Serious Monkey Business: A Short Take on Cynomolgus Monkeys in Research

What are cynomolgus monkeys?

Cynomolgus monkeys (Macaca fascicularis), also known as the long-tailed or crab-eating macaque, are non-human primates (NHP) commonly used in biomedical research.  There are 10 subspecies of these macaques and they are found predominantly in southeast Asia.  The cynomolgus monkeys are typically 15-22 inches long, and the females weigh between 7-13 pounds, while males can weigh between 11-20 pounds.

Why use cynomolgus monkeys and how are they used in biomedical research?

Cynomolgus monkeys are frequently used in biomedical research because researchers believe these monkeys are the ideal models due to the 90-93% genetic similarity to and recent evolutionary divergence from humans.  They are used for basic research studies in disease pathology and treatment, vaccine development, immunology, and cardiology, amongst others.  Cynomolgus monkeys are also used for toxicology and efficacy studies for drug development in the pharmaceutical industry based on certain FDA Guidance for Industry.

However, the usefulness of performing in vivo experiments in these animals has been recently called into question.  Examples include the failure of HIV modeling due to lack of AIDS development in monkeys and inability to successfully translate HIV vaccine research into humans.  Another instance is the TGN1412 case for development of the anti-CD28 agonist antibody.  Here, cynomolgus monkeys were poor models since their CD4 T cells do not express CD28; therefore, high doses of the antibody in toxicology studies displayed no effects in animals (Eastwood et al, Br J Pharmacol. 2010 Oct;161(3):512-26.).  However, administration of the molecule into humans led to cytokine release syndrome, which almost proved fatal in test subjects.

The effectiveness of using cynomolgus monkeys may come down to a case by case basis.  By performing ex vivo studies with cynomolgus monkey samples, such as peripheral mononuclear blood cells (PBMCs) or whole blood, researchers may be able to glean some insight into whether in vivo studies would be beneficial.  In addition, regulatory agencies, including the FDA and EMA, suggest and may even require studies with non-human cells to assess cross-species reactivity.

What are ex vivo applications for cynomolgus monkey samples?

Cynomolgus PBMCs can be used to study Fc-dependent function, such as antibody-dependent cellular cytotoxicity (ADCC, please see our webpage and blog on ADCC), of therapeutic antibodies.  A study on the efficacy of different human antibody isotypes in different cell types demonstrated that ADCC was similar between human and cynomolgus effector cells (Warncke et al, J Immunol, 2012 May 1; 188(9):4405-11.).  Therefore, ADCC experiments can be performed with cynomolgus PBMCs and humanized therapeutic antibodies.

Cynomolgus PBMCs can also be used as targets for ADCC assays if the target molecule is expressed on the cells.  Rituximab, an anti-CD20 antibody approved for some B cell cancers, was able to perform ADCC on cynomolgus B cells, which express CD20, with human effector cells (Schroder et al, Transpl Immunol, 2003 Oct-Nov; 12 (1):19-28.).  Further, in vivo studies using cynomolgus monkeys exhibited B cell depletion when rituximab was administered.  However, proper reagents, such as control antibodies, must be used when performing these assays to ensure the cytotoxicity observed is antibody/target antigen driven and not by some molecule foreign to human effectors cells.

Serum from cynomolgus monkeys can be used for complement dependent cytotoxicity assays (CDC, please see our webpage and blog on CDC) to test complement driven function by therapeutic antibodies as there may be subtle differences between complement components (Hengjie et al, Xenotransplantation. 2008 Feb;15(1):14-9.).  Component proteins required for CDC are found in cynomolgus serum and can be used in CDC assays with human target cells that express the target antigen for the therapeutic antibody.  Therefore, human therapeutic antibodies can recruit cynomolgus complement proteins to promote target cell lysis.  Unfortunately, cynomolgus complement activity is often examined after infusion reactions are observed from in vivo studies (Tawara et al, J Immunol. 2008 Feb 15;180(4):2294-8.).

Cynomolgus serum and plasma is also often used to set the baseline and generate concentration reference ranges for a variety of measurements, such as cytokine release measurements.  Serum or plasma from these animals will contain cytokines that can be detected using kits in which a reference range is required to extrapolate and quantitate the amount of cytokines in test samples.

Finally, serum or plasma from these animals can also be used as a reagent for various assays.  ELISA, ELISPOT, and western blots are all immunoassays that require initial blocking to prevent nonspecific binding, and cynomolgus serum can be used to accomplish it.  Alternatively, cynomolgus serum or plasma can be used for spike studies to model ELISAs to detect therapeutic antibodies from ex vivo studies.

Where do cynomolgus products come from?

Because the use of NHPs is a controversial subject, care must be taken to vet third party vendors that sell NHP samples.  Companies that process the samples to obtain products, such as iQ Biosciences, must ensure the sourcing vendors are responsible and operate according to local regulations and laws.  While iQ Biosciences does provide cynomolgus PBMCs and serum, they ensure the samples are sourced from a responsible third party vendor.  Please see our webpage for more information about our cynomolgus products.

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