Conferma™ Sandwich ELISAs

• What Is a Sandwich ELISA?
• Need for Validation of Research ELISAs
• In-House Critical Reagent Development
• Physiochemical Characterization of Critical Reagents
• Verification of Lots
• Lot-to-Lot Consistency with Conferma™ ELISAs
• Conferma™ Sandwich ELISA Products
• References

Thorough analytical verification of an assay is of great importance in the qualification of biomarkers for clinical research and therapeutic development. The Conferma™ Sandwich ELISAs are created with a focus on their critical components. The monoclonal capture and detection antibodies and accompanying recombinant protein standard are rigorously evaluated from lot-to-lot using physiochemical characterization techniques. Combined with finished kit quality control (QC) analysis, the start to finish Conferma™ ELISA validation provides a high degree of consistency with each lot to give you confidence in your research.

Figure 1. Three lots of IL-6 ELISA run independently. The curves show excellent similarity.

What Is a Sandwich ELISA?

A sandwich ELISA is a common enzyme-linked immunosorbent assay (ELISA) procedure that measures the antigen level of a sample. The antigen is “sandwiched” between two antibodies, the capture antibody and the detection antibody. These antibodies can be either monoclonal (mAb) or polyclonal antibodies, however our Conferma™ ELISAs utilize mAbs. Sandwich ELISAs are considered to be one of the more sensitive and specific types of ELISAs as two unique epitopes are required to determine that the correct protein has been identified.

Figure 2. Illustration of how sandwich ELISAs work.

Learn about troubleshooting common ELISA problems in our ELISA Troubleshooting Guide.

Need for Validation of Research ELISAs

The immunoassay has undergone many re-inventions over the last few decades, moving from single to multiple analyte detection with increasing levels of sensitivity and specificity. Over time there has been an influx of commercially available kits by numerous vendors. The majority of these kits fall within the Research Use Only (RUO) category and are required to be labeled as such by the U.S. Food and Drug Administration (FDA). However, unlike In Vitro Diagnostic (IVD) assays, there are no regulatory requirements for the validation and confirmation of RUO assays. With no requirement for validation, the burden of responsibility falls to the end-user to evaluate and accept the manufacturer’s claims. This has led to a range of commentary by both academic and industrial assay users, reflected in the 2015 paper by Khan et al., who are looking to provide a framework for commercial assay validation in the hands of a researcher.¹

A key aspect of an assay’s analytical validation is the evaluation of lot-to-lot reproducibility, which has often been traced back to the variability within the assay’s components. Papers published by King et al. in 2014 and O’Hara et al. in 2012 indicate strategies that may be used to generate and monitor critical reagents used in ligand binding assays, which could be applied to both in-house and commercial vendors.^2,3

To address these concerns, the Conferma™ ELISAs are built with the following key principles:

1. Critical reagents produced in-house.
2. Lot-to-lot physiochemical characterization of critical reagents.
3. Finished kit single lot manufacture. Kits manufactured and quality controlled at component and completed kit level.
4. Lot-to-lot sample bridging between completed kits lots.

In-House Critical Reagent Development

Developing the critical reagents in-house ensures control of both the supply and the manufacturing. It also provides the ability to obtain the samples necessary to send to our corporate Center of Excellence for Mass Spectrometry in St. Louis, MO, who utilize 1D Gel Analysis, Amino Acid Analysis (AAA), Liquid Chromatography–Mass Spectrometry (LC-MS), Reverse Phase – LC-MS (RP-LC-UV-MS), and Surface Plasmon Resonance (SPR, Biacore™ T-200 system), where appropriate, to characterize and compare the reagents (pre- and post-biotinylation in the case of the detection mAbs) lot-to-lot.

Table 1. Example of RP-LC-UV-MS data showing the measured mass of each lot of reagents as well as the amount of biotin bound to the detection mAb post-biotinylation.

Reagent	Sample	Measured Masses (Da)	Biotin Conjugated Using MS Moles of Biotin/Moles of Antibody
Calibrator	Lot 028M4878V	20977	NA
Calibrator	Lot 015M4836V	20977	NA
Capture mAb	IL6.2F2(Lot RB1811028)	148728	NA
Capture mAb	IL6.2F2(Lot RB1812003)	148735	NA
Capture mAb	IL6.2F2(Lot RB1912001)	148728	NA
Detection mAb	IL6.2E3(Lot RB1811029)	148937	NA
Detection mAb	IL6.2E3(Lot RB1812002)	148934	NA
Detection mAb	IL6.2E3(Lot RB1912002)	148933	NA
Detection mAb Bt	IL6.2E3 Bt (Lot RB1811029)	Distribution with Bt=4 at 150744	3
Detection mAb Bt	IL6.2E3 Bt (Lot RB1812002)	Distribution with Bt=4 at 150744	4
Detection mAb Bt	IL6.2E3 Bt (Lot RB1912002)	Distribution with Bt=4 at 150748	8

Physiochemical Characterization of Critical Reagents

The characterization of the critical reagents provides for an extremely granular evaluation of the materials lot-to-lot. The assessment (using AAA, Mass-Spec, and 1D-Gel Analysis) of the recombinant protein calibrator (used in the standards and QCs) allows us to confirm that there is no change in mass or sequence coverage. Additionally, the work done on the mAbs confirms both the consistency of the mass and an assessment of the biotin bound to the detection antibody, which can be reflected in the optical density (OD) of the standard curve.

