Tumors adapt rapidly to thwart vaccine-induced T cell attack but this adaptive response can be overcome by manipulation of costimulation and immune checkpoints (48.30)

Abstract We have developed a prototypic recombinant adenovirus vaccine encoding dopachrome tautomerase (rHuAd5-hDCT) that leads to moderate suppression of B16F10 melanoma growth through a CD8+ T cell- and IFN-γ-dependent mechanism. The immunogenicity of rHuAd5-hDCT was improved by concomitant 4-1BB stimulation leading to enhanced control of tumor growth; however, most tumors ultimately relapsed. Gene expression analysis revealed a rapid adaptation of the tumor environment within 5 days of vaccination. Intratumoral IFN-γ and TNF-α expression increased rapidly following vaccination but, paradoxically, expression was almost completely attenuated at the time of highest infiltration by vaccine-induced CD8+ T cells. We also noted robust, yet transient, induction of PD-L1 and PD-L2 in the tumor following vaccination, which correlated with the attenuation of IFN-γ and TNF-α expression. Blockade of PD-1 signaling in combination with rHuAd5-hDCT enhanced effector cytokine expression in the tumor and improved growth control, but the tumors ultimately relapsed. Strikingly, the combination of PD-1 blockade and 4-1BB stimulation with rHuAd5-hDCT produced a synergistic enhancement in intratumoral T cell activity, resulting in complete regression despite no increase in the functionality or number of tumor infiltrating CD8+ T cells. These results punctuate the need to understand the dynamic changes within the tumor to optimize cancer immunotherapy.