Immune cell response to external and internal signals: Regulation of breast tumor infiltrating leukocytes by cell surface ADAM proteases and neutrophil precursor cells by the mitochondrial CLPB

Abstract

The immune system constitutes a dynamic network involving lymphoid organs, cells, humoral factors, and cytokines. Its crucial role becomes most evident when dysregulation occurs - insufficient activity of the immune system leads to severe infections and immunodeficiency- related tumors, and excessive activity of the immune system contributes to allergic and autoimmune diseases. There are two distinct categories of immune responses. Innate responses involve the use of phagocytic cells like neutrophils, monocytes, and macrophages, while acquired responses encompass the proliferation of antigen-specific B and T cells. Innate responses remain constant regardless of the number of encounters with the infectious agent, while acquired responses enhance upon repeated exposure to a specific infection. The goal of my research was to explore the regulation of the immune system in two diseases, cancer and neutropenia. Several studies have now shown a correlation between the immune infiltrate in various human cancers, patient prognosis, and therapeutic responses. It has been shown that the anomalous infiltration of immune cells into tumors or normal tissues might facilitate tumor progression, invasion, and metastasis. The clinical success of cancer immune checkpoint blockade (ICB) has further redirected the focus onto tumor infiltrating immune cells. In my research, I investigated the composition of immunosuppressive cell populations, like TIMs (Tumor-Infiltrating Macrophages) and TINs (Tumor-Infiltrating Neutrophils), or PMN-MDSCs (Polymorphonuclear Myeloid-Derived Suppressor Cells), as well as adaptive immune cell populations like T cells, B cells, in the tumor microenvironment using a mouse model of claudin- low breast cancer. I showed that ADAM12 and ADAM9, which belong to the cell surface family of ADAM metalloproteases, affect the composition of tumor infiltrating immune cells. I found that the deletion of ADAM12 in tumor cells results in reduced numbers of TINs/PMN-MDSCs and an increase in the numbers of tumor-infiltrating B cells and T cells. Importantly, the lack of ADAM12 in breast cancer cells enhances tumor sensitivity to the ICB therapy, but the initial response eventually leads to acquired therapy resistance. However, the deficiency of ADAM9 in cancer cells leads to an increase in both TINs/PMN-MDSCs and B cells, and this alteration does not enhance the efficiency of ICB therapy. Neutropenias constitute a diverse group of hematological disorders marked by the impaired maturation of neutrophilic granulocytes. The human mitochondrial CLPB protein is a widely expressed homolog of caseinolytic peptidase B, belonging to the ATPases associated with diverse cellular activities (AAA+) family. Previous studies indicated that the presence of biallelic mutations in the CLPB gene is linked to a syndrome encompassing 3-methylglutaconic aciduria with cataracts, neurologic disease, and variable neutropenia. In contrast, a different group of monoallelic CLPB mutations is the cause of severe congenital neutropenia (SCN). In my study, I explored the role of CLPB in neutrophil differentiation and assessed its impact on mitochondrial function. I found a significant decrease in mitochondrial membrane potential (MMP) in cells with CLPB knockout. Additionally, we noted a reduction in cell viability during differentiation of neutrophil precursors with CLPB knockout. Collectively, these findings provide new insights into the complex roles of immune cells in the disease.