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Immuno-oncology has revolutionized cancer treatment by harnessing the body’s own immune system to treat diseases with immunotherapies such as immune checkpoint inhibitors, CAR-T cells, vaccines and monoclonal antibodies. Determining which immunotherapy should be used for a patient with a specific cancer is crucial, as the response to a particular treatment protocol can vary considerably. Diagnostic tools that measure specific biomarkers can be used to predict how a patient will respond to an immunotherapy and can help stratify them into different treatment groups to inform clinical treatment pathway decisions. In recent years, antibody development tools have evolved to address the demands of immuno-oncology diagnostics and therapeutics and in turn, these tools have opened new areas of research and commercial opportunities.
Abcam has developed the expertise, skills and capacity to rapidly develop custom antibodies for important immuno-oncology targets such as BCMA, CTLA4, PD-1 and PD-L1. In this article, two of its in-house experts, Dr Joyce Young, VP Custom Services and Dr Jacinto Villanueva, Director of Platform Development, Custom Solutions, comment on the different technologies being routinely deployed to accelerate custom antibody discovery and development for research and diagnostic use, and to support therapeutic applications.
Most monoclonal antibodies are typically produced in mice, yet their antibody-producing cells are unable to generate every kind of antibody required. To overcome the limitations of mouse cells, Abcam exploits the unique properties of the rabbit immune system to derive recombinant rabbit monoclonal antibodies using NGS, hybridoma or direct B cell cloning processes.
Rabbits have a unique immune system compared with other species, such as mouse, rat, and chicken. They have a large B cell repertoire that can generate a very diverse range of antibodies. The rabbit immune system also optimizes affinity by using two mechanisms of affinity maturation: gene conversion and somatic hypermutation. This means that they produce high-affinity antibodies, even against antigens that are not immunogenic in mice, having a significantly higher affinity for a target antigen on average than most mouse monoclonal antibodies. Rabbit antibodies are also better at distinguishing subtle differences, such as epitope variations, post-translational modifications, and conformational changes due to the larger and more diverse B cell repertoire. The result of these features is rabbit antibodies that are specific and very sensitive to the target molecules of interest. Use of recombinant monoclonals further helps ensure reproducibility and reduces batch-to-batch variability.
Furthermore, every RabMAb® antibody is tested in key applications unique to a given project, to meet the agreed acceptance criteria and to ensure that the resulting product is fit for purpose. Knockout (KO) cell-line validation can also be carried out; the specificity of KO-validated antibodies being confirmed by western blot and other applications in some cases, using wild-type and KO cell lines, adding another layer of validation that helps confirm an antibody's specificity to its target.
Proprietary recombinant RabMAb® rabbit monoclonal technology was recently used to develop a panel of antibodies to a promising immunotherapy and diagnostic target known as B cell maturation antigen (BCMA). BCMA upregulation has been identified in B cell malignancies such as multiple myeloma and there is a range of therapeutic candidates currently in the pipelines of a number of pharmaceutical and biotech companies. Antibodies that bind both mouse and human versions of BCMA are needed to support fundamental research into the biology of BCMA in parallel to efforts being carried out to advance potential therapeutics.
As the rabbit immune system offers options for both human and mouse reactivity, RabMAb® technology was used to produce a series of high-affinity (ie sub-nM) anti-BCMA antibodies. These antibodies cross-react with both species, and are also suitable for multiple applications including immunocytochemistry (ICC), flow cytometry, western blotting and immunoprecipitation. Moreover, antibodies displaying antagonism for BCMA ligand binding were also characterized.
"It only takes weeks to go from immunization to having an accurate hit"
In addition to being able to generate specific immuno-oncology antibody formats for particular application requirements, Abcam’s expertise in rabbit monoclonal technologies also offers a significant speed advantage, as highlighted by Dr Villanueva: “Abcam’s proprietary rabbit monoclonal technology has now advanced to the point that it only takes weeks to go from immunization to having an accurate hit. We have both direct B cell cloning and hybridoma-dependent processes at our disposal to discover best-in-class recombinant rabbit monoclonal antibodies. This is a big improvement, as previously it could have taken up to a year to develop an antibody that is a specific and selective binder.”
Another approach to antibody discovery is NGS. The NGS method enables the discovery of many more unique clones compared to other methods. Abcam’s proprietary bioinformatic analytics allow detailed interrogation of the antibody repertoire, which enables the rational selection of the desired pool of antibodies. This approach gives researchers access to a comprehensive database of antigen-specific binders, helping to identify the best antibody for the task at hand.
