, fluorescence-guided surgery, immunohistochemistry, and pretargeted radioimmunotherapy applications.

Description

PLATFORM FOR ASSESSING IN VIVO AND IN VITRO HAPTEN-CAPTURE IN A CELL BOUND SYSTEM CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of and priority to U.S. Provisional Patent Application No.63/045,618, filed June 29, 2020, the contents of which are incorporated by reference herein in its entirety. STATEMENT OF GOVERNMENT SUPPORT [0002] This invention was made with government support under CA008748 and CA184746 awarded by the National Institutes of Health. The government has certain rights in the invention. TECHNICAL FIELD [0003] The present technology relates generally to compositions and methods for assaying the in vitro and in vivo properties of candidate DOTA-based hapten probes (e.g., radioactive and non-radioactive DOTA-based hapten probes) that may be useful for imaging, dosimetry, in vivo cell tracking, flow cytometry, cell sorting/purification, fluorescence-guided surgery, immunohistochemistry, and pretargeted radioimmunotherapy applications. The DOTA-based hapten probes may comprise a detectable label (e.g., a chromogenic, enzymatic, radioisotopic, isotopic, fluorescent, toxic, chemiluminescent, nuclear magnetic resonance contrast agent or other label). BACKGROUND [0004] The following description of the background of the present technology is provided simply as an aid in understanding the present technology and is not admitted to describe or constitute prior art to the present technology. [0005] Currently available reporter genes are limited by potential immunogenicity, lack of specificity, or their corresponding probes display unfavorable in vivo pharmacokinetics. The availability of a tightly controlled model system with well-characterized target expression could facilitate in vitro and in vivo characterization of probe binding. Such a tool is essential to develop suitable reporter gene/probe combinations to enable interrogation of target engagement in complex clinical situations with potential heterogeneous expression rates, variation in perfusion, and non-specific background uptake. SUMMARY OF THE PRESENT TECHNOLOGY [0006] In one aspect, the present disclosure provides a fusion protein comprising a DOTA binding fragment fused to a transmembrane domain, and a reporter gene, wherein the DOTA binding fragment comprises a heavy chain immunoglobulin variable domain (VH) sequence and a light chain immunoglobulin variable domain (VL) sequence of SEQ ID NO: 1 and SEQ ID NO: 5, respectively. The V_H domain sequence may be located at the N-terminus or the C-terminus of the V_L domain sequence. [0007] Additionally or alternatively, in some embodiments, the sequence of an intra- peptide linker between the V_H domain sequence and the V_L domain sequence in the DOTA binding fragment is any one of SEQ ID NOs: 9-11. [0008] In any and all embodiments of the fusion protein of the present technology, the DOTA binding fragment is located at the N-terminus of the transmembrane domain and/or the reporter gene is located at the C-terminus of the transmembrane domain. [0009] Additionally or alternatively, in some embodiments, the reporter gene is a fluorescent reporter gene, a chemiluminescent reporter gene, or a bioluminescent reporter gene. Examples of suitable fluorescent reporter genes include, but are not limited to, GFP, YFP, CFP, RFP, TagBFP, Azurite, EBFP2, mKalama1, Sirius, Sapphire, T-Sapphire, ECFP, Cerulean, SCFP3A, mTurquoise, monomeric Midoriishi-Cyan, TagCFP, mTFP1, EGFP, Emerald, Superfolder GFP, Monomeric Azami Green, TagGFP2, mUKG, mWasabi, EYFP, Citrine, Venus, SYFP2, TagYFP, Monomeric Kusabira-Orange, mKOκ, mKO2, mOrange, mOrange2, mRaspberry, mCherry, dsRed, mStrawberry, mTangerine, tdTomato, TagRFP, TagRFP-T, mApple, mRuby, mPlum, HcRed-Tandem, mKate2, mNeptune, NirFP, TagRFP657, IFP1.4, iRFP, mKeima Red, LSS-mKate1, LSS-mKate2, PA-GFP, PAmCherry1, PATagRFP, Kaede (green), Kaede (red), KikGR1 (green), KikGR1 (red), PS- CFP2, PS-CFP2, mEos2 (green), mEos2 (red), PSmOrange, and Dronpa. Examples of bioluminescent reporter genes include, but are not limited to, Aequorin, firefly luciferase, Renilla luciferase, red luciferase, luxAB, and nanoluciferase. Examples of suitable chemiluminescent reporter genes include β-galactosidase, horseradish peroxidase (HRP), and alkaline phosphatase. [0010] In any of the foregoing embodiments, the fusion protein further comprises a spacer domain interspersed between the DOTA binding fragment and the transmembrane domain. In some embodiments, the spacer domain is a Fc domain. In certain embodiments, the Fc domain comprises a Fc fragment of human IgG. In some embodiments, the Fc fragment comprises or consists of an amino acid sequence having at least 80% (e.g., at least 80%, 85%, 90%, 95%, 97%, 99%, or more) identity to the Fc region (e.g., CH2 domain and CH3 domain) of a human IgG including the amino acid sequence of any one of SEQ ID NOs: 12-16. [0011] In any and all embodiments of the fusion protein of the present technology, the transmembrane domain may comprise an amino acid sequence that is at least 80% (e.g., at least 80%, 85%, 90%, 95%, 97%, 99%, or more) identical to an amino acid sequence of a transmembrane region of CD4 (SEQ ID NO: 17), CD8 (SEQ ID NO: 20), CD28 (SEQ ID NO: 21), CD3ζ (SEQ ID NO: 22), or 4-1BB ligand receptor (SEQ ID NO: 24). In some embodiments, the transmembrane domain comprises the amino acid sequence of SEQ ID NO: 17, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22 or SEQ ID NO: 24. [0012] Additionally or alternatively, in some embodiments, the fusion protein comprises the amino acid sequence of SEQ ID NO: 18. [0013] Additionally or alternatively, in some embodiments, the fusion protein of the present technology further comprises an endoplasmic reticulum signal sequence. In certain embodiments, the endoplasmic reticulum signal sequence is a CD4 signal peptide comprising the sequence MNRGVPFRHLLLVLQLALLPAATQG (SEQ ID NO: 23). Additionally or alternatively, in some embodiments, the fusion protein does not include an internal ribosome entry site (IRES), or a 2A self-cleaving peptide. [0014] In one aspect, the present disclosure provides a recombinant nucleic acid sequence encoding any and all embodiments of the fusion proteins disclosed herein. In some embodiments, the recombinant nucleic acid sequence comprises the sequence of SEQ ID NO: 19. [0015] In another aspect, the present disclosure provides an expression vector comprising any and all embodiments of the recombinant nucleic acid sequences disclosed herein. In some embodiments, the recombinant nucleic acid sequence is operably linked to an expression control sequence. The expression control sequence may be an inducible promoter or a constitutive promoter. Additionally or alternatively, in some embodiments, the expression vector is a plasmid, a cosmid, a bacmid, a bacterial artificial chromosome (BAC), a yeast artificial chromosome (YAC), or a viral vector. [0016] In yet another aspect, the present disclosure provides a recombinant mammalian cell comprising any and all embodiments of the expression vectors described herein. The recombinant mammalian cell may be cancerous or non-cancerous. In certain embodiments, the recombinant mammalian cell is a human embryonic kidney 293 cell. Additionally or alternatively, the expression control sequence may be heterologous or native to the recombinant mammalian cell. [0017] In one aspect, the present disclosure provides a method for determining in vitro binding kinetics of a DOTA-based hapten (e.g., radioactive or non-radioactive DOTA-based hapten) comprising contacting a DOTA-based hapten (e.g., radioactive or non-radioactive DOTA-based hapten) with any embodiment of the recombinant mammalian cell described herein, and determining the binding activity of the DOTA-based hapten (e.g., radioactive or non-radioactive DOTA-based hapten) to the recombinant mammalian cell, wherein the recombinant mammalian cell exhibits cell surface expression of any embodiment of the fusion protein of the present technology, and wherein the DOTA-based hapten comprises, or is directly or indirectly linked to a detectable label (e.g., spectroscopic, photochemical, biochemical, immunochemical, electromagnetic, radioactive, fluorescent, chemifluorescent, or chemiluminescent label). The binding activity of the DOTA-based hapten (e.g., radioactive or non-radioactive DOTA-based hapten) may be determined via saturation binding assays or competition binding assays. In certain embodiments, the method further comprises determining a mean equilibrium dissociation constant (Kd) of the DOTA-based hapten (e.g., radioactive or non-radioactive DOTA-based hapten) and a mean Bmax (sites/cell) for the fusion protein. [0018] In one aspect, the present disclosure provides a method for detecting the presence of a DOTA-based hapten in vivo comprising (a) administering to a subject an amount of a recombinant mammalian cell of the present technology that is effective to establish a xenograft, (b) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten is configured to localize to the xenograft, and comprises, or is directly or indirectly linked to a detectable label; and (c) detecting the presence of the DOTA-based hapten in the subject by detecting signal levels emitted by the detectable label of the DOTA-based hapten that are higher than a reference value. The detectable label may be a spectroscopic, photochemical, biochemical, immunochemical, electromagnetic, radioactive, fluorescent, chemifluorescent, or chemiluminescent label. The signal emitted by the detectable label of the DOTA-based hapten may be detected using positron emission tomography (PET), single photon emission computed tomography (SPECT), MRI, bioluminescence, or fluorescence. [0019] In one aspect, the present disclosure provides a method for detecting the presence of a DOTA-based hapten in vivo comprising (a) administering to a subject an amount of a recombinant mammalian cell of the present technology that is effective to establish a xenograft, (b) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (c) detecting the presence of the DOTA-based hapten in the subject by detecting radioactive levels emitted by the DOTA-based hapten that are higher than a reference value. The radioactive levels emitted by the DOTA-based hapten may be detected using positron emission tomography (PET) or single photon emission computed tomography (SPECT). [0020] Additionally or alternatively, in some embodiments, the method further comprises quantifying radioactive levels emitted by the DOTA-based hapten that is localized to the xenograft, and/or radioactive levels emitted by the DOTA-based hapten that is localized in one or more normal tissues or organs of the subject. In certain embodiments, the one or more normal tissues or organs are selected from the group consisting of heart, muscle, gallbladder, esophagus, stomach, small intestine, large intestine, liver, pancreas, lungs, bone, bone marrow, kidneys, urinary bladder, brain, skin, spleen, thyroid, and soft tissue. In any of the preceding embodiments, the method further comprises determining biodistribution scores by computing a ratio of the radioactive levels emitted by the DOTA-based hapten that is localized to the xenograft relative to the radioactive levels emitted by the DOTA-based hapten that is localized in the one or more tissues or organs of the subject. Additionally or alternatively, in some embodiments, the method further comprises calculating estimated absorbed radiation doses for the xenograft and the one or more tissues or organs of the subject based on the biodistribution scores. In some embodiments, the method further comprises computing a therapeutic index for the DOTA-based hapten based on the estimated absorbed radiation doses for the xenograft and the one or more tissues or organs of the subject. [0021] In one aspect, the present disclosure provides a method for tracking recombinant mammalian cells in a subject in vivo comprising (a) administering to the subject any embodiment of the recombinant mammalian cell described herein in an amount that is effective to establish a xenograft; (b) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten is configured to localize to the xenograft, and comprises, or is directly or indirectly linked to a detectable label; and (c) detecting signal emitted by the detectable label of the DOTA-based hapten that is localized to the xenograft. The detectable label may be a spectroscopic, photochemical, biochemical, immunochemical, electromagnetic, radioactive, fluorescent, chemifluorescent, or chemiluminescent label. In some embodiments, the method further comprises monitoring cell proliferation, cell growth, and/or apoptosis of the xenograft. [0022] In another aspect, the present disclosure provides a method for tracking recombinant mammalian cells in a subject in vivo comprising (a) administering to the subject any embodiment of the recombinant mammalian cell described herein in an amount that is effective to establish a xenograft; (b) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (c) detecting radioactive levels emitted by the DOTA-based hapten that is localized to the xenograft. In some embodiments, the method further comprises monitoring cell proliferation, cell growth, and/or apoptosis of the xenograft. [0023] In yet another aspect, the present disclosure provides a method for determining the therapeutically effective amount of a DOTA-based hapten for pretargeted radioimmunotherapy (PRIT) comprising (a) administering to the subject any embodiment of the recombinant mammalian cell described herein in an amount that is effective to establish a xenograft; (b) administering to the subject an amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (c) determining that the amount of the DOTA-based hapten is therapeutically effective for PRIT when the subject exhibits a decrease in xenograft volume compared to that observed in the subject prior to administration of the DOTA-based hapten. [0024] Additionally or alternatively, in some embodiments of the methods disclosed herein, the DOTA-based hapten is administered intravenously, intramuscularly, intraarterially, intrathecally, intracapsularly, intraorbitally, intradermally, intraperitoneally, transtracheally, subcutaneously, intracerebroventricularly, orally, intratumorally, or intranasally. In certain embodiments, the DOTA-based hapten is administered into the cerebral spinal fluid or blood of the subject. [0025] Examples of DOTA-based haptens include, but are not limited to, DOTA, Proteus-DOTA, DOTA-Bn, DOTA-desferrioxamine, DOTA-Phe-Lys(HSG)-D-Tyr- Lys(HSG)-NH₂, Ac-Lys(HSG)D-Tyr-Lys(HSG)-Lys(Tscg-Cys)-NH₂, DOTA-D-Asp-D- Lys(HSG)-D-Asp-D-Lys(HSG)-NH2; DOTA-D-Glu-D-Lys(HSG)-D-Glu-D-Lys(HSG)-NH2, DOTA-D-Tyr-D-Lys(HSG)-D-Glu-D-Lys(HSG)-NH2, DOTA-D-Ala-D-Lys(HSG)-D-Glu- D-Lys(HSG)-NH₂, DOTA-D-Phe-D-Lys(HSG)-D-Tyr-D-Lys(HSG)-NH₂, Ac-D-Phe-D- Lys(DOTA)-D-Tyr-D-Lys(DOTA)-NH2, Ac-D-Phe-D-Lys(DTPA)-D-Tyr-D-Lys(DTPA)- NH2, Ac-D-Phe-D-Lys(Bz-DTPA)-D-Tyr-D-Lys(Bz-DTPA)-NH2, Ac-D-Lys(HSG)-D-Tyr- D-Lys(HSG)-D-Lys(Tscg-Cys)-NH₂, DOTA-D-Phe-D-Lys(HSG)-D-Tyr-D-Lys(HSG)-D- Lys(Tscg-Cys)-NH₂, (Tscg-Cys)-D-Phe-D-Lys(HSG)-D-Tyr-D-Lys(HSG)-D-Lys(DOTA)- NH2, Tscg-D-Cys-D-Glu-D-Lys(HSG)-D-Glu-D-Lys(HSG)-NH2, (Tscg-Cys)-D-Glu-D- Lys(HSG)-D-Glu-D-Lys(HSG)-NH₂, Ac-D-Cys-D-Lys(DOTA)-D-Tyr-D-Ala-D- Lys(DOTA)-D-Cys-NH₂, Ac-D-Cys-D-Lys(DTPA)-D-Tyr-D-Lys(DTPA)-NH₂, Ac-D- Lys(DTPA)-D-Tyr-D-Lys(DTPA)-D-Lys(Tscg-Cys)-NH2, Ac-D-Lys(DOTA)-D-Tyr-D- Lys(DOTA)-D-Lys(Tscg-Cys)-NH2, NH2-benzyl (Bn) DOTA, DOTA-RGD, DOTA-PEG- E(c(RGDyK))₂, DOTA-8-AOC-BBN, DOTA-PESIN, p-NO2-benzyl-DOTA, DOTA-biotin- sarcosine (DOTA-biotin), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid mono (N- hydroxysuccinimide ester) (DOTA-NHS), and DOTATyrLysDOTA. [0026] In any and all embodiments of the methods disclosed herein, the radionuclide is an alpha particle-emitting isotope, a beta particle-emitting isotope, or an Auger-emitter. Examples of radionuclides include ²¹³Bi, ²¹¹At, ²²⁵Ac, ¹⁵²Dy, ²¹²Bi, ²²³Ra, ²¹⁹Rn, ²¹⁵Po, ²¹¹Bi, ²²¹Fr, ²¹⁷At, ²⁵⁵Fm, ⁸⁶Y, ⁹⁰Y, ⁸⁹Sr, ¹⁶⁵Dy, ¹⁸⁶Re, ¹⁸⁸Re, ¹⁷⁷Lu, ⁶⁷Cu, ¹¹¹In, ⁶⁷Ga, ⁵¹Cr, ⁵⁸Co, ^99mTc, ^103mRh, ^195mPt, ¹¹⁹Sb, ¹⁶¹Ho, ^189mOs, ¹⁹²Ir, ²⁰¹Tl, ²⁰³Pb, ⁶⁸Ga, ²²⁷Th, or ⁶⁴Cu. In any of the preceding embodiments of the methods disclosed herein, the subject is human. BRIEF DESCRIPTION OF THE DRAWINGS [0027] Fig.1 illustrates that the cellular systems comprising the membrane-bound C825 reporter of the present technology are useful for characterizing the in vitro and in vivo properties of candidate DOTA-based haptens (e.g., radioactive or non-radioactive DOTA- based hapten) that may be useful for imaging, dosimetry, in vivo cell tracking, flow cytometry, cell sorting/purification, fluorescence-guided surgery, immunohistochemistry, and pretargeted radioimmunotherapy applications. [0028] Fig.2A shows a schematic structure of retroviral vector SFG-C825. Fig.2B shows the expression levels of the membrane-bound C825 reporter of the present technology in HEK 293T cells transfected with the membrane-bound C825 reporter (293T-C825) and non-transfected HEK 293T cells (controls) using flow cytometry. Fig.2C shows that [¹⁷⁷Lu]LuDOTA-Bn and [¹¹¹In]InPr DOTA-based radiohaptens bind with similar magnitude (10% vs 9%, respectively) to C825-expressing 293T cells over 1 hr, whereas no significant uptake was observed in 293T control cells (reported as mean ± SD). Fig.2D shows an in vitro saturation binding curve of [¹¹¹In]InPr to 293T-C825 cells. Representative data are shown for Figs.2B-2D. Experiments were performed in triplicate (Figs.2C-2D). [0029] Fig.3A shows serial PET/CT imaging in a mouse harboring both 293T and 293T- C825 tumors (dual tumors) after intravenous administration of [⁸⁶Y]YDOTA-Bn. Maximum intensity projection (MIP) PET/CT images and axial PET images at 0.5, 1.5, 18 and 22 h post-injection demonstrate specific uptake at the 293T-C825 tumor site (arrows). Minimal uptake above background at the wild-type 293T tumor site served as a control (arrow heads). Figs.3B-3C show image-based biodistribution (n=3) and time-activity curves for the mouse shown in Fig.3A. [⁸⁶Y]YDOTA-Bn PET images demonstrate specific uptake in 293T-C825 xenografts (n=3). [0030] Fig.4A shows MOBY reference phantom (Keenan MA et al., J Nucl Med. 51:471–476 (2010); Larsson E et al.,. Acta Oncol.50:973–980 (2011)) with bilateral tumor regions used in PARaDIM absorbed dose calculations. See Carter et al., J Nucl Med 60(12):1802-1811 (2019). Fig.4B shows the absorbed dose map (maximum intensity projection) for [²²⁵Ac]AcPr and [¹⁷⁷Lu]LuDOTA-Bn in a dual 293T/293T-C825 tumor bearing mouse model. Arrows highlight high levels of [²²⁵Ac]AcPr and [¹⁷⁷Lu]LuDOTA-Bn at 293T-C825 tumor site. Fig.4C shows an organ-level mean absorbed dose of [²²⁵Ac]AcPr (left) and [¹⁷⁷Lu]LuDOTA-Bn (right) to 293T-C825 and 293T cells and normal tissues. [0031] Fig.5A shows ex vivo biodistribution for [²²⁵Ac]AcPr in a dual 293T/293T-C825 tumor bearing mouse model. TNR: tumor-to-normal tissue ratio; Mean ± SD; (n = 4); **, P < 0.01. Fig.5B shows autoradiography (AR) and H&E-staining of tumor tissue. CK WSS = cytokeratin. Ex vivo biodistribution, autoradiography and immunohistochemistry confirm successful targeting of 293T-C825 tumors with [²²⁵Ac]AcPr. [0032] Fig.6A shows that tumor growth was considerably slower in mice bearing 293T- C825 xenografts that were