Abstract 4047: CD8+T cell-mediated tumor-specific induction of the NKG2D ligands to trigger NKG2D-dependent tumor cell death in vivo

Introduction: High profile studies have shown that restoring NKG2D ligand expression greatly promotes antitumor immune surveillance and tumor regression, but malignant tumor cells often down-regulate NKG2D ligands to escape from immune surveillance. Previous studies showed that engineering tumor cells with NKG2D ligand resulted in inhibition of tumor progression. However, it is not feasible to engineer each tumor cell with NKG2D ligand in clinical treatment. Therefore, a therapeutic treatment that can restore NKG2D ligand on tumor cells is required to promote tumor immune surveillance. In this regard, many therapeutic approaches were discovered to induce NKG2D ligands on tumor cells in vitro. Unfortunately, no effective in vivo approaches are available to restore this ligand across different types of tumors because the classic in vitro stress signal-dependent NKG2D ligand induction has rarely been duplicated in solid tumors in vivo. Experimental procedure: This study reveals a unique approach_two independent co-administration of immune stimulatory signal interleukin-12 and doxorubicin_restores the NKG2D ligands in multiple murine and human tumor types. The induction of NKG2D ligands was determined using immunoblotting, flow cytometry and immunohistochemistry staining. The comparison of Rae-1 induction in immune competent mice versus immune deficient mice (nude, Rag2 -/- or Pfp -/-) implied that mature CD8+T cells are the most critical immune subpopulation. The concentration of interferon γ in tumors was measured using ELISA assay. The accumulation of NKG2D positive immune cells in tumor sections was examined using immunofluorescence straining, followed by TUNEL assay to determine tumor cell death. Results: We showed for the first time that a chemoimmunotherapy led to the tumor specific restoration of NKG2D ligands in a variety of tumor models in vivo. Systemic delivery of interleukin-12 gene therapy plus doxorubicin effectively restored murine NKG2D ligand Rae-1 in vivo in two subcutaneous tumor models (LLC and CT26), one orthotopic tumor model (K7M3) and one spontaneous breast carcinoma model. Significantly, such therapeutic approach can also stimulate human NKG2D ligands in xenograft tumor models. Intriguingly, this tumor-specific Rae-1 induction in vivo requires CD8+T cells. This NKG2D ligand-restoring therapy itself can also attract endogenous NKG2D-positive cells to attack tumor cells. Along with the tumor-specific NKG2D ligand induction, the promoted immune surveillance leads to massive tumor cell death. Conclusion: This study provides the first therapeutic treatment for inducing immune surveillance ligand in tumors in vivo. Further, it reveals a CD8+T cell-dependent novel mechanism for the restoration of NKG2D ligand. The revealed in vivo NKG2D ligand restoring approach could be translated for cancer prevention and treatment. Citation Format: Jiemiao Hu, Xueqing Xia, Eugenie S. Kleinerman, Shulin Li. CD8+T cell-mediated tumor-specific induction of the NKG2D ligands to trigger NKG2D-dependent tumor cell death in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4047. doi:10.1158/1538-7445.AM2015-4047