Purpose: Because toll-like receptor (TLR) agonists have been well characterized as dendritic cell (DC) activators, we hypothesized that the admixture of TLR4 agonist into a cellular vector could improve the antitumor response in vivo.
Experimental design: Granulocyte macrophage colony stimulating factor secreting whole cell tumor cell vector (GVAX) was formulated with lipopolysaccharide (LPS), a TLR4 agonist, and its intratumoral therapeutic efficacy was tested in three different murine models. We utilized immunohistochemistry, fluorescence-activated cell sorting, enzyme-linked immunosorbent spot (ELISPOT), and in vivo CTL analysis to assess both local innate immune responses within the tumor tissue as well as the downstream generation of antitumor T-cell responses.
Results: Intratumoral treatment of LPS-absorbed GVAX showed efficacy in improving an antitumor response in vivo in comparison with GVAX alone. Improved antitumor efficacy of this novel admixture was not present in TLR4 signaling impaired mice. In the CT26 model, 40% to 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(+) DCs in comparison with 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.
Conclusion: TLR4 on antigen-presenting cells in the tumor microenvironment may be targeted by using cell-based vectors for improved antitumor response in vivo.
©2011 AACR.