Rhesus Macaques (Macaca mulatta) in Biomedical Research

Overview

Figure 1. Rhesus macaque. Source: Bill Sutton, Oregon National Primate Research Center

Rhesus macaques (Macaca mulatta) are one of the most widely used species of nonhuman primates in biomedical research with over 70 years of use (Figure 1). The genome of rhesus monkeys is 93.45% homologous to humans (1), making them excellent translational models of human disease. Knowledge of their genome has allowed for more in-depth evaluation of diseases at the level of the genome as well as genomic manipulation of the species.

Rhesus monkeys have been used in nearly every area of biomedical research, including infectious disease and vaccine development, aging, cardiovascular disease, metabolic diseases, neurologic diseases, addiction studies, and cancer research (2). Due to their vast use in biomedical research, this document is by no means a complete summary of their use as a translational model and instead highlights a few of the major areas of research in which they are used. One of their most well-known influences on modern medicine is their involvement in the identification of a red blood cell surface protein known as the Rh factor (which is an abbreviation of “rhesus”) in 1937 (2). This factor is widely used today in human blood typing. Rhesus were also critical for development of the polio vaccine in the 1950s (2), an advancement that has prevented more than 10 million cases of polio-related paralysis in humans (3). These instances are just a few of many advancements in the scientific and medical fields owed to the use of this species.

Natural History

Like some other species of macaques, rhesus are medium-sized Old World monkeys found in many parts of Asia, including India, Afghanistan, Kashmir, Vietnam, Nepal, Thailand, Bhutan, Bangladesh, China, Laos, Myanmar, and Pakistan (4). They live in both terrestrial and arboreal habitats that span from the lowlands up to over 12,000 ft in elevation (4, 5). In the wild, they primarily live in large multimale-multifemale social groups consisting of 10-50 members and follow a strict hierarchical system dependent on lineage and association of the female members (6). Rhesus are a sexually dimorphic species that breed seasonally (6). They are omnivorous, feeding on fruit, seeds, insects, and small mammals in the wild and typically live up to 29 years, which can be exceeded in captivity (6). Like some other species of macaques, rhesus are medium-sized Old World monkeys found in many parts of Asia, including India, Afghanistan, Kashmir, Vietnam, Nepal, Thailand, Bhutan, Bangladesh, China, Laos, Myanmar, and Pakistan (4). They live in both terrestrial and arboreal habitats that span from the lowlands up to over 12,000 ft in elevation (4, 5). In the wild, they primarily live in large multimale-multifemale social groups consisting of 10-50 members and follow a strict hierarchical system dependent on lineage and association of the female members (6). Rhesus are a sexually dimorphic species that breed seasonally (6). They are omnivorous, feeding on fruit, seeds, insects, and small mammals in the wild and typically live up to 29 years, which can be exceeded in captivity (6).

Although rhesus macaques originate from Asia, there are two major subgroups of this species: Indian-origin and Chinese-origin. These subgroups differ in appearance, genetic composition (including allele frequency, mitochondrial DNA, and major histocompatibility complex loci), and susceptibility to certain diseases (7, 8, 9). For example, Indian-origin rhesus macaques are highly susceptible to infection with Simian Immunodeficiency Virus (SIV), a viral analogue to Human Immunodeficiency Virus (HIV), whereas Chinese-origin rhesus are more resistant to infection and tend to have a slower disease progression (10). These differences highlight the importance of choosing specific species or subgroups of a species for research studies.

Models of Disease

Infectious Diseases

Rhesus are commonly used to model HIV infection, as the species is susceptible to a similar virus, SIV. Asian species of macaques, including rhesus monkeys, infected with SIV develop Simian Acquired Immunodeficiency Syndrome (SAIDS) and exhibit a disease similar to human AIDS (11). As mentioned above, the disease susceptibility and progression vary between different subgroups of rhesus macaques; however, Indian-origin rhesus infected with SIV typically develop SAIDS within 1-2 years after infection (12). In addition, the particular strains of virus used for infection can be altered to change the progression of disease or amplify a particular aspect of disease to better model specific syndromes observed in human patients. For example, some strains preferentially target the nervous system and are better at modeling neurologic abnormalities observed in HIV-infected humans (12, Figure 2). Studies with SIV-infected rhesus macaques have provided invaluable knowledge of how HIV interacts with cells in the body in order to develop antiretroviral therapies, novel adjunctive treatments, and vaccines (13-16).

