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ISRN Immunology
Volume 2012 (2012), Article ID 926817, 11 pages
http://dx.doi.org/10.5402/2012/926817
Research Article

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

1Faculdade de Biociências e Instituto de Pesquisas Biomédicas, Pontifícia Universidade Católica do Rio Grande do Sul (PUCRS), Avenida Ipiranga 6690, 2° Andar, 90680-001 Porto Alegre, RS, Brazil
2Departments of Molecular Microbiology and Immunology, Veterans Affairs Medical Center, Oregon Health and Science University, Portland, OR 97239, USA

Received 9 May 2012; Accepted 20 June 2012

Academic Editors: K. Müller and A. Vicente

Copyright © 2012 Fabio Luiz Dal Moro Maito et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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.