BLOOD DONORS AND BLOOD COLLECTION Cellular immune response to hepatitis C virus (HCV) in nonviremic blood donors with indeterminate anti-HCV reactivity Tobias Hitziger, Michael Schmidt, Volkmar Schottstedt, Holger Hennig, Alexandra Schumann, Stefan Ross, Mengji Lu, Erhard Seifried, and Michael Roggendorf BACKGROUND: Blood donors with indeterminate hepatitis C virus antibody (anti-HCV) reactivity are rejected from blood donation. As they are mostly non- viremic, the source of these reactions remains unclear. Reasons for such findings can be resolved HCV infec- tions as well as unspecific antibody reactions. The aim of this study was to investigate HCV-specific T-cell response in blood donors to determine the reason for the weak antibody detection. STUDY DESIGN AND METHODS: Anti-HCV reactivity was tested in 72 blood donors initially diagnosed with an indeterminate HCV result by enzyme-linked immun- osorbent assay and immunoblot. Cellular immune response was measured by proliferation assay and enzyme-linked immunosorbent spot analysis after stimulation with viral proteins core, NS3, and NS4. RESULTS: In 56% of donors anti-HCV reactivity was detectable in the screening assay whereas 72% had a reaction in the confirmation immunoblot. Forty-six percent of donors had a cellular immune response against HCV proteins. The response was most frequent to NS3 protein. CONCLUSION: In almost half of donors the indetermi- nate result in serologic testings could be explained by a previous resolved HCV infection as the pattern of T-cell response was similar to these patients. These findings indicate that HCV-specific antibodies disappear more rapidly after resolved infection than HCV-specific T cells. These results are important for counseling blood donors and patients with indeterminate serologic results. H epatitis C virus (HCV) infection is one of the major causes of acute and chronic liver disease, including cirrhosis and liver cancer. In the past, blood transfusion contributed substantially to HCV infections. Therefore, after identifi- cation of the virus in 1989 suitable screening tests for this infection became important to ensure the safety of blood and blood products for recipients. 1 The detection of virus-specific antibodies by immune assays (IAs) indicates exposure to the virus. Recombinant immunoblot assays (RIBAs) in which specific antibodies against different viral proteins can be identified are used to confirm IA results. A binding of antibodies to two or more HCV antigens in these tests is considered as HCV-specific humoral immune response. Viremia in patients’ sera can be identified by the amplification of viral RNA by reverse transcription-polymerase chain reaction (RT-PCR) or transcription-mediated amplification, both of which indi- cate an acute or chronic infection. After infection, viral RNA appears in the plasma within a few days and typically peaks 6 to 10 weeks later; 2-4 ABBREVIATIONS: CMIA = chemiluminescent microparticle immunoassay; ELISpot = enzyme-linked immunosorbent spot; IA(s) = immune assay(s); S/CO = sample/cutoff ratio; SI = stimulation index. From the Institute ofVirology, University Hospital Essen, Essen; DRK Blutspendedienst Baden-Württemberg–Hessen, Frankfurt; DRK BlutspendedienstWest, Hagen; Institute of Transfusion Medicine, University Hospital of Luebeck, Campus Luebeck, Luebeck, Germany. Address reprint requests to: Michael Roggendorf, MD, Insti- tute of Virology, University Hospital Essen, Virchowstrasse 179, 45147 Essen, Germany; e-mail: michael.roggendorf@uni-due.de. Supported in parts by a grant from the Robert-Koch- Institute to the German National Reference Centre for Hepatitis C and the Deutsche Forschungsgemeinschaft (GK 1045/1). Received for publication October 17, 2008; revision received December 21, 2008, and accepted December 22, 2008. doi: 10.1111/j.1537-2995.2009.02113.x TRANSFUSION 2009;49:1306-1313. 1306 TRANSFUSION Volume 49, July 2009