A reservoir of stem-like CD8+ T cells in the tumor-draining lymph node preserves the ongoing antitumor immune response.

"Stem-like" TCF1+ CD8+ T (TSL) cells are necessary for long-term maintenance of T cell responses and the efficacy of immunotherapy, but, as tumors contain signals that should drive T cell terminal differentiation, how these cells are maintained in tumors remains unclear. In this study, we found that a small number of TCF1+ tumor-specific CD8+ T cells were present in lung tumors throughout their development. Yet, most intratumoral T cells differentiated as tumors progressed, corresponding with an immunologic shift in the tumor microenvironment (TME) from "hot" (T cell inflamed) to "cold" (non­T cell inflamed). By contrast, most tumor-specific CD8+ T cells in tumor-draining lymph nodes (dLNs) had functions and gene expression signatures similar to TSL from chronic lymphocytic choriomeningitis virus infection, and this population was stable over time despite the changes in the TME. dLN T cells were the developmental precursors of, and were clonally related to, their more differentiated intratumoral counterparts. Our data support the hypothesis that dLN T cells are the developmental precursors of the TCF1+ T cells in tumors that are maintained by continuous migration. Last, CD8+ T cells similar to TSL were also present in LNs from patients with lung adenocarcinoma, suggesting that a similar model may be relevant in human disease. Thus, we propose that the dLN TSL reservoir has a critical function in sustaining antitumor T cells during tumor development and in protecting them from the terminal differentiation that occurs in the TME.

Inducible de novo expression of neoantigens in tumor cells and mice.

Inducible expression of neoantigens in mice would enable the study of endogenous antigen-specific naïve T cell responses in disease and infection, but has been difficult to generate because leaky antigen expression in the thymus results in central T cell tolerance. Here we develop inversion-induced joined neoantigen (NINJA), using RNA splicing, DNA recombination and three levels of regulation to prevent leakiness and allow tight control over neoantigen expression. We apply NINJA to create tumor cell lines with inducible neoantigen expression, which could be used to study antitumor immunity. We also show that the genetic regulation in NINJA mice bypasses central and peripheral tolerance mechanisms and allows for robust endogenous CD8 and CD4 T cell responses on neoantigen induction in peripheral tissues. NINJA will enable studies of how T cells respond to defined neoantigens in the context of peripheral tolerance, transplantation, autoimmune diseases and cancer.

Investigating Tumor-Associated Tertiary Lymphoid Structures in Murine Lung Adenocarcinoma.

Genetically engineered mouse models (GEMMs), in which autochthonous tumors develop into advanced-stage disease in the presence of a functional immune system, have contributed significantly to the understanding of most types of cancer. Using a GEMM of lung adenocarcinoma, we have found that immune cells are present in complex, highly organized, lymph node (LN)-like structures known as the tumor-associated tertiary lymphoid structures (TA-TLS). TA-TLS have been characterized in human lung cancer patients, but not in animal tumor models, and hence remain untapped targets for therapeutic interventions. We have shown that TA-TLS emerge as a result of tumor growth and that therapeutically depleting regulatory T cells (Tregs) from TA-TLS results in tumor elimination. Hence, a strong antitumor immune response exists but is suppressed in TA-TLS. Here, we describe a high-throughput immunofluorescence (IF) analysis pipeline for visualization and quantification of TA-TLS. Imaging the relatively small size of TA-TLS within tumor-bearing lung lobes using confocal microscopy is a labor-intensive process that can take up to 1 month. We have optimized this process and reduced the time required per lung lobe to 1-2 weeks using automated microscopy methods. Combining IF with multicolor fluorescence-activated cell sorting (FACS), we are able to interrogate not only the size and location of TA-TLS but also the activation status of immune cells within these structures. Using these techniques, investigation of TLS in lung adenocarcinoma combines cutting-edge technological tools in cancer biology and immunology to interrogate a fundamental, but poorly understood, tumor-associated immune structure.