Silencing of HLA class I on primary human hepatocytes as a novel strategy for reduction in alloreactivity.

In contrast to the whole liver, primary hepatocytes are highly immunogenic. Thus, alternative strategies of immunomodulation after hepatocyte transplantation are of special interest. Silencing of HLA class I expression is expected to reduce the strength of allogeneic immune responses and to improve graft survival. In this study, primary human hepatocytes (PHH) were isolated using a two-step-collagenase perfusion-technique and co-cultured with allogeneic lymphocytes in terms of a mixed lymphocyte hepatocyte culture. Expression of HLA class I on PHH was silenced using lentiviral vectors encoding for ß2-microglobulin-specific short hairpin RNA (shß2m) or non-specific shRNA (shNS) as control. The delivery of shß2m into PHH caused a decrease by up to 96% in ß2m transcript levels and a down-regulation of HLA class I cell surface expression on PHH by up to 57%. Proliferative T cell alloresponses against HLA-silenced PHH were significantly lower than those observed form fully HLA-expressing PHH. In addition, significantly lower secretion of pro-inflammatory cytokines was observed. Levels of albumin, urea and aspartate-aminotransferase did not differ in supernatants of cultured PHH. In conclusion, silencing HLA class I expression on PHH might represent a promising approach for immunomodulation in the transplant setting without compromising metabolic function of silenced hepatocytes.

Back signaling of HLA class I molecules and T/NK cell receptor ligands in epithelial cells reflects the rejection-specific microenvironment in renal allograft biopsies.

The role of endothelial cells in the pathophysiology of antibody-mediated rejection after renal transplantation has been widely investigated. We expand this scenario to the impact of epithelial cells on the microenvironment during rejection. Primary proximal tubular epithelial cells were stimulated via HLA class I, CD155 and CD166 based on their potential signal-transducing capacity to mediate back signaling after encounter with either T/NK cells or donor-specific antibodies. Upon crosslinking of these ligands with mAbs, PTEC secreted IL-6, CXCL1,8,10, CCL2, and sICAM-1. These proteins were also released by PTEC as consequence of a direct interaction with T/NK cells. Downmodulation of the receptor CD226 on effector cells confirmed the involvement of this receptor/ligand pair in back signaling. In vivo, CD155 and CD166 expression was detectable in proximal and distal tubuli of renal transplant biopsies, respectively. The composition of the protein microenvironment in these biopsies showed a substantial overlap with the PTEC response. Cluster and principal component analyses of the microenvironment separated unsuspicious from rejection biopsies and, furthermore, ABMR, TCMR, and borderline rejection. In conclusion, our results provide evidence that epithelial cells may contribute to the rejection process and pave the way to a better understanding of the pathomechanisms of kidney allograft rejection.