Abstract 1686: TSC2 enhances antitumor immunity and potentiates PD-1 and CTLA-4 blockade

Tuberous sclerosis complex (TSC) is an incurable multisystem genetic disease characterized by mTORC1-hyperactive hamartomatous tumors of brain, kidney, and lung. TSC is caused by mutations in the two TSC1 or TSC2 tumor-suppressor genes. mTORC1 inhibitors lead to partial antitumor responses in TSC, with tumor regrowth upon treatment cessation. Understanding the interaction between T cells and tumor cells has led to the development of successful checkpoint blockade immunotherapy targeting PD-1, programmed cell death-ligand 1 (PD-L1), and CTLA-4. These therapies have proven to be highly effective in treating several malignancies, including non-small cell lung cancer (NSCLC), renal cell carcinoma (RCC), melanoma, bladder cancer and Hodgkin's lymphoma. It is currently unknown whether benign tumors, such as those arising in TSC, will also respond to checkpoint blockade therapy. Using multiparametric flow cytometry and immunohistochemistry of human angiomyolipomas and pulmonary LAM, we discovered that PD-1 is highly expressed on tumor-infiltrating T cells. Using immunocompetent preclinical models of TSC, we found that dual blockade of PD-1 and CTLA-4 inhibited the growth of TSC2-deficient tumors by 77% (p < 0.0001). This was associated with increased tumor-infiltrating CD8+ and CD4+ T cells and decreased Tregs, G-MDSCs and regulatory CD11b+ DCs. Strikingly, we discovered that complete regression of established tumors can be achieved in 37% of the mice using anti-PD-1 monotherapy and in 62% of the mice using combined anti-PD-1 and anti-CTLA-4 therapy. We also assessed a treatment regimen of rapamycin followed by PD-1 blockade and found that this sequential treatment delays regrowth of TSC2-deficient tumors. Furthermore, TSC2 re-expression in TSC2-deficient tumors promoted antitumor responses via increasing T cells and decreasing CD11b+Ly6G+Ly6Cmed G-MDSCs and CD11b+ DCs infiltration into tumors. Importantly, we found that the potency of dual PD-1 and CTLA-4 blockade is significantly enhanced by TSC2 re-expression. Our data indicate that PD-1 is upregulated on T cells in TSC-associated tumors and that dual blockade of PD-1 and CTLA-4 pathways is effective in delaying tumor growth and improving long-term survival, with long-term complete tumor responses. Therefore, PD-1 and/or CTLA-4 blockade may represent a promising dual immunotherapy for patients with TSC-associated tumors and women with the sporadic form of LAM. Our data may have relevance for the many sporadic human tumors with mTORC1 hyperactivation (~50% of all human malignancies) and also for other hamartomatous tumor syndromes such as neurofibromatosis. Furthermore, the specific role of intratumoral TSC2 in antitumor T cell responses that we discovered may help to elucidate the response to immunotherapy in sporadic human malignancies with mutations in the TSC genes, which include a subset of bladder cancer and renal cell carcinoma. Citation Format: Heng-Jia Liu, Patrick Lizotte, Heng Du, Maria Speranza, Spencer Vaughan, Nicola Alesi, Kwok-Kin Wong, Gordon Freeman, Arlene Sharpe, Elizabeth Henske. TSC2 enhances antitumor immunity and potentiates PD-1 and CTLA-4 blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1686.