Scientific breakthroughs in research with monkeys
Here you can read more about the scientific breakthroughs that research with monkeys has contributed to. The two species of monkeys used in research at Karolinska Institutet (KI) are rhesus macaques and crab-eating macaques.
Vaccine research
What happens in the body when we are vaccinated?
For more than two decades, researchers at Karolinska Institutet have studied how different vaccines affect the immune system. The goal is to understand how vaccines work—from the moment they are injected until the body builds protection against disease. Through advanced studies in cells, animals, and humans, researchers have been able to track how vaccines move through the body and how they activate key parts of the immune system.
These studies have produced important knowledge about how vaccines spread in the body, how long they remain, and how they stimulate immune responses. This research helps us develop better vaccines and smarter vaccination strategies.
What happens immediately after vaccination?
When a vaccine is injected into a muscle, the body reacts immediately. A local inflammation occurs, a kind of “alarm response”which quickly attracts immune cells. These cells help absorb the vaccine and initiate the body’s defense.
Researchers at KI have shown that both traditional protein-based vaccines and modern mRNA vaccines activate the immune system in lymph nodes near the injection site. There, immune cells—T cells and B cells—are trained to recognize and fight viruses.
How mRNA vaccines work
mRNA vaccines, such as those used during the SARS-CoV-2 pandemic, work by giving the body instructions to produce parts of a virus. The vaccines are harmless, but they help the immune system learn to recognize and defend against the virus.
KI studies have shown that mRNA vaccines activate special structures in lymph nodes called germinal centers. There, B cells which produce antibodies are trained to better recognize viruses and create long-lasting protection.
It has also been shown that helper cells, called T follicular helper cells, play an important role. These cells help B cells become more effective and produce stronger antibody responses. They also contribute to the formation of memory cells, which provide long-term protection.
KI researchers have identified which cells produce vaccine antigens after mRNA vaccination and demonstrated that activation of vaccine-specific T and B cells occurs exclusively in the lymph nodes draining the injection site. This was a groundbreaking finding that received significant attention during the SARS-CoV-2 pandemic.
What influences vaccine effectiveness?
The composition of a vaccine affects how well it works. If the vaccine remains longer at the injection site or in lymph nodes, immune cells have more time to respond. It may also be important that the antigen—the component the immune system is trained to recognize—is presented in a way that activates many B-cell receptors simultaneously.
KI research has also shown that the immune environment at the time of vaccination plays a role. If the immune system is already activated in a certain way, it can influence how T cells respond and develop.
Additives that enhance the effect
Substances added to vaccines, known as adjuvants, play an important role. Adjuvants strengthen the body’s response and help the immune system react more effectively. KI researchers have shown that the choice of adjuvant influences both the quantity and quality of antibodies produced.
Breakthroughs in RSV vaccines – protection against respiratory infections
KI researchers have also contributed to developing new vaccines against RSV (respiratory syncytial virus), which causes severe respiratory infections, particularly in young children and the elderly.
Together with international collaborators, KI researchers have tested a new type of vaccine based on nanoparticles. These nanoparticles act as small carriers that display multiple copies of viral proteins (antigens) at once.
By analyzing immune responses to this RSV vaccine candidate, KI researchers showed that a broad and diverse B-cell response provides better protection—not only against RSV but also against related viruses.
The results have been so promising that they contributed to the approval of the first RSV vaccines—a major step forward for public health.
The importance of vaccine research
KI’s research has received strong recognition in both academia and industry. The results have been published in peer-reviewed scientific journals and have contributed to increased knowledge, transparency, and collaboration worldwide.
Many studies were conducted using animal models, particularly monkeys, because their immune systems closely resemble those of humans. This has been crucial for understanding how vaccines work in the body—knowledge necessary for developing new vaccines against current and future diseases.
Research transforming psychiatry
For several decades, Karolinska Institutet has been a leader in research using PET (positron emission tomography) technology to understand mental disorders and develop new medicines.
PET acts like an advanced camera that shows how the brain functions, which is invaluable for understanding diseases such as schizophrenia, depression, and autism.
Special tracers—small molecules that act as markers in the brain—are developed to enable this research. These bind to signaling systems that are altered or disrupted in mental disorders. By tracking these markers with PET, researchers can study brain function and how drugs affect it.
Before research can be conducted in humans, sufficient data must be gathered from other species. Many breakthroughs would not have been possible without studies in monkeys, whose brains are similar to humans.
The Dopamine System in Mental Disorders
One of the most important signalling systems is the dopamine system, which is affected in schizophrenia, addiction, and depression.
In the 1980s, KI researchers developed the tracer [11C]raclopride, which binds to dopamine receptors. This development was revolutionary—first studied in monkeys and later in humans—and is now used worldwide.
This research led to a deeper understanding of how dopamine works and how drugs affect the system. It also laid the foundation for the dopamine hypothesis of schizophrenia, shaping how the disease is understood today.
PET studies have also shown the importance of finding the correct drug dosage—enough for effectiveness but without severe side effects. This is known as the therapeutic window and is crucial for safe and effective treatment.
Research at KI enables faster and more accurate Parkinson’s diagnosis
Parkinson’s disease is a severe condition affecting both patients and their families. The earlier it is detected, the greater the chance to introduce treatments that relieve symptoms and improve quality of life.
PET imaging has made a major difference. To obtain the best information, specialized biomarkers are needed—substances that act as tracers in the brain.
Earlier diagnosis – key to better treatment
A major breakthrough at KI was the development of the biomarker [18F]FE-PE2I. Initial studies in monkeys showed excellent properties and provided highly detailed information about the brain’s dopamine system, which is affected in Parkinson’s disease.
When results were later compared with healthy humans, the findings matched closely. This shows that [18F]FE-PE2I is a powerful tool for early detection and monitoring of Parkinson’s disease—allowing faster, safer diagnosis and better treatment opportunities.
Research with monkeys has improved cancer treatment
Studies involving monkeys have played a crucial role in developing life-saving methods—both in diagnostics and more effective drugs. A clear example is the cancer drug Osimertinib (Tagrisso).
To understand how this drug works in the body, advanced PET studies were first conducted in macaques. PET makes it possible to track how drugs spread and act in the body.
These early studies revealed something groundbreaking: Osimertinib was the only drug able to cross the blood-brain barrier—a natural protective barrier that prevents many drugs from reaching the brain.
This discovery was critical because brain tumors are difficult to treat due to this barrier. Later human studies confirmed that Osimertinib reaches the brain and has clear therapeutic effects.
Thanks to this research, thousands of cancer patients worldwide now have better access to effective treatment