treated with [²²⁵Ac]AcPr, whereas tumor volumes increased rapidly in [²²⁵Ac]AcPr treated mice in the control 293T group. Fig.6B shows Kaplan-Meier survival analysis (293T-C825 vs 293T tumors, P = 0.006). These data demonstrate that therapy with [²²⁵Ac]AcPr results in anti-tumor response and improved overall survival. [0033] Fig.7 shows the chemical structures of [¹⁷⁷Lu]LuDOTA-Bn, [⁸⁶Y]YDOTA-Bn, [¹¹¹In]InPr, [²²⁵Ac]AcPr and their corresponding Radio-HPLC. [0034] Fig.8 shows serial PET imaging in dual 293T/293T-C825 tumor bearing mice after intravenous administration of [⁸⁶Y]YDOTA-Bn. Maximum intensity projection (MIP) PET/CT images at 0.5, 1.5, 18 and 22 h post-injection demonstrate specific uptake at the 293T-C825 tumor site. Minimal uptake above background at the 293T tumor site (serving as a control). [0035] Figs.9A-9C show time-activity curves derived from serial [⁸⁶Y]YDOTA-Bn PET imaging in dual 293T/293T-C825 tumor bearing mice (n=3). [0036] Fig.10 shows that in vivo treatment with [²²⁵Ac]AcPr did not result in substantial systemic toxicity, such as a substantial change in body weight. [0037] Fig.11 shows that [¹⁷⁷Lu]LuDOTA-Bn radiohapten (0.1 µCi) binds with variable magnitude (4%, 2% and 9%, respectively) to membrane-bound C825-expressing 293T cells over 1 hr, whereas no significant uptake was observed in 293T control cells (reported as mean ± SD). Experiments were performed in triplicate. The amino acid sequence of C825- Hinge-GFP is SEQ ID NO: 18. The orientation of the C825-GFP construct from the N- terminus to the C-terminus is DOTA scFv (see italicized domain of SEQ ID NO: 18)—CD4 transmembrane domain (see boldface domain of SEQ ID NO: 18)—GFP (see underlined domain of SEQ ID NO: 18). C825-TM-GFP differs from C825-GFP in that it contains an extra 29 amino acid residues located at the N-terminus of the CD4 transmembrane domain (WQCLLSDSGQVLLESNIKVLPTWSTPVQP (SEQ ID NO: 29)) . [0038] Fig.12A shows ex vivo biodistribution data for [⁸⁶Y]Y-DOTA-Bn, (n = 4–5 per cohort). Fig.12B shows ex vivo biodistribution data for [¹⁷⁷Lu]Lu-DOTA-Bn, (n = 4–5 per cohort). Fig.12C shows ex vivo biodistribution data for [²²⁵Ac]Ac-Pr, (n = 4–5 per cohort). [0039] Fig.13 shows blood clearance curves used for blood half-life derivation for [¹⁷⁷Lu]Lu-DOTABn (0.4 h), [⁸⁶Y]Y-DOTA-Bn (0.6 h), and [²²⁵Ac]Ac-Pr (0.4 h). [0040] Fig.14 shows in vivo growth curves for wild-type 293T and 293T-huC825 (n = 10 per cohort). DETAILED DESCRIPTION [0041] It is to be appreciated that certain aspects, modes, embodiments, variations and features of the present methods are described below in various levels of detail in order to provide a substantial understanding of the present technology. [0042] In practicing the present methods, many conventional techniques in molecular biology, protein biochemistry, cell biology, immunology, microbiology and recombinant DNA are used. See, e.g., Sambrook and Russell eds. (2001) Molecular Cloning: A Laboratory Manual, 3rd edition; the series Ausubel et al. eds. (2007) Current Protocols in Molecular Biology; the series Methods in Enzymology (Academic Press, Inc., N.Y.); MacPherson et al. (1991) PCR 1: A Practical Approach (IRL Press at Oxford University Press); MacPherson et al. (1995) PCR 2: A Practical Approach; Harlow and Lane eds. (1999) Antibodies, A Laboratory Manual; Freshney (2005) Culture of Animal Cells: A Manual of Basic Technique, 5th edition; Gait ed. (1984) Oligonucleotide Synthesis; U.S. Patent No. 4,683,195; Hames and Higgins eds. (1984) Nucleic Acid Hybridization; Anderson (1999) Nucleic Acid Hybridization; Hames and Higgins eds. (1984) Transcription and Translation; Immobilized Cells and Enzymes (IRL Press (1986)); Perbal (1984) A Practical Guide to Molecular Cloning; Miller and Calos eds. (1987) Gene Transfer Vectors for Mammalian Cells (Cold Spring Harbor Laboratory); Makrides ed. (2003) Gene Transfer and Expression in Mammalian Cells; Mayer and Walker eds. (1987) Immunochemical Methods in Cell and Molecular Biology (Academic Press, London); and Herzenberg et al. eds (1996) Weir’s Handbook of Experimental Immunology. Methods to detect and measure levels of polypeptide gene expression products (i.e., gene translation level) are well-known in the art and include the use of polypeptide detection methods such as antibody detection and quantification techniques. (See also, Strachan & Read, Human Molecular Genetics, Second Edition. (John Wiley and Sons, Inc., NY, 1999)). [0043] The advantage of the recombinant membrane-bound C825 reporter described herein is its picomolar affinity to DOTA-based hapten probes, thereby allowing the probes to bind C825-expressing cells at a target site with high sensitivity and specificity, which results in minimal accumulation in normal tissue and non-C825 reporter expressing cells. Indeed, the probe [⁸⁶Y]YDOTA-Bn, remained bound to 293T-C825 cells beyond 22 h, whereas the unbound probe rapidly and continuously cleared from normal organs resulting in excellent tumor-to-background ratios and high-contrast images. These properties thus permit the accurate and reliable detection of small numbers of C825-expressing cells. The dosimetric calculations and favorable TIs observed using the recombinant membrane-bound C825 reporter disclosed herein demonstrate that the compositions of the present technology are useful for characterizing the therapeutic applications of DOTA-based radiohapten probes (e.g., [²²⁵Ac]AcPr, and [¹⁷⁷Lu]LuDOTA-Bn), especially when using high specific activity preparations. Furthermore, the recombinant membrane-bound C825 reporter disclosed herein enables a dosimetry-based treatment approach on a personalized or individual basis. [0044] Accordingly, cellular systems comprising the membrane-bound C825 reporter of the present technology enables interrogation of target engagement by DOTA-based haptens (e.g., radioactive or non-radioactive DOTA-based haptens) both in vitro and in vivo, and is useful for characterizing the theranostic potential of newly synthesized radioactive or non- radioactive DOTA-based hapten probes. Definitions [0045] Unless defined otherwise, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this technology belongs. As used in this specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the content clearly dictates otherwise. For example, reference to “a cell” includes a combination of two or more cells, and the like. Generally, the nomenclature used herein and the laboratory procedures in cell culture, molecular genetics, organic chemistry, analytical chemistry and nucleic acid chemistry and hybridization described below are those well-known and commonly employed in the art. [0046] As used herein, the term “about” in reference to a number is generally taken to include numbers that fall within a range of 1%, 5%, or 10% in either direction (greater than or less than) of the number unless otherwise stated or otherwise evident from the context (except where such number would be less than 0% or exceed 100% of a possible value). [0047] As used herein, the “administration” of an agent or drug to a subject includes any route of introducing or delivering to a subject a compound to perform its intended function. Administration can be carried out by any suitable route, including but not limited to, orally, intranasally, parenterally (intravenously, intramuscularly, intraperitoneally, or subcutaneously), intracranially, rectally, intrathecally, intratumorally or topically. Administration includes self-administration and the administration by another. [0048] As used herein, the term “antibody” collectively refers to immunoglobulins or immunoglobulin-like molecules including by way of example and without limitation, IgA, IgD, IgE, IgG and IgM, combinations thereof, and similar molecules produced during an immune response in any vertebrate, for example, in mammals such as humans, goats, rabbits and mice, as well as non-mammalian species, such as shark immunoglobulins. As used herein, “antibodies” (includes intact immunoglobulins) and “antigen binding fragments” specifically bind to a molecule of interest (or a group of highly similar molecules of interest) to the substantial exclusion of binding to other molecules (for example, antibodies and antibody fragments that have a binding constant for the molecule of interest that is at least 10³ M^-1 greater, at least 10⁴ M^-1 greater or at least 10⁵ M^-1 greater than a binding constant for other molecules in a biological sample). The term “antibody” also includes genetically engineered forms such as chimeric antibodies (for example, humanized murine antibodies), heteroconjugate antibodies (such as, bispecific antibodies). See also, Pierce Catalog and Handbook, 1994-1995 (Pierce Chemical Co., Rockford, Ill.); Kuby, J., Immunology, 3^rd Ed., W.H. Freeman & Co., New York, 1997. [0049] More particularly, antibody refers to a polypeptide ligand comprising at least a light chain immunoglobulin variable region or heavy chain immunoglobulin variable region which specifically recognizes and binds an epitope of an antigen. Antibodies are composed of a heavy and a light chain, each of which has a variable region, termed the variable heavy (VH) region and the variable light (VL) region. Together, the VH region and the VL region are responsible for binding the antigen recognized by the antibody. Typically, an immunoglobulin has heavy (H) chains and light (L) chains interconnected by disulfide bonds. There are two types of light chain, lambda (λ) and kappa ( ^). There are five main heavy chain classes (or isotypes) which determine the functional activity of an antibody molecule: IgM, IgD, IgG, IgA and IgE. Each heavy and light chain contains a constant region and a variable region, (the regions are also known as “domains”). In combination, the heavy and the light chain variable regions specifically bind the antigen. Light and heavy chain variable regions contain a “framework” region interrupted by three hypervariable regions, also called “complementarity-determining regions” or “CDRs”. The extent of the framework region and CDRs have been defined (see, Kabat et al., Sequences of Proteins of Immunological Interest, U.S. Department of Health and Human Services, 1991, which is hereby incorporated by reference). The Kabat database is now maintained online. The sequences of the framework regions of different light or heavy chains are relatively conserved within a species. The framework region of an antibody, that is the combined framework regions of the constituent light and heavy chains, largely adopt a β-sheet conformation and the CDRs form loops which connect, and in some cases form part of, the β-sheet structure. Thus, framework regions act to form a scaffold that provides for positioning the CDRs in correct orientation by inter- chain, non-covalent interactions. [0050] The CDRs are primarily responsible for binding to an epitope of an antigen. The CDRs of each chain are typically referred to as CDR1, CDR2, and CDR3, numbered sequentially starting from the N-terminus, and are also typically identified by the chain in which the particular CDR is located. Thus, a V_H CDR3 is located in the variable domain of the heavy chain of the antibody in which it is found, whereas a V_L CDR1 is the CDR1 from the variable domain of the light chain of the antibody in which it is found. An antibody that binds a DOTA hapten will have a specific V_H region and the V_L region sequence, and thus specific CDR sequences. Antibodies with different specificities (i.e. different combining sites for different antigens) have different CDRs. Although it is the CDRs that vary from antibody to antibody, only a limited number of amino acid positions within the CDRs are directly involved in antigen binding. These positions within the CDRs are called specificity determining residues (SDRs). An antibody or antigen binding fragment thereof specifically binds to an antigen. [0051] As used herein, the term “antibody-related polypeptide” means antigen-binding antibody fragments, including single-chain antibodies, that can comprise the variable region(s) alone, or in combination, with all or part of the following polypeptide elements: hinge region, CH₁, CH₂, and CH₃ domains of an antibody molecule. Also included in the technology are any combinations of variable region(s) and hinge region, CH₁, CH₂, and CH₃ domains. Antibody-related molecules useful in the present methods, e.g., but are not limited to, Fab, Fab′ and F(ab′)₂, Fd, single-chain Fvs (scFv), single-chain antibodies, disulfide- linked Fvs (sdFv) and fragments comprising either a V_L or V_H domain. Examples include: (i) a Fab fragment, a monovalent fragment consisting of the VL, VH, CL and CH1 domains; (ii) a F(ab′)2 fragment, a bivalent fragment comprising two Fab fragments linked by a disulfide bridge at the hinge region; (iii) a Fd fragment consisting of the V_H and CH₁ domains; (iv) a Fv fragment consisting of the VL and VH domains of a single arm of an antibody, (v) a dAb fragment (Ward et al., Nature 341: 544-546, 1989), which consists of a VH domain; and (vi) an isolated complementarity determining region (CDR). As such “antibody fragments” or “antigen binding fragments” can comprise a portion of a full length antibody, generally the antigen binding or variable region thereof. Examples of antibody fragments or antigen binding fragments include Fab, Fab', F(ab')₂, and Fv fragments; diabodies; nanobodies; camelids; linear antibodies; single-chain antibody molecules; and multi-specific antibodies formed from antibody fragments. [0052] As used herein, the terms “single-chain antibodies” or “single-chain Fv (scFv)” refer to an antibody fusion molecule of the two domains of the Fv fragment, V_L and V_H. Single-chain antibody molecules may comprise a polymer with a number of individual molecules, for example, dimer, trimer or other polymers. Furthermore, although the two domains of the F_v fragment, V_L and V_H, are coded for by separate genes, they can be joined, using recombinant methods, by a synthetic linker that enables them to be made as a single protein chain in which the VL and VH regions pair to form monovalent molecules (known as single-chain F_v (scF_v)). Bird et al. (1988) Science 242:423-426 and Huston et al. (1988) Proc. Natl. Acad Sci. USA 85:5879-5883. Such single-chain antibodies can be prepared by recombinant techniques or enzymatic or chemical cleavage of intact antibodies. [0053] Any of the above-noted antibody fragments are obtained using conventional techniques known to those of skill in the art, and the fragments are screened for binding specificity and neutralization activity in the same manner as are intact antibodies. [0054] As used herein, an “antigen” refers to a molecule to which an antibody can selectively bind. The antigen may be a protein, carbohydrate, nucleic acid, lipid, hapten, or other naturally occurring or synthetic compound. In some embodiments, the target antigen may be a DOTA-based hapten. An antigen may also be administered to an animal to generate an immune response in the animal. [0055] The term “antigen binding fragment” refers to a fragment of the whole immunoglobulin structure which possesses a part of a polypeptide responsible for binding to antigen. Examples of the antigen binding fragment useful in the present technology include scFv, (scFv)₂, scFvFc, Fab, Fab′ and F(ab′)₂, but are not limited thereto. [0056] By “binding affinity” is meant the strength of the total noncovalent interactions between a single binding site of a molecule (e.g., an antibody) and its binding partner (e.g., an antigen or antigenic peptide). The affinity of a molecule X for its partner Y can generally be represented by the dissociation constant (KD). Affinity can be measured by standard methods known in the art, including those described herein. A low-affinity complex contains an antibody that generally tends to dissociate readily from the antigen, whereas a high-affinity complex contains an antibody that generally tends to remain bound to the antigen for a longer duration. [0057] As used herein, the term “biological sample” means sample material derived from living cells. Biological samples may include tissues, cells, protein or membrane extracts of cells, and biological fluids (e.g., ascites fluid or cerebrospinal fluid (CSF)) isolated from a subject, as well as tissues, cells and fluids present within a subject. Biological samples can also be obtained from biopsies of internal organs or from cancers. Biological samples can be obtained from subjects for diagnosis or research or can be obtained from non-diseased individuals, as controls or for basic research. Samples may be obtained by standard methods including, e.g., venous puncture and surgical biopsy. In certain embodiments, the biological sample is a tissue sample obtained by needle biopsy. [0058] As used herein, “B_max” is the total density (concentration) of receptors in a sample of tissue. [0059] The terms “cancer” or “tumor” are used interchangeably and refer to the presence of cells possessing characteristics typical of cancer-causing cells, such as uncontrolled proliferation, immortality, metastatic potential, rapid growth and proliferation rate, and certain characteristic morphological features. Cancer cells are often in the form of a tumor, but such cells can exist alone within an animal, or can be a non-tumorigenic cancer cell. As used herein, the term “cancer” includes premalignant, as well as malignant cancers. Examples of cancers include, but are not limited to, neuroblastoma, melanoma, non- Hodgkin's lymphoma, Epstein-Barr related lymphoma, Hodgkin's lymphoma, retinoblastoma, small cell lung cancer, brain tumors, leukemia, epidermoid carcinoma, prostate cancer, renal cell carcinoma, transitional cell carcinoma, breast cancer, ovarian cancer, lung cancer colon cancer, liver cancer, stomach cancer, and other gastrointestinal cancers. [0060] As used herein, a "control" is an alternative sample used in an experiment for comparison purpose. A control can be "positive" or "negative." For example, where the purpose of the experiment is to determine a correlation of the efficacy of a therapeutic agent for the treatment for a particular type of disease, a positive control (a compound or composition known to exhibit the desired therapeutic effect) and a negative control (a subject or a sample that does not receive the therapy or receives a placebo) are typically employed. [0061] “Detectable label” as used herein refers to a molecule or a compound or a group of molecules or a group of compounds used to identify a nucleic acid, protein, molecule, or compound of interest. In some embodiments, the detectable label may be detected directly. In other embodiments, the detectable label may be a part of a binding pair, which can then be subsequently detected. Signals from the detectable label may be detected by various means and will depend on the nature of the detectable label. Detectable labels may be isotopes, fluorescent moieties, colored substances, and the like. Examples of means to detect detectable labels include but are not limited to spectroscopic, photochemical, biochemical, immunochemical, electromagnetic, radiochemical, or chemical means, such as fluorescence, chemifluorescence, or chemiluminescence, or any other appropriate means. [0062] As used herein, the term “effective amount” refers to a quantity sufficient to achieve a desired effect (e.g., a diagnostic or therapeutic/prophylactic effect). In the