An important test within the process is SPR carried out on a Biacore™ T-200 platform. This test allows us to understand the relationship between the mAbs and the calibrator. We are looking for the mAbs to have, and maintain, a high affinity against the calibrator with an equilibrium dissociation constant (K_d) <0.5 nM. The activity of each lot of mAb should also be consistent lot-to-lot. This technique is carried out pre- and post-biotinylation in the case of a detection mAb to judge the effect of the preparation. The purpose of the SPR testing is to verify that the biotinylation did not impact the affinity of the mAb and to confirm post-biotinylation consistency from batch to batch.

Table 2. Example of SPR data from various lots of mAb against their calibrator material.

No.	Ligand (Ab)	IL-6 Analyte (Ag)	Kd (nM)	% Activity
1	17M4830V-Control	028M4878V	0.04	85
2	IL6.2F2.Capture.RB1811028	015M4836V	0.13	86
3	IL6.2F2.Capture.RB1811028	028M4878V	0.05	84
4	IL6. 2E3.Capture.RB1812003	015M4836V	0.14	88
5	IL6.2E3.Capture.RB1812003	028M4878V	0.06	88
6	IL6.2E3.Capture.RB1912001	028M4878V	0.05	93
7	IL6.2E3.Detection.RB1811029	015M4836V	0.13	67
8	IL6.2E3.Detection.RB1811029.Biotinylated	015M4836V	0.11	63
9	IL6.2E3.Detection.RB1811029	028M4878V	0.08	70
10	IL6.2E3.Detection.RB1811029.Biotinylated	028M4878V	0.06	68
11	IL6.2.E3.Detection.RB1812002	015M4836V	0.11	66
12	IL6.2E3.Detection.RB181200 2.Biotinylated	015M4836V	0.12	64
13	IL6.2.E3.Detection.RB1812002	028M4878V	0.10	72
14	IL6.2E3.Detection.RB1812002.Biotinylated	028M4878V	0.10	68
15	IL6.2.E3.Detection.RB1912002	028M4878V	0.06	83
16	IL6.2E3.Detection.RB1912002.Biotinylated	028M4878V	0.06	75

Verification of Lots

When each batch of raw materials is confirmed, they are then utilized by the manufacturing group to create individual lots of assays. While the mAbs and recombinant proteins can be stable and stored for a long time, careful QC procedures are required to ensure that the new lots produced from the raw materials are consistent with previous lots across all QC parameters (e.g. component relative potency and curve mathematical parallelism). The Conferma™ assays add finished kit biological sample testing, with kits from the new and prior lot run against a library of samples to ensure that they are effectively bridged.

The details and data from the process outlined here are made available for evaluation in two forms, firstly a Verification Report is produced which details the work done in establishing the assays reagents, feasibility, and testing. Secondly, each lot of assays has a Certificate of Analysis consisting of the component lot details, the expected OD of the standard curves, and details of the sample testing.

Discover more details on this whole process with our Conferma™ IL-6 ELISA application note.

Lot-to-Lot Consistency with Conferma™ ELISAs

By establishing this process, we are looking to address a key need within the industry -- establishing assays with a high level of lot-to-lot consistency, anchored by consistent critical reagents and evaluated sample bridging. As we develop assays based on this process you will find them, and their accompanying documentation listed on this page in the table below.

Conferma™ Sandwich ELISA Products

Cat. No.	Analyte	Verification Report
EZIL6-98K	IL-6	IL-6 Verification Report
EZIL8-100K	IL-8	IL-8 Verification Report
EZMCP1-99KRM	MCP-1	MCP-1 Verification Report

References

1. Khan MU, Bowsher RR, Cameron M, Devanarayan V, Keller S, King L, Lee J, Morimoto A, Rhyne P, Stephen L, et al. 2015. Recommendations for adaptation and validation of commercial kits for biomarker quantification in drug development. Bioanalysis. 7(2):229-242. https://doi.org/10.4155/bio.14.274

2. King LE, Farley E, Imazato M, Keefe J, Khan M, Ma M, Pihl KS, Sriraman P. 2014. Ligand Binding Assay Critical Reagents and Their Stability: Recommendations and Best Practices from the Global Bioanalysis Consortium Harmonization Team. AAPS J. 16(3):504-515. https://doi.org/10.1208/s12248-014-9583-x

3. O?Hara DM, Theobald V, Egan AC, Usansky J, Krishna M, TerWee J, Maia M, Spriggs FP, Kenney J, Safavi A, et al. 2012. Ligand Binding Assays in the 21st Century Laboratory: Recommendations for Characterization and Supply of Critical Reagents. AAPS J. 14(2):316-328. https://doi.org/10.1208/s12248-012-9334-9