There are numerous viral, vector-borne, and bacterial diseases that infect rhesus macaques (17), providing a useful model for examining the course of disease, development of novel treatments, and testing vaccinations. Some examples include Zika Virus, Yellow Fever Virus, Dengue Virus, West Nile Virus, and tuberculosis (18-23). Further, although the presentation of disease in rhesus differs from that observed in humans, rhesus have been pivotal in development of vaccines against SARS-CoV-2 and treatments for COVID-19 (24, 25).

Figure 2. Brain tissue from a SIV-infected rhesus macaque indicating severe inflammation of gray matter (left) and degeneration of white matter (right). Source: Abee CR, et al. 2012. Nonhuman Primates in Biomedical Research. 2nd Edition.

Type 2 Diabetes Mellitus

Macaques are excellent models of human metabolic diseases, such as type 2 diabetes mellitus. Diabetes can develop spontaneously or be induced experimentally in rhesus macaques fed a diet high in fat and cholesterol. Characteristics and pathologic progression of diabetes in macaques are similar to those observed in humans, including an elevated fasting blood glucose level, obesity, insulin resistance, and accumulation of a protein called amyloid within the pancreas (26-29). These striking similarities in disease progression allow for evaluation of risk factors contributing to development of diabetes, the effect of environmental factors such as diet and stress on disease development, progression of type 2 diabetes, and the study of novel pharmacologic therapies to treat diabetes. Not only are rhesus macaques ideal models of the disease itself, but they also develop many diabetes-related sequelae observed in human cases, such as cardiovascular disease and atherosclerosis (30), retinopathy (31), nephropathy (32), and lipid accumulation in organs, allowing for adjunctive study of these co-morbidities as well.

Neurodegenerative Diseases

Macaque species are especially useful for studying neurodegenerative conditions. One advantage of using macaques over other species is the ability to perform cognitive testing and objectively measure cognitive decline during disease progression. Interestingly, rhesus have cognitive capabilities at different life stages similar to those recognized in humans and have been shown to develop gradual, progressive cognitive decline as they age (33-39). Moreover, macaques have similar neuroanatomy and neurophysiology to humans (40), allowing for direct correlation of findings.

Figure 3. Brain tissue from a 35-year old rhesus macaque demonstrating Aβ plaques (brown). Source: Haque RU and Levey AI (2019) PNAS. There are several neurologic diseases and features of neurodegenerative diseases in humans that either occur naturally or can be induced in rhesus monkeys. Aged rhesus monkeys are frequently used to study brain mechanisms involved in development of Alzheimer’s Disease, as they naturally accumulate misfolded proteins (Aβ amyloid) in their brain similar to those typically observed in human patients (41-43, Figure 3). Despite the development of these lesions, macaques don’t tend to develop any neuronal loss or dementia-like conditions, which are features often exhibited by humans with Alzheimer’s Disease (37-39). This highlights one way in which differences in disease progression of an animal model can be useful in the study of human diseases. Parkinson’s Disease can be induced experimentally in rhesus by administration of a compound called 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (44). These animals have been shown to have similar loss of brain cells (dopaminergic neurons), motor dysfunction, and behavioral abnormalities observed in human Parkinsonian patients (44), providing a comparable model for novel therapy development. Huntington’s Disease can also be induced experimentally by genetic expression of the mutant gene responsible for development of Huntington’s Disease, HTT, in rhesus monkeys (45, Figure 4). Animals expressing HTT exhibit abnormal movements (dystonia and chorea) and pathology seen in humans with Huntington’s Disease (45). Multiple sclerosis (MS) is another inducible neurodegenerative disease model in rhesus, which is generated by administration of certain proteins (myelin oligodendrocyte glycoprotein or myelin basic protein) into the brain. This induces an autoimmune response (immune system targeting normal tissues) and leads to inflammation and gradual loss of white matter in the brain (46-49). These models of neurodegenerative diseases have allowed for thorough study of the origin and progression of disease as well as significant advances in development of novel treatments.

Figure 4. Transgenic infant rhesus macaques that express a mutated human huntingtin gene to induce Huntington’s disease (left). Successful insertion of the transgene in these animals is tracked by simultaneous expression of green fluorescent protein (right). Source: Yang SH, et al. (2008) Nature.

