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Research with monkeys

Monkeys are used in research only when it is not possible to use other species. They are employed primarily in studies into the disorders, structure and function of the brain, and in research aimed at developing vaccines or treatments for severe infectious diseases. Monkeys are needed for this work because they are so closely related to humans.

In studies of the safety of drug candidates before being used in humans documentation according to GLP (Good Laboratory Practice) is required. Monkeys are used only in cases where the drug authorities require that these tests are performed on monkeys.

The Astrid Fagræus Laboratory (KM-F)

The Astrid Fagraeus Laboratory (KM-F), where experiments with monkeys are performed, includes one of the few facilities in Sweden with authorization to conduct animal testing under GLP. KM-F is also the first in Sweden to become accredited by AAALAC International Organization for its high quality of animal welfare.

Read more about housing of monkeys at Astrid Fagraeus laboratory

Rhesus macaque at AFL, credit: CM/KI.

Malaria vaccine research

Positive development – but difficult to reach all the way

In recent years there has been a positive development in the world as regard to malaria incidence, and the number of infected individuals has declined by about 20 percent since 2010. However, malaria still pose a huge global health burden. In 2017, there were about 219 million malaria infected people in the world, most of them in southern Africa, according to the WHO. The number of deaths from the disease in 2017 was estimated to 435 000 people, of which about 60 percent were children under the age of five. Research from KI aims to help the development of a vaccine that could save the lives of hundreds of thousands of children.

Malaria mosquito, credit: iStockphoto.
Malariamygga, foto: iStock.

Malaria is caused by parasites which are far more complex than the viruses and bacteria that we have vaccines for today. The malaria parasite has multiple stages in their life cycle where in each stage they express different antigens (proteins that are able create an immune response). This makes it very challenging for the development of an effective vaccine. Another challenge is that different types of vaccine responses (antibodies or cytotoxic T cell responses) are required for protection depending on where the parasite is in its life cycle. An intimate understanding of the interaction between the host immune system and the vaccine and how sustained and protective immunity can be generated is therefore critical.

To get a complete picture of the interactions between the immune system and the vaccine and to evaluate whether a protective and enduring immunity develops, it is necessary to use primates, such as rhesus macaques, in research. Primate immune system is very similar to the human, which is different in several respects to the rodent's for example. The kinetics, functions and levels of antibody response and T-cells are also very similar.

The ability to test the relevant doses of vaccine and the anatomical similarities between monkey and human is a great advantage when to evaluate the results and draw conclusions to proceed to clinical trials in humans. It is, for example, not possible to evaluate intramuscular administration of the vaccine, which is by far the most common method to give the vaccine, in mice. The target group for a vaccine is usually healthy people, including children. This adds an extra safety aspect, as the vaccine needs to be proven both exceptionally safe to use and protect against the disease before administered to humans.

More about malaria on the WHO website

Research on rhesus macaques at KM-F

During 2017, researchers at the Astrid Fagraeus Laboratory (KM-F) completed a malaria vaccine trial, including a total of 24 rhesus macaques which were brought in from the US via Germany. The ethical permit for this research covers the use of 120 rhesus macaques, but the current plan is to use no more than 24 animals. The development of the current vaccine is the result of decades of research in which several research groups from different countries have contributed. The vaccine has been refined in several stages and has undergone extensive laboratory testing and then tested on mice. It has now reached the last stage before it will begin to be tested in humans.

The malaria vaccine tested at the KM-F is based on a unique conserved antigen that has been selected for its low variability. Previous studies have shown that vaccination with this antigen prevents mosquitoes to reproduce and transmit the malaria parasite. This makes it potentially possible to eradicate malaria from a geographical area. However, the antigen must be displayed in such a way that it stimulates the immune system to induce a protective response. Vaccines based on the same technology have already been tested against other diseases in humans with good results.

The level of response to the malaria vaccine that is needed to inhibit the parasite's reproduction in mosquitoes and further transmission to humans has already been established in previous studies. Researchers at KM-F can therefore compere their results with these known levels, and there is no need to infect the monkeys in the present study with live malaria parasites.

The malaria vaccine trial at KM-F has shown very promising results, with vaccine responses that are above what have been detected in previous studies. Samples from the animals have been analyzed by several different methods in mulitple laboratories, to measure the strength, quality and durability of the vaccine responses, and the study results will be published in a scientific journal. A team of researchers and malaria experts from academia, the vaccine industry, and funders are discussing the progress into clinical trials in humans. Our hope is that this vaccine has the potential to be the first to protect against malaria.

