End-stage liver disease due to Hepatitis C virus (HCV) infection often requires liver transplantation (OLT). The implanted organ is most often derived from a genetically unrelated (deceased) organ donor. From an immunological point of view, the implanted liver can thus be seen as a �foreign� organ in the transplanted organ recipient. As HCV infects the implanted liver, the new liver will present viral antigen on its surface to the host�s T cells and a second round of T cell responses to HCV may be induced. These HCV-specific T cells recognize viral antigen presented by so-called histocompatibility Leukocyte Antigens (HLA), a highly polymorphic group of human genes that specialize in antigen presentation to T cells. As donor and organ recipient are, in general, mismatched in their HLA genes, the T cells that existed in the organ recipient before the transplantation can no longer �see� their viral antigen on the infected liver cells. Despite this quite evident limitation, essentially all studies that attempt to associate HCV-specific T cell-immunity with HCV-related liver-transplantation outcome have assessed these responses in vitro exclusively in the autologous setting (i.e. in the context of �self� HLA molecules, without using organ:donor-derived antigen presenting cells [APCs]). The hypothesis of the present application is that donor-HLA molecules on the implanted liver induce new T cell responses against HCV, which can help in the control of viral replication (as these T cells can actually �see� the viral antigens on the infected new liver). The presence of these T cells will be assessed in two ways:

i) Based on a comprehensive screening using peptide sets spanning the entire HCV proteome, plus APCs derived from the organ donor, donor-HLA-restricted T cells will be stimulated, expanded and characterized.

ii) By comparing viral sequences before and after organ transplantation, specific mutations will be identified that could represent viral escape from donor-HLA-restricted T�cell responses. Subsequent HLA footprint analyses, reverse genetics and traditional epitope-mapping studies will be used to demonstrate the existence of donor-HLA-restricted T cells to HCV post-transplantation.

A successful outcome of these studies would identify donor-HLA-restricted T cell responses as a potentially crucial parameter in the outcome of HCV-related liver transplantation. These findings would help to more effectively allocate scarce liver organs to the immunologically most suitable recipients and help further develop immune-based therapeutic interventions to improve liver transplantation outcome.