Systemic administration of a TLR7 agonist attenuates regulatory T cells by dendritic cell modification and overcomes resistance to PD-L1 blockade therapy.

Naoto Nishii,Yuta Kondo,Yoshihisa Kashima,Lixin Li,Hiroyuki Harada,Shigenori Nagai,Walter Lau,Miyuki Azuma,Yulong Xia,Tatsukuni Ohno,Hidetake Tachinami

doi:10.18632/oncotarget.24327

Abstract

Research on immune checkpoint blockade therapy has made great progress in cancer immunotherapy, but the number of patients who benefit from this therapy remains limited. In this study, we examined the effects of monotherapy with systemic low-dose resiquimod, a synthesized TLR7 agonist, and examined its combined effects with PD-L1 blockade in two PD-L1 blockade-resistant tumor models (SCCVII and Colon 26). Resiquimod monotherapy in SCCVII tumors, representing impaired CD8+ T cell function and accelerated regulatory T cells (Tregs) within the tumors, efficiently reduced tumor growth with more recruitment of CD8+ T cells and a reduction of Treg. The results of resiquimod monotherapy in Colon 26, representing impaired Treg recruitment, were inferior to that in SCCVII. Combined resiquimod treatment with PD-L1 blockade exerted clear additional effects, as it was associated with reduced tumor size, attenuation of Tregs, and an increased ratio of CD8+ T cells/Tregs in both tumors. Systemic administration of low-dose resiquimod induced a transient and rapid activation of plasmacytoid and conventional dendritic cells, resulting in enhanced priming of T cells in regional lymph nodes. Experiments with more limited doses of resiquimod that did not yield beneficial effects after single treatment, showed additional effects to PD-L1 blockade and comparable antitumor effects when the frequency of anti-PD-L1 therapy was decreased. Our results suggest that systemic administration of low-dose resiquimod is useful as a companion drug to PD-1/PD-L1 blockade therapy.

Highlights

The blockade of immune checkpoint molecules, such as CTLA-4 and PD-1, efficiently enhances antitumor immune responses by eliminating the immunoregulatory function of effector T cells, regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), and tumorassociated macrophages (TAMs) [1,2,3,4]
A significantly lower proportion of CD8+ T cells expressed IFN-γ. These results show that the tumor microenvironment (TME) in SCCVII had impaired effector cytotoxic T lymphocytes (CTLs) and a high recruitment of immunoregulatory TAMs and Tregs
We demonstrated the differential effects of systemic low-dose resiquimod administration in monotherapy and in combined treatment with PD-L1 blockade in two PDL1 blockade-resistant tumor models that exhibit different profiles of tumor-infiltrating lymphocyte (TIL)

Summary

Introduction

The blockade of immune checkpoint molecules, such as CTLA-4 and PD-1, efficiently enhances antitumor immune responses by eliminating the immunoregulatory function of effector T cells, regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), and tumorassociated macrophages (TAMs) [1,2,3,4]. Head and neck cancers (HNCs) do not frequently express the tumor-specific mutated antigens (called “neoantigens”) that elicit T-cell immunoreactivity and influence sensitivity to immune checkpoint blockade www.impactjournals.com/oncotarget therapy [5, 6], and their tumor microenvironment (TME) contains abundant regulatory cells, such as Tregs and MDSCs [7,8,9]. TLR7/8-mediated signaling induces the production of NF-kB-mediated proinflammatory cytokines and chemokines, and type I interferon (IFN) by activating antigen-presenting cells (APCs), resulting in the augmentation of effector T cells [12, 17, 18]. Imidazoquinolines have been applied in the clinical setting only in the form of a topical treatment or a locally administrated drug for the treatment of non-melanoma skin cancers and viral skin lesions to avoid TLR tolerance and adverse proinflammatory and proapoptotic effects [19,20,21,22]

Methods

Results

Conclusion