Role of intratumoral high endothelial venules in tumor immunity

点击翻译按钮获取中文摘要

Project Summary Immune checkpoint inhibition emerged as promising cancer treatment strategies. However, only a subset of patients respond to these therapies at present. Significant clinical evidence indicates that abundant tumor infiltration of effector T cells and B cells is a prerequisite for the success of the immune checkpoint inhibition therapies. However, these lymphocytes are largely excluded from many patients' tumors, which makes the tumor unresponsive to the immunotherapies. High endothelial venules (HEV) are specialized venules that serve as gateways for naïve lymphocyte recruitment, and these blood vessels can develop ectopically in tumors. High HEV density in tumors correlate with favorable clinical outcomes, suggesting that the promotion of intratumoral HEV formation would offer a novel opportunity to improve immunotherapies. The small GTPase R-Ras balances angiogenic sprouting and vessel maturation, and normalizes tumor blood vessels. Several lines of evidence indicate the importance of R-Ras for the formation of intratumoral HEVs. We hypothesize that intratumoral HEVs shape the tumor immune landscape through efficient recruitment of lymphocytes, thereby creating the immunostimulatory microenvironment favorable for immune checkpoint inhibition therapies. We propose a critical role of R-Ras in this process by facilitating HEV formation in tumors. Using novel genetic models of loss- and gain-of-function of R-Ras in endothelial cells, Aim 1 will demonstrate that R-Ras facilitates the formation of HEVs within the tumor vasculature and determine how these HEVs affect the tumor infiltration of T cells, B cells, dendritic cells, and other immune cell types in immunogenic mouse mammary tumor and melanoma. The influence of intratumoral HEVs on cytokine environment will also be determined. The analyses will be conducted by immunofluorescence, ELISA, FACS, and RNAseq. Clinical cancer specimens will be examined to corroborate the findings from the mouse studies. Aim 2 will functionally characterize tumor HEVs and analyze intratumoral priming of HEV-recruited T cells to a specific antigen using adoptive transfer of naïve OT-1 T cells to OVA-expressing tumors. Aim 3 will determine how intratumoral HEVs impact the immune destruction of tumors and the responsiveness to PD-1/PD-L1 inhibition therapies. As the gateways for T cell/B cell recruitment to tumors, intratumoral HEVs are potential new targets to reprogram the tumor immune landscape and to improve patients' response to immune checkpoint inhibitors. The expected outcome of this study will provide the proof-of-concept for such ideas.