Identify Primary Receptors and Off-Targets

Our unique and unrivaled Retrogenix Cell Microarray Technology identifies interactions both with cell surface receptors and secreted proteins by screening test ligands for binding against over 6,300 full length proteins that are individually over-expressed in human cells. This physiologically-relevant system, coupled with our broad protein coverage, allows even low affinity interactions to be detected with a high degree of sensitivity and specificity. The technology is currently being used by the world’s top 20 drug developers to bring new therapeutics to market faster yielding high success rates, high specificity, low false positive rates, and rapid turnaround.

Off-Target Screening Off-Target Screening
Understand cross-reactivity to reduce toxicity-based attrition and aid lead selection.

Target Deconvolution Target Deconvolution
Accelerate phenotypic drug discovery through target deconvolution of phenotypic molecules.

Receptor Identification Receptor Identification
Uncover receptors for proteins, viruses, and more complex ligands such as whole cells.

CAR Cell Specificity Screening CAR Cell Specificity Screening
Safely utilize a patient’s own immune system by precisely recognizing specific tumors.


Physiological System for Detecting Ligand-Receptor Interactions

Identifying precisely how a biological or chemical entity interacts with the human cell is fundamental to furthering our understanding of both normal biological and disease processes as well as revealing the mechanism of action of drugs and their potential for toxicity. The cell microarray screening provides a fast, accurate, and effective solution for discovering the human cell surface and secreted protein targets of antibodies, proteins, viruses, and small molecules. This allows our global pharmaceutical clients to:

  • Overcome the critical deconvolution step in phenotypic drug discovery
  • Uncover high quality and exploitable drug targets
  • Explore safety liabilities of lead candidates using the most comprehensive human expressed off-target system

The biologically relevant system detects specific interactions with a high degree of sensitivity. This unique tool uses proprietary arrays of expression vectors – encoding over 6,300 full-length human plasma membrane and tethered secreted proteins – spotted onto slides. Human cells grown over the top become reverse-transfected resulting in cell surface expression of each respective protein at distinct slide locations. The test molecule is applied, and specific binding analyzed and confirmed using an appropriate detection system.

Study Design Selection

Dendritic cell assay; frequency in PBMC by flow cytometry

A variety of study types for all stages of the drug discovery process (i.e. BLA / IND-enabling, lead selection) are available via the Retrogenix Cell Microarray technology.




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A High Quality Comprehensive Screen

Human cell microarray technology has long been the leading tool for discovering primary receptors and assessing potential off-target binding against expressed human proteins. Over a decade of continual development has ensured that our library is of the highest quality.

Initially representing only plasma membrane monomers, the library now uniquely, includes cell surface heterodimers as well as secreted proteins that have been identified as key off-targets for screening through our close collaborations with toxicology teams at leading pharmaceutical companies. Our rigorous bioinformatics approach ensures that miscategorized proteins are always excluded from our library, safeguarding the specificity of our results and providing clients with the confidence that real targets will be discovered and won’t be masked by a raft of false positives.

Cell Microarray Screening
Large Screening Library over 6,300*
Inclusion Criteria Rigorous. Stringent bioinformatics and literature review for each target (quality prioritized over quantity)
Broad Representation Human plasma membrane monomers, heterodimers; secreted proteins
Choice of Binding Conditions Fixed or unfixed cells
Biological Reference Human Cell Environment. Cell surface expressed proteins; relevant post-translational modifications, folding, dimerization etc.
Versatile Detection Method Immuno-fluorescence (variety of labels, tags & secondaries), 3H for small molecules
Hit Validation Three- to four-fold. Cell microarray confirmation (x 2) & flow cytometry (1 or 2)
Rapid Speed From 3 weeks
Cell Therapy Specificity Screening Comprehensive. Final cell therapy product (CAR T cells) as well as precursors (scFv, mAbs etc)
False Positive Rate Very low, reliable screening results
Data for IND/BLA Submissions Results widely accepted for required cross-reactivity assessment (FDA, EMA, NMPA & PMDA)
Validated Results Published studies include: Nature, Cancer Cell, JBC, SLAS, mAbs, JMC, Nature Medicine and JMB.
Widely Used 20 / 20 top pharma, plus more than 200 other clients globally
Collaborative Approach Contact our team to discuss your project


