The identification of tissue-resident memory T cells (TRM cells) has significantly improved our understanding of immunity. In the last decade, studies have demonstrated that TRM cells are induced after an acute T-cell response, remain in peripheral organs for several years, and contribute to both an efficient host defense and autoimmune disease. TRM cells are found in the kidneys of healthy individuals and patients with various kidney diseases. A better understanding of these cells and their therapeutic targeting might provide new treatment options for infections, autoimmune diseases, graft rejection, and cancer. In this review, we address the definition, phenotype, and developmental mechanisms of TRM cells. Then, we further discuss the current understanding of TRM cells in kidney diseases, such as infection, autoimmune disease, cancer, and graft rejection after transplantation.

BackgroundIL-17A–producing CD4+ T helper (TH17) cells play a critical role in autoimmune and chronic inflammatory diseases, such as crescentic GN. The proinflammatory effects of IL-17 are mediated by the activation of the IL-17RA/IL-17RC complex. Although the expression of these receptors on epithelial and endothelial cells is well characterized, the IL-17 receptor expression pattern and function on hematopoietic cells, e.g., CD4+ T cell subsets, remains to be elucidated.MethodsCrescentic GN (nephrotoxic nephritis) was induced in IL-17A, IFNγ, and Foxp3 triple-reporter mice for sorting of renal CD4+ T cell subsets and subsequent single-cell RNA sequencing. Moreover, we generated TH17 cell–specific IL-17RA and IL-17RC gene–deficient mice and studied the functional role of IL-17 signaling in TH17 cells in crescentic GN, imiquimod-induced psoriasis, and in the CD4+CD45RBhigh T cell transfer colitis model.ResultsWe identified a specific expression of the IL-17 receptor A/C complex on CD4+ TH17 cells. Single-cell RNA sequencing of TH17 cells revealed the activation of the IL-17 receptor signaling pathway in experimental crescentic GN. Disruption of the IL-17RC signaling pathway in CD4+ T cells and, most importantly, specifically in CD4+ TH17 cells, potentiates the IL-17 cytokine response and results in an accelerated course of experimental crescentic GN. Comparable results were observed in experimental models of psoriasis and colitis.ConclusionsOur findings indicate that IL-17 receptor C signaling has a previously unrecognized function in the regulation of CD4+ TH17 cells and in the control of organ-specific autoimmunity and might provide new insights into the development of more efficient anti-TH17 treatment strategies.

The discovery of tissue-resident memory T cells (TRM cells) reinterpreted the potential of human tissue-specific immunity. Following T cell receptor (TCR) activation and clonal expansion, effector T cells migrate to peripheral tissues where they remain long-term and differentiate to TRM cells after antigen clearance. This allows for prompt immunological responses upon antigen re-encounter. In addition to their protective properties in acute infections, recent studies have revealed that TRM cells might lead to aggravation of autoimmune diseases, such as lupus nephritis (LN) and anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (GN). These diseases present as proliferative and crescentic glomerulonephritis (cGN), which is a life-threatening condition leading to end-stage renal disease (ESRD) if left untreated. A better understanding of renal TRM cells might lead to identifying new therapeutic targets for relapsing autoimmune diseases of the kidney. In this review, we summarize the current knowledge of renal TRM cells and discuss their potential pathophysiological roles in renal autoimmune diseases.