Heritable Diseases

Many diseases occur due to mutations within an individual’s DNA, which sometimes can be passed onto their children. Rhesus macaques have been found to harbor some of the same mutations, making them useful models for several heritable conditions. One example is a disease called Bardet-Biedl Syndrome (BBS), caused by mutations that lead to altered structure and function of cilia within the body (50). This syndrome is characterized by retinal dystrophy, obesity, cardiac abnormalities, developmental delays, and renal dysfunction, among other deficits, and develops slowly throughout an individual’s childhood or early adulthood (50). A small population of rhesus macaques at the Oregon National Primate Research Center were discovered to have a genetic mutation that causes BBS development (51), allowing these animals to participate in the characterization of disease and development of therapies for this condition. Age-related macular degeneration (AMD) is another condition influenced by genetic mutations at several loci in both humans and rhesus macaques (52). This disease is characterized by deposition of proteins and lipids in the deep layers of the retina, i.e. drusen, and progresses to central blindness (52, Figure 5). AMD has been observed in aged rhesus within many populations and mimics early to intermediate human disease, making monkeys useful models for testing novel therapeutics (52). Some human cancers are caused by genetic mutations, including Lynch Syndrome, one of the most common inherited nonpolypoid colorectal cancers (53). This form of cancer is induced by mutations in several genes, one of which was identified in rhesus macaques and also causes nonpolypoid colorectal cancer in this species (53). Rhesus monkeys, especially those with this specific mutation, are currently being studied for screening techniques and development of novel treatments for colon cancer. There are a multitude of other genetic diseases that have been identified in rhesus monkeys as well as other nonhuman primate species that can be found on the NPRC website: https://nprcresearch.org/primate/new-model-development/model-citations.php

Figure 5. Retina of a normal rhesus macaque (left), and two rhesus macaques with drusen (middle and right, arrows), a characteristic of age-related macular degeneration. Source: Francis, P. J., et al. (2008) Human molecular genetics

Other Areas of Research
There are numerous other areas of research in which rhesus macaques have been used, including drug and alcohol addiction (2), metabolic diseases (23), radiation exposure and therapies (45), cardiovascular disease (8), reproduction and contraception development (49), anesthesia (4, 37), and organ transplantation (1), to list a few.

