Purpose Immunotherapy using vaccines or adoptively transferred tumor infiltrating lymphocytes (TILs) is limited by T cell functional inactivation within the solid tumor microenvironment. The purpose of this study was to determine if a similar tumor-induced inhibition occurred with genetically-modified cytotoxic T cells expressing chimeric antibody receptors (CARs) targeting tumor-associated-antigens. Methods Human T cells expressing CAR targeting mesothelin or fibroblast activation protein and containing CD3ζ and 4-1BB cytoplasmic domains were intravenously injected into immunodeficient mice bearing large, established human mesothelin- expressing flank tumors. CAR TILs were isolated from tumors at various time points and evaluated for effector functions and status of inhibitory pathways. Results CAR T cells were able to traffic into tumors with varying efficiency and proliferate. They were able to slow tumor growth, but did not cause regressions or cures. The CAR TILs underwent rapid loss of functional activity that limited their therapeutic efficacy. This hypofunction was reversible when the T cells were isolated away from the tumor. The cause of the hypofunction appeared to be multifactorial and was associated with upregulation of intrinsic T cell inhibitory enzymes (diacylglycerol kinase and SHP-1) and the expression of surface inhibitory receptors (PD-1, LAG3, TIM3, 2B4). Conclusions Advanced generation human CAR T cells are reversibly inactivated within the solid tumor microenvironment of some tumors by multiple mechanisms. The model described here will be an important tool for testing T cell-based strategies or systemic approaches to overcome this tumor-induced inhibition. Our results suggest that PD-1 pathway antagonism may augment human CAR T cell function.

Each year, more than 700,000 people undergo cancer surgery in the United States. However, more than 40% of those patients develop recurrences and have a poor outcome. Traditionally, the medical community has assumed that recurrent tumors arise from selected tumor clones that are refractory to therapy. However, we found that tumor cells have few phenotypical differences after surgery. Thus, we propose an alternative explanation for the resistance of recurrent tumors. Surgery promotes inhibitory factors that allow lingering immunosuppressive cells to repopulate small pockets of residual disease quickly. Recurrent tumors and draining lymph nodes are infiltrated with M2 (CD11b + F4/80 hi CD206 hi and CD11b + F4/80 hi CD124 hi ) macrophages and CD4 + Foxp3 + regulatory T cells. This complex network of immunosuppression in the surrounding tumor microenvironment explains the resistance of tumor recurrences to conventional cancer vaccines despite small tumor size, an intact antitumor immune response, and unaltered cancer cells. Therapeutic strategies coupling antitumor agents with inhibition of immunosuppressive cells potentially could impact the outcomes of more than 250,000 people each year.immunology | tumor macrophages | T regulatory cells

Mesothelin is a cell-surface glycoprotein present on mesothelial cells and elicits T-cell responses in a variety of cancers including pancreatic and ovarian cancer. Breast cancer is not known to express mesothelin. We postulated that mesothelin may be a unique tumor associated antigen in triple negative breast cancer (TNBC), a less common breast cancer subtype which may have been underrepresented in prior studies that characterized mesothelin expression. Therefore, we screened 99 primary breast cancer samples by immunohistochemistry analysis using formalin fixed paraffin embedded archival tumor tissues subtypes and confirmed that mesothelin was overexpressed in the majority of TNBC (67%) but only rarely in < 5% ER(+) or Her2-neu (+) breast cancer respectively. To determine whether mesothelin may be exploited as a novel immunotherapy target in breast cancer, an in vitro cell killing assay was performed to compare the ability of genetically modified T cells expressing a chimeric antibody receptor (CAR) specific for mesothelin (mesoCAR T-cells) or non-transduced T-cells to kill mesothelin-expressing primary breast cancer cells. A significantly higher anti-tumor cytotoxicity by mesoCAR T-cells was observed (31.7% vs. 8.7%, p<0.001). Our results suggest that mesothelin has promise as a novel immunotherapy target for TNBC for which effective targeted therapy is lacking to date.

Progression of premalignant lesions is restrained by oncogene-induced senescence. Oncogenic Ras triggers senescence in many organs, including the lung, which exhibits high levels of the angiogenesis inhibitor thrombospondin-1 (TSP-1). The contribution of TSP-1 upregulation to the modulation of tumorigenesis in the lung is unclear. Using a mouse model of lung cancer, we have shown that TSP-1 plays a critical and cell-autonomous role in suppressing Kras-induced lung tumorigenesis independent of its antiangiogenic function. Overall survival was decreased in a Kras-driven mouse model of lung cancer on a Tsp-1 -/-background. We found that oncogenic Kras-induced TSP-1 upregulation in a p53-dependent manner. TSP-1 functioned in a positive feedback loop to stabilize p53 by interacting directly with activated ERK. TSP-1 tethering of ERK in the cytoplasm promoted a level of MAPK signaling that was sufficient to sustain p53 expression and a senescence response. Our data identify TSP-1 as a p53 target that contributes to maintaining Ras-induced senescence in the lung.

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