Sensitive and selective detection assays are essential for the accurate measurement of analytes in both clinical and research laboratories. Immunoassays that rely on nonoverlapping antibodies directed against the same target analyte (e.g., sandwich enzyme-linked immunosorbent assays (ELISAs)) are commonly used molecular detection technologies. Use of split enzyme reporters has simplified the workflow for these traditionally complex assays. However, identifying functional antibody pairs for a given target analyte can be cumbersome, as it generally involves generating and screening panels of antibodies conjugated to reporters. Accordingly, we sought a faster and easier reporter conjugation strategy to streamline antibody screening. We describe here the development of such a method that is based on an optimized ternary NanoLuc luciferase. This bioluminescence complementation system is comprised of a reagent-based thermally stable polypeptide (LgTrip) and two small peptide tags (β9 and β10) with lysine-reactive handles for direct conjugation onto antibodies. These reagents enable fast, single-step, wash-free antibody labeling and sensitive functional screening. Simplicity, speed, and utility of the one-pot labeling technology are demonstrated in screening antibody pairs for the analyte interleukin-4. The screen resulted in the rapid development of a sensitive homogeneous immunoassay for this clinically relevant cytokine.

We have utilized NanoLuc® Binary Technology (NanoBiT®) to develop a homogeneous and rapid assay method (≤ 70 min completion time) to measure cytokines released from cells in culture without the need for sample transfer and requiring only a standard, plate-reading luminometer for signal acquisition. Separate antibodies to a specific cytokine are labeled with the small, 11-amino acid subunit of NanoBiT luciferase (SmBiT) or its 17.6 kDa complementary subunit (LgBiT). When SmBiT- and LgBiT-labeled antibodies converge on the target cytokine, the resultant proximity of SmBiT and LgBiT reconstitutes a bright luciferase that produces light proportional to analyte levels. In this manner, immunoassays have been developed for several cytokines, including IL-1β, IL-2, IL-6 and IFN-γ. In general, these assays share LLODs < 10 pg/ml and linearity over three logs of analyte concentration, mitigating the need for sample dilution. Following 24 h treatment of human PBMCs in 96-well plates with vehicle, LPS, R848, or a combination of PMA and ionomycin, cytokine detection reagents were added directly to the culture wells containing cells and medium. Depending on stimulus, maximal signal to background ratios (S/B) achieved for the cytokines were 347-, 450-, 580- and 655-fold for IL-1β, IL-2, IL-6 and IFN-γ, respectively. In a cell model comprised of activated T cells and target Raji B cells induced for 20 h with increasing bispecific T-cell engager Blincyto®, release of IL-2 and IFN-γ were observed with an EC50 of ~0.2 ng/ml and maximal S/B for IL-2 and IFN-γ of 82- and 168-fold, respectively. The implementation of this novel detection chemistry will enable rapid “add-and-read” assays for cytokine detection for both low- and high-throughput applications.

Cytokines play a major role in cancer biology as inflammatory and immunomodulatory agents and are frequently measured in cell culture models and other biological samples. Various methods are available for in vitro measurement of cytokines, but they typically require sample transfer, sample dilutions, multiple wash steps, time-consuming protocols, and/or specialized instrumentation. We have utilized NanoLuc® Binary Technology (NanoBiT®) to develop a completely homogeneous and rapid assay method (< 70 min completion time) to measure cytokines released from cells in culture without the need for sample transfer and requiring only a standard, plate-reading luminometer for signal acquisition. In this approach, separate antibodies to a specific cytokine are individually labeled with either the small, 11-amino acid subunit of NanoBiT luciferase (SmBiT) or its 17.6 kDa complementary subunit (LgBiT). When SmBiT- and LgBiT-labeled antibodies converge on the target cytokine, the resultant proximity of SmBiT and LgBiT subunits reconstitutes a bright luciferase that produces light proportional to analyte levels when the substrate furimazine is present. Utilizing this technology, homogeneous bioluminescent immunoassays have been developed for several cytokines, including IL-1β, IL-2, IL-6 and IFN-γ. These assays share excellent sensitivities (LODs typically < 10 pg/ml) and broad linear ranges extending over three or more logs of analyte concentration, significantly mitigating the need for sample dilutions. Following 24-hour treatment of human PBMCs in 96-well plate format with vehicle, LPS, R848, or a combination of PMA and ionomycin, cytokine detection reagents were added directly to the culture wells containing cells and medium. Depending on cell stimulus, maximal signal to background ratios (S/B) achieved for the various cytokines assayed were 347-, 450-, 580- and 655-fold for IL-1β, IL-2, IL-6 and IFN-γ, respectively. In a separate cell model comprised of activated T cells and target Raji B cells induced for 20 hours with increasing concentrations of the bispecific T-cell engager Blincyto®, dose-dependent release of IL-2 and IFN-γ were observed with an EC50 of ~0.2 ng/ml and maximal S/B for IL-2 and IFN-γ release of 82- and 168-fold, respectively. In all cases, a calibration curve of recombinant cytokine enabled straightforward conversion of relative light units (RLU) to concentration of released cytokines. The implementation of this novel detection chemistry will enable rapid “add-and-read” assays for cytokine detection amenable for both low- and high-throughput screening applications. Citation Format: Dan F. Lazar, Kevin R. Kupcho, Casey A. Sondgeroth, David V. Thompson, Martha A. O'Brien, Julia K. Gilden, Kevin Hsiao, James J. Cali. Rapid and sensitive determination of cytokine release from cells without the need for sample transfer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5595.

Rapid (< 70 min), add-and-read assays for cytokine determination were developed with Lumit™ immunoassay technology. Separate antibodies labeled with complementary SmBiT or LgBiT subunits bind to their shared cytokine target, resulting in proximity-driven reconstitution of NanoBiT luciferase and luminescence signal. Lumit immunoassays for human IL-1β, IL-2, IL-4, IL-6, IL-10, IFN-γ, and TNF-α exhibit LLODs < 10 pg/ml and linearity > 3 logs of analyte in 96-well format. Maximal S/B ratios are greater than 1000, and an assay signal T1/2 of 2 h accommodates batch plate processing. 384-well, assay performance (Z′ > 0.7) on treated human peripheral blood mononuclear cells (hPBMC) indicates the assay format is amenable to screening applications. Assay reagents were added directly to cell wells for multiple culture models. For hPBMC, LPS, R848, or a combination of PMA and ionomycin (CSC) produced dose-and time-dependent release of cytokines with a wide range of responses, all measurable without sample dilution. In a mix of purified CD8+ T cells and target Raji B cells treated with the bispecific T-cell engager Blincyto®, IL-2, IFN-γ, and TNF-α release was observed with an EC50 of ~0.2 ng/ml and max S/B ratios of 82-, 168-, and 31-fold, respectively. For Th2 cells, significant release of IL-4 was observed in response to CSC treatment. An alternative to the no-transfer assay method, split-sample analysis, can be performed to easily determine the levels of multiple cytokines released in the same cell well. The implementation of this novel detection chemistry will enable simple and rapid assay of cytokine release from cells for both low-and high-throughput applications, including quantitative assessments of T cell activation and differentiation.