References

1. Gibbs RA, et al. (2007). Evolutionary and biomedical insights from the Rhesus Macaque genome. Science; 316, 222–234.
2. Fox, JG, et al. (2015). Laboratory Animal Medicine, 3rd edition. Academic Press: San Diego, CA. Chapter 17 – Biology and Diseases of Nonhuman Primates, p. 798-807.
3. Centers for Disease Control and Prevention. (2014, March 3). CDC Global Health - Immunization - Infographic: Eradicate polio. Centers for Disease Control and Prevention. Retrieved December 5, 2021, from https://www.cdc.gov/globalhealth/immunization/infographic/eradicate_polio.htm.
4. Wang S and Quan G. (1986). Primate status and conservation in China. In: Benirschke, K. (Ed.), Primates: The Road to Self-Sustaining Populations. Springer-Verlag, New York, pp. 213–220.
5. Seth PK and Seth S. (1993). Structure, function, and diversity of Indian rhesus monkeys, In: New Perspectives in Anthropology. MD Publications, Pvt. Ltd., New Delhi, India, pp. 47-82.
6. Fooden J. (2000) Systematic review of the rhesus macaque (Macaca mulatta). Zoology (Field Museum of Natural History); 96, 1–180.
7. Viray J, Rolfs B, and Smith DG. (2001). Comparison of the frequencies of major histocompatibility (MHC) class-II DQA1 alleles in Indian and Chinese rhesus macaques (Macaca mulatta). Comp. Med. 51, 555–561.
8. Doxiadis GG, et al. (2003) Evolutionary stability of MHC class II haplotypes in diverse rhesus macaque populations. Immunogenetics; 55:540–551.
9. Ferguson B, et al. (2007) Single nucleotide polymorphisms (SNPs) distinguish Indian-origin and Chinese-origin rhesus macaques (Macaca mulatta). BMC Genomics; 8, 43.
10. Trichel AM, Rajakumar PA, and Murphey-Corb M. (2002). Species specific variation in SIV disease progression between Chinese and Indian subspecies of rhesus macaque. J. Med. Primatol. 31, 171–178.
11. Mansfield KG, et al. (1995). Origins of simian immunodeficiency virus infection in macaques at the New England Regional Primate Research Center. J. Med. Primatol., 24, 116-122.
12. Ringler DJ, et al. (1988). Simian immunodeficiency virus-induced meningoencephalitis: Natural history and retrospective study. Ann. Neurol., 23(Suppl), S101-S107.
13. Williams K, et al. (2005). Magnetic resonance spectroscopy reveals that activated monocytes contribute to neuronal injury in SIV neuroAIDS. J. Clin. Invest., 115, 2534-2545.
14. Marcondes MC, et al. (2009). Early antiretroviral treatment prevents the development of central nervous system abnormalities in simian immunodeficiency virus-infected rhesus monkeys. AIDS, 23, 1187-1195.
15. Ratai EM, et al. (2010). Proton magnetic resonance spectroscopy reveals neuroprotection by oral minocycline in a nonhuman primate model of accelerated NeuroAIDS. PLoS One, 5, e10523.
16. Rahman MA and Robert-Guroff M. (2019) Accelerating HIV vaccine development using non-human primate models. Expert Rev Vaccines. 18(1):61-73.
17. Gardner MB and Luciw PA. (2008) Macaque Models of Human Infectious Disease, ILAR Journal, 49(2): 220–255.
18. Dudley DM, et al. (2016) A rhesus macaque model of Asian-lineage Zika virus infection. Nat Commun.; 7:12204.
19. Wertheimer AM, et al. (2010) Immune Response to the West Nile Virus in Aged Non-Human Primates. J PLoS One. 5(12):e15514.
20. Marchevsky RS, et al. (2003). Neurovirulence of yellow fever 17DD vaccine virus to rhesus monkeys. Virology, 316, 55-63.
21. Trindade GF, et al. (2008). Limited replication of yellow fever 17DD and 17DDengue recombinant viruses in rhesus monkeys. An Acad. Bras. Cienc., 80, 311-321.
22. Maximova OA, et al. (2008). Comparative neuropathogenesis and neurovirulence of attenuated flaviviruses in nonhuman primates. J. Virol., 82, 5255-5268.
23. Foreman TW, et al. (2017) Translational Research in the Nonhuman Primate Model of Tuberculosis. ILAR Journal; 58(2): 151–159.
24. Yu P, et al. (2020) Age-related rhesus macaque models of COVID-19. Animal Model Exp Med. 3(1):93-97.
25. McMahan K, et al. (2021) Correlates of protection against SARS-CoV-2 in rhesus macaques. Nature. 590(7847):630-634.
26. Hansen BC & Bodkin NL. (1986). Heterogeneity of insulin responses: Phases leading to type 2 (non-insulin-dependent) diabetes mellitus in the rhesus monkey. Diabetologia; 29, 713-719.
27. Hansen BC & Bodkin NL. (1990). Beta-cell hyperresponsiveness: Earliest event in development of diabetes in monkeys. Am. J. Physiol.; 259, R612-R617.
28. Bodkin NL. (2000) The rhesus monkey (Macaca mulatta): A unique and valuable model for the study of spontaneous diabetes mellitus and associated conditions. In A. F. Sima, & E. Shafrir (Eds.), Animal Models in Diabetes: A Primer (pp. 309-325). Singapore: Taylor & Francis, Inc.
29. de Koning EJP, et al. (1993) Diabetes mellitus in Macaca mulatta monkeys is characterised by islet amyloidosis and reduction in beta-cell population. Diabetologia; 36:378-384.
30. Clarkson TB, et al. (1985) Nonhuman primate models of atherosclerosis: Potential for the study of diabetes mellitus and hyperinsulinemia. Metabolism; 34:51-59.
