Disruption of TET2 Dioxygenase Enhances Antitumor Efficiency in CD8+ Tumor Infiltrating Lymphocytes

Background: T cell exhaustion is a dysfunctional state of T cell that occurs during many chronic infections and cancer [1,2]. T cell exhaustion is generally defined by poor effector function, continuous expression of inhibitory receptors and a distinctive transcriptional state when compared with functional effector T cells [2]. Exhaustion prevents optimal control of infection and tumors. Recently, a clearer picture of the functional and phenotypic profiles of exhausted T cells has emerged and T cell exhaustion has been defined in many experimental and clinical settings. Although the involved pathways remain to be fully defined, advances in the molecular delineation of T cell exhaustion are clarifying the underlying causes of this state of differentiation and also suggest promising therapeutic opportunities. A recent study reported disruption of TET2 to promote the therapeutic efficacy of CD19 targeted T cells during cancer immunotherapy [3]. Furthermore, Tet2 deficient macrophages could alter the tumor microenvironment to reduce tumor burden during melanoma progression [4]. Together, these data suggest, contrary to the tacit belief of Tet2 as a tumor suppressor, deletion of Tet2 in specific subsets of immune cells might enhance anti-tumor immunity to benefit cancer therapy. In this study, we set out to explore the role of Tet2 in CD8+ tumor infiltrating lymphocytes (TIL) during melanoma progression.

Methods: We intradermally injected B16-OVA mouse melanoma cell lines in B6.SJL-Ptprca Pepcb/BoyJ (CD45.1) mice, and use this as an in vivo model to monitor melanoma progression [5]. In parallel, we injected WT-OTI and Tet2KO-OTI CD8+ T cells into CD45.1 mice injected with B16-OVA cells. Melanoma progression was monitored by measuring the tumor sizes for two weeks. At the end point, spleen and tumor infiltrated CD45.2+CD8+ cells were collected and analyzed. RNA-seq, ATAC-seq and CMS-IP-seq experiments were carried out to examine genome-wide gene expression, chromatin accessibility and DNA hydroxymethylation, with the goal of unveiling the underlying molecular mechanisms.

Results: Compared with the control mice injected with WT-OTI CD8+ T cells, we observed a strong delay of melanoma disease progression and up to 80% reduction in tumor sizes in mice injected with Tet2KO-OTI CD8+ T cells. Flow cytometry analysis showed no significant changes in CD8+ T cell populations in major lymphoid organs. However, we detected a pronounced reduction of T cell exhaustion in Tet2KO CD8+ TILs compared with the WT group. Further transcriptome and integrative epigenome analysis revealed that Tet2 deleted TILs showed augmented activation of immune related pathways and reduction of the expression of immunosuppressive genes.

Conclusion: Our novel findings demonstrated the therapeutic potential of Tet2 inactivation in immune cells during cancer immunotherapy. In our study, we observed that Tet2 depleted CD8+ TILs displayed increased anti-tumor efficiency in a mouse model of melanoma. Tet2 deletion could effectively alleviate T cell exhaustion to boost CD8+ TIL function. Nonetheless, since Tet2 deficiency is closely associated with various hematology disorders [6,7]; cautions must be taken to balance the tumor promoting and immune-boosting properties of Tet2 during cancer therapy. A temporally controllable system to inactivate Tet2 in specific immune cells might be most desirable for pursuing future therapeutic intervention by targeting Tet2.

References

1. Thommen, D. S. & Schumacher, T. N. (2018). Cancer Cell33, 547-562.

2. Wherry, E. J. (2011). Nat Immunol12, 492-499.

3. Fraietta, J. A., Nobles, C. L., Sammons, M. A.et al. (2018). Nature558, 307-312.

4. Pan, W., Zhu, S., Qu, K.et al. (2017). Immunity47, 284-297 e285.

5. Mognol, G. P., Spreafico, R., Wong, V.et al. (2017). Proc Natl Acad Sci U S A114, E2776-E2785.

6. Couronne, L., Bastard, C. & Bernard, O. A. (2012). N Engl J Med366, 95-96.

7. Delhommeau, F., Dupont, S., Della Valle, V.et al. (2009). N Engl J Med360, 2289-2301.