Regional metastatic differentiated thyroid cancer (mDTC) provides a unique model in which to study the tumor-immune interface. These lymph node (LN) metastases persist for years, generally without progression to distant metastases. While the immune system likely impedes disease progression, it is unsuccessful in eliminating disease. Our previous studies revealed that programmed death-1 (PD-1)+ T cells were enriched in tumor-involved lymph nodes (TILN). Tumor-associated leukocytes and tumor cells were collected from grossly involved LNs from 12 patients to further characterize the phenotype and functional potential of mDTC-associated PD-1+ T cells. PD-1+CD4+ and PD-1+CD8+ T cells were enriched in 8/12 TILN samples. PD-1+ T cells co-expressed Tim-3 and CD69 and failed to down-regulate CD27. CD8+ T cells, but not CD4+ T cells, from these samples were variably deficient in their ability to produce effector cytokines when compared to control TILN that lacked resident PD-1+ T cells. PD-1+CD8+ T cells were capable of exocytosis but lacked intracellular perforin. Surprisingly, T cell proliferative capacity was largely maintained in all samples. Thus, while PD-1 expression by mDTC-associated CD8+ T cells was associated with dysfunction, exhaustion was not complete. Notably, molecular markers of exhaustion did not translate to dysfunction in all samples or in CD4+ T cells. Regulatory T cells, PD-L1, and galectin-9 were commonly found in mDTC and likely contributed to the initiation of T cell exhaustion and disease progression. Therapies that release the effects of PD-1 and Tim-3 and reduce the suppressive effects of Tregs may encourage tumor elimination in patients with mDTC.
- Received October 27, 2014.
- Revision received January 23, 2015.
- Accepted February 10, 2015.
- Copyright © 2015, American Association for Cancer Research.