Tissue-resident memory T (TRM) cells provide protective immunity to infection by rapidly responding to antigen in non-lymphoid tissues. These non-migrating memory T cells are characterized by surface expression of CD69 and CD103. In transplanted kidneys the existence, origin and properties of TRM cells are unclear. In this study, we used the unique tissue resource of transplant nephrectomies to determine whether TRM cells reside in rejected kidney allografts and whether these cells are of donor or recipient origin.Materials and Methods
Thirteen transplant nephrectomy specimens were studied. These grafts failed because of acute (n=4) or chronic (n=9) rejection and were removed after a mean time of 6.7 years (range: 8 days – 26 years). Half of the explanted renal allograft (cortex and medulla) was processed into a single cell suspension. Isolated cells were stained and analyzed by flow cytometry to determine their phenotype. The origin of the cells was measured by mAb directed against HLA epitopes of the donor or acceptor.Results
Functional CD3+ T cells were isolated from all explanted kidney allografts as 57.8 ± 16.5% (mean ± SD) of the cells had the capacity to produce IFNγ; 16.1 ± 6.8% produced IL-2; 1.8 ± 1.2% IL-17, and 4.6 ± 5.2% IL-4 after PMA/ionomycin stimulation. The isolated T cells consisted of 43.2 ± 19.1% CD4+ T cells and 45.3 ± 20.6% CD8+ T cells.Of the CD8+ T cells, 27.9 ± 15.5% expressed CD69 and CD103, reflecting CD8+ TRM cells. The majority of these TRM cells did not express CD28 (61.6 ± 18.2%), indicating a phenotype associated with highly-reactive effector functions. The isolated CD4+ T cells also included a population of TRM cells, though this fraction was relatively small (1.9 ± 2.2%). We confirmed that CD69+CD103+ TRM cells were exclusively present in the renal allografts and not in the circulation of healthy controls (p=0.002). No differences in proportions of TRM cells were found between acute and chronically rejecting kidney allografts.Results
High proportions of donor CD4+ and CD8+ T cells were present in the renal allografts removed within the first month after transplantation (6.8 ± 5.7% CD4+ T cells; 9.8 ± 9.2% CD8+ T cells) compared to low proportions in the renal allografts removed after one month (0.4 ± 0.3% CD4+ T cells; 0.3 ± 0.3% CD8+ T cells). Remarkably, within the CD8+ TRM cells the ratio between donor versus recipient cells was 3.6 times higher compared to this ratio within the total CD8+ T cells.Conclusion
Our results demonstrate that both donor and patient CD4+ and CD8+ TRM cells reside in the rejecting transplanted kidney. Over time, the donor TRM cells disappear from the allograft.