Project 3: Development of Novel Therapies and Biomarkers for TNBC Patients - Abstract Triple Negative Breast Cancer (TNBC = Estrogen Receptor-negative, Progesterone Receptor-negative and HER2-negative) is amongst the most clinically challenging to treat because of its poor prognosis and limited treatment options. TNBC is a known heterogenous clinical group that shows significant variation based upon histology, gene expression patterns, response to therapy, and even for patient survival outcomes. Despite this heterogeneity there are key recurrent biological features of clinical importance including consistently high proliferation rates, and a likelihood of having immune infiltrates. The typical association with immune cell features led to the testing, and now approval, of drugs that target the immune system, thus highlighting the importance of tumor cell to immune cell interactions in TNBC. We will build upon this foundation and our genomic profiling data coming from human TNBC clinical trials and Genetically Engineered Mouse Models, to develop and test here new combinatorial therapies for possible use in TNBC, and which will be guided by biomarker-based patient selection. Specifically, we will evaluate combination regimens with an anti-PD1 backbone containing CD40LG agonist antibody to boost Bcell and/or Dendritic cell function, and combinations containing drugs that inhibit macrophage function. Lastly, we have identified a unique metabolic vulnerability in TNBC that is a high dependence upon pyrimidine biosynthesis. Here we will target pyrimidine biosynthesis alone in mouse models and in human clinical trials, and we will perform combinatorial screens in vitro and in vivo to identify optimal partner drugs that would synergize with pyrimidine biosynthesis inhibitors. In all cases, single cell genomics using RNAseq and spatial transcriptomics imaging will be performed in order to inform about biological responses and to develop and validate biomarkers for future patient selection.