Image taken in vivo following the injection of anti-CD20 antibodies, showing cancer cells (in magenta) and macrophages (in green) attacking tumor cells. © Institut Pasteur – Dynamics of Immune Responses Unit

Monoclonal antibodies are part of the therapeutic arsenal for eliminating cancer cells. Some make use of the immune system to act and belong to a class of treatment called “immunotherapies.” But how do these antibodies function within the tumor? And how can we hope to improve their efficacy? Using innovative in vivo imaging approaches, scientists from the Institut Pasteur and Inserm visualized in real time how anti-CD20 antibodies, used to treat B-cell lymphoma, guide the immune system to attack tumor cells. Their findings were published in the journal Science Advances on February 19, 2021.

Anti-CD20 antibodies are used in clinical practice to treat patients with B-cell lymphoma, a type of blood cancer. The treatment, often used in combination with chemotherapy, has been largely proven to improve the prognosis of patients but some respond less effectively than others. It is therefore critical to better understand how these therapies actually work to then be able to overcome their weaknesses.

Scientists from the Dynamics of Immune Responses Unit (Institut Pasteur/Inserm), led by Philippe Bousso, visualized the effect of the anti-CD20 antibody within the tumor seconds following injection and relied on tumor cells that change color as they die. Using this strategy, they demonstrate that macrophages play an essential role in the efficacy of the therapy, by ingesting tumor cells coated with antibodies.

“What surprised us was the observation that this elimination phase, which begins immediately after the injection of the antibody, became less effective after just a few hours,” explains Capucine Grandjean, lead author of the study. The scientists also showed that the quantity of macrophages in the tumor was very likely to be insufficient to destroy all cancer cells.

In revealing some of the weaknesses of these antibodies, the scientists have opened up new avenues for the development of next-generation therapies. In particular, increasing the presence and activity of macrophages in the tumor represents a promising strategy to boost the efficacy of these therapeutic antibodies.

Senescent cells. © Inserm/Lemaitre, Jean Marc/U661

Until now considered highly promising in the fight against aging, the therapeutic strategy of eliminating the senescent cells that accumulate in the body is being challenged by the team of Dmitry Bulavin, Inserm researcher at the Institute for Research on Cancer and Aging of Nice (Inserm/CNRS/Université Côte d’Azur). Their research using mice has shown that in the liver the first senescent cells appear in a population of hepatic cells that play a major role in detoxifying the body. When they studied the elimination of these senescent cells, the researchers saw that the effect on liver function deterioration was worse than that of aging. Their findings,published in Cell Metabolism, provide new avenues for ensuring longer life expectancy in good health.

Aging is associated with the deterioration of many functions of the body and the onset of age-related diseases. Eyesight, hearing, muscle, heart and kidney function decline and the risks of cancer, cardiovascular disease and dementia steadily increase.

Also observed is the accumulation of so-called “senescent” cells in the tissues. While unable to divide due to having lost their function, these cells can induce inflammation and the production of oxidized residues that are toxic to the body. Removing these senescent cells from the body to reduce inflammation and restore tissue and organ function is seen as an interesting therapeutic strategy. Medicines whose mode of action is based on eliminating the survival factors of senescent cells (thus leading to their death) are even in development.

Senescent cells in the liver appear in green on the image. ©Dmitry Bulavin

However, before continuing with the development of these therapeutic strategies, Dmitry Bulavin, Inserm researcher at the Institute for Research on Cancer and Aging of Nice (IRCAN, Inserm/CNRS/Université Côte d’Azur) and his team consider that it is first necessary to gain a deeper understanding of the emergence of these cells, their impacts on the body, and to study whether eliminating them would not have any unexpected harmful effects.

To do this, the researchers developed genetically-modified mouse models in order to track in vivo the appearance and localization of senescent cells over time, by monitoring the expression of gene p16 – a senescence marker common to all cell types.

