A rapid noninvasive assay for the detection of renal transplant injury

Abstract

Background: The copy number of donor-derived cell-free DNA (dd-cfDNA) in blood correlates with acute rejection (AR) in heart transplantation. We analyzed urinary dd-cfDNA as a surrogate marker of kidney transplant injury.

Methods: Sixty-three biopsy-matched urine samples (41 stable and 22 allograft injury) were analyzed from female recipients of male donors for chromosome Y (donor)-specific dd-cfDNA. All biopsies were semiquantitatively scored by a single pathologist. Standard statistical measures of correlation and significance were used.

Results: There was baseline scatter for urinary dd-cfDNA/μg urine creatinine across different patients, even at the time of stable graft (STA) function (undetected to 12.26 copies). The mean urinary dd-cfDNA in AR (20.5 ± 13.9) was significantly greater compared with STA (2.4 ± 3.3; P<0.0001) or those with chronic allograft injury (CAI; 2.4 ± 2.4; P=0.001) but no different from BK virus nephropathy (BKVN; 20.3±15.7; P=0.98). In AR and BKVN, the intrapatient drift was highly significant versus STA or CAI patients (10.3 ± 7.4 in AR; 12.3 ± 8.4 in BKVN vs. -0.5 ± 3.5 in STA and 2.3 ± 2.6 in CAI; P<0.05). Urinary dd-cfDNA correlated with protein/creatinine ratio (r=0.48; P<0.014) and calculated glomerular filtration rate (r=-0.52; P<0.007) but was most sensitive for acute allograft injury (area under the curve=0.80; P<0.0006; 95% confidence interval, 0.67-0.93).

Conclusion: Urinary dd-cfDNA after renal transplantation has patient specific thresholds, reflecting the apoptotic injury load of the donor organ. Serial monitoring of urinary dd-cfDNA can be a surrogate sensitive biomarker of acute injury in the donor organ but lacks the specificity to distinguish between AR and BKVN injury.

Conflict of interest statement

The remaining authors declare no conflicts of interest.

Figures

FIGURE 1

Change in the copy number of urinary ChrY dd-cfDNA over time after transplantation is presented for three representative patients. The copy number of dd-cfDNA increases at time of injury from baseline as defined by dd-cfDNA copy number at a stable allograft tissue biopsy.

FIGURE 2

ChrY dd-cfDNA can be a surrogate sensitive biomarker of acute injury in the donor organ. A, mean urinary ChrY dd-cfDNA in AR (20.5±13.9) was significantly greater compared with STA (2.4±3.3) or those with CAI (2.4±2.4) but no different from BKVN (20.3±15.7). In BKVN, mean levels were also statistically greater than those seen in both STA and CAI (P<0.01). Bar graphs present mean±SEM. B, in AR and BKVN, the intrapatient drift was highly significant vs. STA or CAI patients (10.3±7.4 in AR; 12.3±8.4 in BKVN vs. −0.5±3.5 in STA and 2.3±2.6 in CAI). This finding was also significant for BKVN when compared with either STA or CAI categories (P<0.05). Box plots show mean, minimum, and maximum values.