Due to the highly immunogenic nature of renal cell carcinoma (RCC), the tumor microenvironment (TME) is enriched with various innate and adaptive immune subsets. In particular, gamma-delta (γδ) T cells can act as potent attractive mediators of adoptive cell transfer immunotherapy because of their unique properties such as non-reliance on major histocompatibility complex expression, their ability to infiltrate human tumors and recognize tumor antigens, relative insensitivity to immune checkpoint molecules, and broad tumor cytotoxicity. Therefore, it is now critical to better characterize human γδ T-cell subsets and their mechanisms in RCCs, especially the stage of differentiation. In this study, we aimed to identify γδ T cells that might have adaptive responses against RCC progression. We characterized γδ T cells in peripheral blood and tumor-infiltrating lymphocytes (TILs) in freshly resected tumor specimens from 20 RCC patients. Furthermore, we performed a gene set enrichment analysis on RNA-sequencing data from The Cancer Genome Atlas (TCGA) derived from normal kidneys and RCC tumors to ascertain the association between γδ T-cell infiltration and anti-cancer immune activity. Notably, RCC-infiltrating CD3^low Vγ9Vδ1 T cells with a terminally differentiated effector memory phenotype with up-regulated activation/exhaustion molecules were newly detected as predominant TILs, and the cytotoxic activity of these cells against RCC was confirmed in vitro. In an additional analysis of the TCGA RCC dataset, γδ T-cell enrichment scores correlated strongly with those for CTLs, Th1 cells, “exhausted” T cells, and M1 macrophages, suggesting active involvement of γδ T cells in anti-tumor rather than pro-tumor activity, and Vδ1 cells were more abundant than Vδ2 or Vδ3 cells in RCC tumor samples. Thus, we posit that Vγ9Vδ1 T cells may represent an excellent candidate for adoptive immunotherapy in RCC patients with a high risk of relapse after surgery.

Mixed epithelial and stromal tumor of the kidney (MESTK), a benign rare tumor with malignant transformation potential, is thought to be derived from fetal or immature cells originating from the mesonephric and Müllerian ducts. However, due to its rarity, little is known about the anti-tumor immune responses in MESTK. Herein, we present five cases of MESTK and evaluate the population of tumor-infiltrating lymphocytes (TILs) using a freshly obtained MESTK sample. Microscopically, TILs were scattered or clustered in large aggregates in the stroma in all five cases; furthermore, three cases exhibited heavy, large lymphocytic aggregates with no well-organized tertiary lymphoid structures with germinal centers. Flow cytometric analysis of TILs in one freshly obtained MESTK sample revealed that >40% of CD3⁺ T cells were effector memory Fas⁺CD28⁻ γδ T cells expressing high levels of programmed cell death protein 1 and inducible T-cell co-stimulator, but low levels of CD44 and CD27. Most αß T cells exhibited a naïve phenotype. Additionally, we detected many activated class-switched CD21⁺CD27⁺ B cells as well as CD11c^highIgM^high marginal zone B-like and CD27⁻CD21⁻CD23⁻ immunoglobulin (Ig)D^highIgM^low age-associated B-like cells. Collectively, for the first time, we report the immune microenvironment pattern of MESTK to oncogenic stress.