Fibrosis instead of senescence

The researchers observed that the first senescent cells appeared primarily and in large quantities in the liver and more particularly in the sinusoidal endothelial cells found on its surface. These cells play a major role in detoxifying the body, enabling the passage of molecular “waste” from the blood to the liver where it is broken down and then eliminated. “To begin with, senescence has no impact on the filtering activity, which continues to function correctly. But over time, this function decreases and toxic residues inducing oxidative stress start to build up in the body. This early-onset mechanism could be a trigger for aging and the onset of age-related diseases. So we focused on this tissue to study the impact of the spontaneous elimination of senescent cells in our animal model”, explains Bulavin.

The team observed that the mice that underwent elimination of their senescent liver cells generally did not do as well as the others.

The Lepista inversa fungus has restorative properties to correct certain genetic mutations. © Christine Bailly

An ordinary edible mushroom could be a game-changer when it comes to the treatment of rare genetic diseases. These affect hundreds of millions of people worldwide who often find themselves powerless in the absence of effective therapy. A team led by Fabrice Lejeune, Inserm researcher at the CANcer Heterogeneity, Plasticity and Resistance to THERapies laboratory (Inserm/ CNRS/ Université de Lille/Institut Pasteur de Lille/Lille University Hospital), in collaboration with a team from the French National Museum of Natural History, has shown that an active ingredient contained in the Lepista inversa mushroom has repair properties, making it possible to correct certain genetic mutations, known as “nonsense” mutations. Their findings have been published in Nature Communications[1].

Rare diseases constitute a major public health problem, affecting 300 million people worldwide. Of genetic origin in 80% of cases, there is currently no curative treatment for these hereditary conditions which include cystic fibrosis, hemophilia, and Duchenne muscular dystrophy. However, it has now been established that specific genetic mutations, known as “nonsense” mutations, are implicated in almost 10% of cases of rare genetic diseases.

DNA is made up of nucleotides, organic compounds that code the amino acids implicated in the synthesis of the proteins needed for the body to function correctly. In practice, “nonsense” mutations introduce a “stop codon” in the mutated gene – a sequence of nucleotides that brings the synthesis of the corresponding protein to a premature halt. From that point, the protein is no longer available as such, leading to the onset of the clinical symptoms of the disease.

Identifying how to correct these mutations therefore represents a major challenge for rare genetic disease researchers such as Fabrice Lejeune and his team at the CANcer Heterogeneity, Plasticity and Resistance to THERapies laboratory (Inserm/ CNRS/ Université de Lille/Institut Pasteur de Lille/Lille University Hospital), working in collaboration with the Chemical library / Extract library and JRU 7245 CNRS Communication Molecules and Adaptation of Micro-organisms of the National Museum of Natural History in Paris.

In 2017, the latter had already made a surprising discovery by showing that extracts from the ordinary edible mushroom Lepista inversa could repair nonsense mutations in three cell lines isolated from patients with cystic fibrosis.

Repair properties

In their new study, published in Nature Communications, the research teams have for the first time identified the active substance in the mushroom that is capable of correcting the nonsense mutations associated with the UGA stop codon, the most common of the three stop codons of the human genetic code.

By fractionating extracts of the Lepista inversa mushroom, the researchers were able to identify one of its active substances – compound DAP (2,6 diaminopurine). They showed that this compound repairs nonsense mutations in human cell lines, and also in animal models. It is also of very low toxicity.

This discovery opens up interesting therapeutic avenues for patients with rare genetic diseases. “The idea is to be able to correct the clinical aspects by repairing the nonsense mutations linked to the UGA codon and by restoring the function of the mutated gene. It must be noted that it is not about giving the mushroom to patients to consume directly, given that it contains other compounds whose effects we cannot control, but rather about developing treatments based on the active substance identified here”, emphasizes Lejeune.

The next step for the researchers will involve testing this active substance in other animal models in order to then be able to rapidly launch clinical trials should the results remain promising.

[1] A patent was filed for the discovery via SATT Lutech: Purine derivative for use in the treatment or prevention of diseases caused by a nonsense mutation – October 2017 – S. Rebuffat, S. Amand, C. Maulay-Bailly and F. Lejeune -PCT/EP2017/076846; WO2018073413A1

Video showing T lymphocytes (green) attacking a tumor (blue and orange). In vivo real-time experiments show how T lymphocytes act both locally and remotely within the tumor. © Ronan Thibaut and Philippe Bousso, Institut Pasteur / Inserm

How does the immune system act to limit tumor development? Using in vivo imaging tools, scientists from the Institut Pasteur and Inserm described the spatiotemporal activity of tumor-infiltrating T lymphocytes, both locally and remotely. Their research was published in the journal Nature Cancer on March 9, 2020.