context of therapeutic or prophylactic applications, the amount of a composition administered to the subject will vary depending on the composition, the degree, type, and severity of the disease and on the characteristics of the individual, such as general health, age, sex, body weight and tolerance to drugs. The skilled artisan will be able to determine appropriate dosages depending on these and other factors. The compositions can also be administered in combination with one or more additional therapeutic compounds. In the methods described herein, the therapeutic compositions may be administered to a subject having one or more signs or symptoms of a disease or condition described herein. As used herein, a "therapeutically effective amount" of a composition refers to composition levels in which the physiological effects of a disease or condition are ameliorated or eliminated. A therapeutically effective amount can be given in one or more administrations. [0063] As used herein, the term “epitope” means a protein determinant capable of specific binding to an antibody. Epitopes usually consist of chemically active surface groupings of molecules such as amino acids or sugar side chains and usually have specific three dimensional structural characteristics, as well as specific charge characteristics. Conformational and non-conformational epitopes are distinguished in that the binding to the former but not the latter is lost in the presence of denaturing solvents. In some embodiments, the epitope is a conformational epitope or a non-conformational epitope. [0064] As used herein, “expression” includes one or more of the following: transcription of the gene into precursor mRNA; splicing and other processing of the precursor mRNA to produce mature mRNA; mRNA stability; translation of the mature mRNA into protein (including codon usage and tRNA availability); and glycosylation and/or other modifications of the translation product, if required for proper expression and function. [0065] As used herein, an “expression control sequence” refers to polynucleotide sequences which are necessary to affect the expression of coding sequences to which they are operably linked. Expression control sequences are sequences which control the transcription, post- transcriptional events and translation of nucleic acid sequences. Expression control sequences include appropriate transcription initiation, termination, promoter and enhancer sequences; efficient RNA processing signals such as splicing and polyadenylation signals; sequences that stabilize cytoplasmic mRNA; sequences that enhance translation efficiency (e.g., ribosome binding sites); sequences that enhance protein stability; and when desired, sequences that enhance protein secretion. The nature of such control sequences differs depending upon the host organism; in prokaryotes, such control sequences generally include promoter, ribosomal binding site, and transcription termination sequence. The term “control sequences” is intended to encompass, at a minimum, any component whose presence is essential for expression, and can also encompass an additional component whose presence is advantageous, for example, leader sequences. [0066] The term “Fc region”, “Fc domain”, or “Fc fragment” as used herein refers to a C- terminal region of an immunoglobulin heavy chain, which is capable of binding to a mammalian Fc(gamma) or Fc(Rn) receptor, e.g., human Fc(gamma) or Fc(Rn) receptor. An Fc receptor (FcR) refers to a receptor that binds to an Fc fragment or the Fc region of an antibody. In certain embodiments, the FcR is a native human FcR sequence. In some embodiments, the FcR binds an IgG antibody (a gamma receptor) and includes receptors of the FcγRI, FcγRII, and FcγRIII subclasses, including allelic variants and alternatively spliced forms of these receptors. FcγRII receptors include FcγRIIA (an “activating receptor”) and FcγRIIB (an “inhibiting receptor”), which have similar amino acid sequences that differ primarily in the cytoplasmic domains thereof. FcRs are described in Ravetch and Kinet, 1991, Ann. Rev. Immunol., 9:457-92; Capel et al., 1994, Immunomethods, 4:25-34; and de Haas et al., 1995, J. Lab. Clin. Med., 126:330-41. “FcR” also includes the neonatal receptor, FcRn, which is responsible for the transfer of maternal IgGs to the fetus (Guyer et al., 1976 J. Immunol., 117:587; and Kim et al., 1994, J. Immunol., 24:249) and contributes to the prolonged in vivo elimination half-lives of antibodies and Fc-fusion proteins in vivo. The Fc fragment, region, or domain may be a native sequence Fc region. Although the boundaries of the Fc region of an immunoglobulin heavy chain might vary, the human IgG heavy chain Fc region is usually defined to stretch from an amino acid residue at position Cys226, or from Pro230, to the carboxyl-terminus thereof. The numbering of the residues in the Fc region is that of the EU index as in Kabat. Kabat et al., Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, Md., 1991. The Fc region of an immunoglobulin generally comprises two constant domains, CH2 and CH3. [0067] The term "fusion protein" as used herein refers to a hybrid polypeptide which comprises protein domains from at least two different proteins. One protein may be located at the amino-terminal (N-terminal) portion of the fusion protein or at the carboxy-terminal (C-terminal) protein thus forming an "amino-terminal fusion protein" or a "carboxy-terminal fusion protein," respectively. A protein may comprise different domains, for example, a DOTA binding fragment (e.g., C825 scFv), a transmembrane domain, and a reporter gene. In some embodiments, the fusion protein optionally comprises a spacer domain (e.g., an IgG Fc domain). Fusion of a DOTA binding fragment (e.g., C825 scFv) with a transmembrane domain, and a reporter gene results in a detectably labelled membrane-bound DOTA binding molecule that permits the specific capture of radioactive or non-radioactive DOTA-based hapten probes. Accordingly, the fusion protein of the present technology is useful in characterizing in vitro and in vivo properties of radioactive or non-radioactive DOTA-based hapten probes, such as uptake, pharmacokinetics (e.g., affinity), biodistribution, specificity, cytotoxicity, and the like. In some embodiments, a fusion protein is in a complex with, or is in association with a radioactive or non-radioactive DOTA-based hapten probe. Any of the proteins provided herein may be produced by any method known in the art. For example, the proteins provided herein may be produced via recombinant protein expression and purification, which is especially suited for fusion proteins comprising a peptide linker. Methods for recombinant protein expression and purification are well known, and include those described by Green and Sambrook, Molecular Cloning: A Laboratory Manual (4.sup.th ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (2012)), the entire contents of which are incorporated herein by reference. [0068] “Gene” as used herein refers to a DNA sequence that comprises regulatory and coding sequences necessary for the production of an RNA, which may have a non-coding function (e.g., a ribosomal or transfer RNA) or which may include a polypeptide or a polypeptide precursor. The RNA or polypeptide may be encoded by a full length coding sequence or by any portion of the coding sequence so long as the desired activity or function is retained. Although a sequence of the nucleic acids may be shown in the form of DNA, a person of ordinary skill in the art recognizes that the corresponding RNA sequence will have a similar sequence with the thymine being replaced by uracil, i.e., "T" is replaced with "U." [0069] As used herein, a “heterologous nucleic acid sequence” is any nucleic acid sequence placed at a location where it does not normally occur. A heterologous nucleic acid sequence may comprise a sequence that does not naturally occur in a cell, or it may comprise only sequences naturally found in the cell, but placed at a non-normally occurring location in the cell. In some embodiments, the heterologous nucleic acid sequence is not an endogenous sequence. In certain embodiments, the heterologous nucleic acid sequence is an endogenous sequence that is derived from a different cell. In other embodiments, the heterologous nucleic acid sequence is a sequence that occurs naturally in a cell but is then relocated to another site where it does not naturally occur, rendering it a heterologous sequence at that new site. [0070] As used herein, “humanized” forms of non-human (e.g., murine) antibodies are chimeric antibodies which contain minimal sequence derived from non-human immunoglobulin. For the most part, humanized antibodies are human immunoglobulins in which hypervariable region residues of the recipient are replaced by hypervariable region residues from a non-human species (donor antibody) such as mouse, rat, rabbit or nonhuman primate having the desired specificity, affinity, and capacity. In some embodiments, Fv framework region (FR) residues of the human immunoglobulin are replaced by corresponding non-human residues. Furthermore, humanized antibodies may comprise residues which are not found in the recipient antibody or in the donor antibody. These modifications are made to further refine antibody performance such as binding affinity. Generally, the humanized antibody will comprise substantially all of at least one, and typically two, variable domains (e.g., Fab, Fab′, F(ab′)₂, or Fv), in which all or substantially all of the hypervariable loops correspond to those of a non-human immunoglobulin and all or substantially all of the FR regions are those of a human immunoglobulin consensus FR sequence although the FR regions may include one or more amino acid substitutions that improve binding affinity. The number of these amino acid substitutions in the FR are typically no more than 6 in the H chain, and in the L chain, no more than 3. The humanized antibody optionally may also comprise at least a portion of an immunoglobulin constant region (Fc), typically that of a human immunoglobulin. For further details, see Jones et al., Nature 321:522-525 (1986); Reichmann et al., Nature 332:323-329 (1988); and Presta, Curr. Op. Struct. Biol.2:593-596 (1992). See e.g., Ahmed & Cheung, FEBS Letters 588(2):288- 297 (2014). [0071] As used herein, the term “hypervariable region” refers to the amino acid residues of an antibody which are responsible for antigen-binding. The hypervariable region generally comprises amino acid residues from a “complementarity determining region” or “CDR” (e.g., around about residues 24-34 (L1), 50-56 (L2) and 89-97 (L3) in the V_L, and around about 31- 35B (H1), 50-65 (H2) and 95-102 (H3) in the V_H (Kabat et al., Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, MD. (1991)) and/or those residues from a “hypervariable loop” (e.g., residues 26- 32 (L1), 50-52 (L2) and 91-96 (L3) in the V_L, and 26-32 (H1), 52A-55 (H2) and 96-101 (H3) in the VH (Chothia and Lesk J. Mol. Biol.196:901-917 (1987)). [0072] As used herein, the term “hypervariable region” refers to the amino acid residues of an antibody which are responsible for antigen-binding. The hypervariable region generally comprises amino acid residues from a “complementarity determining region” or “CDR” (e.g., around about residues 24-34 (L1), 50-56 (L2) and 89-97 (L3) in the VL, and around about 31- 35B (H1), 50-65 (H2) and 95-102 (H3) in the V_H (Kabat et al., Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, MD. (1991)) and/or those residues from a “hypervariable loop” (e.g., residues 26- 32 (L1), 50-52 (L2) and 91-96 (L3) in the VL, and 26-32 (H1), 52A-55 (H2) and 96-101 (H3) in the V_H (Chothia and Lesk J. Mol. Biol.196:901-917 (1987)). [0073] As used herein, the terms “individual”, “patient”, or “subject” can be an individual organism, a vertebrate, a mammal, or a human. In some embodiments, the individual, patient or subject is a human. [0074] As used herein, the term “intact antibody” or “intact immunoglobulin” means an antibody that has at least two heavy (H) chain polypeptides and two light (L) chain polypeptides interconnected by disulfide bonds. Each heavy chain is comprised of a heavy chain variable region (abbreviated herein as HCVR or V_H) and a heavy chain constant region. The heavy chain constant region is comprised of three domains, CH1, CH2 and CH3. Each light chain is comprised of a light chain variable region (abbreviated herein as LCVR or V_L) and a light chain constant region. The light chain constant region is comprised of one domain, CL. The VH and VL regions can be further subdivided into regions of hypervariability, termed complementarity determining regions (CDR), interspersed with regions that are more conserved, termed framework regions (FR). Each V_H and V_L is composed of three CDRs and four FRs, arranged from amino-terminus to carboxyl-terminus in the following order: FR1, CDR1, FR2, CDR2, FR3, CDR3, FR4. The variable regions of the heavy and light chains contain a binding domain that interacts with an antigen. The constant regions of the antibodies can mediate the binding of the immunoglobulin to host tissues or factors, including various cells of the immune system (e.g., effector cells) and the first component (Clq) of the classical complement system. [0075] As used herein, “linker” typically refers to a portion of a molecule or entity that connects two or more different regions of interest (e.g., particular structural and/or functional domains or moieties of interest). The linker may lack a defined or rigid structure and/or may not materially alter the relevant function of the domain(s) or moiety(ies) within the two or more different regions of interest. In some embodiments, the linker is or comprises a polypeptide and may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 or more amino acids long. In certain embodiments, a polypeptide linker may have an amino acid sequence that is or comprises GGGGSGGGGSGGGGS (i.e., [G4S]3) (SEQ ID NO: 9), GGGGSGGGGSGGGGSGGGGS (i.e., [G₄S]₄) (SEQ ID NO: 10), or GGGGSGGGGSGGGGSGGGGSGGGGSGGGGS (i.e., [G₄S]₆) (SEQ ID NO: 11). [0076] As used herein, “operably linked” means that expression control sequences are positioned relative to a nucleic acid of interest to initiate, regulate or otherwise control transcription of the nucleic acid of interest. In some embodiments, transcription of a polynucleotide operably linked to an expression control element (e.g., a promoter) is controlled, regulated, or influenced by the expression control element. [0077] As used herein, the term “polynucleotide” or “nucleic acid” means any RNA or DNA, which may be unmodified or modified RNA or DNA. Polynucleotides include, without limitation, single- and double-stranded DNA, DNA that is a mixture of single- and double-stranded regions, single- and double-stranded RNA, RNA that is mixture of single- and double-stranded regions, and hybrid molecules comprising DNA and RNA that may be single-stranded or, more typically, double-stranded or a mixture of single- and double- stranded regions. In addition, polynucleotide refers to triple-stranded regions comprising RNA or DNA or both RNA and DNA. The term polynucleotide also includes DNAs or RNAs containing one or more modified bases and DNAs or RNAs with backbones modified for stability or for other reasons. [0078] As used herein, the terms “polypeptide”, “peptide” and “protein” are used interchangeably herein to mean a polymer comprising two or more amino acids joined to each other by peptide bonds or modified peptide bonds, i.e., peptide isosteres. Polypeptide refers to both short chains, commonly referred to as peptides, glycopeptides or oligomers, and to longer chains, generally referred to as proteins. Polypeptides may contain amino acids other than the 20 gene-encoded amino acids. Polypeptides include amino acid sequences modified either by natural processes, such as post-translational processing, or by chemical modification techniques that are well known in the art. Such modifications are well described in basic texts and in more detailed monographs, as well as in a voluminous research literature. [0079] The term “promoter” as used herein refers to any sequence that regulates the expression of a coding sequence, such as a gene. Promoters may be constitutive, inducible, repressible, or tissue-specific, for example. A “promoter” is a control sequence that is a region of a polynucleotide sequence at which initiation and rate of transcription are controlled. It may contain genetic elements at which regulatory proteins and molecules may bind such as RNA polymerase and other transcription factors. [0080] As used herein, the term “recombinant” when used with reference, e.g., to a cell, or nucleic acid, protein, or vector, indicates that the cell, nucleic acid, protein or vector, has been modified by the introduction of a heterologous nucleic acid or protein or the alteration of a native nucleic acid or protein, or that the material is derived from a cell so modified. Thus, for example, recombinant cells express genes that are not found within the native (non- recombinant) form of the cell or express native genes that are otherwise abnormally expressed, under expressed or not expressed at all. [0081] As used herein, an endogenous nucleic acid sequence in the cell of an organism (or the encoded protein product of that sequence) is deemed “recombinant” herein if a heterologous sequence is placed adjacent to the endogenous nucleic acid sequence, such that the expression of this endogenous nucleic acid sequence is altered. In this context, a heterologous sequence is a sequence that is not naturally adjacent to the endogenous nucleic acid sequence, whether or not the heterologous sequence is itself endogenous to the organism (originating from the same organism or progeny thereof) or exogenous (originating from a different organism or progeny thereof). By way of example, a promoter sequence can be substituted (e.g., by homologous recombination) for the native promoter of a gene in the cell of an organism, such that this gene has an altered expression pattern. This gene would be “recombinant” because it is separated from at least some of the sequences that naturally flank it. A nucleic acid is also considered “recombinant” if it contains any modifications that do not naturally occur in the corresponding nucleic acid in a cell. For instance, an endogenous coding sequence is considered “recombinant” if it contains an insertion, deletion or a point mutation introduced artificially, e.g., by human intervention. A “recombinant nucleic acid” also includes a nucleic acid integrated into a host cell chromosome at a heterologous site and a nucleic acid construct present as an episome. [0082] As used herein, a “reporter gene” refers to a polynucleotide sequence encoding a gene product (e.g., polypeptide) that can generate, under appropriate conditions, a detectable signal that allows detection of the presence and/or quantity of the gene product. [0083] As used herein, a “spacer domain” is a polypeptide that links two distinct regions or domains of a protein (e.g., the distinct regions of a fusion protein). In some embodiments, spacer domains have no specific biological activity, and their purpose is simply to link two protein domains, or to preserve the minimum distance or spatial relationship between said protein domains. Additionally or alternatively, is some embodiments, the