CD56(+)CD57(+) infiltrates as the most predominant subset of intragraft natural killer cells in renal transplant biopsies with antibody-mediated rejection

Little is known about the characteristics and clinical implications of specific subsets of intragraft natural killer (NK) cells in kidney transplant recipients. We analyzed 39 for-cause renal transplant biopsies performed at our center from May 2015 to July 2017. According to histopathologic reports, 8 patients (20.5%) had no rejection (NR), 11 (28.2%) had T cell-mediated rejections (TCMR) only, and 20 (51.3%) had antibody-mediated rejection (ABMR). NK cells were defined as CD3(–)CD56(+) lymphocytes that are positive for CD57, CD49b, NKG2A, or KIR. The density of NK cells was significantly higher in the ABMR group (2.57 ± 2.58/mm(2)) than in the NR (0.12 ± 0.22/mm(2)) or the TCMR (0.25 ± 0.34/mm(2)) group (P = 0.002). Notably, CD56(+)CD57(+) infiltrates (2.16 ± 1.89) were the most frequently observed compared with CD56(+)CD49b(+) (0.05 ± 0.13), CD56(+)NKG2A(+) (0.21 ± 0.69), and CD56(+)KIR(+) (0.15 ± 0.42) cells in the ABMR group (P < 0.001). Death-censored graft failure was significantly higher in patients with NK cell infiltration than those without (Log-rank test, P = 0.025). In conclusion, CD56(+)CD57(+) infiltrates are a major subset of NK cells in kidney transplant recipients with ABMR and NK cell infiltration is significantly associated with graft failure post-transplant.