Some cells in the immune system, like T lymphocytes, are capable of attacking cancer cells. Promising new therapies known as immunotherapies, recognized by the 2018 Nobel Prize in Medicine, attempt to boost the immune system’s response to cancer.

But how exactly do T lymphocytes act in tumors? T lymphocytes are killer cells that are capable of infiltrating a tumor and destroying cancer cells, one by one, through direct contact. This destruction of cancer cells is a highly local phenomenon that only occurs in the immediate vicinity of killer cells. But during these contacts, T lymphocytes also produce soluble molecules known as cytokines. Scientists from the Institut Pasteur and Inserm set out to understand the effect of one of these cytokines, known as interferon-gamma (IFN-γ), on the tumor microenvironment.

They used highly powerful imaging techniques to visualize, in real time and in vivo in mice, both the behavior of T lymphocytes and also the effect of IFN-γ within the tumor. The scientists observed that rather than acting locally, the cytokines spread rapidly within the tumor and affect cancer cells that may be distant from the T cells.

“This remote action within the tumor is very interesting because it enables T lymphocytes to act on a large number of cancer cells, especially those that may have developed mechanisms to escape the immune system,” explains lead author Philippe Bousso, an Inserm researcher and Head of the Dynamics of Immune Responses Unit at the Institut Pasteur.

In their research, the scientists also demonstrated that the number of T lymphocytes that successfully infiltrate the tumor is correlated with the quantity of cytokine produced and determines the extent of tumor cell response. A study of melanoma patient cells supports this model of remote action by immune cells. Stimulating this collective response could therefore represent a key target for future immunotherapy approaches.

Glioblastomas are the most common tumors of the central nervous system Image taken using a Zeiss Axioimager Z1 widefield epifluorescence microscope. Inserm/Guichet, Pierre-Olivier

Glioblastomas are the most common type of brain tumor, and their prognosis is often highly unfavorable. A collaborative study by Jean-Léon Thomas, Inserm researcher at the Brain & Spine Institute (Inserm/CNRS/Sorbonne Université) and Pitié-Salpêtrière Hospital AP-HP, and Akiko Iwasaki (Department of Immunology, Yale University School of Medicine, USA), has revealed the beneficial role played by the meningeal lymphatic vascular network in treating these tumors – in the short and longer term. Their findings have been published in Nature.

Glioblastomas are not just the most commonly occurring type of brain tumor, they are also the most severe. With an estimated prevalence of 1/100,000, they mainly affect patients between 45 and 70 years of age. Treatment currently involves surgery combined with radiation therapy and chemotherapy. Therapeutic benefit, in terms of survival, remains modest (currently around 18 months), inciting researchers to continue to explore new avenues of potential treatment.

Eric Song (Yale University), first author of this study, Jean-Léon Thomas, Akiko Iwasaki and their colleagues studied the meningeal lymphatic network to see whether it regulates the immune system in response to the presence of a brain tumor. A veritable pipework of lymphatic vessels in the meninges surrounding the brain, the meningeal lymphatic network has been generating particular interest since the publication of studies over the previous five years showing its connection to the lymph nodes of the neck (where immune cells proliferate and differentiate), and its role of draining immune cells into the latter.

In their latest study, published in Nature, the researchers worked with animal models of glioblastoma. They showed that the tumor would disappear following prior enlargement of the meningeal lymphatics – achieved by injecting the meninges with lymphatic growth factor VEGF-C. The growth of the meningeal lymphatic network induced by VEGF-C (as can be seen in the photo) was correlated with the mass entry of immune T cells (CD4 and CD8), which under normal conditions are absent, into the tumor environment.

This short-term response destroys the tumor and is accompanied by the persistence of “memory cells” specifically directed against the tumor cells, which makes it possible to reject the same tumor in the longer term.

