Abstract A002: Dissecting the brain metastatic microenvironment to uncover immune and molecular correlates of response to immunotherapy
Authors: Daugherty-Lopes Amelie , Perez-Guijarro Eva , Gopalan Vishaka , Rappaport Jessica , Chen Quanyi , Huang April , Lam Khiem C. , Chin Sung , Ebersole Jessica , Wu Emily , Needle Gabriel , Church Isabella , Kyriakopoulos George , Xie Shaojun , Zaho Yongmei , Gruen Charli , Sassano Antonella , Araya Romina E , Thorkelsson Andres , Smith Cari , Lee Maxwell P. , Hannenhalli Sridhar , Day Chi-Ping , Merlino Glenn , Goldszmid Romina S. , Xie Shaojun 
Published: November 2024

Abstract
Despite promising results with immune checkpoint blockade (ICB) therapy, brain metastases (BrM) remain a deadly complication for cancer patients. Understanding the highly specialized brain metastatic tumor microenvironment (BrTME) is crucial for identifying determinants of response, however, progress has been hindered by limited access to patient samples and scarcity of relevant preclinical models. Here, we developed two mouse melanoma BrM models by intracardiac injection of cells derived from our previously established M4-B2905 melanoma mouse cell line. We characterized their mutational landscape and performed single-cell phenotypic and transcriptomic analysis, demonstrating that these models recapitulate the cellular and molecular features of human melanoma BrMs. Comparative and interactome analysis of our models revealed key factors contributing to ICB response and resistance. We found that the responsive model (BR1) was characterized by tumor cells that polarize microglia toward reactive states via inflammatory programs and response to IFN signaling. These microglia express high levels of antigen presentation and immunostimulatory molecules, triggering T cell recruitment and activation and promoting ICB therapy response. In contrast, in the resistant model (BR3), the tumor cells express neurological molecular signatures and ligands that sustain microglia homeostasis. This results in poor T cell infiltration predominantly composed of naïve cells, evading immune reaction and promoting ICB resistance. While we showed that systemic ICB therapy induced BrTME changes in both models, differences between responder and resistant models were maintained, emphasizing the importance of tumor cell-intrinsic programs in dictating the BrTME. We validated the translational relevance of our findings and demonstrated that BR1 signatures positively correlate with T cell infiltration and are associated with improved patient outcomes, whereas BR3 signatures negatively correlate with T cells and are found in patients with worse prognosis. Here we address an important challenge in the field by providing clinically relevant BrM models that recapitulate both the cellular and molecular features of human disease and the variability of ICB response seen in patients. We further reveal mechanistic insights into BrM ICB response and identify potential therapeutic targets to modulate the BrTME.
Citation Format: Amelie Daugherty-Lopes, Eva Perez-Guijarro, Vishaka Gopalan, Jessica Rappaport, Quanyi Chen, April Huang, Khiem C. Lam, Sung Chin, Jessica Ebersole, Emily Wu, Gabriel Needle, Isabella Church, George Kyriakopoulos, Shaojun Xie, Yongmei Zaho, Charli Gruen, Antonella Sassano, Romina E Araya, Andres Thorkelsson, Cari Smith, Maxwell P. Lee, Sridhar Hannenhalli, Chi-Ping Day, Glenn Merlino, Romina S. Goldszmid, Shaojun Xie. Dissecting the brain metastatic microenvironment to uncover immune and molecular correlates of response to immunotherapy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr A002.