Introduction
Kidney transplantation is the optimal treatment for most patients with
chronic renal failure (1). However, the long term success of kidney
transplantation is far from optimal (2). In 2017, 10-year all-cause
graft failure was 49.7% for deceased donor kidney recipients and 34.1%
for living donor kidney transplants (3). Immunological rejection, a
major cause of graft failure, is driven by attack of the graft by T
cells (T cell mediated rejection, or TCMR) or antibodies (antibody
mediated rejection, or ABMR), or in some cases a combination of these
two mechanisms (mixed rejection). A key early contributor to long-term
graft loss is subclinical immune injury that leads to chronic damage of
the renal allograft (4-8). Until recently there have been no
commercially available fully validated non-invasive tests to monitor
patients with stable renal function for silent rejection (9). As a
result, a significant number of centers rely on surveillance (protocol)
biopsies to detect early silent rejection, whereas other centers who
choose not to perform these wait for clinical evidence of graft injury
and damage (10, 11).