Fluorescence tagging to monitor CD8 T cell recirculation from the tumor to the tumor-draining lymph node: the impact of focal radiation therapy on recirculation

Abstract

Abstract T cells are continuously moving through tissues and recirculating back into the peripheral blood via lymph nodes. In cancer, tumor-specific T cells are enriched in the tumor environment and their presence is associated with improved outcome in patients and in preclinical models. T cells are known to contribute to tumor control following radiotherapy despite evidence indicating that radiation can be directly cytotoxic to lymphocytes. The impact of radiation therapy on recirculation of T cells through the tumor to the tumor draining lymph node (TDLN) and their trafficking to distant sites is unclear. By photoconverting tumor infiltrating cells using focal UV in Kaede mice we can use fluorescence tagging to directly identify T cells in the TDLN that originated in the tumor. We demonstrate that radiation therapy significantly decreases CD8 T cell trafficking from the tumor to the TDLN. Using single cell RNASeq and flow cytometry, we demonstrate that radiation therapy is locally cytotoxic to proliferating effector CD8 T cells within the tumor environment. This results in the loss of this effector population in the TDLN following treatment. Using flow cytometry and direct blockade of T cell entry into the LN, we characterize the CD8 T cells in the TDLN that proliferate following radiation therapy. Our data demonstrate that radiation therapy is locally cytotoxic and restricts CD8 T cell recirculation to the TDLN. Since tumor control following radiation therapy is partially dependent on CD8 T cell responses, these data force us to re-evaluate both the type and location of T cell populations that contribute to tumor control following radiation therapy. Supported by grants from the NIH (R01CA182311, R01CA244142, R01CA208644)