31. Johnson MA, et al. (2005). Ocular structure and function in an aged monkey with spontaneous diabetes mellitus. Exp. Eye Res., 80, 37-42.
32. Cusumano AM, et al. (2002) Glomerular hypertrophy is associated with hyperinsulinemia and precedes overt diabetes in aging rhesus monkeys. Am. J. Kidney Dis.; 40:1075-1085.
33. Rapp PR and Amaral DG. (1989). Evidence for task-dependent memory dysfunction in the aged monkey. J. Neurosci. 9, 3568–3576.
34. Peters A, et al. (1996). Neurobiological bases of age-related cognitive decline in the rhesus monkey. J. Neuropathol. Exp. Neurol. 55, 861–874.
35. Nagahara AH, Bernot T, and Tuszynski MH. (2010). Age-related cognitive deficits in rhesus monkeys mirror human deficits on an automated test battery. Neurobiol. Aging; 31, 1020–1031.
36. Messaoudi I, et al. (2011). Nonhuman primate models of human immunology. Antioxid. Redox. Signal. 14, 261–273.
37. Lai ZC, et al. (1995). Executive system dysfunction in the aged monkey: spatial and object reversal learning. Neurobiol. Aging; 16, 947–954.
38. Herndon JG, Moss MB, Rosene DL, and Killiany RJ. (1997). Patterns of cognitive decline in aged rhesus monkeys. Behav. Brain Res.; 87, 25–34.
39. Moore TL, et al. (2006). Executive system dysfunction occurs as early as middleage in the rhesus monkey. Neurobiol. Aging. 27, 1484–1493.
40. Lemon RN & Griffiths J. (2005). Comparing the function of the corticospinal system in different species: Organizational differences for motor specialization? Muscle Nerve, 32, 261-279.
41. Heilbroner PL and Kemper TL. (1990). The cytoarchitectonic distribution of senile plaques in three aged monkeys. Acta Neuropathol. 81, 60–65.
42. Uno H. (1993). The incidence of senile plaques and multiple infarction in aged macaque brain. Neurobiol. Aging; 14, 673–674.
43. Stonebarger GA, Bimonte-Nelson HA, and Urbanski HF. (2021) The Rhesus Macaque as a Translational Model for Neurodegeneration and Alzheimer’s Disease. Front. Aging Neurosci. 13:734173.
44. Barraud Q, Lambrecq V, et al. (2009). Sleep disorders in Parkinson’s disease: The contribution of the MPTP non-human primate model. Exp. Neurol.; 219, 574e582.
45. Yang SH, et al. (2008) Towards a transgenic model of Huntington's disease in a non-human primate. Nature. 453(7197):921-4.
46. Van Lambalgen R & Jonker M. (1987). Experimental allergic encephalomyelitis in rhesus monkeys: II. Treatment of EAE with anti-T lymphocyte subset monoclonal antibodies. Clin. Exp. Immunol., 68, 305-312.
47. Slierendregt BL, et al. (1995). Identification of an Mhc-DPB1 allele involved in susceptibility to experimental autoimmune encephalomyelitis in rhesus macaques. Int. Immunol., 7, 1671-1679.
48. Mein LE, et al. (1997). Encephalitogenic potential of myelin basic protein-specific T cells isolated from normal rhesus macaques. Am. J. Pathol., 150, 445-453.
49. Furlan R, et al. (2009). Animal models of multiple sclerosis. Methods Mol. Biol.; 549, 157-173.
50. Forsythe, E. & Beales, P. L. (2013). Bardet-Biedl syndrome. European journal of human genetics: EJHG. 21(1): 8–13.
51. Peterson SM, et al. (2019) Bardet-Biedl Syndrome in rhesus macaques: A nonhuman primate model of retinitis pigmentosa. Exp Eye Res. 189:107825.
52. Francis, P. J., et al. (2008). Rhesus monkeys and humans share common susceptibility genes for age-related macular disease. Human molecular genetics. 17(17): 2673–2680.
53. Brammer, D. W., et al. (2018). MLH1-rheMac hereditary nonpolyposis colorectal cancer syndrome in rhesus macaques. Proceedings of the National Academy of Sciences of the United States of America. 115(11): 2806–2811.
54. Banks ML, Czoty PW, and Negus SS. (2017). Utility of Nonhuman Primates in Substance Use Disorders Research, ILAR Journal, 58(2): 202–215.
55. Havel PJ, Kievit P, Comuzzie AG, Bremer AA. (2017) Use and Importance of Nonhuman Primates in Metabolic Disease Research: Current State of the Field. ILAR J.; 58(2):251-268.
56. Schultheiss TE, et al. (1994). Volume effects in rhesus monkey spinal cord. Int. J. Radiat. Oncol. Biol. Phys., 29, 67-72.
57. Cox LA, et al. (2017) Nonhuman Primates and Translational Research—Cardiovascular Disease. ILAR Journal, 58(2): 235–250.
58. Stouffer RL and Woodruff TK. (2017) Nonhuman Primates: A Vital Model for Basic and Applied Research on Female Reproduction, Prenatal Development, and Women's Health, ILAR Journal, 58(2): 281–294.
59. Misenhimer HR and Ramsey EM. (1970) The Effect of Anesthesia and Surgery in Pregnant Rhesus Monkeys. Gynecol Obstet Invest. 1:105-114.
60. Baxter MG and Alvarado MC. (2017) Monkey in the Middle: Translational Studies of Pediatric Anesthetic Exposure. Anesthesiology; 126(1):6-8.
61. Anderson DJ and Kirk AD. (2013). Primate models in organ transplantation. Cold Spring Harbor perspectives in medicine; 3(9), a015503.
62. Abee CR, et al. 2012. Nonhuman Primates in Biomedical Research. 2nd Edition. Volume 2 – Diseases. Academic Press: San Diego, CA. Chapter 15 – Nervous System Disorders of Nonhuman Primates and Research Models, p. 760.