constituent amino acids of the spacer domains may be selected based on physicochemical properties, such as flexibility, hydrophilicity, net charge, proteolytic sensitivity or lack thereof, and lack of immunogenicity. [0084] As used herein, “specifically binds” refers to a molecule (e.g., an antibody or antigen binding fragment thereof) which recognizes and binds another molecule (e.g., an antigen or hapten), but that does not substantially recognize and bind other molecules. The terms “specific binding,” “specifically binds to,” or is “specific for” a particular molecule (e.g., an antigen, or an epitope on an antigen, or hapten), as used herein, can be exhibited, for example, by a molecule having a K_D for the molecule to which it binds to of about 10⁻⁴ M, 10⁻⁵ M, 10⁻⁶ M, 10⁻⁷ M, 10⁻⁸ M, 10⁻⁹ M, 10⁻¹⁰ M, 10⁻¹¹ M, or 10⁻¹² M. The term “specifically binds” may also refer to binding where a molecule (e.g., an antibody or antigen binding fragment thereof) binds to a particular antigen, or an epitope on a particular antigen, or hapten, without substantially binding to any other antigen, epitope, or hapten. [0085] “Treating” or “treatment” as used herein covers the treatment of a disease or disorder described herein, in a subject, such as a human, and includes: (i) inhibiting a disease or disorder, i.e., arresting its development; (ii) relieving a disease or disorder, i.e., causing regression of the disorder; (iii) slowing progression of the disorder; and/or (iv) inhibiting, relieving, or slowing progression of one or more symptoms of the disease or disorder. In some embodiments, treatment means that the symptoms associated with the disease are, e.g., alleviated, reduced, cured, or placed in a state of remission. [0086] It is also to be appreciated that the various modes of treatment of disorders as described herein are intended to mean “substantial,” which includes total but also less than total treatment, and wherein some biologically or medically relevant result is achieved. The treatment may be a continuous prolonged treatment for a chronic disease or a single, or few time administrations for the treatment of an acute condition. [0087] As used herein, a "vector" refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. One type of vector is a "plasmid," which generally refers to a circular double stranded DNA loop into which additional DNA segments may be ligated, but also includes linear double- stranded molecules such as those resulting from amplification by the polymerase chain reaction (PCR) or from treatment of a circular plasmid with a restriction enzyme. Other vectors include cosmids, bacterial artificial chromosomes (BAC) and yeast artificial chromosomes (YAC). Another type of vector is a viral vector, wherein additional DNA segments may be ligated into the viral genome. Certain vectors are capable of autonomous replication in a host cell into which they are introduced (e.g., vectors having an origin of replication which functions in the host cell). Other vectors can be integrated into the genome of a host cell upon introduction into the host cell, and are thereby replicated along with the host genome. Moreover, certain vectors are capable of directing the expression of genes to which they are operatively linked. Such vectors are referred to herein as "recombinant expression vectors" (or simply "expression vectors"). Compositions Including the Recombinant Membrane-Bound C825 Reporter of the Present Technology [0088] The fusion proteins of the present technology comprise a humanized DOTA binding fragment fused to a transmembrane domain, and a reporter gene. The humanized DOTA binding fragment comprises a heavy chain immunoglobulin variable domain (VH) sequence and a light chain immunoglobulin variable domain (V_L) sequence of SEQ ID NO: 1 and SEQ ID NO: 5, respectively. The VH domain sequence may be located at the N-terminus or the C-terminus of the VL domain sequence. huC825 V_H HVQLVESGGGLVQPGGSLRLSCAASGFSLTDYGVHWVRQAPGKGLEWLGVIWSGG GTAYNTALISRFTISRDNSKNTLYLQMNSLRAEDTAVYYCARRGSYPYNYFDAWGC GTLVTVSS (SEQ ID NO: 1) huC825 V_L QAVVTQEPSLTVSPGGTVTLTCGSSTGAVTASNYANWVQQKPGQCPRGLIGGHNNR PPGVPARFSGSLLGGKAALTLLGAQPEDEAEYYCALWYSDHWVIGGGTKLTVLG (SEQ ID NO: 5) [0089] The VH CDR1, VH CDR2 and VH CDR3 sequences of SEQ ID NO: 1 are DYGVH (SEQ ID NO: 2), VIWSGGGTAYNTALIS (SEQ ID NO: 3), RGSYPYNYFDA (SEQ ID NO: 4), respectively, and are underlined in order of appearance. The V_L CDR1, V_L CDR2 and VL CDR3 sequences of SEQ ID NO: 5 are GSSTGAVTASNYAN (SEQ ID NO: 6), GHNNRPP (SEQ ID NO: 7), and ALWYSDHWV (SEQ ID NO: 8), respectively, and are underlined in order of appearance. Additionally or alternatively, in some embodiments, the sequence of an intra-peptide linker between the V_H domain sequence and the V_L domain sequence in the DOTA binding fragment is any one of SEQ ID NOs: 9-11. [0090] In any and all embodiments of the fusion protein of the present technology, the DOTA binding fragment is located at the N-terminus of the transmembrane domain and/or the reporter gene is located at the C-terminus of the transmembrane domain. [0091] Additionally or alternatively, in some embodiments, the reporter gene is a fluorescent reporter gene, a chemiluminescent reporter gene, or a bioluminescent reporter gene. Examples of suitable fluorescent reporter genes include, but are not limited to, GFP, YFP, CFP, RFP, TagBFP, Azurite, EBFP2, mKalama1, Sirius, Sapphire, T-Sapphire, ECFP, Cerulean, SCFP3A, mTurquoise, monomeric Midoriishi-Cyan, TagCFP, mTFP1, EGFP, Emerald, Superfolder GFP, Monomeric Azami Green, TagGFP2, mUKG, mWasabi, EYFP, Citrine, Venus, SYFP2, TagYFP, Monomeric Kusabira-Orange, mKOκ, mKO2, mOrange, mOrange2, mRaspberry, mCherry, dsRed, mStrawberry, mTangerine, tdTomato, TagRFP, TagRFP-T, mApple, mRuby, mPlum, HcRed-Tandem, mKate2, mNeptune, NirFP, TagRFP657, IFP1.4, iRFP, mKeima Red, LSS-mKate1, LSS-mKate2, PA-GFP, PAmCherry1, PATagRFP, Kaede (green), Kaede (red), KikGR1 (green), KikGR1 (red), PS- CFP2, PS-CFP2, mEos2 (green), mEos2 (red), PSmOrange, and Dronpa. Examples of bioluminescent reporter genes include, but are not limited to, Aequorin, firefly luciferase, Renilla luciferase, red luciferase, luxAB, and nanoluciferase. Examples of suitable chemiluminescent reporter genes include β-galactosidase, horseradish peroxidase (HRP), and alkaline phosphatase. Peroxidases generate peroxide that oxidizes luminol in a reaction that generates light, whereas alkaline phosphatases remove a phosphate from a substrate molecule, destabilizing it and initiating a cascade that results in the emission of light. [0092] In any of the foregoing embodiments, the fusion protein further comprises a spacer domain interspersed between the DOTA binding fragment and the transmembrane domain. In some embodiments, the spacer domain is a Fc domain. In certain embodiments, the Fc domain comprises a Fc fragment of a mammalian IgG, e.g., human IgG. In some embodiments, the Fc fragment comprises or consists of the Fc region (e.g., CH2 domain and CH3 domain) of a mammalian IgG, e.g., human IgG. In certain embodiments, the Fc fragment comprises or consists of the Fc region (e.g., CH2 domain and CH3 domain) of human IgG1, human IgG2, human IgG3, or human IgG4. Exemplary sequences of Fc regions of (e.g., CH2 domain and CH3 domain) human IgG_1, human IgG_2, human IgG_3, or human IgG₄ are provided below: [0093] Fc region of Human IgG1 (SEQ ID NO: 12) GPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPRE EQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVY TLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLY SKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK [0094] Fc region of Human IgG₂ (SEQ ID NO: 13) GPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVQFNWYVDGVEVHNAKTKPRE EQFNSTFRVVSVLTVVHQDWLNGKEYKCKVSNKGLPAPIEKTISKTKGQPREPQVYT LPPSREEMTKNQVSLTCLVKGFYPSDISVEWESNGQPENNYKTTPPMLDSDGSFFLYS KLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK [0095] Fc region of Human IgG3 (SEQ ID NO: 14) GPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVQFKWYVDGVEVHNAKTKPRE EQYNSTFRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKTKGQPREPQVYT LPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESSGQPENNYNTTPPMLDSDGSFFLYS KLTVDKSRWQQGNIFSCSVMHEALHNRFTQKSLSLSPGK [0096] Fc region of Human IgG₄ (SEQ ID NO: 15) GPSVFLFPPKPKDTLMISRTPEVTCVVVDVSQEDPEVQFNWYVDGVEVHNAKTKPRE EQFNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKGLPSSIEKTISKAKGQPREPQVYT LPPSQEEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYS RLTVDKSRWQEGNVFSCSVMHEALHNHYTQKSLSLSLGK [0097] IgG4 CH2-CH3 spacer domain (SEQ ID NO: 16) DLEPKSPDKTHTCPPCPAPPVAGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPE VKFNWYVDGVEVHNAKTKPREEQYQSTYRVVSVLTVLHQDWLNGKEYKCKVSNK ALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESN GQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKS LSLSPGK [0098] In some embodiments, the Fc fragment comprises or consists of an amino acid sequence having at least 80% (e.g., at least 80%, 85%, 90%, 95%, 97%, 99%, or more) identity to the Fc region (e.g., CH2 domain and CH3 domain) of a human IgG including the amino acid sequence of any one of SEQ ID NOs: 12-16. Additionally or alternatively, the Fc fragment comprises one or more mutations to prevent interaction with Fc ^Rs. Examples of Fc mutations that prevent interaction with Fc ^Rs are described in Hudecek et al., Cancer Immunol Res 3(2):125-35 (2015). [0099] In accordance with the presently disclosed subject matter, the transmembrane domain of the fusion protein may comprise an amino acid sequence that is at least 80% (e.g., at least 80%, 85%, 90%, 95%, 97%, 99%, or more) identical to an amino acid sequence of a transmembrane region of CD4 (SEQ ID NO: 17), CD8 (SEQ ID NO: 20), CD28 (SEQ ID NO: 21), CD3ζ (SEQ ID NO: 22) or 4-1BB ligand receptor (SEQ ID NO: 24). [00100] In certain embodiments, the transmembrane domain comprises an amino acid sequence that is at least 80% (e.g., at least 80%, 85%, 90%, 95%, 97%, 99%, or more) identical to an amino acid sequence of a transmembrane region of CD4, as set forth in SEQ ID NO: 17 as provided below: MALIVLGGVAGLLLFIGLGIFFCVRCRH (SEQ ID NO: 17) [00101] In certain embodiments, the transmembrane domain comprises an amino acid sequence that is at least 80% (e.g., at least 80%, 85%, 90%, 95%, 97%, 99%, or more) identical to an amino acid sequence of a transmembrane region of CD8, as set forth in SEQ ID NO: 20 as provided below: PTTTPAPRPPTPAPTIASQPLSLRPEACRPAAGGAVHTRGLDFACDIYIWAPLAGTCGV LLLSLVITLYCN (SEQ ID NO: 20) [00102] In certain embodiments, the transmembrane domain comprises an amino acid sequence that is at least 80% (e.g., at least 80%, 85%, 90%, 95%, 97%, 99%, or more) identical to an amino acid sequence of a transmembrane region of CD28, as set forth in SEQ ID NO: 21 as provided below: FWVLVVVGGVLACYSLLVTVAFIIFWV (SEQ ID NO: 21) [00103] In certain embodiments, the transmembrane domain comprises an amino acid sequence that is at least 80% (e.g., at least 80%, 85%, 90%, 95%, 97%, 99%, or more) identical to an amino acid sequence of a transmembrane region of CD3ζ, as set forth in SEQ ID NO: 22 as provided below: LCYLLDGILFIYGVILTALFL (SEQ ID NO: 22) [00104] In certain embodiments, the transmembrane domain comprises an amino acid sequence that is at least 80% (e.g., at least 80%, 85%, 90%, 95%, 97%, 99%, or more) identical to an amino acid sequence of a transmembrane region of 4-1BB ligand receptor, as set forth in SEQ ID NO: 24 as provided below: IISFFLALTSTALLFLLFFLTLRFSVV (SEQ ID NO: 24) [00105] Additionally or alternatively, in some embodiments, the fusion protein comprises the amino acid sequence of SEQ ID NO: 18. HVQLVESGGGLVQPGGSLRLSCAASGFSLTDYGVHWVRQAPGKGLEWLGVIWSGGGTAY NTALISRFTISRDNSKNTLYLQMNSLRAEDTAVYYCARRGSYPYNYFDAWGCGTLVTVSSGG GGSGGGGSGGGGSQAVVTQEPSLTVSPGGTVTLTCGSSTGAVTASNYANWVQQKPGQCP RGLIGGHNNRPPGVPARFSGSLLGGKAALTLLGAQPEDEAEYYCALWYSDHWVIGGGTKL TVLGDLEPKSPDKTHTCPPCPAPPVAGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHE DPEVKFNWYVDGVEVHNAKTKPREEQYQSTYRVVSVLTVLHQDWLNGKEYKCKV SNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEW ESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYT QKSLSLSPGKMALIVLGGVAGLLLFIGLGIFFCVRCRHMVSKGEELFTGVVPILVE LDGDVNGHKFSVSGEGEGDATYGKLTLKFICTTGKLPVPWPTLVTTLTYGVQCFSRY PDHMKQHDFFKSAMPEGYVQERTIFFKDDGNYKTRAEVKFEGDTLVNRIELKGIDFK EDGNILGHKLEYNYNSHNVYIMADKQKNGIKVNFKIRHNIEDGSVQLADHYQQNTPI GDGPVLLPDNHYLSTQSALSKDPNEKRDHMVLLEFVTAAGITLGMDELYK (SEQ ID NO: 18) *C825 scFv is underlined, Transmembrane domain is in boldface, GFP is underlined. [00106] Additionally or alternatively, in some embodiments, the fusion protein of the present technology further comprises an endoplasmic reticulum signal sequence. In certain embodiments, the endoplasmic reticulum signal sequence is a CD4 signal peptide comprising the sequence MNRGVPFRHLLLVLQLALLPAATQG (SEQ ID NO: 23). Additionally or alternatively, in some embodiments, the fusion protein of the present technology further comprises a CD8 signal peptide (e.g., MALPVTALLLPLALLLHAARP (SEQ ID NO: 25) or MRPRLWLLLAAQLTVLHGNSV (SEQ ID NO: 26)), a CD28 signal peptide (e.g., MLRLLLALNLFPSIQVTG (SEQ ID NO: 27)), or an IL2 signal peptide (e.g., MYRMQLLSCIALSLALVTNS (SEQ ID NO: 28)). [00107] Additionally or alternatively, in some embodiments, the fusion protein does not include an internal ribosome entry site (IRES), or a 2A self-cleaving peptide. [00108] In one aspect, the present disclosure provides a recombinant nucleic acid sequence encoding any and all embodiments of the fusion proteins disclosed herein. In some embodiments, the recombinant nucleic acid sequence comprises the sequence of SEQ ID NO: 19: 1 accatgaacc gaggcgtgcc tttcagacat ttgttgcttg ttctccaact ggccctcctt 61 cccgctgcga cacaaggcca tgtacaactc gtggagtctg ggggcgggct ggtgcagcca 121 ggaggaagtc ttaggcttag ttgcgctgcc tccggatttt ctcttacaga ttacggagta 181 cactgggtcc gacaagcacc cggcaaaggt cttgaatggc ttggggttat ttggagtggt 241 ggcggtactg catataatac agccttgatt agtcgattta ccattagtcg agacaacagt 301 aaaaatactt tgtacctcca gatgaattcc cttcgcgccg aagatacagc ggtatattat 361 tgcgcccgga gaggtagtta tccctacaat tattttgatg cctggggatg cggcacattg 421 gttacagtgt cttctggcgg tggcggaagt ggcggcggcg gatcaggagg aggagggtct 481 caggccgttg tcactcagga gccgtctctc accgtatctc ctggagggac ggtgactttg 541 acctgtgggt cctctacagg agctgtcact gcctcaaact atgccaactg ggtacaacag 601 aagccgggtc agtgtccccg cggtcttatc gggggccata ataaccgccc tcccggtgtg 661 cccgcgcggt ttagcggatc tttgctcggt ggtaaggccg ctttgaccct tttgggggcc 721 caaccagagg acgaggcgga atactactgc gccttgtggt atagcgacca ctgggtaatc 781 gggggcggga ccaagctcac ggttctcgga gatctcgagc ccaaatctcc tgacaaaact 841 cacacatgcc caccgtgccc agcacctcct gtggccggac cgtcagtctt cctcttcccc 901 ccaaaaccca aggacaccct catgatctcc cggacccctg aggtcacatg cgtggtggtg 961 gacgtgagcc acgaagaccc tgaggtcaag ttcaactggt acgtggacgg cgtggaggtg 1021 cataatgcca agacaaagcc gcgggaggag cagtaccaga gcacgtaccg tgtggtcagc 1081 gtcctcaccg tcctgcacca ggactggctg aatggcaagg agtacaagtg caaggtctcc 1141 aacaaagccc tcccagcccc catcgagaaa accatctcca aagccaaagg gcagccccga 1201 gaaccacagg tgtacaccct gcccccatcc cgggatgagc tgaccaagaa ccaggtcagc 1261 ctgacctgcc tggtcaaagg cttctatccc agcgacatcg ccgtggagtg ggagagcaat 1321 gggcaaccgg agaacaacta caagaccacg cctcccgtgc tggactccga cggctccttc 1381 ttcctctaca gcaagctcac cgtggacaag agcaggtggc agcaggggaa cgtcttctca 1441 tgctccgtga tgcatgaggc tctgcacaac cactacacgc agaagagcct ctccctgtct 1501 ccgggtaaaa aagatcccaa ggccgcagca atggctctca tcgtcttggg tggggtcgca 1561 gggctgctcc tgtttatagg cctgggtatt ttcttctgcg ttcggtgtcg gcatatggtg 1621 agcaagggcg aggagctgtt caccggggtg gtgcccatcc tggtcgagct ggacggcgac 1681 gtaaacggcc acaagttcag cgtgtccggc gagggcgagg gcgatgccac ctacggcaag 1741 ctgaccctga agttcatctg caccaccggc aagctgcccg tgccctggcc caccctcgtg 1801 accaccctga cctacggcgt gcagtgcttc agccgctacc ccgaccacat gaagcagcac 1861 gacttcttca agtccgccat gcccgaaggc tacgtccagg agcgcaccat cttcttcaag 1921 gacgacggca actacaagac ccgcgccgag gtgaagttcg agggcgacac cctggtgaac 1981 cgcatcgagc tgaagggcat cgacttcaag gaggacggca acatcctggg gcacaagctg 2041 gagtacaact acaacagcca caacgtctat atcatggccg acaagcagaa gaacggcatc 2101 aaggtgaact tcaagatccg ccacaacatc gaggacggca gcgtgcagct cgccgaccac 2161 taccagcaga acacccccat cggcgacggc cccgtgctgc tgcccgacaa ccactacctg 2221 agcacccagt ccgccctgag caaagacccc aacgagaagc gcgatcacat ggtcctgctg 2281 gagttcgtga ccgccgccgg gatcactctc ggcatggacg agctgtacaa g (SEQ ID NO: 19) [00109] In another aspect, the present disclosure provides an expression vector comprising any and all embodiments of the recombinant nucleic acid sequences disclosed herein. In some embodiments, the recombinant nucleic acid sequence is operably linked to an expression control sequence. The expression control sequence may be an inducible promoter or a constitutive promoter. In yet another aspect, the present disclosure provides a recombinant mammalian cell comprising any and all embodiments of the expression vectors described herein. The recombinant mammalian cell may be cancerous or non-cancerous. In certain embodiments, the recombinant mammalian cell is a human embryonic kidney 293 cell. [00110] The gene sequence of the fusion protein of the present technology can be introduced as a linear construct, a circular plasmid, or a viral vector, which can be incorporated and inherited as a transgene integrated into the host genome, or as an extrachromosomal plasmid (Gassmann, et al., Proc. Natl. Acad. Sci. USA (1995) 92: 1292). The expression vector may be a DNA or RNA vector. Additionally or alternatively, in some embodiments, the expression vector is a plasmid, a cosmid, a bacmid, a bacterial artificial chromosome (BAC), a yeast artificial chromosome (YAC), or a viral vector. [00111] Any viral vector capable of accepting the coding sequences for the transcript(s) to be expressed can be used, for example, vectors derived from adenovirus (AV); adeno- associated virus (AAV); retroviruses (e.g., lentiviruses (LV), Rhabdoviruses, murine leukemia virus); herpes virus, and the like. Viral vectors can be constructed based on, but not limited to, adeno-associated virus (for a review, see Muzyczka, et al, Curr. Topics Micro. Immunol. (1992) 158:97-129)); adenovirus (see, for example, Berkner, et al, BioTechniques (1998) 6:616), Rosenfeld et al. (1991, Science 252:431-434), and Rosenfeld et al. (1992), Cell 68: 143-155)); alphavirus as well as others known in the art. Retroviruses have been used to introduce a variety of genes into many different cell types, including epithelial cells, in vitro and/or in vivo (see, e.g., Eglitis, et al, Science (1985) 230: 1395-1398; Danos and Mulligan, Proc. Natl. Acad. Sci. USA (1998) 85:6460-6464; Wilson et al, 1988, Proc. Natl. Acad. Sci. USA 85:3014-3018; Armentano et al, 1990, Proc. Natl. Acad. Sci. USA 87:61416145; Huber et al, 1991, Proc. Natl. Acad. Sci. USA 88:8039-8043; Ferry et al, 1991, Proc. Natl. Acad. Sci. USA 88:8377-8381; Chowdhury et al, 1991, Science 254: 1802- 1805; van Beusechem. et al, 1992, Proc. Natl. Acad. Sci. USA 89:7640-19 ; Kay et al, 1992, Human Gene Therapy 3:641-647; Dai et al, 1992, Proc. Natl. Acad. Sci. USA 89: 10892- 10895; Hwu et al, 1993, J. Immunol.150:4104-4115; U.S. Patent No.4,868,116; U.S. Patent No. 4,980,286; PCT Application WO 89/07136; PCT Application WO 89/02468; PCT Application WO 89/05345; and PCT Application WO 92/07573). Recombinant retroviral vectors capable of transducing and expressing genes inserted into the genome of a cell can be produced by transfecting the recombinant retroviral genome into suitable