Toll-like receptor (TLR)
ligands are increasingly being used as adjuvants in
cancer vaccine trials to harness innate immunity and prime effective antitumor immune responses. Despite some success, enhancing
tumor antigen presentation, promoting a protective antitumor response, and overcoming the immunosuppressive tumor microenvironment pose considerable challenges that necessitate further improvements in
vaccine design. Here, we show that expression of the TLR
ligand flagellin within
tumor cells constitutes an effective antitumor vaccination strategy that relies on simultaneous engagement of TLR5 and the
Nod-like receptors (NLRs) NLRC4/NAIP5 (
neuronal apoptosis inhibitory protein 5) by
flagellin along with associative recognition of
tumor antigen for optimal antigen presentation to T cells. Although TLR5 signaling was critical for mediating rapid macrophage-dependent clearance of
flagellin-expressing
tumor cells in vivo, TLR5 and NLRC4/NAIP5 were equally important for priming antitumor CD4(+) and CD8(+) T cells and suppressing
tumor growth. Vaccination with irradiated
flagellin-expressing
tumor cells prevented
tumor development, and disrupting
flagellin recognition by TLR5 or NLRC4/NAIP5 impaired protective immunization against an existing or subsequent
tumor. Our findings delineate a new strategy to induce anticancer immune responses consisting of introducing microbial structures with dual TLR and NLR stimulatory activity into
tumor cells. This ensures recognition of
tumor-derived
antigen within the inflammatory context of microbial recognition and additionally activates both the phagocytic and the cytosolic pathways of innate immune defense against the
tumor.