Natural Killer (NK) Cells: The Missing Link between Antibody-Mediated Rejection (ABMR) and Chronic Lung Allograft Dysfunction (CLAD)?

Abstract

The long-term success of lung transplantation (LTx) is limited by CLAD. The complement-independent pathway of ABMR, driven by antibody-dependent cellular cytotoxicity (ADCC) may contribute to CLAD. ADCC is mediated through the CD16 Fc receptor expressed on NK cells, however a role for different NK cell subsets in mediating ABMR is yet to be elucidated. In this pilot study, we investigated whether the presence of donor-specific antibodies (DSA) following LTx effects NK cell ADCC and whether particular NK cell subsets exhibited superior ADCC activity. Peripheral blood mononuclear cells (PBMC) were isolated from LTx recipients at 3 and 12-months post-LTx. NK cell ADCC activity (degranulation (CD107a) and the production of cytokines from PBMC (interferon gamma (IFN-γ) and tumor necrosis alpha (TNF-α))) was measured by flow cytometry following antibody-dependent activation (ADA). The detection of anti-human leukocyte antigen (HLA) antibodies at the same time points was determined by Luminex. LTx recipients were classified as DSA positive (DSA+, presence of anti-donor HLA antibodies, n=12), anti-HLA antibody positive (HLA+, presence of anti-HLA antibodies but not to donor HLA, n=12) or no HLA antibodies (Ab-, no anti-HLA antibodies detected, n=7). Surprisingly, a higher proportion of NK cells expressed the activating receptor NKG2C in the DSA+ group (p=0.0078). Furthermore, NKG2C+ NK cells isolated from recipients with HLA antibodies were significantly more activated than NKG2A+ cells. Following ADA, a higher proportion of NKG2C+ NK cells produced cytokines in DSA+ (IFNγ, p=0.0095) and HLA+ (IFNγ: p=0.0317; TNFα: p=0.0159) recipients, compared to NKG2A+ cells. In addition, CD16 expression was more down-regulated following ADA in DSA+ recipients (p=0.0084). Our data shows that the presence of DSA impacts on the phenotype and function of NK cells following LTx. Moreover, as previous research has shown an association between NKG2C expression, cytomegalovirus (CMV) infection and CLAD, our study potentially provides a missing link between CMV infection and CLAD. Future confirmation of NKG2C+ NK cells as mediators of ABMR will lead to development of targeted diagnostic criteria and specific therapies to offer early therapeutic interventions to prevent CLAD, thereby improving LTx outcomes.