*Purpose: Subclinical rejection may lead to long-term graft injury and can currently only be detected by repeated biopsies. A noninvasive method is needed to monitor stable transplant recipients.

*Methods: We profiled gene expression changes in RNA isolated from the urine sediment of renal transplant recipients enrolled in the Clinical Trials of Organ Transplantation (CTOT)-08 study. Urine was collected at the time of surveillance biopsy (3-6 months post-transplant) and samples were classified as transplant excellent (Tx, n=15), no evidence of rejection with stable graft function; subclinical rejection (SCARC, n=18), histological signs of acute rejection with stable graft function; or clinical rejection (CLARC, n=16), acute rejection on biopsy and increased serum creatinine.

*Results: Using the Nanostring PanCancer Immunology codeset we measured expression of 795 genes in RNA isolated from the urine sediment. Gene expression levels in the SCARC subjects fell into two groups, with one group having a low-absent expression of inflammatory gene transcripts and the other having upregulated expression of many inflammatory genes. We also observed distinct gene expression patterns in urine RNA from the Tx, SCARC with inflammatory gene expression, and CLARC groups and pathway analysis revealed mechanistic differences in subclinical and clinical rejection samples. In both rejection groups, the antigen presentation, TCR signaling, costimulation by CD28, and interferon gamma signaling pathways were among those with greater than two-fold enrichment scores. Genes that were upregulated only in SCARC subjects represented the neutrophil degranulation, interleukin signaling, and senescence-associated secretory phenotype pathways. Genes that were overexpressed only in CLARC subjects belonged to the MHC class II antigen presentation pathway (4-fold enrichment, p 0.01). In addition, we identified a set of 22 genes upregulated at low levels (between 2 and 5-fold) in subclinical rejection whose expression is markedly increased (from 5 to 16-fold) in clinical rejection.

*Conclusions: The urine RNA expression of genes from pathways that differ between SCARC and CLARC subjects could provide a means to monitor the development of immune injury during subclinical graft injury before it becomes clinically evident.

« Back to 2020 American Transplant Congress