Functional Natural Killer-cell Genetics and Microvascular Inflammation After Kidney Transplantation: An Observational Cohort Study

Abstract

Background: Recent evidence highlights the pivotal role of natural killer (NK) cells in allograft rejection.

Methods: We explored associations of missing self and gene polymorphisms determining the phenotype and/or functionality of NK cells with microvascular inflammation (MVI) in a single-center cohort of 507 consecutive kidney transplant recipients. Patients were genotyped for killer cell Ig-like receptors and polymorphisms in 4 selected genes ( FCGR3AV/F158 [rs396991], KLRC2wt/del , KLRK1HNK/LNK [rs1049174], and rs9916629-C/T).

Results: MVI was detected in 69 patients (13.6%). In a proportional odds model, the KLRC2del/del variant reduced MVI risk (odds ratio [OR] 0.26; 95% confidence interval [CI], 0.05-0.93; P = 0.037) independent of donor-specific antibodies, HLA class II eplet mismatch, and number of biopsies. Conversely, missing self (OR 1.40; 95% CI, 1.08-1.80; P = 0.011) and the rs9916629 T/T gene variant increased the risk (OR 1.70; 95% CI, 1.08-2.68; P = 0.021). Graft loss tended to be more frequent among patients with missing self ≥2 (hazard ratio 1.97; 95% CI, 0.89-4.37; P = 0.097), without influence on estimated glomerular filtration trajectories. FCGR3A variants were associated with MVI only in patients with preformed and/or de novo donor-specific antibodies (OR 4.14; 95% CI, 0.99-17.47; P = 0.052).

Conclusions: Missing self and NK-cell genetics may contribute to MVI, underscoring the important role of NK cells in transplant rejection.

Graphical abstract

FIGURE 1.

Study flowchart. Between 2015 and 2021, 535 patients underwent kidney transplantation at the University Hospital Basel. Out of these, 507 were included in the study. Forty-eight patients who did not undergo biopsies were excluded from the primary endpoint analysis (microvascular inflammation). eGFR, estimated glomerular filtration rate.

FIGURE 2.

Genetic background of NK-cell activation in the microcirculation. A, The schematic illustration of NK activation pathways potentially contributing to microcirculation inflammation. These include NK-cell activation via interaction of MHC class I polypeptide-related sequence MIC A/B with NKG2D, NKG2c with HLA-E, Fc gamma receptor IIIA FcγRIIIA with donor-specific antibodies bound to HLA and the NK cells associated rs9916629‐C allele. Furthermore, the mechanism of missing self is shown, depicting a KIR and the absence of the corresponding HLA class I. The missing self-types are shown in the gray box. B, The mechanism of missing self. KIRs bind to corresponding HLA class I molecules, as depicted in the gray box (A). The binding of KIR with its corresponding HLA class I molecule leads to the inactivation of the NK cell. The absence of the corresponding HLA class I molecule results in missing self and the activation of NK cells. C, Delineates observed and possible combinations between the distinct genetic variants and missing self. Combinations are depicted using black dots and connected lines, with the upper part of the graph indicating the number of participants for individual combinations. D, The correlation between HLA class I mismatch (HLA-A + HLA-B + HLA-C) and missing self. The panel illustrates the detection of missing self in some of the HLA class I-matched donor-recipient pairs (eg, donor expressed only C1, recipient expresses C1 and C2). E, The prevalence of KIR genes relevant for missing self-calculation within the studied kidney transplant cohort. DSA, donor-specific antibody; KIR, killer cell immunoglobulin-like receptor; NK, natural killer cell.

FIGURE 3.

Natural killer cell genetics in relation to morphologic results. The results of proportional odds regression models are shown for microvascular inflammation (g+ptc score; A) and the extent of tubulointerstitial inflammation (t + i score; B). Both models included a donor-specific antibody result and eplet mismatch in HLA class II as forced variables; hence, the estimates should be interpreted with caution.

FIGURE 4.

Graft survival in relation to functional natural killer cell genetics. Kaplan-Meier death-censored graft survival was analyzed in relation to missing self, FCGR3A, KLRC2, KLRK1, and rs9916629-C/T genotypes. The Cox regression model was adjusted for the presence of donor-specific antibodies and eplet mismatch in HLA class II. For survival analyses, missing self was dichotomized into high (≥2) and low missing self-types (<2). Individual single-gene polymorphisms were dichotomized as described in the methods section. CI, confidence interval; HR, hazard ratio.