Hepatitis C virus infection : molecular analysis of transmission and immunity

Abstract

Hepatitis C virus (HCV) is an important cause for chronic liver disease worldwide. Infection by HCV may resolve spontaneously, but in the majority of cases a chronic infection is established, that may result in liver cirrhosis and hepatocellular cancer. HCV is parenterally transmitted, but up to 50% of patients lack a history of known parenteral exposure.

The present study is focused on two aspects of HCV infection: Detection of inapparent transmission of HCV in hospitals, and investigation of the role of the antibody response for control and resolution of the HCV infection. The prevalence and incidence of HCV infection were studied in 236 haemodialysis patients, and time of seroconversion to HCV was determined by retrospective analysis of stored serum samples. 36 patients (15%) were anti-HCV positive. Seroconversion was usually temporally associated to blood transfusions, but seroconversion more than 6 months after transfusion and lack of transfusion in some cases suggested additional routes of transmission. Subsequently, the HCV strains were investigated by sequencing of the hypervariable region (HVR1) of the E2 gene in 14 patients in one of the dialysis units. Five patients shared a common viral strain, and two patients were sharing a second strain. Blood donors could be ruled out as the source of infection. The patients had not shared dialysis machines, but were treated on the same shift.

The same approach was utilised for analysing a high incidence of HCV infections in a haematology ward. The HCV strain was analysed in 37 patients. Five clusters of highly related viruses were found, involving 30 of the patients. Blood products could again be ruled out as the common source of infection. The pattern of new mutations in the virus suggested spread from patient to patient. All patients in each cluster had been treated in the ward during overlapping time periods. Thus, in the two investigated hospital settings, transmission between patients seemed to occur frequently, and was a major cause for infection also in multi-transfused patients. The antibody response to the HVRI during acute infection was analysed in five dialysis patients infected by the same viral strain. A new assay for HVRI antibody detection based on recombinant bacteriophage was developed for this purpose. Results indicated that early appearance of anti-HVRI antibodies - but not anti-HCV antibodies in general - may predict clearance of the infection.

To further analyse the nature of protective antibodies to HCV, human monoclonal antibodies to the HCV envelope protein E2 were isolated from a combinatorial antibody library displayed on bacteriophage. The antibody library was derived from a chronically HCV infected individual. Seven distinct antibody clones directed to E2 were characterised. All bind a conformation dependent epitope that seems conserved between different isolates, and all clones inhibit the binding of recombinant E2 protein to target cells, indicating a potential neutralising activity. This suggests the existence of a conserved neutralising epitope in the HCV envelope. The cloned human antibodies directed to it may prove useful for immunotherapy or prophylaxis.