packaging cell lines such as PA317 and Psi-CRIP (Comette et al, 1991, Human Gene Therapy 2:5-10; Cone et al, 1984, Proc. Natl. Acad. Sci. USA 81 :6349). Recombinant adenoviral vectors can be used to infect a wide variety of cells and tissues in susceptible hosts (e.g., rat, hamster, dog, and chimpanzee) (Hsu et al, 1992, J. Infectious Disease, 166:769). [00112] The expression control sequence may be heterologous or native to the recombinant mammalian cell. Additionally or alternatively, in some embodiments, the expression control sequence may be an inducible promoter or a constitutive promoter. In some embodiments, the promoter driving transcription of the recombinant nucleic acid encoding the fusion protein of the present technology within the expression vector may be a eukaryotic RNA polymerase I (e.g., ribosomal RNA promoter), RNA polymerase II (e.g., CMV early promoter or actin promoter or U1 snRNA promoter), RNA polymerase III promoter (e.g., U6 snRNA or 7SK RNA promoter), or a prokaryotic promoter (for example the T7 promoter, provided the expression plasmid also encodes T7 RNA polymerase required for transcription from a T7 promoter). In certain embodiments, the promoter directs tissue- specific or cell-specific expression. Additionally or alternatively, in some embodiments, transcription may be regulated by an inducible regulatory sequence such as a regulatory sequence that is sensitive to certain physiological regulators. Such inducible expression systems, suitable for the control of transgene expression in cells or in mammals include regulation by ecdysone, estrogen, progesterone, tetracycline, ampicillin, doxycycline, glucose, saccharides, chemical inducers of dimerization, isopropyl-beta-D-l- thiogalactopyranoside (IPTG) and the like. A person skilled in the art would be able to choose the appropriate regulatory/promoter sequence for the expression vector. [00113] Successful introduction of expression vectors into host cells can be monitored using various known methods. Selection of expression vectors suitable for inserting nucleic acid sequences for expressing transcripts into the vector, and methods of delivering the vector to the cells of interest are within the skill in the art. For example, transient transfection can be signaled with a reporter, such as a fluorescent marker, such as Green Fluorescent Protein (GFP). Stable transfection of cells ex vivo can be ensured using markers that provide the transfected cell with resistance to specific environmental factors (e.g., antibiotics and drugs), such as hygromycin B resistance. The delivery of the expression vector containing recombinant DNA can by performed by abiologic or biologic systems including but not limited to liposomes, virus-like particles, transduction particles derived from phage or viruses, and conjugation. Uses of the Recombinant Membrane-Bound C825 Reporter of the Present Technology [00114] The methods of the present technology are useful for assaying the in vitro and in vivo properties of candidate detectably labelled DOTA-based hapten probes that may be useful for imaging, dosimetry, in vivo cell tracking, flow cytometry, cell sorting/purification, fluorescence-guided surgery, immunohistochemistry, and pretargeted radioimmunotherapy applications. The DOTA-based hapten probes may comprise a chromogenic, enzymatic, radioisotopic, isotopic, fluorescent, toxic, chemiluminescent, nuclear magnetic resonance contrast agent or other detectable label. [00115] In one aspect, the present disclosure provides a method for determining in vitro binding kinetics of a radioactive or non-radioactive DOTA-based hapten comprising contacting a radioactive or non-radioactive DOTA-based hapten with any embodiment of the recombinant mammalian cell described herein, and determining the binding activity of the DOTA-based hapten to the recombinant mammalian cell, wherein the recombinant mammalian cell exhibits cell surface expression of any embodiment of the fusion protein of the present technology, and wherein the DOTA-based hapten comprises, or is directly or indirectly linked to a detectable label (e.g., spectroscopic, photochemical, biochemical, immunochemical, electromagnetic, radioactive, fluorescent, chemifluorescent, or chemiluminescent label). [00116] The binding activity of the DOTA-based hapten may be determined via saturation binding assays or competition binding assays. In certain embodiments, the method further comprises determining a mean equilibrium dissociation constant (Kd) of the DOTA-based hapten and a mean Bmax (sites/cell) for the fusion protein. [00117] In one aspect, the present disclosure provides a method for detecting the presence of a DOTA-based hapten in vivo comprising (a) administering to a subject an amount of a recombinant mammalian cell of the present technology that is effective to establish a xenograft, (b) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten is configured to localize to the xenograft, and comprises, or is directly or indirectly linked to a detectable label; and (c) detecting the presence of the DOTA-based hapten in the subject by detecting signal levels emitted by the detectable label of the DOTA-based hapten that are higher than a reference value. The detectable label may be a spectroscopic, photochemical, biochemical, immunochemical, electromagnetic, radioactive, fluorescent, chemifluorescent, or chemiluminescent label. The signal emitted by the detectable label of the DOTA-based hapten may be detected using positron emission tomography (PET), single photon emission computed tomography (SPECT), MRI, bioluminescence, or fluorescence. [00118] In one aspect, the present disclosure provides a method for detecting the presence of a DOTA-based hapten in vivo comprising (a) administering to a subject an amount of a recombinant mammalian cell of the present technology that is effective to establish a xenograft, (b) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (c) detecting the presence of the DOTA-based hapten in the subject by detecting radioactive levels emitted by the DOTA-based hapten that are higher than a reference value. The radioactive levels emitted by the DOTA-based hapten may be detected using positron emission tomography (PET) or single photon emission computed tomography (SPECT). In some embodiments, the reference value is expressed as injected dose per gram (%ID/g). The reference value may be calculated by measuring the radioactive levels present in normal tissues, and computing the average radioactive levels present in normal tissues ^ standard deviation. In some embodiments, the ratio of radioactive levels between a tumor and normal tissue is about 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, 80:1, 85:1, 90:1, 95:1 or 100:1. [00119] Additionally or alternatively, in some embodiments, the method further comprises quantifying radioactive levels emitted by the DOTA-based hapten that is localized to the xenograft, and/or radioactive levels emitted by the DOTA-based hapten that is localized in one or more normal tissues or organs of the subject. In certain embodiments, the one or more normal tissues or organs are selected from the group consisting of heart, muscle, gallbladder, esophagus, stomach, small intestine, large intestine, liver, pancreas, lungs, bone, bone marrow, kidneys, urinary bladder, brain, skin, spleen, thyroid, and soft tissue. In any of the preceding embodiments, the method further comprises determining biodistribution scores by computing a ratio of the radioactive levels emitted by the DOTA-based hapten that is localized to the xenograft relative to the radioactive levels emitted by the DOTA-based hapten that is localized in the one or more tissues or organs of the subject. Additionally or alternatively, in some embodiments, the method further comprises calculating estimated absorbed radiation doses for the xenograft and the one or more tissues or organs of the subject based on the biodistribution scores. In some embodiments, the method further comprises computing a therapeutic index for the DOTA-based hapten based on the estimated absorbed radiation doses for the xenograft and the one or more tissues or organs of the subject. [00120] In one aspect, the present disclosure provides a method for tracking recombinant mammalian cells in a subject in vivo comprising (a) administering to the subject any embodiment of the recombinant mammalian cell described herein in an amount that is effective to establish a xenograft; (b) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten is configured to localize to the xenograft, and comprises, or is directly or indirectly linked to a detectable label; and (c) detecting signal emitted by the detectable label of the DOTA-based hapten that is localized to the xenograft. The detectable label may be a spectroscopic, photochemical, biochemical, immunochemical, electromagnetic, radioactive, fluorescent, chemifluorescent, or chemiluminescent label. In some embodiments, the method further comprises monitoring cell proliferation, cell growth, and/or apoptosis of the xenograft. [00121] In another aspect, the present disclosure provides a method for tracking recombinant mammalian cells in a subject in vivo comprising (a) administering to the subject any embodiment of the recombinant mammalian cell described herein in an amount that is effective to establish a xenograft; (b) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (c) detecting radioactive levels emitted by the DOTA-based hapten that is localized to the xenograft. In some embodiments, the method further comprises monitoring cell proliferation, cell growth, and/or apoptosis of the xenograft. [00122] In yet another aspect, the present disclosure provides a method for determining the therapeutically effective amount of a DOTA-based hapten for pretargeted radioimmunotherapy (PRIT) comprising (a) administering to the subject any embodiment of the recombinant mammalian cell described herein in an amount that is effective to establish a xenograft; (b) administering to the subject an amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (c) determining that the amount of the DOTA-based hapten is therapeutically effective for PRIT when the subject exhibits a decrease in xenograft volume compared to that observed in the subject prior to administration of the DOTA-based hapten. [00123] Additionally or alternatively, in some embodiments of the methods disclosed herein, the DOTA-based hapten is administered intravenously, intramuscularly, intraarterially, intrathecally, intracranially, intracapsularly, intraorbitally, intradermally, intraperitoneally, transtracheally, subcutaneously, intracerebroventricularly, orally, intratumorally, or intranasally. In certain embodiments, the DOTA-based hapten is administered into the cerebral spinal fluid or blood of the subject. [00124] In some embodiments of the methods disclosed herein, the radioactive levels emitted by the DOTA-based hapten are detected between 2 to 120 hours after the DOTA- based hapten is administered. In certain embodiments of the methods disclosed herein, the radioactive levels emitted by the DOTA-based hapten are expressed as the percentage injected dose per gram tissue (%ID/g). The reference value may be calculated by measuring the radioactive levels present in normal tissues, and computing the average radioactive levels present in normal tissues ^ standard deviation. In some embodiments, the reference value is the standard uptake value (SUV). See Thie JA, J Nucl Med.45(9):1431-4 (2004). In some embodiments, the ratio of radioactive levels between a xenograft and normal tissue is about 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, 80:1, 85:1, 90:1, 95:1 or 100:1. [00125] Examples of DOTA-based haptens include, but are not limited to, DOTA, Proteus-DOTA, DOTA-Bn, DOTA-desferrioxamine, DOTA-Phe-Lys(HSG)-D-Tyr- Lys(HSG)-NH₂, Ac-Lys(HSG)D-Tyr-Lys(HSG)-Lys(Tscg-Cys)-NH₂, DOTA-D-Asp-D- Lys(HSG)-D-Asp-D-Lys(HSG)-NH2; DOTA-D-Glu-D-Lys(HSG)-D-Glu-D-Lys(HSG)-NH2, DOTA-D-Tyr-D-Lys(HSG)-D-Glu-D-Lys(HSG)-NH2, DOTA-D-Ala-D-Lys(HSG)-D-Glu- D-Lys(HSG)-NH₂, DOTA-D-Phe-D-Lys(HSG)-D-Tyr-D-Lys(HSG)-NH₂, Ac-D-Phe-D- Lys(DOTA)-D-Tyr-D-Lys(DOTA)-NH2, Ac-D-Phe-D-Lys(DTPA)-D-Tyr-D-Lys(DTPA)- NH2, Ac-D-Phe-D-Lys(Bz-DTPA)-D-Tyr-D-Lys(Bz-DTPA)-NH2, Ac-D-Lys(HSG)-D-Tyr- D-Lys(HSG)-D-Lys(Tscg-Cys)-NH₂, DOTA-D-Phe-D-Lys(HSG)-D-Tyr-D-Lys(HSG)-D- Lys(Tscg-Cys)-NH₂, (Tscg-Cys)-D-Phe-D-Lys(HSG)-D-Tyr-D-Lys(HSG)-D-Lys(DOTA)- NH2, Tscg-D-Cys-D-Glu-D-Lys(HSG)-D-Glu-D-Lys(HSG)-NH2, (Tscg-Cys)-D-Glu-D- Lys(HSG)-D-Glu-D-Lys(HSG)-NH₂, Ac-D-Cys-D-Lys(DOTA)-D-Tyr-D-Ala-D- Lys(DOTA)-D-Cys-NH₂, Ac-D-Cys-D-Lys(DTPA)-D-Tyr-D-Lys(DTPA)-NH₂, Ac-D- Lys(DTPA)-D-Tyr-D-Lys(DTPA)-D-Lys(Tscg-Cys)-NH2, Ac-D-Lys(DOTA)-D-Tyr-D- Lys(DOTA)-D-Lys(Tscg-Cys)-NH2, NH2-benzyl (Bn) DOTA, DOTA-RGD, DOTA-PEG- E(c(RGDyK))₂, DOTA-8-AOC-BBN, DOTA-PESIN, p-NO2-benzyl-DOTA, DOTA-biotin- sarcosine (DOTA-biotin), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid mono (N- hydroxysuccinimide ester) (DOTA-NHS), and DOTATyrLysDOTA. [00126] In any and all embodiments of the methods disclosed herein, the radionuclide is an alpha particle-emitting isotope, a beta particle-emitting isotope, or an Auger-emitter. Examples of radionuclides include ²¹³Bi, ²¹¹At, ²²⁵Ac, ¹⁵²Dy, ²¹²Bi, ²²³Ra, ²¹⁹Rn, ²¹⁵Po, ²¹¹Bi, ²²¹Fr, ²¹⁷At, ²⁵⁵Fm, ⁸⁶Y, ⁹⁰Y, ⁸⁹Sr, ¹⁶⁵Dy, ¹⁸⁶Re, ¹⁸⁸Re, ¹⁷⁷Lu, ⁶⁷Cu, ¹¹¹In, ⁶⁷Ga, ⁵¹Cr, ⁵⁸Co, ^99mTc, ^103mRh, ^195mPt, ¹¹⁹Sb, ¹⁶¹Ho, ^189mOs, ¹⁹²Ir, ²⁰¹Tl, ²⁰³Pb, ⁶⁸Ga, ²²⁷Th, or ⁶⁴Cu. In any of the preceding embodiments of the methods disclosed herein, the subject is human. Kits [00127] The present technology provides kits for use in any of the methods described herein. In one aspect, the present disclosure provides kits including any of the recombinant mammalian cells disclosed herein and instructions for characterizing the in vitro and in vivo properties of candidate DOTA-based hapten probes that may be useful for imaging, dosimetry, in vivo cell tracking, flow cytometry, cell sorting/purification, fluorescence-guided surgery, immunohistochemistry, and pretargeted radioimmunotherapy applications. In any of the embodiments disclosed herein, the DOTA-based hapten probes comprise a detectable label (e.g., a chromogenic, enzymatic, radioisotopic, isotopic, fluorescent, toxic, chemiluminescent, nuclear magnetic resonance contrast agent or other label). [00128] In another aspect, the kits may include non-endogenous expression vectors comprising nucleic acids encoding any of the fusion proteins disclosed herein, mammalian host cells, and instructions for transforming the non-endogenous expression vectors into the mammalian host cells and using the transformed cells to assay the in vitro and in vivo properties of candidate DOTA-based hapten probes that may be useful for imaging, dosimetry, in vivo cell tracking, flow cytometry, cell sorting/purification, fluorescence-guided surgery, immunohistochemistry, and pretargeted radioimmunotherapy applications. The mammalian host cells may be recombinant, non-recombinant, cancerous, or non-cancerous. In any of the embodiments disclosed herein, the kits can also comprise, e.g., a buffering agent, a preservative, a stabilizing agent, cell culture medium, cell culture supplements and the like. [00129] The kits of the present technology can further comprise components necessary for detecting expression levels and/or activity of the reporter gene and/or the DOTA binding fragment of the fusion protein of the present technology. The kits can also contain a control sample or a series of control samples, which can be assayed and compared to the test sample. Each component of the kit can be enclosed within an individual container and all of the various containers can be within a single package, along with instructions for interpreting the results of the assays performed using the kit. The kits of the present technology may contain a written product on or in the kit container. The written product describes how to use the reagents contained in the kit, e.g., for characterizing the in vitro and in vivo properties of candidate DOTA-based hapten probes that may be useful for imaging, dosimetry, in vivo cell tracking, flow cytometry, cell sorting/purification, fluorescence-guided surgery, immunohistochemistry, and pretargeted radioimmunotherapy applications. In certain embodiments, the use of the reagents can be according to the methods of the present technology. EXAMPLES [00130] The present technology is further illustrated by the following Examples, which should not be construed as limiting in any way. Example 1: Materials and Methods [00131] Design and Assembly of Membrane-bound C825 Reporter Gene. A membrane- bound C825 gene construct containing the human CD4 endoplasmic reticulum signal sequence, the C825 scFv, and a CD4 transmembrane domain was purchased (Integrated DNA Technologies, Coralville, IA, USA). The IgG4-CH2CH3 spacer domain (hinge) was cloned using Gibson assembly in between the C825 scFv and the CD4 transmembrane domain to generate C825-hinge. eGFP was cloned into the vector to create C825-hinge-GFP (Fig.2A). Cloning was verified by sequencing (Integrated Genomics Operation, MSK, New York, NY) and transduction was confirmed by flow cytometric analysis using GFP fluorescence and/or anti-Fc antibody. [00132] Cell lines. Human embryonic kidney 293T (HEK 293T; 293T) and gpg29 fibroblasts (H29) were purchased from the American Type Culture Collection (ATCC; Manassas, VA). Plasmids encoding the SFG γ-retroviral (RV) vector were prepared as previously described in K. Ghani et al., Human gene therapy 20, 966-974 (2009). H29 packaging cells were transfected using CaPO4 (Promega) and the supernatant was subsequently used to generate 293T cells expressing C825-hinge-GFP (293T-C825-hinge- GFP). Cell lines were grown in RPMI-1640 medium (MSKCC Media Core). All media was supplemented with 10% fetal bovine serum, 2mMol L-glutamine, 100 IU/mL penicillin and 100 μg/mL streptomycin. [00133] Flow Cytometry. Data was collected using a Guava easyCyte HT Flow Cytometer or a BD LSR Fortessa and analyzed using Flowjo v10.4 software (Flowjo, Ashland, OR, USA). 293T cells were analyzed with APC conjugated anti-human Fc antibody (Jackson ImmunoResearch, West Grove, PA) to assess huC825 expression. [00134] Synthesis and Radiolabeling of [¹⁷⁷Lu]LuDOTA-Bn, [⁸⁶Y]YDOTA-Bn, [¹¹¹In]InPr, [²²⁵Ac]AcPr. Radiochemistry was performed in appropriately shielded chemical fume hoods equipped with electronic flow monitoring and sliding leaded glass windows. A CRC-55tR dose calibrator was used to measure radioactivity using manufacturer recommended calibration settings (Capintec Inc., Florham Park, NJ). Buffers and water used for radiochemical synthesis were treated with 5% (w/v) Chelex ion exchange resin (BT Chelex 100 Resin, Bio-Rad Inc., Hercules, CA) to remove adventitious heavy metals. Plasticware (e.g., pipet tips and microcentrifuge tubes) were trace metal grade/RNA grade. Radio-HPLC was performed on a Shimadzu Prominence HPLC system comprised of an LC-20AB dual pump module, DGU-20A3R degasser, SIL-20ACHT autosampler, SPD-20A UV-Vis detector and a Bioscan Flow-Count B-FC-1000 with PMT/NaI radioactivity detector in-line. Separations were run on an analytical 4.6 x 250 mm Gemini-NX C18 or Fusion RP C18 HPLC column (Phenomenex, Inc. Torrance, CA). HPLC conditions were: mobile phase A – 10 mM pH 5 NH4OAc, B - CH3CN, 1.0 mL/min flow rate, λ = 254 nm, injection volume 5– 20 µL, gradient: 0 % B to 40 % B over 10 min. Samples of free radiometals, reaction mixtures and purified products were diluted 1:5 in 5 mM DTPA or EDTA prior to analysis. Multiple peaks were usually observed due to conformational isomerism of radiometallated DOTA species. Attempts to isolate a single peak was impractical and ultimately unnecessary, because re-isomerization/re-equilibration occurs rapidly, and all conformer peaks disappear when bound by the anti-[M]DOTA radiohapten capture platform (C825). [00135] Radiosynthesis of [¹⁷⁷Lu]LuDOTA-Bn. Radiolabeled DOTA-Bn was prepared as previously described by incubating DOTA-Bn (p-NH₂-Bn-DOTA, molecular weight 655 Da; Macrocyclics) and ¹⁷⁷Lu (carrier-added, specific activity about 1,110 GBq/mg; Perkin Elmer) at 80 °C for 1 h. See Cheal et al., Molecular Cancer Therapeutics 13, 1803-1812 (2014). [00136] Radiosynthesis of [¹¹¹In]InPr. No carrier added [¹¹¹In]InCl₃ (47.4 MBq/1.28 mCi) in 50 µL of 0.05 M HCl (Nuclear Diagnostic Products, Inc. Plainview, NY, USA) was transferred to a metal-free 0.5 mL microcentrifuge tube and diluted with 50 µL of metal-free 0.5M NH₄OAc (pH 5.3) and mixed gently. 