Intratumoral Administration of TLR4 Agonist Absorbed into a Cellular Vector Improves Antitumor Responses

Abstract

Purpose Since TLR agonists have been well characterized as DC activators, we hypothesized that the admixture of TLR4 agonist into a cellular vector could improve the anti-tumor response in vivo. Experimental Design GM-CSF secreting whole cell tumor cell vector (GVAX) was formulated with LPS, a TLR4 agonist, and its intratumoral therapeutic efficacy was tested in three different murine models. We utilized immunohistochemistry, FACS, ELISPOT, and in vivo CTL analysis to assess both local innate immune responses within the tumor tissue as well as the downstream generation of anti-tumor T-cell responses. Results Intratumoral treatment of LPS absorbed GVAX showed efficacy in improving an antitumor response in vivo in comparison to GVAX alone. Improved anti-tumor efficacy of this novel admixture was not present in TLR4 signaling impaired mice. In the CT26 model, 40-60% of the mice showed regression of the transplanted tumor. When rechallenged with CT26 tumor cells, these mice proved to be immunized against the tumor. Tumors treated with TLR4 agonist absorbed GVAX showed increased infiltrating CD4 and CD8 T-cells as well as increased numbers of CD86+ cells in the tumor tissue. Draining lymph nodes from the treated mice had enhanced number of activated CD86+, MHCII+, and CD80+ dendritic cells in comparison to GVAX alone and mock treated groups. ELISPOT assay and in vivo CTL assay showed increased numbers of CTLs specific for the AH1 tumor antigen in mice treated with LPS absorbed GVAX. Conclusions TLR4 on APCs in the tumor microenvironment may be targeted using cell-based vectors for improved anti-tumor response in vivo.

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