IL-17A-Expressing CD4+ T Cells Must Acquire the Expression of T-Bet and IFN-γto Destroy Tumor Cells In Vivo.

Abstract 468 We have recently demonstrated that Th17-polarized TCR transgenic CD4+ T cells specific for TRP-1 melanoma antigen are superior to Th1-polarized cells in mediating effective anti-tumor responses against advanced disease after adoptive transfer. The therapeutic activity of Th17-skewed cells is critically dependent on their ability to secrete IFN-γ, suggesting that the Th17 subset might evolve in vivo. However, the developmental program of Th17-polarized cells in vivo remains substantially un- elucidated. We developed a novel TCR-transduction technique that enabled us to rapidly confer specificity for a cognate antigen upon any population of T cells, regardless of its genetic background, its previous polarization history or its state of differentiation. Using adoptive transfers into tumor-bearing hosts, we were able to study the functionality of these genetically-engineered T cells in vivo. In vitro, CD4+ T cells cultured in type 17 conditions acquired end-effector phenotype (CD62Llow, CD45RBlow), but proliferated slower than cells grown in type 1 condition. Thus, we hypothesized that Th17-polarized cells might represent a less mature, more central-memory like subset. This notion was supported by their ability to secrete high quantities of IL-2 and higher expression of IL-7 receptor. In contrast, Th1-polarized cells upon in vitro re-stimulation upregulated PRDM1 that encodes BLIMP1, a molecule associated with the end-effector senescent phenotype. Moreover, Th1-skewed cells overexpressed caspase 3 and were prone to activation-induced cell death as measured by annexin V assay, while type 17 cells were resistant to apoptosis, and robustly expanded in secondary cultures. Using the TCR gene transfer technique we tested the treatment outcomes when Th17-polarized cells deficient for IL-17A were used. In contrast to wild-type (WT)-derived Th17 cells that effectively eradicated established tumors, we observed significant impairment of treatment with IL-17A-deficent cells. Similarly, we observed reduction in treatment efficacy when CCR6-deficient Th17 cells were transferred. CCR6 is a receptor for CCL20, a chemokine highly induced Th17 cells and thought to contribute to the trafficking of those cells to the site of inflammation. In both cases however, the addition of exogenous vaccination and IL-2 significantly improved treatment efficacy. Thus, we concluded that Th17-associated factors play the role in the anti-cancer activity of type 17 cells. To address the question whether plasticity of Th17-skewed effectors is important for their function upon ACT, we treated animals with TCR-transduced Th17-skewed cells derived from IFN-γ-deficient CD4+ cells as well as from t-bet-deficient mice, which are not able to develop type 1 responses. In contrast to WT-derived Th17 effectors, IFN-γ-deficient cells did not show any anti-tumor activity, while t-bet-deficient Th17 cells were able to mediate only minimal delay in tumor growth, suggesting that indeed the capacity to acquire Th1-like properties is essential for the anti-tumor function of Th17-skewed lymphocytes. Overall, here we demonstrate that TCR gene engineered Th17-polarized cells can efficiently treat advanced tumor. The high activity of in vitro-generated anti-tumor Th17 cells relies on the contribution of type 17-associated characteristics, including both the secretion of inflammatory factors IL-17A and CCL20, as well as the superior capacity to survive and expand upon the secondary stimulation. Importantly however, type 1-defining t-bet-mediated plasticity in the lineage commitment is required for the full therapeutic effect, underscoring the dualistic nature of Th17-skewed cells. Disclosures: No relevant conflicts of interest to declare.