The lymphatic endothelium in the context of radioimmuno-oncology

Abstract

Simple Summary The introduction of immunotherapy within the usual strategies for cancer treatment has meant an enormous advance in the survival of patients with very restrictive prognoses. However, a high percentage of patients still cannot benefit from it. The lack of response to immunotherapy is mainly due to resistance from the tumor stroma itself. The lymphatic endothelium constitutes a permeable vascular system from the stroma specially dedicated to balancing tissue homeostasis and leukocyte emigration. Most solid carcinomas present lymphatic microvasculature that participates in tumor progression ambivalently. On one hand, it facilitates the transit of immune cells toward the lymph nodes and therefore promotes the antitumor response; on the other hand, they constitute an accessible route through which tumor cells metastasize to the lymph nodes. Due to this double function, it is not easy to establish strategies that educate the lymphatic endothelium only in its antitumor function without compromising its participation in the immune response. In this review, we study how combinations of radiotherapy and immunotherapy can modulate lymphatic function to use them in therapeutic approaches. The study of lymphatic tumor vasculature has been gaining interest in the context of cancer immunotherapy. These vessels constitute conduits for immune cells' transit toward the lymph nodes, and they endow tumors with routes to metastasize to the lymph nodes and, from them, toward distant sites. In addition, this vasculature participates in the modulation of the immune response directly through the interaction with tumor-infiltrating leukocytes and indirectly through the secretion of cytokines and chemokines that attract leukocytes and tumor cells. Radiotherapy constitutes the therapeutic option for more than 50% of solid tumors. Besides impacting transformed cells, RT affects stromal cells such as endothelial and immune cells. Mature lymphatic endothelial cells are resistant to RT, but we do not know to what extent RT may affect tumor-aberrant lymphatics. RT compromises lymphatic integrity and functionality, and it is a risk factor to the onset of lymphedema, a condition characterized by deficient lymphatic drainage and compromised tissue homeostasis. This review aims to provide evidence of RT's effects on tumor vessels, particularly on lymphatic endothelial cell physiology and immune properties. We will also explore the therapeutic options available so far to modulate signaling through lymphatic endothelial cell receptors and their repercussions on tumor immune cells in the context of cancer. There is a need for careful consideration of the RT dosage to come to terms with the participation of the lymphatic vasculature in anti-tumor response. Here, we provide new approaches to enhance the contribution of the lymphatic endothelium to radioimmuno-oncology.