Identify Aggressive Breast Cancer Sooner

In almost all solid tumors—i.e. cancers with a solid tissue structure—the detection of tumor cells in the lymph nodes is considered a decisive marker for the progression of the disease. Lymph node involvement has a significant influence on the choice of treatment and the chances of survival for patients.

In particular, solid tumors in the breast, on the skin or in the gastrointestinal tract use the lymphatic system as the main route for distant metastasis, for example to the lungs, liver and bones. However, lymph nodes also play an important role in the immune system. They serve as a meeting place for various immune cells that cooperate to recognize and fight pathogens.

This interface between metastasis and immunity is precisely the field of research pursued by Dr. Angela Riedel, molecular biotechnologist and junior group leader at the Mildred Scheel Early Career Centre (MSNZ) at Würzburg University Hospital (UKW). She has just published her latest discoveries in Immunity. With her small team, she succeeded in conducting an extensive and comprehensive study that included data from both patients and mouse models to generate and substantiate the hypotheses.

Together, they examined the lymph nodes of mouse models and patients with triple-negative breast cancer (TNBC). This is an aggressive form of breast cancer that accounts for about 10 to 15% of all breast cancer cases and often affects young women. Targeted standard therapies such as modern hormone therapies are not an option here due to the absence of three key characteristics.

Premetastatic environment in the lymph node—monocytes become corrupt, FRCs become accomplices

Their research focused on the tumor-draining lymph node closest to the breast cancer. As it is the first to filter the fluid secreted by the tumor, it is also known as the sentinel lymph node (SLN). Riedel and her research group were the first to demonstrate that the tumor manipulates the environment of the draining lymph nodes even before it settles there. This leads to an altered immune response, which in turn promotes the development of distant metastases.

"We need to understand metastasis better in order to prevent it," emphasizes Riedel. "This is because the growth of metastases in vital organs poses a significant challenge to the successful cure of breast cancer patients. However, by addressing the immune evasion mechanism in the lymph nodes, we can reduce the risk of metastasis."

Her research group identified fibroblastic reticulum cells (FRCs) as the main players in the reprogramming of lymph nodes. These cells form the structural framework of the lymph nodes and release special signals via the cytokines CCL2 and CCL7 that attract monocytes. Monocytes are the largest white blood cells and play a key role in the immune system. However, Riedel's team observed that the monocytes in TNBC lymph nodes became corrupted and blocked the activity of T cells, which are normally responsible for fighting cancer cells.

Metastatic niches provide shelter for tumor cells

"Using the latest methods, such as spatial transcriptomics, single-cell RNA sequencing, proteomics, and immunofluorescence, which we established independently in the laboratory, we were able to decipher that these suppressive monocytes accumulate together with FRCs and T cells in specific niches within the lymph nodes," reports Moutaz Helal, who, together with Greta Mattavelli, is the first author of the highly regarded study.

He joined Angela Riedel's group in April 2020 as part of his master's thesis and has been a doctoral student since October 2021. After completing his bachelor's degree in pharmacy in Egypt, he completed his master's degree in molecular oncology as part of the biochemistry program at the University of Würzburg. At MSNZ, he finally discovered his love for bioinformatics. He emphasizes the exceptional quality and modernity of MSNZ's equipment and campus core facilities.

But how do FRCs support immune escape and promote the formation of these dangerous pre-metastatic niches? The team was able to show that FRCs are activated via Toll-like receptor 4 (TLR4). Typically, TLR4 is a sensor on the surface of cells of the immune system that acts as an alarm system, reporting dangers. However, it is sometimes misused by tumors to slow down the immune system.

Fewer metastases in the lungs due to targeted TLR4 blockade

The group wondered: What happens when this receptor is specifically blocked in the draining lymph node? "Our studies in mice showed that targeted inhibition in combination with modern PD1 immunotherapy can restore T-cell activity and significantly reduce distant metastasis in the lungs," reports Greta Mattavelli.

The Italian-born scientist calls the day she first saw the therapy succeed in the mouse model "a day to remember." Greta Mattavelli started her Ph.D. in October 2020 as the first doctoral student in Riedel's group. She earned her bachelor's and master's degrees in medical and molecular biotechnology in Milan.

In the study, she supervised the laboratory work, which sometimes required night shifts and weekend work for the entire team. And she is more than familiar with the routes across campus to the gynecological clinic and pathology department.

In collaboration with the UKW Gynecological Department headed by Prof. Dr. Achim Wöckel and the Institute of Pathology headed by Prof. Dr. Andreas Rosenwald, the team was able to confirm in patient samples that the same process can also be observed in human TNBC patients. This means that therapies targeting this lymph node environment could also improve the prognosis for patients with aggressive breast cancer.

PD-L1 on monocytes in lymph nodes as a marker for PD-1 immunotherapy

At the beginning of 2018, immunotherapy, typically combined with chemotherapy, became the primary treatment recommended in clinical guidelines for patients with PD-L1-positive primary tumors. Background: The surface protein PD-L1 (programmed death ligand 1) expressed by the tumor binds to the PD-1 receptor on T cells and signals them not to attack the tumor. Immunotherapy with antibodies blocks this binding, so that the tumor loses its camouflage and the body's own T cells can once again develop their natural defenses.

However, PD-L1 is also often found in high concentrations on monocytes in pre-metastatic lymph nodes. PD-1 immunotherapy, which releases the brake and reactivates the T cells, could therefore also be effective in the early stages of breast cancer, regardless of the immunohistochemical analysis of the mammary carcinoma. According to Riedel, PD-L1 expression on cells of the tumor-draining lymph node could be investigated as a marker for PD-1 immunotherapy.