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Non-human primates in research and safety testing

2. Why are primates needed in research and safety testing?

  • 2.1 Why are primates needed in the safety testing of pharmaceuticals?
  • 2.2 Why are primates needed in research on infectious diseases?
  • 2.3 Why are primates needed in research on the human brain?
  • 2.4 Why are primates needed in research on organ transplants?

2.1 Why are primates needed in the safety testing of pharmaceuticals?

Only few candidate pharmaceuticals are actually tested on primates
Only few candidate pharmaceuticals are actually tested on primates
Source: Understanding animal research

Before a new pharmaceutical can be introduced on the market, it has to be tested on humans during clinical trials. The purpose of animal testing is to safeguard the health of the people taking part in these trials. The vast majority of drugs initially selected for development are rejected during this process, either because they are not effective or because they cause unwanted side-effects.

First, newly designed drugs go through a series of preliminary laboratory tests that do not involve animals. Based on the results, the best ‘candidate’ drugs are then tested on animals to see if they work, and to identify any possible health risks. Drugs are often tested on rats but the results are difficult to extrapolate to humans because of some fundamental differences between the two species. Therefore, pharmaceuticals must also be tested on a second species other than rodents, often dogs. Normally, there is no routine requirement for the use of non-human primates as a second species. While safety testing of new pharmaceuticals and other medical products represents one of the major uses of these primates, only few candidate pharmaceuticals are actually tested on them.

Primates should only be used when it is scientifically demonstrated that none of the other non-rodent species commonly used in safety testing is appropriate for the purpose of the study.

For instance, because no other animal species is as close to humans in their anatomy or in the way they respond to drugs, primates may be preferred over other mammals to test the safety of the following drugs:

  • drugs with possible effects on female genital organs
  • drugs with possible effects on the eyes
  • drugs that may cause vomiting
  • drugs that affect how the blood coagulates
  • certain antibodies
  • drugs with psychoactive properties
  • drugs capable of causing birth defects

Primates have been used effectively to test the safety of major new treatments for diseases such as severe asthma and certain eye diseases.

Regarding the potential effects of a drug on reproduction, rabbits and rodents such as mice and rats are often used, but the results are not accurate. Studies on primates are more likely to identify possible hazards to humans. For instance, a new drug developed to treat multiple myeloma, a type of cancer affecting immunity cells in the bone marrow, was safe for rats but produced limb abnormalities in the offspring of pregnant primates so we now know that it cannot be given to pregnant women.

Because humans and primates develop in a similar way in the early years, young primates may also be the preferred option for specific safety testing of drugs aimed at infants and children.

In some cases primates are not the best animal choice, for instance dogs are more suitable for testing toxicity to the liver. It is also important to note that animal testing on primates does not always predict all harmful effects on humans. Therefore, safety assessments of new products require information from both animal and non-animal testing. More...

2.2 Why are primates needed in research on infectious diseases?

There is an urgent need to develop vaccines, antibiotics, antivirals and other medicines that are effective against current and emerging health threats such as HIV, malaria, tuberculosis, severe acute respiratory syndrome (SARS), and avian influenza.

Before they are used on humans, vaccines must be tested on animals to see if they are safe and effective. The choice of a particular animal species depends on the disease but, often, non-human primates (NHPs) remain the most suitable option because their immune systems are very similar to that of humans. Sometimes, primates are even the only choice because they are the only mammals besides humans, which can catch certain diseases (e.g. smallpox).

Primates may be needed to quickly detect new diseases that could affect a large number of people across the world and spread over a wide geographical area. For instance, studies on primates were used effectively to prevent a pandemic spread of SARS in 2003. More...

2.2.1 HIV

Non-human primates (NHPs) are the only mammals that mimic important aspects of HIV infection in humans. They are used to understand how the immune system works and how AIDS develops. This work is important because the spread of HIV/AIDS can probably not be stopped without the use of an easily accessible vaccine.

Even though the HIV-vaccines tested to date have failed to provide the desired immune protection to patients in clinical trials, results of studies on primates are coherent with effects seen subsequently in humans and there is a growing consensus that any candidate vaccines should be studied even more thoroughly on primates before moving into large and expensive trials on human patients. More...

2.2.2 Tuberculosis

The current tuberculosis vaccine was developed at the beginning of the 20th century and, although it is still widely used worldwide, its effectiveness varies. As for many infectious diseases, there is no animal species that is perfectly suited to study tuberculosis and to draw conclusions applying to humans. Therefore, information needs to be gathered from different animal species. New vaccines are tested first on mice and guinea pigs. Only the most promising vaccines are then tested on non-human primates (NHPs) before proceeding to clinical trials in humans. More...