As Dr Young explains, “Much of our NGS capabilities development has been focused on delivering the required bioinformatics and applying that to the successful interrogation of the rabbit immune response. The additional diversity of the rabbit immune system makes NGS a rather complex beast to tackle. However, it’s now a robust platform that has greatly enriched Abcam’s Custom Products offering.”
"When we find an initial clone that is only adequate, we can make it exceptional with NGS"
NGS uses a large pool of potential candidates that means there is a greater chance of discovering an antibody that best binds its target. The process includes taking an in-depth look into the whole immune response, scanning for the “relatives” of promising clones in order to optimize binding. A bioinformatics approach is then used to select a set of binders most beneficial to the desired application, including potential diagnostic or therapeutic use. Dr Villanueva, sees NGS as an “exciting” technology, “because when we find an initial clone that is only adequate, we can make it exceptional with NGS.”
As Dr Young describes: “we can harness and interpret our data to produce a map showing how different B cells are related to each other, which allows us to be more successful in identifying the best binder, with our offering retaining native pairing of the heavy and light chains.” As an NGS screen results in thousands of unique antibody sequences, these can also be used to support an intellectual property filing to protect antibody discovery for a given target. Use of Abcam’s NGS platform can therefore result in efficient, targeted results and effective IP protection.
Abcam has also leveraged recombinant rabbit monoclonal antibody discovery through direct rabbit B cell cloning to deliver a series of “CAL” recombinant rabbit monoclonal antibodies. These are optimized for exceptional performance in FFPE IHC, and many are recognized in the field of IHC pathology and diagnostics. Most of these clones have enhanced validation having been tested in multiple tissue microarrays of normal and tumor human tissue as well as mouse/rat cross-reactivity in IHC, and been tested in flow cytometry, ICC and western blotting. Being recombinant provides lot-to-lot consistency, specificity and sensitivity, and easy scalability. Examples include PD-L1 clone CAL10 (ab237726), CTLA4 clone CAL49 (ab237712) and PD-1 clone CAL20 (ab237728).
Phage display has become incredibly useful for fast antibody discovery and is an entirely in vitro system offering the opportunity to make antibodies against intractable targets such as toxins that were previously expensive, difficult-to-do and time-consuming. Abcam’s AxioMx™ high-throughput phage display antibody discovery platform uses high-diversity synthetic libraries that are designed to allow efficient affinity maturation and rapid cloning to give a full recombinant antibody. Antibody discovery using this technique has benefits across a wide array of applications and can provide a suitable discovery approach for certain challenging targets.
Says Dr Young: “New platforms such as Abcam’s AxioMx™ have sped up the antibody discovery process by harnessing rapid binder enrichment techniques using diverse libraries, such that we can develop antibodies within days to weeks rather in than months or years. And we can target antibodies to difficult molecules including those that are toxic or not immunogenic, with a speed that’s incomparable to most other antibody discovery platforms.”
Selecting the right combination of technologies to use to produce antibodies that address critical immuno-oncology needs requires a unique combination of scientific and industry expertise. Dr Young explains: “Our approach is to scope each project and determine the best platform or combination of platforms to provide our clients with an effective solution, using advanced high-throughput screening to quickly analyze lead panels of antibodies that might be suitable.
Being specialists at making antibodies has been core to Abcam’s mission since its foundation over 20 years ago. Today, it is also actively working to meet the industry’s needs for the development of exceptional, high-performing IHC antibodies to key diagnostic and therapeutic targets in immuno-oncology R&D. This includes challenging immuno-oncology targets, assay support and applications such as investigating the tumor microenvironment for biomarker discovery and detection through FFPE biopsies and novel and/or challenging targets.
“We’re able to support our customers from bench to bedside,” explains Dr Villanueva, "and we do this by leveraging our powerful antibody platforms from the earliest stages of antibody discovery when target confirmation is the objective, through development and into regulated manufacture.”
Abcam supports antibody development across the in vitro diagnostic (IVD) sector. Support includes lab-developed tests and rapid assay platforms; companion diagnostics and when required, Abcam can even supply its reagents for all phases of clinical trials. Abcam’s IVD IHC clones are developed in compliance with the FDA’s Quality Systems Regulations (21 CFR, Part 820) and ISO 13485. Its RabMAb® antibodies are used in seven FDA-approved companion diagnostic assays including PD-L1 and it routinely supplies ASR-grade material to the market. Abcam works with its partners through flexible licensing and commercial structures to enable a broad range of support options, products and services.
Abcam’s antibody platform technologies, combined with its Custom Team’s extensive industry experience delivers antibody solutions that are applied across a wide range of immuno-oncology targets. Its “end-to-end” expertise supports portfolio development and enhancement, with robust IP protection that gives confidence from early-stage R&D right through to the clinic.