Function of PD-1 Signaling on the Activity of B cells in the Tumor Microenvironment in Breast Cancer

ABSTRACT The success of PD-1-targeted immune checkpoint inhibitor (ICI) therapy has revolutionized cancer treatment, becoming a new standard of care for various types of cancer. However, the treatment outcomes for triple negative breast cancer are still limited. To enhance the efficacy of checkpoint inhibitor therapy, it is important to

gain a deeper understanding of PD-1 regulation in the tumor microenvironment. B cells in the tumor immune microenvironment have been understudied, despite their growing recognition as key players in shaping the tumor microenvironment. The presence of tumor-infiltrated B cells indicates the prognosis

of many types of cancer. Interestingly, our previous research in pre-clinical models has shown that the sensitivity to dual ICI therapy, including the PD-1-targeted treatment, is dependent on B cells, and to a lesser extent, CD8+ T cells. These findings emphasize the importance of studying the PD-1 signaling in B cells to improve the clinical

outcomes of checkpoint inhibitor therapy. The goal of this study is to understand how PD-1 signaling pathway regulates B cells in the tumor microenvironment. One of the main mechanisms for PD-1 to modulate T cell function is through reprogramming T cell metabolism, allowing them to meet the energy requirements needed for differentiation into various

subpopulations. We hypothesize that the PD-1 activation on tumor-infiltrated B cells alters the metabolic program and B cell fate decision similar to T cells. PD-1-targeted therapy potentially impacts B cells in proliferation, survival, differentiation, and function through metabolic reprogramming, which serve as a main mechanism for

PD-1 to regulate the antitumor function of B cells. Aim 1. To evaluate our hypothesis, we will dissect how PD- 1-targeted therapy modulates B cell differentiation through metabolic switch ex vivo. We will combine primary murine B cell culture with state-of-the-art metabolic profiling tools to determine if and how PD-1 blockage directly

altered B cell differentiation and metabolism. This approach allows the evaluation of the glycolysis and fatty acid metabolic machinery in B cell to control these cells differentiation into germinal center B cells, antibody-secreting cells, and other functional subsets of B cells. Aim 2. We will use PD-1 fate mapping mice (PD-

1Cre/tdTomato.Rosa26floxp-YFP) and transgenic breast cancer models to examine how PD-1-blockage guides B cell fate decisions and function in vivo. Elucidating the interaction between B cells and the PD-1 signaling pathway, which has so far escaped the attention of the cancer immunology field, would strongly enhance the clinical

activity of ICI therapy in tumors where B cells are critical to the anti-tumor response.