2.6 nmoles of proteus-DOTA (Pr; DO3A-PEG₄- [^natLu]Lu-DOTA-Bn; 2.6µL of 1mM solution in water) was added to this solution, mixed gently by pipetting and placed in a heat block at 90°C for 60 min. After cooling for 5 min, the entirety was gravity loaded on a 30 mg Strata-X SPE cartridge (Phenomenex, Torrance CA), which had been equilibrated with 1 mL of ethanol and 1 mL of water. Water (100 µL) was used to rinse the reaction tube and passed through the cartridge. The column was washed slowly dropwise with 200 µL of water, and gently blown dry with nitrogen gas. The product was slowly eluted dropwise with 200 µL of ethanol, formulated in normal saline (Hospira, Lake Forest, IL) and sterile filtered to obtain “[¹¹¹In]InPr” [¹¹¹In]InDO3ABn-PEG4- [^natLu]LuDOTA-Bn (40.7 MBq (1.10 mCi), 86% ncd yield, AM = 18.5 MBq/nmol (500µCi/nmol) at time of synthesis. Radio-HPLC of crude and purified material confirmed that no free radiometal remained (major isomer tR=8.0 min, 97.5% radiochemical purity). [00137] Radiosynthesis of [⁸⁶Y]YDOTA-Bn. Radiosynthesis of [⁸⁶Y]YDOTA-Bn was prepared as previously described (Cheal et al., Molecular Cancer Therapeutics 13, 1803- 1812 (2014)). [⁸⁶Y]YCl₃ (252 MBq/6.80 mCi) in 300 µL of 0.04M HCl (MDACC CRF; Cyclotron Radiochemistry Facility MD Anderson Cancer Center, Houston, TX) was transferred to a metal-free 0.5 mL microcentrifuge tube and diluted with 300 µL of metal-free 0.5M NH₄OAc (pH 5.3) and mixed gently. “DOTA-Bn”, 4’-aminobenzyl DOTA (Macrocyclics, Inc. Plano, TX, USA; 305 nmol, 10 µL of 20 mg/mL solution in water) was added to this solution, and mixed gently and placed in a heat block at 80°C for 40 min. After cooling for 5 min, complete conversion was confirmed by radio-HPLC, and the crude material was gravity loaded on a 30 mg Strata-X SPE cartridge (Phenomenex, Torrance CA), which had been equilibrated with 1 mL of ethanol and 1mL of water. The column was washed with 100 µL of water, then gently blown dry with nitrogen gas. The product, [⁸⁶Y]YDOTA-Bn, was slowly eluted dropwise with 400 µL of ethanol (221 MBq/5.98mCi; 87.7% ndc yield), then formulated with normal saline (Hospira, Lake Forest, IL) and sterile filtered (99.4% radiochemical purity; minor isomer t_R=7.1min, major isomer t_R=7.4 min). [00138] Radiosynthesis of [²²⁵Ac]AcPr. Carrier free [²²²Ac]Ac (2.146 x 10⁶ GBq/g [5.80 x 10⁴ Ci/g]) was obtained from Oak Ridge National Laboratory as a dried nitrate residue. The [²²⁵Ac]Ac nitrate was dissolved in 0.2 M Optima grade hydrochloric acid for subsequent radiochemistry. [²²⁵Ac]Ac-activity measurements were made at secular equilibrium using a CRC-15R radioisotope calibrator (Capintec, Inc.) set at 775 and multiplied the displayed activity value by 5; samples were positioned at the bottom and center of the well for measurement. [²²⁵Ac]Ac nitrate (20 µL, 2.442 MBq / 66.0 µCi) was mixed with 100 µL of 10 mg/mL Proteus-DOTA (Pr) (1 mg; 0.74 µmoles) in a 1.8 mL Nunc vial. Next, 15 µL of L-ascorbic acid solution (150 g/L) and 100 µL of 3 M ammonium acetate solution was added. The pH of the solution was verified to be ~5.5 by spotting 1 µL of the reaction mixture onto Hydrion pH paper (range, 5.0-9.0). The reaction was incubated at 60°C for 30 min, and then purified using a Sephadex C-25 column pre-equilibrated with 6 mL of normal sterile isotonic saline solution (NSS). The reaction mixture was added to the column and eluted with 4 mL of NSS to recover all removable activity ([²²⁵Ac]AcPr; the % activity that washed off the resin was the % [²²⁵Ac]Ac that was complexed by Pr). The activity of ([²²⁵Ac]AcPr) was determined to be 2.294 MBq [62.0 µCi], giving a radiochemical yield of 94%. The final specific activity (SA) was 2.22 GBq/g [0.06 Ci/g] or 3108 GBq/mol [84 Ci/mol]. [00139] Determination of In Vitro Uptake of the Reporter Probes [¹⁷⁷Lu]LuDOTA-Bn and [¹¹¹In]InPr, Assessment of binding kinetics and quantitation of binding sites. 500,000293T or 293T-C825 cells were suspended in RPMI + 10% fetal calf serum and incubated at 37 °C for 1 h with [¹⁷⁷Lu]LuDOTA-Bn (3.7 kBq; S.A.3.7 MBq/nmoles) or with [¹¹¹In]InPr (3.7 kBq; S.A.18.5 MBq/nmoles) (0.00008 - 8 nM; in triplicate) in a final volume of 300 µL. Tubes were incubated with gentle shaking at 37 °C for 1 h. Cells were harvested onto glass fiber filters (Whatman) and washed twice with cold TRIS buffer (Brandel M-24T), counted in a WIZARD2 automatic γ-counter (PerkinElmer, Waltham, MA) and labeling efficiency (%LE; i.e., radioactivity bound to the cells) was calculated. Untransduced 293T cells served as a negative control. All experiments were conducted in triplicate. Activity standards were also harvested each time to correct for non-specific binding. Standard saturation binding parameters were obtained using GraphPad Prism. [00140] Animal Experiments – Xenograft model to assess kinetics of radio-hapten capture using [⁸⁶Y]YDOTA-Bn. 293T-C825 cells (3 × 10⁶ in 200 µL) were injected subcutaneously (s.c.) over the left shoulder and 293T cells (3 × 10⁶ in 200 µL) over the right shoulder into female athymic nude mice (6-8 weeks old, obtained from Envigo). Seven days later, the mice received intravenous (IV) radiotracer administration followed by PET imaging studies. [00141] Small-Animal PET/CT Imaging. Small-animal PET/CT scans were performed using the Inveon PET/CT system (Siemens). Mice were anesthetized using 1.5-2% isoflurane (Baxter Healthcare) and i.v. injected with [⁸⁶Y]Y-DOTA-Bn (3.7 MBq). At 0.5, 1.5, 18, and 22 h, the same mice underwent 30-min static scans. Data were corrected for decay and detector dead-time and images were reconstructed by 3D OSEM maximum a posteriori (2 OSEM iterations; 18 MAP iterations) into 128 ^128 matrix (0.78 ^0.78 ^0.80 mm voxel dimensions). Image counts per voxel per second were converted to activity concentrations (Bq/mL) using a system-specific calibration factor, and subsequently normalized by injected activity to units of percentage injected activity per gram (%ID/g) decay corrected to time of injection. CT scans were reconstructed using a modified Feldkamp cone beam reconstruction algorithm to generate 512 ^512 ^768 voxel image volumes (0.197 ^0.197 ^0.197 mm voxel dimensions). [00142] Image-based Biodistribution. Volumes of interest (VOIs) were defined using a combination of manual and semi-automatic segmentation techniques within 3D Slicer v4.10; CT anatomical guidance was used in segmenting the heart/heart contents, lungs, liver, stomach contents, intestine contents, kidneys, skeleton, muscle, and tumor tissue. PET guidance was used for determining activity within the urinary bladder. To correct mean intensities in small-scale VOIs (tumor tissue, gallbladder, kidneys) for partial volume effects arising from the considerable positron range of ⁸⁶Y, the following equation was utilized (Kessler et al., J Comput Assist Tomogr 8, 514-522 (1984)): [00143] where NT is the corrected mean VOI intensity, NT,m is the measured intensity, NB is the background intensity (taken as muscle). Hot-spot and cold-spot recovery coefficients (HSRC and CSRC, respectively) used in calculation of N_T’s, were computed via Monte Carlo simulation in PHITS v3.10(Sato et al., Journal of Nuclear Science and Technology 55, 684- 690 (2018)) using the method of Carter et al., Molecular imaging and biology 22, 73-84 (2020). [00144] Biodistribution Studies of [⁸⁶Y]Y-DOTA-Bn, [¹⁷⁷Lu]Lu-DOTA-Bn, and [²²⁵Ac]Ac- Pr. Biodistribution studies were performed to measure the uptake of the radiotracers in organs and normal tissues. 293T-huC825 cells (3 × 10⁶ in 200 μL) were injected subcutaneously over the right shoulder and 293T cells (3 × 10⁶ in 200 μL) were injected subcutaneously over the left shoulder of 6–8 week old female athymic nude mice (Envigo, Indianpolis, IN). Seven days later, the mice received intravenous radiotracer administration of [⁸⁶Y]Y-DOTA-Bn (3.7 MBq) and were sacrificed at 0.5, 3, 20 and 48 h p.i. for biodistribution analysis of the tracer in tumor and selected normal tissues (n = 4–5 per time point). For [¹⁷⁷Lu]Lu-DOTA-Bn (3.7 MBq) mice were sacrificed at 0.5, 3, 20 and 48 h and at 7 d p.i. (n = 4–5 per time point). For [²²⁵Ac]Ac-Pr (SA: 37 kBq/742 pmol) mice were sacrificed at 0.5, 3, 20 h and at 7 and 12 d p.i. (n = 4–5 per time point). Mice were euthanized by asphyxiation with CO₂. Blood was collected immediately via cardiac puncture while the organs of interest was harvested. The wet weights of each tissue were calculated, and the radioactivity bound to each organ was counted in a WIZARD² automatic γ-counter (PerkinElmer). The percentage of tracer uptake expressed as percentage injected dose per gram was calculated as the activity bound to the tissue per organ weight per actual injected dose decay corrected to the time of counting. [00145] Dosimetry. Dosimetry of [¹⁷⁷Lu]Lu-DOTA-Bn, and [²²⁵Ac]Ac-Pr was performed using two different approaches: 1) using time-integrated activity coefficients derived directly from measured biodistribution of [¹⁷⁷Lu]Lu-DOTA-Bn or [²²⁵Ac]Ac-Pr, and 2) using time- integrated activity coefficients derived from [⁸⁶Y]Y-DOTA-Bn biodistribution. In the second approach, %ID/g values at each time point (i.e. biological uptake/clearance) of [¹⁷⁷Lu]Lu- DOTA-Bn and [²²⁵Ac]Ac-Pr were assumed to be given by measured %ID/g values for [86Y]Y-DOTA-Bn; activity-time curves for [¹⁷⁷Lu]Lu-DOTA-Bn and [²²⁵Ac]Ac-Pr were then derived by applying the respective multiplicative factors for physical decay to express the activity-time curves as ‘effective clearance’ vs. time. [00146] Mean organ uptake values were transposed into a mouse dosimetry phantom utilizing a relative organ mass scaling method. For most organs, the adjusted activity-time curves were integrated via the trapezoidal method until the last measured time point, after which clearance was assumed to occur by radionuclide physical decay only. The time- integrated activities were normalized by the administered activity to obtain time-integrated activity coefficients, in units of hours, needed for input into the PARaDIM Monte Carlo dosimetry system. Measured blood activity concentrations were assumed to be representative of the bone marrow. The time integrated activity coefficient for the urinary bladder was obtained using whole-body activity clearance constants input into the voiding bladder model implemented in OLINDA 1.1 software. For the walled organs consisting of separate ‘wall’ and ‘contents’ regions, the time-integrated activity coefficients were assigned to the contents. For all ²²⁵Ac dosimetry calculations, decay of the radioactive progeny was assumed to occur at the same location as the original ²²⁵Ac decay. Absorbed dose contributions for each member of the decay chain were summed, with appropriate weighting to account for the branching ratios. [00147] Assessment of in vivo targeting with [²²⁵Ac]AcPr. 293T-C825 cells (3 × 10⁶ in 200 µL) were injected subcutaneously (s.c.) over the left shoulder and 293T cells (3 × 10⁶ in 200 µL) over the right shoulder into female athymic nude mice (6-8 weeks old, obtained from Envigo). Seven days later, the mice received intravenous (IV) radiotracer administration of [²²⁵Ac]AcPr (SA: 37 kBq/742 pmol) and sacrificed at 24 h p.i. for biodistribution analysis of [²²⁵Ac]AcPr in tumor and selected normal tissues. [00148] To assess tumor growth, a total of 20 mice were inoculated s.c. with 293T-C825 (3 ×10⁶ in 200 µL) or 293T cells (3 ×10⁶ in 200 µL) over the right shoulder. Seven days later, the mice received intravenous (IV) radiotracer administration of [²²⁵Ac]AcPr (SA: 37 kBq/742 pmol) and the mice and established tumors were monitored biweekly until 120 days or until mice reached the set endpoint (tumor diameter > 10 mm); tumor volumes (TVs) were estimated using the formula for the volume (V) of an ellipsoid: V=4/3π(length/2×width/2×height/2), with dimensions in millimeters. Mice were monitored for outward signs of toxicity, including lethargy, loss of appetite, or disseminated intravascular coagulation. Mice were euthanized when the TV was greater than 2000 mm³ or when they met euthanasia criteria (weight loss, signs of distress) in accordance with MSK’s Institutional Animal Care and Use Committee. [00149] Autoradiography and Immunohistochemical Staining. To evaluate the localization of [²²⁵Ac]AcPr in the tumor tissue, 293T and 293T-C825 tumors were harvested at 24 h p.i. and snap frozen in optimal-cutting-temperature compound (Tissue Tek). Tissue was cut into 10-µm slices using cryostat sectioning. Coronal cryosections were exposed to a storage phosphor autoradiography plate (Fujifilm, BAS-MS2325, Fuji Photo Film) overnight at -20°C for radiotracer localization and analyzed using ImageJ, version 1.47u (rsbweb.nih.gov/ij/). [00150] Immunohistochemistry was performed on a Leica Bond RX automated stainer using Bond reagents (Leica Biosystems, Buffalo Grove, IL), including a polymer detection system (DS9800, Novocastra Bond Polymer Refine Detection, Leica Biosystems). The chromogen was 3,3 diaminobenzidine tetrachloride (DAB), and sections were counterstained with hematoxylin. Staining was performed with primary antibodies against cytokeratin (CK WSS) (DAKO) and against Ki67 (Cell Signaling) and using the same and adjacent cryosections. Adjacent sections were hematoxylin- and eosin-stained for morphologic evaluation. Stained slides were evaluated by a pathologist. [00151] Statistics and Data Reporting. All experimental data are presented as mean±standard deviation. All in vitro experiments were performed in triplicate, Graph Pad Prism 7 software (Graph Pad software, Inc., La Jolla, CA) was used for statistical analysis. The differences between means were tested by appropriate tests including t-test. The significance level used was P < 0.05. Survival determined from the time of tumor cell injection was analyzed by the Kaplan-Meier method. Example 2: Generation of 293T-C825 Cells and In vitro Characterization [00152] To generate 293T cells expressing C825 (293T-C825), a retroviral vector encoding the scFv C825-GFP fusion protein (Fig.2A) was transduced into 293T cells. Subsequently, these cells were sorted using flow cytometric analysis and sorting for GFP+ cells. C825 cell surface expression of > 95 % was verified by flow cytometry using an anti- Fc antibody, which binds to the hinge domain (Fig.2B). In in vitro binding assays (Fig.2C), 293T-C825 cells exhibited high accumulation of [¹⁷⁷Lu]LuDOTA-Bn, whereas low accumulation was noted in 293T cells. Comparable ratios were observed following incubation with [¹¹¹In]In Pr. A scheme of the DOTA-based radiohapten probes used in these studies and their radiosynthetic details are shown in Fig.1 and Fig.7. To further characterize the in vitro kinetics of radiohapten capture and cell surface expression of the reporter gene, standard saturation binding assays were performed using [¹¹¹In]InPr (Fig.2D). Three independent saturation binding assays were used to determine a mean Kd (equilibrium binding constant) of 240 ± 122 pM and a mean Bmax (sites/cell) of 17000 ± 4400, mean R² of 0.983 ± 0.006. Thus, 293T-C825 cells expressed membrane-bound C825, thus permitting specific binding of DOTA-based radiohapten probes in vitro. The observed picomolar binding affinity facilitates efficient and rapid hapten binding to C825-expressing 293T cells, which is a critical feature for in vivo theranostic applications. Example 3: In vivo PET/CT Imaging using [⁸⁶Y]YDOTA-Bn in Xenografts Harboring 293T- C825 Cells [00153] To assess the suitability of using 293T-C825 cells as a test system for imaging as well as to measure the kinetics of the radiohapten capture in vivo, experiments in nude mice bearing subcutaneously implanted xenografts of 293T-C825 cells were initially conducted and xenografts of wild-type 293T cells were used as a control. [00154] Following i.v. injection of [⁸⁶Y]YDOTA-Bn, PET/CT scans demonstrated uptake at the site of 293T-C825 xenografts as early as at 0.5 h post injection (4.08 ± 2.67 %ID/g) (Figs.3A-3C, and Figs.8-9), whereas uptake that was only minimally above blood pool was seen in 293T tumors (2.07 ± 0.50 %ID/g, n = 3). Tracer uptake persisted in 293T-C825 tumors, whereas it continuously cleared from 293T tumors. [⁸⁶Y]YDOTA-Bn cleared rapidly from normal organs and was eliminated predominantly renally (~80% of administered activity excreted to the urine within 30 min p.i.), which was consistent with previous reports (Cheal et al., European Journal Nuclear Medicine and Molecular Imaging 43, 925-937 (2016); Orcutt et al., Molecular imaging and biology 13, 215-221 (2011)). Maximal absolute 293T-C825 tumoral uptake was observed at 22 h and was significantly higher than 293T control (p = 0.0079). Highest tumor-to-normal background contrast was observed at later time points. These results suggest that [⁸⁶Y]YDOTA-Bn imaging be performed at least 1.5 h post-injection to allow for clearance of the radiotracer from tissues and maximize tumor signal to background. Waiting longer than 24-36 h may be suboptimal due to sensitivity losses given the 14.7 h half-life of ⁸⁶Y, although longitudinal ⁸⁶Y imaging for dosimetry has been demonstrated over 4−5 days. Example 4: Dosimetry Studies in Xenografts Harboring 293T-C825 Cells [00155] [⁸⁶Y]YDOTA-Bn biodistribution data were used to prospectively estimate dosimetry for the purposes of determining appropriate administered activities for the α- emitting therapeutic analogue [²²⁵Ac]AcPr and for the β-emitting therapeutic analogue [¹⁷⁷Lu]LuDOTA-Bn in mice. [00156] These comparisons entailed Monte Carlo dosimetry computations, which utilized PARaDIM and the MOBY mouse phantom, (1) derived directly from measured biodistributions of [¹⁷⁷Lu]Lu-DOTA-Bn and [²²⁵Ac]Ac-Pr (Figs.12A-12C) as a quantitative “gold standard” estimate, or (2) corresponding prospective dosimetry estimates extrapolated based on the assumption that the biokinetics of [²²⁵Ac]Ac-Pr and [¹⁷⁷Lu]Lu-DOTA-Bn are equivalent to those of [⁸⁶Y]Y-DOTA-Bn. The estimated or measured biokinetic data were appropriately adjusted for radioactive decay and integrated via the trapezoidal method to obtain time-integrated activity coefficients needed for dosimetry calculations. [00157] Importantly, these estimates are in first order due to the limited time window for [⁸⁶Y]YDOTA-Bn imaging (limited by half-life). Time-integrated activity coefficients were estimated