The TLR7 agonists imiquimod and gardiquimod improve DC-based immunotherapy for melanoma in mice

Abstract

Toll-like receptors (TLRs) are a family of highly conserved germline-encoded pattern-recognition receptors that are essential for host immune responses. TLR ligands represent a promising class of immunotherapeutics or vaccine adjuvants with the potential to generate an effective antitumor immune response. The TLR7/8 agonists have aroused interest because they not only activate antigen-presenting cells but also promote activation of T and natural killer (NK) cells. However, the exact mechanism by which stimulation of these TLRs promotes immune responses remains unclear, and different TLR7/8 agonists have been found to induce different responses. In this study, we demonstrate that both gardiquimod and imiquimod promote the proliferation of murine splenocytes, stimulate the activation of splenic T, NK and natural killer T (NKT) cells, increase the cytolytic activity of splenocytes against B16 and MCA-38 tumor cell lines, and enhance the expression of costimulatory molecules and IL-12 by macrophages and bone marrow-derived dendritic cells (DCs). In a murine model, both agonists improved the antitumor effects of tumor lysate-loaded DCs, resulting in delayed growth of subcutaneous B16 melanoma tumors and suppression of pulmonary metastasis. Further, we found that gardiquimod demonstrated more potent antitumor activity than imiquimod. These results suggest that TLR7/8 agonists may serve as potent innate and adaptive immune response modifiers in tumor therapy. More importantly, they can be used as vaccine adjuvants to potentiate the efficiency of DC-based tumor immunotherapy.

Immunomodulatory Effect of Imiquimod Through CCL22 Produced by Tumor-associated Macrophages in B16F10 Melanomas

“…To investigate the immunomodulatory mechanisms responsible for the decrease of Tregs, we evaluated the immunomodulatory effects of topical IQM. We determined the mRNA expression of type 1 and 2 T helper cell (Th1/Th2)-related chemokines and CCL2, which is a key chemokine for the induction of antitumor effects in B16F10 melanoma (3,4,7,10), in tumors from IQM-treated and untreated mice by using qRT-PCR. Compared to untreated mice, topical IQM significantly decreased the mRNA expression of Th2/Tregrelated chemokines (CCL17 and CCL22) in the tumor microenvironment (Figure 2A).…”

“…Starting on day 6, imiquimod cream (5%) was topically administered to the tumors three times a week. Tumor-bearing animals were sacrificed when the tumors displayed severe ulceration or reached a size of 1,000 mm 3 .…”

“…Several reports have suggested that IQM may be an optimal reagent for invasive melanoma when used in combination with other therapies (3,4,7,10,11). Turza et al reported that IQM was effective in 10 cases of superficial dermal and subcutaneous metastasis of melanoma when used in combination with intralesional interleukin (IL)-2 (9).…”

“…As a TLR7 agonist, IQM stimulates innate immunity, including tumor-associated macrophages (TAMs) (1)(2)(3). In an experimental murine model, the addition of IQM to cryosurgery increased the cellular immune response against tumor antigens, leading to complete rejection of B16OVA melanoma (4).…”

Critical role of Toll-like receptor signaling in NK cell activation

“…Our recent results showed that Imiquimod and another TLR7 agonist, Gardiquimod, promoted the proliferation and activation of splenic T, NK and NKT cells, and increased the cytolytic ability of NK cells against melanoma B16. When combined with DC vaccine, both Imiquimod and Gardiquimod exert more powerful inhibition of the growth of subcutaneous B16 melanoma and suppression of the pulmonary metastasis, demonstrating that TLR7-stimulated anti-tumor effect by NK cells needs the help of DCs [56]. Taken together, the activation of NK cells mediated by TLR7/8 agonists should be accompanied by the stimulation of other cytokines.…”