Study Procedure

In the recently completed study, the animals received the malaria vaccine three times, and their immune responses were carefully monitored by collecting regular blood samples (approx 1-2 per month) for about a year. In the last procedure, a superficial lymph node and a bone marrow biopsy collected for a more detailed analysis of the immunological memory of malaria being built by the vaccine. The animals were not exposed to malaria parasites, as the ability to block parasite reproduction by the vaccine responses can be evaluated using a laboratory assay of the blood samples.

None of the monkeys developed fever, showed altered behavior or had symptoms e.g. at the injection area. Standard testing of liver and kidney enzymes after immunization showed a transient but mild effect similar to those found by known vaccines. Weight gain, growth and activity were normal in all animals throughout the study.

Rhesus macaque taking a bath at the AFL anomal house. Credit: CM/KI.
Rhesus macaque taking a bath at AFL. Credit: CM/KI. Photo: Comparative Medicine

Since the monkeys were not exposed to malaria nor developed disease during the malaria study, the animals could eventually be included in tests of other vaccines. In this way, researchers could avoid the import of new monkeys, keeping the total number of experimental animals as low as possible. The new studies were conducted to investigate the direct and local response to different types of vaccines, using a method developed at Karolinska Institutet. In these studies, extensive sampling from injection areas and local lymph nodes were performed, and in order to avoid suffering, the monkeys were euthanized with an overdose of anesthetics in connection to the sampling procedure.

Animal housing at KM-F

During their time at KM-F, the monkeys have been living in groups of two or three individuals who grew up together and get along with each other. Monkeys at KM-F live in an enriched environment that gives them the ability to express their natural behaviours. At KM-F, significant focus is directed towards creating harmonic and social milieus for the animals. All animals at the facility have established relationships with their personal care-taker who trains and offers daily intellectual and physical exercises, as well as access to water games.

More about living and social environments for macaques at KM-F

Research into the brain's function

PET technology in brain research

Positron emission tomography (PET) has enabled major progress in biomedical research, particularly in research into the structure and function of the brain. It is also important for detecting tumours and developing new medications. PET involves labelling organic molecules with a radioactive isotope and then injecting these tracers into one of the patient's blood vessels. The positron camera is then used to monitor how the molecules are absorbed into the brain. Before a tracer can be used on patients, it must first be tested on research animals, normally monkeys as they are closest to human beings in terms of brain structure and function.

The PET research carried out on the KM-F monkeys is intended to develop new tracers so that PET can be used to investigate signal systems in the living human brain. These systems are vital for diagnosing and treating neurological and neuropsychiatric disorders such as Alzheimer's, Parkinson's, schizophrenia, depression and ADHD.

The close correlation between the results from monkey experiments and subsequent studies with humans has meant that researchers at Karolinska Institutet (KI) have been able to confirm the value of the monkey studies for developing suitable tracers. This work has included producing markers to investigate subtypes of dopamine, serotonin, noradrenaline and GABA receptors.

Researchers at KI have developed a tracer that has made it possible for the first time to investigate the serotonin transporter (SERT). They have shown in studies using monkeys that the marker binds selectively to SERT, paving the way for studies with humans. This method will be used in investigations into depressive disorders and into the mode of action and clinical guidelines for antidepressants.

What happens with monkeys in a PET trial?

The monkeys used for PET trials are totally healthy and live together for many years in compatible groups of four to ten. In this type of experiment a monkey is used roughly once a month, though often less frequently. It is anaesthetised in its cage at the AFL and remains anaesthetised throughout the experiment. Several hours later once it has fully regained consciousness it is returned to its cage. By way of preparation, a cannula is inserted into one of the monkey's legs at the AFL so that researchers can administer the tracer safely and take blood samples. Blood samples are taken during the experiment to enable analysis of the tracer in the blood plasma.

Each day will generally involve two experiments. The first sees the tracer being injected so that researchers can study its distribution in the brain. The second PET experiment is identical to the first except that a known reference substance is injected 10-20 minutes before the tracer. The reference substance binds to the receptor in question, thus preventing the tracer from doing so. These experiments demonstrate the degree to which the tracer binds specifically to the receptor, and are extremely important for subsequent studies on humans.