Beneficial modulation of the tumor microenvironment and generation of anti-tumor responses by TLR9 agonist lefitolimod alone and in combination with checkpoint inhibitors

Abstract

Activation of Toll-like receptor 9 (TLR9) is known to foster innate and adaptive immune responses and thus improve immune-mediated control of malignant disease. Lefitolimod is a potent TLR9 agonist without chemical modification developed for immunotherapeutic strategies. Modulation of the tumor microenvironment (TME) is a crucial requirement for the response to various immunotherapies: Immunogenic (“hot”) tumors, characterized by their T cell-infiltrated TME, respond better compared to non-immunogenic (“cold”) tumors. It has been speculated that the mode-of-action of lefitolimod provides the necessary signals for activation of immune cells, their differentiation into anti-tumor effector cells and their recruitment into the TME. We investigated the effect of lefitolimod on TME, and its potency to induce synergistic anti-tumor effects when combined with immune checkpoint inhibitory antibodies (CPI) in a murine model. Indeed, we could show that treatment with single-agent lefitolimod beneficially modulated the TME, via infiltration of activated CD8+ cells and a shift in the macrophage population toward M1 phenotype. The result was a pronounced anti-tumor effect correlated with the magnitude of infiltrated immune cells and tumor-specific T cell responses. In line with this, lefitolimod led to persistent anti-tumor memory in the EMT-6 model after tumor re-challenge. This was accompanied by an increase of tumor-specific T cell responses and cross-reactivity against different tumor cells. Lefitolimod clearly augmented the limited anti-tumor effect of the CPI anti-PD1 in an A20 and anti-PD-L1 in a CT26 model. These properties of potent immune surveillance reactivation render lefitolimod an ideal candidate as therapeutic agent for immuno-oncology, e.g. improving CPI strategies.

CD19-targeting fusion protein combined with PD1 antibody enhances anti-tumor immunity in mouse models

“…This is because there are fewer TILs in CT26 tumor tissues. 51 Thus, our study established that combined treatment could significantly inhibit the growth of tumor cells. This combined treatment strategy could be further extended to other fields including chronic infectious disease, particularly for the control of viral infection.…”

TLR9 activation cooperates with T cell checkpoint blockade to regress poorly immunogenic melanoma

“…MGN1703 is a potent, clinical-stage TLR9 agonist which has recently been described [10]. The mouse anti-mouse CTLA-4 antibody 9D9 is an exceptionally efficient depleter of Tregs when expressed with the mouse IgG2a isotype, and is not subject to antibody-mediated neutralization over repeated administration as is the hamster-derived 9H10 clone used previously [11].…”

“…Mechanistically, the addition of checkpoint blockade improves intratumoral ratios of CD8 T cells relative to suppressive stroma in the uninjected lesion and improves functional attributes of these critical effectors of anti-tumor immunity. Finally, we show that by combining both an enhanced potency TLR9 agonist (MGN1703 [10]) and a depletion-optimized CTLA-4 antibody (9D9-mIgG2a [11]), half of pre-implanted parental B16-F10 melanoma can be cured.…”

Adjuvant Effect of Toll-Like Receptor 9 Activation on Cancer Immunotherapy Using Checkpoint Blockade

“…Another studies revealed that CpG-ODN can revert resistence to PD-1 blockade therapy by expending CD8+ T cells in colon cancer animal model, enhances the efficacy of anti-PD-1 in head and neck cancer animal model (198,199). CpG-ODN modulates tumor microenvironment, turns "cold" tumor into "hot" tumor, enhances the anti-tumor effect of immune checkpoint blockade in colon cancer animal model (200). Moreover, CpG-ODN delivered by inhalation is capable of priming T-cell responses against a poorly immunogenic lung tumor (201).…”