LTβR Agonism Promotes Antitumor Immune Responses via Modulation of the Tumor Microenvironment

The presence of high endothelial venules (HEV) and tertiary lymphoid structures (TLS) in solid tumors is correlated with favorable prognosis and better responses to immune checkpoint blockade in many cancer types. Elucidation of the molecular mechanisms underlying intratumoral HEV and TLS formation and their contribution to antitumor responses may facilitate the development of improved treatment strategies. Lymphotoxin beta receptor (LT beta R) signaling is a critical regulator of lymph node organogenesis and can cooperate with antiangiogenic and immune checkpoint blockade treatment to augment tumor-associated HEV formation. In this study, we demonstrated that LT beta R signaling modulates the tumor microenvironment via multiple mechanisms to promote antitumor T-cell responses. Systemic activation of the LT beta R pathway via agonistic antibody treatment induced tumor-specific HEV formation, upregulated the expression of TLS-related chemokines, and enhanced dendritic cell (DC) and T-cell infiltration and activation in syngeneic tumor models. In vitro studies confirmed direct effects of LT beta R agonism on DC activation and maturation and associated DC-mediated T-cell activation. Single-agent LT beta R agonist treatment inhibited syngeneic tumor growth in a CD8+ T-cell-dependent and HEV-dependent manner, and the LT beta R agonist enhanced antitumor effects of anti-PD-1 and CAR T-cell therapies. An in vivo tumor screen for TLS-inducing cytokines revealed that the combination of LT beta R agonism and lymphotoxin alpha expression promoted robust intratumoral TLS induction and enhanced tumor responses to anti-CTLA4 treatment. Collectively, this study highlights crucial functions of LT beta R signaling in modulating the tumor microenvironment and could inform future HEV/TLS-based strategies for cancer treatments.Significance: LT beta R mediates tumor-specific high endothelial venule formation and immunomodulation of the tumor microenvironment that promotes antitumor immune responses, supporting LT beta R agonism as an approach to enhance the antitumor efficacy of immunotherapies.