Nevertheless, the researchers’ experiments show that it is in combination with an immunotherapy already used in neuro-oncology that the transient VEGF-C treatment is the most effective, enabling complete eradication of the existing glioblastoma. “Our study highlights the fact that reinforcing the network of meningeal lymphatic vessels increases tumor antigen traffic from the meninges to the lymph nodes”, explains Thomas.

With his colleagues, he concludes that the major role of this network is to transport, from the meninges, an immune alert message triggering activation of the lymphocytes directed against the tumor.

The findings of this study therefore open up new avenues in the treatment of brain tumors by targeting the meningeal lymphatic vessels and their associated lymph nodes.

Tertiary lymphoid structures are cellular aggregates that contain many B-cells (in purple) located near tumors. This is the area where the antitumor immune response starts. ©Antoine Bougouin/Centre de recherche des Cordelier/Inserm, Sorbonne Université, Université de Paris

How can we improve and better personalize the treatment of soft tissue sarcomas, these particularly resistant and aggressive forms of cancer? An international team led by Wolf Hervé Fridman with researchers from Inserm, Sorbonne Université and Université de Paris at the Cordeliers Research Center, in collaboration with the French League against cancer and Institut Bergonié, has shown that B cells also play a major role in predicting of patient’s response to immunotherapy.  It was previously thought only T cells could be used in this way. Their findings, to be published in Nature, pave the way for the personalization of treatments for patients with soft tissue sarcomas.

Soft tissue sarcomas are a heterogenous group of aggressive, chemotherapy-resistant cancers that affect the soft tissues of the body (fat, muscles, fibrous tissue, blood and lymphatic vessels, nerves, etc.). In the current clinical trials, only 15% of patients respond to immunotherapy, which raises the question of the needless exposure of the other patients to the toxicity of these treatments. Identifying markers that predict their response to immunotherapy is therefore crucial. A strategy that until now has been essentially focused on the T cells – immune cells capable of recognizing cells that are infected, cancerous or foreign to the body.

Through research published in Nature, a group led by Wolf Hervé Fridman with members from Inserm, Sorbonne Université and Université de Paris at the Cordeliers Research Center, in collaboration with the “Tumor identity card” team from the French League against cancer, Institut Bergonié, and teams from the USA and Taiwan, studied the question of identifying other potential markers.

They analyzed 608 tumors, classifying them into three groups according to the composition of their microenvironment[1]: immunologically poor tumors (low in immune cells and poorly vascularized), highly vascularized tumors, and immunologically rich tumors. The latter present aggregates of various cell types with high levels of B cells, the immune cells responsible for the production of antibodies. These aggregates are called tertiary lymphoid structures. The researchers observed that an anti-tumor immune response initiates within them, thereby showing that the B cells could play an anti-tumor role.

What is more, in a phase 2 clinical trial, the patients with immunologically rich tumors showed a high response rate (50%) to one immunotherapy: pembrolizumab. These patients also had a higher survival rate than those with immunologically poor or highly vascularized tumors.

A second study by a US team, co-signed by Wolf Hervé Fridman’s team at Cordeliers Research Center (Inserm/Sorbonne Université/Université de Paris), and published in parallel in Nature, extended these observations to include melanoma and kidney cancer.

The results of these studies show that in addition to the T cells that are usually researched, the B cells play an essential role in the response to immunotherapy for certain cancers. These cells bring new hope for the treatment of soft tissue sarcomas, which are particularly resistant to standard therapies. In addition, from a personalized medicine standpoint, these findings could help orient clinical decisions and patient treatment by means of a simple test to identify those whose tumors are immunologically rich.

On the basis of these results, an initial French clinical trial coordinated by Antoine Italiano (Institut Bergonié, Université de Bordeaux), co-author of the first article, and which includes patients with such tumors, is currently ongoing within the French Sarcoma Group.

[1] The tumor microenvironment corresponds to the biological elements that surround the tumor (blood vessels, immune cells, various types of cells, signaling molecules, extracellular matrix, etc.) and with which it interacts.