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658 CD8 T cell activation in cancer is comprised of two distinct phases
  1. Nataliya Prokhnevska,
  2. Maria Cardenas,
  3. Rajesh Valanparambil,
  4. Ewelina Sobierajska,
  5. Caroline Jansen,
  6. Viraj Master,
  7. Martin Sanda and
  8. Haydn Kissick
  1. Emory University, Atlanta, GA, United States


Background CD8 T cell are a crucial part of the immune response to tumors, with CD8 infiltration predicting disease progression in numerous cancer types. Recently two subsets of CD8 T cells that respond to tumors have been described, a stem-like (TCF1+) CD8 T cell that can give rise to a more cytotoxic terminally differentiated (TD) (TCF1-Tim3+) CD8 T cell. In this study we aimed to understand the origin of stem-like TCF1+ CD8 T cells within tumors.

Methods Human patient TDLN and tumor samples from kidney and prostate cancer were processed after resection and used for flow cytometry, RNA-seq, TCR-seq and whole genome DNA methylation analysis. We also used a prostate cancer mouse model that expresses the LCMV GP protein (TRAMPC1-LCMV-GP) to track tumor-specific CD8 T cells in both TDLNs and tumors.

Results We studied human prostate and kidney cancer tumor-draining lymph nodes (TDLN) and found that CD8 T cells are activated but fail to acquire an effector phenotype within the TDLN. Instead, they share functional, transcriptional, and epigenetic traits with stem-like cells in the tumor. We also found that activated CD8 T cells from TDLNs shared TCR overlap with both CD8 subsets within tumors. This suggests that these activated cells are a precursor to the stem-like CD8 T cells in tumors. To further test this hypothesis, we used our TRAMPC1-LCMV-GP tumor model to study tumor-specific CD8 T cell activation. We found that CD8 T cells are activated in TDLNs but fail to acquire an effector program. These cells then establish the stem-like CD8s within tumor where they require additional co-stimulation from antigen presenting cells to differentiate into TCF1- TD CD8 T cells. This is strikingly different from canonical CD8 T cell activation to acute viruses, where the effector program is acquired immediately. We also showed that human stem-like CD8 T cells require co-stimulation and TCR stimulation to divide and differentiate into terminally differentiated CD8s in-vitro, and DCs from autologous tumors can also induce this differentiation.

Conclusions Overall this work shows a model of CD8 T cell activation in response to tumors that has two distinct phases. The first occurs in the TDLN where CD8 T cells are initially activated, the second occurs in the tumor where CD8 T cells acquire an effector function after additional co-stimulation. This model of T cell differentiation adds to our understanding of basic CD8 T cell biology and has important implications to improve our current immunotherapies.

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