Treatment of Large Established Murine Melanoma with Th17 Polarized CD4+ T Helper Cells Genetically Engineered to Express MHC Class IIRestricted T Cell Receptor

Adoptive cell transfer (ACT) of tumor-specific T lymphocytes is a powerful strategy for targeted therapy of cancer, but most of the research in this area has been focused on cytotoxic CD8⁺ T cells, which directly lyse MHC class I expressing targets. We have recently demonstrated that CD4⁺ TCR transgenic Th cells specific for self/tumor antigen tyrosinase-related protein 1 (TRP-1) have the ability to reject large established B16 murine melanoma in a model closely mimicking advanced human disease. Moreover, we showed that Th17-polarized cells were more effective in mediating complete tumor rejection than Th1-skewed cells that were capable of producing high quantities of interferon γ (IFN-γ). Interestingly, while Th1 and Th17 populations varied significantly in their phenotype, cytokines profiles, persistence and proliferation patterns in vivo, the Th17 anti-tumor function was critically dependent on the ability of the transferred cells to secrete IFN-γ. This suggests that the Th17 population might gradually acquire Th1-like properties in vivo, and that transcription factors regulating Th17 differentiation (ROR- γt) as well as IFN-γ production and Th1 polarization (t-bet) might be crucial for the effective rejection of the tumor. In order to emulate clinically relevant gene-therapy scenario we inserted TRP-1 TCR into open-repertoire CD4⁺ T cells from wild-type donors using a retroviral vector. Prior to transduction Th cells were stimulated under neutral (Th0) and polarizing Th1 and Th17 conditions. The majority of transduced cells expressed the Vβ14 chain, released appropriate polarization-defining cytokines upon specific antigenic stimulation in vitro and caused development of massive autoimmune vitiligo upon adoptive cell transfer into wild-type and Rag1−l/&minus mice. Gene-modified cells were readily detectable in Rag1−/− animals by flow-cytometry for more than 4 month after transfer. No off-target GVHD-like toxicities resulting from potential miss-pairing of endogenous and inserted TCR chains were observed. Th0 or Th1 and Th17-polarized TCR-transduced cells were all capable of treating mice bearing large (50–100mm²) B16 tumors, but complete cures with long-term survival occurred more robustly in animals treated with Th17-polarized effectors. To address the question whether plasticity of Th17-skewed effectors is important for their function upon ACT, we treated animals with TCR-transduced Th17-polarized cells derived from t-bet-deficient donors, which are not able to develop Th1-type responses, most importantly, not capable of producing IFN-γ. In contrast to WT-derived Th17 effectors used as a control, t-bet-deficient Th17 cells were able to mediate only minimal delay in tumor growth, suggesting that indeed the ability to acquire Th1-like properties is essential for the anti-tumor function of Th17-skewed lymphocytes. Currently, the clinical effectiveness of the ACT therapy might be hampered by the lack of high-avidity autologous effectors recognizing self/tumor antigens due to the central tolerance mechanisms. Here we demonstrate that the mature effector Th cells can be genetically engineered to express TCR recognizing MHC class II self/tumor antigen and those cells mediate powerful anti-cancer effect in vivo in a realistic model. While tumor-specific Th17-skewed CD4⁺ T cells are most effective in this setting, t-bet-mediated plasticity in lineage commitment is required for the full therapeutic effect.