under the assumption that biological clearance (namely, whole organ mean standardized uptake values as a function of time) was equivalent among [⁸⁶Y]YDOTA-Bn, [²²⁵Ac]AcPr and [¹⁷⁷Lu]LuDOTA-Bn. Further, it was assumed that clearance following the last imaging time-point (22 h) was due to radioactive decay only, and thus the absorbed dose estimates likely represent upper limits. Highest radiation absorbed doses were calculated for the kidneys, urinary bladder wall, and gallbladder wall (Figs.4A-4C). The critical organ for [¹⁷⁷Lu]Lu-DOTA-Bn was observed to be the urinary bladder wall, which received a mean radiation absorbed dose coefficient of 46.9 cGy/MBq. For [²²⁵Ac]Ac-Pr, the critical organs were the kidneys and the urinary bladder wall (2890 and 2670 cGy/MBq, respectively). [00158] Mean estimated absorbed doses (cGy/MBq) of [²²⁵Ac]AcPr to 293T-C825, bone marrow, liver, and kidney were 15870 (range 3296–39419), 120 (range 95–169), 278 (range 247–324) and 1283 (range 989–1517), respectively. Mean estimated absorbed doses (cGy/MBq) of [¹⁷⁷Lu]LuDOTA-Bn to 293T-C825, bone marrow, liver, and kidney were 47 (range 10–117), 0.5 (range 0.4–0.7), 1 (range 0.9–1.2) and 4 (range 3–5), respectively. Respective therapeutic indices (TIs) for [²²⁵Ac]AcPr for tumor radiation-absorbed dose of 107 (tumor/bone marrow) and 12 (tumor/kidney) could potentially be achieved. Respective potential therapeutic indices (TIs) for [¹⁷⁷Lu]LuDOTA-Bn for tumor radiation-absorbed dose of 80 (tumor/bone marrow) and 11 (tumor/kidney) were calculated. [00159] The dosimetry results are supported by the blood clearance data (Fig.13), which showed similar behavior of [⁸⁶Y]Y-DOTABn, [¹⁷⁷Lu]Lu-DOTA-Bn, and [²²⁵Ac]Ac-Pr at 0.5 h. Example 5: Ex vivo Biodistribution and Autoradiography Verify In vivo Targeting with [²²⁵Ac]AcPr in Xenografts Harboring 293T-C825 Cells [00160] A pilot study using the same cellular test system in nude mice was conducted to evaluate the relationship between systemically administered [²²⁵Ac]AcPr in tumor and normal tissues. Briefly, dual 293T/293T-C825 tumor bearing tumor-bearing mice (n = 4) were intravenously injected with [²²⁵Ac]AcPr (37 kBq; 742 pmol). Ex vivo biodistribution studies confirmed significant increased uptake in 293T-C825 tumors (0.59 ± 0.27 %ID/g) compared to 293T tumors (0.13 ± 0.09 %ID/g) (P = 0.009) (Fig.5A). Taking into account the tracer- specific activity and dose, this value corresponds to an absolute probe uptake of 4.34 ± 1.97 pmol/g. Substantial clearance from normal tissues, such as blood, and minimal accumulation in normal tissue including liver was seen. The rapid blood clearance was corroborated by the serial ex vivo biodistribution data (Figs.12A-12C, 13). The slightly higher accumulation in the kidneys is related to the predominant renal clearance. Intestinal uptake was variable. The rather low mean 293T-C825 tumor-to-kidney ratio of 0.6 in comparison to prior data with the higher specific activity preparation for the [⁸⁶Y]YDOTA-Bn yielding a mean tumor-to-kidney ratio of 13.9 at comparable time points suggests probable saturation of the receptors on the 293T-C825 tumors following [²²⁵Ac]AcPr administration. [00161] Autoradiography, H&E, and Ki67 staining of the 293T-C825 tumor tissue indicated that the areas with highest activity concentration corresponded to areas of inflammation (Fig.5B). There was no evidence of cytokeratin-positive cells except for mammary gland epithelial cells. A small proportion of the inflammatory cells had nuclear staining on ki67. The findings were consistent with focally extensive, chronic inflammation without evidence of neoplastic cells. In summary, no tumor was found on 8 consecutive sections examined from the sample shown in Fig.5B. Such area of chronic inflammation is often observed at subcutaneous tumor sites in mice after a tumor shows complete regression in response to a treatment. These results thus demonstrate a complete response of the tumor to [²²⁵Ac]AcPr administration. [00162] Minimal nonspecific tracer uptake in 293T tumor tissue by ARG (consisting of adipose tissue and skeletal muscle) was observed (Fig.5B). The adipose tissue contains a moderately well demarcated tumor composed of nests of epithelioid cells with a high nucleus:cytoplasm ratio. These cells show cytoplasmic immunoreactivity for cytokeratin (CK WSS), and a very high proportion (> 95%) of these cells show nuclear Ki67 immunoreactivity. Thus, the 293T sample showed a tumor consistent with an undifferentiated epithelial neoplasm based on morphology on H&E and cytokeratin expression on IHC. The 293T tumor was highly proliferative based on ki67 IHC staining. [00163] To evaluate the in vivo growth of unmodified 293T and 293T-huC825 in mice not treated with [²²⁵Ac]Ac-Pr, twice weekly caliper-based tumor measurements were performed until the mice needed to be sacrificed. These results showed comparable and continuous in vivo growth (Fig.14). Example 6: In vivo Treatment with [²²⁵Ac]AcPr Results in Improved Overall Survival [00164] To assess treatment efficacy, 293T or 293T-C825 bearing tumor-bearing mice (n = 10 per cohort) were intravenously injected with [²²⁵Ac]AcPr (37 kBq; 742 pmol). Tumor response data from the two treatment groups are shown in Figs.6A-6B. In the 293T-C825 group, 7 of 10 mice achieved complete response and remained tumor free until the end of the study period (120 d post-treatment). In the control group, 2 of 10 mice remained tumor free. Of note, these two mice had non-measurable tumors at the day of the treatment. Nevertheless, these mice were not excluded from the treatment as no minimal tumor volume at the day of the treatment had been defined. The treatment with [²²⁵Ac]AcPr resulted in significant improved survival in the 293T-C825 group (P = 0.006) (Fig.6B). No systemic toxicity such as signs of lethargy, loss of appetite or body weight (Fig.10) was observed. Based on dose calculations and prior data, no acute toxicity nor chronic toxicity such as radiation damage to the kidneys were expected nor observed (Cheal et al., Journal Nuclear Medicine 59:123 (2018)). In view of the rather low specific activity, the observed treatment efficacy indicates potential for improved outcomes and higher TIs upon using a higher specific activity preparation of [²²⁵Ac]AcPr. [00165] Fig.11 shows that [¹⁷⁷Lu]LuDOTA-Bn radiohapten (0.1 µCi) binds with variable magnitude (4%, 2% and 9%, respectively) to membrane-bound C825-expressing 293T cells over 1 hr, whereas no significant uptake was observed in 293T control cells (reported as mean ± SD). EXEMPLARY EMBODIMENTS [00166] The present disclosure may be described in terms of the following non-limiting embodiments: [00167] Embodiment 1: The present application in one aspect provides a fusion protein comprising a DOTA binding fragment fused to a transmembrane domain, and a reporter gene, wherein the DOTA binding fragment comprises a heavy chain immunoglobulin variable domain (V_H) sequence and a light chain immunoglobulin variable domain (V_L) sequence of SEQ ID NO: 1 and SEQ ID NO: 5, respectively. [00168] Embodiment 2: The fusion protein of Embodiment 1, wherein the sequence of an intra-peptide linker between the V_H domain sequence and the V_L domain sequence in the DOTA binding fragment is any one of SEQ ID NOs: 9-11. [00169] Embodiment 3: The fusion protein of Embodiment 1 or Embodiment 2, wherein the V_H domain sequence is located at the N-terminus or the C-terminus of the V_L domain sequence. [00170] Embodiment 4: The fusion protein of any one of Embodiments 1-3, wherein the DOTA binding fragment is located at the N-terminus of the transmembrane domain. [00171] Embodiment 5: The fusion protein of any one of Embodiments 1-4, wherein the reporter gene is located at the C-terminus of the transmembrane domain. [00172] Embodiment 6: The fusion protein of any one of Embodiments 1-5, further comprising a spacer domain interspersed between the DOTA binding fragment and the transmembrane domain. [00173] Embodiment 7: The fusion protein of Embodiment 6, wherein the spacer domain is a Fc domain. [00174] Embodiment 8: The fusion protein of Embodiment 7, wherein the Fc domain comprises a Fc fragment of human IgG. [00175] Embodiment 9: The fusion protein of Embodiments 8, wherein the Fc fragment of human IgG comprises the amino acid sequence of any one of SEQ ID NOs: 12-16. [00176] Embodiment 10: The fusion protein of any one of Embodiments 1-9, wherein the transmembrane domain comprises an amino acid sequence that is at least 90% identical to an amino acid sequence of a transmembrane region of CD8, CD28, CD3ζ, or CD4. [00177] Embodiment 11: The fusion protein of any one of Embodiments 1-10, wherein the transmembrane domain comprises the amino acid sequence of SEQ ID NO: 17. [00178] Embodiment 12: The fusion protein of any one of Embodiments 1-11, wherein the reporter gene is a fluorescent reporter gene, a chemiluminescent reporter gene, or a bioluminescent reporter gene. [00179] Embodiment 13: The fusion protein of Embodiment 12, wherein the fluorescent reporter gene is GFP, YFP, CFP, RFP, TagBFP, Azurite, EBFP2, mKalama1, Sirius, Sapphire, T-Sapphire, ECFP, Cerulean, SCFP3A, mTurquoise, monomeric Midoriishi-Cyan, TagCFP, mTFP1, EGFP, Emerald, Superfolder GFP, Monomeric Azami Green, TagGFP2, mUKG, mWasabi, EYFP, Citrine, Venus, SYFP2, TagYFP, Monomeric Kusabira-Orange, mKOκ, mKO2, mOrange, mOrange2, mRaspberry, mCherry, dsRed, mStrawberry, mTangerine, tdTomato, TagRFP, TagRFP-T, mApple, mRuby, mPlum, HcRed-Tandem, mKate2, mNeptune, NirFP, TagRFP657, IFP1.4, iRFP, mKeima Red, LSS-mKate1, LSS- mKate2, PA-GFP, PAmCherry1, PATagRFP, Kaede (green), Kaede (red), KikGR1 (green), KikGR1 (red), PS-CFP2, PS-CFP2, mEos2 (green), mEos2 (red), PSmOrange, or Dronpa. [00180] Embodiment 14: The fusion protein of Embodiment 12, wherein the bioluminescent reporter gene is Aequorin, firefly luciferase, Renilla luciferase, red luciferase, luxAB, or nanoluciferase. [00181] Embodiment 15: The fusion protein of Embodiment 12, wherein the chemiluminescent reporter gene is β-galactosidase, horseradish peroxidase (HRP), or alkaline phosphatase. [00182] Embodiment 16: The fusion protein of any one of Embodiments 1-15, wherein the fusion protein comprises the amino acid sequence of SEQ ID NO: 18. [00183] Embodiment 17: The fusion protein of any one of Embodiments 1-16, further comprising an endoplasmic reticulum signal sequence. [00184] Embodiment 18: The fusion protein of any one of Embodiments 1-17, wherein the fusion protein does not include an internal ribosome entry site (IRES), or a 2A self-cleaving peptide. [00185] Embodiment 19: A recombinant nucleic acid sequence encoding the fusion protein of any one of Embodiments 1-18. [00186] Embodiment 20: A recombinant nucleic acid sequence comprising SEQ ID NO: 19. [00187] Embodiment 21: An expression vector comprising the recombinant nucleic acid sequence of Embodiment 19 or Embodiment 20. [00188] Embodiment 22: The expression vector of Embodiment 21, wherein the recombinant nucleic acid sequence is operably linked to an expression control sequence. [00189] Embodiment 23: The expression vector of Embodiment 22, wherein the expression control sequence is an inducible promoter or a constitutive promoter. [00190] Embodiment 24: A recombinant mammalian cell comprising the expression vector of any one of Embodiments 21-23. [00191] Embodiment 25: The recombinant mammalian cell of Embodiment 24, wherein the expression vector is a plasmid, a cosmid, a bacmid, a bacterial artificial chromosome (BAC), a yeast artificial chromosome (YAC), or a viral vector. [00192] Embodiment 26: The recombinant mammalian cell of Embodiment 24 or Embodiment 25, wherein the expression control sequence is heterologous or native to the recombinant mammalian cell. [00193] Embodiment 27: The recombinant mammalian cell of any one of Embodiments 24-26, wherein the mammalian cell is cancerous or non-cancerous. [00194] Embodiment 28: The recombinant mammalian cell of any one of Embodiments 24-27, wherein the mammalian cell is a human embryonic kidney 293 cell. [00195] Embodiment 29: A kit comprising the recombinant mammalian cell of any one of Embodiments 24-28 and instructions for use. [00196] Embodiment 30: A kit comprising the expression vector of any one of Embodiments 21-23, mammalian host cells, and instructions for use. [00197] Embodiment 31: A method for determining in vitro binding kinetics of a DOTA- based hapten comprising contacting a DOTA-based hapten with the recombinant mammalian cell of any one of Embodiments 24-28, and determining the binding activity of the DOTA- based hapten to the recombinant mammalian cell, wherein the recombinant mammalian cell exhibits cell surface expression of the fusion protein of any one of Embodiments 1-18, and wherein the DOTA-based hapten comprises, or is directly or indirectly linked to a detectable label. [00198] Embodiment 32: The method of Embodiment 31, wherein the binding activity of the DOTA-based hapten is determined via saturation binding assays or competition binding assays. [00199] Embodiment 33: The method of Embodiment 31 or 32, further comprising determining a mean equilibrium dissociation constant (Kd) of the DOTA-based hapten and a mean Bmax (sites/cell) for the fusion protein. [00200] Embodiment 34: A method for detecting the presence of a DOTA-based hapten in a subject that has been administered the recombinant mammalian cell of any one of Embodiments 24-28 in an amount that is effective to establish a xenograft comprising (a) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (b) detecting the presence of the DOTA-based hapten in the subject by detecting radioactive levels emitted by the DOTA-based hapten that are higher than a reference value. [00201] Embodiment 35: The method of Embodiment 34, wherein the radioactive levels emitted by the DOTA-based hapten are detected using positron emission tomography (PET) or single photon emission computed tomography (SPECT). [00202] Embodiment 36: The method of Embodiment 34 or Embodiment 35, further comprising quantifying radioactive levels emitted by the DOTA-based hapten that is localized to the xenograft. [00203] Embodiment 37: The method of any one of Embodiments 34-36, further comprising quantifying radioactive levels emitted by the DOTA-based hapten that is localized in one or more tissues or organs of the subject, wherein the one or more tissues or organs are selected from the group consisting of heart, muscle, gallbladder, esophagus, stomach, small intestine, large intestine, liver, pancreas, lungs, bone, bone marrow, kidneys, urinary bladder, brain, skin, spleen, thyroid, and soft tissue. [00204] Embodiment 38: The method of Embodiment 37, further comprising determining biodistribution scores by computing a ratio of the radioactive levels emitted by the DOTA- based hapten that is localized to the xenograft relative to the radioactive levels emitted by the DOTA-based hapten that is localized in the one or more tissues or organs of the subject. [00205] Embodiment 39: The method of Embodiment 38, further comprising calculating estimated absorbed radiation doses for the xenograft and the one or more tissues or organs of the subject based on the biodistribution scores. [00206] Embodiment 40: The method of Embodiment 39, further comprising computing a therapeutic index for the DOTA-based hapten based on the estimated absorbed radiation doses for the xenograft and the one or more tissues or organs of the subject. [00207] Embodiment 41: A method for tracking recombinant mammalian cells in a subject in vivo comprising (a) administering to the subject the recombinant mammalian cell of any one of Embodiments 24-28 in an amount that is effective to establish a xenograft; (b) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (c) detecting radioactive levels emitted by the DOTA-based hapten that is localized to the xenograft. [00208] Embodiment 42: The method of Embodiment 41, further comprising monitoring cell proliferation, cell growth, and/or apoptosis of the xenograft. [00209] Embodiment 43: A method for determining the therapeutically effective amount of a DOTA-based hapten for pretargeted radioimmunotherapy (PRIT) comprising (a) administering to the subject the recombinant mammalian cell of any one of Embodiments 24- 28 in an amount that is effective to establish a xenograft; (b) administering to the subject an amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (c) determining that the amount of the DOTA-based hapten is therapeutically effective for PRIT when the subject exhibits a decrease in xenograft volume compared to that observed in the subject prior to administration of the DOTA-based hapten. [00210] Embodiment 44: The method of any one of Embodiments 31-43, wherein the DOTA-based hapten is selected from the group consisting of DOTA, Proteus-DOTA, DOTA- Bn, DOTA-desferrioxamine, DOTA-Phe-Lys(HSG)-D-Tyr-Lys(HSG)-NH2, Ac-Lys(HSG)D- Tyr-Lys(HSG)-Lys(Tscg-Cys)-NH2, DOTA-D-Asp-D-Lys(HSG)-D-Asp-D-Lys(HSG)-NH2; DOTA-D-Glu-D-Lys(HSG)-D-Glu-D-Lys(HSG)-NH₂, DOTA-D-Tyr-D-Lys(HSG)-D-Glu- D-Lys(HSG)-NH2, DOTA-D-Ala-D-Lys(HSG)-D-Glu-D-Lys(HSG)-NH2, DOTA-D-Phe-D- Lys(HSG)-D-Tyr-D-Lys(HSG)-NH2, Ac-D-Phe-D-Lys(DOTA)-D-Tyr-D-Lys(DOTA)-NH2, Ac-D-Phe-D-Lys(DTPA)-D-Tyr-D-Lys(DTPA)-NH₂, Ac-D-Phe-D-Lys(Bz-DTPA)-D-Tyr- D-Lys(Bz-DTPA)-NH2, Ac-D-Lys(HSG)-D-Tyr-D-Lys(HSG)-D-Lys(Tscg-Cys)- NH2, DOTA-D-Phe-D-Lys(HSG)-D-Tyr-D-Lys(HSG)-D-Lys(Tscg-Cys)-NH2, (Tscg-Cys)- D-Phe-D-Lys(HSG)-D-Tyr-D-Lys(HSG)-D-Lys(DOTA)-NH₂, Tscg-D-Cys-D-Glu-D- Lys(HSG)-D-Glu-D-Lys(HSG)-NH₂, (Tscg-Cys)-D-Glu-D-Lys(HSG)-D-Glu-D-Lys(HSG)- NH2, Ac-D-Cys-D-Lys(DOTA)-D-Tyr-D-Ala-D-Lys(DOTA)-D-Cys-NH2, Ac-D-Cys-D- Lys(DTPA)-D-Tyr-D-Lys(DTPA)-NH₂, Ac-D-Lys(DTPA)-D-Tyr-D-Lys(DTPA)-D- Lys(Tscg-Cys)-NH₂, Ac-D-Lys(DOTA)-D-Tyr-D-Lys(DOTA)-D-Lys(Tscg-Cys)-NH₂, NH₂- benzyl (Bn) DOTA, DOTA-RGD, DOTA-PEG-E(c(RGDyK))2, DOTA-8-AOC-BBN, DOTA-PESIN, p-NO2-benzyl-DOTA, DOTA-biotin-sarcosine (DOTA-biotin), 1,4,7,10- tetraazacyclododecane-1,4,7,10-tetraacetic acid mono (N-hydroxysuccinimide ester) (DOTA- NHS), and DOTATyrLysDOTA. [00211] Embodiment 45: The method of any one of Embodiments 31-44, wherein the radionuclide is an alpha particle-emitting isotope, a beta particle-emitting isotope, or an Auger-emitter. [00212] Embodiment 46: The method of any one of Embodiments 31-45, wherein the radionuclide is ²¹³Bi, ²¹¹At, ²²⁵Ac, ¹⁵²Dy, ²¹²Bi, ²²³Ra, ²¹⁹Rn, ²¹⁵Po, ²¹¹Bi, ²²¹Fr, ²¹⁷At, ²⁵⁵Fm, ⁸⁶Y, ⁹⁰Y, ⁸⁹Sr, ¹⁶⁵Dy, ¹⁸⁶Re, ¹⁸⁸Re, ¹⁷⁷Lu, ⁶⁷Cu, ¹¹¹In, ⁶⁷Ga, ⁵¹Cr, ⁵⁸Co, ^99mTc, ^103mRh, ^195mPt, ¹¹⁹Sb, ¹⁶¹Ho, ^189mOs, ¹⁹²Ir, ²⁰¹Tl, ²⁰³Pb, ⁶⁸Ga, ²²⁷Th, or ⁶⁴Cu. EQUIVALENTS [00213] The present technology is not to be limited in terms of the particular embodiments described in this application, which are intended as single illustrations of individual aspects of the present technology. Many modifications and variations of this present technology can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the present technology, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the present technology. It is to be understood that this present technology is not limited to particular methods, reagents, compounds compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. [00214] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group. [00215] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like, include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth. [00216] All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.

