Single-cell RNA Sequencing Reveals A Tumor-Promoting Role of EGR1+CD4+ T Cells in Papillary Thyroid Cancer

Papillary thyroid cancer (PTC) is the most common thyroid malignancy. Based on single-cell RNA sequencing, a previously unrecognized CD4+ T cell subset was identified, termed EGR1+CD4+ T cells. This subset produced high levels of IL-10 and IFN-γ in response to phorbol 12-myristate 13-acetate (PMA) and ionomycin, and showed distinct molecular pathway activity compared to CD4+ Tregs. CD4+ T cell-specific overexpression of EGR1 in vitro enhanced tumor cell proliferation, invasion, and migration when co-cultured with PTC cell lines. The expression profiling analysis of immune checkpoint molecules indicated that CD96 was commonly up-regulated in EGR1+CD4+ T cells, CD4+ Tregs, and other T cell subsets, especially in tumor tissues. Single CD96 blockade significantly increased the levels of IFN-γ, IL-17a, and IL-10 in EGR1+CD4+ T cells and inhibited the proliferation of PTC tumor cells. Co-blockade of CD96/TIGIT significantly enhanced the production of IFN-γ, TNF-α, and IL-17a in both EGR1+CD4+ T cells and CD3+CD4+ T cells, which also suppressed cell proliferation, invasion, and migration when co-cultured with PTC tumor cells. These findings indicated that EGR1+CD4+ T cells were a novel CD4+ T cell subset with specific functions. Single CD96 blockade or co-blockade of CD96/TIGIT enhanced antitumor immunity of EGR1+CD4+ T cells, which might be promising therapeutic strategies in PTC treatment.