A31 A Reservoir of Tumor-Specific CD8 T Cells in Lung Cancer Resides in the Draining Lymph Node

Abstract

Recent work has described the population of CD8 T cells that respond to anti-PD-1 therapy (marked by TCF1 and PD-1), but it remains unclear how these T cells are maintained within the immunosuppressive tumor microenvironment (TME) of lung cancer. To understand this, we developed a genetically engineered model in which Kras-G12D expressing p53 deficient lung adenocarcinomas express a known neoantigen called the iNversion INduced Joined neoAntigen (NINJA). NINJA allows us to follow neoantigen-specific CD8 T cells over the course of tumor development. We find that ∼20% of tumor-specific T cells in early 8-wk tumors are TCF1+, but by 17-20 wks, this TCF1+ has significantly shrunk, and there has been a concomitant increase in the expression of markers of T-cell terminal differentiation (Tim3). This is consistent with the idea that T cells receive signals in the TME that drive terminal differentiation and restrict responses to immunotherapy. We reasoned that if the signals driving terminal differentiation were provided in the TME, neoantigen-specific T cells in the tumor-draining lymph node (dLN) may remain less differentiated over the course of tumor development. Analysis of tumor-specific T cells in the dLNs of 8-wk and 17-wk tumors showed that they were mostly TCF1+. Moreover, single-cell transcriptional analyses suggested that these cells were less differentiated than their counterparts in tumors. T-cell receptor (TCR) signals are a major driver of terminal differentiation, and we observed that tumor-specific T cells in the dLN were not receiving TCR signals, while all T cells in the TME were positive for TCR signals. This suggested at least two models for how antitumor T cells function: 1) tumor-reactive T cells in dLNs and TME could function independently of one another, or 2) tumor-reactive T cells might have a role in sustaining the antitumor T-cell response over the course of lung-tumor development through migration. Consistent with the latter model, TCR sequencing of dLN and TME neoantigen-specific T cells showed a close clonal relationship: 13 of the top 15 clones in the TME were present in the dLN, and the hierarchy of clonal dominance was maintained. This was also true in 17-wk tumor-bearing mice, suggesting that the population of tumor-specific CD8 T cells in the dLN serves as a reservoir of less differentiated cells that can continuously replenish the T cells in the TME, helping to sustain the antitumor T-cell response over the course of tumor development. Critically, it is unclear whether current immunotherapeutic strategies leverage this reservoir of T cells, raising the possibility that this population of dLN tumor-specific T cells could be targeted to provide significant additional benefit for patients receiving immunotherapy.