Versatile Technology

Retrogenix Cell Microarray Technology is compatible with a wide range of different ligands. We have successfully screened:

  • Antibodies and related molecules: mAbs, bispecifics, antibody-drug conjugates (ADCs), antibody fragments such as ScFvs, Fabs DARPins and mimetics, Fc-fusion proteins
  • Complex ligands: viruses, organelles, and whole cells, including CAR
  • Proteins and peptides: directly fluorescently conjugated or tagged proteins (Fc-tagged, biotinylated, Flag-tagged, His-tagged), monomers, multimers, protein-specific secondaries, polyclonal antisera, purified and media supernatants
  • Small molecules: 3H-labeled


Graphic image showing the binding of a test article to an overexpressed human protein in HEK293 cells using the Retrogenix Cell Microarray.

Graphic images showing the binding of a test article to an overexpressed human protein in HEK293 cells using the Retrogenix Cell Microarray. Image on the right shows the fluorescence that shows binding.

Graphic image showing the fluorescently tagged receptor on the cell. This is a graphic representation of what the data results will read. Purple for no off target binding and green if there is off target binding.


Highest Quality Protein Library

With over 10 years of expansion and refinement, our cell microarray libraries now have over 6,300 proteins for screening. This is the largest set of plasma membrane and secreted proteins expressed in human cells. As data from our specificity screens are frequently used to support BLA/IND submissions, it is crucial that we ensure the Retrogenix Cell Microarray Technology retains its high success rates as our capabilities continue to grow. The high degree of confidence our clients have when using this technology has allowed many of them to successfully base IND regulatory submissions on our screening data, both with and without supplementary immunohistochemistry-based (IHC) tissue cross-reactivity (TCR) studies. Currently, more than 86% of high confidence plasma membrane proteins are included in the platform, providing excellent coverage across the major sub-classes of cell surface proteins.

The Plasma Membrane Proteome: Coverage of Key Protein Sub-classes

Bar chart showing the percentage of coverage for the key protein sub classes for the cell microarray assays.

Coverage of The Human Secretome By Key Protein Sub-Classes

Bar chart showing the percentage of coverage of The Human Secretome By Key Protein Sub-classes for the cell microarray assays.

Tethering ‘Secreted’ Proteins

As secreted proteins are not naturally localized on the cell surface, novel cDNA constructs have been developed which result in expression of ‘secreted’ proteins fused to inert transmembrane and intracellular domains. As these proteins are tethered to the membrane, binding can be detected using the same workflow as the plasma membrane library. Our bioinformatics collaboration on this project resulted in a ‘high confidence’ list of secreted proteins being generated, for priority inclusion in the library. Of these, more than 90% are now expressed in our collection, with more under development. We continue to innovate and develop the cell microarray technology to broaden the applications of our platform and provide valuable data that informs both discovery and safety assessment.

After over 10 years of expansion and refinement, our cell microarray library now has more than 6,300 proteins for screening. This is the largest set of plasma membrane and secreted proteins expressed in human cells. As data from our specificity screens are frequently used to support BLA/IND submissions, it is crucial that we ensure The Retrogenix Cell Microarray Technology retains its high success rates as our capabilities continue to grow. Currently, more than 86% of high confidence plasma membrane proteins are included in the platform, providing excellent coverage across the major sub-classes of cell surface proteins.

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Supporting Regulatory Submissions

Data from Retrogenix Cell Microarray IND-enabling specificity studies have been included in numerous successful regulatory applications, as both standalone data, and complementary data to other cross reactivity studies. To help understand the wider impact of specificity assessment, and to quantify the extent to which it is being used in conjunction with IND-enabling methods, such as IHC-based tissue cross reactivity (TCR) screening, we perform an ongoing feedback process which allows us to collate and share data on how recently screened biotherapeutics are progressing.

