Intratumoral TLR-4 Agonist Injection Is Critical for Modulation of Tumor Microenvironment and Tumor Rejection

Abstract

The tumor microenvironment shelters a complex network of mechanisms that enables local Immunosuppression to support tumor growth. In this study we found that, B16F10 melanoma growth is inversely correlated with peritumoral infiltrate cell number and with cell numbers in draining lymph nodes. Tumor growth ensued even when a foreign antigen was expressed by B16F10 cells in the presence of naïve specific CD8 + T cells. Treatment with TLR agonists has shown to sometimes result in tumor regression, however, not always with long-lasting effects. We compared the relevance of different injection regimens of lipopolysaccharide (LPS). Tumor growth was arrested only by intratumoral LPS injection after the tumor was already established. This result was accompanied by a dramatic change in DC activation inside the tumor. Intratumoral LPS also enhanced antigen presentation and tumor-specific CD4 + T cell production of IFN-γ. Injection of LPS before tumor challenge or codelivery of tumor cells and LPS did not have any effect on tumor progression. Our results suggest that an efficient antitumor immune response leading to tumor regression can be achieved with proper TLR4 activation inside the tumor tissue, impacting the tumor microenvironment. These findings are relevant for the design of treatment for patients with malignant melanomas.

TLR4-Based Immunotherapeutics in Cancer: A Review of the Achievements and Shortcomings

“…They also suggested that the intratumoral injection could lead to the rapid activation of DCs as well as the infiltration of the T-cells in the tumor, which might be the reason for the observed tumor rejection. They concluded that it is mainly the DCs present in the tumor, rather than the macrophages, that are major targets for LPS activation …”

In situ vaccination: Cancer immunotherapy both personalized and off‐the‐shelf

“…Mice with subcutaneous glioblastoma or rats with subcutaneous glioma tumors treated with intratumoral LPS experience partial and complete tumor regression and these responses are lessened in T cell deficient animals (Chicoine et al., 2001; Won et al., 2003; Mariani et al., 2007). Similarly, intratumoral injection of LPS in B16 melanoma mice results in tumor regression in those mice with increased activation of DC and T cells (Maito et al., 2012). By contrast, another study on the same model reported that LPS only reduced tumor growth when given in the context of a GM–CSF–expressing whole‐cell vaccine (Davis et al., 2011).…”

In Situ Vaccination as a Strategy to Modulate the Immune Microenvironment of Hepatocellular Carcinoma

“…While systemic LPS administration causes severe side effects, intra-tumoral applications have been suggested previously (178). Several studies reported that TLR4 agonists have been successfully harnessed as adjuvants in several models of other tumor entities like malignant melanoma and clinically, in BCG immunotherapy (179,180). While in vitro activation of the surface TLRs 1/2 and 4 and the endosomal TLRs 3 and 9 has a similar activating effect on splenic DCs, in vivo data showed that stimulation of the surface TLRs 1/2 and 4 suppressed CD8+ T cell responses (181).…”