Natural Killer Cells in Bronchoalveolar Lavage are Associated with Antibody-Mediated Rejection, CLAD, and Death in Lung Transplant Recipients

Abstract

Natural killer (NK) cells mediate complement-independent cytotoxicity by binding donor specific antibodies (DSA) through the activating Fc receptor CD16A. We hypothesized that CD16+ NK cells in bronchoalveolar lavage (BAL) would be associated with antibody-mediated rejection (AMR) and subsequent chronic lung allograft dysfunction (CLAD). BAL was prospectively collected during 507 bronchoscopies from 195 lung transplant recipients. NK cell populations in BAL were assessed by flow cytometry. Samples with low total cell counts were excluded. AMR was graded according to ISHLT criteria. Associations between outcomes and NK cell groups were determined with generalized estimating equations. The impact of CD16+ NK cell exposure on CLAD-free survival as a time-dependent covariate was determined by Cox proportional hazards models adjusted for subject characteristics. Absolute NK cells were increased in BAL from subjects with higher numbers of HLA mismatches (p=0.006). Compared to subjects with 0-2 HLA mismatches (1x105cells/L), there were increased absolute CD16+ NK cells in subjects with 3-6 HLA mismatches (250%, p=0.01), 7-10 mismatches (560%, p<0.0001), and subjects with more than 10 mismatches (560%, p=0.001). However, BAL NK cell populations did not differ based on the presence of DSA at the time of bronchoscopy. Subjects with clinical AMR (definite, n = 6; probable, n = 12; possible, n= 18) had significantly increased CD16+ NK cells both in absolute numbers and as a percentage of NK cells in BAL compared to subjects with no AMR (Fig 1A, p<0.0001). Elevated absolute CD16+ NK cells were also associated with an increased risk for CLAD or death (Fig 1B, HR 1.3, CI 1.03-1.6, adjusted p=0.02). BAL CD16+ NK cells were associated with HLA donor and recipient mismatching, AMR, and subsequent risk of CLAD or death. NK cells may mediate allograft injury observed in AMR, and NK cell phenotyping may prove a useful adjunct in assessing AMR.