Abstract PS17-45: Metastatic tissues display organ specific immune infiltration archetypes; lessons from a rapid autopsy tissue collection study

Immune composition in the tumor microenvironment (TME) of patient tumors has proven to play a central role in the development of metastases and response to therapy. Evidence has suggested that the metastatic TME is immune aberrant, however difficulty in obtaining biopsies of metastatic tumors has made assessment of the immune TME difficult. Here we utilize a rapid autopsy tissue collection protocol to assess the infiltration and composition of the immune TME in numerous metastatic tissue sites, paired disease-free tissue sites, and the associated tissue draining lymph nodes. Post-mortem tissues were collected from nine metastatic breast cancer patients shortly after death through City of Hope’s “Legacy Project for Rapid Tissue Donation” Program. The average post-mortem interval (PMI) for tissue collection was 6 hours. Collected specimens include metastatic lesions and paired non-cancer samples from every cancer-involved organ, disease-free specimens from non-involved major organs, distant and tumor-draining lymph nodes (both cancer-infiltrated and disease free), as well as blood and spleens. Immediately following collection, specimens were processed into single cell suspension for flow cytometry. Over 80 immune cell phenotypes were assessed, including CD8+ and CD4+ T cell subsets, B cell subsets, natural killer (NK) cells, tumor associated macrophages (TAMs), dendritic cell subsets, and other immune cells. Tumor infiltrated tissues were found to have comparable immune cell densities and composition compared to paired disease-free tissues of the same organ type. However, immune cell densities in metastatic tissues and disease-free tissues were significantly different between organ types, with lung immune infiltration consistently being greater than liver, brain, and skin tissues. Differences in immune composition between tissue sites were also observed. Notably, liver tissues favored the presence of IL-2 producing central memory CD8+ T cells, while lung tissues favored the presence of CD8+ tissue resident memory T cells and CD16+ NK cells. Relative to disease-free lung tissues, tumor infiltrated lungs contained diminished frequencies of CD8+ tissue resident memory T cells and altered B cell and monocyte phenotypes. Increased levels of targetable immune pathways were observed, including increased PD-L1 and CTLA-4 expressing cells in skin metastases, and increased GARP+ B cells in bone marrow metastases. These data suggest that immune monitoring and trafficking of metastatic tissues site is dictated by organ type, which can be altered in composition by tumor infiltration. Further studies such as these may reveal organ-specific mechanisms of response to therapeutic interventions. Identity of organ location for tumor metastases may guide choices for immunotherapeutic interventions. Citation Format: Colt Egelston, Weihua Guo, Eliza R. Bacon, Kena Ihle, Diana Simons, Christian Avalos, JIayi Tan, Jian Ye, Lei Wang, Minhui Lim, James R. Waisman, Peter P Lee. Metastatic tissues display organ specific immune infiltration archetypes; lessons from a rapid autopsy tissue collection study [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-45.