Abstract PL03-02: From microniches to single cells: Understanding the impact of intratumoral microbes on spatial and cellular heterogeneity in cancer

Abstract The tumor microenvironment (TME) is a dynamic network that includes a variety of non-malignant cells such as endothelial cells, fibroblasts, and immune cells, which play a crucial role in tumor behavior. Advances in molecular analysis have recently identified the presence of intratumoral microbiota in several solid cancer types. However, the specific ways these microorganisms interact with human cells within the TME and contribute to disease progression are not yet fully understood. Our recent research provides new insights into how bacterial components of the intratumoral microbiota contribute to tumor heterogeneity, particularly in head and neck and colorectal cancers. To investigate these interactions, we have adapted and applied emerging technologies in spatial transcriptomics, spatial proteomics, and single-cell sequencing (INVADEseq). Our spatial analyses show that the intratumoral microbiota are not distributed randomly within human tumors; instead, they localize to distinct microniches that promote immune and epithelial cell functions supportive of cancer progression. These bacterial-colonized microniches are characterized by myeloid cell infiltration, upregulation of MAPKs and immune checkpoint proteins, and reduced T-cell levels. Furthermore, INVADEseq single-cell RNA sequencing has enabled us to identify the dominant host cell-associated bacteria, the human cell types they infect, and their impact on the transcriptional programs of infected cells from patient tumor specimens. In oral squamous cell carcinoma, Fusobacterium and Treponema species have been identified as the dominant cell-associated bacterial taxa, primarily infecting subsets of macrophages and aneuploid cancer epithelial cells and upregulating pathways associated with cancer progression. Our findings offer insights into the complex interplay between intratumoral microbiota and human components of the TME, emphasizing their role in supporting intratumoral heterogeneity and influencing cancer progression. Understanding these dynamics holds significant promise for the development of targeted therapeutic strategies aimed at disrupting bacterial-human spatial and cellular interactions within the TME. Citation Format: Susan Bullman. From microniches to single cells: Understanding the impact of intratumoral microbes on spatial and cellular heterogeneity in cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr PL03-02.