We survey pharma, biotech, and non-profit sponsors who have undertaken at least one specificity screening project via our cell microarray. Our data covers a sample of projects from mid-2015 to November 2021; approximately one third of respondents have submitted regulatory applications, with a further 13% currently waiting to file. Following our last data collation in mid-2021, results showed that:

  • The screening data have been used in at least 79 regulatory IND submissions. Notably, our specificity screening data was also included in the licensing application for Novartis’ Kymriah (tisagenlecleucel) which, in 2017, was the first CAR T immunotherapy to receive FDA approval.
  • Retrogenix Cell Microarray Technology screening data is accepted globally; with submissions to the US FDA, EMA (and other European regulators), PMDA (Japan) and NMPA (China).
  • In a third of submissions (33%), the required cross-reactivity assessments came solely from our screening. In the remaining submissions our data was used in tandem with other cross reactivity studies.
  • 95% of submissions using our cell microarray data have been approved to date, with the remaining 5% still within the approvals pipeline.

* These figures were last updated in November 2021.

Further details of how our IND-enabling specificity data are being accepted by global regulators can be found by following the button below.

View IND stats


Frequently Asked Questions (FAQs) for The Cell Microarray Technology

  • What type of molecules can be screened using Retrogenix Cell Microarray Technology?

    This versatile platform can screen a wide range of test articles, including antibodies (mono and multispecific), antibody-related molecules (such as, scFv, Fab, VHH, ADC), proteins, peptides, cell therapies (such as CAR), and small molecules.

  • What is the sensitivity of the cell microarray?

    Ligand-target interactions of 10 micromolar can be detected in the absence of any amplification strategy. This is more than adequate for most studies, however, amplification strategies can be employed when needed to detect lower affinity interactions.

  • Which protein tags or labels are compatible with the platform?

    As long as we can detect gain-of-binding to the cells on our platform, we can theoretically screen any molecule. We have vast experience with a variety of detection strategies, including anti-Fc, biotin-streptavidin, anti-Flag, anti-His, directly fluorescently tagged, and radiolabeled molecules. Cell-based therapeutics are typically labeled in our laboratories with a fluorescent dye. We are also able to optimize the procedure for a new method should it be necessary to use a detection system that we have not encountered before. Please contact us if you have a specific requirement.

  • Who owns the data and the IP generated when a new drug target is identified?

    You do. Charles River Laboratories does not lay claim to any IP generated from the data/results generated unless there has been prior agreement to share IP.

  • Are screens performed on live or fixed cells?

    Both. Contrary to conventional thinking, we regularly see a clearer target: ligand binding on fixed cell screens and have observed a good correlation when comparing interactions found on fixed and live cells. Therefore, we typically perform fixed cell screens as standard, although live cell screening may be more appropriate and can also be conducted.

  • What data will I receive?

    Clients will receive details of any interaction(s) displayed on the platform. For the majority of study types, this will be provided in the form of an IND-enabling safety style report. On request, we can also present and discuss the results via a web meeting. Depending on study type, follow up on hit validation may also be available and can be carried out directly following a study at the High Peak site.

  • How much purified test article is required for a screen?

    This depends on the type of test article, molecular weight, and study design. For a soluble protein, we typically require between 200ug and 5mg.

  • Is endogenous expression of the target protein in HEK cells an issue?

    A pre-screen step against untransfected HEK293 cells is always carried out to check that endogenous expression of the target (and therefore potential background binding) will not be an issue. Over 90% of molecules progress past the pre-screen step to be screened against the full library of proteins. In cases where background binding may pose a significant challenge, we can discuss the option of modifying or terminating the study.

  • What cell types are the target proteins over-expressed on the platform?

    Currently, our human protein library is expressed in human HEK293 cells to ensure correct post-translation modifications, folding, and localization in human cells to produce a physiologically relevant system. R&D is also being performed to explore the use of other cell lines as alternative expression systems.