Impact of Human HLA-E and NKG2C Variants and of HCMV Ul40 Genotype Populations on HCMV Replication in Lung Transplant Recipients

Abstract

Human Cytomegalovirus (HCMV) is an important viral pathogen in lung-transplant recipients (LTRs), which may cause tissue-invasive disease. The risk for HCMV-replication depends on HCMV-specific immune responses, which may limit viral spread after lung-transplantation. NKG2C+ Natural-Killer (NK-) cells limit HCMV replication, even under immunosuppressive therapy. NK-cell activation can be mediated by the NKG2C receptor, which binds to HLA-E molecules on the surface of HCMV-infected cells, and these are stabilized by an HCMV-encoded UL40 peptide. NKG2C, HLA-E and UL40 occur naturally as different variants. We investigated whether these variants differently influence the individual NK-cell response and have impact on the extent of HCMV-replication after lung transplantation. We included 137 lung transplant recipients (LTRs), who received the transplant between 2013 and 2016 at the Medical University of Vienna and who had either no or low HCMV replication (N=69) or developed high level viremia (>1000 copies HCMV DNA/ml plasma, N=68) post-transplantation. We assessed donor and recipient NKG2Cwt/del and HLA-E*0101/0103 variants as well as the UL40 peptide variants of the infecting HCMV strains. We further investigated UL40 kinetics by NGS and UL40 dependent NK-cell cytotoxicity and proliferation. In total, we detected 18 different UL40 peptides in low- and high viremic LTRs. Specific UL40 peptide variants were differently distributed in the blood of LTRs and the VMAPRTLIL variant occurred more frequently in highly viremic patients, while the VMTPRTLIL variant was detectable preferably in patients with low viremia (p=0.004). This difference was not associated with altered cytotoxicity, but with differences in the proliferation of NK-cells (p=0.002). In homozygous HLA-E recipients, UL40 strains seem to emerge over time towards low affinity. In addition, recipient encoded NKG2Cwt/del and donor encoded heterozygous HLA-E*0101/0103 variants were associated with development of high-level viremia in the follow-up (p=0.01 and p=0.007, respectively). The present data provide evidence that the NKG2C/UL40/HLA-E axis and variations thereof have a substantial impact on the patients' individual NK-cell response and on the development of high-level viremia post-transplantation.