Quantification of Immune Variables from Liquid Biopsy in Breast Cancer Patients Links Vδ2+ γδ T Cell Alterations with Lymph Node Invasion

Simple Summary V delta 2(+) gamma delta T cells have potent antitumor properties both in vitro and in murine preclinical models of breast cancers. However, in the context of human breast cancer, there is a lack of information for potential phenotypic alterations of this crucial immune cell subset. This is partly due to V delta 2(+) gamma delta T cells scarcity in surgical specimens. To break this deadlock, we assessed V delta 2(+) gamma delta T cell phenotypes using untreated breast cancer patients' peripheral blood, so-called minimally invasive "liquid biopsy". We show that circulating V delta 2(+) gamma delta T cell phenotypic alterations are already established at diagnosis and related to tumor progression. Notably, terminally differentiated V delta 2(+) gamma delta T cells expressing canonical markers of replicative senescence and exhaustion were significantly associated with tumor-draining lymph node invasion. Our results shed light on the interest of using liquid biopsy to monitor rare events and support V delta 2(+) gamma delta T cell involvement in breast cancer pathogenesis and progression. The rationale for therapeutic targeting of V delta 2(+) gamma delta T cells in breast cancer is strongly supported by in vitro and murine preclinical investigations, characterizing them as potent breast tumor cell killers and source of Th1-related cytokines, backing cytotoxic alpha beta T cells. Nonetheless, insights regarding V delta 2(+) gamma delta T cell phenotypic alterations in human breast cancers are still lacking. This paucity of information is partly due to the challenging scarcity of these cells in surgical specimens. alpha beta T cell phenotypic alterations occurring in the tumor bed are detectable in the periphery and correlate with adverse clinical outcomes. Thus, we sought to determine through an exploratory study whether V delta 2(+) gamma delta T cells phenotypic changes can be detected within breast cancer patients' peripheral blood, along with association with tumor progression. By using mass cytometry, we quantified 130 immune variables from untreated breast cancer patients' peripheral blood. Supervised analyses and dimensionality reduction algorithms evidenced circulating V delta 2(+) gamma delta T cell phenotypic alterations already established at diagnosis. Foremost, terminally differentiated V delta 2(+) gamma delta T cells displaying phenotypes of exhausted senescent T cells associated with lymph node involvement. Thereby, our results s