Dendritic cells (DCs) were adenovirally engineered to constitutively and durably secrete the potent Th1-biasing
cytokines interleukin (IL)-12 (AdIL12DC) and/or
IL-18 (AdIL18DC) and evaluated for their ability to promote therapeutic antitumor immunity in murine
sarcoma models. Injection of either AdIL12DC or AdIL18DC into day 7 CMS4 or MethA
tumors resulted in
tumor rejection or slowed
tumor growth when compared with control cohorts. Importantly, intratumoral injection with DCs engineered to secrete both
IL-12 and
IL-18 (AdIL12/IL18DC) resulted in complete and the most acute rejection of any treatment group analyzed. This strategy was also effective in promoting the regression of contralateral, untreated
tumors. Both CD4+ and CD8+ T cells were required for
tumor rejection. CD8+ splenic T cells from mice treated with AdIL12/IL18DC produced the highest levels of IFN-gamma in response to
tumor rechallenge in vitro and displayed the broadest repertoire of Tc1-type reactivity to
acid-eluted,
tumor-derived
peptides among all treatment cohorts. This apparent enhancement in cross-presentation of
tumor-associated
epitopes in vivo may result from the increased capacity of engineered DCs to kill
tumor cells, survive
tumor-induced apoptosis, and present immunogenic MHC/
tumor peptide complexes to T cells after intratumoral injection. In support of this hypothesis,
cytokine gene-engineered DCs expressed higher levels of MHC and costimulatory molecules, as well as
Fas ligand and membrane-bound
tumor necrosis factor alpha, with the latter markers associated with elevated tumoricidal activity in vitro.
Cytokine gene-engineered DCs appeared to have a survival advantage in situ when injected into
tumor lesions, to be found in approximation with regions of
tumor apoptosis, and to have the capacity to ingest apoptotic
tumor bodies. These results support the ability of combined
cytokine gene transfer to enhance multiple effector functions mediated by intralesionally injected DCs that may concertedly promote cross-priming and the accelerated immune-mediated rejection of
tumors.