Claims

CLAIMS 1. A fusion protein comprising a DOTA binding fragment fused to a transmembrane domain, and a reporter gene, wherein the DOTA binding fragment comprises a heavy chain immunoglobulin variable domain (VH) sequence and a light chain immunoglobulin variable domain (V_L) sequence of SEQ ID NO: 1 and SEQ ID NO: 5, respectively.

2. The fusion protein of claim 1, wherein the sequence of an intra-peptide linker between the VH domain sequence and the VL domain sequence in the DOTA binding fragment is any one of SEQ ID NOs: 9-11.

3. The fusion protein of claim 1 or claim 2, wherein the VH domain sequence is located at the N-terminus or the C-terminus of the VL domain sequence.

4. The fusion protein of any one of claims 1-3, wherein the DOTA binding fragment is located at the N-terminus of the transmembrane domain.

5. The fusion protein of any one of claims 1-4, wherein the reporter gene is located at the C-terminus of the transmembrane domain.

6. The fusion protein of any one of claims 1-5, further comprising a spacer domain interspersed between the DOTA binding fragment and the transmembrane domain.

7. The fusion protein of claim 6, wherein the spacer domain is a Fc domain.

8. The fusion protein of claim 7, wherein the Fc domain comprises a Fc fragment of human IgG.

9. The fusion protein of claim 8, wherein the Fc fragment of human IgG comprises the amino acid sequence of any one of SEQ ID NOs: 12-16.

10. The fusion protein of any one of claims 1-9, wherein the transmembrane domain comprises an amino acid sequence that is at least 90% identical to an amino acid sequence of a transmembrane region of CD8, CD28, CD3ζ, or CD4.

11. The fusion protein of any one of claims 1-10, wherein the transmembrane domain comprises the amino acid sequence of SEQ ID NO: 17.

12. The fusion protein of any one of claims 1-11, wherein the reporter gene is a fluorescent reporter gene, a chemiluminescent reporter gene, or a bioluminescent reporter gene.

13. The fusion protein of claim 12, wherein the fluorescent reporter gene is GFP, YFP, CFP, RFP, TagBFP, Azurite, EBFP2, mKalama1, Sirius, Sapphire, T-Sapphire, ECFP, Cerulean, SCFP3A, mTurquoise, monomeric Midoriishi-Cyan, TagCFP, mTFP1, EGFP, Emerald, Superfolder GFP, Monomeric Azami Green, TagGFP2, mUKG, mWasabi, EYFP, Citrine, Venus, SYFP2, TagYFP, Monomeric Kusabira- Orange, mKOκ, mKO2, mOrange, mOrange2, mRaspberry, mCherry, dsRed, mStrawberry, mTangerine, tdTomato, TagRFP, TagRFP-T, mApple, mRuby, mPlum, HcRed-Tandem, mKate2, mNeptune, NirFP, TagRFP657, IFP1.4, iRFP, mKeima Red, LSS-mKate1, LSS-mKate2, PA-GFP, PAmCherry1, PATagRFP, Kaede (green), Kaede (red), KikGR1 (green), KikGR1 (red), PS-CFP2, PS-CFP2, mEos2 (green), mEos2 (red), PSmOrange, or Dronpa.

14. The fusion protein of claim 12, wherein the bioluminescent reporter gene is Aequorin, firefly luciferase, Renilla luciferase, red luciferase, luxAB, or nanoluciferase.

15. The fusion protein of claim 12, wherein the chemiluminescent reporter gene is β- galactosidase, horseradish peroxidase (HRP), or alkaline phosphatase.

16. The fusion protein of any one of claims 1-15, wherein the fusion protein comprises the amino acid sequence of SEQ ID NO: 18.

17. The fusion protein of any one of claims 1-16, further comprising an endoplasmic reticulum signal sequence.

18. The fusion protein of any one of claims 1-17, wherein the fusion protein does not include an internal ribosome entry site (IRES), or a 2A self-cleaving peptide.

19. A recombinant nucleic acid sequence encoding the fusion protein of any one of claims 1-18.

20. A recombinant nucleic acid sequence comprising SEQ ID NO: 19.

21. An expression vector comprising the recombinant nucleic acid sequence of claim 19 or claim 20.

22. The expression vector of claim 21, wherein the recombinant nucleic acid sequence is operably linked to an expression control sequence.

23. The expression vector of claim 22, wherein the expression control sequence is an inducible promoter or a constitutive promoter.

24. A recombinant mammalian cell comprising the expression vector of any one of claims 21-23.

25. The recombinant mammalian cell of claim 24, wherein the expression vector is a plasmid, a cosmid, a bacmid, a bacterial artificial chromosome (BAC), a yeast artificial chromosome (YAC), or a viral vector.

26. The recombinant mammalian cell of claim 24 or claim 25, wherein the expression control sequence is heterologous or native to the recombinant mammalian cell.

27. The recombinant mammalian cell of any one of claims 24-26, wherein the mammalian cell is cancerous or non-cancerous.

28. The recombinant mammalian cell of any one of claims 24-27, wherein the mammalian cell is a human embryonic kidney 293 cell.

29. A kit comprising the recombinant mammalian cell of any one of claims 24-28 and instructions for use.

30. A kit comprising the expression vector of any one of claims 21-23, mammalian host cells, and instructions for use.

31. A method for determining in vitro binding kinetics of a DOTA-based hapten comprising contacting a DOTA-based hapten with the recombinant mammalian cell of any one of claims 24-28, and determining the binding activity of the DOTA-based hapten to the recombinant mammalian cell, wherein the recombinant mammalian cell exhibits cell surface expression of the fusion protein of any one of claims 1-18, and wherein the DOTA-based hapten comprises, or is directly or indirectly linked to a detectable label.

32. The method of claim 31, wherein the binding activity of the DOTA-based hapten is determined via saturation binding assays or competition binding assays.

33. The method of claim 31 or 32, further comprising determining a mean equilibrium dissociation constant (Kd) of the DOTA-based hapten and a mean Bmax (sites/cell) for the fusion protein.

34. A method for detecting the presence of a DOTA-based hapten in a subject that has been administered the recombinant mammalian cell of any one of claims 24-28 in an amount that is effective to establish a xenograft comprising (a) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (b) detecting the presence of the DOTA-based hapten in the subject by detecting radioactive levels emitted by the DOTA-based hapten that are higher than a reference value.

35. The method of claim 34, wherein the radioactive levels emitted by the DOTA-based hapten are detected using positron emission tomography (PET) or single photon emission computed tomography (SPECT).

36. The method of claim 34 or claim 35, further comprising quantifying radioactive levels emitted by the DOTA-based hapten that is localized to the xenograft.

37. The method of any one of claims 34-36, further comprising quantifying radioactive levels emitted by the DOTA-based hapten that is localized in one or more tissues or organs of the subject, wherein the one or more tissues or organs are selected from the group consisting of heart, muscle, gallbladder, esophagus, stomach, small intestine, large intestine, liver, pancreas, lungs, bone, bone marrow, kidneys, urinary bladder, brain, skin, spleen, thyroid, and soft tissue.

38. The method of claim 37, further comprising determining biodistribution scores by computing a ratio of the radioactive levels emitted by the DOTA-based hapten that is localized to the xenograft relative to the radioactive levels emitted by the DOTA- based hapten that is localized in the one or more tissues or organs of the subject.

39. The method of claim 38, further comprising calculating estimated absorbed radiation doses for the xenograft and the one or more tissues or organs of the subject based on the biodistribution scores.

40. The method of claim 39, further comprising computing a therapeutic index for the DOTA-based hapten based on the estimated absorbed radiation doses for the xenograft and the one or more tissues or organs of the subject.

41. A method for tracking recombinant mammalian cells in a subject in vivo comprising (a) administering to the subject the recombinant mammalian cell of any one of claims 24-28 in an amount that is effective to establish a xenograft; (b) administering to the subject an effective amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (c) detecting radioactive levels emitted by the DOTA-based hapten that is localized to the xenograft.

42. The method of claim 41, further comprising monitoring cell proliferation, cell growth, and/or apoptosis of the xenograft.

43. A method for determining the therapeutically effective amount of a DOTA-based hapten for pretargeted radioimmunotherapy (PRIT) comprising (a) administering to the subject the recombinant mammalian cell of any one of claims 24-28 in an amount that is effective to establish a xenograft; (b) administering to the subject an amount of a DOTA-based hapten, wherein the DOTA-based hapten comprises a radionuclide, and is configured to localize to the xenograft; and (c) determining that the amount of the DOTA-based hapten is therapeutically effective for PRIT when the subject exhibits a decrease in xenograft volume compared to that observed in the subject prior to administration of the DOTA-based hapten.

44. The method of any one of claims 31-43, wherein the DOTA-based hapten is selected from the group consisting of DOTA, Proteus-DOTA, DOTA-Bn, DOTA- desferrioxamine, DOTA-Phe-Lys(HSG)-D-Tyr-Lys(HSG)-NH₂, Ac-Lys(HSG)D-Tyr- Lys(HSG)-Lys(Tscg-Cys)-NH2, DOTA-D-Asp-D-Lys(HSG)-D-Asp-D-Lys(HSG)- NH₂; DOTA-D-Glu-D-Lys(HSG)-D-Glu-D-Lys(HSG)-NH₂, DOTA-D-Tyr-D- Lys(HSG)-D-Glu-D-Lys(HSG)-NH₂, DOTA-D-Ala-D-Lys(HSG)-D-Glu-D- Lys(HSG)-NH2, DOTA-D-Phe-D-Lys(HSG)-D-Tyr-D-Lys(HSG)-NH2, Ac-D-Phe- D-Lys(DOTA)-D-Tyr-D-Lys(DOTA)-NH2, Ac-D-Phe-D-Lys(DTPA)-D-Tyr-D- Lys(DTPA)-NH₂, Ac-D-Phe-D-Lys(Bz-DTPA)-D-Tyr-D-Lys(Bz-DTPA)-NH₂, Ac- D-Lys(HSG)-D-Tyr-D-Lys(HSG)-D-Lys(Tscg-Cys)-NH2, DOTA-D-Phe-D- Lys(HSG)-D-Tyr-D-Lys(HSG)-D-Lys(Tscg-Cys)-NH2, (Tscg-Cys)-D-Phe-D- Lys(HSG)-D-Tyr-D-Lys(HSG)-D-Lys(DOTA)-NH2, Tscg-D-Cys-D-Glu-D- Lys(HSG)-D-Glu-D-Lys(HSG)-NH₂, (Tscg-Cys)-D-Glu-D-Lys(HSG)-D-Glu-D- Lys(HSG)-NH₂, Ac-D-Cys-D-Lys(DOTA)-D-Tyr-D-Ala-D-Lys(DOTA)-D-Cys-NH₂, Ac-D-Cys-D-Lys(DTPA)-D-Tyr-D-Lys(DTPA)-NH2, Ac-D-Lys(DTPA)-D-Tyr-D- Lys(DTPA)-D-Lys(Tscg-Cys)-NH2, Ac-D-Lys(DOTA)-D-Tyr-D-Lys(DOTA)-D- Lys(Tscg-Cys)-NH₂, NH₂-benzyl (Bn) DOTA, DOTA-RGD, DOTA-PEG- E(c(RGDyK))2, DOTA-8-AOC-BBN, DOTA-PESIN, p-NO2-benzyl-DOTA, DOTA- biotin-sarcosine (DOTA-biotin), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid mono (N-hydroxysuccinimide ester) (DOTA-NHS), and DOTATyrLysDOTA.

45. The method of any one of claims 31-44, wherein the radionuclide is an alpha particle- emitting isotope, a beta particle-emitting isotope, or an Auger-emitter.

46. The method of any one of claims 31-45, wherein the radionuclide is ²¹³Bi, ²¹¹At, 2²⁵Ac, ¹⁵²Dy, ²¹²Bi, ²²³Ra, ²¹⁹Rn, ²¹⁵Po, ²¹¹Bi, ²²¹Fr, ²¹⁷At, ²⁵⁵Fm, ⁸⁶Y, ⁹⁰Y, ⁸⁹Sr, ¹⁶⁵Dy, 1⁸⁶Re, ¹⁸⁸Re, ¹⁷⁷Lu, ⁶⁷Cu, ¹¹¹In, ⁶⁷Ga, ⁵¹Cr, ⁵⁸Co, ^99mTc, ^103mRh, ^195mPt, ¹¹⁹Sb, ¹⁶¹Ho, 1^89mOs, ¹⁹²Ir, ²⁰¹Tl, ²⁰³Pb, ⁶⁸Ga, ²²⁷Th, or ⁶⁴Cu.