2.2.3 Malaria

It is very difficult to develop a vaccine against malaria because there are four different parasites that cause the disease and because each parasite goes through four different stages during the course of its infection of a human host, each time presenting different substances that the human immune system has to fight (antigens). In addition, any vaccine has to account for human genetic differences that also influence the level to which the human body can defend itself against the disease.

The owl monkey and the squirrel monkey are the only species (besides the chimpanzee) that are susceptible to the human malaria parasite, and they are used in very limited numbers for preliminary testing of vaccines.


2.2.4 Other infectious diseases

Currently about 170 million people worldwide are infected with the Hepatitis C virus and the only species besides humans that is susceptible to Hepatitis C is the chimpanzee. Vaccines are first tested on cells grown in the laboratory and on other species such as baboons and genetically modified mice. Chimpanzees are only used for testing the effectiveness of very promising candidate vaccines.

Currently, in Europe, no research is conducted on chimpanzees, and research groups that are studying this virus use laboratories in the USA and other parts of the world to carry out the necessary experiments. More...

2.3 Why are primates needed in research on the human brain?

Brain injuries and diseases such as epilepsy, damage to blood vessels in the brain, depression, drug addiction, Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis have a large impact on society. Therefore, brain research is urgently needed and likely to grow.

Research in neuroscience aims to understand how the brain works when it is healthy and when it is affected by a disease or an injury. Despite great progress over the last 50 years, our knowledge of the brain is still limited. Much of what we know is based on studies on cats, rats and even invertebrates. However, information from these relatively simple brains is of limited use when trying to understand and treat brain injuries and disorders that involve complex interactions between different parts of the human brain. As non-human primates (NHPs) and humans have very similar brains, experiments on primates remain crucial. At present, primates are the only animals available to study how the activity of a single nerve cell is related to more complicated brain functions.

Experiments on primates have been particularly valuable in a number of cases:

  • to understand how humans see, hear, feel, control movement, think and reason.
  • to establish a method with a type of pacemaker in the brain to control the symptoms of Parkinson’s disease. This method seems promising to treat other brain diseases.
  • to develop techniques where patients can use their brain to control the movement of paralysed limbs or command computers.
  • to gain unique insights into brain diseases in newborn and premature babies.
  • to study mental health and to do research on conditions such as depression as large primate colonies have complex social structures and some individuals behave in the same way as human psychiatric patients.

The use of animals in pain research is very controversial. Research in this area is nevertheless vital because 19% of adult Europeans live with moderate to severe long-term pain, seriously affecting the quality of their social and working lives. Animal experiments mainly involve rodents and only very rarely primates. In some areas of pain research it might be possible to replace animals with human volunteers and patients.

Stem cell technology uses undifferentiated cells that can multiply and become any sort of cell in the body. This technology opens the possibility to use cells from patients to repair their own tissue and would eliminate the problem of rejection of transplanted tissues or organs and ethical issues concerning embryos. Such techniques are being developed for the treatment of Parkinson’s disease, Huntington’s disease, strokes and spinal cord and brain injuries, but will likely need to be tested on primates first.

Experiments on primates are useful not only to understand diseases and find ways to cure them but also to develop alternative laboratory, non-animal testing methods and computer models.

Experiments which require entering the skull of non-human primates, raise difficult ethical concerns. New, non-invasive techniques to assess brain structure and function are developing rapidly and are increasingly used in clinical studies and in research. Although powerful, they can only study brain activity close to the surface. Studying regions deeper in the brain still requires invasive techniques and non-human primates. More...

2.4 Why are primates needed in research on organ transplants?

Transplantation is a surgical procedure in which tissue or whole organs are transferred from one organism to another. It is used to replace irreparable damaged or non-functioning vital organs such as kidneys, lungs, liver and heart. Transplanted cells are also used to treat diseases such as cystic fibrosis, diabetes and Parkinson’s disease. However, there is a serious shortage of donors and 10-20% of patients on the waiting list for organ transplants die before a donor organ becomes available.

To alleviate this problem, animals have been considered as a source of organs for transplantation and the most suitable species is likely to be the pig, since its organs are similar in size to human organs. However, before pig organs are transplanted into humans, they need to be tested on non-human primates to see if such transplants are feasible and effective. Tests on rodents would not be credible because their immune system is quite different to that of humans. Humans, Old-World primates and great apes are the only species with a particular type of antibodies that make them reject pig organs and therefore tests need to be done on these species.

Transplanted patients need to take medication to suppress their immune systems considerably so that they do not reject the foreign organ, and this can have long-term side effects. There are also concerns about potential infections that might be transmitted from source animals to transplanted humans and about how well the transplanted organ would work. Despite these difficulties, some primates transplanted with pig organs have survived for 2 to 3 years which proves that transplants with animal organs are viable. More...

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