Analysis of hepatitis C virus quasispecies in liver transplantation

Abstract

The hepatitis C virus (HCV) is an RNA virus that replicates with a high rate of mutation, especially in the hypervariable region 1 (HVR-1). Continuous viral mutations lead to a mixed and changing populations of mutants, called quasispecies. The nature of the HCV quasispecies may have implications for viral persistence and pathogenies. Studies with liver transplant patients suggest a relationship between the degree of immunosuppression and the complexity of the quasispecies. This study evaluated whether immunosuppressive therapy modifies the evolution of HCV quasispecies among liver transplant recipients compared with immunocompetent HCV patients. Two groups were studied: 11 patients who underwent OLT for HCV-related cirrhosis and 10 control group patients. Two serum samples from each patient were obtained to analyze the HCV HVR1 region by RT-PCR. SSCP analysis failed to show statistically significant differences in the number of quasispecies at basal and final time points or at pretransplant versus posttransplant (7.3 2 vs 6.7 3 in control patients, respectively, and 4.4 2 vs 4.1 1 in transplanted patients, respectively). No significant difference was observed between missing or new variants in the control (2.8 2 vs 2.3 2, respectively) or transplanted group (2.5 2 vs 2.2 1, respectively). Upon sequence analysis, the genetic complexity was significantly lower among samples after OLT in transplanted patients (0.057 0.04 [pretransplant] vs 0.035 0.02 [posttransplant]; P .048). However, no significant differences were found among control patients in basal versus final samples (0.04 0.03 vs 0.066 0.04, respectively). Our findings seem to demonstrate that viral quasispecies diversity is lower among patients receiving a liver transplant. HEPATITIS C VIRUS (HCV) is a major causative agent for chronic liver disease leading to orthotopic liver transplantation (OLT). After OLT, HCV recurrence occurs in most patients. HCV has been characterized as a positive-sense, single-stranded RNA virus like many other RNA viruses, the HCV genome shows high mutation frequencies. The resulting genetic diversity, especially in the hypervariable region (HVR-1) of the envelope gene (E2), makes HCV exist as a viral quasispecies, which are defined as a complex population of different (but closely related) HCV genomes with sequences differing by only a few nucleotides that circulate simultaneously in each individual patient. The evolution of the quasispecies seems to have important implications for escape from immune surveillance. If this is the case, viral persistence in HCV infection may be related to the emergence of variants in the quasispecies. Studies with liver transplant patients suggest a relationship between the degree of immunosuppression and the complexity of the quasispecies. In the present study we evaluated whether immunosuppressive therapy could modify the evolution of HCV quasispecies among liver transplant recipients when compared with immunocompetent HCV patients. Our findings seem to demonstrate that viral quasispecies diversity is lower among patients receiving a liver transplant. From the Departments of Gastroenterology (J.M.G., S.D.C.T., G.M.G., M.G.G., J.M.V.-G., P.M., R.B.M.), Department of General Surgery (E.D.V.L.), and Department of Infectious Diseases (J.F.A.), Hospital Ramon y Cajal, Madrid, Spain. Address reprint request to R. Barcena Marugan, MD, Department of Gastroenterology, Hospital Ramon y Cajal, Ctra, Colmenar Km 9.1, 28034 Madrid, Spain. E-mail: rbarcena@