Assessment of Circulating Protein Signatures for Kidney Transplantation in Pediatric Recipients

Abstract

Identification and use of non-invasive biomarkers for kidney transplantation monitoring is an unmet need. A total of 121 biobanked sera collected from 111 unique kidney transplant (KT) patients (children and adolescent) and 10 age-matched healthy normal controls were used to profile serum proteins using semi-quantitative proteomics. The proteomics data were analyzed to identify panels of serum proteins that were specific to various transplant injuries, which included acute rejection (AR), BK virus nephropathy (BKVN), and chronic allograft nephropathy (CAN). Gene expression data from matching peripheral blood mononuclear cells were interrogated to investigate the association between soluble serum proteins and altered gene expression of corresponding genes in different injury phenotypes. Analysis of the proteomics data identified from different patient phenotypes, with criteria of false discovery rate <0.05 and at least twofold changes in either direction, resulted in a list of 10 proteins that distinguished KT injury from no injury. Similar analyses to identify proteins specific to chronic injury, acute injury, and AR after kidney transplantation identified 22, 6, and 10 proteins, respectively. Elastic-Net logistic regression method was applied on the 137 serum proteins to classify different transplant injuries. This algorithm has identified panels of 10 serum proteins specific for AR, BKVN, and CAN with classification rates 93, 93, and 95%, respectively. The identified proteins could prove to be potential surrogate biomarkers for routine monitoring of the injury status of pediatric KT patients.

Keywords: acute rejection; kidney transplantation; protein biomarkers; serum proteins; transplant injury.

Figure 1

Study sample classification scheme. STA, stable kidney graft with normal function; AR, acute rejection; CAN, chronic allograft nephropathy; CNIT, calcineurin inhibitor toxicity; BKVN, BK virus nephropathy.

Figure 2

Serum proteins specific to different transplant injury phenotypes were identified. (A) A principal component analysis (PCA) plot generated by 10 serum proteins that separate samples collected from patients with kidney injury from samples collected from patients with no kidney injury. (B) A PCA plot generated by 22 serum proteins that separate chronic injury samples from samples collected from patients with no chronic injury in their kidney. (C) A PCA plot generated by six serum proteins that separate serum samples from the patients with acute injury from the samples collected from patients with no acute injury. (D) A PCA plot generated by 10 serum proteins that separate serum samples from the patients with acute rejection (AR) from the samples collected from patients with no AR.

Figure 3

10 protein biomarker models for different kidney injury phenotypes. (A) A box-and-whisker plot for 10 protein panel specific for transplantation when compared to no transplant healthy normal controls (HC). (B) A box-and-whisker plot for 10 protein panel specific for kidney injury due to kidney transplantation when compared to well-functioning kidneys after transplantation [stable graft function (STA)] and healthy normal controls (HC). (C) A box-and-whisker plot for 10 protein panel specific for acute rejection (AR) when compared to no AR phenotypes. (D) A box-and-whisker plot for 10 protein panel specific for BK virus nephropathy (BKVN) when compared to serum from patients with absence of BKVN.